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  • 2020-2024  (64)
  • 1985-1989  (1)
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  • 1
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    On the Variability of Stratification in the Freshwater-Influenced Laptev Sea Region (2020)
    Frontiers
    Details
    Publication Date: 2023-02-08
    Description: In this paper, we investigate the seasonal and spatial variability of stratification on the Siberian shelves with a case study from the Laptev Sea based on shipboard hydrographic measurements, year-round oceanographic mooring records from 2013 to 2014 and chemical tracer-based water mass analyses. In summer 2013, weak onshore-directed winds caused spreading of riverine waters throughout much of the eastern and central shelf. In contrast, strong southerly winds in summer 2014 diverted much of the freshwater to the northeast, which resulted in 50% less river water and significantly weaker stratification on the central shelf compared with the previous year. Our year-long records additionally emphasize the regional differences in water column structure and stratification, where the northwest location was well-mixed for 6 months and the central and northeast locations remained stratified into spring due to the lower initial surface salinities of the river-influenced water. A 26 year record of ocean reanalysis highlights the region’s interannual variability of stratification and its dependence on winds and sea ice. Prior the mid-2000s, river runoff to the perennially ice-covered central Laptev Sea shelf experienced little surface forcing and river water was maintained on the shelf. The transition toward less summer sea ice after the mid-2000s increased the ROFI’s (region of freshwater influence) exposure to summer winds. This greatly enhanced the variability in mixed layer depth, resulting in several years with well-mixed water columns as opposed to the often year-round shallow mixed layers before. The extent of the Lena River plume is critical for the region since it modulates nutrient fluxes and primary production, and further controls intermediate heat storage induced by lateral density gradients, which has implications for autumnal freeze-up and the eastern Arctic sea ice volume. MAIN POINTS 1. CTD surveys and moorings highlight the regional and temporal variations in water column stratification on the Laptev Sea shelf. 2. Summer winds increasingly control the extent of the region of freshwater influence under decreasing sea ice. 3. Further reductions in sea ice increases surface warming, heat storage, and the interannual variability in mixed layer depth.
    Type: Article , PeerReviewed
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  • 2
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    Satellite-based sea ice thickness changes in the Laptev Sea from 2002 to 2017: comparison to mooring observations (2020)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2023-02-08
    Description: The gridded sea ice thickness (SIT) climate data record (CDR) produced by the European Space Agency (ESA) Sea Ice Climate Change Initiative Phase 2 (CCI-2) is the longest available, Arctic-wide SIT record covering the period from 2002 to 2017. SIT data are based on radar altimetry measurements of sea ice freeboard from the Environmental Satellite (ENVISAT) and CryoSat-2 (CS2). The CCI-2 SIT has previously been validated with in situ observations from drilling, airborne remote sensing, electromagnetic (EM) measurements and upward-looking sonars (ULSs) from multiple ice-covered regions of the Arctic. Here we present the Laptev Sea CCI-2 SIT record from 2002 to 2017 and use newly acquired ULS and upward-looking acoustic Doppler current profiler (ADCP) sea ice draft (VAL) data for validation of the gridded CCI-2 and additional satellite SIT products. The ULS and ADCP time series provide the first long-term satellite SIT validation data set from this important source region of sea ice in the Transpolar Drift. The comparison of VAL sea ice draft data with gridded monthly mean and orbit trajectory CCI-2 data, as well as merged CryoSat-2–SMOS (CS2SMOS) sea ice draft, shows that the agreement between the satellite and VAL draft data strongly depends on the thickness of the sampled ice. Rather than providing mean sea ice draft, the considered satellite products provide modal sea ice draft in the Laptev Sea. Ice drafts thinner than 0.7 m are overestimated, while drafts thicker than approximately 1.3 m are increasingly underestimated by all satellite products investigated for this study. The tendency of the satellite SIT products to better agree with modal sea ice draft and underestimate thicker ice needs to be considered for all past and future investigations into SIT changes in this important region. The performance of the CCI-2 SIT CDR is considered stable over time; however, observed trends in gridded CCI-2 SIT are strongly influenced by the uncertainties of ENVISAT and CS2 and the comparably short investigation period.
    Type: Article , PeerReviewed
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  • 3
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    The MOSAiC ice floe: sediment-laden survivor from the Siberian shelf (2020)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2023-02-08
    Description: In September 2019, the research icebreaker Polarstern started the largest multidisciplinary Arctic expedition to date, the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) drift experiment. Being moored to an ice floe for a whole year, thus including the winter season, the declared goal of the expedition is to better understand and quantify relevant processes within the atmosphere–ice–ocean system that impact the sea ice mass and energy budget, ultimately leading to much improved climate models. Satellite observations, atmospheric reanalysis data, and readings from a nearby meteorological station indicate that the interplay of high ice export in late winter and exceptionally high air temperatures resulted in the longest ice-free summer period since reliable instrumental records began. We show, using a Lagrangian tracking tool and a thermodynamic sea ice model, that the MOSAiC floe carrying the Central Observatory (CO) formed in a polynya event north of the New Siberian Islands at the beginning of December 2018. The results further indicate that sea ice in the vicinity of the CO (〈40 km distance) was younger and 36 % thinner than the surrounding ice with potential consequences for ice dynamics and momentum and heat transfer between ocean and atmosphere. Sea ice surveys carried out on various reference floes in autumn 2019 verify this gradient in ice thickness, and sediments discovered in ice cores (so-called dirty sea ice) around the CO confirm contact with shallow waters in an early phase of growth, consistent with the tracking analysis. Since less and less ice from the Siberian shelves survives its first summer (Krumpen et al., 2019), the MOSAiC experiment provides the unique opportunity to study the role of sea ice as a transport medium for gases, macronutrients, iron, organic matter, sediments and pollutants from shelf areas to the central Arctic Ocean and beyond. Compared to data for the past 26 years, the sea ice encountered at the end of September 2019 can already be classified as exceptionally thin, and further predicted changes towards a seasonally ice-free ocean will likely cut off the long-range transport of ice-rafted materials by the Transpolar Drift in the future. A reduced long-range transport of sea ice would have strong implications for the redistribution of biogeochemical matter in the central Arctic Ocean, with consequences for the balance of climate-relevant trace gases, primary production and biodiversity in the Arctic Ocean.
    Type: Article , PeerReviewed
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  • 4
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    The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) (2021)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: Permafrost degradation in the catchment of major Siberian rivers, combined with higher precipitation in a warming climate, could increase the flux of terrestrially derived dissolved organic matter (tDOM) into the Arctic Ocean (AO). Each year, ∼ 7.9 Tg of dissolved organic carbon (DOC) is discharged into the AO via the three largest rivers that flow into the Laptev Sea (LS) and East Siberian Sea (ESS). A significant proportion of this tDOM-rich river water undergoes at least one freeze–melt cycle in the land-fast ice that forms along the coast of the Laptev and East Siberian seas in winter. To better understand how growth and melting of land-fast ice affect dissolved organic matter (DOM) dynamics in the LS and ESS, we determined DOC concentrations and the optical properties of coloured dissolved organic matter (CDOM) in sea ice, river water and seawater. The data set, covering different seasons over a 9-year period (2010–2019), was complemented by oceanographic measurements (T, S) and determination of the oxygen isotope composition of the seawater. Although removal of tDOM cannot be ruled out, our study suggests that conservative mixing of high-tDOM river water and sea-ice meltwater with low-tDOM seawater is the major factor controlling the surface distribution of tDOM in the LS and ESS. A case study based on data from winter 2012 and spring 2014 reveals that the mixing of about 273 km3 of low-tDOM land-fast-ice meltwater (containing ∼ 0.3 Tg DOC) with more than 200 km3 of high-tDOM Lena River water discharged during the spring freshet (∼ 2.8 Tg DOC yr−1) plays a dominant role in this respect. The mixing of the two low-salinity surface water masses is possible because the meltwater and the river water of the spring freshet flow into the southeastern LS at the same time every year (May–July). In addition, budget calculations indicate that in the course of the growth of land-fast ice in the southeastern LS, ∼ 1.2 Tg DOC yr−1 (± 0.54 Tg) can be expelled from the growing ice in winter, together with brines. These DOC-rich brines can then be transported across the shelves into the Arctic halocline and the Transpolar Drift Current flowing from the Siberian Shelf towards Greenland. The study of dissolved organic matter dynamics in the AO is important not only to decipher the Arctic carbon cycle but also because CDOM regulates physical processes such as radiative forcing in the upper ocean, which has important effects on sea surface temperature, water column stratification, biological productivity and UV penetration.
    Type: Article , PeerReviewed
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  • 5
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    On the Along‐Slope Heat Loss of the Boundary Current in the Eastern Arctic Ocean (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: This study presents recent observations to quantify oceanic heat fluxes along the continental slope of the Eurasian part of the Arctic Ocean, in order to understand the dominant processes leading to the observed along-track heat loss of the Arctic Boundary Current (ABC). We investigate the fate of warm Atlantic Water (AW) along the Arctic Ocean continental margin of the Siberian Seas based on 11 cross-slope conductivity, temperature, depth transects and direct heat flux estimates from microstructure profiles obtained in summer 2018. The ABC loses on average urn:x-wiley:21699275:media:jgrc24332:jgrc24332-math-0006(108) J m−2 per 100 km during its propagation along the Siberian shelves, corresponding to an average heat flux of 47 W m−2 out of the AW layer. The measured vertical heat flux on the upper AW interface of on average 10 W m−2 in the deep basin, and 3.7 W m−2 above the continental slope is larger than previously reported values. Still, these heat fluxes explain less than 20% of the observed heat loss within the boundary current. Heat fluxes are significantly increased in the turbulent near-bottom layer, where AW intersects the continental slope, and at the lee side of a topographic irregularity. This indicates that mixing with ambient colder water along the continental margins is an important contribution to AW heat loss. Furthermore, the cold halocline layer receives approximately the same amount of heat due to upward mixing from the AW, compared to heat input from the summer-warmed surface layer above. This underlines the importance of both surface warming and increased vertical mixing in a future ice-free Arctic Ocean in summer.
    Type: Article , PeerReviewed
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  • 6
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    Turbulent Mixing and the Formation of an Intermediate Nepheloid Layer Above the Siberian Continental Shelf Break (2021)
    AGU | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Intermediate nepheloid layers (INLs) form important pathways for the cross-slope transport and vertical export of particulate matter, including carbon. While intermediate maxima in particle settling fluxes have been reported in the Eurasian Basin of the Arctic Ocean, direct observations of turbid INLs above the continental slope are still lacking. In this study, we provide the first direct evidence of an INL, coinciding with enhanced mid-water turbulent dissipation rates, over the Laptev Sea continental slope in summer 2018. Current velocity data show a period of enhanced downslope flow with depressed isopcynals, suggesting that the enhanced turbulent dissipation is probably the consequence of the presence of an unsteady lee wave. Similar events occur mostly during ice free periods, suggesting an increasing frequency of episodic cross-slope particle transport in the future. The discovery of the INL and the episodic generation mechanism provide new insights into particle transport dynamics in this rapidly changing environment.
    Type: Article , PeerReviewed
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  • 7
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    Structure and Seasonal Variability of the Arctic Boundary Current North of Severnaya Zemlya (2023)
    Details
    Publication Date: 2023-11-13
    Description: We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using seven oceanographic moorings, deployed across the continental slope north of Severnaya Zemlya in 2015–2018. Transports and individual water masses were quantified based on temperature and salinity recorders and current profilers. Our results were compared with observations from the northeast Svalbard and the central Laptev Sea continental slopes to evaluate the hydrographic transformation along the ABC pathway. The highest velocities (〉0.30 m s〈sup〉−1〈/sup〉) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 m s〈sup〉−1〈/sup〉 in the deep basin. The ABC showed seasonal variability with velocities two times higher in winter than in summer. Compared to upstream conditions in Svalbard, water mass distribution changed significantly within 20 km of the shelf edge due to mixing with‐ and intrusion of shelf waters. The ABC transported 4.15 ± 0.3 Sv in the depth range 50–1,000 m, where 0.88 ± 0.1, 1.5 ± 0.2, 0.61 ± 0.1 and 1.0 ± 0.15 Sv corresponded to Atlantic Water (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW). 62–70% of transport was constrained to within 30–40 km of the shelf edge, and beyond 84 km, transport increases were estimated to be 0.54 Sv. Seasonality of TAW derived from local shelf‐processes and advection of seasonal‐variable Fram Strait waters, while BSBW transport variability was dominated by temperature changes with maximum transport coinciding with minimum temperatures. Further Barents Sea warming will likely reduce TAW and BSBW transport leading to warmer conditions along the ABC pathway.
    Description: Plain Language Summary: We assessed the structure and seasonal variability of the flow and water masses of the Arctic Boundary Current (ABC) in the region north of Severnaya Zemlya. This current is important in the Arctic Ocean as it transports relatively warm and saline waters along the Eurasian Arctic continental slope. We quantified the flow, transport and hydrographic variability of the ABC. Compared to observations from upstream, our results indicate that the water masses away from the shelf break maintained the hydrographic characteristics from upstream. In contrast, the water masses near the shelf break were significantly cooled and freshened due to intrusion of‐ and mixing with shelf waters. The water masses near the shelf break showed a seasonal signal in volume transport and temperature which derives from local shelf processes, advection of seasonal‐variable waters along the ABC pathway and the seasonal cooling of the Barents Sea. If the warming trend in the Barents Sea continues, warmer waters are expected to be advected eastward along the Eurasian continental slope by the ABC.
    Description: Key Points: We quantify the Arctic Boundary Current (ABC) transport north of Severnaya Zemlya with a 2015–2018 mooring array. Hydrographic changes along the ABC pathway are most prominent at the continental slope due to the interaction with shelf water. Seasonality of water masses from the shelf sea was observed in transport, temperature and off‐shelf excursions within the ABC.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: EC Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: Russian Science Foundation http://dx.doi.org/10.13039/501100006769
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.pangaea.de/10.1594/PANGAEA.951363
    Description: https://doi.pangaea.de/10.1594/PANGAEA.951394
    Description: https://doi.pangaea.de/10.1594/PANGAEA.951394
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954244
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954249
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954299
    Description: https://doi.pangaea.de/10.1594/PANGAEA.954352
    Keywords: ddc:551.48 ; Arctic Boundary Current ; seasonal transport variability ; water mass transport ; along‐slope current
    Language: English
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    CITATION GEO-LEO
  • 8
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    Temperature and salinity measurements on the Laptev Sea shelf in 2013-2014 at mooring site "1893-T1" (2020)
    PANGAEA
    In:  Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven
    Details
    Publication Date: 2023-03-16
    Description: A total of four moorings ("1893", "Taymyr", "Kotelny", "Vilkitsky") was deployed in September 2013 during the Transdrift 21 - expedition and recovered in September 2014 during Transdrift 22 aboard the Viktor Buinitsky. The expeditions were carried out in the framework of the German-Russian "Laptev Sea Systems" partnership, and within the BMBF-funded "Transdrift"-project. The moorings were equipped with RDI-Workhorse ADCPs for current measurements and Seabird SBE37 for temperature and salinity measurements. Sampling intervals were 1 hour for ADCP, and 30 minutes for SBE37. Currents were corrected for misalignment based on angles extracted from: https://geomag.nrcan.gc.ca/calc/mdcal-en.php Not all SBE37 models included a pressure sensor. If pressure was recorded, the data files provide pressure and the converted water depth. For models without a pressure sensor, the data file lists only a constant value indicating the targeted instrument depth. Temperature and salinity data were despiked, and outliers exceeding three times the standard deviation were removed and interpolated.
    Keywords: 1893-T1-13; Arctic Ocean; AWI_PhyOce; CTD, SEA-BIRD SBE 37; DATE/TIME; Density, sigma-theta (0); DEPTH, water; Gear identification number; Laptev Sea; Laptev Sea System; LSS; Mooring (long time); MOORY; oceanographic moorings; Physical Oceanography @ AWI; Pressure, water; Salinity; System Laptev-Sea: Transdrift; Temperature, water; TRANSDRIFT; Transdrift-XXI; VB13; VB13_16-5a; Viktor Buynitskiy
    Type: Dataset
    Format: text/tab-separated-values, 441575 data points
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    DATA PANGAEA
  • 9
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    Daily mean sea ice draft from moored upward-looking Acoustic Doppler Current Profiler (ADCP) at site Anabar-0708 in the Laptev Sea (2020)
    PANGAEA
    Details
    Publication Date: 2023-03-16
    Keywords: ADCP; Anabar-07; AWI_SeaIce; DATE/TIME; IP07-2_1-1M, Anabar-0708; Ivan Petrov; Laptev Sea; Laptev Sea System; Latitude of event; Longitude of event; LSS; Mooring (long time); MOORY; sea ice draft; Sea ice draft; Sea Ice Physics @ AWI; System Laptev-Sea: Transdrift; TD07; TRANSDRIFT; Transdrift-XII; Upward looking Acoustic Doppler Current Profiler
    Type: Dataset
    Format: text/tab-separated-values, 359 data points
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    DATA PANGAEA
  • 10
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    Daily mean sea ice draft from moored upward-looking Acoustic Doppler Current Profiler (ADCP) at site Anabar-0910 in the Laptev Sea (2020)
    PANGAEA
    Details
    Publication Date: 2023-03-16
    Keywords: ADCP; Anabar-09; Anabar-0910; AWI_SeaIce; DATE/TIME; Laptev Sea; Laptev Sea System; Latitude of event; Longitude of event; LSS; Mooring (long time); MOORY; sea ice draft; Sea ice draft; Sea Ice Physics @ AWI; System Laptev-Sea: Transdrift; TRANSDRIFT; Transdrift-XVI; Upward looking Acoustic Doppler Current Profiler; Yakov Smirnitskiy
    Type: Dataset
    Format: text/tab-separated-values, 236 data points
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    DATA PANGAEA
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