ALBERT

Description: Mixed‐mode fluid‐filled cracks represent a common means of fluid transport within the Earth's crust. They often show complex propagation paths which may be due to interaction with crustal heterogeneities or heterogeneous crustal stress. Previous experimental and numerical studies focus on the interplay between fluid over-pressure and external stress but neglect the effect of other crack parameters. In this study, we address the role of crack length on the propagation paths in the presence of an external heterogeneous stress field. We make use of numerical simulations of magmatic dike and hydrofracture propagation, carried out using a two‐dimensional boundary element model, and analogue experiments of air‐filled crack propagation into a transparent gelatin block. We use a 3‐D finite element model to compute the stress field acting within the gelatin block and perform a quantitative comparison between 2‐D numerical simulations and experiments. We show that, given the same ratio between external stress and fluid pressure, longer fluid‐filled cracks are less sensitive to the background stress, and we quantify this effect on fluid‐filled crack paths. Combining the magnitude of the external stress, the fluid pressure, and the crack length, we define a new parameter, which characterizes two end member scenarios for the propagation path of a fluid‐filled fracture. Our results have important implications for volcanological studies which aim to address the problem of complex trajectories of magmatic dikes (i.e., to forecast scenarios of new vents opening at volcanoes) but also have implications for studies that address the growth and propagation of natural and induced hydrofractures.

Description: Published

Description: 2064–2081

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: Tsunami deposits present an important archive for understanding tsunami histories and dynamics. Most research in this field has focused on onshore preserved remains, while the offshore deposits have received less attention. In 2009, during a coring campaign with theItalian Navy Magnaghi, four 1 m long gravity cores (MG cores) were sampled from the northern part of Augusta Bay, along a transect in 60 to 110 m water depth. These cores were taken in the same area where a core (MS06) was collected in 2007 about 2.3 km offshore Augusta at a water depth of 72 m below sea level. Core MS06 consisted of a 6.7 m long sequence that included 12 anomalous intervals interpreted as the primary effect of tsunami backwash waves in the last 4500 years. In this study, tsunami deposits were identified, based on sedimentology and displaced benthic foraminifera (as for core MS06) reinforced by X-ray fluorescence data. Two erosional surfaces (L1 and L2) were recognized coupled with grain size increase, abundant Posidonia oceanica seagrass remains and a significant amount of Nubecularia lucifuga, an epiphytic sessile benthic foraminifera considered to be transported from the inner shelf. The occurrence of Ti/Ca and Ti/Sr increments, coinciding with peaks in organic matter (Mo inc/coh) suggests terrestrial run-off coupled with an input of organic matter. The L1 and L2 horizons were attributed to two distinct historical tsunamis (AD 1542 and AD 1693) by indirect age-estimation methods using 210Pb profiles and the comparison of Volume Magnetic Susceptibility data between MG cores and MS06 cores. One most recent bioturbated horizon (Bh), despite not matching the above listed interpretative features, recorded an important palaeoenvironmental change that may correspond to the AD 1908 tsunami. These findings reinforce the value of offshore sediment records as an underutilized resource for the identification of past tsunamis.

Description: Published

Description: 1553-1576

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: JCR Journal

Description: The purpose of this list of digital platforms is to facilitate the research of scientific data (articles, books, conferences, websites, indexers, etc.) by students of all undergraduate levels. The interface of platforms have similarities and because of this, low degree of difficulty of use. I emphasize that the key to an excellent literature search on digital platforms is to choose the right "keyword".

Description: Sedimentary architecture and morphogenetic evolution of a polar bay-mouth gravel-spit system are revealed based on topographic mapping, sedimentological data, radiocarbon dating and ground-penetrating radar investigations. Data document variable rates of spit progradation in reaction to atmospheric warming synchronous to the termination of the last glacial re-advance (LGR, 0.45–0.25 ka BP), the southern hemisphere equivalent of the Little Ice Age cooling period. Results show an interruption of spit progradation that coincides with the proposed onset of accelerated isostatic rebound in reaction to glacier retreat. Spit growth resumed in the late 19th century after the rate of isostatic rebound decreased, and continues until today. The direction of modern spit progradation, however, is rotated northwards compared with the growth axis of the early post-LGR spit. This is interpreted to reflect the shift and strengthening in the regional wind field during the last century. A new concept for the interplay of polar gravel-spit progradation and glacio-isostatic adjustment is presented, allowing for the prediction of future coastal evolution in comparable polar settings.

Description: Here we evaluate five atmospheric reanalyses in an Arctic gateway during late summer. The reanalyses include ERA5, ERA-Interim, JRA-55, CFSv2 and MERRA-2. We use observations from 50 radiosondes launched in the Fram Strait around 79-80˚N, between 25 August – 11 September 2017. Crucially, data from 27 radiosondes were not transmitted to the Global Telecommunications System (GTS), and therefore not assimilated into any reanalysis. In most reanalyses, the magnitude of wind speed and humidity errors are similar for profiles with and without data assimilation. In cases without data assimilation, correlation coefficients (R) exceed 0.88 for temperature, wind speed and specific humidity, in all reanalyses. Overall, the newly released ERA5 has higher correlation coefficients than any other reanalyses as well as smaller biases and root mean square errors, for all three variables. The largest improvements identified in ERA5 are in its representation of the wind field, and temperature profiles over warm water.

Description: The importance of macrobenthos in benthic‐pelagic coupling and early diagenesis of organic carbon (OC) has long been recognized but has not been quantified at a regional scale. By using the southern North Sea as an exemplary area we present a modelling attempt to quantify the budget of total organic carbon (TOC) reworked by macrobenthos in seafloor surface sediments. Vertical profiles in sediments collected in the field indicate a significant but nonlinear correlation between TOC and macrobenthic biomass. A mechanistic model is used to resolve the bi‐directional interaction between TOC and macrobenthos. A novelty of this model is that bioturbation is resolved dynamically depending on variations in local food resource and macrobenthic biomass. The model is coupled to 3D hydrodynamic‐biogeochemical simulations to hindcast the mutual dependence between sedimentary TOC and macrobenthos from 1948 to 2015. Agreement with field data reveals a satisfactory model performance. Our simulations show that the preservation of TOC in the North Sea sediments is not only determined by pelagic conditions (hydrodynamic regime and primary production) but also by the vertical distribution of TOC, bioturbation intensity, and the vertical positioning of macrobenthos. Macrobenthos annually ingest 20%–35% and in addition vertically diffuse 11%–22% of the total budget of TOC in the upper‐most 30 cm sediments in the southern North Sea. This result indicates a central role of benthic animals in modulating the OC cycling at the sediment‐water interface of continental margins.

Description: Age control and paleoceanographic evidence of marine sediment records might be challenged if authors solely build their stratigraphy on visual correlation to apparently well‐dated records from the same ocean basin, using, for example, highly resolved X‐ray fluorescence‐based element‐count records and correlation tools such as AnalySeries. While per se perfectly reasonable, this approach bears the risk of missing stratigraphic gaps in the sedimentary record and thus might result in imprecise and/or flawed interpretations. Here we present a unique series of 14 planktic 14C ages from a 7‐cm section of East Pacific Rise core PS75/059‐2. The ages suggest a 14‐ky‐long period of low‐to‐zero deposition during Last Glacial Maximum, mainly marked by continuous redistribution of winnowed foraminifers, probably the result of enhanced bottom currents, moreover, by some bioturbational mixing. On the basis of this data we demonstrate the impact of the hiatus on a South Pacific transect of apparent benthic ventilation ages (ΔΔ14C values) and their meaning for estimates of CO2 stored in Last Glacial Maximum Pacific deep waters.

Description: Satellite‐derived data suggest an increase in annual primary production following the loss of summer sea ice in the Arctic Ocean. The scarcity of field data to corroborate this enhanced algal production incited a collaborative project combining six annual cycles of sequential sediment trap measurements obtained over a 17‐year period in the Eurasian Arctic Ocean. Here we present microalgal fluxes measured at ~200 m to reflect the bulk of algal carbon production. Ice algae contributed to a large proportion of the microalgal carbon export before complete ice melt and possible detection of their production by satellites. In the northern Laptev Sea, annual microalgal carbon fluxes were lower during the 2007 minimum ice extent than in 2006. In 2012, early snowmelt led to early microalgal carbon flux in the Nansen Basin. Hence, a change in the timing of snowmelt and ice algae release may affect productivity and export over the Arctic basins.

Description: Sea ice dynamics determine the drift and deformation of sea ice. Nonlinear physics, usually expressed in a viscous‐plastic rheology, makes the sea ice momentum equations notoriously difficult to solve. At increasing sea ice model resolution the nonlinearities become stronger as linear kinematic features (leads) appear in the solutions. Even the standard elastic‐viscous‐plastic (EVP) solver for sea ice dynamics, which was introduced for computational efficiency, becomes computationally very expensive, when accurate solutions are required, because the numerical stability requires very short, and hence more, subcycling time steps at high resolution. Simple modifications to the EVP solver have been shown to remove the influence of the number of subcycles on the numerical stability. At low resolution appropriate solutions can be obtained with only partial convergence based on a significantly reduced number of subcycles as long as the numerical procedure is kept stable. This previous result is extended to high resolution where linear kinematic features start to appear. The computational cost can be strongly reduced in Arctic Ocean simulations with a grid spacing of 4.5 km by using modified and adaptive EVP versions because fewer subcycles are required to simulate sea ice fields with the same characteristics as with the standard EVP.

Description: Quaternary East Asian winter monsoon (EAWM) evolution has long been attributed to high‐latitude Northern Hemisphere climate change. However, it cannot explain the distinct relationships of the EAWM in the northern and southern East Asian marginal sea in paleoclimatic records. Here we present an EAWM record of the northern East China Sea over the past 300 ka and a transient climate simulation with the Kiel Climate Model through the Holocene. Both proxy record and simulation suggest anticorrelated long‐term EAWM evolution between the northern East China Sea and the South China Sea. We suggest that this spatial discrepancy of EAWM can be interpreted as El Niño–Southern Oscillation (ENSO)‐like controlling, which generates cyclonic/anticyclonic wind anomalies in the northern/southern East Asian marginal sea. This research explains much of the controversy in nonorbital scale variability of Quaternary EAWM records in the East Asian marginal sea and supports a potent role of tropical forcing in East Asian winter climate change.

Description: The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide and global modeling efforts – thereby enhancing predictions of the WG in global ocean circulation and climate.

Description: The East Antarctic Ice Sheet (EAIS) is underlain by a series of low‐lying subglacial sedimentary basins. The extent, geology, and basal topography of these sedimentary basins are important boundary conditions governing the dynamics of the overlying ice sheet. This is particularly pertinent for basins close to the grounding line wherein the EAIS is grounded below sea level and therefore potentially vulnerable to rapid retreat. Here we analyze newly acquired airborne geophysical data over the Pensacola‐Pole Basin (PPB), a previously unexplored sector of the EAIS. Using a combination of gravity and magnetic and ice‐penetrating radar data, we present the first detailed subglacial sedimentary basin model for the PPB. Radar data reveal that the PPB is defined by a topographic depression situated ~500 m below sea level. Gravity and magnetic depth‐to‐source modeling indicate that the southern part of the basin is underlain by a sedimentary succession 2–3 km thick. This is interpreted as an equivalent of the Beacon Supergroup and associated Ferrar dolerites that are exposed along the margin of East Antarctica. However, we find that similar rocks appear to be largely absent from the northern part of the basin, close to the present‐day grounding line. In addition, the eastern margin of the basin is characterized by a major geological boundary and a system of overdeepened subglacial troughs. We suggest that these characteristics of the basin may reflect the behavior of past ice sheets and/or exert an influence on the present‐day dynamics of the overlying EAIS.

Description: The Red Sea is a deep marine basin often considered as small‐scale version of the global ocean. Hydrographic observations and ocean‐atmosphere modeling indicate Red Sea deep water was episodically renewed by wintertime open‐ocean deep convections during 1982–2001, suggesting a renewal time on the order of a decade. However, the long‐term pacing of Red Sea deep water renewals is largely uncertain. We use an annually resolved coral oxygen isotope record of winter surface water conditions to show that the late twentieth century deep water renewals were probably unusual in the context of the preceding ~100 years. More frequent major events are detected during the late Little Ice Age, particularly during the early nineteenth century characterized by large tropical volcanic eruptions. We conclude that Red Sea deep water renewal time is on the order of a decade up to a century, depending on the mean climatic conditions and large‐scale interannual climate forcing.

Description: To counteract global warming, a geoengineering approach that aims at intervening in the Arctic ice‐albedo feedback has been proposed. A large number of wind‐driven pumps shall spread seawater on the surface in winter to enhance ice growth, allowing more ice to survive the summer melt. We test this idea with a coupled climate model by modifying the surface exchange processes such that the physical effect of the pumps is simulated. Based on experiments with RCP 8.5 scenario forcing, we find that it is possible to keep the late‐summer sea ice cover at the current extent for the next ∼60 years. The increased ice extent is accompanied by significant Arctic late‐summer cooling by ∼1.3 K on average north of the polar circle (2021–2060). However, this cooling is not conveyed to lower latitudes. Moreover, the Arctic experiences substantial winter warming in regions with active pumps. The global annual‐mean near‐surface air temperature is reduced by only 0.02 K (2021–2060). Our results cast doubt on the potential of sea ice targeted geoengineering to mitigate climate change.

Description: Ocean heat transport through the Barents Sea Opening (BSO) has strong impacts on the Barents Sea ice extent and the climate. In this paper we quantified the contributions from different atmospheric forcing components to the trend and interannual variability of the BSO heat transport. Ocean‐ice model simulations were conducted in which the interannual variation of atmospheric forcing was maintained only in or outside the Arctic in two different simulations. The sum of their BSO heat transport anomalies reasonably replicated the trend and variability from a hindcast simulation. The upward trend of the BSO heat transport mainly stems from the increasing ocean temperature in the subpolar North Atlantic. For the interannual variability, the local wind and upstream forcing are similarly important. The location of the Atlantic Water boundary current in the Nordic Seas, influenced by the cyclonic atmospheric circulation, is crucial in determining part of the BSO inflow variability.

Description: Kelps are important providers and constituents of marine ecological niches, the coastal kelp forests. Kelp species have differing distribution ranges, but mainly thrive in temperate and arctic regions. Although the principal factors determining biogeographic distribution ranges are known, genomics could provide additional answers to this question. We sequenced DNA from two Laminaria species with contrasting distribution ranges, Laminaria digitata and Laminaria solidungula. Laminaria digitata is found in the Northern Atlantic with a southern boundary in Brittany (France) or Massachusetts (USA) and a northern boundary in the Arctic, whereas L. solidungula is endemic to the Arctic only. From the raw reads of DNA, we reconstructed both chloroplast genomes and annotated them. A concatenated data set of all available brown algae chloroplast sequences was used for the calculation of a robust phylogeny, and sequence variations were analyzed. The two Laminaria chloroplast genomes are collinear to previously analyzed kelp chloroplast genomes with important exceptions. Rearrangements at the inverted repeat regions led to the pseudogenization of ycf37 in L. solidungula, a gene possibly required under high light conditions. This defunct gene might be one of the reasons why the habitat range of L. solidungula is restricted to lowlight sublittoral sites in the Arctic. The inheritance pattern of single nucleotide polymorphisms suggests incomplete lineage sorting of chloroplast genomes in kelp species. Our analysis of kelp chloroplast genomes shows that not only evolutionary information could be gleaned from sequence data. Concomitantly, those sequences can also tell us something about the ecological conditions which are required for species well‐being.

Description: During the last decade the Arctic has experienced increasing human development while many native communities continue to live a subsistence lifestyle. Off-road winter tundra travel for resource exploration is most cost effective and least environmentally damaging during winter when the tundra is frozen and snow covered. Climate warming, which is occurring at an amplified rate in the Arctic, likely changes the period when access to the off-road tundra travel is possible. There currently exists, however, large uncertainty as to how climate change will impact the low-cost winter travel access across the tundra. Here we defined safe tundra access when soil temperatures are below a soil type dependent freezing temperature and snow cover is at least 20 cm. Our analysis is based on the simulated soil temperatures and snow depths of Land Surface Models (LSMs) contributing to “The Inter-Sectoral Impact Model Intercomparison Project” (ISIMIP). ISIMIP simulations are based on a common protocol, the same input data, the same spatial (0.5°) and temporal resolution (daily modeling output), and span over the period 1861-2100. The LSMs are forced by four different bias-corrected global circulation models (IPSL-CM5A-LR, GFDL-ESM2M, MIROC5, HadGEM2-ES) and three different future conditions (represented via representative concentration pathways (RCP) 2.6, 6.0, 8.5). The simulation results of our model ensemble (60 model combinations) show consistent permafrost warming and changing snow cover patterns at 60°N. Annual off-road tundra travel is considerably reduced (〉50%) under future climate change scenarios, especially under the RCP8.5. The main reduction can be observed in the spring and autumn (〉30%). The results of the multi-model ensemble differ in magnitude, however, their overall trend is consistent. Our results suggest a high vulnerability and substantial changes to the (subsistence) livelihoods of native communities and increasing costs for off-road resource exploration.

Description: A new global climate model setup using FESOM2.0 for the sea ice‐ocean component and ECHAM6.3 for the atmosphere and land surface has been developed. Replacing FESOM1.4 by FESOM2.0 promises a higher efficiency of the new climate setup compared to its predecessor. The new setup allows for long‐term climate integrations using a locally eddy‐resolving ocean. Here it is evaluated in terms of (1) the mean state and long‐term drift under preindustrial climate conditions, (2) the fidelity in simulating the historical warming, and (3) differences between coarse and eddy‐resolving ocean configurations. The results show that the realism of the new climate setup is overall within the range of existing models. In terms of oceanic temperatures, the historical warming signal is of smaller amplitude than the model drift in case of a relatively short spin‐up. However, it is argued that the strategy of “de‐drifting” climate runs after the short spin‐up, proposed by the HighResMIP protocol, allows one to isolate the warming signal. Moreover, the eddy‐permitting/resolving ocean setup shows notable improvements regarding the simulation of oceanic surface temperatures, in particular in the Southern Ocean.

Description: The Central Asian Pamir Mountains (Pamirs) are a high‐altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial‐interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31‐kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. δD values of terrestrial biomarkers showed insolation‐driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive δD shifts driven by changes in precipitation seasonality were observed at ca. 31–30, 28–26, and 17–14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation‐evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.

Description: Climate change and sustainable use of natural capital demand increased collaboration across the sciences. The first steps for effective collaboration often focus on improving interoperability between observation and analyses methodologies. This is traditionally done through a combination of standards and best practices. The ocean observation community and observing infrastructures - with regionally diverse members working in physics, chemistry, biology and engineering - is looking toward a dynamic consensus-building approach to match the rapid pace of technological evolution. This is an essential part of the long-term cooperation among ocean observing infrastructures. In the last 12 months, the ocean observing community has implemented an Ocean Best Practices System (OBPS). This System was recently adopted by the Intergovernmental Ocean Commission as an international project under GOOS and IODE. The System consists of a permanent OBPS repository hosted by IODE with state-of-the-art semantic discovery and metadata indexing for improved access to best practices and, eventually, to the data associated with them. There have been discussions to understand how to deal with differing best practices and standards on the same observation or analyses objective and other issues that arise from a comprehensive ocean best practices system. A recent survey, to be described, offers options on alternative approaches. Further, we have created a forum, in “Frontiers in Marine Science” for discussion of best practices and their applications. This presentation will cover options for evolving and sustaining ocean best practices across infrastructures. The recommendations build upon the community survey, the OGC experience, the outcomes of the OceanObs’19 conference as well as inputs from the Decade for Ocean Sciences community meetings. The extension of this work to other communities will also be examined.

Description: IODP Exp. 383 recovered two Pleistocene sedimentary sequences from the upper continental slope along the southernmost Chilean margin that are well positioned to monitor changes in the Antarctic Circumpolar Current (ACC) upstream of the Drake Passage and the history of Patagonian glaciation. These sites are characterized by high sedimentation rates and a complex distribution of siliciclastic sediments with infrequent decimeter-scale beds of calcareous biogenic sediments. Unravelling ocean circulation and climate history from these sites requires a primary understanding of sedimentary provenance and transport mechanisms derived from a complete lithological characterization of the sequence. Here, we integrate downcore shipboard physical properties with sedimentological observations to fully characterize the sequences, evaluate potential for correlation and constrain regional depositional processes. Site U1542 (52°S; 1101 m water depth) consists of a 249 m spliced sedimentary sequence containing Middle Pleistocene to Holocene sediments. It mainly consists of clayey silt that is often interbedded with thin (~75 cm) beds of calcareous sand-bearing clayey to sandy silt with foraminifera and nannofossils or foraminifera-rich nannofossil ooze. Site U1544 (55°S; 2090 m water depth) consists of a 98 m sedimentary sequence obtained from a single hole. Sediments are also dominated by silty clay, but exhibit slightly thicker beds of calcareous ooze and a significantly higher proportion of cm- to dm-scale sand beds that are interpreted as turbidites. Based on the lithology of the recovered sediments and proximity to a glaciated continental margin, terrigenous sediment is likely delivered to these locations by a combination of ice rafting, glacial meltwater plumes, episodic downslope transport from the outer continental shelf and fine-grained sediments transported by the Cape Horn Current entering the Drake Passage as the northern branch of the ACC.

Description: - We provide the first isotopic geochronological constraints on brittle deformation in the NA by illite K-Ar dating of brittle fault rocks - A combined structural-geochronological approach constrains a Late Miocene-Early Pliocene regional compressive stress state

Description: The Northern Apennines (NA) orogenic wedge formed during Oligocene-Miocene convergence and westward subduction of Adria beneath the European Plate. Extension ensued in the Mid-Late Miocene in response to Adria roll-back, causing opening of the back-arc Northern Tyrrhenian Sea. Whether extension continues uninterrupted since the Mid-Late Miocene or it was punctuated by short-lived compressional events, remains, however, uncertain. We used the K-Ar method to date a set of brittle-ductile and brittle deformation zones from the Island of Elba to contribute to this debate. We dated the low-angle Zuccale Fault (ZF), the Capo Norsi-Monte Arco Thrust (CN-MAT), and the Calanchiole Shear Zone (CSZ). The CN-MAT and CSZ are moderately west dipping, top-to-the-east thrusts in the immediate footwall of the ZF. The CSZ slipped 6.14 ± 0.64 Ma (〈0.1 μm fraction) and the CN-MAT 4.90 ± 0.27 Ma ago (〈0.4 μm fraction). The ZF, although cutting the two other faults, yielded an older age of 7.58 ± 0.11 Ma (〈0.1 μm fraction). The ZF gouge, however, contains an illitic detrital contaminant from the Paleozoic age flysch deformed in its hanging wall and the age thus is a maximum faulting age. Removal of ~1% of a 300-Ma-old contaminant brings the ZF faulting age to 〈4.90 Ma. Our results provide the first direct dating of brittle deformation in the Apennines, constraining Late Miocene-Early Pliocene regional compression. They call for a refinement of current NA geodynamic models in the framework of the Northern Tyrrhenian Sea extension.

Description: Published

Description: 3229–3243

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: On behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union, and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2017. The journal could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate all that you do, and we are very grateful for your willingness and readiness to serve in this role.

Description: Published

Description: 566

Description: 1VV. Altro

Description: JCR Journal

Description: Pore Pressure Pulse Drove the 2012 Emilia (Italy)Series of EarthquakesGiuseppe Pezzo1, Pasquale De Gori1, Francesco Pio Lucente1, and Claudio Chiarabba11Istituto Nazionale di Geofisica e Vulcanologia, Rome, ItalyAbstractThe 2012 Emilia earthquakes sequence is thefirst debated case in Italy of destructive eventpossibly induced by anthropic activity. During this sequence, two main earthquakes occurred separated by9 days on contiguous thrust faults. Scientific commissions engaged by the Italian government reportedcomplementary scenarios on the potential trigger mechanism ascribable to exploitation of a nearby oilfield.In this study, we combine a refined geodetic source model constrained by precise aftershock locationsand an improved tomographic model of the area to define the geometrical relation between the activatedfaults and investigate possible triggering mechanisms. An aftershock decay rate that deviates from theclassical Omori-like pattern andVp/Vschanges along the fault system suggests that natural pore pressurepulse drove the space-time evolution of seismicity and the activation of the second main shock

Description: Published

Description: 682-690

Description: 4T. Sismicità dell'Italia

Description: JCR Journal

Description: Near-fault ground motion records often present impulsive signals, characterized by a largeamplitude in the velocity wavefield and by the energy concentrated in a short time window as comparedto the total earthquake duration. Thispulse-likebehavior is ascribed to the directivity of the seismic rupture,and it requires a stronger demand to the buildings not predicted by the classical design spectra. In this workwe investigate the pulse occurrence and duration in near-fault synthetic seismograms generated from anensemble ofk 2source models. We exploited the fault geometry of theMw= 6.3, 2009 L’Aquila earthquake,which represents a typical example of normal-fault earthquake for which several records in the fault vicinityare available for comparison with synthetics. We show that impulsive records are sensitive to the rupturevelocity, to the hypocenter depth, and to the station location, whether it is on the hanging wall or on thefootwall. The pulse duration was also shown to be proportional to the risetime, and it scales with thesource-receiver distance and inversely with the rupture velocity. We model these results as an effectof the coupled along-strike and updip directivity

Description: Published

Description: 7707-7721

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: JCR Journal

Description: Changes in water level are commonly reported in regions struck by a seismic event. The sign and amplitude of such changes depend on the relative position of measuring points with respect to the hypocenter, and on the poroelastic properties of the rock. We apply a porous media flow model (TOUGH2) to describe groundwater flow and water‐level changes associated with the first ML5.9 mainshock of the 2012 seismic sequence in Emilia (Italy). We represent the earthquake as an instantaneous pressure step, whose amplitude was inferred from the properties of the seismic source inverted from geodetic data. The results are consistent with the evolution recorded in both deep and shallow water wells in the area and suggest that our description of the seismic event is suitable to capture both timing and magnitude of water‐level changes. We draw some conclusions about the influence of material heterogeneity on the pore pressure evolution, and we show that to reproduce the observed maximum amplitude it is necessary to take into account compaction in the shallow layer.

Description: Published

Description: 452–463

Description: 4T. Sismicità dell'Italia

Description: JCR Journal

Description: On behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union (AGU), and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2018. Reviews of Geophysics is the top rated journal in Geophysics and Geochemistry and it could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate the time spent reading and commenting on manuscripts, and we are very grateful for your willingness and readiness to serve in this role. Reviews of Geophysics published 20 review papers and an editorial in 2018, covering most of the AGU Section topics, and for this we were able to rely on the efforts of 85 dedicated reviewers from 20 countries. Many reviewers answered the call multiple times. Thank you again. We look forward to a 2019 of exciting advances in the field and communicating those advances to our community and to the broader public.

Description: Published

Description: 4

Description: 5TM. Informazione ed editoria

Description: JCR Journal

Description: The deglacial history of CO2 release from the deep North Pacific remains unresolved. This is due to conflicting indications about subarctic Pacific ventilation changes based on various marine proxies, especially for Heinrich Stadial 1 (HS-1) when a rapid atmospheric CO2 rise occurs. Here, we use a complex Earth System Model to investigate the deglacial North Pacific overturning and its control on ocean stratification. Our results show an enhanced intermediate-to-deep ocean stratification coeval with intensified North Pacific Intermediate Water (NPIW) formation during HS-1, compared to the Last Glacial Maximum. The stronger NPIW formation causes lower salinities and higher temperatures at intermediate depths. By lowering NPIW densities, this enlarges vertical density gradient and thus enhances intermediate-to-deep ocean stratification during HS-1. Physically, this process prevents the North Pacific deep waters from a better communication with the upper oceans, thus prolongs the existing isolation of glacial Pacific abyssal carbons during HS-1.

Description: Peat plateaus and palsas are characteristic morphologies of sporadic permafrost, and the transition from permafrost to permafrost‐free ground typically occurs on spatial scales of meters. They are particularly vulnerable to climate change and are currently degrading in Fennoscandia. Here we present a spatially distributed data set of ground surface temperatures for two peat plateau sites in northern Norway for the year 2015–2016. Based on these data and thermal modeling, we investigate how the snow depth and water balance modulate the climate signal in the ground. We find that mean annual ground surface temperatures are centered around 2 to 2.5 °C for stable permafrost locations and 3.5 to 4.5 °C for permafrost‐free locations. The surface freezing degree days are characterized by a noticeable threshold around 200 °C.day, with most permafrost‐free locations ranging below this value and most stable permafrost ones above it. Freezing degree day values are well correlated to the March snow cover, although some variability is observed and attributed to the ground moisture level. Indeed, a zero curtain effect is observed on temperature time series for saturated soils during winter, while drained peat plateaus show early freezing surface temperatures. Complementarily, modeling experiments allow identifying a drainage effect that can modify 1‐m ground temperatures by up to 2 °C between drained and water accumulating simulations for the same snow cover. This effect can set favorable or unfavorable conditions for permafrost stability under the same climate forcing.

Description: An approach is presented for high-field MRI studies of the cardiovascular system (CVS) of a marine crustacean, the edible crab Cancer pagurus, submerged in highly conductive seawater. Structure and function of the CVS were investigated at 9.4 T. Cardiac motion was studied using self-gated CINE MRI. Imaging protocols and radio-frequency coil arrangements were tested for anatomical imaging. Haemolymph flow was quantified using phase-contrast angiography. Signal-to-noise-ratios and flow velocities in afferent and efferent branchial veins were compared with Student’s t test (n = 5). Seawater induced signal losses were dependent on imaging protocols and RF coil setup. Internal cardiac structures could be visualized with high spatial resolution within 8 min using a gradient-echo technique. Variations in haemolymph flow in different vessels could be determined over time. Maximum flow was similar within individual vessels and corresponded to literature values from Doppler measurements. Heart contractions were more pronounced in lateral and dorso-ventral directions than in the anterior–posterior direction. Choosing adequate imaging protocols in combination with a specific RF coil arrangement allows to monitor various parts of the crustacean CVS with exceptionally high spatial resolution despite the adverse effects of seawater at 9.4 T.

Description: We characterize the differences in the upward planetary‐scale wave propagation during observed weak polar vortex (WPV) events between heavy‐ and light‐sea‐ice years in the Barents‐Kara Sea based on a composite analysis for the period of 1979–2015. Upward wave propagation during WPV events in heavy‐ice years is dominated by the wavenumber 1 component. In contrast, WPV events occurring in light‐ice years are characterized by stronger wavenumber 2 propagation, which is caused by the tropospheric wavenumber 2 response to sea‐ice reduction in the Barents‐Kara Sea. The above observed features are supported by an Atmospheric General Circulation Model experiment. Thus, under present climate conditions, Arctic sea‐ice loss is a possible factor modulating the wave propagation during the WPV events. We also find that the WPV events in light‐ice years have stronger stratosphere‐troposphere coupling, followed by colder midlatitude surface conditions particularly over Eurasia.

Description: This study assesses the response on ice dynamics of Petermann Glacier, a major outlet glacier in northern Greenland, to the 2012 and a possible future calving event. So far Petermann Glacier has been believed to be dynamically stable as another large calving event in 2010 had no significant impact on flow velocity or grounding line retreat. By analyzing a time series of remotely sensed surface velocities, we find an average acceleration of 10% between winter 2011/2012 and winter 2016/2017. This increase in surface velocity is not linear but can be separated into two parts, starting in 2012 and 2016 respectively. By conducting modeling experiments, we show that the first speedup can be directly connected to the 2012 calving event, while the second speedup is not captured. However, on recent remote sensing imagery newly developing fractures are clearly visible ∼12 km upstream from the terminus, propagating from the eastern fjord wall to the center of the ice tongue, indicating a possible future calving event. By including these fracture zones as a new terminus position in the modeling domain, we are able to reproduce the second speedup, suggesting that surface velocities remain on the 2016/2017 level after the anticipated calving event. This indicates that, from a dynamical point of view, the terminus region has already detached from the main ice tongue.

Description: The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community‐sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive‐specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom‐up and top‐down approaches.

Description: Microalgae are capable of acclimating to dynamic light environments, as they have developed mechanisms to optimize light harvesting and photosynthetic electron transport. When absorption of light exceeds photosynthetic capacity, various physiological protective mechanisms prevent damage of the photosynthetic apparatus. Xanthophyll pigments provide one of the most important photoprotective mechanisms to dissipate the excess light energy and prevent photoinhibition. In this study, we coupled a mechanistic model for phytoplankton photoinhibition with the global biogeochemical model Regulated Ecosystem Model version 2. The assumption that photoinhibition is small in phytoplankton communities acclimated to ambient light allowed us to predict the photoprotective needs of phytoplankton. When comparing the predicted photoprotective needs to observations of pigment content determined by high‐performance liquid chromatography, our results showed that photoprotective response seems to be mediated in most parts of the ocean by a variable ratio of xanthophyll pigments to chlorophyll. The variability in the ratio appeared to be mainly driven by changes in phytoplankton community composition. Exceptions appeared at high latitudes where other energy dissipating mechanisms seem to play a role in photoprotection and both taxonomic changes and physiological acclimation determine community pigment signature. Understanding the variability of community pigment signature is crucial for modeling the coupling of light absorption to carbon fixation in the ocean. Insights about how much of this variability is attributable to changes in community composition may allow us to improve the match between remotely sensed optical data and the underlying phytoplankton community.

Description: Deciduous larch is a weak competitor when growing in mixed stands with evergreen taxa but is dominant in many boreal forest areas of Eastern Siberia. However, it is hypothesized that certain factors such as a shallow active layer thickness and high fire frequency favor larch dominance. Our aim is to understand how thermohydrological interactions between vegetation, permafrost, and atmosphere stabilize the larch forests and the underlying permafrost in Eastern Siberia. A tailored version of a one-dimensional land surface model (CryoGrid) is adapted for the application in vegetated areas and used to reproduce the energy transfer and thermal regime of permafrost ground in typical boreal larch stands. In order to simulate the responds of Arctic trees to local climate and permafrost conditions we have implemented a multilayer canopy parameterization originally developed for the Community Land Model (CLM-ml_v0). The coupled model is capable of calculating the full energy balance above, within and below the canopy including the radiation budget, the turbulent fluxes and the heat budget of the permafrost ground under several forcing scenarios. We will present first results of simulations performed for different study sites in larch-dominated forests of Eastern Siberia and Mongolia under current and future climate conditions. Model performance is thoroughly evaluated based on comprehensive in-situ soil temperature and radiation measurements at our study sites.

Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Noble gases in deepwater oils of the U.S. Gulf of Mexico. Geochemistry, Geophysics, Geosystems , 19, 4218 – 4235.(2018): doi:10.1029/2018GC007654.

Description: Hydrocarbon migration and emplacement processes remain underconstrained despite the vast potential economic value associated with oil and gas. Noble gases provide information about hydrocarbon generation, fluid migration pathways, reservoir conditions, and the relative volumes of oil versus water in the subsurface. Produced gas He-Ne-Ar-Kr-Xe data from two distinct oil fields in the Gulf of Mexico (Genesis and Hoover-Diana) are used to calibrate a model that takes into account both water-oil solubility exchange and subsequent gas cap formation. Reconstructed noble gas signatures in oils reflect simple (two-phase) oil-water exchange imparted during migration from the source rock to the trap, which are subsequently modified by gas cap formation at current reservoir conditions. Calculated, oil to water volume ratios (Vo/Vw) in Tertiary-sourced oils from the Hoover-Diana system are 2–3 times greater on average than those in the Jurassic sourced oils from the Genesis reservoirs. Higher Vo/Vw in Hoover-Diana versus Genesis can be interpreted in two ways: either (1) the Hoover reservoir interval has 2–3 times more oil than any of the individual Genesis reservoirs, which is consistent with independent estimates of oil in place for the respective reservoirs, or (2) Genesis oils have experienced longer migration pathways than Hoover-Diana oils and thus have interacted with more water. The ability to determine a robust Vo/Vw , despite gas cap formation and possible gas cap loss, is extremely powerful. For example, when volumetric hydrocarbon ratios are combined with independent estimates of hydrocarbon migration distance and/or formation fluid volumes, this technique has the potential to differentiate between large and small oil accumulations.

Description: We thank ExxonMobil for funding and providing the samples. In addition, we thank James Scott and two anonymous reviewers for their comprehensive and constructive reviews, as well as Janne Blichert-Toft for editorial handling.

Description: 2019-04-10

Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 123(12), (2018): 8674-8687, doi:10.1002/2018JC013766.

Description: A large collaborative program has studied the coupled air‐ice‐ocean‐wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year.

Description: This program was supported by the Office of Naval Research, Code 32, under Program Managers Scott Harper and Martin Jeffries. The crew of R/V Sikuliaq provide outstanding support in collecting the field data, and the US National Ice Center, German Aerospace Center (DLR), and European Space Agency facilitated the remote sensing collections and daily analysis products. RADARSAT‐2 Data and Products are from MacDonald, Dettwiler, and Associates Ltd., courtesy of the U.S. National Ice Center. Data, supporting information, and a cruise report can be found at http://www.apl.uw.edu/arcticseastate

Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 123(12), (2018): 8887-8901, doi:10.1029/2018JC013797.

Description: Sea ice is one of the determining parameters of the climate system. The presence of melt ponds on the surface of Arctic sea ice plays a critical role in the mass balance of sea ice. A total of nine cores was collected from multiyear ice refrozen melt ponds and adjacent hummocks during the 2015 Arctic Sea State research cruise. The depth profiles of water isotopes, salinity, and ice texture for these sea ice cores were examined to provide information about the development of refrozen melt ponds and water balance generation processes, which are otherwise difficult to acquire. The presence of meteoric water with low oxygen isotope values as relatively thin layers indicates melt pond water stability and little mixing during formation and refreezing. The hydrochemical characteristics of refrozen melt pond and seawater depth profiles indicate little snowmelt enters the upper ocean during melt pond refreezing. Due to the seasonal characters of deuterium excess for Arctic precipitation, water balance calculations utilizing two isotopic tracers (oxygen isotope and deuterium excess) suggest that besides the melt of snow cover, the precipitation input in the melt season may also play a role in the evolution of melt ponds. The dual‐isotope mixing model developed here may become more valuable in a future scenario of increasing Arctic precipitation. The layers of meteoric origin were found at different depths in the refrozen melt pond ice cores. Surface topography information collected at several core sites was examined for possible explanations of different structures of refrozen melt ponds.

Description: The coauthors (S. F. A., S. S., T. M., and B. W.) wish to thank the other DRI participants and the Captain and crew of the Sikuliaq's October 2015 cruise for their assistance in the sample collections analyzed in the paper. Jim Thomson (Chief Scientist), Scott Harper (ONR Program Manager), and Martin Jeffries (ONR Program Manager) are particularly acknowledged for their unwavering assistance and leadership during the 5 years of the SeaState DRI. We thank Guy Williams for production of the aerial photo mosaic. Funding from the Office of Naval Research N00014‐13‐1‐0435 (S. F. A. and B. W.), N00014‐13‐1‐0434 (S. S.), and N00014‐13‐1‐0446 (T. M.) supported this research through grants to UTSA, UColorado, and WHOI, respectively. This project was also funded (in part) by the University of Texas at San Antonio, Office of the Vice President for Research (Y. G. and S. F. A.). Data for the stable isotope mixing models used in this study are shown in supporting information Tables S1–S3.

Description: 2019-05-15

Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Freymond, C. V., Lupker, M., Peterse, F., Haghipour, N., Wacker, L., Filip, F., et al. (2018). Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter. Geochemistry, Geophysics, Geosystems, 19, 2453 2462. doi: 10.1029/2018GC007539.

Description: Fluvial export of organic carbon (OC) and burial in ocean sediments comprises an important carbon sink, but fluxes remain poorly constrained, particularly for specific organic components. Here OC and lipid biomarker contents and isotopic characteristics of suspended matter determined in depth profiles across an active channel close to the terminus of the Danube River are used to constrain instantaneous OC and biomarker fluxes and integrated compositions during high to moderate discharges. During high (moderate) discharge, the total Danube exports 8 (7) kg/s OC, 7 (3) g/s higher plant‐derived long‐chain fatty acids (LCFA), 34 (21) g/s short‐chain fatty acids (SCFA), and 0.5 (0.2) g/s soil bacterial membrane lipids (brGDGTs). Integrated stable carbon isotopic compositions were TOC: −28.0 (−27.6)‰, LCFA: −33.5 (−32.8)‰ and Δ14C TOC: −129 (−38)‰, LCFA: −134 (−143)‰, respectively. Such estimates will aid in establishing quantitative links between production, export, and burial of OC from the terrestrial biosphere.

Description: This project was funded by the Swiss National Science Foundation SNF. Grant Number: 200021_140850. F.P. acknowledges funding from NWO‐VENI grant 863.13.016. We thank the sampling crews from both field campaigns (Björn Buggle, James Saenz, Alissa Zuijdgeest, Marilu Tavagna, Stefan Eugen Filip, Silvia Lavinia Filip, Mihai, Clayton Magill, Thomas Blattmann, and Michael Albani), Daniel Montluçon for lab support and Hannah Gies for PCGC work. Figures, tables, and equations can be found in supporting information.

Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans, 123(11), (2018): 7877-7895. doi: 10.1029/2018JC014290.

Description: A three‐dimensional, primitive‐equation, ocean circulation model coupled with a Lagrangian particle‐tracking algorithm is used to investigate the dispersal and settlement of planktonic larvae released from discrete hydrothermal habitats on the East Pacific Rise segment at 9–10°N. Model outputs show that mean circulation is anticyclonic around the ridge segment, which consists of a northward flow along the western flank and a southward flow along the eastern flank. Those flank jets are dispersal expressways for the along‐ridge larval transport and strongly affect its overall direction and spatial‐temporal variations. It is evident from model results that the transform faults bounding the ridge segment and off axis topography (the Lamont Seamount Chain) act as topographic barriers to larval dispersal in the along‐ridge direction. Furthermore, the presence of an overlapping spreading center and an adjacent local topographic high impedes the southward along‐ridge larval transport. The model results suggest that larval recolonization within ridge‐crest habitats is enhanced by the anticyclonic circulation around the ridge segment, and the overall recolonization rate is higher for larvae having a short precompetency period and an altitude above the bottom sufficient to avoid influence by the near‐bottom currents Surprisingly, for larvae having a long precompetency period (〉10 days), the prolonged travel time allowed some of those larvae to return to their natal vent clusters, which results in an unexpected increase in connectivity among natal and neighboring sites. Overall, model‐based predictions of connectivity are highly sensitive to the larval precompetency period and vertical position in the water column.

Description: The sediment‐trap data presented in this paper are included in Table S1. The bathymetric data used in the model can be downloaded from the Global Multi‐Resolution Topography (GMRT) Synthesis of Marine Geoscience Data System (MGDS) (https://www.gmrt.org/GMRTMapTool). The ocean current time series data used in this work were acquired in 2006‐2007 by Andreas Thurnherr at the Earth Institute of Columbia University. Those data can be accessed in the supporting information. D.J. McGillicuddy gratefully acknowledges support from the National Science Foundation and the Holger W. Jannasch and Columbus O'Donnell Iselin Shared Chairs for Excellence in Oceanography. L.S. Mullineaux acknowledges with gratitude support from the National Science Foundation and the Woods Hole Oceanographic Institution (WHOI) Ocean life fellowship. We appreciate the operation support from the Captain and crew of R/V Atlantis and the Alvin submersible group. We are thankful to V.K. Kosnyrev for developing the coupling interface between the ocean‐circulation and particle‐tracking models. We are grateful to J.W. Lavelle for his intellectual support for the modeling work presented in this paper. We thank Houshuo Jiang for sponsoring our use of the cluster computer at WHOI.

Description: 2019-05-06

Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans, 123(11), (2018): 7983-8003. doi:10.1029/2018JC014298.

Description: A melt pond (MP) distribution equation has been developed and incorporated into the Marginal Ice‐Zone Modeling and Assimilation System to simulate Arctic MPs and sea ice over 1979–2016. The equation differs from previous MP models and yet benefits from previous studies for MP parameterizations as well as a range of observations for model calibration. Model results show higher magnitude of MP volume per unit ice area and area fraction in most of the Canada Basin and the East Siberian Sea and lower magnitude in the central Arctic. This is consistent with Moderate Resolution Imaging Spectroradiometer observations, evaluated with Measurements of Earth Data for Environmental Analysis (MEDEA) data, and closely related to top ice melt per unit ice area. The model simulates a decrease in the total Arctic sea ice volume and area, owing to a strong increase in bottom and lateral ice melt. The sea ice decline leads to a strong decrease in the total MP volume and area. However, the Arctic‐averaged MP volume per unit ice area and area fraction show weak, statistically insignificant downward trends, which is linked to the fact that MP water drainage per unit ice area is increasing. It is also linked to the fact that MP volume and area decrease relatively faster than ice area. This suggests that overall the actual MP conditions on ice have changed little in the past decades as the ice cover is retreating in response to Arctic warming, thus consistent with the Moderate Resolution Imaging Spectroradiometer observations that show no clear trend in MP area fraction over 2000–2011.

Description: We gratefully acknowledge the support of the NASA Cryosphere Program (grants NNX15AG68G, NNX17AD27G, and NNX14AH61G), the Office of Naval Research (N00014‐12‐1‐0112), the NSF Office of Polar Programs (PLR‐1416920, PLR‐1603259, PLR‐1602521, and ARC‐1203425), and the Department of Homeland Security (DHS, 2014‐ST‐061‐ML‐0002). The DHS grant is coordinated through the Arctic Domain Awareness Center (ADAC), a DHS Center of Excellence, which conducts maritime research and development for the Arctic region. The views and conclusions in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the DHS. MODIS‐derived MP area data are available at https://icdc.cen.uni‐hamburg.de/1/daten/cryosphere/arctic‐meltponds.html. MP area fraction statistics derived from MEDEA images are available from http://psc.apl.uw.edu/melt‐pond‐data/. Sea ice thickness and snow observations are available at http://psc.apl.washington.edu/sea_ice_cdr. CFS forcing data used to drive MIZMAS are available at https://www.ncdc.noaa.gov/data‐access/model‐data/model‐datasets/climate‐forecast‐system‐version2‐cfsv2.

Description: 2019-04-18

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gruen, D. S., Wolfe, J. M., & Fournier, G. P.. Paleozoic diversification of terrestrial chitin-degrading bacterial lineages. BMC Evolutionary Biology, 19, (2019): 34, doi:10.1186/s12862-019-1357-8.

Description: Background Establishing the divergence times of groups of organisms is a major goal of evolutionary biology. This is especially challenging for microbial lineages due to the near-absence of preserved physical evidence (diagnostic body fossils or geochemical biomarkers). Horizontal gene transfer (HGT) can serve as a temporal scaffold between microbial groups and other fossil-calibrated clades, potentially improving these estimates. Specifically, HGT to or from organisms with fossil-calibrated age estimates can propagate these constraints to additional groups that lack fossils. While HGT is common between lineages, only a small subset of HGT events are potentially informative for dating microbial groups. Results Constrained by published fossil-calibrated studies of fungal evolution, molecular clock analyses show that multiple clades of Bacteria likely acquired chitinase homologs via HGT during the very late Neoproterozoic into the early Paleozoic. These results also show that, following these HGT events, recipient terrestrial bacterial clades likely diversified ~ 300–500 million years ago, consistent with established timescales of arthropod and plant terrestrialization. Conclusions We conclude that these age estimates are broadly consistent with the dispersal of chitinase genes throughout the microbial world in direct response to the evolution and ecological expansion of detrital-chitin producing groups. The convergence of multiple lines of evidence demonstrates the utility of HGT-based dating methods in microbial evolution. The pattern of inheritance of chitinase genes in multiple terrestrial bacterial lineages via HGT processes suggests that these genes, and possibly other genes encoding substrate-specific enzymes, can serve as a “standard candle” for dating microbial lineages across the Tree of Life.

Description: This work was supported by a National Science Foundation (NSF) Graduate Research Fellowship Program Award to DSG., and Simons Collaboration on the Origins of Life Award #339603 and NSF Integrated Earth Systems Program Award #1615426 to GPF. The funding agencies for this study had no role in study design, data collection, data analysis and interpretation, or in writing the manuscript.

Description: Understanding the patterns and characteristics of sedimentary deposits on the conjugate Australian‐Antarctic margins is critical to reveal the Cretaceous‐Cenozoic tectonic, oceanographic, and climatic conditions in the basin. However, unraveling its evolution has remained difficult due to the different seismic stratigraphic interpretations on each margin and sparse drill sites. Here, for the first time, we collate all available seismic reflection profiles on both margins and use newly available offshore drilling data to develop a consistent seismic stratigraphic framework across the Australian‐Antarctic basins. We find sedimentation patterns similar in structure and thickness, prior to the onset of Antarctic glaciation, enabling the basinwide correlation of four major sedimentary units and their depositional history. We interpret that during the warm and humid Late Cretaceous (~83–65 Ma), large onshore river systems on both Australia and Antarctica resulted in deltaic sediment deposition offshore. We interpret that the onset of clockwise bottom currents during the early Paleogene (~58–48 Ma) formed prominent sediment drift deposits along both continental rises. We suggest that these currents strengthened and progressed farther east through the Eocene. Coevally, global cooling (〈48 Ma) and progressive aridification led to a large‐scale decrease in sediment input from both continents. Two major Eocene hiatuses recovered by the Integrated Ocean Discovery Program site U1356A at the Antarctic continental slope likely formed during this preglacial phase of low sedimentation and strong bottom currents. Our results can be used to constrain future paleo‐oceanographic modeling of this region and aid the understanding of the oceanographic changes accompanying the transition from a greenhouse to icehouse world.

Description: Increasing sea surface temperatures (SST) and blooms of lipid‐poor, filamentous cyanobacteria can change mesozooplankton metabolism and foraging strategies in marine systems. Lipid shortage and imbalanced diet may challenge the build‐up of energy pools of lipids and proteins, and access to essential fatty acids (FAs) and amino acids (AAs) by copepods. The impact of cyanobacterial blooms on individual energy pools was assessed for key species temperate Temora longicornis and boreal Pseudo‐/Paracalanus spp. that dominated field mesozooplankton communities isolated by sea‐sonal stratification in the central Baltic Sea during the hot and the cold summer. We looked at (a) total lipid and protein levels, (b) FA trophic markers and AA composition, and (c) compound‐specific stable carbon isotopes (δ13C) in bulk mesozooplankton and in a subset of parameters in particulate organic matter. Despite lipid‐poor cyanobacterial blooms, the key species were largely able to cover both energy pools, yet a tendency of lipid reduction was observed in surface animals. Omni‐ and car‐nivory feeding modes, FA trophic makers, and δ13C patterns in essential compounds emphasized that cyanobacterial FAs and AAs have been incorporated into meso‐zooplankton mainly via feeding on mixo‐ and heterotrophic (dino‐) flagellates and detrital complexes during summer. Foraging for essential highly unsaturated FAs from (dino‐) flagellates may have caused night migration of Pseudo‐/Paracalanus spp. from the deep subhalocline waters into the upper waters. Only in the hot summer (SST〉19.0°C) was T. longicornis submerged in the colder subthermocline water (~4°C). Thus, the continuous warming trend and simultaneous feeding can eventually lead to competition on the preferred diet by key copepod species below the thermocline in stratified systems. A comparison of δ13C patterns of essential AAs in surface meso‐zooplankton across sub‐basins of low and high cyanobacterial biomasses revealed the potential of δ13C‐AA isoscapes for studies of commercial fish feeding trails across the Baltic Sea food webs.

Description: In the Northern Patagonian gulfs of Argentina (Golfo Nuevo and Golfo San José), blooms of toxigenic microalgae and the detection of their associated phycotoxins are recurrent phenomena. The present study evaluated the transfer of phycotoxins from toxigenic microalgae to mesozooplankton in Golfo Nuevo and Golfo San José throughout an annual cycle (December 2014–2015 and January 2015–2016, respectively). In addition, solid-phase adsorption toxin tracking (SPATT) samplers were deployed for the first time in these gulfs, to estimate the occurrence of phycotoxins in the seawater between the phytoplankton samplings. Domoic acid was present throughout the annual cycle in SPATT samplers, whereas no paralytic shellfish poisoning toxins were detected. Ten toxigenic species were identified: Alexandrium catenella, Dinophysis acuminata, Dinophysis acuta, Dinophysis tripos, Dinophysis caudata, Prorocentrum lima, Pseudo-nitzschia australis, Pseudo-nitzschia calliantha, Pseudo-nitzschia fraudulenta, and Pseudo-nitzschia pungens. Lipophilic and hydrophilic toxins were detected in phytoplankton and mesozooplankton from both gulfs. Pseudo-nitzschia spp. were the toxigenic species most frequent in these gulfs. Consequently, domoic acid was the phycotoxin most abundantly detected and transferred to upper trophic levels. Spirolides were detected in phytoplankton and mesozooplankton for the first time in the study area. Likewise, dinophysistoxins were found in mesozooplankton from both gulfs, and this is the first report of the presence of these phycotoxins in zooplankton from the Argentine Sea. The dominance of calanoid copepods indicates that they were the primary vector of phycotoxins in the pelagic trophic web.

Description: Climate warming in regions of ice‐rich permafrost can result in widespread thermokarst development, which reconfigures the landscape and damages infrastructure. We present multisite time series observations which couple ground temperature measurements with thermokarst development in a region of very cold permafrost. In the Canadian High Arctic between 2003 and 2016, a series of anomalously warm summers caused mean thawing indices to be 150–240% above the 1979–2000 normal resulting in up to 90 cm of subsidence over the 12‐year observation period. Our data illustrate that despite low mean annual ground temperatures, very cold permafrost (〈−10 °C) with massive ground ice close to the surface is highly vulnerable to rapid permafrost degradation and thermokarst development. We suggest that this is due to little thermal buffering from soil organic layers and near‐surface vegetation, and the presence of near‐surface ground ice. Observed maximum thaw depths at our sites are already exceeding those projected to occur by 2090 under representative concentration pathway version 4.5.

Description: In the South Atlantic, a reorganization of the Mid‐Atlantic Ridge began before anomaly C34n (83.6 Ma) and ended before anomaly C30n (66.4 Ma), complicating tectonics of Rio Grande Rise and older Walvis Ridge (WR), which formed together at the Mid‐Atlantic Ridge. This reorganization is poorly understood because magnetic anomalies C30n‐C34n are poorly defined near WR. We interpreted these anomalies along westernWRto improve knowledge of Rio Grande Rise‐WRtectonic development. Anomaly trends indicate that Valdivia Bank has an E‐W age progression, perpendicular to that predicted by hot spot models. Anomaly spacing and width is irregular and anomalous near WR, implying a series of ridge jumps and possibly a microplate between anomalies C34n and C32n. Eastward ridge jumps transferred microplate lithosphere to the South American plate. This study shows that Late Cretaceous tectonic evolution of the Rio Grande Rise‐WRlarge igneous provinces was more complex than previously understood.

Description: The last interglacial (LIG; Marine Isotope Substage 5e, ~127–117 ka) experienced globally warmer than modern temperatures; however, profound differences in regional climate occurred that are relevant to the assessment of future climate change scenarios. Tropical Atlantic sea surface temperature (SST) and hydrology are intrinsic to the spatiotemporal evolution of past and future climate. We present eight monthly resolved coral Sr/Ca and δ18O records (130–118 ka) to reconstruct mean western tropical Atlantic SST and seawater δ18O changes during the LIG. Cooler and fresher than modern surface waters are indicated for the middle of the LIG at ~126 ka. This was followed by a rapid transition to modern‐like SSTs and salinities that characterized the remaining part of the LIG. Our results, which account for differences found among corals, proxies, and SST calibration uncertainties, agree with western tropical Atlantic sediment records. Together, they suggest that an oceanic regime existed that differed from today.

Description: Seismological findings show a complex scenario of plume upwellings from a deep thermo-chemical anomaly (superplume) beneath the East African Rift System (EARS). It is unclear if these geophysical observations represent a true picture of the superplume and its influence on magmatism along the EARS. Thus, it is essential to find a geochemical tracer to establish where upwellings are connected to the deep-seated thermo-chemical anomaly. Here we identify a unique non-volatile superplume isotopic signature (‘C’) in the youngest (after 10 Ma) phase of widespread EARS rift-related magmatism where it extends into the Indian Ocean and the Red Sea. This is the first sound evidence that the superplume influences the EARS far from the low seismic velocities in the magma-rich northern half. Our finding shows for the first time that superplume mantle exists beneath the rift the length of Africa from the Red Sea to the Indian Ocean offshore southern Mozambique

Description: Ultraslow spreading ridges are poorly understood plate boundaries consisting of magmatic and amagmatic segments that expose mostly mantle peridotite and only traces of basalt and gabbro. The slowest part of the global spreading system is represented by the eastern Gakkel Ridge in the Central Arctic Ocean, where crustal accretion is characterized by extreme focusing of melt to discrete magmatic centers. Close to its eastern tip lies the unusual 5,310 m deep Gakkel Rift Deep (GRD) with limited sediment infill, which is in strong contrast to the broader sediment-filled rift valleys to the east and west. Here, we report an 40Ar/39Ar age of 3.65±0.01 Ma for a pillow basalt from a seamount located on the rim the GRD confirming ultraslow spreading rates of ~7 mm/yr close to the Laptev Sea as suggested from aeromagnetic data. Its geochemistry points to an alkaline lava, attributed to partial melting of a source that underwent prior geochemical enrichment. We note that the GRD extracts compositionally similar melts as the sparsely magmatic zone further west but at much slower spreading velocities of only ~6-7 mm/yr, indicating the widespread occurrence of similarly fertile mantle in the High Arctic. This enriched source differs from sub-continental lithospheric mantle that influences magmatism along the Western Volcanic Zone (Goldstein et al. 2008) and is similar to metasomatized mantle - shown to influence melt genesis along the Eastern Volcanic Zone.

Description: Coupled subseasonal forecast systems with dynamical sea ice have the potential of providing important predictive information in polar regions. Here, we evaluate the ability of operational ensemble prediction systems to predict the location of the sea ice edge in Antarctica. Compared to the Arctic, Antarctica shows on average a 30% lower skill, with only one system remaining more skillful than aclimatological benchmark up to ∼30 days ahead. Skill tends to be highest in the west Antarctic sectorduring the early freezing season. Most of the systems tend to overestimate the sea ice edge extent and fail to capture the onset of the melting season. All the forecast systems exhibit large initial errors. We conclude that subseasonal sea ice redictions could provide marginal support for decision-making only in selected seasons and regions of the Southern Ocean. However, major progress is possible through investments in model development, forecast initialization and calibration.

Description: The Neotethyan oceanic Diamante-Terranova unit (DIATU; southern Apennines–Calabria–Peloritani Terrane system) includes basic rocks that during the Cenozoicwere subducted and metamorphosed to lawsonite-blueschist facies conditions.Petrological and structural observations (both at the meso- and micro-scale) showthat lawsonite growth was continuous during three distinctive ductile deformationstages (D1–D3).....

Description: Published

Description: 691-714

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 19(11), (2018): 4218-4235. doi: 10.1029/2018GC007654

Description: Hydrocarbon migration and emplacement processes remain underconstrained despite the vast potential economic value associated with oil and gas. Noble gases provide information about hydrocarbon generation, fluid migration pathways, reservoir conditions, and the relative volumes of oil versus water in the subsurface. Produced gas He‐Ne‐Ar‐Kr‐Xe data from two distinct oil fields in the Gulf of Mexico (Genesis and Hoover‐Diana) are used to calibrate a model that takes into account both water‐oil solubility exchange and subsequent gas cap formation. Reconstructed noble gas signatures in oils reflect simple (two‐phase) oil‐water exchange imparted during migration from the source rock to the trap, which are subsequently modified by gas cap formation at current reservoir conditions. Calculated, oil to water volume ratios (Vo/Vw) in Tertiary‐sourced oils from the Hoover‐Diana system are 2–3 times greater on average than those in the Jurassic sourced oils from the Genesis reservoirs. Higher Vo/Vw in Hoover‐Diana versus Genesis can be interpreted in two ways: either (1) the Hoover reservoir interval has 2–3 times more oil than any of the individual Genesis reservoirs, which is consistent with independent estimates of oil in place for the respective reservoirs, or (2) Genesis oils have experienced longer migration pathways than Hoover‐Diana oils and thus have interacted with more water. The ability to determine a robust Vo/Vw, despite gas cap formation and possible gas cap loss, is extremely powerful. For example, when volumetric hydrocarbon ratios are combined with independent estimates of hydrocarbon migration distance and/or formation fluid volumes, this technique has the potential to differentiate between large and small oil accumulations.

Description: We thank ExxonMobil for funding and providing the samples. In addition, we thank James Scott and two anonymous reviewers for their comprehensive and constructive reviews, as well as Janne Blichert‐Toft for editorial handling.

Description: 2019-04-10

Description: Here we provide two ArcGIS map packages with georeferenced files on the spatial distribution of sponges and echinoderms in the wider Weddell Sea (Antarctica), which were created in the context of the development of a marine protected area (MPA) in the Weddell Sea. Sponges: The map of interpolated occurrence of sponges is based on quantitative abundance data (Gerdes 2014 a - o) and on semi-quantitative data obtained by W. Arntz (retired; formerly AWI) (see Teschke & Brey 2019a for presence / absence records of the latter dataset). The abundance data were classified to be merged with the semi-quantitative data and an inverse distance weighted method was performed on the united dataset. Areas with very common occurrence of sponges occurred on the shelf near Brunt Ice Shelf along Riiser - Larsen Ice Shelf to Ekstrøm Ice Shelf. Echinoderms: A cluster analysis with species x station datasets of asteroids (Teschke & Brey 2019b), ophiuroids (Teschke & Brey 2019c) and holothurians (Gutt et al. 2014) from the Antarctic Weddell Sea indicated a particular cold-water echinoderm fauna on the Filchner shelf. We approximated this potential habitat by bottom temperature ≤ -1°, based on seawater temperature data from the Finite Element Sea Ice - Ocean Model provided by R. Timmermann (AWI). More information on the spatial analysis is given in working paper WG-EMM-16/03 submitted to the CCAMLR Working Group on Ecosystem Monitoring and Management (available at https://www.ccamlr.org/en/wg-emm-16).

Description: Here we provide four ArcGIS map packages with georeferenced files on the spatial distribution of demersal and pelagic fishes in the wider Weddell Sea (Antarctica), which were created in the context of the development of a marine protected area (MPA) in the Weddell Sea. Antarctic toothfish: The map of Dissostichus mawsoni occurrence probability is based on catch per unit effort (CPUE) data from the database of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) (data request: 03-08-2016) and on bathymetric data from the International Bathymetric Chart of the Southern Ocean (IBCSO). We fitted a four-parameter Weibull model to the simulated CPUE data per depth interval by means of the R package \textquotesinglefitdistrplus\textquotesingle. The highest D. mawsoni occurrence probability was shown at depths between 1500 and 2000 m and only approximately 20 % of the Antarctic toothfish population occurred deeper than 2000 m. Antarctic silverfish: The map of interpolated abundances of Pleuragramma antarctica was based on pelagic trawl survey data, which were collected during "Polarstern" cruises ANT-I/2, ANT-III/3 and in the context of the Lazarev Sea Krill Survey (LAKRIS) ("Polarstern" cruises ANT-XXI/4, ANT-XXIII/6, ANT-XXIV/2). The first mentioned data were provided by V. Siegel (retired; formerly Th\"unen Institute), the LAKRIS data by H. Flores (AWI). Those data were complemented by benthic trawl survey data, which were collected during seven "Polarstern" cruises between 1996 and 2011 (ANT-XIII/3, ANT-XV/3, ANT-XVII/3, ANT-XIX/5, ANT-XXI/2, ANT-XXIII/8, ANT-XXVII/3) and were provided by R. Knust (AWI) as well as by data on counts of fish species from trawl and dredge samples by Drescher et. (2012), Ekau et al. (2012a, b), Hureau et al. (2012), Kock et al. (2012) and W\"ohrmann et al. (2012). An inverse distance weighted interpolation was performed for a 10 nautical mile radius around each record. Areas with highest numbers of P. antarctica (〉 36 individuals/1000 m²) occurred offshore Riiser -Larsen Ice Shelf and on the southern Weddell Sea continental shelf offshore Filchner Ice Shelf. Demersal fish: The map of predicted habitat suitability for demersal fish is based on data, which were collected during seven "Polarstern" cruises between 1996 and 2011 (ANT-XIII/3, ANT-XV/3, ANT-XVII/3, ANT-XIX/5, ANT-XXI/2, ANT-XXIII/8, ANT-XXVII/3) and were provided by R. Knust (AWI). The habitat suitability model was developed by the use of the modelling package "biomod2". Most suitable habitat conditions for demersal fish in the wider Weddell Sea occurred on the continental shelf between approx. 5° and 30°W, on the shelf west and east of the tip of the Antarctic Peninsula as well as around the South Shetland and South Orkney Islands. Nesting sites of demersal fish: The map on observation of nesting sites of demersal fish is based on data, which were collected during "Polarstern" cruises ANT-XXVII/3, ANT-XXIX/9 and ANT-XXXI/2 and were obtained by T. Lund\"alv (retired; formerly University of Gothenburg), D. Gerdes (retired; formerly AWI) and E. Riginella (University of Padova), respectively. Those data were complemented by a literature research. Most nesting sites were observed west of 25°W, north of the tip of the Antarctic Peninsula and along the west coast of the Antarctic Peninsula. More information is given in the working paper WG-EMM-16/03 submitted to the CCAMLR Working Group on Ecosystem Monitoring and Management CCAMLR (available at https://www.ccamlr.org/en/wg-emm-16). Revised versions of the spatial analysis are described in working paper WG-SAM-17/30 and WS-SM-18/13 submitted to the CCAMLR Working Group on Statistics, Assessments and Modelling and the CCAMLR Workshop on Spatial Management, respectively (available at https://www.ccamlr.org/en/wg-sam-17; https://www.ccamlr.org/en/ws-sm-1

Description: Here, we provided four ArcGIS map packages with georeferenced files on the spatial distribution of Antarctic krill, Euphausia superba, (adults and larvae) and ice krill, Euphausia crystallorophias, in the wider Weddell Sea. The files were created in the context of the development of a marine protected area in the Weddell Sea. Antarctic krill (adults): The map of predicted habitat suitability for adult Antarctic krill was based on krill data from the database KRILLBASE (Atkinson et al., 2017; data request: 26-09-13). Those data were complemented by krill data, which were collected (a) during the Norwegian Antarctic research expedition 1976/77 (M/V "Polarsirkel"), (b) during two Soviet research cruises (RV "Gizhiga", 1977; RV "Volny Vetter", 1983), (c) in the context of the Lazarev Sea Krill Survey ("Polarstern" cruises ANT-XXI/4, ANT-XXIII/2, ANT-XXIII/6, ANT-XXIV/2) as well as (d) during "Polarstern" cruise ANT-XXIX/3. The habitat suitability model was developed by the use of the modelling package "biomod2". As predictor variables, we used (i) dissolved oxygen from the World Ocean Atlas 2013, (ii) ice coverage from AMSR-E sea ice maps, (iii) seawater temperature data from the Finite Element Sea Ice - Ocean Model (FESOM) provided by R. Timmermann (AWI), (iv) bathymetric data from the International Bathymetric Chart of the Southern Ocean (IBCSO) and (v) SeaWiFS chlorophyll-a concentration data. Most suitable habitat conditions for the Antarctic krill seem to occur near the tip of the Antarctic Peninsula, on the continental slope between 15°W and 15°E and on the Maud Rise plateau. Antarctic krill (larvae): The map of interpolated abundances of krill larvae is based on abundance data, which were collected (a) during the Norwegian Antarctic research expeditions 1976/77, 1977/78 and 1979/80 (M/V "Polarsirkel"), (b) in the context of the First International BIOMASS Experiment survey (FIBEX) (Walther Herwig cruise 1981) and the Lazarev Sea Krill Survey (LAKRIS) ("Polarstern" cruises ANT-XXI/4, ANT-XXIII/6) as well as (c) during "Polarstern" cruise ANT-VII/4 and the combined "Polarstern" (ANT-VIII/2) and R.V. "Akademik Fedorova" cruise. An inverse distance weighted (IDW) interpolation was performed for a 30 km radius around each krill larvae record. Areas with highest numbers of E. superba larvae (〉 1000 individuals/m²) occurred west of the Prime Meridian from approximately 65°S to the ice shelf. Ice krill (adults): The map of the potential habitat of E. crystallorophias was approximated by water depth from 0 m to 550 m, using bathymetric data from IBCSO, and mean sea surface temperature ≤ 0°C based on temperature data from FESOM provided by R. Timmermann (AWI). The map of interpolated density of individuals of E. crystallorophias is based on abundance data, which were collected (a) during the Norwegian Antarctic research expedition 1979/80 (M/V "Polarsirkel"), (b) during the German Antarctic research cruise 1975/76 with "Walther Herwig", (c) in the context of the Lazarev Sea Krill Survey ("Polarstern" cruises ANT-XXI/4, ANT-XXIII/2, ANT-XXIII/6, ANT-XXIV/2) as well as (d) during "Polarstern" cruise ANT-V/1-3, ANT-VII/4 and ANT-XXIX/3. An IDW interpolation was performed for a 30 km radius around each record of ice krill. Areas with highest densities of E. crystallorophias individuals occurred on the south-eastern Weddell Sea shelf and near the tip of the Antarctic Peninsula. Volker Siegel (retired; formerly Th\"unen Institute) provided the data for the Antarctic krill and ice krill. More information on the spatial analysis is given in working paper WG-EMM-16/03 submitted to the CCAMLR Working Group on Ecosystem Monitoring and Management (available at https://www.ccamlr.org/en/wg-emm-16)

Description: Here we provide four ArcGIS map packages with georeferenced files on the spatial distribution of Antarctic petrels, Ad\'elie penguins (breeders and non-breeders) and Emperor penguins in the wider Weddell Sea (Antarctica), which were created in the context of the development of a marine protected area in the Weddell Sea. Antarctic petrel (Thalassoica antarctica): We approximated potential foraging habitats of T. antarctica according to existing literature by ice coverage from AMSR-E sea ice maps, bathymetric data from the International Bathymetric Chart of the Southern Ocean (IBCSO), and seawater temperature data from the Finite Element Sea Ice - Ocean Model (FESOM) provided by R. Timmermann (AWI). Subsequently, we combined our Antarctic petrel model with the kernel utilization distribution model from Descamps et al. (2016). The authors kindly provided us with shape files showing the kernel utilization summer and winter distribution of Antarctic petrel breeding at Svarthamaren. Breeding locations and estimated number of breeding pairs were taken from van Franeker et al. (1999). Favourable habitat conditions for Antarctic petrels were predicted for the Lazarev Sea and along the eastern coast of the Weddell Sea, particularly for the area off the Fimbul Ice Shelf and along the coast between approx. 15°E to 10°W within a water depth range from approx. 500 m to 2500 m. Breeding Ad\'elie penguins (Pygoscelis adeliae): The map of potential foraging habitats of breeding P. adeliae is based on British Antarctic Survey (BAS) Inventory data from Phil Trathan (ID 754) and Mike Dunn and P. Trathan (ID 764, 773, 779), a dataset from BAS (P. Trathan) and Instituto Ant\'artico Argentino (Mercedes Santos) (ID 753) and a dataset from the US AMLR Program from Jefferson Hinke and Wayne Trivelpiece (NOAA) (ID 910), which are stored in the Birdlife International\textquotesingles Seabird Tracking Database (data request: 20-10-2015). Suitable foraging habitats for breeding Ad\'elies from colonies from which no tracking data were not available were approximated by a 50 km buffer and a 50-100 km ring buffer around each colony according to the recommendations of a CCAMLR MPA planning workshop. Breeding locations and estimated abundance of breeding pairs were taken from Lynch and LaRue (2014). The tracking data were processed with a state-space model described by Johnson et al. (2008) and were implemented in the R package crawl (Johnson 2011). Jefferson Hinke (NOAA) kindly provided us with support running the R script. Highly suitable foraging habitats occurred about 50 km away from the colonies on King Georg Island, the colony in Hope Bay (Graham Land) and the colonies on the South Orkney Islands. Non-breeding Ad\'elie penguins (Pygoscelis adeliae): The map of potential foraging habitats of non-breeding P. adeliae is based on British Antarctic Survey (BAS) Inventory data from Phil Trathan (ID 754) and Mike Dunn and P. Trathan (ID 773, 779), a dataset from BAS (P. Trathan) and Instituto Ant\'artico Argentino (Mercedes Santos) (ID 753) and a dataset from the US AMLR Program from Jefferson Hinke and Wayne Trivelpiece (NOAA) (ID 910), which are stored in the Birdlife International\textquotesingles Seabird Tracking Database (data request: 20-10-2015). The tracking data were processed with a state-space model described by Johnson et al. (2008) and were implemented in the R package crawl (Johnson 2011). Jefferson Hinke (NOAA) kindly provided us with support running the R script. Highest habitat utilisation was concentrated in relative small areas (e.g., close to King Georg Island). However, the non-breeding Ad\'elies seemed to roam through large parts of the Weddell Sea. Emperor penguins (Aptenodytes forsteri): The probability map of A. forsteri occurrence was developed as a function of distance to colony and colony size from Fretwell et al. (2012, 2014) as well as from sea ice concentration from AMSR-E sea ice maps. Our model of emperor penguin foraging distribution during breeding season showed that the probability of occurrence is highest at the Halley and Dawson colony near Brunt Ice Shelf and at the Atka colony near Ekstrøm Ice Shelf. More information on the spatial analysis is given in working paper WG-EMM-16/03 and WG-SAM-17/30 (for T. antarctica) submitted to the CCAMLR Working Group on Ecosystem Monitoring and Management (EMM) and the CCAMLR Working Group on Statistics, Assessments and Modelling (SAM), respectively (available at https://www.ccamlr.org/en/wg-emm-16 and https://www.ccamlr.org/en/wg-s

Description: Here we provide two ArcGIS map packages with georeferenced files on the spatial distribution of seals in the wider Weddell Sea (Antarctica), which were created in the context of the development of a marine protected area in the Weddell Sea. Spatial distribution of seals based on aerial surveys: The map of the spatial distribution of crabeater seals is based on modelled seal abundances from Flores et al. (2008) and Forcada et al. (2012). These modelled abundances were supplemented by abundance data derived from Bester et al. (1995, 2002) and by point data from Pl\"otz et al. (2011a-e), which were translated into abundance values by the count method for line transect data. The calculated data on seal abundances from Pl\"otz et al. (2011a-e) and Bester et al. (1995, 2002) were interpolated using the inverse distance weighted method. The combined data set of modelled and interpolated abundances showed highest absolute seal abundances offshore the Riiser-Larsen Ice Shelf and Quarisen Ice Shelf. Spatial distribution of seals based on tracking data: The map of probability of seal occurrence is based on all tracking data publicly available for the wider Weddell Sea from the MEOP data portal "Marine Mammals Exploring the Oceans Pole to Pole" (data request: 14-11-2016). In addition, we have used MEOP data (UK data: ct27, ct70; German data: ct113, wd06, wd07) for which unconditional sharing is not yet accepted. These data were provided by Lars Boehme (University of St. Andrews) and Horst Bornemann (AWI), respectively. Furthermore, the data from the MEOP data portal were complemented by tracking data sets on southern elephant seals (Tosh et al. 2009, James et al. 2012), Weddell seals (McIntyre et al. 2013) and crabeater seals (Nachtsheim et al. 2016). All tracking data united were processed with a state-space model described by Johnson et al. (2008) and were implemented in the R package crawl (Johnson 2011). The tracking data analysis indicated frequent occurrence of seals in a larger area off the Brunt and Filchner Ice Shelf (approx. 25°W-40°W), and in smaller patches along the eastern Weddell Sea ice shelfs as well as in the region around the tip of the Antarctic Peninsula. More information on the spatial analysis is given in working paper WG-EMM-16/03 and WG-SAM-17/30 submitted to the CCAMLR Working Group on Ecosystem Monitoring and Management (EMM) and the CCAMLR Working Group on Statistics, Assessments and Modelling (SAM), respectively (available at https://www.ccamlr.org/en/wg-emm-16 and https://www.ccamlr.org/en/wg-sam-17

Description: Here we provide four ArcGIS map packages with georeferenced files on the spatial distribution of Antarctic petrels, Ad\'elie penguins (breeders and non-breeders) and Emperor penguins in the wider Weddell Sea (Antarctica), which were created in the context of the development of a marine protected area in the Weddell Sea. Antarctic petrel (Thalassoica antarctica): We approximated potential foraging habitats of T. antarctica according to existing literature by ice coverage from AMSR-E sea ice maps, bathymetric data from the International Bathymetric Chart of the Southern Ocean (IBCSO), and seawater temperature data from the Finite Element Sea Ice - Ocean Model (FESOM) provided by R. Timmermann (AWI). Subsequently, we combined our Antarctic petrel model with the kernel utilization distribution model from Descamps et al. (2016). The authors kindly provided us with shape files showing the kernel utilization summer and winter distribution of Antarctic petrel breeding at Svarthamaren. Breeding locations and estimated number of breeding pairs were taken from van Franeker et al. (1999). Favourable habitat conditions for Antarctic petrels were predicted for the Lazarev Sea and along the eastern coast of the Weddell Sea, particularly for the area off the Fimbul Ice Shelf and along the coast between approx. 15°E to 10°W within a water depth range from approx. 500 m to 2500 m. Breeding Ad\'elie penguins (Pygoscelis adeliae): The map of potential foraging habitats of breeding P. adeliae is based on British Antarctic Survey (BAS) Inventory data from Phil Trathan (ID 754) and Mike Dunn and P. Trathan (ID 764, 773, 779), a dataset from BAS (P. Trathan) and Instituto Ant\'artico Argentino (Mercedes Santos) (ID 753) and a dataset from the US AMLR Program from Jefferson Hinke and Wayne Trivelpiece (NOAA) (ID 910), which are stored in the Birdlife International\textquotesingles Seabird Tracking Database (data request: 20-10-2015). Suitable foraging habitats for breeding Ad\'elies from colonies from which no tracking data were not available were approximated by a 50 km buffer and a 50-100 km ring buffer around each colony according to the recommendations of a CCAMLR MPA planning workshop. Breeding locations and estimated abundance of breeding pairs were taken from Lynch and LaRue (2014). The tracking data were processed with a state-space model described by Johnson et al. (2008) and were implemented in the R package crawl (Johnson 2011). Jefferson Hinke (NOAA) kindly provided us with support running the R script. Highly suitable foraging habitats occurred about 50 km away from the colonies on King Georg Island, the colony in Hope Bay (Graham Land) and the colonies on the South Orkney Islands. Non-breeding Ad\'elie penguins (Pygoscelis adeliae): The map of potential foraging habitats of non-breeding P. adeliae is based on British Antarctic Survey (BAS) Inventory data from Phil Trathan (ID 754) and Mike Dunn and P. Trathan (ID 773, 779), a dataset from BAS (P. Trathan) and Instituto Ant\'artico Argentino (Mercedes Santos) (ID 753) and a dataset from the US AMLR Program from Jefferson Hinke and Wayne Trivelpiece (NOAA) (ID 910), which are stored in the Birdlife International\textquotesingles Seabird Tracking Database (data request: 20-10-2015). The tracking data were processed with a state-space model described by Johnson et al. (2008) and were implemented in the R package crawl (Johnson 2011). Jefferson Hinke (NOAA) kindly provided us with support running the R script. Highest habitat utilisation was concentrated in relative small areas (e.g., close to King Georg Island). However, the non-breeding Ad\'elies seemed to roam through large parts of the Weddell Sea. Emperor penguins (Aptenodytes forsteri): The probability map of A. forsteri occurrence was developed as a function of distance to colony and colony size from Fretwell et al. (2012, 2014) as well as from sea ice concentration from AMSR-E sea ice maps. Our model of emperor penguin foraging distribution during breeding season showed that the probability of occurrence is highest at the Halley and Dawson colony near Brunt Ice Shelf and at the Atka colony near Ekstrøm Ice Shelf. More information on the spatial analysis is given in working paper WG-EMM-16/03 and WG-SAM-17/30 (for T. antarctica) submitted to the CCAMLR Working Group on Ecosystem Monitoring and Management (EMM) and the CCAMLR Working Group on Statistics, Assessments and Modelling (SAM), respectively (available at https://www.ccamlr.org/en/wg-emm-16 and https://www.ccamlr.org/en/wg-s

Description: Here we provide two ArcGIS map packages with georeferenced files on the spatial distribution of seals in the wider Weddell Sea (Antarctica), which were created in the context of the development of a marine protected area in the Weddell Sea. Spatial distribution of seals based on aerial surveys: The map of the spatial distribution of crabeater seals is based on modelled seal abundances from Flores et al. (2008) and Forcada et al. (2012). These modelled abundances were supplemented by abundance data derived from Bester et al. (1995, 2002) and by point data from Pl\"otz et al. (2011a-e), which were translated into abundance values by the count method for line transect data. The calculated data on seal abundances from Pl\"otz et al. (2011a-e) and Bester et al. (1995, 2002) were interpolated using the inverse distance weighted method. The combined data set of modelled and interpolated abundances showed highest absolute seal abundances offshore the Riiser-Larsen Ice Shelf and Quarisen Ice Shelf. Spatial distribution of seals based on tracking data: The map of probability of seal occurrence is based on all tracking data publicly available for the wider Weddell Sea from the MEOP data portal "Marine Mammals Exploring the Oceans Pole to Pole" (data request: 14-11-2016). In addition, we have used MEOP data (UK data: ct27, ct70; German data: ct113, wd06, wd07) for which unconditional sharing is not yet accepted. These data were provided by Lars Boehme (University of St. Andrews) and Horst Bornemann (AWI), respectively. Furthermore, the data from the MEOP data portal were complemented by tracking data sets on southern elephant seals (Tosh et al. 2009, James et al. 2012), Weddell seals (McIntyre et al. 2013) and crabeater seals (Nachtsheim et al. 2016). All tracking data united were processed with a state-space model described by Johnson et al. (2008) and were implemented in the R package crawl (Johnson 2011). The tracking data analysis indicated frequent occurrence of seals in a larger area off the Brunt and Filchner Ice Shelf (approx. 25°W-40°W), and in smaller patches along the eastern Weddell Sea ice shelfs as well as in the region around the tip of the Antarctic Peninsula. More information on the spatial analysis is given in working paper WG-EMM-16/03 and WG-SAM-17/30 submitted to the CCAMLR Working Group on Ecosystem Monitoring and Management (EMM) and the CCAMLR Working Group on Statistics, Assessments and Modelling (SAM), respectively (available at https://www.ccamlr.org/en/wg-emm-16 and https://www.ccamlr.org/en/wg-sam-17

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 20(5), (2019):2462-2472, doi:10.1029/2019GC008250.

Description: Methane hydrate occurs naturally under pressure and temperature conditions that are not straightforward to replicate experimentally. Xenon has emerged as an attractive laboratory alternative to methane for studying hydrate formation and dissociation in multiphase systems, given that it forms hydrates under milder conditions. However, building reliable analogies between the two hydrates requires systematic comparisons, which are currently lacking. We address this gap by developing a theoretical and computational model of gas hydrates under equilibrium and nonequilibrium conditions. We first compare equilibrium phase behaviors of the Xe·H2O and CH4·H2O systems by calculating their isobaric phase diagram, and then study the nonequilibrium kinetics of interfacial hydrate growth using a phase field model. Our results show that Xe·H2O is a good experimental analog to CH4·H2O, but there are key differences to consider. In particular, the aqueous solubility of xenon is altered by the presence of hydrate, similar to what is observed for methane; but xenon is consistently less soluble than methane. Xenon hydrate has a wider nonstoichiometry region, which could lead to a thicker hydrate layer at the gas‐liquid interface when grown under similar kinetic forcing conditions. For both systems, our numerical calculations reveal that hydrate nonstoichiometry coupled with hydrate formation dynamics leads to a compositional gradient across the hydrate layer, where the stoichiometric ratio increases from the gas‐facing side to the liquid‐facing side. Our analysis suggests that accurate composition measurements could be used to infer the kinetic history of hydrate formation in natural settings where gas is abundant.

Description: This work was funded in part by the U.S. Department of Energy, DOE [awards DE‐FE0013999 and DE‐SC0018357 (to R. J.) and DOE Interagency Agreement DE‐FE0023495 (to W. F. W.)]. X. F. acknowledges support by the Miller Research Fellowship at the University of California Berkeley. W. F. W. acknowledges support from the U.S. Geological Survey's Gas Hydrate Project and the Survey's Coastal, Marine Hazards and Resources Program. L. C. F. acknowledges funding from the Spanish Ministry of Economy and Competitiveness (grants RYC‐2012‐11704 and CTM2014‐54312‐P). L. C. F. and R. J. acknowledge funding from the MIT International Science and Technology Initiatives, through a Seed Fund grant. The simulation data are available on the UC Berkeley Dash repository at https://doi.org/10.6078/D1G67B.

Description: 2019-11-06

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Biogeosciences, 124(6), (2019): 1591-1603, doi:10.1029/2018JG004803.

Description: Tropical dry forests in eastern and southern Africa cover 2.5 × 106 km2, support wildlife habitat and livelihoods of more than 150 million people, and face threats from land use and climate change. To inform conservation, we need better understanding of ecosystem processes like nutrient cycling that regulate forest productivity and biomass accumulation. Here we report on patterns in nitrogen (N) cycling across a 100‐year forest regrowth chronosequence in the Tanzanian Miombo woodlands. Soil and vegetation indicators showed that low ecosystem N availability for trees persisted across young to mature forests. Ammonium dominated soil mineral N pools from 0‐ to 15‐cm depth. Laboratory‐measured soil N mineralization rates across 3‐ to 40‐year regrowth sites showed no significant trends and were lower than mature forest rates. Aboveground tree N pools increased at 6 to 7 kg N·ha−1·yr−1, accounting for the majority of ecosystem N accumulation. Foliar δ15N 〈0‰ in an N‐fixing canopy tree across all sites suggested that N fixation may contribute to ecosystem N cycle recovery. These results contrast N cycling in wetter tropical and Neotropical dry forests, where indicators of N scarcity diminish after several decades of regrowth. Our findings suggest that minimizing woody biomass removal, litter layer, and topsoil disturbance may be important to promote N cycle recovery and natural regeneration in Miombo woodlands. Higher rates of N mineralization in the wet season indicated a potential that climate change‐altered rainfall leading to extended dry periods may lower N availability through soil moisture‐dependent N mineralization pathways, particularly for mature forests.

Description: This study depended on the knowledge, insights, and cooperation of many people and institutions. We thank the Millennium Villages Project‐Mbola site for providing introductions to the landscape and village headmen in many regions. We thank the ARI‐Tumbi staff (now TARI‐Tumbi) in Tabora, Tanzania for providing invaluable logistical support in identifying forest regrowth sites and help with labwork in Tabora, Tanzania. We thank other key local organizations, including Tabora Development Foundation Trust (Dick Mlimuka, Oscar Kisanji) and Tanzania Forest Service (Bw. Relingo), for logistical support and transportation. We thank many village headmen and farmers for access to forest sites within their lands for sampling. Finally, we would like to thank the MBL Stable Isotope laboratory and Dr. Marshall Otter for his expertise with producing and interpreting soil and leaf C, N and stable isotope data. This study was funded in part by NSF PIRE Grant OISE 0968211, a Dissertation Support Grant to Marc Mayes from Brown University (2015–2016), and completed with permission and cooperation from the Tanzania Commission on Science and Technology (COSTECH permits 2013‐261‐NA‐2014‐199 and 2015‐183‐ER‐2014‐199). Data and code for analyses can be accessed at a Github repository: https://github.com/mtm17/MiomboN.git.

Description: 2019-11-08

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in [citation], doi:[doi]. Johnson, W. M., Longnecker, K., Soule, M. C. K., Arnold, W. A., Bhatia, M. P., Hallam, S. J., Van Mooy, B. A. S., & Kujawinski, E. B. Metabolite composition of sinking particles differs from surface suspended particles across a latitudinal transect in the South Atlantic. Limnology and Oceanography, (2019), doi:10.1002/lno.11255.

Description: Marine sinking particles transport carbon from the surface and bury it in deep‐sea sediments, where it can be sequestered on geologic time scales. The combination of the surface ocean food web that produces these particles and the particle‐associated microbial community that degrades them creates a complex set of variables that control organic matter cycling. We use targeted metabolomics to characterize a suite of small biomolecules, or metabolites, in sinking particles and compare their metabolite composition to that of the suspended particles in the euphotic zone from which they are likely derived. These samples were collected in the South Atlantic subtropical gyre, as well as in the equatorial Atlantic region and the Amazon River plume. The composition of targeted metabolites in the sinking particles was relatively similar throughout the transect, despite the distinct oceanic regions in which they were generated. Metabolites possibly derived from the degradation of nucleic acids and lipids, such as xanthine and glycine betaine, were an increased mole fraction of the targeted metabolites in the sinking particles relative to surface suspended particles, while algal‐derived metabolites like the osmolyte dimethylsulfoniopropionate were a smaller fraction of the observed metabolites on the sinking particles. These compositional changes are shaped both by the removal of metabolites associated with detritus delivered from the surface ocean and by production of metabolites by the sinking particle‐associated microbial communities. Furthermore, they provide a basis for examining the types and quantities of metabolites that may be delivered to the deep sea by sinking particles.

Description: The authors would like to thank the captain and crew of the R/V Knorr and R/V Atlantic Explorer, as well as Justin Ossolinski, Catherine Carmichael, and Sean Sylva for helping to make this data set possible. Special thanks to Colleen Durkin for sharing her data and providing feedback on the manuscript. Funding for this work came from the National Science Foundation (NSF Grant OCE‐1154320 to EBK and KL) and a WHOI Ocean Ventures Fund award to WMJ. The instruments in the WHOI FT‐MS Facility were purchased with support from the Gordon & Betty Moore Foundation and NSF. Support for WMJ was provided by a National Defense Science and Engineering Fellowship. Sequencing was performed under the auspices of the US Department of Energy (DOE) JGI Community Science Program (CSP) project (CSP 1685) supported by the Office of Science of US DOE Contract DE‐AC02‐ 05CH11231. Additional work related to sample collection and processing was supported by the G. Unger Vetlesen and Ambrose Monell Foundations, the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Institute for Advanced Study (CIFAR), and the Canada Foundation for Innovation through grants awarded to SJH. MPB was supported by a CIFAR Global Scholarship and NSERC postdoctoral fellowship.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Long, M. H., Sutherland, K., Wankel, S. D., Burdige, D. J., & Zimmerman, R. C. Ebullition of oxygen from seagrasses under supersaturated conditions. Limnology and Oceanography, (2019), doi:10.1002/lno.11299.

Description: Gas ebullition from aquatic systems to the atmosphere represents a potentially important fraction of primary production that goes unquantified by measurements of dissolved gas concentrations. Although gas ebullition from photosynthetic surfaces has often been observed, it is rarely quantified. The resulting underestimation of photosynthetic activity may significantly bias the determination of ecosystem trophic status and estimated rates of biogeochemical cycling from in situ measures of dissolved oxygen. Here, we quantified gas ebullition rates in Zostera marina meadows in Virginia, U.S.A. using simple funnel traps and analyzed the oxygen concentration and isotopic composition of the captured gas. Maximum hourly rates of oxygen ebullition (3.0 mmol oxygen m−2 h−1) were observed during the coincidence of high irradiance and low tides, particularly in the afternoon when oxygen and temperature maxima occurred. The daily ebullition fluxes (up to 11 mmol oxygen m−2 d−1) were roughly equivalent to net primary production rates determined from dissolved oxygen measurements indicating that bubble ebullition can represent a major component of primary production that is not commonly included in ecosystem‐scale estimates. Oxygen content comprised 20–40% of the captured bubble gas volume and correlated negatively with its δ18O values, consistent with a predominance of mixing between the higher δ18O of atmospheric oxygen in equilibrium with seawater and the lower δ18O of oxygen derived from photosynthesis. Thus, future studies interested in the metabolism of highly productive, shallow water ecosystems, and particularly those measuring in situ oxygen flux, should not ignore the bubble formation and ebullition processes described here.

Description: Two anonymous reviewers provided thoughtful contributions that improved this manuscript. We thank Miraflor Santos, Victoria Hill, David Ruble, Jeremy Bleakney, and Brian Collister for assistance in the field and the staff of the Anheuser‐Busch Coastal Research Center for logistical support. This work was supported by NSF OCE grants 1633951 (to MHL) and 1635403 (to RCZ and DJB), NASA Fellowship NESSF NNX15AR62H (to KS), and a fellowship from the Hansewissenschaftskolleg (Institute for Advanced Studies; to SDW).

Description: The cumulative Greenland freshwater flux anomaly has exceeded 5,000 km3 since the 1990s. The volume of this surplus freshwater is expected to cause substantial freshening in the North Atlantic. Analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s. The sources of this freshening are yet to be determined. In this study, the relationship between the surplus Greenland freshwater flux and this freshening is tested by analyzing the propagation of the Greenland freshwater anomaly and its impact on salinity in the subpolar North Atlantic based on observational data and numerical experiments with and without the Greenland runoff. A passive tracer is continuously released during the simulations at freshwater sources along the coast of Greenland to track the Greenland freshwater anomaly. Tracer budget analysis shows that 44% of the volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic by the end of the simulation. This volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50–100 m. However, in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations. Therefore, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening. Impacts on salinity in the subpolar seas of the freshwater transport through Fram Strait and precipitation are discussed.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dukhovskoy, D. S., Yashayaev, I., Proshutinsky, A., Bamber, J. L., Bashmachnikov, I. L., Chassignet, E. P., Lee, C. M., & Tedstone, A. J. Role of Greenland freshwater anomaly in the recent freshening of the subpolar North Atlantic. Journal of Geophysical Research-Oceans, 124(5), (2019): 3333-3360, doi:10.1029/2018JC014686.

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(7), (2019): 4416-4432, doi: 10.1029/2019JC015185.

Description: Synoptic and historical shipboard data, spanning the period 1981–2017, are used to investigate the seasonal evolution of water masses on the northeastern Chukchi shelf and quantify the circulation patterns and their impact on nutrient distributions. We find that Alaskan coastal water extends to Barrow Canyon along the coastal pathway, with peak presence in September, while the Pacific Winter Water (WW) continually drains off the shelf through the summer. The depth‐averaged circulation under light winds is characterized by a strong Alaskan Coastal Current (ACC) and northward flow through Central Channel. A portion of the Central Channel flow recirculates anticyclonically to join the ACC, while the remainder progresses northeastward to Hanna Shoal where it bifurcates around both sides of the shoal. All of the branches converge southeast of the shoal and eventually join the ACC. The wind‐forced response has two regimes: In the coastal region the circulation depends on wind direction, while on the interior shelf the circulation is sensitive to wind stress curl. In the most common wind‐forced state—northeasterly winds and anticyclonic wind stress curl—the ACC reverses, the Central Channel flow penetrates farther north, and there is mass exchange between the interior and coastal regions. In September and October, the region southeast of Hanna Shoal is characterized by elevated amounts of WW, a shallower pycnocline, and higher concentrations of nitrate. Sustained late‐season phytoplankton growth spurred by this pooling of nutrients could result in enhanced vertical export of carbon to the seafloor, contributing to the maintenance of benthic hotspots in this region.

Description: The authors acknowledge the hard work and dedication of the many crew members who sailed on the different cruises of the USCGC Healy and the R/V Palmer. This study would not have been possible without their ongoing efforts to carry out successful science operations. Seth Danielson performed the quality control of the Barrow wind data. Funding was provided by the following sources: National Oceanic and Atmospheric Administration (NOAA) Grant NA14‐OAR4320158 (P. L., R. P., and L. M.), National Science Foundation (NSF) Grants OPP‐1702371 and OPP‐1733564 (R. P. and F. B.) and PLR‐1303617 (R. P., K. A., and K. L.), NSF Graduate Research Fellowship Program DGE‐0645962 (K. L.), National Aeronautics and Space Administration award NNX10AF42G (R. P., K. A., and K. L.), and NOAA's Ocean Observing and Monitoring Division, Climate Program Office Fund 100007298 (C. M.). This publication is partially funded by the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063 and is contribution EcoFOCI‐0924 to the Ecosystems and Fisheries‐Oceanography Coordinated Investigations, 4944 to PMEL. The CTD and shipboard ADCP data of the eight cruises are available from http://www.rvdata.us/, and the nutrients data can be accessed from https://arcticdata.io/.

Description: 2019-12-07

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(6), (2019): 3490-3507, doi:10.1029/2018JC014675.

Description: Offshore permafrost plays a role in the global climate system, but observations of permafrost thickness, state, and composition are limited to specific regions. The current global permafrost map shows potential offshore permafrost distribution based on bathymetry and global sea level rise. As a first‐order estimate, we employ a heat transfer model to calculate the subsurface temperature field. Our model uses dynamic upper boundary conditions that synthesize Earth System Model air temperature, ice mass distribution and thickness, and global sea level reconstruction and applies globally distributed geothermal heat flux as a lower boundary condition. Sea level reconstruction accounts for differences between marine and terrestrial sedimentation history. Sediment composition and pore water salinity are integrated in the model. Model runs for 450 ka for cross‐shelf transects were used to initialize the model for circumarctic modeling for the past 50 ka. Preindustrial submarine permafrost (i.e., cryotic sediment), modeled at 12.5‐km spatial resolution, lies beneath almost 2.5 ×106km2 of the Arctic shelf. Our simple modeling approach results in estimates of distribution of cryotic sediment that are similar to the current global map and recent seismically delineated permafrost distributions for the Beaufort and Kara seas, suggesting that sea level is a first‐order determinant for submarine permafrost distribution. Ice content and sediment thermal conductivity are also important for determining rates of permafrost thickness change. The model provides a consistent circumarctic approach to map submarine permafrost and to estimate the dynamics of permafrost in the past.

Description: Boundary condition data are available online via the sources referenced in the manuscript. This work was partially funded by a Helmholtz Association of Research Centres (HGF) Joint Russian‐German Research Group (HGF JRG 100). This study is part of a project that has received funding from the European Unions Horizon 2020 research and innovation program under grant agreement 773421. Submarine permafrost studies in the Kara and Laptev Seas were supported by Russian Foundation for Basic Research (RFBR/RFFI) grants 18‐05‐60004 and 18‐05‐70091, respectively. The International Permafrost Association (IPA) and the Association for Polar Early Career Scientists (APECS) supported research coordination that led to this study. We acknowledge coordination support of the World Climate Research Programme (WCRP) through their core project on Climate and Cryosphere (CliC). Thanks to Martin Jakobsson for providing a digitized version of the preliminary IHO delineation of the Arctic seas and to Guy Masters for access to the observational geothermal database. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Description: 2019-10-17

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46 (2019): 10484–10494, doi:10.1029/2019GL083719.

Description: Tropical cyclones (hurricanes) generate intense surface ocean cooling and vertical mixing resulting in nutrient upwelling into the photic zone and episodic phytoplankton blooms. However, their influence on the deep ocean remains unknown. Here we present evidence that hurricanes also impact the ocean's biological pump by enhancing export of labile organic material to the deep ocean. In October 2016, Category 3 Hurricane Nicole passed over the Bermuda Time Series site in the oligotrophic NW Atlantic Ocean. Following Nicole's passage, particulate fluxes of lipids diagnostic of fresh phytodetritus, zooplankton, and microbial biomass increased by 30–300% at 1,500 m depth and 30–800% at 3,200 m depth. Mesopelagic suspended particles following Nicole were also enriched in phytodetrital material and in zooplankton and bacteria lipids, indicating particle disaggregation and a deepwater ecosystem response. Predicted climate‐induced increases in hurricane frequency and/or intensity may significantly alter ocean biogeochemical cycles by increasing the strength of the biological pump.

Description: This work and the Oceanic Flux Program time series were supported by the National Science Foundation Chemical Oceanography Program Grant OCE 1536644. The Bermuda Atlantic Time Series and Hydrostation S time series were supported by NSF Grants OCE 1756105 and OCE 1633125, respectively. We acknowledge the contributions of BATS technicians with CTD and pigment analyses. We sincerely thank the officers and crew of R/V Atlantic Explorer (Bermuda Institute of Ocean Sciences) for their expert assistance on the cruises. The data used in this study are listed in the figures, tables, and references, and are also available in the NSF's Biological and Chemical Oceanography Data Management Office (BCO‐DMO, https://doi.org/10.1575/1912/bco‐dmo.775902.1).

Description: 2020-02-16

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(5), (2019): 2943-2968, doi:10.1029/2019JC015071.

Description: In the Southern Ocean, polynyas exhibit enhanced rates of primary productivity and represent large seasonal sinks for atmospheric CO2. Three contrasting east Antarctic polynyas were visited in late December to early January 2017: the Dalton, Mertz, and Ninnis polynyas. In the Mertz and Ninnis polynyas, phytoplankton biomass (average of 322 and 354 mg chlorophyll a (Chl a)/m2, respectively) and net community production (5.3 and 4.6 mol C/m2, respectively) were approximately 3 times those measured in the Dalton polynya (average of 122 mg Chl a/m2 and 1.8 mol C/m2). Phytoplankton communities also differed between the polynyas. Diatoms were thriving in the Mertz and Ninnis polynyas but not in the Dalton polynya, where Phaeocystis antarctica dominated. These strong regional differences were explored using physiological, biological, and physical parameters. The most likely drivers of the observed higher productivity in the Mertz and Ninnis were the relatively shallow inflow of iron‐rich modified Circumpolar Deep Water onto the shelf as well as a very large sea ice meltwater contribution. The productivity contrast between the three polynyas could not be explained by (1) the input of glacial meltwater, (2) the presence of Ice Shelf Water, or (3) stratification of the mixed layer. Our results show that physical drivers regulate the productivity of polynyas, suggesting that the response of biological productivity and carbon export to future change will vary among polynyas.

Description: This work was cofunded by the Australian Antarctic Division research projects AAS 4131 and 4291. This project was also supported by the Australian Government Cooperative Research Centres Programme through the Antarctic Climate & Ecosystems (ACE CRC). S. Moreau and C. Genovese were supported by the Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership (project ID SR140300001). V. Puigcorbé and M. Roca‐Martí are grateful for the support from Pere Masque and Edith Cowan University. M.C. Arroyo was supported by the Dickhut Fellowship, administered by the Virginia Institute of Marine Science. The authors would like to thank the officers and crew of the R/V Aurora Australis for their logistic support, the CSIRO hydrochemists for their analyses of nutrient concentrations, and E. J. Yang for her microscope analysis of phytoplankton species. We also want to thank two anonymous reviewers for their very good comments on this study. The data presented in this paper are available on the Australian Antarctic Division (AAD) Data Centre at https://data.aad.gov.au/aadc/metadata/metadata_by_parameter.cfm.

Description: 2019-09-28

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(3), (2019): 1778-1794, doi:10.1029/2018JC014775.

Description: Abyssal ocean warming contributed substantially to anthropogenic ocean heat uptake and global sea level rise between 1990 and 2010. In the 2010s, several hydrographic sections crossing the South Pacific Ocean were occupied for a third or fourth time since the 1990s, allowing for an assessment of the decadal variability in the local abyssal ocean properties among the 1990s, 2000s, and 2010s. These observations from three decades reveal steady to accelerated bottom water warming since the 1990s. Strong abyssal (z 〉 4,000 m) warming of 3.5 (±1.4) m°C/year (m°C = 10−3 °C) is observed in the Ross Sea, directly downstream from bottom water formation sites, with warming rates of 2.5 (±0.4) m°C/year to the east in the Amundsen‐Bellingshausen Basin and 1.3 (±0.2) m°C/year to the north in the Southwest Pacific Basin, all associated with a bottom‐intensified descent of the deepest isotherms. Warming is consistently found across all sections and their occupations within each basin, demonstrating that the abyssal warming is monotonic, basin‐wide, and multidecadal. In addition, bottom water freshening was strongest in the Ross Sea, with smaller amplitude in the Amundsen‐Bellingshausen Basin in the 2000s, but is discernible in portions of the Southwest Pacific Basin by the 2010s. These results indicate that bottom water freshening, stemming from strong freshening of Ross Shelf Waters, is being advected along deep isopycnals and mixed into deep basins, albeit on longer timescales than the dynamically driven, wave‐propagated warming signal. We quantify the contribution of the warming to local sea level and heat budgets.

Description: S. G. P. was supported by a U.S. GO‐SHIP postdoctoral fellowship through NSF grant OCE‐1437015, which also supported L. D. T. and S. M. and collection of U.S. GO‐SHIP data since 2014 on P06, S4P, P16, and P18. G. C. J. is supported by the Global Ocean Monitoring and Observation Program, National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce and NOAA Research. B. M. S and S. E. W. were supported by the Australian Government Department of the Environment and CSIRO through the Australian Climate Change Science Programme and by the National Environmental Science Program. We are grateful for the hard work of the science parties, officers, and crew of all the research cruises on which these CTD data were collected. We also thank the two anonymous reviewers for their helpful comments that improve the manuscript. This is PMEL contribution 4870. All CTD data sets used in this analysis are publicly available at the website (https://cchdo.ucsd.edu).

Description: 2019-08-20

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(3), (2019): 2088-2109, doi:10.1029/2018JC014583.

Description: As observations and models improve their resolution of oceanic motions at ever finer horizontal scales, interest has grown in characterizing the transition from the geostrophically balanced flows that dominate at large‐scale to submesoscale turbulence and waves that dominate at small scales. In this study we examine the mesoscale‐to‐submesoscale (100 to 10 km) transition in an eastern boundary current, the southern California Current System (CCS), using repeated acoustic Doppler current profiler transects, sea surface height from high‐resolution nadir altimetry and output from a (1/48)° global model simulation. In the CCS, the submesoscale is as energetic as in western boundary current regions, but the mesoscale is much weaker, and as a result the transition lacks the change in kinetic energy (KE) spectral slope observed for western boundary currents. Helmholtz and vortex‐wave decompositions of the KE spectra are used to identify balanced and unbalanced contributions. At horizontal scales greater than 70 km, we find that observed KE is dominated by balanced geostrophic motions. At scales from 40 to 10 km, unbalanced contributions such as inertia‐gravity waves contribute as much as balanced motions. The model KE transition occurs at longer scales, around 125 km. The altimeter spectra are consistent with acoustic Doppler current profiler/model spectra at scales longer than 70/125 km, respectively. Observed seasonality is weak. Taken together, our results suggest that geostrophic velocities can be diagnosed from sea surface height on scales larger than about 70 km in the southern CCS.

Description: This research was funded by NASA (NNX13AE44G, NNX13AE85G, NNX16AH67G, NNX16AO5OH, and NNX17AH53G). We thank Sung Yong Kim for providing the high‐frequency radar spectral estimates and the two anonymous reviewers for providing useful comments and suggestions that greatly improved the manuscript. High‐frequency ALES data for Jason‐1 and Jason‐2 altimeters are available upon request (https://openadb.dgfi.tum.de/en/contact/ALES). Both AltiKa and Sentinel‐3 altimeter products were produced and distributed by the Copernicus Marine and Environment Monitoring Service (CMEMS; http://www.marine.copernicus.eu). D. M. worked on the modeling component of this study at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). High‐end computing resources were provided by the NASA Advanced Supercomputing (NAS) Division of the Ames Research Center. The LLC output can be obtained from the ECCO project (ftp://ecco.jpl.nasa.gov/ECCO2/LLC4320/). The ADCP data are available at the Joint Archive for Shipboard ADCP data (JASADCP; http://ilikai.soest.hawaii.edu/sadcp).

Description: 2019-08-21

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 20(3), (2019): 1485-1507, doi:10.1029/2018GC007985.

Description: In 2015 a geothermal exploration well was drilled on the island of Tutuila, American Samoa. The sample suite from the drill core provides 645 m of volcanic stratigraphy from a Samoan volcano, spanning 1.45 million years of volcanic history. In the Tutuila drill core, shield lavas with an EM2 (enriched mantle 2) signature are observed at depth, spanning 1.46 to 1.44 Ma. These are overlain by younger (1.35 to 1.17 Ma) shield lavas with a primordial “common” (focus zone) component interlayered with lavas that sample a depleted mantle component. Following ~1.15 Myr of volcanic quiescence, rejuvenated volcanism initiated at 24.3 ka and samples an EM1 (enriched mantle 1) component. The timing of the initiation of rejuvenated volcanism on Tutuila suggests that rejuvenated volcanism may be tectonically driven, as Samoan hotspot volcanoes approach the northern terminus of the Tonga Trench. This is consistent with a model where the timing of rejuvenated volcanism at Tutuila and at other Samoan volcanoes relates to their distance from the Tonga Trench. Notably, the Samoan rejuvenated lavas have EM1 isotopic compositions distinct from shield lavas that are geochemically similar to “petit spot” lavas erupted outboard of the Japan Trench and late stage lavas erupted at Christmas Island located outboard of the Sunda Trench. Therefore, like the Samoan rejuvenated lavas, petit spot volcanism in general appears to be related to tectonic uplift outboard of subduction zones, and existing geochemical data suggest that petit spots share similar EM1 isotopic signatures.

Description: Reviews from Kaj Hoernle and three anonymous reviewers are gratefully acknowledged. M. G. J. acknowledges support from the American Samoa Power Authority and National Science Foundation grants OCE‐1736984 and EAR‐1624840. The Tutuila drill core was the brainchild of Tim Bodell, without whom we would still have no stratigraphic record of Tutuila volcanism. The support of Utu Abe Malae and Matamua Katrina Mariner was instrumental to the project's success. We dedicate this paper to the memory of Abe Malae and his efforts to support science and education in American Samoa. Images of the entire drill core are available online (escholarship.org/uc/item/6gg6p61w). All data presented are either part of this study or previously published and are referenced in text.

Description: 2019-08-13