scholarly journals Semidiurnal Tides on the Laptev Sea Shelf with Implications for Shear and Vertical Mixing

2014 ◽  
Vol 44 (1) ◽  
pp. 202-219 ◽  
Author(s):  
Markus A. Janout ◽  
Yueng-Djern Lenn
Keyword(s):  
Sea Ice ◽  
Vertical Mixing ◽  
Outer Shelf ◽  
The Arctic ◽  
Laptev Sea ◽  
Surface Mixed Layer ◽  
Diapycnal Mixing ◽  
Inner Shelf ◽  
Lena River ◽  
The Laptev Sea

Abstract The Arctic continental shelf seas hold a globally significant source of freshwater that impacts Arctic Ocean stratification, circulation, and climate. This freshwater can be injected below the surface mixed layer by intense turbulent kinetic energy dissipation events, as resolved by Laptev Sea microstructure observations. The tides provide a major source of energy that can be dissipated and hence drive diapycnal mixing in the Laptev Sea. Multiyear ADCP mooring records from locations across the shelf reveal that semidiurnal tides are dominated by the M2 and S2 constituents, with the largest amplitudes on the outer shelf. Throughout most of the shelf, tides are clockwise polarized and sheared by stratification, as characteristic near the M2 critical latitude. Interannual variations of the tidal and shear structures on the inner shelf are mainly determined by the stratification-setting Lena River freshwater plume. In all locations, M2 tides are enhanced under sea ice, and therefore changes in the seasonal ice cover may lead to changes in tides and water column structure. The main conclusions of this study are that (i) tides play a comparatively greater role year-round on the outer shelf relative to the inner shelf; (ii) a sea ice reduction will overall decrease the predictability of the currents, especially on the inner shelf; and (iii) the freshwater distribution directly impacts diapycnal mixing by setting the vertical tidal structure. These combined effects imply that future sea ice loss will increase the variability and vertical mixing of freshwater, particularly on the inner shelf, where the Lena River first enters the Laptev Sea.

scholarly journals Intermittent Intense Turbulent Mixing under Ice in the Laptev Sea Continental Shelf

2011 ◽  
Vol 41 (3) ◽  
pp. 531-547 ◽  
Author(s):  
Yueng-Djern Lenn ◽  
Tom P. Rippeth ◽  
Chris P. Old ◽  
Sheldon Bacon ◽  
Igor Polyakov ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Sea Ice ◽  
Vertical Mixing ◽  
Heat Fluxes ◽  
The Arctic ◽  
Laptev Sea ◽  
Mixing Processes ◽  
Temperature Conductivity ◽  
Bottom Boundary ◽  
The Laptev Sea

Abstract Vertical mixing in the bottom boundary layer and pycnocline of the Laptev Sea is evaluated from a rapidly sampled 12-h time series of microstructure temperature, conductivity, and shear observations collected under 100% sea ice during October 2008. The bottom boundary turbulent kinetic energy dissipation was observed to be enhanced (ε ∼ 10−4 W m−3) beyond background levels (ε ∼ 10−6 W m−3), extending up to 10 m above the seabed when simulated tidal currents were directed on slope. Upward heat fluxes into the halocline-class waters along the Laptev Sea seabed peaked at ∼4–8 W m−2, averaging out to ∼2 W m−2 over the 12-h sampling period. In the Laptev Sea pycnocline, an isolated 2-h episode of intense dissipation (ε ∼ 10−3 W m−3) and vertical diffusivities was observed that was not due to a localized wind event. Observations from an acoustic Doppler current meter moored in the central Laptev Sea near the M2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under-ice stress vector. Upward cross-pycnocline heat fluxes from the Arctic halocline peaked at ∼54 W m−2, resulting in a 12-h average of ∼12 W m−2. These results highlight the intermittent nature of Arctic shelf sea mixing processes and how these processes can impact the transformation of Arctic Ocean water masses. The observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near-inertial kinetic energy to drive vertical mixing on the Arctic shelves.

scholarly journals On the biogeochemical signature of the Lena River from its headwaters to the Arctic Ocean

2011 ◽  
Vol 8 (2) ◽  
pp. 2093-2143 ◽  
Author(s):  
I. P. Semiletov ◽  
I. I. Pipko ◽  
N. E. Shakhova ◽  
O. V. Dudarev ◽  
S. P. Pugach ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Arctic Ocean ◽  
River Discharge ◽  
Total Carbon ◽  
The Arctic ◽  
Time Shift ◽  
Laptev Sea ◽  
Lena River ◽  
The Arctic Ocean ◽  
The Laptev Sea

Abstract. The Lena River integrates biogeochemical signals from its vast drainage basin and its signal reaches far out over the Arctic Ocean. Transformation of riverine organic carbon into mineral carbon, and mineral carbon into the organic form in the Lena River watershed, can be considered a quasi-equilibrated processes. Increasing the Lena discharge causes opposite effects on total organic (TOC) and inorganic (TCO2) carbon: TOC concentration increases, while TCO2 concentration decreases. Significant inter-annual variability in mean values of TCO2, TOC, and their sum (TC) has been found. This variability is determined by changes in land hydrology which cause differences in the Lena River discharge, because a negative correlation may be found between TC in September and mean discharge in August (a time shift of about one month is required for water to travel from Yakutsk to the Laptev Sea). Total carbon entering the sea with the Lena discharge is estimated to be almost 10 Tg C y−1. The annual Lena River discharge of particulate organic carbon (POC) may be equal to 0.38 Tg (moderate to high estimate). If we instead accept Lisytsin's (1994) statement concerning the precipitation of 85–95% of total particulate matter (PM) (and POC) on the marginal "filter", then only about 0.03–0.04 Tg of POC reaches the Laptev Sea from the Lena River. The Lena's POC export would then be two orders of magnitude less than the annual input of eroded terrestrial carbon onto the shelf of the Laptev and East Siberian seas, which is about 4 Tg. The Lena River is characterized by relatively high concentrations of primary greenhouse gases: CO2 and dissolved CH4. During all seasons the river is supersaturated in CO2 compared to the atmosphere: up to 1.5–2 fold in summer, and 4–5 fold in winter. This results in a narrow zone of significant CO2 supersaturation in the adjacent coastal sea. Spots of dissolved CH4 in the Lena delta channels may reach 100 nM, but the CH4 concentration decreases to 5–20 nM towards the sea, which suggests only a minor role of riverborne export of CH4 for the East Siberian Arctic Shelf (ESAS) CH4 budget in coastal waters. Instead, the seabed appears to be the source that provides most of the CH4 to the Arctic Ocean.

scholarly journals Satellite-based sea ice thickness changes in the Laptev Sea from 2002 to 2017: comparison to mooring observations

2020 ◽  
Vol 14 (7) ◽  
pp. 2189-2203
Author(s):  
H. Jakob Belter ◽  
Thomas Krumpen ◽  
Stefan Hendricks ◽  
Jens Hoelemann ◽  
Markus A. Janout ◽  
...  
Keyword(s):  
Sea Ice ◽  
Source Region ◽  
European Space Agency ◽  
The Arctic ◽  
Ice Thickness ◽  
Laptev Sea ◽  
Validation Data ◽  
Data Set ◽  
Sea Ice Thickness ◽  
The Laptev Sea

Abstract. 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.

scholarly journals Structure and dynamics of mesoscale eddies over the Laptev Sea continental slope in the Arctic Ocean

2018 ◽  
Author(s):  
Andrey Pnyushkov ◽  
Igor V. Polyakov ◽  
Laurie Padman ◽  
An T. Nguyen
Keyword(s):  
Arctic Ocean ◽  
Continental Slope ◽  
Mesoscale Eddies ◽  
The Arctic ◽  
Laptev Sea ◽  
Surface Mixed Layer ◽  
Fram Strait ◽  
Structure And Dynamics ◽  
The Arctic Ocean ◽  
The Laptev Sea

Abstract. Heat fluxes steered by mesoscale eddies may be a significant (but still not quantified) source of heat to the surface mixed layer and sea ice cover in the Arctic Ocean, as well as a source of nutrients for enhancing seasonal productivity in the near-surface layers. Here we use four years (2007–2011) of velocity and hydrography records from a moored profiler over the Laptev Sea slope, and 15 months (2008–2009) of acoustic Doppler current profiler data from a nearby mooring, to investigate the structure and dynamics of eddies at the continental margin of the eastern Eurasian Basin. Typical eddy scales are radii of order of 10 km, heights of six hundred meters, and maximum velocities of ~ 0.1 m s −1. Eddies are approximately equally divided between cyclonic and anticyclonic polarizations, contrary to prior observations from the deep basins and along the Lomonosov Ridge. Eddies are present in the mooring records about 20–25 % of the time, taking about one week to pass through the mooring at an average frequency of about one eddy per month. We found the eddies observed are formed in two distinct regions–near Fram Strait, where the western branch of Atlantic Water (AW) enters the Arctic Ocean, and near Severnaya Zemlya, where the Fram Strait and Barents Sea branches of the AW inflow merge. These eddies, embedded in the Arctic Circumpolar Boundary Current, carry anomalous water properties along the eastern Arctic continental slope. The enhanced diapycnal mixing that we found within EB eddies suggests a potentially important role for eddies in the vertical redistribution of heat in the Arctic Ocean interior.

scholarly journals Sea ice circulation in the Laptev Sea and ice export to the Arctic Ocean: Results from satellite remote sensing and numerical modeling

2000 ◽  
Vol 105 (C7) ◽  
pp. 17143-17159 ◽  
Author(s):  
Vitaly Y. Alexandrov ◽  
Thomas Martin ◽  
Josef Kolatschek ◽  
Hajo Eicken ◽  
Martin Kreyscher ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Numerical Modeling ◽  
Sea Ice ◽  
Arctic Ocean ◽  
Satellite Remote Sensing ◽  
The Arctic ◽  
Laptev Sea ◽  
The Arctic Ocean ◽  
The Laptev Sea

scholarly journals Bioindication of the water salinity dynamics by the microalgae communities in the Lena River Delta, Laptev Sea, Russian Arctic

2021 ◽  
Vol 6 (3) ◽  
pp. 15-28
Author(s):  
S. S. Barinova ◽  
V. A. Gabyshev ◽  
A. P. Ivanova ◽  
O. I. Gabysheva
Keyword(s):  
Species Composition ◽  
River Delta ◽  
Water Bodies ◽  
Water Salinity ◽  
The Arctic ◽  
Laptev Sea ◽  
Russian Arctic ◽  
Lena River ◽  
Lena River Delta ◽  
The Laptev Sea

The Lena River in the Laptev Sea forms a vast delta, one of the largest in the world. The Ust-Lensky State Nature Reserve saves biodiversity on the Lena Delta territory beyond the Arctic Circle, in the zone of continuous permafrost. In recent years, large-scale plans for the development of extractive industries are implemented in this Russian Arctic sector. In this regard, the study of biodiversity and bioindication properties of aquatic organisms in the Lena River estuary area is becoming more and more relevant. This study aims to identify the species composition of microalgae in lotic and lentic water bodies of the Lena River Delta and use their indicator property for water salinity. It was a trace indicator of species distribution over the delta and their dynamics along the delta main watercourses to assess the impact of river waters on the Laptev Sea coastal areas. For this, all previously published materials on algae and chemical composition of the region waters as well as data obtained in recent years for the waters of the lower Lena reach were involved. In total, 700 species considered to 10 phyla were analyzed: Cyanobacteria (83), Euglenozoa (13), Ochrophyta (Chrysophyta, Xanthophyta) (41), Eustigmatophyta (4), Bacillariophyta (297), Miozoa (20), Cryptophyta (3), Rhodophyta (1), Chlorophyta (125), and Charophyta (111). The available materials of the field and reference observations were analyzed using several statistical methods. The study results indicate that hydrological conditions are the main factor regulating the spatial structure of the species composition of the microalgae communities in the Lena River Delta. The distribution of groups of salinity indicators across flowing water bodies reflects the effect of water salinity, and this allows suggesting possible sources of this effect. The mechanism of tracking the distribution of environmental indicators itself is a sensitive method, that reveals even their subtle changes in them; therefore, as an integral method, it can be helpful for further monitoring.

Mercury and methylmercury along a transect from the Lena river estuary across the Laptev Sea Shelf

2020 ◽  
Author(s):  
Van Liem Nguyen ◽  
Birgit Wild ◽  
Örjan Gustafsson ◽  
Igor Semiletov ◽  
Oleg Dudarev ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Arctic Ocean ◽  
River Delta ◽  
The Arctic ◽  
Laptev Sea ◽  
Terrestrial Organic Matter ◽  
Lena River ◽  
The Arctic Ocean ◽  
The Laptev Sea

<p>Widespread accelerated permafrost thawing is predicted for this century and beyond. This threatens to remobilize the large amounts of Mercury (Hg) currently ‘locked’ in Arctic permafrost soils to the Arctic Ocean and thus potentially lead to severe consequences for human and wildlife health. Future risks of Arctic Hg in a warmer climate are, however, poorly understood. One crucial knowledge gap to fill is the fate of Hg once it enters the marine environment on the continental shelves. Arctic rivers are already today suggested to be the main source of Hg into the Arctic Ocean, with dissolved and particulate organic matter (DOM and POM, respectively) identified as important vectors for the land to sea transport.</p><p>In this study, we have investigated total Hg (HgT) and monomethylmercury (MeHg) concentrations in surface sediments from the East Siberian Arctic Shelf (ESAS) along a transect from the Lena river delta to the Laptev Sea continental slope. The ESAS is the world’s largest continental shelf and receives large amounts of organic carbon by the great Arctic Russian rivers (e.g., Lena, Indigirka and Kolyma), remobilized from continuous and discontinuous permafrost regions in the river catchments, and from coastal erosion. Data on HgT and MeHg levels in ESAS sediments is however limited. Here, we observed concentrations of Hg ranging from 30 to 96 ng Hg g<sup>-1</sup> d.w. of HgT, and 0.03 to 9.5 ng Hg g<sup>-1</sup> d.w. of MeHg. Similar concentrations of HgT were observed close to the river delta (54 ± 19 ng Hg g<sup>-1</sup> d.w.), where >95 % of the organic matter is of terrestrial origin, and the other section of the transect (42 ± 7 ng Hg g<sup>-1</sup> d.w.) where the terrestrial organic matter is diluted with carbon from marine sources. In contrast, we observed higher concentrations of MeHg close to the river delta (0.72 ± 0.71 ng Hg g<sup>-1</sup> d.w. as MeHg) than further out on the continental shelf (0.031 ± 0.71 ng Hg g<sup>-1</sup> d.w. as MeHg). We also observed a positive correlation between the MeHg:Hg ratio and previously characterized molecular markers of terrestrial organic matter (Bröder et al. Biogeosciences (2016) & Nature Com. (2018)). We thus suggest riverine inputs, rather than in situ MeHg formation, to explain observed MeHg trends.</p>

scholarly journals Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea

2019 ◽  
Vol 16 (6) ◽  
pp. 1305-1319 ◽  
Author(s):  
Sarah Conrad ◽  
Johan Ingri ◽  
Johan Gelting ◽  
Fredrik Nordblad ◽  
Emma Engström ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Salinity Gradient ◽  
River Mouth ◽  
The Arctic ◽  
Shelf Zone ◽  
Laptev Sea ◽  
Lena River ◽  
Freshwater Plume ◽  
The Laptev Sea ◽  
Particles And Colloids

Abstract. Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate (>0.22 µm), colloidal (0.22 µm–1 kDa), and truly dissolved (<1 kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57 µM with Fe dominantly as particulate Fe. The loss of >99 % of particulate Fe and about 90 % of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative δ56Fe values (relative to IRMM-14). The colloidal Fe phase showed negative δ56Fe values close to the river mouth (about −0.20 ‰) and positive δ56Fe values in the outermost stations (about +0.10 ‰). We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative δ56Fe values, representing chemically reactive ferrihydrites. The positive δ56Fe values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant δ56Fe composition in the Arctic Ocean.

Particulate and dissolved organic carbon composition in the Lena River and its Delta, from Yakutsk to the Arctic Ocean.

2021 ◽  
Author(s):  
Olga Ogneva ◽  
Gesine Mollenhauer ◽  
Matthias Fuchs ◽  
Juri Palmtag ◽  
Tina Sanders ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Arctic Ocean ◽  
Main Channel ◽  
The Arctic ◽  
Laptev Sea ◽  
Lena River ◽  
The Arctic Ocean ◽  
The Laptev Sea ◽  
Lena Delta

&lt;p&gt;Rapid climate warming in the Arctic intensifies permafrost thaw, increases active layer depth in summer and enhances riverbank and coastal erosion. All of these cause additional release of organic matter (OM) into streams and rivers. OM will be (1) transformed and modified during transport and subsequently discharged into the Arctic Ocean, or (2) removed from the active cycling by sedimentation. Here, the nearshore zone (which includes deltas, estuaries and coasts) is of great importance, where the major transformation processes of terrestrial material take place. Despite the importance of deltas for the biogeochemical cycle, their functioning is poorly understood. For our study we examined the Lena River nearshore, which represents the world&amp;#8217;s third largest delta and supplies the second highest annual water and sediment discharge into the Arctic Ocean. Running through almost the entirety of East Siberia from Lake Baikal to the Laptev Sea, the Lena River drains an area of &amp;#8764;2,61&amp;#215;10&lt;sup&gt;6&lt;/sup&gt; km&lt;sup&gt;2&lt;/sup&gt;&amp;#160; with approximately 90% underlain by permafrost. Our aims were to investigate the spatial variation of OM concentration and isotopic composition during transit from terrestrial permafrost source to the ocean interface, and to compare riverine and deltaic OM composition. We measured particulate and dissolved organic carbon (POC and DOC) concentrations and their associated &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C and &amp;#8710;&lt;sup&gt;14&lt;/sup&gt;C values in water samples collected along a &amp;#8764;1500 km long Lena River transect from Yakutsk downstream to the river outlet into the Laptev Sea.&lt;/p&gt;&lt;p&gt;We find significant qualitative and quantitative differences between the OM composition in the Lena River main channel and its delta. Further, we found suspended matter and POC concentrations decreased during transit from river to the Arctic Ocean.&amp;#160; DOC concentrations in the Lena delta were almost 50% lower than OM from the main channel. We found that deltaic POC is depleted in &lt;sup&gt;13&lt;/sup&gt;C relative to fluvial POC, and that its &lt;sup&gt;14&lt;/sup&gt;C signature suggests a modern composition indicating phytoplankton origin. This observation likely reflects the difference in hydrological conditions between the delta and the river main channel, caused by lower flow velocity and average water depth. We propose that deltaic environments provide favorable growth conditions for riverine primary producers such as algae and aquatic plants. Deltaic DOC is depleted in &lt;sup&gt;14&lt;/sup&gt;C compared to riverine, especially in samples taken from the water surface, which indicates contributions from an additional old carbon stock source, specific for the Lena Delta. We suggest that this C is released from deltaic bank erosion and partly stays floating on the surface. In conclusion, we found a strong impact of deltaic processes on the fate and dominant signatures of OM discharged into the Arctic Ocean.&lt;/p&gt;

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