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  • 1
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    On the Propagation Path of Magma‐Filled Dikes and Hydrofractures: The Competition Between External Stress, Internal Pressure, and Crack Length (2019)
    Wiley
    Details
    Publikationsdatum: 2021-03-09
    Beschreibung: 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.
    Beschreibung: Published
    Beschreibung: 2064–2081
    Beschreibung: 2V. Struttura e sistema di alimentazione dei vulcani
    Beschreibung: JCR Journal
    Schlagwort(e): Magmatic dykes ; hydrofractures ; Numerical symulations ; Analogue experiments ; 04.08. Volcanology ; 05.05. Mathematical geophysics
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Gas emission strength and evolution of the molar ratio of BrO/SO2 in the plume of Nyiragongo in comparison to Etna (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2021-06-25
    Beschreibung: Airborne and ground-based differential optical absorption spectroscopy observations have been carried out at the volcano Nyiragongo (Democratic Republic of Congo) tomeasure SO2 and bromine monoxide (BrO) in the plume inMarch 2004 and June 2007, respectively. Additionally filter pack andmulticomponent gas analyzer system (Multi-GAS)measurements were carried out in June 2007. Ourmeasurements provide valuable information on the chemical composition of the volcanic plume emitted fromthe lava lake of Nyiragongo. The main interest of this study has been to investigate for the first time the bromine emission flux of Nyiragongo (a rift volcano) and the BrO formation in its volcanic plume. Measurement data and results from a numerical model of the evolution of BrO in Nyiragongo volcanic plume are compared with earlier studies of the volcanic plume of Etna (Italy). Even though the bromine flux from Nyiragongo (2.6 t/d) is slightly greater than that from Etna (1.9 t/d), the BrO/SO2 ratio (maximum 7 × 10 5) is smaller than in the plume of Etna (maximum 2.1 × 10 4). A one-dimensional photochemical model to investigate halogen chemistry in the volcanic plumes of Etna and Nyiragongo was initialized using data from Multi-GAS and filter pack measurements. Model runs showed that the differences in the composition of volcanic volatiles led to a smaller fraction of total bromine being present as BrO in the Nyiragongo plume and to a smaller BrO/SO2 ratio.
    Beschreibung: Published
    Beschreibung: 277-291
    Beschreibung: 4V. Vulcani e ambiente
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Intraplate volcano Nyiragongo is bromine rich although chlorine poor ; BrO/Br in volcanic plumes depends on initial plume composition ; Determination of Nyiragongo chlorine, bromine, sulfur emission strength ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 3
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    Seismic hydraulic fracture migration originated by successive deep magma pulses: The 2011–2013 seismic series associated to the volcanic activity of El Hierro Island (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2020-12-15
    Beschreibung: In thismanuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of El Hierro, Canary Islands, during 2011–2013. We estimated temporal variations of the Gutenberg-Richter b value throughout the period of analysis, and performed high-precision relocations of the preeruptive and syneruptive seismicity using a realistic 3-D velocity model. Our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust. These magma pulses occurred within a small and well-defined volume resulting in the emplacement of fresh magma along the crust-mantle boundary underneath El Hierro. We analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust. Our results suggest that very high earthquake rates underneath El Hierro represent the response of a stable lower crust to stress perturbations with pulsatory character, linked to the injection of magma from the mantle. Magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms. The absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity, had diffusive character. We conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill. Our conceptual model considers pulsatorymagma injection fromthe uppermantle and its propagation along the Moho.We suggest, within this framework, that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement.
    Beschreibung: Published
    Beschreibung: 7749–7770
    Beschreibung: 1T. Geodinamica e interno della Terra
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): b value, relocation, Hydraulic fracturing, Magma influx ; 05. General::05.02. Data dissemination::05.02.99. General or miscellaneous
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 4
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    New coring study in Augusta Bay expands understanding of offshore tsunami deposits (Eastern Sicily, Italy) (2019)
    Wiley
    Details
    Publikationsdatum: 2021-01-25
    Beschreibung: 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.
    Beschreibung: Published
    Beschreibung: 1553-1576
    Beschreibung: 6T. Studi di pericolosità sismica e da maremoto
    Beschreibung: JCR Journal
    Schlagwort(e): Eastern Sicily ; tsunami ; foraminifera ; sedimentology ; XRF core scanning ; 04.04. Geology
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Are there new findings in the search for ULF magnetic precursors to earthquakes? (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2021-02-10
    Beschreibung: Moore (1964) in a letter published in Nature reported disturbances in geomagnetic field data prior to the 27 March 1964 Alaska earthquake. After the publication of this report, many papers have shown magnetic changes preceding earthquakes. However, a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated. As a consequence, after 50 years, magnetic disturbances in the geomagnetic field are still candidate precursory phenomena. Some researchers consider the investigation of ultra low frequency (ULF: 0.001–10 Hz) magnetic data the correct approach for identifying precursory signatures of earthquakes. Other researchers, instead, have recently reviewed many published ULF magnetic changes that preceded earthquakes and have shown that these are not actual precursors. The recent studies by Currie and Waters (2014) and Han et al. (2014) aim to provide relevant new findings in the search for ULF magnetic precursory signals. However, in order to contribute to science, alleged precursors must be shown to be valid and reproducible by objective testing. Here we will briefly discuss the state of the art in the search for ULF magnetic precursors, paying special attention to the recent findings of Currie and Waters (2014) and Han et al. (2014). We do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ULF magnetic records.
    Beschreibung: Published
    Beschreibung: 10289–10304
    Beschreibung: 1A. Geomagnetismo e Paleomagnetismo
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Geomagnetic field ; Magnetic anomalies ; Earthquake precursors ; 01. Atmosphere::01.03. Magnetosphere::01.03.03. Magnetospheric physics ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 6
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    Transient variability of the Miocene Antarctic ice Sheet smaller than equilibrium differences (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46(8), pp. 4288-4298, ISSN: 0094-8276
    Details
    Publikationsdatum: 2021-02-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 7
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    Reaction of a polar gravel‐spit system to atmospheric warming and glacier retreat as reflected by morphology and internal sediment geometries (South Shetland Islands, Antarctica) (2019)
    Wiley
    In:  EPIC3Earth Surface Processes and Landforms, Wiley, 44(5), pp. 1148-1162, ISSN: 0197-9337
    Details
    Publikationsdatum: 2019-04-29
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev , info:eu-repo/semantics/article
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  • 8
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    Improved performance of ERA5 in Arctic gateway relative to four global atmospheric reanalyses (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46, ISSN: 0094-8276
    Details
    Publikationsdatum: 2019-07-10
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 9
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    The budget of macrobenthic reworked organic carbon ‐ a modelling case study of the North Sea (2019)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Biogeosciences, Wiley, 124, pp. 1446-1471, ISSN: 2169-8961
    Details
    Publikationsdatum: 2019-08-13
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 10
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    East Pacific Rise Core PS75/059‐2: Glacial‐to‐Deglacial Stratigraphy Revisited (2019)
    Wiley
    In:  EPIC3Paleoceanography and Paleoclimatology, Wiley, 34, pp. 432-435
    Details
    Publikationsdatum: 2019-06-23
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 11
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    Quantifying manganese and nitrogen cycle coupling in manganese-rich, organic carbon-starved marine sediments: Examples from the Clarion-Clipperton fracture zone (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43, ISSN: 0094-8276
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    Publikationsdatum: 2016-12-07
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 12
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    Discussion of Different Model Approaches for the Flow Behavior of Ice (2016)
    Wiley
    In:  EPIC3Proceedings in Applied Mathematics and Mechanics, Wiley, 16(1), pp. 313-314, ISSN: 16177061
    Details
    Publikationsdatum: 2017-11-13
    Beschreibung: Ice of Antarctic ice shelves is assumed to behave on long-term as an incompressible viscous fluid, which is dominated on short time scales by the elastic response. Hence, a viscoelastic material model is required. The thermodynamic pressure is treated differently in elastic and viscous models. For small deformations, the elastic isometric stress for ν → 0.5 gives similar results to those solving for pressure in an incompressible laminar flow model. A viscous model, in which the thermodynamic pressure is approximated by an elastic isometric stress, can be easily extended to viscoelasticity.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , notRev
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  • 13
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    Algal Export in the Arctic Ocean in Times of Global Warming (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publikationsdatum: 2019-06-16
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 14
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    Fast EVP Solutions in a High‐Resolution Sea Ice Model (2019)
    Wiley
    In:  EPIC3Journal of Advances in Modeling Earth Systems, Wiley, ISSN: 1942-2466
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    Publikationsdatum: 2020-08-27
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 15
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    Asynchronous variation in the Quaternary East Asian winter monsoon associated with the tropical Pacific ENSO‐like system (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46, ISSN: 0094-8276
    Details
    Publikationsdatum: 2019-07-15
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 16
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    The Weddell Gyre, Southern Ocean: present knowledge and future challenges (2019)
    Wiley
    In:  EPIC3Reviews of Geophysics, Wiley, 57, ISSN: 8755-1209
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    Publikationsdatum: 2019-08-01
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 17
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    Subglacial Geology and Geomorphology of the Pensacola‐Pole Basin, East Antarctica (2019)
    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 20, ISSN: 1525-2027
    Details
    Publikationsdatum: 2020-07-02
    Beschreibung: 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.
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  • 18
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    An aerobic eukaryotic parasite with functional mitochondria that likely lacks a mitochondrial genome (2019)
    American Association for the Advancement of Science
    In:  EPIC3Science Advances, American Association for the Advancement of Science, 5(4), ISSN: 2375-2548
    Details
    Publikationsdatum: 2020-02-12
    Beschreibung: Dinoflagellates are microbial eukaryotes that have exceptionally large nuclear genomes; however, their organelle genomes are small and fragmented and contain fewer genes than those of other eukaryotes. The genus Amoebophrya (Syndiniales) comprises endoparasites with high genetic diversity that can infect other dinoflagellates, such as those forming harmful algal blooms (e.g., Alexandrium). We sequenced the genome (~100 Mb) of Amoebophrya ceratii to investigate the early evolution of genomic characters in dinoflagellates. The A. ceratii genome encodes almost all essential biosynthetic pathways for self-sustaining cellular metabolism, suggesting a limited dependency on its host. Although dinoflagellates are thought to have descended from a photosynthetic ancestor, A. ceratii appears to have completely lost its plastid and nearly all genes of plastid origin. Functional mitochondria persist in all life stages of A. ceratii, but we found no evidence for the presence of a mitochondrial genome. Instead, all mitochondrial proteins appear to be lost or encoded in the A. ceratii nucleus.
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  • 19
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    Climate Noise Influences Ice Sheet Mean State (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publikationsdatum: 2019-09-16
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  • 20
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    Pacing of Red Sea Deep Water Renewal During the Last Centuries (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46(8), pp. 4413-4420, ISSN: 0094-8276
    Details
    Publikationsdatum: 2019-10-07
    Beschreibung: 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.
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  • 21
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    Sea Ice Targeted Geoengineering Can Delay Arctic Sea Ice Decline but not Global Warming (2019)
    American Geophysical Union
    In:  EPIC3Earth's Future, American Geophysical Union, 7(12), pp. 1296-1306, ISSN: 2328-4277
    Details
    Publikationsdatum: 2021-02-15
    Beschreibung: 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.
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  • 22
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    Ocean Heat Transport Into the Barents Sea: Distinct Controls on the Upward Trend and Interannual Variability (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46(22), pp. 13180-13190, ISSN: 0094-8276
    Details
    Publikationsdatum: 2020-01-07
    Beschreibung: 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.
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  • 23
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    Lossof a chloroplast encoded function could influence species range in kelp (2019)
    Wiley
    In:  EPIC3Ecology and Evolution, Wiley, 9(15), pp. 1-12
    Details
    Publikationsdatum: 2019-12-28
    Beschreibung: 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.
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  • 24
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    Die Wälder der Antarktis (2019)
    Wiley
    In:  EPIC3Biologie in unserer Zeit, Wiley, 49(6), pp. 436-442, ISSN: 0045-205X
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    Publikationsdatum: 2019-12-20
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  • 25
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    Reduced winter off-road tundra travel under climate change (2019)
    American Geophysical Union
    In:  EPIC3AGU Fall meeting, San Francisco, CA, 2019-12-09-2019-12-13USA, American Geophysical Union
    Details
    Publikationsdatum: 2019-12-17
    Beschreibung: 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.
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  • 26
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    Evaluation of FESOM2.0 Coupled to ECHAM6.3: Preindustrial and HighResMIP Simulations (2019)
    Wiley
    In:  EPIC3Journal of Advances in Modeling Earth Systems, Wiley, 11(11), pp. 3794-3815, ISSN: 1942-2466
    Details
    Publikationsdatum: 2021-02-16
    Beschreibung: 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.
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  • 27
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    Hydroclimate in the Pamirs Was Driven by Changes in Precipitation‐Evaporation Seasonality Since theLast Glacial Period (2019)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46(23), pp. 13972-13983, ISSN: 0094-8276
    Details
    Publikationsdatum: 2020-01-27
    Beschreibung: 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.
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  • 28
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    Interoperability Across Ocean Research Infrastructures Through Use Of Ocean Best Practices (2019)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2019, San Francisco, California, USA, 2019-12-09-2019-12-13American Geophysical Union
    Details
    Publikationsdatum: 2020-02-12
    Beschreibung: 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.
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  • 29
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    Sedimentary perspectives of Pleistocene ocean circulation and climate change from the southernmost Chilean continental margin (2019)
    American Geophysical Union
    In:  EPIC3AGU Centennial Fall Meeting, San Francisco, CA, USA, 2019-12-09-2019-12-13American Geophysical Union
    Details
    Publikationsdatum: 2020-05-14
    Beschreibung: 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.
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  • 30
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    Carbon isotope offsets between benthic foraminifer species of the genus Cibicides (Cibicidoides) in the glacial sub-Antarctic Atlantic (2016)
    Wiley
    In:  EPIC3Paleoceanography, Wiley, 31(12), pp. 1583-1602, ISSN: 0883-8305
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    Publikationsdatum: 2017-01-15
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  • 31
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    Arctic pathways of Pacific Water: Arctic Ocean Model Intercomparison experiments (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 121(1), pp. 27-59, ISSN: 0148-0227
    Details
    Publikationsdatum: 2016-11-23
    Beschreibung: Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings heat, fresh water and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper pathways of PW are investigated using simulations with six state-of-the art regional and global Ocean General Circulation Models (OGCMs). In the simulations PW is tracked by a passive tracer, released in Bering Strait. Simulated PW water spreads from the Bering Strait region in three major branches. One of them starts in the Barrow Canyon, bringing PW along continental slope of Alaska into the Canadian Straits and then into Baffin Bay. The other initiates in the vicinity of the Herald Canyon and transports PW along the continental slope of the East-Siberian Sea into the transpolar drift, and then through Fram Strait and the Greenland Sea. The third branch begins near the Herald Shoal and the central Chukchi shelf and brings PW waters into the Beaufort Gyre. Models suggest that the spread of PW through the Arctic Ocean depends on the atmospheric circulation. In the models the wind, acting via Ekman pumping, drives the seasonal and interannual variability of PW in the Canadian Basin of the Arctic Ocean. The wind effects the simulated PW pathways by changing vertical shear of the relative vorticity of the ocean flow in the Canada Basin. This article is protected by copyright. All rights reserved.
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  • 32
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    On the atmospheric response experiment to a Blue Arctic Ocean (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43(19), pp. 10394-10402, ISSN: 0094-8276
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: We demonstrated atmospheric responses to a reduction in Arctic sea ice via simulations in which Arctic sea ice decreased stepwise from the present-day range to an ice-free range. In all cases, the tropospheric response exhibited a negative Arctic Oscillation (AO)-like pattern. An intensification of the climatological planetary-scale wave due to the present-day sea ice reduction on the Atlantic side of the Arctic Ocean induced stratospheric polar vortex weakening and the subsequent negative AO. Conversely, strong Arctic warming due to ice-free conditions across the entire Arctic Ocean induced a weakening of the tropospheric westerlies corresponding to a negative AO without troposphere-stratosphere coupling, for which the planetary-scale wave response to a surface heat source extending to the Pacific side of the Arctic Ocean was responsible. Because the resultant negative AO-like response was accompanied by secondary circulation in the meridional plane, atmospheric heat transport into the Arctic increased, accelerating the Arctic amplification.
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  • 33
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    Modeling the global bomb-tritium transient signal with the AGCM LMDZ-iso: a method to evaluate aspects of the hydrological cycle (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 121(21), pp. 12612-12629, ISSN: 0148-0227
    Details
    Publikationsdatum: 2018-03-26
    Beschreibung: Improving the representation of the hydrological cycle in atmospheric general circulation models (AGCMs) is one of the main challenges in modeling the Earth’s climate system. One way to evaluate model performance is to simulate the transport of water isotopes. Among those available, tritium is an extremely valuable tracer, because its content in the different reservoirs involved in the water cycle (stratosphere, troposphere, and ocean) varies by order of magnitude. Previous work incorporated natural tritium into Laboratoire de Météorologie Dynamique Zoom (LMDZ)-iso, a version of the LMDZ general circulation model enhanced by water isotope diagnostics. Here for the first time, the anthropogenic tritium injected by each of the atmospheric nuclear bomb tests between 1945 and 1980 has been first estimated and further implemented in the model; it creates an opportunity to evaluate certain aspects of LDMZ over several decades by following the bomb tritium transient signal through the hydrological cycle. Simulations of tritium in water vapor and precipitation for the period 1950–2008, with both natural and anthropogenic components, are presented in this study. LMDZ-iso satisfactorily reproduces the general shape of the temporal evolution of tritium. However, LMDZ-iso simulates too high a bomb tritium peak followed by too strong a decrease of tritium in precipitation. The too diffusive vertical advection in AGCMs crucially affects the residence time of tritium in the stratosphere. This insight into model performance demonstrates that the implementation of tritium in an AGCM provides a new and valuable test of the modeled atmospheric transport, complementing water stable isotope modeling.
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    Modern precipitation δ18O and trajectory analysis over the Himalaya-Tibet Orogen from ECHAM5-wiso simulations (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 121(18), pp. 10,432-10,452, ISSN: 0148-0227
    Details
    Publikationsdatum: 2016-12-14
    Beschreibung: Variations in oxygen isotope ratios (δ18O) measured from modern precipitation and geologic archives provide a promising tool for understanding modern and past climate dynamics and tracking elevation changes over geologic time. In areas of extreme topography, such as the Tibetan Plateau, the interpretation of δ18O has proven challenging. This study investigates the climate controls on temporal (daily and 6 h intervals) and spatial variations in present-day precipitation δ18O (δ18Op) across the Tibetan Plateau using a 30 year record produced from the European Centre/Hamburg ECHAM5-wiso global atmospheric general circulation model (GCM). Results indicate spatial and temporal agreement between model-predicted δ18Op and observations. Large daily δ18Op variations of 25 to +5‰ occur over the Tibetan Plateau throughout the 30 simulation years, along with interannual δ18Op variations of ~2‰. Analysis of extreme daily δ18Op indicates that extreme low values coincide with extreme highs in precipitation amount. During the summer, monsoon vapor transport from the north and southwest of the plateau generally corresponds with high δ18Op, whereas vapor transport from the Indian Ocean corresponds with average to low δ18Op. Thus, vapor source variations are one important cause of the spatial-temporal differences in δ18Op. Comparison of GCM and Rayleigh Distillation Model (RDM)-predicted δ18Op indicates a modest agreement for the Himalaya region (averaged over 86°–94°E), confirming application of the simpler RDM approach for estimating δ18Op lapse rates across Himalaya.
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  • 35
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    Sea ice leads in the Arctic Ocean: Model assessment, interannual variability and trends (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43, pp. 7019-7027, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-09-06
    Beschreibung: Sea ice leads in the Arctic are important features that give rise to strong localized atmospheric heating; they provide the opportunity for vigorous biological primary production, and predicting leads may be of relevance for Arctic shipping. It is commonly believed that traditional sea ice models that employ elastic-viscous-plastic (EVP) rheologies are not capable of properly simulating sea ice deformation, including lead formation, and thus, new formulations for sea ice rheologies have been suggested. Here we show that classical sea ice models have skill in simulating the spatial and temporal variation of lead area fraction in the Arctic when horizontal resolution is increased (here 4.5 km in the Arctic) and when numerical convergence in sea ice solvers is considered, which is frequently neglected. The model results are consistent with satellite remote sensing data and discussed in terms of variability and trends of Arctic sea ice leads. It is found, for example, that wintertime lead area fraction during the last three decades has not undergone significant trends.
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  • 36
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    Layering of surface snow and firn at Kohnen Station, Antarctica - noise or seasonal signal? (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Earth Surface, Wiley, 121, pp. 1849-1860, ISSN: 21699003
    Details
    Publikationsdatum: 2016-11-14
    Beschreibung: The density of firn is an important property for monitoring and modeling the ice sheet as well as to model the pore close-off and thus to interpret ice core-based greenhouse gas records. One feature, which is still in debate, is the potential existence of an annual cycle of firn density in low-accumulation regions. Several studies describe or assume seasonally successive density layers, horizontally evenly distributed, as seen in radar data. On the other hand, high-resolution density measurements on firn cores in Antarctica and Greenland showed no clear seasonal cycle in the top few meters. A major caveat of most existing snow-pit and firn-core based studies is that they represent one vertical profile from a laterally heterogeneous density field. To overcome this, we created an extensive dataset of horizontal and vertical density data at Kohnen Station, Dronning Maud Land on the East Antarctic Plateau. We drilled and analyzed three 90 m long firn cores as well as 160 one meter long vertical profiles from two elongated snow trenches to obtain a two dimensional view of the density variations. The analysis of the 45 m wide and 1 m deep density fields reveals a seasonal cycle in density. However, the seasonality is overprinted by strong stratigraphic noise, making it invisible when analyzing single firn cores. Our density dataset extends the view from the local ice-core perspective to a hundred meter scale and thus supports linking spatially integrating methods such as radar and seismic studies to ice and firn cores.
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  • 37
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    Preglacial to glacial sediment thickness grids for the Southern Pacific margin of West Antarctica (2016)
    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 17, ISSN: 1525-2027
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    Publikationsdatum: 2016-10-29
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  • 38
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    Temporal variation of the deep circulation of the South China Sea since the Last Glacial Maximum (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43, pp. 8590-8599, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-12-14
    Beschreibung: Deepwater circulation plays a central role in global climate. Compared with the Atlantic, the Pacific deepwater circulation’s history remains unclear. The Luzon overflow, a branch of the North Pacific deep water, determines the ventilation rate of the South China Sea (SCS) basin. Sedimentary magnetic properties in the SCS reflect millennial-scale fluctuations in deep current intensity and orientation. The data suggest a slightly stronger current at the Last Glacial Maximum compared to the Holocene. But, the most striking increase in deep current occurred during Heinrich stadial 1 (H1) and to a lesser extent during the Younger Dryas (YD). Results of a transient deglacial experiment suggest that the northeastern current strengthening at the entrance of the SCS during H1 and the YD, times of weak North Atlantic Deep Water formation, could be linked to enhanced formation of North Pacific Deep Water.
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    Unprecedented permafrost thaw dynamics on a decadal time scale: Batagay mega thaw slump development, Yana Uplands, Yakutia, Russia (2016)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, San Francisco, USA, 2016-12-12-2016-12-16San Francisco, American Geophysical Union
    Details
    Publikationsdatum: 2016-12-23
    Beschreibung: Ice-rich permafrost that formed in glacial periods of the Quaternary is highly vulnerable to thaw under ongoing climate warming and anthropogenic disturbance. The mega thaw slump near the village of Batagay (Yakutia, Russia) is an outstanding example of permafrost degradation and demonstrates that thermo-erosion processes may occur in unexpected locations, develop very rapidly in particular after disturbances, and leave behind deep rutted badlands. Retrogressive thaw slumps are particularly frequent along riverbanks and coastlines of regions where buried glacier ice or ice-rich glacial till have been mapped. In East Siberia, syngenetic Late Pleistocene Ice Complex (Yedoma) permafrost deposits accumulate volumetric ground ice contents of up to 80-90% % and extend tens of meters below the ground surface. Beyond the Yedoma main distributional range in the coastal lowlands of the Laptev and East Siberian seas, these deposits are also found on slopes of the Verkhoyan Mountain Range and in valleys of surrounding foothills, providing favorable preconditions for rapid thaw development. The Batagay mega slump exposes a profile of 30m thick Yedoma deposits underlain by ice saturated alluvial sand of around 60 m thickness and another very ice-rich layer at the base. We present data from a multi-sensor remote sensing time series investigation of the mega slump in order to assess the planimetric and volumetric dimensions and its decadal and interannual expansion rates. For ortho-rectification purposes and for volumetric analyses, we photogrammetrically derived highly detailed digital elevation models. The height difference between the headwall and the slump outflow is 145 m along a distance of 2300 m, while the maximum slump width is 840 m. Our analysis does not show any signs of stabilization after several decades (since 1980s) of slump growth, with the headwall retreating with observed rates of generally 〉10 m and more recently up to 30m per year. Reconstruction of a paleo-surface revealed that the slump has carved into the rolling topography to a depth of up to 73 m. The current size of the slump is 〉69 ha, while it had thawed 〉25 × 106 m³ of ice-rich permafrost through 2016. The majority of sediment released from the slump episodically dams up the Batagay River, forming a large temporary lake which then empties catastrophically.
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  • 40
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    Hierarchical structures in Northern Hemispheric extratropical winter ocean-atmosphere interactions (2016)
    Wiley
    In:  EPIC3International Journal of Climatology, Wiley, pp. 1-16, ISSN: 08998418
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: In recent years extensive studies on the Earth’s climate system have been carried out by means of advanced complex network statistics. The great majority of these studies, however, have been focusing on investigating correlation structures within single climatic fields directly on or parallel to the Earth’s surface. Here, we develop a novel approach of node weighted coupled network measures to study correlations between ocean and atmosphere in the Northern Hemisphere extratropics and construct 18 coupled climate networks, each consisting of two subnetworks. In all cases, one subnetwork represents monthly sea-surface temperature (SST) anomalies, while the other is based on the monthly geopotential height (HGT) of isobaric surfaces at different pressure levels covering the troposphere as well as the lower stratosphere. The weighted cross-degree density proves to be consistent with the leading coupled pattern obtained from maximum covariance analysis. Network measures of higher order allow for a further analysis of the correlation structure between the two fields and consistently indicate that in the Northern Hemisphere extratropics the ocean is correlated with the atmosphere in a hierarchical fashion such that large areas of the ocean surface correlate with multiple statistically dissimilar regions in the atmosphere. Ultimately we show that this observed hierarchy is linked to large-scale atmospheric variability patterns, such as the Pacific North American pattern, forcing the ocean on monthly time scales.
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  • 41
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    Spectral albedo and transmittance of thin young Arctic sea ice (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, ISSN: 0148-0227
    Details
    Publikationsdatum: 2017-01-20
    Beschreibung: Spectral albedo and transmittance in the range 400-900nm were measured on three separate dates on less than 15 cm thick new Arctic sea ice growing on Kongsfjorden, Svalbard at 78: 9 degrees N, 11: 9 degrees E. Inherent optical properties, including absorption coefficients of particulate and dissolved material, were obtained from ice samples and fed into a radiative transfer model, which was used to analyze spectral albedo and transmittance and to study the influence of clouds and snow on these. Integrated albedo and transmittance for photosynthetically active radiation (400-900 nm) were in the range 0.17-0.21 and 0.77-0.86, respectively. The average albedo and transmittance of the total solar radiation energy were 0.16 and 0.51, respectively. Values inferred from the model indicate that the ice contained possibly up to 40% brine and only 0.6% bubbles. Angular redistribution of solar radiation by clouds and snow was found to influence both the wavelength-integrated value and the spectral shape of albedo and transmittance. In particular, local peaks and depressions in the spectral albedo and spectral transmittance were found for wavelengths within atmospheric absorption bands. Simulated and measured transmittance spectra were within 5% for most of the wavelength range, but deviated up to 25% in the vicinity of 800 nm, indicating the need for more optical laboratory measurements of pure ice, or improved modeling of brine optical properties in this near-infrared wavelength region.
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  • 42
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    Atmospheric conditions in the central Arctic Ocean through the melt seasons of 2012 and 2013: Impact on surface conditions and solar energy deposition into the ice-ocean system (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, ISSN: 0148-0227
    Details
    Publikationsdatum: 2017-01-20
    Beschreibung: Spectral Radiation Buoys and ice mass balance buoys were deployed on first-year ice near the North Pole in April 2012 and 2013, collecting in-band (350-800nm) solar radiation and ice and snow mass balance data over the complete summer melt seasons. With complementary European ERA-Interim reanalysis, National Centers for Environmental Prediction (NCEP) Climate forecast system version 2 (CFSv2) analysis and satellite passive microwave data, we examine the evolution of atmospheric and surface melt conditions in the two differing melt seasons. Prevailing atmospheric conditions contributed to a longer and more continuous melt season in summer 2012 than in 2013, which was corroborated by in situ observations. ERA-Interim reanalysis data showed that longwave radiation likely played a key role in delaying the snowmelt onset in 2013. The earlier melt onset in 2012 reduced the albedo, providing a positive ice-albedo feedback at a time when solar insolation was high. Due to earlier melt onset and later freeze-up in 2012, more solar heat was deposited into the ice-ocean system than in 2013. Summer 2013 was characterized by later melt onset, intermittent freezing events and an earlier fall freeze-up, resulting in considerably fewer effective days of surface melt and a higher average albedo. Calculations for idealized seasonal albedo evolution show that moving the melt onset just 1week earlier in mid-June increases the total absorbed solar radiation by nearly 14% for the summer season. Therefore, the earlier melt onset may have been one of the most important factors driving the more dramatic melt season in 2012 than 2013, though atmospheric circulation patterns, e.g., cyclone in early August 2012, likely contributed as well.
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    Spatial and temporal Antarctic Ice Sheet mass trends, glacio-isostatic adjustment, and surface processes from a joint inversion of satellite altimeter, gravity, and GPS data (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Earth Surface, Wiley, 121(2), pp. 182-200, ISSN: 2169-9011
    Details
    Publikationsdatum: 2016-08-15
    Beschreibung: We present spatiotemporal mass balance trends for the Antarctic Ice Sheet from a statistical inversion of satellite altimetry, gravimetry, and elastic-corrected GPS data for the period 2003–2013. Our method simultaneously determines annual trends in ice dynamics, surface mass balance anomalies, and a time-invariant solution for glacio-isostatic adjustment while remaining largely independent of forward models. We establish that over the period 2003–2013, Antarctica has been losing mass at a rate of −84 ± 22 Gt yr−1, with a sustained negative mean trend of dynamic imbalance of −111 ± 13 Gt yr−1. West Antarctica is the largest contributor with −112 ± 10 Gt yr−1, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade, with a mean rate of −28 ± 7 Gt yr−1 and significantly higher values for the most recent years following the destabilization of the Southern Antarctic Peninsula around 2010. The total mass loss is partly compensated by a significant mass gain of 56 ± 18 Gt yr−1 in East Antarctica due to a positive trend of surface mass balance anomalies.
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    Remote Sensing of Landscape Change in Permafrost Regions (2016)
    Wiley
    In:  EPIC3Permafrost and Periglacial Processes, Wiley, ISSN: 10456740
    Details
    Publikationsdatum: 2016-10-13
    Beschreibung: Amplification of global warming in Arctic and boreal regions is causing significant changes to permafrost-affected landscapes. The nature and extent of the change is complicated by ecological responses that take place across strong gradients in environmental conditions and disturbance regimes. Emerging remote sensing techniques based on a growing array of satellite and airborne platforms that cover a wide range of spatial and temporal scales increasingly allow robust detection of changes in permafrost landscapes. In this review, we summarise recent developments (2010 − 15) in remote sensing applications to detect and monitor landscape changes involving surface temperatures, snow cover, topography, surface water, vegetation cover and structure, and disturbances from fire and human activities. We then focus on indicators of degrading permafrost, including thermokarst lakes and drained lake basins, thermokarst bogs and fens, thaw slumps and active-layer detachment slides, thermal erosion gullies, thermokarst pits and troughs, and coastal erosion and flooding. Our review highlights the expanding sensor capabilities, new image processing and multivariate analysis techniques, enhanced public access to data and increasingly long image archives that are facilitating novel insights into the multi-decadal dynamics of permafrost landscapes. Remote sensing methods that appear especially promising for change detection include: repeat light detection and ranging, interferometric synthetic aperture radar and airborne geophysics for detecting topographic and subsurface changes; temporally dense analyses at high spatial resolution; and multi-sensor data fusion. Remotely sensed data are also becoming used more frequently as driving parameters in permafrost model and mapping schemes.
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    Exhumation history along the eastern Amundsen Sea coast, West Antarctica, revealed by low-temperature thermochronology (2016)
    Wiley
    In:  EPIC3Tectonics, Wiley, 35, pp. 2239-2257, ISSN: 0278-7407
    Details
    Publikationsdatum: 2018-08-10
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    Scientists spend Arctic winter adrift on sea ice (2016)
    American Geophysical Union
    In:  EPIC3EOS, American Geophysical Union
    Details
    Publikationsdatum: 2017-01-19
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    Modeling of Store Gletscher’s calving dynamics, West Greenland, in response to ocean thermal forcing (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43(6), pp. 2659-2666, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-11-15
    Beschreibung: Glacier-front dynamics is an important control on Greenland's ice mass balance. Warmer ocean waters trigger ice-front retreats of marine-terminating glaciers, and the corresponding loss in resistive stress leads to glacier acceleration and thinning. Here we present an approach to quantify the sensitivity and vulnerability of marine-terminating glaciers to ocean-induced melt. We develop a plan view model of Store Gletscher that includes a level set-based moving boundary capability, a parameterized ocean-induced melt, and a calving law with complete and precise land and fjord topographies to model the response of the glacier to increased melt. We find that the glacier is stabilized by a sill at its terminus. The glacier is dislodged from the sill when ocean-induced melt quadruples, at which point the glacier retreats irreversibly for 27 km into a reverse bed. The model suggests that ice-ocean interactions are the triggering mechanism of glacier retreat, but the bed controls its magnitude.
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    Poleward eddy heat flux anomalies associated with recent Arctic sea-ice loss (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-12-21
    Beschreibung: Details of the characteristics of upward planetary wave propagation associated with Arctic sea-ice loss under present climate conditions are examined using reanalysis data and simulation results. Recent Arctic sea-ice loss results in increased stratospheric poleward eddy heat fluxes in the eastern and central Eurasia regions and enhanced upward propagation of planetary-scale waves in the stratosphere. A linear decomposition scheme reveals that this modulation of the planetary waves arises from coupling of the climatological planetary wave field with temperature anomalies for the eastern Eurasia region and with meridional wind anomalies for the central Eurasia region. Propagation of stationary Rossby wave packets results in a dynamic link between these temperature and meridional wind anomalies with sea-ice loss over the Barents–Kara Sea. The results provide strong evidence that recent Arctic sea-ice loss significantly modulates atmospheric circulation in winter to modify poleward eddy heat fluxes so as to drive stratosphere–troposphere coupling processes.
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    Episodic warming of near-bottom waters under the Arctic sea ice on the central Laptev Sea shelf (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publikationsdatum: 2017-09-13
    Beschreibung: A multi-year mooring record (2007-2014) and satellite imagery highlight the strong temperature variability and unique hydrographic nature of the Laptev Sea. This Arctic shelf is a key region for river discharge and sea ice formation and export, and includes submarine permafrost and methane deposits, which emphasizes the need to understand the thermal variability near the seafloor. Recent years were characterized by early ice retreat and a warming near-shore environment. However, warming was not observed on the deeper shelf until year-round under-ice measurements recorded unprecedented warm near-bottom waters of +0.6°C in winter 2012/2013, just after the Arctic sea ice extent featured a record minimum. In the Laptev Sea, early ice retreat in 2012 combined with Lena River heat and solar radiation produced anomalously warm summer surface waters, which were vertically mixed, trapped in the pycnocline, and subsequently transferred toward the bottom until the water column cooled when brine rejection eroded stratification.
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  • 50
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    New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43(2), pp. 600-610, ISSN: 0094-8276
    Details
    Publikationsdatum: 2017-10-17
    Beschreibung: Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground-based, airborne, and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million km2, which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated leveling of the different gravity data sets with respect to an Earth gravity model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high-resolution combined Earth gravity models to be derived and represent a major step forward toward solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica.
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    Predictability of the Arctic sea ice edge (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-02-29
    Beschreibung: Skillful sea ice forecasts from days to years ahead are becoming increasingly important for the operation and planning of human activities in the Arctic. Here we analyze the potential predictability of the Arctic sea ice edge in six climate models. We introduce the integrated ice-edge error (IIEE), a user-relevant verification metric defined as the area where the forecast and the “truth” disagree on the ice concentration being above or below 15%. The IIEE lends itself to decomposition into an absolute extent error, corresponding to the common sea ice extent error, and a misplacement error. We find that the often-neglected misplacement error makes up more than half of the climatological IIEE. In idealized forecast ensembles initialized on 1 July, the IIEE grows faster than the absolute extent error. This means that the Arctic sea ice edge is less predictable than sea ice extent, particularly in September, with implications for the potential skill of end-user relevant forecasts.
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    Carbon cycling fed by methane seepage at the shallow Cumberland Bay, South Georgia, sub-Antarctic (2016)
    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 17, ISSN: 1525-2027
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    Publikationsdatum: 2016-05-09
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    Pacific-Atlantic Circumpolar Deep Water coupling during the last 500 ka (2016)
    Wiley
    In:  EPIC3Paleoceanography, Wiley, 31(6), pp. 639-650, ISSN: 0883-8305
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: Investigating the interbasin deepwater exchange between the Pacific and Atlantic Oceans over glacial-interglacial climate cycles is important for understanding circum-Antarctic Southern Ocean circulation changes and their impact on the global Meridional Overturning Circulation. We use benthic foraminiferal δ13C records from the southern East Pacific Rise to characterize the δ13C composition of Circumpolar Deep Water in the South Pacific, prior to its transit through the Drake Passage into the South Atlantic. A comparison with published South Atlantic deepwater records from the northern Cape Basin suggests a continuous water mass exchange throughout the past 500 ka. Almost identical glacial-interglacial δ13C variations imply a common deepwater evolution in both basins suggesting persistent Circumpolar Deep Water exchange and homogenization. By contrast, deeper abyssal waters occupying the more southern Cape Basin and the southernmost South Atlantic have lower δ13C values during most, but not all, stadial periods. We conclude that these values represent the influence of a more southern water mass, perhaps Antarctic Bottom Water (AABW). During many interglacials and some glacial periods, the gradient between Circumpolar Deep Water and the deeper southern Cape Basin bottom water disappears suggesting either no presence of AABW or indistinguishable δ13C values of both water masses.
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    Microearthquake activity, lithospheric structure, and deformation modes at an amagmatic ultraslow spreading Southwest Indian Ridge segment (2016)
    American Geophysical Union
    In:  EPIC3Geochemistry, Geophysics, Geosystems, American Geophysical Union, 17(7), pp. 2905-2921
    Details
    Publikationsdatum: 2016-09-11
    Beschreibung: While nascent oceanic lithosphere at slow to fast spreading mid-ocean ridges (MOR) is relatively well studied, much less is known about the lithospheric structure and properties at ultraslow MORs. Here we present microearthquake data from a 1 year ocean bottom seismometer deployment at the amagmatic, oblique supersegment of the ultraslow spreading Southwest Indian Ridge. A refraction seismic experiment was performed to constrain upper lithosphere P-velocities and results were used to construct a 1D velocity model for earthquake location. Earthquake foci were located individually and subsequently relocated relative to each other to sharpen the image of seismically active structures. Frequent earthquake activity extends to 31 km beneath the seafloor, indicating an exceptionally thick brittle lithosphere and an undulating brittle-ductile transition that implies significant variations in the along-axis thermal structure of the lithosphere. We observe a strong relation between petrology, microseismicity distribution, and topography along the ridge axis: Peridotite-dominated areas associate with deepest hypocenters, vast volumes of lithosphere that deforms aseismically as a consequence of alteration, and the deepest axial rift valley. Areas of basalt exposure correspond to shallower hypocenters, shallower and more rugged axial seafloor. Focal mechanisms deviate from pure extension and are spatially variable. Earthquakes form an undulating band of background seismicity and do not delineate discrete detachment faults as common on slow spreading ridges. Instead, the seismicity band sharply terminates to the south, immediately beneath the rift boundary. Considering the deep alteration, large steep boundary faults might be present but are entirely aseismic.
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    Influence of plankton community structure on the sinking velocity of marine aggregates (2016)
    Wiley
    In:  EPIC3Global Biogeochemical Cycles, Wiley, 30(8), pp. 1145-1165, ISSN: 0886-6236
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: About 50 Gt of carbon is fixed photosynthetically by surface ocean phytoplankton communities every year. Part of this organic matter is reprocessed within the plankton community to form aggregates which eventually sink and export carbon into the deep ocean. The fraction of organic matter leaving the surface ocean is partly dependent on aggregate sinking velocity which accelerates with increasing aggregate size and density, where the latter is controlled by ballast load and aggregate porosity. In May 2011, we moored nine 25 m deep mesocosms in a Norwegian fjord to assess on a daily basis how plankton community structure affects material properties and sinking velocities of aggregates (Ø 80–400 µm) collected in the mesocosms' sediment traps. We noted that sinking velocity was not necessarily accelerated by opal ballast during diatom blooms, which could be due to relatively high porosity of these rather fresh aggregates. Furthermore, estimated aggregate porosity (Pestimated) decreased as the picoautotroph (0.2–2 µm) fraction of the phytoplankton biomass increased. Thus, picoautotroph-dominated communities may be indicative for food webs promoting a high degree of aggregate repackaging with potential for accelerated sinking. Blooms of the coccolithophore Emiliania huxleyi revealed that cell concentrations of ~1500 cells/mL accelerate sinking by about 35–40%, which we estimate (by one-dimensional modeling) to elevate organic matter transfer efficiency through the mesopelagic from 14 to 24%. Our results indicate that sinking velocities are influenced by the complex interplay between the availability of ballast minerals and aggregate packaging; both of which are controlled by plankton community structure.
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    Lake Baikal amphipods under climate change: thermal constraints and ecological consequences (2016)
    Wiley
    In:  EPIC3Ecosphere, Wiley, 7(3), pp. e01308, ISSN: 21508925
    Details
    Publikationsdatum: 2016-08-23
    Beschreibung: Lake Baikal, the world's most voluminous freshwater lake, has experienced unprecedented warming during the last decades. A uniquely diverse amphipod fauna inhabits the littoral zone and can serve as a model system to identify the role of thermal tolerance under climate change. This study aimed to identify sublethal thermal constraints in two of the most abundant endemic Baikal amphipods, Eulimnogammarus verrucosus and Eulimnogammarus cyaneus, and Gammarus lacustris, a ubiquitous gammarid of the Holarctic. As the latter is only found in some shallow isolated bays of the lake, we further addressed the question whether rising temperatures could promote the widespread invasion of this non-endemic species into the littoral zone. Animals were exposed to gradual temperature increases (4 week, 0.8 °C/d; 24 h, 1 °C/h) starting from the reported annual mean temperature of the Baikal littoral (6 °C). Within the framework of oxygen- and capacity-limited thermal tolerance (OCLTT), we used a nonlinear regression approach to determine the points at which the changing temperature-dependence of relevant physiological processes indicates the onset of limitation. Limitations in ventilation representing the first limits of thermal tolerance (pejus (= “getting worse”) temperatures (Tp)) were recorded at 10.6 (95% confidence interval; 9.5, 11.7), 19.1 (17.9, 20.2), and 21.1 (19.8, 22.4) °C in E. verrucosus, E. cyaneus, and G. lacustris, respectively. Field observations revealed that E. verrucosus retreated from the upper littoral to deeper and cooler waters once its Tp was surpassed, identifying Tp as the ecological thermal boundary. Constraints in oxygen consumption at higher than critical temperatures (Tc) led to an exponential increase in mortality in all species. Exposure to short-term warming resulted in higher threshold values, consistent with a time dependence of thermal tolerance. In conclusion, species-specific limits to oxygen supply capacity are likely key in the onset of constraining (beyond pejus) and then life-threatening (beyond critical) conditions. Ecological consequences of these limits are mediated through behavioral plasticity in E. verrucosus. However, similar upper thermal limits in E. cyaneus (endemic, Baikal) and G. lacustris (ubiquitous, Holarctic) indicate that the potential invader G. lacustris would not necessarily benefit from rising temperatures. Secondary effects of increasing temperatures remain to be investigated.
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    Intensification and poleward shift of subtropical western boundary currents in a warming climate (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 121, pp. 4928-4945, ISSN: 0148-0227
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: A significant increase in sea surface temperature (SST) is observed over the midlatitude western boundary currents (WBCs) during the past century. However, the mechanism for this phenomenon remains poorly understood due to limited observations. In the present paper, several coupled parameters (i.e., sea surface temperature (SST), ocean surface heat fluxes, ocean water velocity, ocean surface winds and sea level pressure (SLP)) are analyzed to identify the dynamic changes of the WBCs. Three types of independent data sets are used, including reanalysis products, satellite-blended observations. and climate model outputs from the fifth phase of the Climate Model Intercomparison Project (CMIP5). Based on these broad ranges of data, we find that the WBCs (except the Gulf Stream) are intensifying and shifting toward the poles as long-term effects of global warming. An intensification and poleward shift of near-surface ocean winds, attributed to positive annular mode-like trends, are proposed to be the forcing of such dynamic changes. In contrast to the other WBCs, the Gulf Stream is expected to be weaker under global warming, which is most likely related to a weakening of the Atlantic Meridional Overturning Circulation (AMOC). However, we also notice that the natural variations of WBCs might conceal the long-term effect of global warming in the available observational data sets, especially over the Northern Hemisphere. Therefore, long-term observations or proxy data are necessary to further evaluate the dynamics of the WBCs.
    Repository-Name: EPIC Alfred Wegener Institut
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    Paleocene Pacific Plate reorganization mirrored in formation of the Suvarov Trough, Manihiki Plateau (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Solid Earth, Wiley, 121(10), pp. 7013-7023, ISSN: 0148-0227
    Details
    Publikationsdatum: 2016-11-14
    Beschreibung: The Suvarov Trough is a graben structure that deviates from the Danger Islands Troughs within the Manihiki Plateau, a Large Igneous Province (LIP) located in the Central Pacific. New high resolution seismic reflection data provide evidence that the graben formed in two phases during the Paleocene (65-45 Ma). In a first phase extension occurred in south-westward direction, pulling apart the northern part of the Suvarov Trough and a parallel trending, unnamed trough. In a second phase a change of extensional force direction occurred from southwest to west-northwest, forming the southern part of the Suvarov Trough that extends onto the High Plateau. The formation of the Suvarov Trough is accompanied by a series of normal fault systems that apparently formed simultaneously. Comparing the seismic results to existing Pacific paleo strain reconstructions, the timing of increased strain and local deformation direction fits well to our findings. We thus suggest that the multiple strike directions of the Suvarov Trough represent an extensional structure that was caused by the major, stepwise Pacific Plate reorganization during the Paleocene.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 59
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    Impact of North American intense fires on aerosol optical properties measured over the European Arctic in July 2015 (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, ISSN: 0148-0227
    Details
    Publikationsdatum: 2020-03-05
    Beschreibung: In this paper impact of intensive biomass burning (BB) in North America in July 2015, on aerosol optical and microphysical properties measured in the European Arctic is discussed. This study was made within the framework of the Impact of Absorbing Aerosols on radiating forcing in the European Arctic (iAREA) project. During the BB event aerosol optical depth (AOD) at 500 nm exceeded 1.2 in Spitsbergen and 0.7 in Andenes (Norway). Ångström Exponent (AE) exceeded 1.4 while the absorbing Ångström Exponent (AAE) varied between 1 and 1.25. BB aerosols were observed in humid atmosphere with a total water vapor column between 2 and 2.5 cm. In such conditions aerosols are activated and may produce clouds at different altitudes. Vertical structure of aerosol plumes over Svalbard, obtained from ceilometers and lidars, shows variability of range corrected signal between surface and middle and upper troposphere. Aerosol backscattering coefficients show values up to 10 -5m-1sr-1at 532 nm. Aerosol surface observations indicate chemical composition typical for biomass burning particles and very high single scattering properties. Scattering and absorption coefficients at 530 nm were up to 130 and 15 Mm-1, respectively. Single scattering albedo at the surface varied from 0.9 to 0.94. The averaged values over the entire atmospheric column, ranged from 0.93 to 0.99. Preliminary statistics of model and sunphotometer data as well as previous studies indicate that this event, in the Arctic region, must be considered extreme (such AOD was not observed in Svalbard since 2005) with a significant impact on energy budget.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 60
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    Sea-ice retreat controls timing of summer plankton blooms in the Eastern Arctic Ocean (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43(24), ISSN: 0094-8276
    Details
    Publikationsdatum: 2017-01-09
    Beschreibung: Two full-year mooring records of sea ice, physical and bio-optical parameters illuminate tight temporal coupling between the retreating seasonal ice edge and the summer phytoplankton bloom on the Laptev Sea shelf. Our records showed no sign of pelagic under-ice blooms despite available nutrients and thinning sea ice in early summer; presumably because stratification had not yet developed. Chlorophyll blooms were detected immediately after the ice retreated in late May 2014 and late July 2015. Despite radically different timing, the blooms were similar in both magnitude and length, interpreted as community-level nutrient limitation. Acoustic backscatter records suggest the delayed 2015-bloom resulted in lower zooplankton abundance, perhaps due to a timing mismatch between ice algal and pelagic blooms and unfavorable thermal conditions. Our observations provide classical examples of ice-edge blooms and further emphasize the complexity of high-latitude shelves and the need to understand vertical mixing processes important for stratification and nutrient fluxes.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 61
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    Sea ice algae chlorophyll a concentrations derived from under-ice spectral radiation profiling platforms (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, ISSN: 0148-0227
    Details
    Publikationsdatum: 2017-01-11
    Beschreibung: Multiscale sea ice algae observations are fundamentally important for projecting changes to sea ice ecosystems, as the physical environment continues to change. In this study, we developed upon previously established methodologies for deriving sea ice-algal chlorophyll a concentrations (chl a) from spectral radiation measurements, and applied these to larger-scale spectral surveys. We conducted four different under-ice spectral measurements: irradiance, radiance, transmittance, and transflectance, and applied three statistical approaches: Empirical Orthogonal Functions (EOF), Normalized Difference Indices (NDI), and multi-NDI. We developed models based on ice core chl a and coincident spectral irradiance/transmittance (N = 49) and radiance/transflectance (N = 50) measurements conducted during two cruises to the central Arctic Ocean in 2011 and 2012. These reference models were ranked based on two criteria: mean robustness R2 and true prediction error estimates. For estimating the biomass of a large-scale data set, the EOF approach performed better than the NDI, due to its ability to account for the high variability of environmental properties experienced over large areas. Based on robustness and true prediction error, the three most reliable models, EOF-transmittance, EOF-transflectance, and NDI-transmittance, were applied to two remotely operated vehicle (ROV) and two Surface and Under-Ice Trawl (SUIT) spectral radiation surveys. In these larger-scale chl a estimates, EOF-transmittance showed the best fit to ice core chl a. Application of our most reliable model, EOF-transmittance, to an 85 m horizontal ROV transect revealed large differences compared to published biomass estimates from the same site with important implications for projections of Arctic-wide ice-algal biomass and primary production.
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  • 62
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    Fram Strait and Greenland Sea transports, water masses, and water mass transformations 1999-2010 (and beyond) (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 121(4), pp. 2314-2346, ISSN: 0148-0227
    Details
    Publikationsdatum: 2017-06-15
    Repository-Name: EPIC Alfred Wegener Institut
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  • 63
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    New Constraints on the Evolution of the Inner Northern Apennines by K-Ar Dating of Late Miocene-Early Pliocene Compression on the Island of Elba, Italy (2019)
    Wiley
    Details
    Publikationsdatum: 2020-06-03
    Beschreibung: - 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
    Beschreibung: 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.
    Beschreibung: Published
    Beschreibung: 3229–3243
    Beschreibung: 1T. Struttura della Terra
    Beschreibung: JCR Journal
    Schlagwort(e): K-Ar dating fault gouge ; Northern Apennines ; Elba Island ; Neogene geodynamics
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    New evidence of CO2 soil degassing anomalies on Piton de la Fournaise volcano and the link with volcano tectonic structures (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: Piton de la Fournaise (PdF) is recognised as one of the world’s most active volcanoes in terms of eruptive frequency and the substantial quantity of lava produced. Yet, with the sole exception of rather modest intracrateric fumarole activity, this seems to be in contrast with an apparent absence of any type of natural fluid emission during periods of quiescence. Measurement campaigns were undertaken during a long-lasting quiescent period (2012-2014) and just after a short lived summit eruption (June 2014) in order to identify potential degassing areas in relation to the main structural features of the volcano (ex. rift zones) with the aim of developing a broader understanding of the geometry of the plumbing and degassing system. In order to assess the possible existence of anomalous soil CO2 flux, 513 measurements were taken along transects roughly orthogonal to the known tectonic lineaments crossing PdF edifice. In addition, 53 samples of gas for C isotope analysis were taken at measurement points that showed a relatively high CO2 concentration in the soil. CO2 flux values range from 10 to 1300 g m-2 d-1 while 13C are between -26.6 to -8‰. The results of our investigation clearly indicate that there is a strong spatial correlation between the anomalous high values of diffusive soil emissions and the main rift zones cutting the PdF massif and, moreover, that generally high soil CO2 fluxes show a d13C signature clearly related to a magmatic origin.
    Beschreibung: INSU (CNRS) and La Réunion Préfecture (Projet pour la quantification de l’aléa volcanique à La Réunion)
    Beschreibung: Published
    Beschreibung: 4388–4404
    Beschreibung: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): CO2 soil degassing anomalies at Piton de la Fournaise ; d13C magmatic signature ; Close link between anomalous CO2 degassing and the main seismotectonic structures ; 04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 65
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    Asynchronous changes of CO2, H2 and He concentrations in soil gases: a theoretical model and experimental results (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: This paper focuses on the chemical composition changes in soil gases through both a theoretical model and laboratory experiments. The model describes the one-dimensional mass transfer process, which is triggered by changes in the flux parameters of the system, and the time-dependent evolution of the composition of the soil gases as a function of i) the pristine gas mixture, ii) the diffusivity of the chemicals, and iii) the thickness of the transited medium. Carbon dioxide (CO2), hydrogen (H2), and helium (He) were used in a laboratory-scale flux simulator to investigate the evolution of the gas composition profile in an artificial soil of constant thickness. The agreement between the theoretical calculations and the experimental results supports the validity of the model. Our results indicate a good reproducibility of the transient changes in the concentrations of CO2, He, and H2 in CO2-rich gas mixtures that contain He and H2 as trace gases. Finally, the theoretical results were used to analyze the H2 and CO2 continuous monitoring data collected at Etna volcano in 2010
    Beschreibung: Published
    Beschreibung: 1565–1583
    Beschreibung: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Beschreibung: 5V. Sorveglianza vulcanica ed emergenze
    Beschreibung: 1IT. Reti di monitoraggio e Osservazioni
    Beschreibung: JCR Journal
    Beschreibung: open
    Schlagwort(e): Soil gases ; Volcanic gas composition ; Hydrogen ; Carbon dioxide ; CO2 ; Helium ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Evidence of underground electric current generation during the 2009 L’Aquila earthquake: Real or instrumental? (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: We investigate magnetic effects in correspondence of the Mw6.1 L’Aquila earthquake. Magnetic and seismic records are analyzed. Rapid and distinct changes and an offset can be seen in magnetic field components after the main shock. We show that these effects result from electromagnetic induction due to the movement of the sensors through the Earth’s magnetic field and from a permanent displacement of the sensors from their original position caused by the passing seismic waves. A transient signal in total field data from an overhauser magnetometer apparently occurs in correspondence with the earthquake. Our analysis shows that the transient was not observed by other sensors that were operating in close proximity to the overhauser. Thus, the transient signal in the total magnetic field data, and the offset in the magnetic field components, cannot be associated with a hypothetical underground electric current generated by the earthquake, as suggested by Nenovski (2015).
    Beschreibung: Published
    Beschreibung: 6153–6161
    Beschreibung: 1A. Geomagnetismo e Paleomagnetismo
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Earthquake ; seismoelectric effect ; 04. Solid Earth::04.05. Geomagnetism::04.05.99. General or miscellaneous ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies ; 04. Solid Earth::04.05. Geomagnetism::04.05.08. Instruments and techniques
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Twenty-five years of continuous borehole tilt and vertical displacement data at Mount Etna: Insights on long-term volcanic dynamics (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: We report a 25 year-long data set (1990–2014) of combined continuous tilt and GPS vertical displacement series recorded at Etna volcano. To our knowledge, this is the first time that such a data set on an active volcano has been presented. We show the coherence of the two series, which help draw new insights on how the volcano, characterized by frequent flank eruptions, works in the long-term (tens of years). This data set provides evidence that after the 1992–1993 flank eruption (the biggest in the last three centuries) and the following major recharging phase (1994–2001), all the ensuing eruptions fall within a single long-term reequilibrium phase (2001–2014).
    Beschreibung: Published
    Beschreibung: 10222–10229
    Beschreibung: 1V. Storia e struttura dei sistemi vulcanici
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): tilt ; gps ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Very shallow dyke intrusion and potential slope failure imaged by ground deformation: The 28 December 2014 eruption on Mount Etna (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: On 28 December 2014, eruptive activity resumed at Mount Etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano. Unlike all previous summit activity, this eruption produced clear deformation at the summit of the volcano. GPS displacements and Sentinel-1A ascending interferogramswere calculated in order to image the ground deformation pattern accompanying the eruption. The displacements observed by GPS depict a local ground deformation pattern, affecting only the upperpart of the volcano.Despite snowcover onthe summit, differential interferometry synthetic aperture radar (DInSAR) data allowed obtainingmore detail onthe grounddeformation pattern on the upper eastern side of the volcano. Three-dimensional GPS displacements inversion located a very shallow NE-SW intrusion just beneath the New Southeast Crater. However, this model cannot justify all the deformation observed by DInSAR thus revealing a gravitational failure of the lava flow field
    Beschreibung: Published
    Beschreibung: 2727–2733
    Beschreibung: 3V. Dinamiche e scenari eruttivi
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Sentinel-1A interferogram details the ground deformation field ; GPS data are analyzed for modeling the dyke intrusion ; Data comparison highlights an incipient slope failure ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 69
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    High-resolution magnetics reveal the deep structure of a volcanic-arc-related basalt-hosted hydrothermal site (Palinuro, Tyrrhenian Sea) (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: High-resolution magnetic surveys have been acquired over the partially sedimented Palinuro massive sulfide deposits in the Aeolian volcanic arc, Tyrrhenian Sea. Surveys flown close to the seafloor using an autonomous underwater vehicle (AUV) show that the volcanic-arc-related basalt-hosted hydrothermal site is associated with zones of lower magnetization. This observation reflects the alteration of basalt affected by hydrothermal circulation and/or the progressive accumulation of a nonmagnetic deposit made of hydrothermal and volcaniclastic material and/or a thermal demagnetization of titanomagnetite due to the upwelling of hot fluids. To discriminate among these inferences, estimate the shape of the nonmagnetic deposit and the characteristics of the underlying altered area—the stockwork—we use high-resolution vector magnetic data acquired by the AUV Abyss (GEOMAR) above a crater-shaped depression hosting a weakly active hydrothermal site. Our study unveils a relatively small nonmagnetic deposit accumulated at the bottom of the depression and locked between the surrounding volcanic cones. Thermal demagnetization is unlikely but the stockwork extends beyond the limits of the nonmagnetic deposit, forming lobe-shaped zones believed to be a consequence of older volcanic episodes having contributed in generating the cones.
    Beschreibung: Published
    Beschreibung: 1950–1961
    Beschreibung: 4V. Vulcani e ambiente
    Beschreibung: 3A. Ambiente Marino
    Beschreibung: 7A. Geofisica di esplorazione
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Hydrothermal alteration ; magnetica anomalies ; Palinuro Seamounts ; Tyrrhenian Sea ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 70
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    Appreciation of Peer Reviewers for 2017 (2019)
    Wiley
    Details
    Publikationsdatum: 2019-03-06
    Beschreibung: 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.
    Beschreibung: Published
    Beschreibung: 566
    Beschreibung: 1VV. Altro
    Beschreibung: JCR Journal
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 71
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    Pore Pressure Pulse Drove the 2012 Emilia (Italy) Series of Earthquakes (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2019-03-29
    Beschreibung: 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
    Beschreibung: Published
    Beschreibung: 682-690
    Beschreibung: 4T. Sismicità dell'Italia
    Beschreibung: JCR Journal
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 72
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    Relation Between Near-Fault Ground Motion Impulsive Signals and Source Parameters (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2019-03-29
    Beschreibung: 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
    Beschreibung: Published
    Beschreibung: 7707-7721
    Beschreibung: 6T. Studi di pericolosità sismica e da maremoto
    Beschreibung: JCR Journal
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Modeling earthquake effects on groundwater levels: evidences from the 2012 Emilia earthquake (Italy) (2019)
    Wiley
    Details
    Publikationsdatum: 2019-09-12
    Beschreibung: 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.
    Beschreibung: Published
    Beschreibung: 452–463
    Beschreibung: 4T. Sismicità dell'Italia
    Beschreibung: JCR Journal
    Schlagwort(e): 2012 Emilia earthquake ; groundwaters ; isotropic stress ; permeability ; porosity ; water wells ; Solid Earth
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Thank You to Our 2018 Peer Reviewers (2019)
    Wiley
    Details
    Publikationsdatum: 2019-10-28
    Beschreibung: 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.
    Beschreibung: Published
    Beschreibung: 4
    Beschreibung: 5TM. Informazione ed editoria
    Beschreibung: JCR Journal
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    Hydrothermal fluid venting in the offshore sector of Campi Flegrei caldera: A geochemical, geophysical and volcanological study (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2020-06-03
    Beschreibung: The ongoing unrest at the Campi Flegrei caldera (CFc) in southern Italy is prompting exploration of its poorly studied offshore sector. We report on a multidisciplinary investigation of the Secca delle Fumose (SdF), a submarine relief known since antiquity as the largest degassing structure of the offshore sector of CFc. We combined high-resolution morphobathymetric and seismostratigraphic data with onshore geological information to propose that the present-day SdF morphology and structure developed during the initial stages of the last CFc eruption at Monte Nuovo in AD 1538. We suggest that the SdF relief stands on the eastern uplifted border of a N-S-trending graben-like structure formed during the shallow emplacement of the Monte Nuovo feeding dike. We also infer that the high-angle bordering faults that generated the SdF relief now preferentially allow the ascent of hot brines (with an equilibrium temperature of 1798C), thereby sustaining hydrothermal degassing on the seafloor. Systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable CO2, pH, and temperature anomaly in the overlying seawater column. Data for the seawater vertical profile can be used to estimate the CO2 and energy (heat) outputs from the SdF area at 50 tons/d ( 0.53 kg/s) and 80 MW, respectively. In view of the cause-effect relationship with the Monte Nuovo eruption, and the substantial gas and energy outputs, we consider that the SdF hydrothermal system needs to be included in monitoring programs of the ongoing CFc unrest.
    Beschreibung: Published
    Beschreibung: 4153–4178
    Beschreibung: 1V. Storia e struttura dei sistemi vulcanici
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Hydrothermal fluid ; Campi Flegrei caldera ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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  • 76
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    Gas hydrate distribution and hydrocarbon maturation north of the Knipovich Ridge, western Svalbard margin (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Solid Earth, Wiley, ISSN: 0148-0227
    Details
    Publikationsdatum: 2016-02-02
    Beschreibung: A bottom-simulating reflector (BSR) occurs west of Svalbard in water depths exceeding 600 m, indicating that gas hydrate occurrence in marine sediments is more widespread in this region than anywhere else on the eastern North Atlantic margin. Regional BSR mapping shows the presence of hydrate and free gas in several areas, with the largest area located north of the Knipovich Ridge, a slow-spreading ridge segment of the Mid Atlantic Ridge system. Here, heat flow is high (up to 330 mW m-2), increasing towards the ridge axis. The coinciding maxima in across-margin BSR width and heat flow suggest that the Knipovich Ridge influenced methane generation in this area. This is supported by recent finds of thermogenic methane at cold seeps north of the ridge termination. To evaluate the source rock potential on the western Svalbard margin, we applied 1D petroleum system modeling at three sites. The modeling shows that temperature and burial conditions near the ridge were sufficient to produce hydrocarbons. The bulk petroleum mass produced since the Eocene is at least 5 kt and could be as high as ~0.2 Mt. Most likely, source rocks are Miocene organic-rich sediments and a potential Eocene source rock that may exist in the area if early rifting created sufficiently deep depocenters. Thermogenic methane production could thus explain the more widespread presence of gas hydrates north of the Knipovich Ridge. The presence of microbial methane on the upper continental slope and shelf indicates that the origin of methane on the Svalbard margin varies spatially.
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  • 77
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    Bias reduction in decadal predictions of West African monsoon rainfall using regional climate models (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, ISSN: 0148-0227
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: The West African monsoon rainfall is essential for regional food production, and decadal predictions are necessary for policy makers and farmers. However, predictions with global climate models reveal precipitation biases. This study addresses the hypotheses that global prediction biases can be reduced by dynamical downscaling with a multimodel ensemble of three regional climate models (RCMs), a RCM coupled to a global ocean model and a RCM applying more realistic soil initialization and boundary conditions, i.e., aerosols, sea surface temperatures (SSTs), vegetation, and land cover. Numerous RCM predictions have been performed with REMO, COSMO-CLM (CCLM), and Weather Research and Forecasting (WRF) in various versions and for different decades. Global predictions reveal typical positive and negative biases over the Guinea Coast and the Sahel, respectively, related to a southward shifted Intertropical Convergence Zone (ITCZ) and a positive tropical Atlantic SST bias. These rainfall biases are reduced by some regional predictions in the Sahel but aggravated by all RCMs over the Guinea Coast, resulting from the inherited SST bias, increased westerlies and evaporation over the tropical Atlantic and shifted African easterly waves. The coupled regional predictions simulate high-resolution atmosphere-ocean interactions strongly improving the SST bias, the ITCZ shift and the Guinea Coast and Central Sahel precipitation biases. Some added values in rainfall bias are found for more realistic SST and land cover boundary conditions over the Guinea Coast and improved vegetation in the Central Sahel. Thus, the ability of RCMs and improved boundary conditions to reduce rainfall biases for climate impact research depends on the considered West African region.
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  • 78
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    Late Miocene uplift of the North-East Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic (2016)
    Wiley
    In:  EPIC3Tectonics, Wiley, 35(2), pp. 257-282, ISSN: 0278-7407
    Details
    Publikationsdatum: 2016-03-25
    Beschreibung: Tectonic models predict that following breakup, rift margins undergo only decaying thermal subsidence during their postrift evolution. However, postbreakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone-East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of synrift deposition in the deep-sea basins and onset of (i) thermomechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermomechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf progradation on the NE Greenland margin. Given an estimated middle to late Miocene (~15–10Ma) age of the IMU, we speculate that the event is synchronous with uplift of the east and west Greenland margins. The correlation between margin uplift and plate motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intraplate stresses related to global tectonics.
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  • 79
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    Modelling climate change impacts on marine fish populations: process-based integration of ocean warming, acidification and other environmental drivers (2016)
    Wiley
    In:  EPIC3Fish and Fisheries, Wiley, pp. n/a-n/a, ISSN: 14672960
    Details
    Publikationsdatum: 2017-03-10
    Beschreibung: Global climate change affects marine fish through drivers such as ocean warming, acidification and oxygen depletion, causing changes in marine ecosystems and socioeconomic impacts. While experimental and observational results can inform about anticipated effects of different drivers, linking between these results and ecosystem-level changes requires quantitative integration of physiological and ecological processes into models to advance research and inform management. We give an overview of important physiological and ecological processes affected by environmental drivers. We then provide a review of available modelling approaches for marine fish, analysing their capacities for process-based integration of environmental drivers. Building on this, we propose approaches to advance important research questions. Examples of integration of environmental drivers exist for each model class. Recent extensions of modelling frameworks increase the potential for including detailed mechanisms and improving model projections. Experimental results on energy allocation, behaviour and physiological limitations will advance the understanding of organism-level trade-offs and thresholds in response to multiple drivers. More explicit representation of life cycles and biological traits can improve description of population dynamics and adaptation, and data on food web topology and feeding interactions help to detail the conditions for possible regime shifts. Identification of relevant processes will also benefit the coupling of different models to investigate spatial–temporal changes in stock productivity and integrated responses of social–ecological systems. Thus, a more process-informed foundation for models will promote the integration of experimental and observational results and increase the potential for model-based extrapolations into a future under changing environmental conditions.
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    Reduced admixture of North Atlantic Deep Water to the deep central South Pacific during the last two glacial periods (2016)
    Wiley
    In:  EPIC3Paleoceanography, Wiley, 31, pp. 1-18, ISSN: 0883-8305
    Details
    Publikationsdatum: 2016-11-15
    Beschreibung: The South Pacific is a sensitive location for the variability of the global oceanic thermohaline circulation given that deep waters from the Atlantic Ocean, the Southern Ocean, and the Pacific Basin are exchanged. Here we reconstruct the deep water circulation of the central South Pacific for the last two glacial cycles (from 240,000 years ago to the Holocene) based on radiogenic neodymium (Nd) and lead (Pb) isotope records complemented by benthic stable carbon data obtained from two sediment cores located on the flanks of the East Pacific Rise. The records show small but consistent glacial/interglacial changes in all three isotopic systems with interglacial average values of 5.8 and 18.757 for εNd and 206Pb/204Pb, respectively, whereas glacial averages are 5.3 and 18.744. Comparison of this variability of Circumpolar Deep Water (CDW) to previously published records along the pathway of the global thermohaline circulation is consistent with reduced admixture of North Atlantic Deep Water to CDW during cold stages. The absolute values and amplitudes of the benthic δ13C variations are essentially indistinguishable from other records of the Southern Hemisphere and confirm that the low central South Pacific sedimentation rates did not result in a significant reduction of the amplitude of any of the measured proxies. In addition, the combined detrital Nd and strontium (87Sr/86Sr) isotope signatures imply that Australian and New Zealand dust has remained the principal contributor of lithogenic material to the central South Pacific.
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    A glimpse beneath Antarctic sea ice: platelet-layer volume from multi-frequency electromagnetic induction sounding (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-01-15
    Beschreibung: In Antarctica, ice crystals emerge from ice shelf cavities and accumulate in unconsolidated layers beneath nearby sea ice. Such sub-ice platelet layers form a unique habitat and serve as an indicator for the state of an ice shelf. However, the lack of a suitable methodology impedes an efficient quantification of this phenomenon on scales beyond point measurements. In this study, we inverted multifrequency electromagnetic (EM) induction soundings, obtained on fast ice with an underlying platelet layer along profiles of 〉100 km length in the eastern Weddell Sea. EM-derived platelet layer thickness and conductivity are consistent with other field observations. Our results suggest that platelet layer volume is higher than previously thought in this region and that platelet layer ice volume fraction is proportional to its thickness. We conclude that multifrequency EM is a suitable tool to determine platelet layer volume, with the potential to obtain crucial knowledge of associated processes in otherwise inaccessible ice shelf cavities.
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  • 82
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    Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-12-09
    Beschreibung: The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea levels in excess of 7 meters in the last warm era, of which probably not much more than 2 meters are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3D thermomechanical ice sheet model forced by an atmosphere ocean general circulation model (AOGCM). Our results show that high LIG sea levels, cannot be reproduced with the atmosphere-ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2-3∘C, accounting for a sea level rise of 3-4 meters during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming.
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  • 83
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    Mg/Ca thermometry in planktic foraminifera: Improving paleotemperature estimations for G. bulloides and N. pachyderma left (2016)
    Wiley
    In:  EPIC3Geochemistry, Geophysics, Geosystems, Wiley, 17(4), pp. 1249-1264, ISSN: 15252027
    Details
    Publikationsdatum: 2016-06-23
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  • 84
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    Simulating soil organic carbon in yedoma deposits during the Last Glacial Maximum in a land surface model (2016)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 43(10), pp. 5133-5142, ISSN: 0094-8276
    Details
    Publikationsdatum: 2016-09-19
    Beschreibung: Substantial quantities of organic carbon (OC) are stored in the thick, ice-rich, and organic-rich sediments called yedoma deposits, distributed in eastern Siberia and Alaska today. Quantifying yedoma carbon stocks during the glacial period is important for understanding how much carbon could have been decomposed during the last deglaciation. Yet processes that yield the formation of thick frozen OC in yedoma deposits are missing in global carbon cycle models. Here we incorporate sedimentation parameterizations into the Organizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE-MICT) land surface model, which leads to reasonable results in OC vertical distribution and regional budgets, compared with site-specific observations and inventories for today's nondegraded yedoma region. Simulated total soil OC stock for the northern permafrost region during the Last Glacial Maximum (LGM) is 1536–1592 Pg C, of which 390–446 Pg C is within today's yedoma region. This result is an underestimation since we did not account for the potentially much larger yedoma area during the LGM than the present day.
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  • 85
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    Cyclic magnetite dissolution in Pleistocene sediments of the abyssal northwest Pacific Ocean: Evidence for glacial oxygen depletion and carbon trapping (2016)
    Wiley
    In:  EPIC3Paleoceanography, Wiley, 31, pp. 600-624, ISSN: 0883-8305
    Details
    Publikationsdatum: 2018-08-10
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  • 86
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    Stability Conditions of Peat Plateaus and Palsas in Northern Norway (2019)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Earth Surface, Wiley, ISSN: 0148-0227
    Details
    Publikationsdatum: 2019-04-03
    Beschreibung: 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.
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  • 87
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    GlobSed: Updated total sediment thickness in the World’s oceans (2019)
    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 20, pp. 1756-1772, ISSN: 1525-2027
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    Publikationsdatum: 2019-05-21
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    Weak Stratospheric Polar Vortex Events Modulated by the Arctic Sea‐Ice Loss (2019)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 124(2), pp. 858-869, ISSN: 0148-0227
    Details
    Publikationsdatum: 2019-02-25
    Beschreibung: 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.
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    Calving Induced Speedup of Petermann Glacier (2019)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Earth Surface, Wiley, 124, pp. 216-228, ISSN: 0148-0227
    Details
    Publikationsdatum: 2019-08-14
    Beschreibung: 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.
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    PaCTS 1.0: A Crowdsourced Reporting Standard for Paleoclimate Data (2019)
    Wiley
    In:  EPIC3Paleoceanography and Paleoclimatology, Wiley, 34(10), pp. 1570-1596, ISSN: 2572-4517
    Details
    Publikationsdatum: 2019-11-25
    Beschreibung: 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.
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    Carbon export fluxes and export efficiency in the central Arctic during the record sea-ice minimum in 2012. A joint 234Th/238U and 210Po/210Pb study (2016)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 121(7), pp. 5030-5049, ISSN: 0148-0227
    Details
    Publikationsdatum: 2016-09-14
    Beschreibung: The Arctic sea-ice extent amounted to its record minimum to date in September 2012. Sea-ice decline increases the absorption of solar energy in the Arctic Ocean, affecting primary production and plankton community. How this will modulate the sinking of POC from the ocean surface remains a key question. In this study we use the 234Th/238U and 210Po/210Pb radionuclide pairs to estimate the magnitude of the POC export fluxes in the upper ocean of the central Arctic in summer 2012, covering time scales from weeks to months, respectively. The 234Th/238U proxy reveals that POC fluxes at the base of the euphotic zone were very low (2 ± 2 mmol C m-2 d-1) in August and September. Relationships obtained between the 234Th export fluxes and the phytoplankton community suggest that prasinophytes would have contributed significantly to downward fluxes in late summer, likely via incorporation into sea-ice algal aggregates and zooplankton-derived material. In turn, the magnitude of the depletion of 210Po in the upper water column over the entire study area indicates that particle export fluxes were more relevant before July/August than later in the season. 210Po fluxes and 210Po-derived POC fluxes correlated positively with sea-ice concentration, showing that particle sinking was more important under heavy sea-ice conditions than under partially ice covered regions. Although the POC fluxes were low, a large fraction of primary production (〉30%) was exported at the base of the euphotic zone in most of the study area during summer 2012, indicating a high export efficiency of the biological pump in the central Arctic.
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    Modeling Photoprotection at Global Scale: The Relative Role of Nonphotosynthetic Pigments, Physiological State, and Species Composition (2019)
    Wiley
    In:  EPIC3Global Biogeochemical Cycles, Wiley, 33, ISSN: 0886-6236
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    Publikationsdatum: 2019-09-10
    Beschreibung: 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.
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    Modeling Permafrost Sensitivity in Arctic Forest (2019)
    American Geophysical Union
    In:  EPIC3AGU Fall meeting 2019, San Francisco, CA, 2019-12-09-2019-12-13USA, American Geophysical Union
    Details
    Publikationsdatum: 2021-08-16
    Beschreibung: 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.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 94
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    Noble Gases in Deepwater Oils of the U.S. Gulf of Mexico (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2019-01-07
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2019-04-10
    Repository-Name: Woods Hole Open Access Server
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  • 95
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    Overview of the Arctic Sea state and boundary layer physics program (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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
    Schlagwort(e): Arctic ; waves ; autumn ; sea ice ; Beaufort ; flux
    Repository-Name: Woods Hole Open Access Server
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  • 96
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    Stable Isotope clues to the formation and evolution of refrozen melt ponds on Arctic Sea ice. (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2019-05-15
    Schlagwort(e): Arctic ; sea ice ; isotope tracer ; melt pond ; oxygen isotope ; deuterium excess
    Repository-Name: Woods Hole Open Access Server
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  • 97
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    Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Schlagwort(e): Danube River ; organic carbon ; biomarker ; radiocarbon ; ADCP
    Repository-Name: Woods Hole Open Access Server
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  • 98
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    Dispersal of hydrothermal vent larvae at East Pacific Rise 9-10 degrees N segment (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2019-05-06
    Schlagwort(e): larva ; dispersal ; hydrothermal vent ; EPR ; connectivity ; supply
    Repository-Name: Woods Hole Open Access Server
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  • 99
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    Melt pond conditions on declining arctic sea ice over 1979-2016: Model development, validation, and results (2019)
    American Geophysical Union
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2019-04-18
    Schlagwort(e): Arctic Ocean ; sea ice ; melt ponds ; numerical modeling ; climate variability
    Repository-Name: Woods Hole Open Access Server
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  • 100
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    Density-driven transport in the umbrella region of volcanic clouds: Implications for tephra dispersion models (2016)
    American Geophysical Union
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: Large explosive volcanic eruptions can generate ash clouds from rising plumes that spread in the atmosphere around a Neutral Buoyancy Level (NBL). These ash clouds spread as inertial intrusions and are advected by atmospheric winds. For low mass flow rates, tephra transport is mainly dictated by wind advection, because ash cloud spreading due to gravity current effects is negligible (passive transport). For large mass flow rates, gravity-driven transport at the NBL can be the dominant transport mechanism. Conditions under which the passive transport assumption is valid have not yet been critically studied. We analyze the conditions when gravity-driven transport is dominant in terms of the cloud Richardson number. Moreover, we couple an analytical model that describes cloud spreading as a gravity current with an advection-diffusion model. This coupled model is used to simulate the evolution of the volcanic cloud during the climatic phase of the 1991 Pinatubo eruption. Citation: Costa, A., A. Folch, and G. Macedonio (2013), Density-driven transport in the umbrella region of volcanic clouds: Implications for tephra dispersion models.
    Beschreibung: This work has benefited from funding provided by the Italian Presidenza del Consiglio dei Ministri - Dipartimento della Protezione Civile (DPC), agreement INGV-DPC 2012-2013. This paper does not necessarily represent DPC official opinion and policies. A.F. acknowledges funding by the Spanish project ATMOST (CGL2009-10244).
    Beschreibung: Published
    Beschreibung: 4823–4827
    Beschreibung: 3V. Dinamiche e scenari eruttivi
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Large explosive eruptions ; Volcanic ash transport ; volcanic modeling ; tephra transport ; 05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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