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  • 1
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    Nitrogen dynamic in Eurasian coastal Arctic ecosystem: Insight from nitrogen isotope (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 31 (5). pp. 836-849.
    Details
    Publication Date: 2020-02-06
    Description: Primary productivity is limited by the availability of nitrogen (N) in most of the coastal Arctic, as a large portion of N is released by the spring freshet and completely consumed during the following summer. Thus, understanding the fate of riverine nitrogen is critical to identify the link between dissolved nitrogen dynamic and coastal primary productivity to foresee upcoming changes in the Arctic seas, such as increase riverine discharge and permafrost thaw. Here, we provide a field-based study of nitrogen dynamic over the Laptev Sea shelf based on isotope geochemistry. We demonstrate that while most of the nitrate found under the surface fresh water layer is of remineralized origin, some of the nitrate originates from atmospheric input and was probably transported at depth by the mixing of brine-enriched denser water during sea-ice formation. Moreover, our results suggest that riverine dissolved organic nitrogen (DON) represents up to 6 times the total riverine release of nitrate and that about 62 to 76% of the DON is removed within the shelf waters. This is a crucial information regarding the near-future impact of climate change on primary productivity in the Eurasian coastal Arctic.
    Type: Article , PeerReviewed
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  • 2
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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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  • 3
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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
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  • 4
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    Water Mass Classification on a Highly Variable Arctic Shelf Region: Origin of Laptev Sea Water Masses and Implications for the Nutrient Budget (2018)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2022-03-09
    Description: Large gradients and inter annual variations on the Laptev Sea shelf prevent the use of uniform property ranges for a classification of major water masses. The central Laptev Sea is dominated by predominantly marine waters, locally formed polynya waters and riverine summer surface waters. Marine waters enter the central Laptev Sea from the northwestern Laptev Sea shelf and originate from the Kara Sea or the Arctic Ocean halocline. Local polynya waters are formed in the Laptev Sea coastal polynyas. Riverine summer surface waters are formed from Lena river discharge and local melt. We use a principal component analysis (PCA) in order to assess the distribution and importance of water masses within the Laptev Sea. This mathematical method is applied to hydro-chemical summer datasets from the Laptev Sea from five years and allows to define water types based on objective and statistically significant criteria. We argue that the PCA derived water types are consistent with the Laptev Sea hydrography and indeed represent the major water masses on the central Laptev Sea shelf. Budgets estimated for the thus defined major Laptev Sea water masses indicate that freshwater inflow from the western Laptev Sea is about half or in the same order of magnitude as freshwater stored in locally formed polynya waters. Imported water dominates the nutrient budget in the central Laptev Sea; and only in years with enhanced local polynya activity is the nutrient budget of the locally formed water in the same order as imported nutrients.
    Type: Article , PeerReviewed
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  • 5
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    Radium Isotopes across the Arctic Ocean show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs (2018)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-05-04
    Description: The first full transarctic section of 228Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the Transpolar Drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased 228Ra input is attributed to stronger wave action on shelves resulting from a longer ice‐free season. A concomitant decrease in the 228Th/228Ra ratio likely results from more rapid transit of surface waters depleted in 228Th by scavenging over the shelf. The 228Ra activities observed in intermediate waters (〈 1500m) in the Amundsen Basin are explained by ventilation with shelf water on a time scale of about 15‐18 years, in good agreement with estimates based on SF6 and 129I/236U. The 228Th excess below the mixed layer up to 1500m depth can complement 234Th and 210Po as tracers of export production, after correction for the inherent excess resulting from the similarity of 228Ra and 228Th decay times. We show with a Th/Ra profile model that the 228Th/228Ra ratio below 1500m is inappropriate for this purpose because it is a delicate balance between horizontal supply of 228Ra and vertical flux of particulate 228Th. The accumulation of 226Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of 230Th in the bottom sediment. We estimate a ventilation time of 480 years for the deep Makarov‐Canada Basin, in good agreement with previous estimates using other tracers.
    Type: Article , PeerReviewed
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  • 6
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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
    Publication Date: 2017-09-13
    Description: 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.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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