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  • Nature Publishing Group
  • American Meteorological Society
  • Public Library of Science (PLoS)
  • 2015-2019  (48,438)
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  • 1
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    Cluster analysis of downscaled and explicitly simulated North Atlantic tropical cyclone tracks (2015)
    American Meteorological Society
    Details
    Publication Date: 2020-11-18
    Description: A realistic representation of the North Atlantic tropical cyclone tracks is crucial as it allows, for example, explaining potential changes in U.S. landfalling systems. Here, the authors present a tentative study that examines the ability of recent climate models to represent North Atlantic tropical cyclone tracks. Tracks from two types of climate models are evaluated: explicit tracks are obtained from tropical cyclones simulated in regional or global climate models with moderate to high horizontal resolution (1°–0.25°), and downscaled tracks are obtained using a downscaling technique with large-scale environmental fields from a subset of these models. For both configurations, tracks are objectively separated into four groups using a cluster technique, leading to a zonal and a meridional separation of the tracks. The meridional separation largely captures the separation between deep tropical and subtropical, hybrid or baroclinic cyclones, while the zonal separation segregates Gulf of Mexico and Cape Verde storms. The properties of the tracks’ seasonality, intensity, and power dissipation index in each cluster are documented for both configurations. The authors’ results show that, except for the seasonality, the downscaled tracks better capture the observed characteristics of the clusters. The authors also use three different idealized scenarios to examine the possible future changes of tropical cyclone tracks under 1) warming sea surface temperature, 2) increasing carbon dioxide, and 3) a combination of the two. The response to each scenario is highly variable depending on the simulation considered. Finally, the authors examine the role of each cluster in these future changes and find no preponderant contribution of any single cluster over the others.
    Description: Published
    Description: 1333–1361
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: tropical cyclones ; atlantic basin ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Impact of Orbital Parameters and Greenhouse Gas on the Climate of MIS 7 and MIS 5 Glacial Inceptions (2015)
    American Meteorological Society
    Details
    Publication Date: 2021-06-22
    Description: This work explores the impact of orbital parameters and greenhouse gas concentrations on the climate of marine isotope stage (MIS) 7 glacial inception and compares it to that of MIS 5. The authors use a coupled atmosphere-ocean general circulation model to simulate the mean climate state of six time slices at 115, 122, 125, 229, 236, and 239 kyr, representative of a climate evolution from interglacial to glacial inception conditions. The simulations are designed to separate the effects of orbital parameters from those of greenhouse gas (GHG). Their results show that, in all the time slices considered, MIS 7 boreal lands mean annual climate is colder than the MIS 5 one. This difference is explained at 70% by the impact of the MIS 7 GHG. While the impact of GHG over Northern Hemisphere is homogeneous, the difference in temperature between MIS 7 and MIS 5 due to orbital parameters differs regionally and is linked with the Arctic Oscillation. The perennial snow cover is larger in all the MIS 7 experiments compared to MIS 5, as a result of MIS 7 orbital parameters, strengthened by GHG. At regional scale, Eurasia exhibits the strongest response to MIS 7 cold climate with a perennial snow area 3 times larger than in MIS 5 experiments. This suggests that MIS 7 glacial inception is more favorable over this area than over North America. Furthermore, at 239 kyr, the perennial snow covers an area equivalent to that of MIS 5 glacial inception (115 kyr). The authors suggest that MIS 7 glacial inception is more extensive than MIS 5 glacial inception over the high latitudes.
    Description: Italian Ministry of Education, University and Research Ministry for Environment, Land and Sea through the project GEMINA
    Description: Published
    Description: 8918-8933
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: open
    Keywords: Arctic Oscillation ; Teleconnections ; Greenhouse gases ; Glaciation ; Paleoclimate ; 02. Cryosphere::02.03. Ice cores::02.03.05. Paleoclimate
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Simulated leakage of high pCO2 water negatively impacts bivalve dominated infaunal communities from the Western Baltic Sea (2016)
    Nature Publishing Group
    In:  EPIC3Scientific Reports, Nature Publishing Group, 6(31447)
    Details
    Publication Date: 2016-11-24
    Description: Carbon capture and storage is promoted as a mitigation method counteracting the increase of atmospheric CO2 levels. However, at this stage, environmental consequences of potential CO2 leakage from sub-seabed storage sites are still largely unknown. In a 3-month-long mesocosm experiment, this study assessed the impact of elevated pCO2 levels (1,500 to 24,400 µatm) on Cerastoderma edule dominated benthic communities from the Baltic Sea. Mortality of C. edule was significantly increased in the highest treatment (24,400 µatm) and exceeded 50%. Furthermore, mortality of small size classes (0-1 cm) was significantly increased in treatment levels ≥6,600 µatm. First signs of external shell dissolution became visible at ≥1,500 µatm, holes were observed at 〉6,600 µatm. C. edule body condition decreased significantly at all treatment levels (1,500-24,400 µatm). Dominant meiofauna taxa remained unaffected in abundance. Densities of calcifying meiofauna taxa (i.e. Gastropoda and Ostracoda) decreased in high CO2 treatments (〉6,600 µatm), while the non - calcifying Gastrotricha significantly increased in abundance at 24,400 µatm. In addition, microbial community composition was altered at the highest pCO2 level. We conclude that strong CO2 leakage can alter benthic infauna community composition at multiple trophic levels, likely due to high mortality of the dominant macrofauna species C. edule.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Strong geologic methane emissions from discontinuous terrestrial permafrost in the Mackenzie Delta, Canada (2017)
    Nature Publishing Group
    In:  EPIC3Scientific Reports, Nature Publishing Group, 7(5828)
    Details
    Publication Date: 2017-10-10
    Description: Arctic permafrost caps vast amounts of old, geologic methane (CH4) in subsurface reservoirs. Thawing permafrost opens pathways for this CH4 to migrate to the surface. However, the occurrence of geologic emissions and their contribution to the CH4 budget in addition to recent, biogenic CH4 is uncertain. Here we present a high-resolution (100 m × 100 m) regional (10,000 km²) CH4 flux map of the Mackenzie Delta, Canada, based on airborne CH4 flux data from July 2012 and 2013. We identify strong, likely geologic emissions solely where the permafrost is discontinuous. These peaks are 13 times larger than typical biogenic emissions. Whereas microbial CH4 production largely depends on recent air and soil temperature, geologic CH4 was produced over millions of years and can be released year-round provided open pathways exist. Therefore, even though they only occur on about 1% of the area, geologic hotspots contribute 17% to the annual CH4 emission estimate of our study area. We suggest that this share may increase if ongoing permafrost thaw opens new pathways. We conclude that, due to permafrost thaw, hydrocarbon-rich areas, prevalent in the Arctic, may see increased emission of geologic CH4 in the future, in addition to enhanced microbial CH4 production.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    Spatio-temporal variability of processes across Antarctic ice-bed-ocean interfaces (2018)
    Nature Publishing Group
    In:  EPIC3Nature Communications, Nature Publishing Group, 9, ISSN: 2041-1723
    Details
    Publication Date: 2018-09-20
    Description: Understanding how the Antarctic ice sheet will respond to global warming relies on knowledge of how it has behaved in the past. The use of numerical models, the only means to quantitatively predict the future, is hindered by limitations to topographic data both now and in the past, and in knowledge of how subsurface oceanic, glaciological and hydrological processes interact. Incorporating the variety and interplay of such processes, operating at multiple spatio-temporal scales, is critical to modeling the Antarctic’s system evolution and requires direct observations in challenging locations. As these processes do not observe disciplinary boundaries neither should our future research.
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    Universal molecular structures in natural dissolved organic matter (2018)
    Nature Publishing Group
    In:  EPIC3Nature Communication, Nature Publishing Group, 9(3178), ISSN: 2041-1723
    Details
    Publication Date: 2019-02-13
    Description: Natural dissolved organic matter (DOM) comprises a broad range of dissolved organic molecules in aquatic systems and is among the most complex molecular mixtures known. Here we show, by comparing detailed structural fingerprints of individual molecular formulae in DOM from a set of four marine and one freshwater environments, that a major component of DOM is molecularly indistinguishable in these diverse samples. Molecular conformity was not only apparent by the co-occurrence of thousands of identical molecular formulae, but also by identical structural features of those isomers that collectively represent a molecular formula. The presence of a large pool of compounds with identical structural features in DOM is likely the result of a cascade of degradation processes or common synthetic pathways that ultimately lead to the formation of a universal background, regardless of origin and history of the organic material. This novel insight impacts our understanding of long-term turnover of DOM as the underlying mechanisms are possibly universal.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Permafrost is warming at a global scale (2019)
    Nature Publishing Group
    In:  EPIC3Nature Communications, Nature Publishing Group, 10(1), pp. 1-11, ISSN: 2041-1723
    Details
    Publication Date: 2021-01-12
    Description: Permafrost warming has the potential to amplify global climate change, because when frozen sediments thaw it unlocks soil organic carbon. Yet to date, no globally consistent assessment of permafrost temperature change has been compiled. Here we use a global data set of permafrost temperature time series from the Global Terrestrial Network for Permafrost to evaluate temperature change across permafrost regions for the period since the International Polar Year (2007–2009). During the reference decade between 2007 and 2016, ground temperature near the depth of zero annual amplitude in the continuous permafrost zone increased by 0.39 ± 0.15 °C. Over the same period, discontinuous permafrost warmed by 0.20 ± 0.10 °C. Permafrost in mountains warmed by 0.19 ± 0.05 °C and in Antarctica by 0.37 ± 0.10 °C. Globally, permafrost temperature increased by 0.29 ± 0.12 °C. The observed trend follows the Arctic amplification of air temperature increase in the Northern Hemisphere. In the discontinuous zone, however, ground warming occurred due to increased snow thickness while air temperature remained statistically unchanged.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 8
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    Host-specific assembly of sponge-associated prokaryotes at high taxonomic ranks (2017)
    Nature Publishing Group
    In:  EPIC3Scientific Reports, Nature Publishing Group, 7(2542), ISSN: 2045-2322
    Details
    Publication Date: 2019-03-07
    Description: Sponges (Porifera) are abundant and diverse members of benthic filter feeding communities in most marine ecosystems, from the deep sea to tropical reefs. A characteristic feature is the associated dense and diverse prokaryotic community present within the sponge mesohyl. Previous molecular genetic studies revealed the importance of host identity for the community composition of the sponge-associated microbiota. However, little is known whether sponge host-specific prokaryotic community patterns observed at 97% 16S rRNA gene sequence similarity are consistent at high taxonomic ranks (from genus to phylum level). In the present study, we investigated the prokaryotic community structure and variation of 24 sponge specimens (seven taxa) and three seawater samples from Sweden. Results show that the resemblance of prokaryotic communities at different taxonomic ranks is consistent with patterns present at 97% operational taxonomic unit level.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev , info:eu-repo/semantics/article
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  • 9
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    The role of stratospheric ozone for Arctic-midlatitude linkages (2019)
    Nature Publishing Group
    In:  EPIC3Scientific Reports, Nature Publishing Group, 9(7962), ISSN: 2045-2322
    Details
    Publication Date: 2019-06-11
    Description: Arctic warming was more pronounced than warming in midlatitudes in the last decades making this region a hotspot of climate change. Associated with this, a rapid decline of sea-ice extent and a decrease of its thickness has been observed. Sea-ice retreat allows for an increased transport of heat and momentum from the ocean up to the tropo- and stratosphere by enhanced upward propagation of planetary-scale atmospheric waves. In the upper atmosphere, these waves deposit the momentum transported, disturbing the stratospheric polar vortex, which can lead to a breakdown of this circulation with the potential to also significantly impact the troposphere in mid- to late-winter and early spring. Therefore, an accurate representation of stratospheric processes in climate models is necessary to improve the understanding of the impact of retreating sea ice on the atmospheric circulation. By modeling the atmospheric response to a prescribed decline in Arctic sea ice, we show that including interactive stratospheric ozone chemistry in atmospheric model calculations leads to an improvement in tropo-stratospheric interactions compared to simulations without interactive chemistry. This suggests that stratospheric ozone chemistry is important for the understanding of sea ice related impacts on atmospheric dynamics.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 10
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    Global analysis reveals climatic controls on the oxygen isotope composition of cave drip water (2019)
    Nature Publishing Group
    In:  EPIC3Nature Communications, Nature Publishing Group, 10(1), pp. 1-7, ISSN: 2041-1723
    Details
    Publication Date: 2019-07-15
    Description: The oxygen isotope composition of speleothems is a widely used proxy for past climate change. Robust use of this proxy depends on understanding the relationship between precipitation and cave drip water δ18O. Here, we present the first global analysis, based on data from 163 drip sites, from 39 caves on five continents, showing that drip water δ18O is most similar to the amount-weighted precipitation δ18O where mean annual temperature (MAT) is 〈 10 °C. By contrast, for seasonal climates with MAT 〉 10 °C and 〈 16 °C, drip water δ18O records the recharge-weighted δ18O. This implies that the δ18O of speleothems (formed in near isotopic equilibrium) are most likely to directly reflect meteoric precipitation in cool climates only. In warmer and drier environments, speleothems will have a seasonal bias toward the precipitation δ18O of recharge periods and, in some cases, the extent of evaporative fractionation of stored karst water.
    Repository Name: EPIC Alfred Wegener Institut
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  • 11
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    Establishing anaerobic hydrocarbon-degrading enrichment cultures of microorganisms under strictly anoxic conditions (2018)
    Nature Publishing Group
    In:  EPIC3Nature Protocols, Nature Publishing Group, 13(6), pp. 1310-1330, ISSN: 1754-2189
    Details
    Publication Date: 2020-02-23
    Description: Traditionally, the description of microorganisms starts with their isolation from an environmental sample. Many environmentally relevant anaerobic microorganisms grow very slowly, and often they rely on syntrophic interactions with other microorganisms. This impedes their isolation and characterization by classic microbiological techniques. We developed and applied an approach for the successive enrichment of syntrophic hydrocarbon-degrading microorganisms from environmental samples. We collected samples from microbial mat-covered hydrothermally heated hydrocarbon-rich sediments of the Guaymas Basin and mixed them with synthetic mineral medium to obtain sediment slurries. Supplementation with defined substrates (i.e., methane or butane), incubation at specific temperatures, and a regular maintenance procedure that included the measurement of metabolic products and stepwise dilutions enabled us to establish highly active, virtually sediment-free enrichment cultures of actively hydrocarbon-degrading communities in a 6-months to several-years' effort. Using methane as sole electron donor shifted the originally highly diverse microbial communities toward defined mixed cultures dominated by syntrophic consortia consisting of anaerobic methane-oxidizing archaea (ANME) and different sulfate-reducing bacteria. Cultivation with butane at 50 °C yielded consortia of archaea belonging to Candidatus Syntrophoarchaeum and Candidatus Desulfofervidus auxilii partner bacteria. This protocol also describes sampling for further molecular characterization of enrichment cultures by fluorescence in situ hybridization (FISH), and transcriptomics and metabolite analyses, which can provide insights into the functioning of hydrocarbon metabolism in archaea and resolve important mechanisms that enable electron transfer to their sulfate-reducing partner bacteria.
    Repository Name: EPIC Alfred Wegener Institut
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  • 12
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    FoodOn: a harmonized food ontology to increase global food traceability, quality control and data integration (2018)
    Nature Publishing Group
    In:  EPIC3npj Science of Food, Nature Publishing Group, 2(23), pp. 1-10
    Details
    Publication Date: 2020-02-12
    Description: The construction of high capacity data sharing networks to support increasing government and commercial data exchange has highlighted a key roadblock: the content of existing Internet-connected information remains siloed due to a multiplicity of local languages and data dictionaries. This lack of a digital lingua franca is obvious in the domain of human food as materials travel from their wild or farm origin, through processing and distribution chains, to consumers. Well defined, hierarchical vocabulary, connected with logical relationships—in other words, an ontology—is urgently needed to help tackle data harmonization problems that span the domains of food security, safety, quality, production, distribution, and consumer health and convenience. FoodOn (http://foodon.org) is a consortium-driven project to build a comprehensive and easily accessible global farm-to-fork ontology about food, that accurately and consistently describes foods commonly known in cultures from around the world. FoodOn addresses food product terminology gaps and supports food traceability. Focusing on human and domesticated animal food description, FoodOn contains animal and plant food sources, food categories and products, and other facets like preservation processes, contact surfaces, and packaging. Much of FoodOn’s vocabulary comes from transforming LanguaL, a mature and popular food indexing thesaurus, into a World Wide Web Consortium (W3C) OWL Web Ontology Language-formatted vocabulary that provides system interoperability, quality control, and software-driven intelligence. FoodOn compliments other technologies facilitating food traceability, which is becoming critical in this age of increasing globalization of food networks.
    Repository Name: EPIC Alfred Wegener Institut
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  • 13
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    Towards a Solution of the Closure Problem for Non-Homogeneous and Anisotropic Turbulence: Non-Gaussian Closures for Convective Atmospheric Boundary Layer Turbulence Based on an Analytically Solvable Multivariate Delta-PDF Model. (2018)
    American Meteorological Society
    In:  EPIC323rd Symposium on Boundary Layers and Turbulence, Renaissance Oklahoma City Convention Center Hotel - Ballroom E, 2018-06-2018-06Renaissance Oklahoma City Convention Center Hotel - Ballroom E, American Meteorological Society
    Details
    Publication Date: 2018-08-08
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 14
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    Evolutionary genomics of the cold-adapted diatom Fragilariopsis cylindrus (2017)
    Nature Publishing Group
    In:  EPIC3Nature, Nature Publishing Group, 541, pp. 536-540, ISSN: 0028-0836
    Details
    Publication Date: 2019-03-08
    Description: The Southern Ocean houses a diverse and productive community of organisms. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis cylindrus based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. cylindrus genome consists of genetic loci with alleles that are highly divergent from those of temperate diatoms (15.1 megabases of the total genome size of 61.1 megabases). These divergent alleles were differentially expressed across environmental conditions, including darkness, low iron, freezing, elevated temperature and increased CO2. Alleles with the largest ratio of non-synonymous to synonymous nucleotide substitutions also show the most pronounced condition-dependent expression, suggesting a correlation between diversifying selection and allelic differentiation. Divergent alleles may be involved in adaptation to environmental fluctuations in the Southern Ocean.
    Repository Name: EPIC Alfred Wegener Institut
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  • 15
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    Projected changes in intense precipitation over Europe at the daily and sub-daily time scales (2015)
    American Meteorological Society
    Details
    Publication Date: 2016-10-06
    Description: Heavy precipitation is a major hazard over Europe. It is well established that climate model projections indicate a tendency towards more extreme daily rainfall events. It is still uncertain, however, how this changing intensity translates at the sub-daily time scales. The main goal of the present study is to examine possible differences in projected changes in intense precipitation events over Europe at the daily and sub-daily (3-hourly) time scales using a state-of-the-science climate model. The focus will be on one Representative Concentration Pathway (RCP 8.5), considered as illustrative of a high rate of increase in greenhouse gas concentrations over this century. There are statistically significant differences in intense precipitation projections (up to 40%) when comparing the results at the daily and sub-daily time scales. Over north-eastern Europe, projected precipitation intensification at the 3-hour scale is lower than at the daily scale. On the other hand, Spain and the western seaboard exhibit an opposite behaviour, with stronger intensification at the 3-hour scale rather than daily scale. While the mean properties of the precipitation distributions are independent of the analysed frequency, projected precipitation intensification exhibits regional differences. This finding has implications on the extrapolation of impacts of intense precipitation events, given the daily time scale the analyses are usually performed at.
    Description: Published
    Description: 6193–6203
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: rainfall ; extreme events ; heavy precipitation ; snow ; europe ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 16
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    Dynamic feeder dyke systems in basaltic volcanoes: the exceptional example o fthe 1809 Etna eruption (Italy) (2015)
    Nature Publishing Group
    Details
    Publication Date: 2017-04-04
    Description: In this paper, we describe the 1809 eruption of Mt. Etna, Italy, which represents one historical rare case in which it is possible to observe details of the internal structure of the feeder system. This is possible thanks to the presence of two large pit craters located in the middle of the eruptive fracture field that allow studying a section of the shallow feeder system. Along the walls of one of these craters, we analysed well-exposed cross sections of the uppermost 15–20 m of the feeder system and related volcanic products. Here, we describe the structure, morphology and lithology of this portion of the 1809 feeder system, including the host rock which conditioned the propagation of the dyke, and compare the results with other recent eruptions. Finally, we propose the dynamic model of the magma behaviour inside a laterally-propagating feeder dyke, demonstrating how this dynamic triggered important changes in the eruptive style (from effusive/Strombolian to phreatomagmatic) during the same eruption. Our results are also useful for hazard assessment related to the development of flank eruptions, potentially the most hazardous type of eruption from basaltic volcanoes in densely urbanized areas, such as Mt. Etna.
    Description: Published
    Description: 1-11
    Description: 2T. Tettonica attiva
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 3V. Dinamiche e scenari eruttivi
    Description: 4V. Vulcani e ambiente
    Description: 6A. Monitoraggio ambientale, sicurezza e territorio
    Description: N/A or not JCR
    Description: open
    Keywords: feeder dyke ; basaltic volcanoes ; flank eruptions ; Etna ; volcanic hazards ; sill ; volcanic rift ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 17
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    On the internal variability of simulated daily precipitation (2015)
    American Meteorological Society
    Details
    Publication Date: 2017-04-04
    Description: Climate model simulations are currently the main tool to provide information about possible future climates. Apart from scenario uncertainties and model error, internal variability is a major source of uncertainty, complicating predictions of future changes. Here, a suite of statistical tests is proposed to determine the shortest time window necessary to capture the internal precipitation variability in a stationary climate. The length of this shortest window thus expresses internal variability in terms of years. The method is applied globally to daily precipitation in a 200-yr preindustrial climate simulation with the CMCC-CM coupled general circulation model. The two-sample Cramér–von Mises test is used to assess differences in precipitation distribution, the Walker test accounts for multiple testing at grid cell level, and field significance is determined by calculating the Bejamini–Hochberg false-discovery rate. Results for the investigated simulation show that internal variability of daily precipitation is regionally and seasonally dependent and that regions requiring long time windows do not necessarily coincide with areas with large standard deviation. The estimated time scales are longer over sea than over land, in the tropics than in midlatitudes, and in the transitional seasons than in winter and summer. For many land grid cells, 30 seasons suffice to capture the internal variability of daily precipitation. There exist regions, however, where even 50 years do not suffice to sample the internal variability. The results show that diagnosing daily precipitation change at different times based on fixed global snapshots of one climate simulation might not be a robust detection method.
    Description: Published
    Description: 3624–3630
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: precipitation ; internal variability ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 18
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    South Asian summer monsoon and the eastern Mediterranean climate: the monsoon-desert mechanism in CMIP5 simulations (2015)
    American Meteorological Society
    Details
    Publication Date: 2017-04-04
    Description: We acknowledge the World Climate Research Programme's Working Group on Coupled Modeling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1 of this paper) for producing and making available their model outputs. For CMIP the U.S. Department of Energy's Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. The financial support of the Italian Ministry of Education, University and Research, and Ministry for Environment, Land and Sea through the project GEMINA and that of INDO-MARECLIM (Project 295092) is gratefully acknowledged. A. Cherchi thankfully acknowledges the generous hospitality of the International Pacific Research Center at UH Manoa, Honolulu. Jan Hafner is thanked for providing the moist static energy budget code used here and Matthew Windlansky is thanked for comments and proof reading. H. Annamalai acknowledges the partial support by the Office of Science (BER) U.S. Department of Energy, Grant DE-FG02-07ER6445, and also by the three institutional grants (JAMSTEC, NASA, NOAA) of the IPRC. Dr. Chen and an anonymous reviewer are acknowledged for the instructive and helpful comments given.
    Description: Dry summers over the eastern Mediterranean are characterized by strong descent anchored by long Rossby waves, which are forced by diabatic heating associated with summer monsoon rainfall over South Asia. The large-scale teleconnection between rising and subsiding air masses is referred to as the "monsoon-desert mechanism.'' This study evaluates the ability of the phase 5 of the Coupled Model Intercomparison Project (CMIP5) models in representing the physical processes involved in this mechanism. An evaluation of statistics between summer climatologies of monsoon diabatic heating and that of vertical velocity over the eastern Mediterranean suggests a linear relationship. Despite large spatial diversity in monsoon heating, descent over the Mediterranean is coherently located and realistic in intensity. To measure the sensitivity of descent to the diversity in the horizontal and vertical distribution of monsoon heating, a series of linear atmosphere model experiments are performed. It is shown that column-integrated heating over both the Bay of Bengal and the Arabian Sea provides the largest descent with a more realistic spatial pattern. In the vertical, CMIP5 models underestimate the diabatic heating at upper levels, while they overestimate it at lower levels, resulting in a weaker forced response and weaker associated descent over the Mediterranean. A moist static energy budget analysis applied to CMIP5 suggests that most models capture the dominant role of horizontal temperature advection and radiative fluxes in balancing descent over the Mediterranean. Based on the objective analysis herein, a subset of models is identified that captures the teleconnection for reasons consistent with observations. The recognized processes vary at interannual time scales as well, with imprints of severe weak/strong monsoons noticeable over the Mediterranean.
    Description: Italian Ministry of Education, University and Research Ministry for Environment, Land and Sea through the project GEMINA INDO-MARECLIM 295092 Office of Science (BER) U.S. Department of Energy DE-FG02-07ER6445 (JAMSTEC) of the IPRC (NASA) of the IPRC (NOAA) of the IPRC
    Description: Published
    Description: 6877-6903
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: open
    Keywords: Rossby waves ; Teleconnections ; Diabatic heating ; Coupled models ; Model evaluation/performance ; Interannual variability ; 03. Hydrosphere::03.01. General::03.01.03. Global climate models
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Estimation and Impact of Nonuniform Horizontal Correlation Length Scales for Global Ocean Physical Analyses (2015)
    American Meteorological Society
    Details
    Publication Date: 2017-04-04
    Description: Optimally modeling background-error horizontal correlations is crucial in ocean data assimilation. This paper investigates the impact of releasing the assumption of uniform background-error correlations in a global ocean variational analysis system. Spatially varying horizontal correlations are introduced in the recursive filter operator, which is used for modeling horizontal covariances in the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC) analysis system. The horizontal correlation length scales (HCLSs) were defined on the full three-dimensional model space and computed from both a dataset of monthly anomalies with respect to the monthly climatology and through the so-called National Meteorological Center (NMC) method. Different formulas for estimating the correlation length scale are also discussed and applied to the two forecast error datasets. The new formulation is tested within a 12-yr period (2000–11) in the ½° resolution system. The comparison with the data assimilation system using uniform background-error horizontal correlations indicates the superiority of the former, especially in eddy-dominated areas. Verification skill scores report a significant reduction of RMSE, and the use of nonuniform length scales improves the representation of the eddy kinetic energy at midlatitudes, suggesting that uniform, latitude, or Rossby radius-dependent formulations are insufficient to represent the geographical variations of the background-error correlations. Furthermore, a small tuning of the globally uniform value of the length scale was found to have a small impact on the analysis system. The use of either anomalies or NMC-derived correlation length scales also has a marginal effect with respect to the use of nonuniform HCLSs. On the other hand, the application of overestimated length scales has proved to be detrimental to the analysis system in all areas and for all parameters.
    Description: This work has received funding from the Italian Ministry of Education, University and Research and the Italian Ministry for the Environment, Land and Sea under the GEMINA project and from the European Commission's Copernicus program, previously known as the GMES program, under the MyOcean and MyOcean2 projects.
    Description: Published
    Description: 2330-2349
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: open
    Keywords: DATA ASSIMILATION SCHEME ; TROPICAL PACIFIC-OCEAN ; PART I ; VARIATIONAL ASSIMILATION ; COVARIANCE FUNCTIONS ; DIFFUSION EQUATION ; SYSTEM ; TEMPERATURE ; IMPLEMENTATION ; MODEL ; 03. Hydrosphere::03.01. General::03.01.04. Ocean data assimilation and reanalysis
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Seismic footprints of shallow dyke propagation at Etna, Italy (2016)
    Nature Publishing Group
    Details
    Publication Date: 2017-04-04
    Description: One of the key issues in forecasting volcanic eruptions is to detect signals that can track the propagation of dykes towards the surface. Continuous monitoring of active volcanoes helps significantly in achieving this goal. The seismic data presented here are unique, as they document surface faulting processes close (tens to a few hundred meters) to their source, namely the dyke tip. They originated nearby - and under - a seismic station that was subsequently destroyed by lava flows during eruptive activity at Etna volcano, Italy, in 2013. On February 20, a ~600 m-long and ~120 m wide NW-SE fracture field opened at an altitude between 2750 and 2900 m. The consequent rock dislocation caused the station to tilt and offset the seismic signal temporarily. Data acquisition continued until the arrival of the lava flow that led to the breakdown of the transmission system. Shallow ground fracturing and repeated low-frequency oscillations occurred during two stages in which the seismic signal underwent a maximum offset ~2.57 E+04 nm/s. Bridging instrumental recordings, fieldwork and conceptual modelling, these data are interpreted as the seismic footprints of a magmatic dyke intrusion that moved at speed ~0.02 m/s (first stage) and 0.46 m/s (second stage).
    Description: This work was supported by the MED-SUV project, which has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No 308665.
    Description: Published
    Description: 11908
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: dyke propagation ; Etna ; seismic signals ; ground fracturing ; conceptual modelling ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Measuring the Sea: Marsili’s Oceanographic Cruise (1679–80) and the Roots of Oceanography (2019)
    American Meteorological Society
    Details
    Publication Date: 2019-03-27
    Description: The first in situ measurements of seawater density that referred to a geographical position at sea and time of the year were carried out by Count Luigi Ferdinando Marsili between 1679 and 1680 in the Adriatic Sea, Aegean Sea, Marmara Sea, and the Bosporus. Not only was this the first investigation with documented oceanographic measurements carried out at stations, but themeasurements were described in such an accurateway that the authorswere able to reconstruct the observations in modern units. These first measurements concern the ‘‘specific gravity’’ of seawaters (i.e., the ratio between fluid densities). The data reported in the historical oceanographic treatise Osservazioni intorno al Bosforo Tracio (Marsili) allowed the reconstruction of the seawater density at different geographic locations between 1679 and 1680. Marsili’s experimental methodology included the collection of surface and deep water samples, the analysis of the samples with a hydrostatic ampoule, and the use of a reference water to standardize the measurements.Acomparison of reconstructed densities with present-day values shows an agreement within 10%–20% uncertainty, owing to various aspects of the measurement methodology that are difficult to reconstruct from the documentary evidence. Marsili also measured the current speed and the depth of the current inversion in the Bosporus, which are consistent with the present-day knowledge. The experimental data collected in the Bosporus enabledMarsili to enunciate a theory on the cause of the two-layer flow at the strait, demonstrated by his laboratory experiment and later confirmed by many analytical and numerical studies.
    Description: American Meteorological Society.
    Description: Published
    Description: 845 - 860
    Description: 4A. Oceanografia e clima
    Description: JCR Journal
    Keywords: Ocean ; Density currents ; Measurements ; Ship observations
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    A novel approach to estimate the eruptive potential and probability in open conduit volcanoes (2016)
    Nature Publishing Group
    Details
    Publication Date: 2017-04-04
    Description: In open conduit volcanoes, volatile-rich magma continuously enters into the feeding system nevertheless the eruptive activity occurs intermittently. From a practical perspective, the continuous steady input of magma in the feeding system is not able to produce eruptive events alone, but rather surplus of magma inputs are required to trigger the eruptive activity. The greater the amount of surplus of magma within the feeding system, the higher is the eruptive probability.Despite this observation, eruptive potential evaluations are commonly based on the regular magma supply, and in eruptive probability evaluations, generally any magma input has the same weight. Conversely, herein we present a novel approach based on the quantification of surplus of magma progressively intruded in the feeding system. To quantify the surplus of magma, we suggest to process temporal series of measurable parameters linked to the magma supply. We successfully performed a practical application on Mt Etna using the soil CO2 flux recorded over ten years.
    Description: Published
    Description: 30471
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: eruptive potential ; eruptive probability ; open conduit volcanoes ; Etna ; Soil CO2 flux ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.08. Risk::05.08.01. Environmental risk
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    Recent Arctic tundra fire initiates widespread thermokarst development (2015)
    Nature Publishing Group
    In:  EPIC3Scientific Reports, Nature Publishing Group, 5, pp. 15865, ISSN: 2045-2322
    Details
    Publication Date: 2015-10-31
    Description: Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burn severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for ~50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions.
    Repository Name: EPIC Alfred Wegener Institut
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    Correction of ADCP compass errors resulting from iron in the instrument’s vicinity (2015)
    American Meteorological Society
    In:  EPIC3Journal of Atmospheric and Oceanic Technology, American Meteorological Society, 32, pp. 591-602
    Details
    Publication Date: 2015-06-19
    Description: Iron in the vicinity of compasses results in magnetic deviations. ADCPs mounted on steel buoyancy devices and deployed on seven moorings on the East Greenland outer shelf and upper slope from 2007 to 2008 suffered from severe magnetic deviations of $〉$90$^\circ$ rendering the ADCP data useless without a compass correction. The effects on the measured velocities, which may also be present in other oceanic velocity measurements, are explained. On each of the moorings, velocity measurements from a different instrument which was assumed not to be affected by magnetic deviation are overlapping in space and time with the compromised ones. A method is described to determine the magnetic compass deviation from the compromised and uncompromised velocity measurements and the compromised compass headings. The method depends on the assumption that at least one instrument per mooring is not compromised. With this method, the magnetic deviation as well as the originally compromised velocity records can be corrected. The method is described in detail and a MATLAB(R) script implementing the method is supplied. The success of the method is demonstrated for one of the moorings.
    Repository Name: EPIC Alfred Wegener Institut
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    Resolving the controls of water vapour isotopes in the Atlantic sector (2019)
    Nature Publishing Group
    In:  EPIC3Nature Communications, Nature Publishing Group, 10, ISSN: 2041-1723
    Details
    Publication Date: 2020-01-21
    Description: Stable water isotopes are employed as hydrological tracers to quantify the diverse implications of atmospheric moisture for climate. They are widely used as proxies for studying past climate changes, e.g., in isotope records from ice cores and speleothems. Here, we present a new isotopic dataset of both near-surface vapour and ocean surface water from the North Pole to Antarctica, continuously measured from a research vessel throughout the Atlantic and Arctic Oceans during a period of two years. Our observations contribute to a better understanding and modelling of water isotopic composition. The observations reveal that the vapour deuterium excess within the atmospheric boundary layer is not modulated by wind speed, contrary to the commonly used theory, but controlled by relative humidity and sea surface temperature only. In sea ice covered regions, the sublimation of deposited snow on sea ice is a key process controlling the local water vapour isotopic composition.
    Repository Name: EPIC Alfred Wegener Institut
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    The fate of the southern Weddell Sea continental shelf in a warming climate (2017)
    American Meteorological Society
    In:  EPIC3Journal of Climate, American Meteorological Society, 30, pp. 4337-4350, ISSN: 0894-8755
    Details
    Publication Date: 2017-12-15
    Description: Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in the Weddell and Ross Seas melt at rates orders ofmagnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet.
    Repository Name: EPIC Alfred Wegener Institut
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    A global multiproxy database for temperature reconstructions of the Common Era (2017)
    Nature Publishing Group
    In:  EPIC3Scientific Data, Nature Publishing Group, 4(170088), pp. 1-33, ISSN: 2052-4463
    Details
    Publication Date: 2017-07-21
    Description: Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.
    Repository Name: EPIC Alfred Wegener Institut
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    Growth of a deep-water, predatory fish is influenced by the productivity of a boundary current system (2015)
    Nature Publishing Group
    In:  EPIC3Nature Scientific Reports, Nature Publishing Group
    Details
    Publication Date: 2017-01-20
    Description: The effects of climate change on predatory fishes in deep shelf areas are difficult to predict because complex processes may govern food availability and temperature at depth. We characterised the net impact of recent environmental changes on hapuku (Polyprion oxygeneios), an apex predator found in continental slope habitats (〉200 m depth) by using dendrochronology techniques to develop a multi-decadal record of growth from otoliths. Fish were sampled off temperate south-western Australia, a region strongly influenced by the Leeuwin Current, a poleward-flowing, eastern boundary current. The common variance among individual growth records was relatively low (3.4%), but the otolith chronology was positively correlated (r = 0.61, p 〈 0.02) with sea level at Fremantle, a proxy for the strength of the Leeuwin Current. The Leeuwin Current influences the primary productivity of shelf ecosystems, with a strong current favouring growth in hapuku. Leeuwin Current strength is predicted to decline under climate change models and this study provides evidence that associated productivity changes may flow through to higher trophic levels even in deep water habitats.
    Repository Name: EPIC Alfred Wegener Institut
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    Seasonal cycle of mesoscale instability of the West Spitsbergen Current (2016)
    American Meteorological Society
    In:  EPIC3Journal of Physical Oceanography, American Meteorological Society, 46(4), pp. 1231-1254
    Details
    Publication Date: 2016-11-03
    Description: The West Spitsbergen Current (WSC) is a topographically steered boundary current that transports warm Atlantic Water northward in Fram Strait. The 16 yr (1997–2012) current and temperature–salinity measurements from moorings in the WSC at 78°50′N reveal the dynamics of mesoscale variability in the WSC and the central Fram Strait. A strong seasonality of the fluctuations and the proposed driving mechanisms is described. In winter, water is advected in the WSC that has been subjected to strong atmospheric cooling in the Nordic Seas, and as a result the stratification in the top 250 m is weak. The current is also stronger than in summer and has a greater vertical shear. This results in an e-folding growth period for baroclinic instabilities of about half a day in winter, indicating that the current has the ability to rapidly grow unstable and form eddies. In summer, the WSC is significantly less unstable with an e-folding growth period of 2 days. Observations of the eddy kinetic energy (EKE) show a peak in the boundary current in January–February when it is most unstable. Eddies are then likely advected westward, and the EKE peak is observed 1–2 months later in the central Fram Strait. Conversely, the EKE in the WSC as well as in the central Fram Strait is reduced by a factor of more than 3 in late summer. Parameterizations for the expected EKE resulting from baroclinic instability can account for the observed EKE values. Hence, mesoscale instability can generate the observed variability, and high-frequency wind forcing is not required to explain the observed EKE.
    Repository Name: EPIC Alfred Wegener Institut
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    Acidification reduced growth rate but not swimming speed of larval sea urchins (2015)
    Nature Publishing Group
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 5 (2015): 9764, doi:10.1038/srep09764.
    Description: Swimming behaviors of planktonic larvae impact dispersal and population dynamics of many benthic marine invertebrates. This key ecological function is modulated by larval development dynamics, biomechanics of the resulting morphology, and behavioral choices. Studies on ocean acidification effects on larval stages have yet to address this important interaction between development and swimming under environmentally-relevant flow conditions. Our video motion analysis revealed that pH covering present and future natural variability (pH 8.0, 7.6 and 7.2) did not affect age-specific swimming of larval green urchin Strongylocentrotus droebachiensis in still water nor in shear, despite acidified individuals being significantly smaller in size (reduced growth rate). This maintenance of speed and stability in shear was accompanied by an overall change in size-corrected shape, implying changes in swimming biomechanics. Our observations highlight strong evolutionary pressure to maintain swimming in a varying environment and the plasticity in larval responses to environmental change.
    Description: K.C. was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution (WHOI), with funding provided by the Coastal Ocean Institute, the Croucher Foundation, and the Royal Swedish Academy of Sciences. S.D. was financially supported by the Linnaeus Centre for Marine Evolutionary Biology at the University of Gothenburg (http://www.cemeb.science.gu.se/) and a Linnaeus grant from the Swedish Research Councils VR and Formas. Additional funding was provided from the European Seventh Framework Programme under grant agreement 265847.
    Repository Name: Woods Hole Open Access Server
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    Radar remote sensing estimates of waves and wave forcing at a tidal inlet (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 32 (2015): 842–854, doi:10.1175/JTECH-D-14-00215.1.
    Description: The time and space variability of wave transformation through a tidal inlet is investigated with radar remote sensing. The frequency of wave breaking and the net wave breaking dissipation at high spatial resolution is estimated using image sequences acquired with a land-based X-band marine radar. Using the radar intensity data, transformed to normalized radar cross section σ0, the temporal and spatial distributions of wave breaking are identified using a threshold developed via the data probability density function. In addition, the inlet bathymetry is determined via depth inversion of the radar-derived frequencies and wavenumbers of the surface waves using a preexisting algorithm (cBathy). Wave height transformation is calculated through the 1D cross-shore energy flux equation incorporating the radar-estimated breaking distribution and bathymetry. The accuracy of the methodology is tested by comparison with in situ wave height observations over a 9-day period, obtaining correlation values R = 0.68 to 0.96, and root-mean-square errors from 0.05 to 0.19 m. Predicted wave forcing, computed as the along-inlet gradient of the cross-shore radiation stress was onshore during high-wave conditions, in good agreement (R = 0.95) with observations.
    Description: These data were collected as part of a joint field program, Data Assimilation and Remote Sensing for Littoral Applications (DARLA) and Rivers and Inlets (RIVET-1), both funded by the Office of Naval Research. The authors were funded through the Office of Naval Research Grant N00014-10-1-0932 and the Office of the Assistant Secretary of Defense for Research and Engineering.
    Description: 2015-10-01
    Keywords: Wave breaking ; Waves, oceanic ; Wind waves ; In situ oceanic observations ; Radars/Radar observations ; Remote sensing
    Repository Name: Woods Hole Open Access Server
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    The role of whitecapping in thickening the ocean surface boundary layer (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2006–2024, doi:10.1175/JPO-D-14-0234.1.
    Description: The effects of wind-driven whitecapping on the evolution of the ocean surface boundary layer are examined using an idealized one-dimensional Reynolds-averaged Navier–Stokes numerical model. Whitecapping is parameterized as a flux of turbulent kinetic energy through the sea surface and through an adjustment of the turbulent length scale. Simulations begin with a two-layer configuration and use a wind that ramps to a steady stress. This study finds that the boundary layer begins to thicken sooner in simulations with whitecapping than without because whitecapping introduces energy to the base of the boundary layer sooner than shear production does. Even in the presence of whitecapping, shear production becomes important for several hours, but then inertial oscillations cause shear production and whitecapping to alternate as the dominant energy sources for mixing. Details of these results are sensitive to initial and forcing conditions, particularly to the turbulent length scale imposed by breaking waves and the transfer velocity of energy from waves to turbulence. After 1–2 days of steady wind, the boundary layer in whitecapping simulations has thickened more than the boundary layer in simulations without whitecapping by about 10%–50%, depending on the forcing and initial conditions.
    Description: We thank Skidmore College for financial and infrastructure support, and Skidmore and the National Science Foundation for funding travel to meetings where early versions of this work were presented. We also thank the National Science Foundation, Oregon State University, Jonathan Nash, and Joe Jurisa for funding and hosting a workshop on River Plume Mixing in October, 2013, where ideas and context for this paper were developed.
    Description: 2016-02-01
    Keywords: Circulation/ Dynamics ; Mixing ; Turbulence ; Wave breaking ; Wind stress ; Atm/Ocean Structure/ Phenomena ; Mixed layer
    Repository Name: Woods Hole Open Access Server
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    Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide (2015)
    Nature Publishing Group
    Details
    Publication Date: 2022-05-25
    Description: This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 6 (2015): 8155, doi:10.1038/ncomms9155.
    Description: Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium Trichodesmium increase under high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. Here we show that experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean.
    Description: Grant support was provided by U.S. National Science Foundation OCE 1260490 and OCE 1143760 to D.A.H., E.A.W., and F.-X.F, and OCE 1260233, OCE OA 1220484, and G.B. Moore Foundation 3782 and 3934 to M.A.S.© The Author(s), [year].
    Repository Name: Woods Hole Open Access Server
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    Robust warming pattern of global subtropical oceans and its mechanism (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 8574–8584, doi:10.1175/JCLI-D-14-00809.1.
    Description: The subsurface ocean response to anthropogenic climate forcing remains poorly characterized. From the Coupled Model Intercomparison Project (CMIP), a robust response of the lower thermocline is identified, where the warming is considerably weaker in the subtropics than in the tropics and high latitudes. The lower thermocline change is inversely proportional to the thermocline depth in the present climatology. Ocean general circulation model (OGCM) experiments show that sea surface warming is the dominant forcing for the subtropical gyre change in contrast to natural variability for which wind dominates, and the ocean response is insensitive to the spatial pattern of surface warming. An analysis based on a ventilated thermocline model shows that the pattern of the lower thermocline change can be interpreted in terms of the dynamic response to the strengthened stratification and downward heat mixing. Consequently, the subtropical gyres become intensified at the surface but weakened in the lower thermcline, consistent with results from CMIP experiments.
    Description: The work was supported by the National Basic Research Program of China (2012CB955600), the National Natural Science Foundation of China (41125019, 41206021), and the U.S. National Science Foundation (AGS 1249145, 1305719).
    Description: 2016-05-01
    Keywords: Circulation/ Dynamics ; Ocean circulation ; Physical Meteorology and Climatology ; Climate change
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    Jurassic zircons from the Southwest Indian Ridge (2016)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 6 (2016): 26260, doi:10.1038/srep26260.
    Description: The existence of ancient rocks in present mid-ocean ridges have long been observed but received less attention. Here we report the discovery of zircons with both reasonably young ages of about 5 Ma and abnormally old ages of approximate 180 Ma from two evolved gabbroic rocks that were dredged from the Southwest Indian Ridge (SWIR) in the Gallieni fracture zone. U–Pb and Lu–Hf isotope analyses of zircons were made using ion probe and conventional laser abrasion directly in petrographic thin sections. Young zircons and their host oxide gabbro have positive Hf isotope compositions (εHf = +15.7–+12.4), suggesting a highly depleted mantle beneath the SWIR. The spread εHf values (from−2.3 to−4.5) of abnormally old zircons, together with the unradiogenic Nd-Hf isotope of the host quartz diorite, appears to suggest an ancient juvenile magmatism along the rifting margin of the southern Gondwana prior to the opening of the Indian Ocean. A convincing explanation for the origin of the unusually old zircons is yet to surface, however, an update of the theory of plate tectonics would be expected with continuing discovery of ancient rocks in the mid-oceanic ridges and abyssal ocean basins.
    Description: This work was supported by the National Natural Science Foundation of China (41573046) to H.C. and the Chinese National Key Basic Research Program (2012CB417300) to H.Z.
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    Paleochannel and beach-bar palimpsest topography as initial substrate for coralligenous buildups offshore Venice, Italy (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 1321, doi:10.1038/s41598-017-01483-z.
    Description: We provide a model for the genesis of Holocene coralligenous buildups occurring in the northwestern Adriatic Sea offshore Venice at 17–24 m depth. High-resolution geophysical surveys and underwater SCUBA diving reconnaissance revealed meandering shaped morphologies underneath bio-concretionned rocky buildups. These morphologies are inferred to have been inherited from Pleistocene fluvial systems reactivated as tidal channels during the post- Last Glacial Maximum transgression, when the study area was a lagoon protected by a sandy barrier. The lithification of the sandy fossil channel-levee systems is estimated to have occurred at ca. 7 cal. ka BP, likely due to the interaction between marine and less saline fluids related to onshore freshwater discharge at sea through a sealed water-table. The carbonate-cemented sandy layers served as nucleus for subsequent coralligenous buildups growth.
    Description: Funded by the Italian Ministry of Education, University and Research within the National Research Program 2011–2013.
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    El Niño increases the risk of lower Mississippi River flooding (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 1772, doi:10.1038/s41598-017-01919-6.
    Description: Mississippi River floods rank among the costliest climate-related disasters in the world. Improving flood predictability, preparedness, and response at seasonal to decadal time-scales requires an understanding of the climatic controls that govern flood occurrence. Linking flood occurrence to persistent modes of climate variability like the El Niño-Southern Oscillation (ENSO) has proven challenging, due in part to the limited number of high-magnitude floods available for study in the instrumental record. To augment the relatively short instrumental record, we use output from the Community Earth System Model (CESM) Last Millennium Ensemble (LME) to investigate the dynamical controls on discharge extremes of the lower Mississippi River. We show that through its regional influence on surface water storage, the warm phase of ENSO preconditions the lower Mississippi River to be vulnerable to flooding. In the 6–12 months preceding a flood, El Niño generates a positive precipitation anomaly over the lower Mississippi basin that gradually builds up soil moisture and reduces the basin’s infiltration capacity, thereby elevating the risk of a major flood during subsequent rainstorms. Our study demonstrates how natural climate variability mediates the formation of extreme floods on one of the world’s principal commercial waterways, adding significant predictive ability to near- and long-term forecasts of flood risk.
    Description: This work was funded through the Postdoctoral Scholar Program of the Woods Hole Oceanographic Institution and the Voss Environmental Postdoctoral Fellows Program at Brown University.
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    The global ocean water cycle in atmospheric reanalysis, satellite, and ocean salinity (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 30 (2017): 3829-3852, doi:10.1175/JCLI-D-16-0479.1.
    Description: This study provides an assessment of the uncertainty in ocean surface (OS) freshwater budgets and variability using evaporation E and precipitation P from 10 atmospheric reanalyses, two combined satellite-based E − P products, and two observation-based salinity products. Three issues are examined: the uncertainty level in the OS freshwater budget in atmospheric reanalyses, the uncertainty structure and association with the global ocean wet/dry zones, and the potential of salinity in ascribing the uncertainty in E − P. The products agree on the global mean pattern but differ considerably in magnitude. The OS freshwater budgets are 129 ± 10 (8%) cm yr−1 for E, 118 ± 11 (9%) cm yr−1 for P, and 11 ± 4 (36%) cm yr−1 for E − P, where the mean and error represent the ensemble mean and one standard deviation of the ensemble spread. The E − P uncertainty exceeds the uncertainty in E and P by a factor of 4 or more. The large uncertainty is attributed to P in the tropical wet zone. Most reanalyses tend to produce a wider tropical rainband when compared to satellite products, with the exception of two recent reanalyses that implement an observation-based correction for the model-generated P over land. The disparity in the width and the extent of seasonal migrations of the tropical wet zone causes a large spread in P, implying that the tropical moist physics and the realism of tropical rainfall remain a key challenge. Satellite salinity appears feasible to evaluate the fidelity of E − P variability in three tropical areas, where the uncertainty diagnosis has a global indication.
    Description: Primary support for the study is provided by the NOAAModeling, Analysis, Predictions, and Projections (MAPP) Program’s Climate Reanalysis Task Force (CRTF) through Grant NA13OAR4310106.
    Description: 2017-11-02
    Keywords: Hydrologic cycle ; Precipitation ; Evaporation ; Salinity ; Water budget ; Reanalysis data
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    Evidence for fungal and chemodenitrification based N2O flux from nitrogen impacted coastal sediments (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 15595, doi:10.1038/ncomms15595.
    Description: Although increasing atmospheric nitrous oxide (N2O) has been linked to nitrogen loading, predicting emissions remains difficult, in part due to challenges in disentangling diverse N2O production pathways. As coastal ecosystems are especially impacted by elevated nitrogen, we investigated controls on N2O production mechanisms in intertidal sediments using novel isotopic approaches and microsensors in flow-through incubations. Here we show that during incubations with elevated nitrate, increased N2O fluxes are not mediated by direct bacterial activity, but instead are largely catalysed by fungal denitrification and/or abiotic reactions (e.g., chemodenitrification). Results of these incubations shed new light on nitrogen cycling complexity and possible factors underlying variability of N2O fluxes, driven in part by fungal respiration and/or iron redox cycling. As both processes exhibit N2O yields typically far greater than direct bacterial production, these results emphasize their possibly substantial, yet widely overlooked, role in N2O fluxes, especially in redox-dynamic sediments of coastal ecosystems.
    Description: D.D.B. acknowledges support from the Max Planck Institute for Marine Microbiology. This work was supported by the National Science Foundation grants to W.Z. and S.D.W. (OCE-1260373) and to S.D.W. (EAR-1252161).
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    Differential specificity between closely related corals and abundant Endozoicomonas endosymbionts across global scales (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in The ISME Journal 11 (2017): 186–200, doi:10.1038/ismej.2016.95.
    Description: Reef-building corals are well regarded not only for their obligate association with endosymbiotic algae, but also with prokaryotic symbionts, the specificity of which remains elusive. To identify the central microbial symbionts of corals, their specificity across species and conservation over geographic regions, we sequenced partial SSU ribosomal RNA genes of Bacteria and Archaea from the common corals Stylophora pistillata and Pocillopora verrucosa across 28 reefs within seven major geographical regions. We demonstrate that both corals harbor Endozoicomonas bacteria as their prevalent symbiont. Importantly, catalyzed reporter deposition–fluorescence in situ hybridization (CARD–FISH) with Endozoicomonas-specific probes confirmed their residence as large aggregations deep within coral tissues. Using fine-scale genotyping techniques and single-cell genomics, we demonstrate that P. verrucosa harbors the same Endozoicomonas, whereas S. pistillata associates with geographically distinct genotypes. This specificity may be shaped by the different reproductive strategies of the hosts, potentially uncovering a pattern of symbiont selection that is linked to life history. Spawning corals such as P. verrucosa acquire prokaryotes from the environment. In contrast, brooding corals such as S. pistillata release symbiont-packed planula larvae, which may explain a strong regional signature in their microbiome. Our work contributes to the factors underlying microbiome specificity and adds detail to coral holobiont functioning.
    Description: This research was supported by a KAUST-WHOI Post-doctoral Partnership Award to MN and a KAUST-WHOI Special Academic Partnership Funding Reserve Award to CRV and AA. Research in this study was further supported by baseline research funds to CRV by KAUST and NSF award OCE-1233612 to AA. RR was supported by the ct-PIRE Project, Robert Lemelson Fellowship, Graduate Research Award (UCLA), Women Divers Hall of Fame—Sister Fund Conservation Award and a Betty and E. P. Franklin Grant in Tropical Biology and Conservation.
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    Assessing the dynamics of organic aerosols over the North Atlantic Ocean (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 45476, doi:10.1038/srep45476.
    Description: The influence of aerosols on climate is highly dependent on the particle size distribution, concentration, and composition. In particular, the latter influences their ability to act as cloud condensation nuclei, whereby they impact cloud coverage and precipitation. Here, we simultaneously measured the concentration of aerosols from sea spray over the North Atlantic on board the exhaust-free solar-powered vessel “PlanetSolar”, and the sea surface physico-chemical parameters. We identified organic-bearing particles based on individual particle fluorescence spectra. Organic-bearing aerosols display specific spatio-temporal distributions as compared to total aerosols. We propose an empirical parameterization of the organic-bearing particle concentration, with a dependence on water salinity and sea-surface temperature only. We also show that a very rich mixture of organic aerosols is emitted from the sea surface. Such data will certainly contribute to providing further insight into the influence of aerosols on cloud formation, and be used as input for the improved modeling of aerosols and their role in global climate processes.
    Description: We gratefully acknowledge the financial support by the H. Dudley Wright and the Henri Moser Foundations, the Rector’s Office and the Institute for Environmental Sciences at the University of Geneva, as well as a generous anonymous donator.
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    Response of the North Pacific tropical cyclone climatology to global warming : application of dynamical downscaling to CMIP5 models (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 30 (2017): 1233-1243, doi:10.1175/JCLI-D-16-0496.1.
    Description: A downscaling approach is applied to future projection simulations from four CMIP5 global climate models to investigate the response of the tropical cyclone (TC) climatology over the North Pacific basin to global warming. Under the influence of the anthropogenic rise in greenhouse gases, TC-track density, power dissipation, and TC genesis exhibit robust increasing trends over the North Pacific, especially over the central subtropical Pacific region. The increase in North Pacific TCs is primarily manifested as increases in the intense and relatively weak TCs. Examination of storm duration also reveals that TCs over the North Pacific have longer lifetimes under global warming. Through a genesis potential index, the mechanistic contributions of various physical climate factors to the simulated change in TC genesis are explored. More frequent TC genesis under global warming is mostly attributable to the smaller vertical wind shear and greater potential intensity (primarily due to higher sea surface temperature). In contrast, the effect of the saturation deficit of the free troposphere tends to suppress TC genesis, and the change in large-scale vorticity plays a negligible role.
    Description: The authors acknowledge support from the Strategic Environmental Research and Development Program (SERDP) (RC-2336). SERDP is the environmental science and technology program of the U.S. Department of Defense (DoD) in partnership with the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA).
    Description: 2017-08-01
    Keywords: Tropical cyclones
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    Multidecadal Indian Ocean variability linked to the Pacific and implications for preconditioning Indian Ocean dipole events (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 30 (2017): 1739-1751, doi:10.1175/JCLI-D-16-0200.1.
    Description: The Indian Ocean has sustained robust surface warming in recent decades, but the role of multidecadal variability remains unclear. Using ocean model hindcasts, characteristics of low-frequency Indian Ocean temperature variations are explored. Simulated upper-ocean temperature changes across the Indian Ocean in the hindcast are consistent with those recorded in observational products and ocean reanalyses. Indian Ocean temperatures exhibit strong warming trends since the 1950s limited to the surface and south of 30°S, while extensive subsurface cooling occurs over much of the tropical Indian Ocean. Previous work focused on diagnosing causes of these long-term trends in the Indian Ocean over the second half of the twentieth century. Instead, the temporal evolution of Indian Ocean subsurface heat content is shown here to reveal distinct multidecadal variations associated with the Pacific decadal oscillation, and the long-term trends are thus interpreted to result from aliasing of the low-frequency variability. Transmission of the multidecadal signal occurs via an oceanic pathway through the Indonesian Throughflow and is manifest across the Indian Ocean centered along 12°S as westward-propagating Rossby waves modulating thermocline and subsurface heat content variations. Resulting low-frequency changes in the eastern Indian Ocean thermocline depth are associated with decadal variations in the frequency of Indian Ocean dipole (IOD) events, with positive IOD events unusually common in the 1960s and 1990s with a relatively shallow thermocline. In contrast, the deeper thermocline depth in the 1970s and 1980s is associated with frequent negative IOD and rare positive IOD events. Changes in Pacific wind forcing in recent decades and associated rapid increases in Indian Ocean subsurface heat content can thus affect the basin’s leading mode of variability, with implications for regional climate and vulnerable societies in surrounding countries.
    Description: This research was supported by a Research Fellowship by the Alexander von Humboldt Foundation, as well as the Ocean Climate Change Institute and the Investment in Science Fund at WHOI.
    Description: 2017-08-15
    Keywords: Indian Ocean ; Ocean dynamics ; Climate variability ; Multidecadal variability ; Pacific decadal oscillation
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    Photochemical alteration of organic carbon draining permafrost soils shifts microbial metabolic pathways and stimulates respiration (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 772, doi:10.1038/s41467-017-00759-2.
    Description: In sunlit waters, photochemical alteration of dissolved organic carbon (DOC) impacts the microbial respiration of DOC to CO2. This coupled photochemical and biological degradation of DOC is especially critical for carbon budgets in the Arctic, where thawing permafrost soils increase opportunities for DOC oxidation to CO2 in surface waters, thereby reinforcing global warming. Here we show how and why sunlight exposure impacts microbial respiration of DOC draining permafrost soils. Sunlight significantly increases or decreases microbial respiration of DOC depending on whether photo-alteration produces or removes molecules that native microbial communities used prior to light exposure. Using high-resolution chemical and microbial approaches, we show that rates of DOC processing by microbes are likely governed by a combination of the abundance and lability of DOC exported from land to water and produced by photochemical processes, and the capacity and timescale that microbial communities have to adapt to metabolize photo-altered DOC.
    Description: Funding for this work was provided by NSF grants OPP 1023270, 1022876, CAREER 1351745, DEB 1147378, 1347042, 0639790, 1147336, 1026843, PLR 1504006, DOE-JGI-CSP 1782, and the Camille and Henry Dreyfus Foundation Postdoctoral Program in Environmental Chemistry.
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    Circulation induced by isolated dense water formation over closed topographic contours (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 2251-2265, doi:10.1175/JPO-D-17-0042.1.
    Description: The problem of localized dense water formation over a sloping bottom is considered for the general case in which the topography forms a closed contour. This class of problems is motivated by topography around islands or shallow shoals in which convection resulting from brine rejection or surface heat loss reaches the bottom. The focus of this study is on the large-scale circulation that is forced far from the region of surface forcing. The authors find that a cyclonic current is generated around the topography, in the opposite sense to the propagation of the dense water plume. In physical terms, this current results from the propagation of low sea surface height from the region of dense water formation anticyclonically along the topographic contours back to the formation region. This pressure gradient is then balanced by a cyclonic geostrophic flow. This basic structure is well predicted by a linear quasigeostrophic theory, a primitive equation model, and in rotating tank experiments. For sufficiently strong forcing, the anticyclonic circulation of the dense plume meets this cyclonic circulation to produce a sharp front and offshore advection of dense water at the bottom and buoyant water at the surface. This nonlinear limit is demonstrated in both the primitive equation model and in the tank experiments.
    Description: MAS was supported by the National Science Foundation under Grant OCE-1534618. Support for CC was given by the WHOI Ocean Climate Change Institute Proposal 27071273.
    Description: 2018-03-20
    Keywords: Bottom currents ; Buoyancy ; Ocean dynamics ; Density currents
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    Defining a critical period for inhibitory circuits within the somatosensory cortex (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 7271, doi:10.1038/s41598-017-07400-8.
    Description: Although experience-dependent changes in brain inhibitory circuits are thought to play a key role during the “critical period” of brain development, the nature and timing of these changes are poorly understood. We examined the role of sensory experience in sculpting an inhibitory circuit in the primary somatosensory cortex (S1) of mice by using optogenetics to map the connections between parvalbumin (PV) expressing interneurons and layer 2/3 pyramidal cells. Unilateral whisker deprivation decreased the strength and spatial range of inhibitory input provided to pyramidal neurons by PV interneurons in layers 2/3, 4 and 5. By varying the time when sensory input was removed, we determined that the critical period closes around postnatal day 14. This yields the first precise time course of critical period plasticity for an inhibitory circuit.
    Description: This work was supported by a fellowship from NUS to SQL, A*STAR intramural funding for the Integrative Neuroscience Programme, Singapore Institute for Clinical Sciences for JCGS, and a Competitive Research Programme (CRP) grant from the National Research Foundation of Singapore (NRF Grant Number 2008 NRF-CRP 002-082).
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    Climate oscillations reflected within the microbiome of Arabian Sea sediments (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 6040, doi:10.1038/s41598-017-05590-9.
    Description: Selection of microorganisms in marine sediment is shaped by energy-yielding electron acceptors for respiration that are depleted in vertical succession. However, some taxa have been reported to reflect past depositional conditions suggesting they have experienced weak selection after burial. In sediments underlying the Arabian Sea oxygen minimum zone (OMZ), we performed the first metagenomic profiling of sedimentary DNA at centennial-scale resolution in the context of a multi-proxy paleoclimate reconstruction. While vertical distributions of sulfate reducing bacteria and methanogens indicate energy-based selection typical of anoxic marine sediments, 5–15% of taxa per sample exhibit depth-independent stratigraphies indicative of paleoenvironmental selection over relatively short geological timescales. Despite being vertically separated, indicator taxa deposited under OMZ conditions were more similar to one another than those deposited in bioturbated intervals under intervening higher oxygen. The genomic potential for denitrification also correlated with palaeo-OMZ proxies, independent of sediment depth and available nitrate and nitrite. However, metagenomes revealed mixed acid and Entner-Dourdoroff fermentation pathways encoded by many of the same denitrifier groups. Fermentation thus may explain the subsistence of these facultatively anaerobic microbes whose stratigraphy follows changing paleoceanographic conditions. At least for certain taxa, our analysis provides evidence of their paleoenvironmental selection over the last glacial-interglacial cycle.
    Description: his work was primarily supported by NSF MGG Grant #1357017 to MJLC, VG, and LG, and the KAUST-WHOI Special Academic Partnership Program OCRF-SP-WHOI-2013 (grants 7000000463 to XI and 7000000464 to MJLC). Additional financial support was provided via a C-DEBI grant #OCE-0939564 to WDO.
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    Pan-Antarctic analysis aggregating spatial estimates of Adélie penguin abundance reveals robust dynamics despite stochastic noise (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 832, doi:10.1038/s41467-017-00890-0.
    Description: Colonially-breeding seabirds have long served as indicator species for the health of the oceans on which they depend. Abundance and breeding data are repeatedly collected at fixed study sites in the hopes that changes in abundance and productivity may be useful for adaptive management of marine resources, but their suitability for this purpose is often unknown. To address this, we fit a Bayesian population dynamics model that includes process and observation error to all known Adélie penguin abundance data (1982–2015) in the Antarctic, covering 〉95% of their population globally. We find that process error exceeds observation error in this system, and that continent-wide “year effects” strongly influence population growth rates. Our findings have important implications for the use of Adélie penguins in Southern Ocean feedback management, and suggest that aggregating abundance across space provides the fastest reliable signal of true population change for species whose dynamics are driven by stochastic processes.
    Description: H.J.L., C.C.-C., G.H., C.Y., and K.T.S. gratefully acknowledge funding provided by US National Aeronautics and Space Administration Award No. NNX14AC32G and U.S. National Science Foundation Office of Polar Programs Award No. NSF/OPP-1255058. S.J., L.L., M.M.H., Y.L., and R.J. gratefully acknowledge funding provided by US National Aeronautics and Space Administration Award No. NNX14AH74G. H.J.L., C.Y., S.J., Y.L., and R.J. gratefully acknowledge funding provided by U.S. National Science Foundation Office of Polar Programs Award No. NSF/PLR-1341548. S.J. gratefully acknowledges support from the Dalio Explore Fund.
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    Long-term passive acoustic recordings track the changing distribution of North Atlantic right whales (Eubalaena glacialis) from 2004 to 2014 (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 13460, doi:10.1038/s41598-017-13359-3.
    Description: Given new distribution patterns of the endangered North Atlantic right whale (NARW; Eubalaena glacialis) population in recent years, an improved understanding of spatio-temporal movements are imperative for the conservation of this species. While so far visual data have provided most information on NARW movements, passive acoustic monitoring (PAM) was used in this study in order to better capture year-round NARW presence. This project used PAM data from 2004 to 2014 collected by 19 organizations throughout the western North Atlantic Ocean. Overall, data from 324 recorders (35,600 days) were processed and analyzed using a classification and detection system. Results highlight almost year-round habitat use of the western North Atlantic Ocean, with a decrease in detections in waters off Cape Hatteras, North Carolina in summer and fall. Data collected post 2010 showed an increased NARW presence in the mid-Atlantic region and a simultaneous decrease in the northern Gulf of Maine. In addition, NARWs were widely distributed across most regions throughout winter months. This study demonstrates that a large-scale analysis of PAM data provides significant value to understanding and tracking shifts in large whale movements over long time scales.
    Description: This research was funded and supported by many organizations, specified by projects as follows: Data recordings from region 1 were provided by K. Stafford and this research effort was funded by the National Science Foundation #NSF-ARC 0532611. Region 2 data were provided by D. K. Mellinger and S. Nieukirk, funded by National Oceanic and Atmospheric Agency (NOAA) and the Office of Naval Research (ONR) #N00014–03–1–0099, NOAA #NA06OAR4600100, US Navy #N00244-08-1-0029, N00244-09-1-0079, and N00244-10-1-0047.
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    Ocean convection linked to the recent ice edge retreat along east Greenland (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 9 (2018): 1287, doi:10.1038/s41467-018-03468-6.
    Description: Warm subtropical-origin Atlantic water flows northward across the Greenland-Scotland Ridge into the Nordic Seas, where it relinquishes heat to the atmosphere and gradually transforms into dense Atlantic-origin water. Returning southward along east Greenland, this water mass is situated beneath a layer of cold, fresh surface water and sea ice. Here we show, using measurements from autonomous ocean gliders, that the Atlantic-origin water was re-ventilated while transiting the western Iceland Sea during winter. This re-ventilation is a recent phenomenon made possible by the retreat of the ice edge toward Greenland. The fresh surface layer that characterises this region in summer is diverted onto the Greenland shelf by enhanced onshore Ekman transport induced by stronger northerly winds in fall and winter. Severe heat loss from the ocean offshore of the ice edge subsequently triggers convection, which further transforms the Atlantic-origin water. This re-ventilation is a counterintuitive occurrence in a warming climate, and highlights the difficulties inherent in predicting the behaviour of the complex coupled climate system.
    Description: Support for this work was provided by the Norwegian Research Council under Grant agreement no. 231647 (L.H. and K.V.), the Bergen Research Foundation under Grant BFS2016REK01 (K.V.), and the Centre for Climate Dynamics at the Bjerknes Centre through the FRESHWATER project (K.V.). Additional funding was provided by the Swiss National Science Foundation grants P2EZP2162267 and P300P2174307 (L.P.), the National Science Foundation grant OCE-1558742 (M.A.S.), the Norway Fulbright Foundation (K.V.), the Canada Fulbright Foundation (G.W.K.M.), and the Natural Sciences and Engineering Research Council of Canada (G.W.K.M.).
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    Tidal and diel orchestration of behaviour and gene expression in an intertidal mollusc (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 4917, doi:10.1038/s41598-018-23167-y.
    Description: Intertidal inhabitants are exposed to the 24-hour solar day, and the 12.4 hour rising and falling of the tides. One or both of these cycles govern intertidal organisms’ behaviour and physiology, yet little is known about the molecular clockworks of tidal rhythmicity. Here, we show that the limpet Cellana rota exhibits robust tidally rhythmic behaviour and gene expression. We assembled a de-novo transcriptome, identifying novel tidal, along with known circadian clock genes. Surprisingly, most of the putative circadian clock genes, lack a typical rhythmicity. We identified numerous tidally rhythmic genes and pathways commonly associated with the circadian clock. We show that not only is the behaviour of an intertidal organism in tune with the tides, but so too are many of its genes and pathways. These findings highlight the plasticity of biological timekeeping in nature, strengthening the growing notion that the role of ‘canonical’ circadian clock genes may be more fluid than previously thought, as exhibited in an organism which has evolved in an environment where tidal oscillations are the dominant driving force.
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    Network-guided genomic and metagenomic analysis of the faecal microbiota of the critically endangered kakapo (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 8128, doi:10.1038/s41598-018-26484-4.
    Description: The kakapo is a critically endangered, herbivorous parrot endemic to New Zealand. The kakapo hindgut hosts a dense microbial community of low taxonomic diversity, typically dominated by Escherichia fergusonii, and has proven to be a remarkably stable ecosystem, displaying little variation in core membership over years of study. To elucidate mechanisms underlying this robustness, we performed 16S rRNA gene-based co-occurrence network analysis to identify potential interactions between E. fergusonii and the wider bacterial community. Genomic and metagenomic sequencing were employed to facilitate interpretation of potential interactions observed in the network. E. fergusonii maintained very few correlations with other members of the microbiota, and isolates possessed genes for the generation of energy from a wide range of carbohydrate sources, including plant fibres such as cellulose. We surmise that this dominant microorganism is abundant not due to ecological interaction with other members of the microbiota, but its ability to metabolise a wide range of nutrients in the gut. This research represents the first concerted effort to understand the functional roles of the kakapo microbiota, and leverages metagenomic data to contextualise co-occurrence patterns. By combining these two techniques we provide a means for studying the diversity-stability hypothesis in the context of bacterial ecosystems.
    Description: This work was supported by funding from the Department of Conservation (DOC) as well as a University of Auckland Faculty Research Development Fund grant (9841 3626187) to MWT, and a University of Auckland Doctoral Scholarship to DWW.
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    Mesoscale eddies influence the movements of mature female white sharks in the Gulf Stream and Sargasso Sea (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 7363, doi:10.1038/s41598-018-25565-8.
    Description: Satellite-tracking of mature white sharks (Carcharodon carcharias) has revealed open-ocean movements spanning months and covering tens of thousands of kilometers. But how are the energetic demands of these active apex predators met as they leave coastal areas with relatively high prey abundance to swim across the open ocean through waters often characterized as biological deserts? Here we investigate mesoscale oceanographic variability encountered by two white sharks as they moved through the Gulf Stream region and Sargasso Sea in the North Atlantic Ocean. In the vicinity of the Gulf Stream, the two mature female white sharks exhibited extensive use of the interiors of clockwise-rotating anticyclonic eddies, characterized by positive (warm) temperature anomalies. One tagged white shark was also equipped with an archival tag that indicated this individual made frequent dives to nearly 1,000 m in anticyclones, where it was presumably foraging on mesopelagic prey. We propose that warm temperature anomalies in anticyclones make prey more accessible and energetically profitable to adult white sharks in the Gulf Stream region by reducing the physiological costs of thermoregulation in cold water. The results presented here provide valuable new insight into open ocean habitat use by mature, female white sharks that may be applicable to other large pelagic predators.
    Description: This work was supported by the WHOI Ocean Life Institute and awards from NASA and NSF.
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    Author correction : Meridional heat transport variability induced by mesoscale processes in the subpolar North Atlantic (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 9 (2018): 2398, doi:10.1038/s41467-018-04809-1.
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    Keystone Arctic paleoceanographic proxy association with putative methanotrophic bacteria (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 10610, doi:10.1038/s41598-018-28871-3.
    Description: Foraminifera in sediments exposed to gas-hydrate dissociation are not expected to have cellular adaptations that facilitate inhabitation of chemosynthesis-based ecosystems because, to date, there are no known endemic seep foraminifera. To establish if foraminifera inhabit sediments impacted by gas-hydrate dissociation, we examined the cellular ultrastructure of Melonis barleeanus (Williamson, 1858) from the Vestnesa gas hydrate province (Arctic Ocean, west of Svalbard at ~79 °N; ~1200-m depth; n = 4). From sediments with gas hydrate indicators, living M. barleeanus had unusual pore plugs composed of a thick, fibrous meshwork; mitochondria were concentrated at the cell periphery, under pore plugs. While there was no evidence of endosymbioses with prokaryotes, most M. barleeanus specimens were associated with what appear to be Type I methanotrophic bacteria. One foraminifer had a particularly large bolus of these microbes concentrated near its aperture. This is the first documented instance of bona fide living M. barleeanus in gas-hydrate sediments and first documentation of a foraminifer living in close association with putative methanotrophs. Our observations have implications to paleoclimate records utilizing this foundational foraminiferal species.
    Description: JMB was funded by a WHOI Independent Study Award (Mellon Grant), with partial support from NSF grant OCE-1634469. GP and CAGE 15-2 cruise were supported by the Research Council of Norway through CAGE Center for Excellence in Arctic Gas Hydrate Environment and Climate project 223259 and NORCRUST (project number 255150).
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    Ecological impacts of the 2015/16 El Niño in the Central Equatorial Pacific (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 99, Suppl. S (2018): S21-S26, doi:10.1175/BAMS-D-17-0128.1.
    Description: NOAA Coral Reef Conservation Program; National Science Foundation OCE 1537338, OCE 1605365, OCE 1031971
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    Coral reef drag coefficients—surface gravity wave enhancement (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1555-1566, doi:10.1175/JPO-D-17-0231.1.
    Description: A primary challenge in modeling flow over shallow coral reefs is accurately characterizing the bottom drag. Previous studies over continental shelves and sandy beaches suggest surface gravity waves should enhance the drag on the circulation over coral reefs. The influence of surface gravity waves on drag over four platform reefs in the Red Sea is examined using observations from 6-month deployments of current and pressure sensors burst sampling at 1Hz for 4–5min. Depth-average current fluctuations U0 within each burst are dominated by wave orbital velocities uw that account for 80%–90%of the burst variance and have a magnitude of order 10 cm s21, similar to the lower-frequency depth-average current Uavg. Previous studies have shown that the cross-reef bottom stress balances the pressure gradient over these reefs. A bottom stress estimate that neglects the waves (rCdaUavgjUavgj, where r is water density and Cda is a drag coefficient) balances the observed pressure gradient when uw is smaller than Uavg but underestimates the pressure gradient when uw is larger than Uavg (by a factor of 3–5 when uw 5 2Uavg), indicating the neglected waves enhance the bottom stress. In contrast, a bottom stress estimate that includes the waves [rCda(Uavg 1 U0)jUavg 1 U0j)] balances the observed pressure gradient independent of the relative size of uw and Uavg, indicating that this estimate accounts for the wave enhancement of the bottom stress. A parameterization proposed by Wright and Thompson provides a reasonable estimate of the total bottom stress (including the waves) given the burst-averaged current and the wave orbital velocity.
    Description: The Red Sea field program was supported by Awards USA 00002 and KSA 00011 made by KAUST. S. Lentz was supported for the analysis by NSF Award OCE-1558343.
    Description: 2019-01-13
    Keywords: Coastal flows ; Currents ; Dynamics ; Gravity waves ; Turbulence
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    The solute carrier SLC9C1 is a Na+/H+-exchanger gated by an S4-type voltage-sensor and cyclic-nucleotide binding (2018)
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 9 (2018): 2809, doi:10.1038/s41467-018-05253-x.
    Description: Voltage-sensing (VSD) and cyclic nucleotide-binding domains (CNBD) gate ion channels for rapid electrical signaling. By contrast, solute carriers (SLCs) that passively redistribute substrates are gated by their substrates themselves. Here, we study the orphan sperm-specific solute carriers SLC9C1 that feature a unique tripartite structure: an exchanger domain, a VSD, and a CNBD. Voltage-clamp fluorimetry shows that SLC9C1 is a genuine Na+/H+ exchanger gated by voltage. The cellular messenger cAMP shifts the voltage range of activation. Mutations in the transport domain, the VSD, or the CNBD strongly affect Na+/H+ exchange, voltage gating, or cAMP sensitivity, respectively. Our results establish SLC9C1 as a phylogenetic chimaera that combines the ion-exchange mechanism of solute carriers with the gating mechanism of ion channels. Classic SLCs slowly readjust changes in the intra- and extracellular milieu, whereas voltage gating endows the Na+/H+ exchanger with the ability to produce a rapid pH response that enables downstream signaling events.
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    Results of the first Arctic Heat Open Science Experiment (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 99 (2018): 513-520, doi:10.1175/BAMS-D-16-0323.1.
    Description: Seasonally ice-covered marginal seas are among the most difficult regions in the Arctic to study. Physical constraints imposed by the variable presence of sea ice in all stages of growth and melt make the upper water column and air–sea ice interface especially challenging to observe. At the same time, the flow of solar energy through Alaska’s marginal seas is one of the most important regulators of their weather and climate, sea ice cover, and ecosystems. The deficiency of observing systems in these areas hampers forecast services in the region and is a major contributor to large uncertainties in modeling and related climate projections. The Arctic Heat Open Science Experiment strives to fill this observation gap with an array of innovative autonomous floats and other near-real-time weather and ocean sensing systems. These capabilities allow continuous monitoring of the seasonally evolving state of the Chukchi Sea, including its heat content. Data collected by this project are distributed in near–real time on project websites and on the Global Telecommunications System (GTS), with the objectives of (i) providing timely delivery of observations for use in weather and sea ice forecasts, for model, and for reanalysis applications and (ii) supporting ongoing research activities across disciplines. This research supports improved forecast services that protect and enhance the safety and economic viability of maritime and coastal community activities in Alaska. Data are free and open to all (see www.pmel.noaa.gov/arctic-heat/).
    Description: This work was supported by NOAA Ocean and Atmospheric Research and the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063 and by the Innovative Technology for Arctic Exploration (ITAE) program at JISAO/PMEL. Jayne, Robbins, and Ekholm were supported by ONR (N00014-12-10110).
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    A method to quantify bedform height and asymmetry from a low-mounted sidescan sonar (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 35 (2018): 893-910, doi:10.1175/JTECH-D-17-0102.1.
    Description: Rotary sidescan sonars are widely used to image the seabed given their high temporal and spatial resolution. This high resolution is necessary to resolve bedform dynamics and evolution; however, sidescan sonars do not directly measure bathymetry, limiting their utility. When sidescan sonars are mounted close to the seabed, bedforms may create acoustical “shadows” that render previous methods that invert the backscatter intensity to estimate bathymetry and are based on the assumption of a fully insonified seabed ineffective. This is especially true in coastal regions, where bedforms are common features whose large height relative to the water depth may significantly influence the surrounding flow. A method is described that utilizes sonar shadows to estimate bedform height and asymmetry. The method accounts for the periodic structure of bedform fields and the projection of the shadows onto adjacent bedforms. It is validated with bathymetric observations of wave-orbital ripples, with wavelengths ranging from 0.3 to 0.8 m, and tidally reversing megaripples, with wavelengths from 5 to 8 m. In both cases, bathymetric-measuring sonars were deployed in addition to a rotary sidescan sonar to provide a ground truth; however, the bathymetric sonars typically measure different and smaller areas than the rotary sidescan sonar. The shadow-based method and bathymetric-measuring sonar data produce estimates of bedform height that agree by 34.0% ± 27.2% for wave-orbital ripples and 16.6% ± 14.7% for megaripples. Errors for estimates of asymmetry are 1.9% ± 2.1% for wave-orbital ripples and 11.2% ± 9.6% for megaripples.
    Description: This project is partially supported by the National Science Foundation through a Graduate Research Fellowship and a Massachusetts Institute of Technology Energy Initiative Fellowship. Additionally, funding used in developing the method was obtained from NSF Grants OCE-1634481 and OCE-1635151. Field work was funded under ONR Grants N00014-06-10329 and N00014-13-1-0364.
    Keywords: Ocean ; Acoustic measurements/effects ; Algorithms ; In situ oceanic observations ; Instrumentation/sensors
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    The balance of salinity variance in a partially stratified estuary: implications for exchange flow, mixing, and stratification (2019)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in he balance of salinity variance in a partially stratified estuary: Implications for exchange flow, mixing, and stratification. Journal of Physical Oceanography, 48(12), (2018) 2887-2899., doi: 10.1175/JPO-D-18-0032.1.
    Description: Salinity variance dissipation is related to exchange flow through the salinity variance balance equation, and meanwhile its magnitude is also proportional to the turbulence production and stratification inside the estuary. As river flow increases, estuarine volume-integrated salinity variance dissipation increases owing to more variance input from the open boundaries driven by exchange flow and river flow. This corresponds to the increased efficient conversion of turbulence production to salinity variance dissipation due to the intensified stratification with higher river flow. Through the spring–neap cycle, the temporal variation of salinity variance dissipation is more dependent on stratification than turbulence production, so it reaches its maximum during the transition from neap to spring tides. During most of the transition time from spring to neap tides, the advective input of salinity variance from the open boundaries is larger than dissipation, resulting in the net increase of variance, which is mainly expressed as vertical variance, that is, stratification. The intensified stratification in turn increases salinity variance dissipation. During neap tides, a large amount of enhanced salinity variance dissipation is induced by the internal shear stress near the halocline. During most of the transition time from neap to spring tides, dissipation becomes larger than the advective input, so salinity variance decreases and the stratification is destroyed.
    Description: TW was supported by the National Key R&D Program of China (Grant 2017YFA0604104), National Natural Science Foundation of China (Grant 41706002), Natural Science Foundation of Jiangsu Province (Grant BK20170864), and MEL Visiting Fellowship (MELRS1617). WRG was supported by NSF Grant OCE 1736539. Part of this work is finished during TW’s visit in MEL and WHOI. We would like to acknowledge John Warner for providing the codes of the Hudson estuary model, and Parker MacCready, the editor, and two reviewers for their insightful suggestions on improving the manuscript.
    Description: 2019-06-06
    Keywords: Estuaries ; Dynamics ; Mixing ; Density Currents
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    Evolution of the freshwater coastal current at the southern tip of Greenland (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 2127-2140, doi:10.1175/JPO-D-18-0035.1.
    Description: Shipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern Greenland as it encounters Cape Farewell. The velocity structure reveals that the coastal current maintains its identity as it flows around the cape and bifurcates such that most of the flow is diverted to the outer west Greenland shelf, while a small portion remains on the inner shelf. Taking into account this inner branch, the volume transport of the coastal current is conserved, but the freshwater transport decreases on the west side of Cape Farewell. A significant amount of freshwater appears to be transported off the shelf where the outer branch flows adjacent to the shelfbreak circulation. It is argued that the offshore transposition of the coastal current is caused by the flow following the isobaths as they bend offshore because of the widening of the shelf on the west side of Cape Farewell. An analysis of the potential vorticity shows that the subsequent seaward flux of freshwater can be enhanced by instabilities of the current. This set of circumstances provides a pathway for the freshest water originating from the Arctic, as well as runoff from the Greenland ice sheet, to be fluxed into the interior Labrador Sea where it could influence convection in the basin.
    Description: Funding for this project was provided by the National Science Foundation under Grant OCE-1259618.
    Description: 2019-03-11
    Keywords: Boundary currents ; Coastal flows ; Instability ; Ocean circulation ; Potential vorticity ; Transport
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    Sparsened neuronal activity in an optogenetically activated olfactory glomerulus (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 14955, doi:10.1038/s41598-018-33021-w.
    Description: Glomeruli are the functional units of olfactory information processing but little remains known about their individual unit function. This is due to their widespread activation by odor stimuli. We expressed channelrhodopsin-2 in a single olfactory sensory neuron type, and used laser stimulation and simultaneous in vivo calcium imaging to study the responses of a single glomerulus to optogenetic stimulation. Calcium signals in the neuropil of this glomerulus were representative of the sensory input and nearly identical if evoked by intensity-matched odor and laser stimuli. However, significantly fewer glomerular layer interneurons and olfactory bulb output neurons (mitral cells) responded to optogenetic versus odor stimuli, resulting in a small and spatially compact optogenetic glomerular unit response. Temporal features of laser stimuli were represented with high fidelity in the neuropil of the glomerulus and the mitral cells, but not in interneurons. Increases in laser stimulus intensity were encoded by larger signal amplitudes in all compartments of the glomerulus, and by the recruitment of additional interneurons and mitral cells. No spatial expansion of the glomerular unit response was observed in response to stronger input stimuli. Our data are among the first descriptions of input-output transformations in a selectively activated olfactory glomerulus.
    Description: Funded by the World Class Institute/National Research Foundation of Korea (KRF: WCI 2009-003) and NIH: DC005259 and NS099691 grants.
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    Sulphur and carbon cycling in the subduction zone mélange (2018)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 15517, doi:10.1038/s41598-018-33610-9.
    Description: Subduction zones impose an important control on the geochemical cycling between the surficial and internal reservoirs of the Earth. Sulphur and carbon are transferred into Earth’s mantle by subduction of pelagic sediments and altered oceanic lithosphere. Release of oxidizing sulphate- and carbonate-bearing fluids modifies the redox state of the mantle and the chemical budget of subduction zones. Yet, the mechanisms of sulphur and carbon cycling within subduction zones are still unclear, in part because data are typically derived from arc volcanoes where fluid compositions are modified during transport through the mantle wedge. We determined the bulk rock elemental, and sulphur and carbon isotope compositions of exhumed ultramafic and metabasic rocks from Syros, Greece. Comparison of isotopic data with major and trace element compositions indicates seawater alteration and chemical exchange with sediment-derived fluids within the subduction zone channel. We show that small bodies of detached slab material are subject to metasomatic processes during exhumation, in contrast to large sequences of obducted ophiolitic sections that retain their seafloor alteration signatures. In particular, fluids circulating along the plate interface can cause sulphur mobilization during several stages of exhumation within high-pressure rocks. This takes place more pervasively in serpentinites compared to mafic rocks.
    Description: This project was supported by NSF-EAR grant 1324566 to E.M.S. and B.C.G., and NSF EAR award 1250470 to M.J.C. We acknowledge support by the German Research Foundation and the Open Access Publication Fund of the Freie Universität Berlin.
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    Estuarine frontogenesis (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 546–561, doi:10.1175/JPO-D-14-0082.1.
    Description: Model studies and observations in the Hudson River estuary indicate that frontogenesis occurs as a result of topographic forcing. Bottom fronts form just downstream of lateral constrictions, where the width of the estuary increases in the down-estuary (i.e., seaward) direction. The front forms during the last several hours of the ebb, when the combination of adverse pressure gradient in the expansion and baroclinicity cause a stagnation of near-bottom velocity. Frontogenesis is observed in two dynamical regimes: one in which the front develops at a transition from subcritical to supercritical flow and the other in which the flow is everywhere supercritical. The supercritical front formation appears to be associated with lateral flow separation. Both types of fronts are three-dimensional, with strong lateral gradients along the flanks of the channel. During spring tide conditions, the fronts dissipate during the flood, whereas during neap tides the fronts are advected landward during the flood. The zone of enhanced density gradient initiates frontogenesis at multiple constrictions along the estuary as it propagates landward more than 60 km during several days of neap tides. Frontogenesis and frontal propagation may thus be essential elements of the spring-to-neap transition to stratified conditions in partially mixed estuaries.
    Description: Support for this research was provided by NSF Grant OCE 0926427.
    Description: 2015-08-01
    Keywords: Circulation/ Dynamics ; Baroclinic flows ; Coastal flows ; Frontogenesis/frontolysis ; Fronts
    Repository Name: Woods Hole Open Access Server
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    Formation of intrathermocline lenses by eddy–wind interaction (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 606–612, doi:10.1175/JPO-D-14-0221.1.
    Description: Mesoscale intrathermocline lenses are observed throughout the World Ocean and are commonly attributed to water mass anomalies advected from a distant origin. An alternative mechanism of local generation is offered herein, in which eddy–wind interaction can create lens-shaped disturbances in the thermocline. Numerical simulations illustrate how eddy–wind-driven upwelling in anticyclones can yield a convex lens reminiscent of a mode water eddy, whereas eddy–wind-driven downwelling in cyclones produces a concave lens that thins the mode water layer (a cyclonic “thinny”). Such transformations should be observable with long-term time series in the interiors of mesoscale eddies.
    Description: Support of this research by the National Science Foundation and National Aeronautics and Space Administration is gratefully acknowledged.
    Description: 2015-08-01
    Keywords: Circulation/ Dynamics ; Eddies ; Ekman pumping/transport ; Mesoscale processes ; Models and modeling ; Ocean models ; Primitive equations model
    Repository Name: Woods Hole Open Access Server
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    Investigating the local atmospheric response to a realistic shift in the Oyashio Sea surface Temperature Front (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 1126–1147, doi:10.1175/JCLI-D-14-00285.1.
    Description: The local atmospheric response to a realistic shift of the Oyashio Extension SST front in the western North Pacific is analyzed using a high-resolution (HR; 0.25°) version of the global Community Atmosphere Model, version 5 (CAM5). A northward shift in the SST front causes an atmospheric response consisting of a weak surface wind anomaly but a strong vertical circulation extending throughout the troposphere. In the lower troposphere, most of the SST anomaly–induced diabatic heating is balanced by poleward transient eddy heat and moisture fluxes. Collectively, this response differs from the circulation suggested by linear dynamics, where extratropical SST forcing produces shallow anomalous heating balanced by strong equatorward cold air advection driven by an anomalous, stationary surface low to the east. This latter response, however, is obtained by repeating the same experiment except using a relatively low-resolution (LR; 1°) version of CAM5. Comparison to observations suggests that the HR response is closer to nature than the LR response. Strikingly, HR and LR experiments have almost identical vertical profiles of . However, diagnosis of the diabatic quasigeostrophic vertical pressure velocity (ω) budget reveals that HR has a substantially stronger response, which together with upper-level mean differential thermal advection balances stronger vertical motion. The results herein suggest that changes in transient eddy heat and moisture fluxes are critical to the overall local atmospheric response to Oyashio Front anomalies, which may consequently yield a stronger downstream response. These changes may require the high resolution to be fully reproduced, warranting further experiments of this type with other high-resolution atmosphere-only and fully coupled GCMs.
    Description: We gratefully acknowledge funding provided by NSF to DS and MN (AGS CLD 1035325) and Y-OK and CF (AGS CLD 1035423) and by DOE to Y-OK (DE-SC0007052).
    Description: 2015-08-01
    Keywords: Atmosphere-ocean interaction ; Atmospheric circulation ; Boundary layer ; Cyclogenesis/cyclolysis ; Diabatic heating ; Extratropical cyclones
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    Minimum entropy decomposition : unsupervised oligotyping for sensitive partitioning of high-throughput marker gene sequences (2015)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in ISME Journal 9 (2015): 968–979, doi:10.1038/ismej.2014.195.
    Description: Molecular microbial ecology investigations often employ large marker gene datasets, for example, ribosomal RNAs, to represent the occurrence of single-cell genomes in microbial communities. Massively parallel DNA sequencing technologies enable extensive surveys of marker gene libraries that sometimes include nearly identical sequences. Computational approaches that rely on pairwise sequence alignments for similarity assessment and de novo clustering with de facto similarity thresholds to partition high-throughput sequencing datasets constrain fine-scale resolution descriptions of microbial communities. Minimum Entropy Decomposition (MED) provides a computationally efficient means to partition marker gene datasets into ‘MED nodes’, which represent homogeneous operational taxonomic units. By employing Shannon entropy, MED uses only the information-rich nucleotide positions across reads and iteratively partitions large datasets while omitting stochastic variation. When applied to analyses of microbiomes from two deep-sea cryptic sponges Hexadella dedritifera and Hexadella cf. dedritifera, MED resolved a key Gammaproteobacteria cluster into multiple MED nodes that are specific to different sponges, and revealed that these closely related sympatric sponge species maintain distinct microbial communities. MED analysis of a previously published human oral microbiome dataset also revealed that taxa separated by less than 1% sequence variation distributed to distinct niches in the oral cavity. The information theory-guided decomposition process behind the MED algorithm enables sensitive discrimination of closely related organisms in marker gene amplicon datasets without relying on extensive computational heuristics and user supervision.
    Description: AME was supported by a G. Unger Vetlesen Foundation grant to the Marine Biological Laboratory and the Alfred P Sloan Foundation.
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    Mixing variability in the Southern Ocean (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 966–987, doi:10.1175/JPO-D-14-0110.1.
    Description: A key remaining challenge in oceanography is the understanding and parameterization of small-scale mixing. Evidence suggests that topographic features play a significant role in enhancing mixing in the Southern Ocean. This study uses 914 high-resolution hydrographic profiles from novel EM-APEX profiling floats to investigate turbulent mixing north of the Kerguelen Plateau, a major topographic feature in the Southern Ocean. A shear–strain finescale parameterization is applied to estimate diapycnal diffusivity in the upper 1600 m of the ocean. The indirect estimates of mixing match direct microstructure profiler observations made simultaneously. It is found that mixing intensities have strong spatial and temporal variability, ranging from O(10−6) to O(10−3) m2 s−1. This study identifies topographic roughness, current speed, and wind speed as the main factors controlling mixing intensity. Additionally, the authors find strong regional variability in mixing dynamics and enhanced mixing in the Antarctic Circumpolar Current frontal region. This enhanced mixing is attributed to dissipating internal waves generated by the interaction of the Antarctic Circumpolar Current and the topography of the Kerguelen Plateau. Extending the mixing observations from the Kerguelen region to the entire Southern Ocean, this study infers a large water mass transformation rate of 17 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) across the boundary of Antarctic Intermediate Water and Upper Circumpolar Deep Water in the Antarctic Circumpolar Current. This work suggests that the contribution of mixing to the Southern Ocean overturning circulation budget is particularly significant in fronts.
    Description: AM was supported by the joint CSIRO–University of Tasmania Quantitative Marine Science (QMS) program and the 2009 CSIRO Wealth from Ocean Flagship Collaborative Fund. BMS was supported by the Australian Climate Change Science Program, jointly funded by the Department of the Environment and CSIRO. KLPs salary support was provided by Woods Hole Oceanographic Institution bridge support funds.
    Description: 2015-10-01
    Keywords: Geographic location/entity ; Southern Ocean ; Circulation/ Dynamics ; Diapycnal mixing ; Fronts ; Ocean circulation ; Topographic effects ; Atm/Ocean Structure/ Phenomena ; Mixing
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    Estimating a submesoscale diffusivity using a roughness measure applied to a tracer release experiment in the Southern Ocean (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 1610–1631, doi:10.1175/JPO-D-14-0047.1.
    Description: The use of a measure to diagnose submesoscale isopycnal diffusivity by determining the best match between observations of a tracer and simulations with varying small-scale diffusivities is tested. Specifically, the robustness of a “roughness” measure to discriminate between tracer fields experiencing different submesoscale isopycnal diffusivities and advected by scaled altimetric velocity fields is investigated. This measure is used to compare numerical simulations of the tracer released at a depth of about 1.5 km in the Pacific sector of the Southern Ocean during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) field campaign with observations of the tracer taken on DIMES cruises. The authors find that simulations with an isopycnal diffusivity of ~20 m2 s−1 best match observations in the Pacific sector of the Antarctic Circumpolar Current (ACC), rising to ~20–50 m2 s−1 through Drake Passage, representing submesoscale processes and any mesoscale processes unresolved by the advecting altimetry fields. The roughness measure is demonstrated to be a statistically robust way to estimate a small-scale diffusivity when measurements are relatively sparse in space and time, although it does not work if there are too few measurements overall. The planning of tracer measurements during a cruise in order to maximize the robustness of the roughness measure is also considered. It is found that the robustness is increased if the spatial resolution of tracer measurements is increased with the time since tracer release.
    Description: We thank the U.K. Natural Environment Research Council and the U.S. National Science Foundation for funding the DIMES project.
    Description: 2015-12-01
    Keywords: Geographic location/entity ; Southern Ocean ; Circulation/ Dynamics ; Diffusion ; Physical Meteorology and Climatology ; Isopycnal mixing ; Observational techniques and algorithms ; Tracers ; Models and modeling ; Model comparison ; Tracers
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    The Kallisti Limnes, carbon dioxide-accumulating subsea pools (2015)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 5 (2015): 12152, doi:10.1038/srep12152.
    Description: Natural CO2 releases from shallow marine hydrothermal vents are assumed to mix into the water column, and not accumulate into stratified seafloor pools. We present newly discovered shallow subsea pools located within the Santorini volcanic caldera of the Southern Aegean Sea, Greece, that accumulate CO2 emissions from geologic reservoirs. This type of hydrothermal seafloor pool, containing highly concentrated CO2, provides direct evidence of shallow benthic CO2 accumulations originating from sub-seafloor releases. Samples taken from within these acidic pools are devoid of calcifying organisms, and channel structures among the pools indicate gravity driven flow, suggesting that seafloor release of CO2 at this site may preferentially impact benthic ecosystems. These naturally occurring seafloor pools may provide a diagnostic indicator of incipient volcanic activity and can serve as an analog for studying CO2 leakage and benthic accumulations from subsea carbon capture and storage sites.
    Description: This research was supported by the Eurofleets Caldera 2012 Project (EU), a NASA Astrobiology Science & Technology for Exploring Planets grant #NNX09AB76G (USA), a CAREER Award grant #OCE-0955674 to R. Camilli from the National Science Foundation (USA), and IPGP (France).
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    The role of wave dynamics and small-scale topography for downslope wind events in southeast Greenland (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric Sciences 72 (2015): 2786–2805, doi:10.1175/JAS-D-14-0257.1.
    Description: In Ammassalik, in southeast Greenland, downslope winds can reach hurricane intensity and represent a hazard for the local population and environment. They advect cold air down the ice sheet and over the Irminger Sea, where they drive large ocean–atmosphere heat fluxes over an important ocean convection region. Earlier studies have found them to be associated with a strong katabatic acceleration over the steep coastal slopes, flow convergence inside the valley of Ammassalik, and—in one instance—mountain wave breaking. Yet, for the general occurrence of strong downslope wind events, the importance of mesoscale processes is largely unknown. Here, two wind events—one weak and one strong—are simulated with the atmospheric Weather Research and Forecasting (WRF) Model with different model and topography resolutions, ranging from 1.67 to 60 km. For both events, but especially for the strong one, it is found that lower resolutions underestimate the wind speed because they misrepresent the steepness of the topography and do not account for the underlying wave dynamics. If a 5-km model instead of a 60-km model resolution in Ammassalik is used, the flow associated with the strong wind event is faster by up to 20 m s−1. The effects extend far downstream over the Irminger Sea, resulting in a diverging spatial distribution and temporal evolution of the heat fluxes. Local differences in the heat fluxes amount to 20%, with potential implications for ocean convection.
    Description: This study was supported by grants of the National Science Foundation (OCE- 0751554 and OCE-1130008) as well as the Natural Sciences and Engineering Research Council of Canada.
    Description: 2016-01-01
    Keywords: Katabatic winds ; Severe storms ; Air-sea interaction ; Mesoscale processes ; Orographic effects ; Model evaluation/performance
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    Centennial changes of the global water cycle in CMIP5 models (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 6489–6502, doi:10.1175/JCLI-D-15-0143.1.
    Description: The global water cycle is predicted to intensify under various greenhouse gas emissions scenarios. Here the nature and strength of the expected changes for the ocean in the coming century are assessed by examining the output of several CMIP5 model runs for the periods 1990–2000 and 2090–2100 and comparing them to a dataset built from modern observations. Key elements of the water cycle, such as the atmospheric vapor transport, the evaporation minus precipitation over the ocean, and the surface salinity, show significant changes over the coming century. The intensification of the water cycle leads to increased salinity contrasts in the ocean, both within and between basins. Regional projections for several areas important to large-scale ocean circulation are presented, including the export of atmospheric moisture across the tropical Americas from Atlantic to Pacific Ocean, the freshwater gain of high-latitude deep water formation sites, and the basin averaged evaporation minus precipitation with implications for interbasin mass transports.
    Description: This research was supported by NASA Grant NNX12AF59GS03.
    Description: 2016-02-15
    Keywords: Climate change ; Climate prediction ; Hydrologic cycle ; Salinity ; Water budget ; Water vapor
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    The Tokar Gap jet : regional circulation, diurnal variability, and moisture transport based on numerical simulations (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 5885–5907, doi:10.1175/JCLI-D-14-00635.1.
    Description: The structure, variability, and regional connectivity of the Tokar Gap jet (TGJ) are described using WRF Model analyses and supporting atmospheric datasets from the East African–Red Sea–Arabian Peninsula (EARSAP) region during summer 2008. Sources of the TGJ’s unique quasi-diurnal nature and association with atypically high atmospheric moisture transport are traced back to larger-scale atmospheric dynamics influencing its forcing. These include seasonal shifts in the intertropical convergence zone (ITCZ), variability of the monsoon and North African wind regimes, and ties to other orographic flow patterns. Strong modulation of the TGJ by regional processes such as the desert heating cycle, wind convergence at the ITCZ surface front, and the local land–sea breeze cycle are described. Two case studies present the interplay of these influences in detail. The first of these was an “extreme” gap wind event on 12 July, in which horizontal velocities in the Tokar Gap exceeded 26 m s−1 and the flow from the jet extended the full width of the Red Sea basin. This event coincided with development of a large mesoscale convective complex (MCC) and precipitation at the entrance of the Tokar Gap as well as smaller gaps downstream along the Arabian Peninsula. More typical behavior of the TGJ during the 2008 summer is discussed using a second case study on 19 July. Downwind impact of the TGJ is evaluated using Lagrangian model trajectories and analysis of the lateral moisture fluxes (LMFs) during jet events. These results suggest means by which TGJ contributes to large LMFs and has potential bearing upon Sahelian rainfall and MCC development.
    Description: This work was supported by a grant from the King Abdullah University of Science and Technology (KAUST) as well as National Science Foundation Grant OCE0927017 and from DOD (MURI) Grant N000141110087, administered by the Office of Naval Research.
    Description: 2016-02-01
    Keywords: Africa ; Orographic effects ; Monsoons ; Atmosphere-land interaction ; Atmosphere-ocean interaction ; Hydrometeorology
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    Length scale of the finite-amplitude meanders of shelfbreak fronts (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2598–2620, doi:10.1175/JPO-D-14-0249.1.
    Description: Through combining analytical arguments and numerical models, this study investigates the finite-amplitude meanders of shelfbreak fronts characterized by sloping isopycnals outcropping at both the surface and the shelfbreak bottom. The objective is to provide a formula for the meander length scale that can explain observed frontal length scale variability and also be verified with observations. Considering the frontal instability to be a mixture of barotropic and baroclinic instability, the derived along-shelf meander length scale formula is [b1/(1 + a1S1/2)]NH/f, where N is the buoyancy frequency; H is the depth of the front; f is the Coriolis parameter; S is the Burger number measuring the ratio of energy conversion associated with barotropic and baroclinic instability; and a1 and b1 are empirical constants. Initial growth rate of the frontal instability is formulated as [b2(1 + a1S1/2)/(1 + a2αS1/2)]NH/L, where α is the bottom slope at the foot of the front, and a2 and b2 are empirical constants. The formulas are verified using numerical sensitivity simulations, and fitting of the simulated and formulated results gives a1 = 2.69, b1 = 14.65, a2 = 5.1 × 103, and b2 = 6.2 × 10−2. The numerical simulations also show development of fast-growing frontal symmetric instability when the minimum initial potential vorticity is negative. Although frontal symmetric instability leads to faster development of barotropic and baroclinic instability at later times, it does not significantly influence the meander length scale. The derived meander length scale provides a framework for future studies of the influences of external forces on shelfbreak frontal circulation and cross-frontal exchange.
    Description: WGZ and GGG were supported by the National Science Foundation through Grant OCE-1129125.
    Description: 2016-04-01
    Keywords: Circulation/ Dynamics ; Instability ; Ocean circulation ; Topographic effects ; Atm/Ocean Structure/ Phenomena ; Fronts ; Models and modeling ; Numerical analysis/modeling
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    Genomic and transcriptomic evidence for scavenging of diverse organic compounds by widespread deep-sea archaea (2015)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 6 (2015): 8933, doi:10.1038/ncomms9933.
    Description: Microbial activity is one of the most important processes to mediate the flux of organic carbon from the ocean surface to the seafloor. However, little is known about the microorganisms that underpin this key step of the global carbon cycle in the deep oceans. Here we present genomic and transcriptomic evidence that five ubiquitous archaeal groups actively use proteins, carbohydrates, fatty acids and lipids as sources of carbon and energy at depths ranging from 800 to 4,950 m in hydrothermal vent plumes and pelagic background seawater across three different ocean basins. Genome-enabled metabolic reconstructions and gene expression patterns show that these marine archaea are motile heterotrophs with extensive mechanisms for scavenging organic matter. Our results shed light on the ecological and physiological properties of ubiquitous marine archaea and highlight their versatile metabolic strategies in deep oceans that might play a critical role in global carbon cycling.
    Description: his project is funded in part by the Gordon and Betty Moore Foundation Grant GBMF2609, National Science Foundation Grants OCE1038006 (G.J.D.) and OCE-1038055 (J.A.B), National Natural Science Foundation of China (grant no. 41506163), Natural Science Foundation of Guangdong Province (grant no. 2014A030310056), Shenzhen City (grant no. JCY20140828163633985 and KQCX2015032416053646) and SZU (grant no. 000066) (M.L.)
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    Thermally forced transients in the thermohaline circulation (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2820–2835, doi:10.1175/JPO-D-15-0101.1.
    Description: The response of a convective ocean basin to variations in atmospheric temperature is explored using numerical models and theory. The results indicate that the general behavior depends strongly on the frequency at which the atmosphere changes relative to the local response time to air–sea heat flux. For high-frequency forcing, the convective region in the basin interior is essentially one-dimensional and responds to the integrated local surface heat flux anomalies. For low-frequency forcing, eddy fluxes from the boundary current into the basin interior become important and act to suppress variability forced by the atmosphere. A theory is developed to quantify this time-dependent response and its influence on various oceanic quantities. The amplitude and phase of the temperature and salinity of the convective water mass, the meridional overturning circulation, the meridional heat flux, and the air–sea heat flux predicted by the theory compare well with that diagnosed from a series of numerical model calculations in both strongly eddying and weakly eddying regimes. Linearized analytic solutions provide direct estimates of each of these quantities and demonstrate their dependence on the nondimensional numbers that characterize the domain and atmospheric forcing. These results highlight the importance of mesoscale eddies in modulating the mean and time-dependent ocean response to atmospheric variability and provide a dynamical framework with which to connect ocean observations with changes in the atmosphere and surface heat flux.
    Description: This study was supported by the National Science Foundation under Grant OCE-1232389.
    Description: 2016-05-01
    Keywords: Circulation/ Dynamics ; Atmosphere-ocean interaction ; Deep convection ; Eddies ; Meridional overturning circulation
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    Spreading of Denmark Strait overflow water in the western subpolar North Atlantic : insights from eddy-resolving simulations with a passive tracer (2016)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2913–2932, doi:10.1175/JPO-D-14-0179.1.
    Description: The oceanic deep circulation is shared between concentrated deep western boundary currents (DWBCs) and broader interior pathways, a process that is sensitive to seafloor topography. This study investigates the spreading and deepening of Denmark Strait overflow water (DSOW) in the western subpolar North Atlantic using two ° eddy-resolving Atlantic simulations, including a passive tracer injected into the DSOW. The deepest layers of DSOW transit from a narrow DWBC in the southern Irminger Sea into widespread westward flow across the central Labrador Sea, which remerges along the Labrador coast. This abyssal circulation, in contrast to the upper levels of overflow water that remain as a boundary current, blankets the deep Labrador Sea with DSOW. Farther downstream after being steered around the abrupt topography of Orphan Knoll, DSOW again leaves the boundary, forming cyclonic recirculation cells in the deep Newfoundland basin. The deep recirculation, mostly driven by the meandering pathway of the upper North Atlantic Current, leads to accumulation of tracer offshore of Orphan Knoll, precisely where a local maximum of chlorofluorocarbon (CFC) inventory is observed. At Flemish Cap, eddy fluxes carry ~20% of the tracer transport from the boundary current into the interior. Potential vorticity is conserved as the flow of DSOW broadens at the transition from steep to less steep continental rise into the Labrador Sea, while around the abrupt topography of Orphan Knoll, potential vorticity is not conserved and the DSOW deepens significantly.
    Description: This work is supported by ONR Award N00014-09-1-0587, the NSF Physical Oceanography Program, and NASA Ocean Surface Topography Science Team Program.
    Description: 2016-06-01
    Keywords: Circulation/ Dynamics ; Abyssal circulation ; Boundary currents ; Ocean circulation ; Ocean dynamics ; Potential vorticity ; Topographic effects
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    An integrated Pan-European perspective on coastal Lagoons management through a mosaic-DPSIR approach (2016)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 6 (2016): 19400, doi:10.1038/srep19400.
    Description: A decision support framework for the management of lagoon ecosystems was tested using four European Lagoons: Ria de Aveiro (Portugal), Mar Menor (Spain), Tyligulskyi Liman (Ukraine) and Vistula Lagoon (Poland/Russia). Our aim was to formulate integrated management recommendations for European lagoons. To achieve this we followed a DPSIR (Drivers-Pressures-State Change-Impacts-Responses) approach, with focus on integrating aspects of human wellbeing, welfare and ecosystem sustainability. The most important drivers in each lagoon were identified, based on information gathered from the lagoons’ stakeholders, complemented by scientific knowledge on each lagoon as seen from a land-sea perspective. The DPSIR cycles for each driver were combined into a mosaic-DPSIR conceptual model to examine the interdependency between the multiple and interacting uses of the lagoon. This framework emphasizes the common links, but also the specificities of responses to drivers and the ecosystem services provided. The information collected was used to formulate recommendations for the sustainable management of lagoons within a Pan-European context. Several common management recommendations were proposed, but specificities were also identified. The study synthesizes the present conditions for the management of lagoons, thus analysing and examining the activities that might be developed in different scenarios, scenarios which facilitate ecosystem protection without compromising future generations.
    Description: This study was supported by the European Commission, under the 7th Framework Programme, through the collaborative research project LAGOONS (contract n° 283157); by European funds through COMPETE and by Portuguese funds through the national Foundation for Science and Technology – FCT (PEst-C/MAR/LA0017/2013). The post-Doc grant SFRH/BPD/41117/2007 (M Dolbeth) and the PhD grant SFRH/BD/79170/2011 (LP Sousa) supported by FCT are also acknowledged.
    Repository Name: Woods Hole Open Access Server
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    Downfront winds over buoyant coastal plumes (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3139-3154, doi:10.1175/JPO-D-16-0042.1.
    Description: Downfront, or downwelling favorable, winds are commonly found over buoyant coastal plumes. It is known that these winds can result in mixing of the plume with the ambient water and that the winds influence the transport, spatial extent, and stability of the plumes. In the present study, the interaction of the Ekman velocity in the surface layer and baroclinic instability supported by the strong horizontal density gradient of the plume is explored with the objective of understanding the potential vorticity and buoyancy budgets. The approach makes use of an idealized numerical model and scaling theory. It is shown that when winds are present the weak stratification resulting from vertical mixing and the strong baroclinicity of the front results in near-zero average potential vorticity q. For weak to moderate winds, the reduction of q by diapycnal mixing is balanced by the generation of q through the geostrophic stress term in the regions of strong horizontal density gradients and stable stratification. However, for very strong winds the wind stress overwhelms the geostrophic stress and leads to a reduction in q, which is balanced by the vertical mixing term. In the absence of winds, the geostrophic stress dominates mixing and the flow rapidly restratifies. Nonlinearity, extremes of relative vorticity and vertical velocity, and mixing are all enhanced by the presence of a coast. Scaling estimates developed for the eddy buoyancy flux, the surface potential vorticity flux, and the diapycnal mixing rate compare well with results diagnosed from a series of numerical model calculations.
    Description: This study was supported by NSF Grants OCE-1433170 (MAS) and OCE-1459677 (LNT).
    Description: 2017-04-07
    Keywords: Coastal flows ; Ekman pumping/transport ; Mesoscale processes ; Wind stress
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    Annual and semiannual cycle of equatorial Atlantic circulation associated with basin-mode resonance (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3011-3029, doi:10.1175/JPO-D-15-0248.1.
    Description: Seasonal variability of the tropical Atlantic circulation is dominated by the annual cycle, but semiannual variability is also pronounced, despite weak forcing at that period. This study uses multiyear, full-depth velocity measurements from the central equatorial Atlantic to analyze the vertical structure of annual and semiannual variations of zonal velocity. A baroclinic modal decomposition finds that the annual cycle is dominated by the fourth mode and the semiannual cycle is dominated by the second mode. Similar local behavior is found in a high-resolution general circulation model. This simulation reveals that the annual and semiannual cycles of the respective dominant baroclinic modes are associated with characteristic basinwide structures. Using an idealized, linear, reduced-gravity model to simulate the dynamics of individual baroclinic modes, it is shown that the observed circulation variability can be explained by resonant equatorial basin modes. Corollary simulations of the reduced-gravity model with varying basin geometry (i.e., square basin vs realistic coastlines) or forcing (i.e., spatially uniform vs spatially variable wind) show a structural robustness of the simulated basin modes. A main focus of this study is the seasonal variability of the Equatorial Undercurrent (EUC) as identified in recent observational studies. Main characteristics of the observed EUC including seasonal variability of transport, core depth, and maximum core velocity can be explained by the linear superposition of the dominant equatorial basin modes as obtained from the reduced-gravity model.
    Description: This study was supported by the Deutsche Forschungsgemeinschaft as part of the Sonderforschungsbereich 754 (SFB754) ‘‘Climate–Biogeochemistry Interactions in the Tropical Ocean’’ and through several research cruises with R/V Meteor, R/V Maria S. Merian, andR/VL’Atalante by the German Federal Ministry of Education and Research as part of the cooperative projects RACE (03F0605B) and SACUS (03G0837A) and by European Union 7th Framework Programme (FP7 2007–13) under Grant Agreement 603521 PREFACE project.
    Keywords: Atlantic Ocean ; Ocean circulation ; In situ oceanic observations ; Ocean models ; Seasonal cycle ; Tropical variability
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    Nutrient enrichment induces dormancy and decreases diversity of active bacteria in salt marsh sediments (2016)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 7 (2016): 12881, doi:10.1038/ncomms12881.
    Description: Microorganisms control key biogeochemical pathways, thus changes in microbial diversity, community structure and activity can affect ecosystem response to environmental drivers. Understanding factors that control the proportion of active microbes in the environment and how they vary when perturbed is critical to anticipating ecosystem response to global change. Increasing supplies of anthropogenic nitrogen to ecosystems globally makes it imperative that we understand how nutrient supply alters active microbial communities. Here we show that nitrogen additions to salt marshes cause a shift in the active microbial community despite no change in the total community. The active community shift causes the proportion of dormant microbial taxa to double, from 45 to 90%, and induces diversity loss in the active portion of the community. Our results suggest that perturbations to salt marshes can drastically alter active microbial communities, however these communities may remain resilient by protecting total diversity through increased dormancy.
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    Expansion and contraction of the Indo-Pacific tropical rain belt over the last three millennia (2016)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 6 (2016): 34485, doi:10.1038/srep34485.
    Description: The seasonal north-south migration of the intertropical convergence zone (ITCZ) defines the tropical rain belt (TRB), a region of enormous terrestrial and marine biodiversity and home to 40% of people on Earth. The TRB is dynamic and has been shown to shift south as a coherent system during periods of Northern Hemisphere cooling. However, recent studies of Indo-Pacific hydroclimate suggest that during the Little Ice Age (LIA; AD 1400–1850), the TRB in this region contracted rather than being displaced uniformly southward. This behaviour is not well understood, particularly during climatic fluctuations less pronounced than those of the LIA, the largest centennial-scale cool period of the last millennium. Here we show that the Indo-Pacific TRB expanded and contracted numerous times over multi-decadal to centennial scales during the last 3,000 yr. By integrating precisely-dated stalagmite records of tropical hydroclimate from southern China with a newly enhanced stalagmite time series from northern Australia, our study reveals a previously unidentified coherence between the austral and boreal summer monsoon. State-of-the-art climate model simulations of the last millennium suggest these are linked to changes in the structure of the regional manifestation of the atmosphere’s meridional circulation.
    Description: Funded by grants from the US National Science Foundation (NSF) Paleo Perspectives on Climate Change (P2C2) program (AGS-1103413), the Center for Global and Regional Environmental Research, and Cornell College (to R.F.D.); and the NSF P2C2 program (AGS-1203704 and AGS-1602455) and the Penzance and John P. Chase Memorial Endowed Funds at WHOI (to C.C.U.).
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    Estimating infrared radiometric satellite sea surface temperature retrieval cold biases in the tropics due to unscreened optically thin cirrus clouds (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 34 (2017): 355-373, doi:10.1175/JTECH-D-15-0226.1.
    Description: Passive longwave infrared radiometric satellite–based retrievals of sea surface temperature (SST) at instrument nadir are investigated for cold bias caused by unscreened optically thin cirrus (OTC) clouds [cloud optical depth (COD) ≤ 0.3]. Level 2 nonlinear SST (NLSST) retrievals over tropical oceans (30°S–30°N) from Moderate Resolution Imaging Spectroradiometer (MODIS) radiances collected aboard the NASA Aqua satellite (Aqua-MODIS) are collocated with cloud profiles from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument. OTC clouds are present in approximately 25% of tropical quality-assured (QA) Aqua-MODIS Level 2 data, representing over 99% of all contaminating cirrus found. Cold-biased NLSST (MODIS, AVHRR, and VIIRS) and triple-window (AVHRR and VIIRS only) SST retrievals are modeled based on operational algorithms using radiative transfer model simulations conducted with a hypothetical 1.5-km-thick OTC cloud placed incrementally from 10.0 to 18.0 km above mean sea level for cloud optical depths between 0.0 and 0.3. Corresponding cold bias estimates for each sensor are estimated using relative Aqua-MODIS cloud contamination frequencies as a function of cloud-top height and COD (assuming they are consistent across each platform) integrated within each corresponding modeled cold bias matrix. NLSST relative OTC cold biases, for any single observation, range from 0.33° to 0.55°C for the three sensors, with an absolute (bulk mean) bias between 0.09° and 0.14°C. Triple-window retrievals are more resilient, ranging from 0.08° to 0.14°C relative and from 0.02° to 0.04°C absolute. Cold biases are constant across the Pacific and Indian Oceans. Absolute bias is lower over the Atlantic but relative bias is higher, indicating that this issue persists globally.
    Description: Authors JWM, NJS, and JZ acknowledge the support of NASA Project NNX14AJ13G andNSF Project IIA-1355466.Author JZ also acknowledges the support of ONR N00014-16-1-2040 (Grant 11843919). Author JWM further recognizes the Naval Research Enterprise Internship Program (NREIP). Support for his NREIP fellowship came from NASA Interagency Agreement NNG15JA17P on behalf of theMicro-Pulse LidarNetwork (E. J. Welton). Authors JRC, JAC and DLW acknowledge the support of Office of Naval Research Code 322 (PE0602435). Author JRC also acknowledges the support of NASA Interagency Agreement RPO201522 on behalf of the CALIPSO Science Team (C. R. Trepte).
    Description: 2017-08-06
    Keywords: Sea surface temperature ; Cirrus clouds ; Lidars/Lidar observations ; Remote sensing ; Satellite observations
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    Multi-iteration approach to studying tracer spreading using drifter data (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 339-351, doi:10.1175/JPO-D-16-0165.1.
    Description: A novel multi-iteration statistical method for studying tracer spreading using drifter data is introduced. The approach allows for the best use of the available drifter data by making use of a simple iterative procedure, which results in the statistically probable map showing the likelihood that a tracer released at some source location would visit different geographical regions, along with the associated arrival travel times. The technique is tested using real drifter data in the North Atlantic. Two examples are considered corresponding to sources in the western and eastern North Atlantic Ocean, that is, Massachusetts Bay–like and Irish Sea–like sources, respectively. In both examples, the method worked well in estimating the statistics of the tracer transport pathways and travel times throughout the entire North Atlantic. The role of eddies versus mean flow is quantified using the same technique, and eddies are shown to significantly broaden the spread of a tracer. The sensitivity of the results to the size of the source domain is investigated and causes for this sensitivity are discussed.
    Description: This work was supported by the Grant OCE-1356630 from the National Science Foundation (NSF). Rypina also acknowledges NSF Grant OCE-1154641 and NASA Grant NNX14AH29G.
    Description: 2017-07-31
    Keywords: Atlantic Ocean ; Mass fluxes/transport ; Ocean circulation ; Trajectories ; Statistics
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    WHOI SDSL data-link project—ethernet telemetry through sea cables (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 34 (2017): 269-275, doi:10.1175/JTECH-D-11-00196.1.
    Description: A data telemetry technique for communicating over standard oceanographic sea cables that achieves a nearly 100-fold increase in bandwidth as compared to traditional systems has been recently developed and successfully used at sea on board two Research Vessel (R/V) Atlantis cruises with an 8.5-km, 0.322-in.-diameter three-conductor sea cable. The system uses commercially available modules to provide Ethernet connectivity through existing sea cables, linking serial and video underwater instrumentation to the shipboard user. The new method applies Synchronous Digital Subscriber Line (SDSL) communications technology to undersea applications, greatly increasing the opportunities to use scientific instrumentation from existing ships and sea cables at minimal cost and without modification.
    Description: This development program has been supported, in part, through research grants from the National Science Foundation (OCE 0447395), the National Aeronautics and Space Administration’s ASTEP program (NNX09AB76G), and a WHOI Green and Hiam Innovative Technology Award.
    Description: 2017-07-23
    Keywords: Instrumentation/sensors
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    Absolute velocity estimates from autonomous underwater gliders equipped with Doppler current profilers (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 34 (2017): 309-333, doi:10.1175/JTECH-D-16-0156.1.
    Description: Doppler current profilers on autonomous underwater gliders measure water velocity relative to the moving glider over vertical ranges of O(10) m. Measurements obtained with 1-MHz Nortek acoustic Doppler dual current profilers (AD2CPs) on Spray gliders deployed off Southern California, west of the Galápagos Archipelago, and in the Gulf Stream are used to demonstrate methods of estimating absolute horizontal velocities in the upper 1000 m of the ocean. Relative velocity measurements nearest to a glider are used to infer dive-dependent flight parameters, which are then used to correct estimates of absolute vertically averaged currents to account for the accumulation of biofouling during months-long glider missions. The inverse method for combining Doppler profiler measurements of relative velocity with absolute references to estimate profiles of absolute horizontal velocity is reviewed and expanded to include additional constraints on the velocity solutions. Errors arising from both instrumental bias and decreased abundance of acoustic scatterers at depth are considered. Though demonstrated with measurements from a particular combination of platform and instrument, these techniques should be applicable to other combinations of gliders and Doppler current profilers.
    Description: Spray glider missions were supported by the National Science Foundation (OCE-1232971, OCE-1233282), the National Oceanic and Atmospheric Administration (NA10OAR4320156, NA15OAR4320071), Eastman Chemical Company, the Oceans and Climate Change Institute at WHOI, and the W. Van Alan Clark Jr. Chair for Excellence in Oceanography at WHOI. RET acknowledges additional support for analysis and publication from the National Science Foundation (OCE-1633911).
    Description: 2017-07-31
    Keywords: Currents ; Acoustic measurements/effects ; Data processing ; Data quality control ; Profilers ; Inverse methods
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    Recent wind-driven variability in Atlantic water mass distribution and meridional overturning circulation (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 633-647, doi:10.1175/JPO-D-16-0089.1.
    Description: Interannual variability in the volumetric water mass distribution within the North Atlantic Subtropical Gyre is described in relation to variability in the Atlantic meridional overturning circulation. The relative roles of diabatic and adiabatic processes in the volume and heat budgets of the subtropical gyre are investigated by projecting data into temperature coordinates as volumes of water using an Argo-based climatology and an ocean state estimate (ECCO version 4). This highlights that variations in the subtropical gyre volume budget are predominantly set by transport divergence in the gyre. A strong correlation between the volume anomaly due to transport divergence and the variability of both thermocline depth and Ekman pumping over the gyre suggests that wind-driven heave drives transport anomalies at the gyre boundaries. This wind-driven heaving contributes significantly to variations in the heat content of the gyre, as do anomalies in the air–sea fluxes. The analysis presented suggests that wind forcing plays an important role in driving interannual variability in the Atlantic meridional overturning circulation and that this variability can be unraveled from spatially distributed hydrographic observations using the framework presented here.
    Description: DGE was supported by a Natural Environment Research Council studentship award at the University of Southampton. JMT’s contribution was supported by the U.S. National Science Foundation (Grant OCE-1332667). GF’s contribution was supported by the U.S. National Science Foundation through Grant OCE-0961713 and by the U.S. National Oceanic and Atmospheric Administration through Grant NA10OAR4310135. The contributions of JDZ and AJGN were supported by the NERC Grant ‘‘Climate scale analysis of air and water masses’’ (NE/ K012932/1). ACNG gratefully acknowledges support from the Leverhulme Trust, the Royal Society, and the Wolfson Foundation. LY was supported by NASA Ocean Vector Wind Science Team (OVWST) activities under Grant NNA10AO86G.
    Keywords: North Atlantic Ocean ; Atmosphere-ocean interaction ; Ekman pumping/transport ; Ocean circulation ; Water masses ; Inverse methods
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    Seasonal variations of leaf and canopy properties tracked by ground-based NDVI imagery in a temperate forest (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 1267, doi:10.1038/s41598-017-01260-y.
    Description: Changes in plant phenology affect the carbon flux of terrestrial forest ecosystems due to the link between the growing season length and vegetation productivity. Digital camera imagery, which can be acquired frequently, has been used to monitor seasonal and annual changes in forest canopy phenology and track critical phenological events. However, quantitative assessment of the structural and biochemical controls of the phenological patterns in camera images has rarely been done. In this study, we used an NDVI (Normalized Difference Vegetation Index) camera to monitor daily variations of vegetation reflectance at visible and near-infrared (NIR) bands with high spatial and temporal resolutions, and found that the infrared camera based NDVI (camera-NDVI) agreed well with the leaf expansion process that was measured by independent manual observations at Harvard Forest, Massachusetts, USA. We also measured the seasonality of canopy structural (leaf area index, LAI) and biochemical properties (leaf chlorophyll and nitrogen content). We found significant linear relationships between camera-NDVI and leaf chlorophyll concentration, and between camera-NDVI and leaf nitrogen content, though weaker relationships between camera-NDVI and LAI. Therefore, we recommend ground-based camera-NDVI as a powerful tool for long-term, near surface observations to monitor canopy development and to estimate leaf chlorophyll, nitrogen status, and LAI.
    Description: This research was supported by US Department of Energy Office of Biological and Environmental Research Grant DE-SC0006951, National Science Foundation Grants DBI-959333 and AGS-1005663, and the University of Chicago and the MBL Lillie Research Innovation Award to J.T. and China Scholarship Council (CSC) to H.Y.
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    Heat, salt, and freshwater budgets for a glacial fjord in Greenland (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2735-2768, doi:10.1175/JPO-D-15-0134.1.
    Description: In Greenland’s glacial fjords, heat and freshwater are exchanged between glaciers and the ocean. Submarine melting of glaciers has been implicated as a potential trigger for recent glacier acceleration, and observations of ocean heat transport are increasingly being used to infer the submarine melt rates. The complete heat, salt, and mass budgets that underlie such methods, however, have been largely neglected. Here, a new framework for exploring glacial fjord budgets is developed. Building on estuarine studies of salt budgets, the heat, salt, and mass transports through the fjord are decomposed, and new equations for calculating freshwater fluxes from submarine meltwater and runoff are presented. This method is applied to moored records from Sermilik Fjord, near the terminus of Helheim Glacier, to evaluate the dominant balances in the fjord budgets and to estimate freshwater fluxes. Throughout the year, two different regimes are found. In the nonsummer months, advective transports are balanced by changes in heat/salt storage within their ability to measure; freshwater fluxes cannot be inferred as a residual. In the summer, a mean exchange flow emerges, consisting of inflowing Atlantic water and outflowing glacially modified water. This exchange transports heat toward the glacier and is primarily balanced by changes in storage and latent heat for melting ice. The total freshwater flux increases over the summer, reaching 1200 ± 700 m3 s−1 of runoff and 1500 ± 500 m3 s−1 of submarine meltwater from glaciers and icebergs in August. The methods and results highlight important components of fjord budgets, particularly the storage and barotropic terms, that have been not been appropriately considered in previous estimates of submarine melting.
    Description: The data collection and analysis was funded by NSF Grants ARC-0909373, OCE-113008, and OCE-1434041.
    Keywords: Geographic location/entity ; Estuaries ; Glaciers ; Circulation/ Dynamics ; Coastal flows ; Atm/Ocean Structure/ Phenomena ; Freshwater ; Snowmelt/icemelt ; Observational techniques and algorithms ; In situ oceanic observations
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    The occurrence, drivers, and implications of submesoscale eddies on the Martha’s Vineyard Inner Shelf (2016)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2645-2662, doi:10.1175/JPO-D-15-0191.1.
    Description: The occurrence, drivers, and implications of small-scale O(2–5) km diameter coherent vortices, referred to as submesoscale eddies, over the inner shelf south of Martha’s Vineyard, Massachusetts, are examined using high-frequency (HF), radar-based, high-resolution (400 m) observations of surface currents. Within the 300 km2 study area, eddies occurred at rates of 1 and 4 day−1 in winter and summer, respectively. Most were less than 5 h in duration, smaller than 4 km in diameter, and rotated less than once over their lifespan; 60% of the eddies formed along the eastern edge of study area, adjacent to Wasque Shoal, and moved westward into the interior, often with relative vorticity greater than f. Eddy generation was linked to vortex stretching on the ebb and flood tide as well as the interaction of the spatially variable tide and the wind-driven currents; however, these features had complex patterns of surface divergence and stretching. Eddies located away from Wasque Shoal were related to the movement of wind-driven surface currents, as wind direction controlled where eddies formed as well as density effects. Using an analysis of particles advected within the radar-based surface currents, the observed eddies were found to be generally leaky, losing 60%–80% of particles over their lifespan, but still more retentive than the background flow. As a result, the combined translation and rotational effects of the observed eddies were an important source of lateral exchange for surface waters over the inner shelf.
    Description: The HF radar data utilized here were obtained using internal funding from the Woods Hole Oceanographic Institution. The analysis was supported by NSF OCE Grant 1332646.
    Description: 2017-02-19
    Keywords: Geographic location/entity ; Continental shelf/slope ; Circulation/ Dynamics ; Currents ; Eddies ; Observational techniques and algorithms ; Radars/Radar observations
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    ACC meanders, energy transfer, and barotropic–baroclinic instability (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 1291-1305, doi:10.1175/JPO-D-16-0160.1.
    Description: Along-stream variations in the dynamics of the Antarctic Circumpolar Current (ACC) impact heat and tracer transport, regulate interbasin exchange, and influence closure of the overturning circulation. Topography is primarily responsible for generating deviations from zonal-mean properties, mainly through standing meanders associated with regions of high eddy kinetic energy. Here, an idealized channel model is used to explore the spatial distribution of energy exchange and its relationship to eddy geometry, as characterized by both eddy momentum and eddy buoyancy fluxes. Variations in energy exchange properties occur not only between standing meander and quasi-zonal jet regions, but throughout the meander itself. Both barotropic and baroclinic stability properties, as well as the magnitude of energy exchange terms, undergo abrupt changes along the path of the ACC. These transitions are captured by diagnosing eddy fluxes of energy and by adopting the eddy geometry framework. The latter, typically applied to barotropic stability properties, is applied here in the depth–along-stream plane to include information about both barotropic and baroclinic stability properties of the flow. These simulations reveal that eddy momentum fluxes, and thus barotropic instability, play a leading role in the energy budget within a standing meander. This result suggests that baroclinic instability alone cannot capture the dynamics of ACC standing meanders, a challenge for models where eddy fluxes are parameterized.
    Description: The authors all acknowledge support from NSF OCE-1235488. MKY also acknowledges support from the AMS Graduate Student Fellowship.
    Description: 2017-10-12
    Keywords: Southern Ocean ; Channel flows ; Stability ; Topographic effects ; Eddies ; Mesoscale models
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    Spiraling pathways of global deep waters to the surface of the Southern Ocean (2017)
    Nature Publishing Group
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 172, doi:10.1038/s41467-017-00197-0.
    Description: Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60–90 years.
    Description: V.T., L.D.T., and M.R.M. were supported by NSF OCE-1357072. A.K.M., H.F.D., and W.W. were supported by the RGCM program of the US Department of Energy under Contract DE-SC0012457. J.L.S. acknowledges NSF’s Southern Ocean Carbon and Climate Observations and Modeling project under NSF PLR-1425989, which partially supported L.D.T. and M.R.M. as well. C.O.D was supported by the National Aeronautics and Space Administration (NASA) under Award NNX14AL40G and by the Princeton Environmental Institute Grand Challenge initiative. A.R.G. was supported by a Climate and Global Change Postdoctoral Fellowship from the National Oceanic and Atmospheric Administration (NOAA). S.M.G. acknowledges the ongoing support of NOAA/GFDL for high-end ocean and climate-modeling activities. J.W. acknowledges support from NSF OCE-1234473.
    Repository Name: Woods Hole Open Access Server
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  • 94
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    Turbulence from breaking surface waves at a river mouth (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 435-453, doi:10.1175/JPO-D-17-0122.1.
    Description: Observations of surface waves, currents, and turbulence at the Columbia River mouth are used to investigate the source and vertical structure of turbulence in the surface boundary layer. Turbulent velocity data collected on board freely drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys are corrected for platform motions to estimate turbulent kinetic energy (TKE) and TKE dissipation rates. Both of these quantities are correlated with wave steepness, which has previously been shown to determine wave breaking within the same dataset. Estimates of the turbulent length scale increase linearly with distance from the free surface, and roughness lengths estimated from velocity statistics scale with significant wave height. The vertical decay of turbulence is consistent with a balance between vertical diffusion and dissipation. Below a critical depth, a power-law scaling commonly applied in the literature works well to fit the data. Above this depth, an exponential scaling fits the data well. These results, which are in a surface-following reference frame, are reconciled with results from the literature in a fixed reference frame. A mapping between free-surface and mean-surface reference coordinates suggests 30% of the TKE is dissipated above the mean sea surface.
    Description: Funding for this project was provided by the Office of Naval Research as part of the RIVET-II DRI, and for the DARLA group.
    Keywords: Ocean ; Estuaries ; Gravity waves ; Turbulence ; Wave breaking ; In situ oceanic observations
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    The interaction of recirculation gyres and a deep boundary current (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 573-590, doi:10.1175/JPO-D-17-0206.1.
    Description: Motivated by the proximity of the Northern Recirculation Gyre and the deep western boundary current in the North Atlantic, an idealized model is used to investigate how recirculation gyres and a deep flow along a topographic slope interact. In this two-layer quasigeostrophic model, an unstable jet imposed in the upper layer generates barotropic recirculation gyres. These are maintained by an eddy-mean balance of potential vorticity (PV) in steady state. The authors show that the topographic slope can constrain the northern recirculation gyre meridionally and that the gyre’s adjustment to the slope leads to increased eddy PV fluxes at the base of the slope. When a deep current is present along the topographic slope in the lower layer, these eddy PV fluxes stir the deep current and recirculation gyre waters. Increased proximity to the slope dampens the eddy growth rate within the unstable jet, altering the geometry of recirculation gyre forcing and leading to a decrease in overall eddy PV fluxes. These mechanisms may shape the circulation in the western North Atlantic, with potential feedbacks on the climate system.
    Description: We gratefully acknowledge an AMS graduate fellowship (IALB) and U.S. National Science Foundation Grants OCE-1332667 and 1332834 (IALB and JMT).
    Description: 2018-09-06
    Keywords: Boundary currents ; Meridional overturning circulation ; Mesoscale processes ; Ocean circulation ; Potential vorticity ; Quasigeostrophic models
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  • 96
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    Comment on “Abyssal upwelling and downwelling driven by near-boundary mixing” (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 739-748, doi:10.1175/JPO-D-17-0089.1.
    Description: McDougall and Ferrari have estimated the global deep upward diapycnal flow in the boundary layer overlying continental slopes that must balance both downward diapycnal flow in the deep interior and the formation of bottom water around Antarctica. The decrease of perimeter of isopycnal surfaces with depth and the observed decay with height above bottom of turbulent dissipation in the deep ocean play a key role in their estimate. They argue that because the perimeter of seamounts increases with depth, the net effect of mixing around seamounts is to produce net downward diapycnal flow. While this is true along much of a seamount, it is shown here that diapycnal flow of the densest water around the seamount is upward, with buoyancy being transferred from water just above. The same is true for midocean ridges, whose perimeter is constant with depth. It is argued that mixing around seamounts and especially midocean ridges contributes positively to the global deep overturning circulation, reducing the amount of turbulence demanded over the continental slopes to balance the buoyancy budget for the bottom and deep water.
    Description: This work was supported by National Science Foundation Grant OCE- 1232962.
    Description: 2018-09-29
    Keywords: Abyssal circulation ; Boundary currents ; Buoyancy ; Diapycnal mixing ; Mass fluxes/transport ; Ocean circulation
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    A note on interior pathways in the meridional overturning circulation (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 643-646, doi:10.1175/JPO-D-17-0240.1.
    Description: A simple oceanic model is presented for source–sink flow on the β plane to discuss the pathways from source to sink when transport boundary layers have large enough Reynolds numbers to be inertial in their dynamics. A representation of the flow as a Fofonoff gyre, suggested by prior work on inertial boundary layers and eddy-driven circulations in two-dimensional turbulent flows, indicates that even when the source and sink are aligned along the same western boundary the flow must intrude deep into the interior before exiting at the sink. The existence of interior pathways for the flow is thus an intrinsic property of an inertial circulation and is not dependent on particular geographical basin geometry.
    Description: 2018-09-12
    Keywords: Abyssal circulation ; Bottom currents ; Nonlinear dynamics ; Ocean circulation ; Ocean dynamics ; Potential vorticity
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    Submesoscale processes at shallow salinity fronts in the Bay of Bengal : observations during the winter monsoon (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 479-509, doi:10.1175/JPO-D-16-0283.1.
    Description: Lateral submesoscale processes and their influence on vertical stratification at shallow salinity fronts in the central Bay of Bengal during the winter monsoon are explored using high-resolution data from a cruise in November 2013. The observations are from a radiator survey centered at a salinity-controlled density front, embedded in a zone of moderate mesoscale strain (0.15 times the Coriolis parameter) and forced by winds with a downfront orientation. Below a thin mixed layer, often ≤10 m, the analysis shows several dynamical signatures indicative of submesoscale processes: (i) negative Ertel potential vorticity (PV); (ii) low-PV anomalies with O(1–10) km lateral extent, where the vorticity estimated on isopycnals and the isopycnal thickness are tightly coupled, varying in lockstep to yield low PV; (iii) flow conditions susceptible to forced symmetric instability (FSI) or bearing the imprint of earlier FSI events; (iv) negative lateral gradients in the absolute momentum field (inertial instability); and (v) strong contribution from differential sheared advection at O(1) km scales to the growth rate of the depth-averaged stratification. The findings here show one-dimensional vertical processes alone cannot explain the vertical stratification and its lateral variability over O(1–10) km scales at the radiator survey.
    Description: S. Ramachandran acknowledges support from the National Science Foundation through award OCE 1558849 and the U.S. Office of Naval Research, Grants N00014-13-1-0456 and N00014-17- 1-2355. A. Tandon acknowledges support from the U.S. Office of Naval Research, Grants N00014-13-1-0456 and N00014-17-1-2355. J. T. Farrar and R. A. Weller were supported by the U.S. Office of Naval Research, Grant N00014-13-1-0453, to collect the UCTD data and process theUCTD and shipboard meteorological data. J. Nash, J. Mackinnon, and A. F. Waterhouse acknowledge support from the U. S. Office of Naval Research, Grants N00014-13-1-0503 and N00014-14-1-0455. E. Shroyer acknowledges support from the U. S. Office of Naval Research, Grants N00014-14-10236 and N00014-15- 12634. A. Mahadevan acknowledges support fromthe U. S. Office of Naval Research, Grant N00014-13-10451. A. J. Lucas and R. Pinkel acknowledge support from the U. S. Office of Naval Research, Grant N00014-13-1-0489.
    Description: 2018-08-26
    Keywords: Indian Ocean ; Baroclinic flows ; Potential vorticity ; Fronts ; Monsoons ; Oceanic mixed layer
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  • 99
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    The transformation of salinity variance : a new approach to quantifying the influence of straining and mixing on estuarine stratification (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 607-623, doi:10.1175/JPO-D-17-0189.1.
    Description: The roles of straining and dissipation in controlling stratification are derived analytically using a vertical salinity variance method. Stratification is produced by converting horizontal variance to vertical variance via straining, that is, differential advection of horizontal salinity gradients, and stratification is destroyed by the dissipation of vertical variance through turbulent mixing. A numerical model is applied to the Changjiang estuary in order to demonstrate the salinity variance balance and how it reveals the factors controlling stratification. The variance analysis reveals that dissipation reaches its maximum during spring tide in the Changjiang estuary, leading to the lowest stratification. Stratification increases from spring tide to neap tide because of the increasing excess of straining over dissipation. Throughout the spring–neap tidal cycle, straining is almost always larger than dissipation, indicating a net excess of production of vertical variance relative to dissipation. This excess is balanced on average by advection, which exports vertical variance out of the estuarine region into the plume. During neap tide, tidal straining shows a general tendency of destratification during the flood tide and restratification during ebb, consistent with the one-dimensional theory of tidal straining. During spring tide, however, positive straining occurs during flood because of the strong baroclinicity induced by the intensified horizontal salinity gradient. These results indicate that the salinity variance method provides a valuable approach for examining the spatial and temporal variability of stratification in estuaries and coastal environments.
    Description: X. Li was supported by the China Scholarship Council. W. R. Geyer was supported by NSF Grants OCE 1736539 and OCE 1634480. J. Zhu was supported by the National Natural Science Foundation of China (41476077 and 41676083). H. Wu was supported by the National Natural Science Foundation of China (41576088 and 41776101).
    Description: 2018-09-08
    Keywords: Ocean ; Estuaries ; Freshwater ; Mixing ; Numerical analysis/modeling ; Regional models
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    A role for the equatorial undercurrent in the ocean dynamical thermostat (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 6245-6261, doi:10.1175/JCLI-D-17-0513.1.
    Description: Reconstructions of sea surface temperature (SST) based on instrumental observations suggest that the equatorial Pacific zonal SST gradient has increased over the twentieth century. While this increase is suggestive of the ocean dynamical thermostat mechanism of Clement et al., observations of a concurrent weakening of the zonal atmospheric (Walker) circulation are not. Here we show, using heat and momentum budget calculations on an ocean reanalysis dataset, that a seasonal weakening of the zonal atmospheric circulation is in fact consistent with cooling in the eastern equatorial Pacific (EEP) and thus an increase in the zonal SST gradient. This cooling is driven by a strengthening Equatorial Undercurrent (EUC) in response to decreased upper-ocean westward momentum associated with weakening equatorial zonal wind stress. This process can help to reconcile the seemingly contradictory twentieth-century trends in the tropical Pacific atmosphere and ocean. Moreover, it is shown that coupled general circulation models (CGCMs) do not correctly simulate this process; we identify a systematic bias in the relationship between changes in equatorial surface zonal wind stress in the EEP and EUC strength that may help to explain why observations and CGCMs have opposing trends in the zonal SST gradient over the twentieth century.
    Description: 2019-01-11
    Keywords: Tropics ; Atmosphere-ocean interaction ; Climate change ; Climate models ; Trends
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