Supplementary material to "Fate of terrigenous organic matter across the Laptev Sea from the mouth of the Lena River to the deep sea of the Arctic interior"

Widespread accelerated permafrost thawing is predicted for this century and beyond. This threatens to remobilize the large amounts of Mercury (Hg) currently &#8216;locked&#8217; 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.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&#8217;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-1 d.w. of HgT, and 0.03 to 9.5 ng Hg g-1 d.w. of MeHg. Similar concentrations of HgT were observed close to the river delta (54 &#177; 19 ng Hg g-1 d.w.), where >95 % of the organic matter is of terrestrial origin, and the other section of the transect (42 &#177; 7 ng Hg g-1 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 &#177; 0.71 ng Hg g-1 d.w. as MeHg) than further out on the continental shelf (0.031 &#177; 0.71 ng Hg g-1 d.w. as MeHg). We also observed a positive correlation between the MeHg:Hg ratio and previously characterized molecular markers of terrestrial organic matter (Br&#246;der et al. Biogeosciences (2016) & Nature Com. (2018)). We thus suggest riverine inputs, rather than in situ MeHg formation, to explain observed MeHg trends.

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Composition of Sedimentary Organic Matter across the Laptev Sea Shelf: Evidences from Rock-Eval Parameters and Molecular Indicators

Water ◽

10.3390/w12123511 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3511

Author(s):

Elena Gershelis ◽

Andrey Grinko ◽

Irina Oberemok ◽

Elizaveta Klevantseva ◽

Natalina Poltavskaya ◽

...

Keyword(s):

Organic Matter ◽

Surface Sediments ◽

Continental Margins ◽

Laptev Sea ◽

Lena River ◽

Nearshore Sediments ◽

Rock Eval ◽

Molecular Indicators ◽

Sedimentation Regime ◽

The Laptev Sea

Global warming in high latitudes causes destabilization of vulnerable permafrost deposits followed by massive thaw-release of organic carbon. Permafrost-derived carbon may be buried in the nearshore sediments, transported towards the deeper basins or degraded into the greenhouse gases, potentially initiating a positive feedback to climate change. In the present study, we aim to identify the sources, distribution and degradation state of organic matter (OM) stored in the surface sediments of the Laptev Sea (LS), which receives a large input of terrestrial carbon from both Lena River discharge and intense coastal erosion. We applied a suite of geochemical indicators including the Rock Eval parameters, traditionally used for the matured OM characterization, and terrestrial lipid biomarkers. In addition, we analyzed a comprehensive grain size data in order to assess hydrodynamic sedimentation regime across the LS shelf. Rock-Eval (RE) data characterize LS sedimentary OM with generally low hydrogen index (100–200 mg HC/g TOC) and oxygen index (200 and 300 CO2/g TOC) both increasing off to the continental slope. According to Tpeak values, there is a clear regional distinction between two groups (369–401 °C for the inner and mid shelf; 451–464 °C for the outer shelf). We suggest that permafrost-derived OM is traced across the shallow and mid depths with high Tpeak and slightly elevated HI values if compared to other Arctic continental margins. Molecular-based degradation indicators show a trend to more degraded terrestrial OC with increasing distance from the coast corroborating with RE results. However, we observed much less variation of the degradation markers down to the deeper sampling horizons, which supports the notion that the most active OM degradation in LS land-shelf system takes part during the cross-shelf transport, not while getting buried deeper.

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

Biogeosciences Discussions ◽

10.5194/bgd-8-2093-2011 ◽

2011 ◽

Vol 8 (2) ◽

pp. 2093-2143 ◽

Cited By ~ 6

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.

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

Marine Biological Journal ◽

10.21072/mbj.2021.06.3.02 ◽

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.

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

Biogeosciences ◽

10.5194/bg-16-1305-2019 ◽

2019 ◽

Vol 16 (6) ◽

pp. 1305-1319 ◽

Cited By ~ 5

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.

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Fate of terrigenous organic matter across the Laptev Sea from the mouth of the Lena River to the deep sea of the Arctic interior

10.5194/bg-2016-159 ◽

2016 ◽

Author(s):

Lisa Bröder ◽

Tommaso Tesi ◽

Joan A. Salvadó ◽

Igor P. Semiletov ◽

Oleg V. Dudarev ◽

...

Keyword(s):

Organic Carbon ◽

Water Depth ◽

Deep Sea ◽

River Mouth ◽

The Arctic ◽

Laptev Sea ◽

Climate Feedbacks ◽

Lena River ◽

Lignin Phenols ◽

Future Work

Abstract. Ongoing global warming in high latitudes may cause an increasing supply of permafrost-derived organic carbon through both river discharge and coastal erosion to the Arctic shelves. Here it can be either buried in sediments, transported to the deep sea or degraded to CO2 and outgassed, potentially constituting a positive feedback to climate change. This study aims to assess the fate of terrestrial organic carbon (TerrOC) in the Arctic marine environment by exploring how it changes in concentration, composition and degradation status across the wide Laptev Sea shelf. We analyzed a suite of terrestrial biomarkers as well as source-diagnostic bulk carbon isotopes (δ13C, Δ14C) in surface sediments from a Laptev Sea transect spanning more than 800 km from the Lena River mouth (~ 10 m water depth) across the shelf to the slope and rise (2000–3000 m water depth). These data provide a broad view on different TerrOC pools and their behavior during cross-shelf transport. The concentrations of lignin phenols, cutin acids and high-molecular weight (HMW) wax lipids (tracers of vascular plants) decrease by 89–99 % along the transect. Molecular-based degradation proxies for TerrOC (e.g., the carbon preference index of HMW lipids, the HMW acids/alkanes ratio and the acid/aldehyde ratio of lignin phenols) display a trend to more degraded TerrOC with increasing distance from the coast. We infer that the degree of degradation of permafrost-derived TerrOC is a function of the time spent under oxic conditions during protracted cross-shelf transport. Future work should therefore seek to constrain cross-shelf transport times in order to compute a TerrOC degradation rate and thereby help to quantify potential carbon-climate feedbacks.

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

10.5194/egusphere-egu21-8005 ◽

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

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&#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 &#8764;2,61&#215;106 km2&#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 &#948;13C and &#8710;14C values in water samples collected along a &#8764;1500 km long Lena River transect from Yakutsk downstream to the river outlet into the Laptev Sea.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.&#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 13C relative to fluvial POC, and that its 14C 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 14C 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.

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

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0240.1 ◽

2014 ◽

Vol 44 (1) ◽

pp. 202-219 ◽

Cited By ~ 18

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.

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Dissolved organic matter at the fluvial–marine transition in the Laptev Sea using in situ data and ocean colour remote sensing

Biogeosciences ◽

10.5194/bg-16-2693-2019 ◽

2019 ◽

Vol 16 (13) ◽

pp. 2693-2713 ◽

Cited By ~ 10

Author(s):

Bennet Juhls ◽

Pier Paul Overduin ◽

Jens Hölemann ◽

Martin Hieronymi ◽

Atsushi Matsuoka ◽

...

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

The Arctic ◽

Laptev Sea ◽

Ocean Colour ◽

In Situ Data ◽

Doc Concentration ◽

Ocean Colour Remote Sensing ◽

The Laptev Sea

Abstract. River water is the main source of dissolved organic carbon (DOC) in the Arctic Ocean. DOC plays an important role in the Arctic carbon cycle, and its export from land to sea is expected to increase as ongoing climate change accelerates permafrost thaw. However, transport pathways and transformation of DOC in the land-to-ocean transition are mostly unknown. We collected DOC and aCDOM(λ) samples from 11 expeditions to river, coastal and offshore waters and present a new DOC–aCDOM(λ) model for the fluvial–marine transition zone in the Laptev Sea. The aCDOM(λ) characteristics revealed that the dissolved organic matter (DOM) in samples of this dataset are primarily of terrigenous origin. Observed changes in aCDOM(443) and its spectral slopes indicate that DOM is modified by microbial and photo-degradation. Ocean colour remote sensing (OCRS) provides the absorption coefficient of coloured dissolved organic matter (aCDOM(λ)sat) at λ=440 or 443 nm, which can be used to estimate DOC concentration at high temporal and spatial resolution over large regions. We tested the statistical performance of five OCRS algorithms and evaluated the plausibility of the spatial distribution of derived aCDOM(λ)sat. The OLCI (Sentinel-3 Ocean and Land Colour Instrument) neural network swarm (ONNS) algorithm showed the best performance compared to in situ aCDOM(440) (r2=0.72). Additionally, we found ONNS-derived aCDOM(440), in contrast to other algorithms, to be partly independent of sediment concentration, making ONNS the most suitable aCDOM(λ)sat algorithm for the Laptev Sea region. The DOC–aCDOM(λ) model was applied to ONNS-derived aCDOM(440), and retrieved DOC concentration maps showed moderate agreement to in situ data (r2=0.53). The in situ and satellite-retrieved data were offset by up to several days, which may partly explain the weak correlation for this dynamic region. Satellite-derived surface water DOC concentration maps from Medium Resolution Imaging Spectrometer (MERIS) satellite data demonstrate rapid removal of DOC within short time periods in coastal waters of the Laptev Sea, which is likely caused by physical mixing and different types of degradation processes. Using samples from all occurring water types leads to a more robust DOC–aCDOM(λ) model for the retrievals of DOC in Arctic shelf and river waters.

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

10.5194/bg-2018-181 ◽

2018 ◽

Cited By ~ 2

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 to 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 ( 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. While 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.

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