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  • 1
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    Atlantic Water advection versus sea-ice advances in the eastern Fram Strait during the last 9 ka - multiproxy evidence for a two-phase Holocene (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Paleoceanography, 28 . pp. 283-295.
    Details
    Publication Date: 2019-09-23
    Description: A sediment core from the West Spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last ~9 ka in the eastern Fram Strait. Our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern Fram Strait occurred stepwise, in response to the postglacial sea-level rise and the related onset of modern sea-ice production on the shallow Siberian shelves. The late Early and Mid Holocene interval (9 to 5 ka) was generally characterized by relatively unstable conditions. High abundance of the subpolar planktic foraminifer species Turborotalita quinqueloba implies strong intensity of Atlantic Water (AW) inflow with high productivity and/or high AW temperatures, resulting in a strong heat flux to the Arctic. A series of short-lived cooling events (8.2, 6.9. and 6.1 ka) occurred superimposed on the warm late Early and Mid Holocene conditions. Our proxy data imply that simultaneous to the complete postglacial flooding of Arctic shallow shelves and the initiation of modern sea-ice production, strong advance of polar waters initiated modern oceanographic conditions in the eastern Fram Strait at ~5.2 ka. The Late Holocene was marked by the dominance of the polar planktic foraminifer species Neogloboquadrina pachyderma, a significant expansion of sea ice/icebergs, and strong stratification of the water column. Although planktic foraminiferal assemblages as well as sea surface and subsurface temperatures suggest a return of slightly strengthened advection of subsurface Atlantic Water after 3 ka, a relatively stable cold-water layer prevailed at the sea surface and the study site was probably located within the seasonally fluctuating marginal ice zone during the Neoglacial period.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1002/palo.20028
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  • 2
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    Correlation of river water and local sea-ice melting on the Laptev Sea shelf (Siberian Arctic) (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 118 (1). pp. 550-561.
    Details
    Publication Date: 2019-09-23
    Description: Hydrographic and stable isotope (δ18O) data from 4 summer surveys in the Laptev Sea are used to derive fractions of sea-ice meltwater and river water. Sea-ice meltwater fractions are found to be correlated to river water fractions. While initial heat of river discharge is too small to melt the observed 0-158 km3 of sea-ice meltwater, arctic rivers contain suspended particles (SPM) and colored dissolved organic material (CDOM) that preferentially absorb solar radiation. Accordingly heat content in surface waters is correlated to river water fractions. But in years when river water is largely absent within the surface layer absolute heat content values increase to considerably higher values with extended exposure time to solar radiation and sensible heat. Nevertheless no net sea-ice melting is observed on the shelf in years when river water is largely absent within the surface layer. The total freshwater volume of the central-eastern Laptev Sea (72-76°N, 122-140°E) varies between ~1000-1500 km3 (34.92 reference salinity). It is dominated by varying river water volumes (~1300-1800 km3) reduced by an about constant freshwater deficit (~350-400 km3) related to sea-ice formation. Net sea-ice melt (~109-158 km3) is only present in years with high river water budgets. Intermediate to bottom layer (〉25 salinities) contain ~60% and 30% of the river budget in years with low and high river budgets, respectively. The average mean residence time of shelf waters was ~2-3 years during 2007-2009.
    Type: Article , PeerReviewed
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    DOI: 10.1002/jgrc.20076
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  • 3
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    Interannual variations in river water content and distribution over the Laptev Sea between 2007 and 2011: The Arctic Dipole connection (2014)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 41 (20). pp. 7237-7244.
    Details
    Publication Date: 2017-04-10
    Description: Five years of oxygen isotope and hydrological surveys reveal interannual variations in the inventory and distribution of river water over the Laptev Sea. In 2007, 2009, and 2010 relatively low amounts of river water (≤1500 km3) were found and were mostly located in the southeastern Laptev Sea. In 2008 and 2011, high amounts of river water (~1600 km3 and ~2000 km3) were found, especially in the central and northern part of the shelf, suggesting a northward export of this water. This temporal pattern is coherent with the summer Arctic Dipole index that was higher in 2008 and 2011. Our results suggest that the Arctic Dipole might influence the export of river water from the Laptev Sea. Moreover, the river water inventory in the Laptev Sea seems related to the freshwater content of the Arctic Ocean with a 2 years lag.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2014GL061814
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  • 4
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    Properties of the Atlantic derived halocline waters over the Laptev Sea continental margin: Evidence from 2002 to 2009 (2011)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 116 (C10). C10024.
    Details
    Publication Date: 2019-09-23
    Description: A series of transects carried out in 2002–2009 across the Laptev Sea continental margin show consistent cross‐slope differences of the lower halocline water (LHW). Over the slope the LHW core is on average warmer and saltier by 0.39°C and 0.26 practical salinity unit, respectively, relative to the off‐slope LHW. Underlying Atlantic water (AW) thermohaline properties exhibit an opposite pattern; it is colder and fresher over the slope and warmer and saltier off the slope. Although on‐slope and off‐slope LHWs have different formation histories, our results suggest that an important part of the heat and salt lost from the AW is gained by the overlying LHW over the continental slope area. This implies the role of enhanced vertical mixing over the sloping topography, which contributes to the difference between the on‐ and off‐slope LHW properties. The distribution of chemical tracers (dissolved oxygen and nutrients) provides further evidence supporting this interpretation and additionally suggests that the LHW may also be influenced by water from the outer shelf.
    Type: Article , PeerReviewed
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    DOI: 10.1029/2011JC007269
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  • 5
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    The impact of Siberian coastal polynyas on shelf-derived Arctic Ocean halocline waters (2012)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 117 (C4). C00G12.
    Details
    Publication Date: 2019-09-23
    Description: Hydrographic and stable oxygen isotope (H218O/H216O) sampling was carried out within the West New Siberian (WNS) coastal polynyas in the southern Laptev Sea in late winters 2008 and 2009. The impact of sea-ice formation on the water column was quantified by a salinity/{lower case delta}18O mass balance. Several stations had vertically homogeneous physical properties in April/May 2008 and featured polynya-formed local bottom water with elevated signals of brine released during sea-ice formation and elevated fractions of river water. The polynya-formed bottom water was fresher than surrounding bottom waters. At other stations salinity/{lower case delta}18O correlation showed well defined mixing lines for bottom and surface layers. In March/April 2009 surface waters were strongly influenced by Lena River water and local polynya activity with elevated brine signals reached to intermediate depth, but did not penetrate the bottom layer in the highly stratified water column. Inventory values of sea-ice formation were comparable in both years, but freshwater distributions from the preceding summers were different. Therefore, the observed difference in the impact of polynya activity on the water column is not primarily controlled by the amount of sea-ice formed during winter but by preconditioning from the preceding summer. Only in years when the river plume is mostly absent in the polynya region stratification is weak and allows winter sea-ice formation to reach the bottom layer. Thus summer stratification controls the influence of local polynya water on the shelf's bottom hydrography and, as bottom water is exported, impacts on the source water of shelf-derived halocline waters.
    Type: Article , PeerReviewed
    Format: text
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    DOI: 10.1029/2011JC007282
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  • 6
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    Shelf-basin exchange times of Arctic surface waters estimated from 228Th/228Ra disequilibrium (2012)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 117 (C3). C03024.
    Details
    Publication Date: 2019-09-23
    Description: The transpolar drift is strongly enriched in 228Ra accumulated on the wide Arctic shelves with subsequent rapid offshore transport. We present new data of Polarstern expeditions to the central Arctic and to the Kara and Laptev seas. Because 226Ra activities in Pacific waters are 30% higher than in Atlantic waters, we correct 226Ra for the Pacific admixture when normalizing 228Ra with 226Ra. The use of 228Ra decay as age marker critically depends on the constancy in space and time of the source activity, a condition that has not yet adequately been tested. While 228Ra decays during transit over the central basin, ingrowth of 228Th could provide an alternative age marker. The high 228Th/228Ra activity ratio (AR = 0.8–1.0) in the central basins is incompatible with a mixing model based on horizontal eddy diffusion. An advective model predicts that 228Th grows to an equilibrium AR, the value of which depends on the scavenging regime. The low AR over the Lomonosov Ridge (AR = 0.5) can be due to either rapid transport (minimum age without scavenging 1.1 year) or enhanced scavenging. Suspended particulate matter load (derived from beam transmission and particulate 234Th) and total 234Th depletion data show that scavenging, although extremely low in the central Arctic, is enhanced over the Lomonosov Ridge, making an age of 3 years more likely. The combined data of 228Ra decay and 228Th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern Eurasian Basin with a river water residence time of at least 3 years.
    Type: Article , PeerReviewed
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    DOI: 10.1029/2011JC007478
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  • 7
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    Changes in distribution of brine waters on the Laptev Sea shelf in 2007 (2010)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 115 . C11008.
    Details
    Publication Date: 2020-06-26
    Description: Combined salinity and δ18O data from summer 2007 reveal a significant change in brine production in the Laptev Sea relative to summer 1994. The distribution of river water and brine enriched waters on the Laptev Sea shelf is derived based on mass balance calculations using salinity and δ18O data. While in 1994 maximal influence of brines is seen within bottom waters [Bauch et al., 2009a], in 2007 the influence of brines is highest within the surface layer and only a moderate influence of brines is observed in the bottom layer. In contrast to 2007, salinity and δ18O data from summer 1994 clearly identify a locally formed brine enriched bottom water mass as mixing endmember between surface layer and inner shelf waters on one side and with higher salinity water from the outer Laptev Sea on the other side. In 2007 the brine enriched waters are predominantly part of the surface regime and the mixing endmember between surface layer and outer shelf waters is replaced by a relatively salty bottom water mass. This relatively salty bottom water probably originates from the western Laptev Sea. The inverted distribution of brines in the water column in 2007 relative to 1994 suggests a less effective winter sea-ice formation in winter 2006/2007 combined with advection of more saline waters from the western Laptev Sea or the outer shelf precedent to 1 the climatically extreme summer 2007. The observed changes result in an altered export of waters from the Laptev Sea to the Arctic Ocean halocline.
    Type: Article , PeerReviewed
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    DOI: 10.1029/2010JC006249
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  • 8
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    The impact of climatic and atmospheric teleconnections on the brine inventory over the Laptev Sea shelf between 2007 and 2011 (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (1). pp. 56-64.
    Details
    Publication Date: 2019-02-01
    Description: Export of brine-enriched water from Siberian shelves is thought to be a key parameter in maintaining the Arctic Halocline, which isolates the fresh and cold surface water from the warm Atlantic water and thus prevent dramatic change in the Arctic sea-ice thermodynamic. In this study, we used five years of oxygen isotope and hydrological summer surveys to better understand the factors controlling the brine inventory and distribution over the Laptev Sea shelf. The inventory was maximal in 2011 and 2007 and minimal in 2010. The brine inventory interannual variations are coherent with the winter Arctic Oscillation index that was maximal in 2011 and 2007 and minimal in 2010, which is known to modulate Arctic winds and sea-ice export pattern. While we should remain cautious since our record is limited to 5-years, our results suggest that the combined effect of the Arctic Oscillation and of the Arctic Dipole is the main factor controlling the annual variations in the inventory of brine-enriched waters from the Laptev Sea shelf between 2007 and 2011, especially during extreme negative Arctic Oscillation and Arctic Dipole conditions as in 2010.
    Type: Article , PeerReviewed
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    DOI: 10.1002/2015GC006063
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  • 9
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    Episodic warming of near-bottom waters under the Arctic sea ice on the central Laptev Sea shelf (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 43 (1). pp. 264-272.
    Details
    Publication Date: 2019-09-23
    Description: A multiyear 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.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015GL066565
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  • 10
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    Sea-ice production over the Laptev Sea shelf inferred from historical summer-to-winter hydrographic observations of 1960s-1990s (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 (13). L13605.
    Details
    Publication Date: 2017-11-07
    Description: The winter net sea-ice production (NSIP) over the Laptev Sea shelf is inferred from continuous summer-to-winter historical salinity records of 1960s–1990s. While the NSIP strongly depends on the assumed salinity of newly formed ice, the NSIP quasi-decadal variability can be linked to the wind-driven circulation anomalies in the Laptev Sea region. The increased wind-driven advection of ice away from the Laptev Sea coast when the Arctic Oscillation (AO) is positive implies enhanced coastal polynya sea-ice production and brine release in the shelf water. When the AO is negative, the NSIP and seasonal salinity amplitude tends to weaken. These results are in reasonable agreement with sea-ice observations and modeling.
    Type: Article , PeerReviewed
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    DOI: 10.1029/2009GL038775
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