scholarly journals Dissolved Organic Matter at the Fluvial-Marine Transition in the Laptev Sea Using in situ Data and Ocean Color Remote Sensing

2019 ◽  
Author(s):  
Bennet Juhls ◽  
Pier Paul Overduin ◽  
Jens Hölemann ◽  
Martin Hieronymi ◽  
Atsushi Matsuoka ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Ocean Color ◽  
The Arctic ◽  
Laptev Sea ◽  
In Situ Data ◽  
Doc Concentration ◽  
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 DOM in samples of this dataset are primarily of terrigenous origin. Observed changes in aCDOM and its spectral slopes indicate that DOM is modified by microbial- and photo-degradation. Ocean Color Remote Sensing (OCRS) provides the absorption coefficient of colored 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 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 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.

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

2019 ◽  
Vol 16 (13) ◽  
pp. 2693-2713 ◽  
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.

scholarly journals Use of absorption optical indices to assess seasonal variability of dissolved organic matter in amazon floodplain lakes

2019 ◽  
Author(s):  
Maria Paula da Silva ◽  
Lino A. Sander de Carvalho ◽  
Evlyn Novo ◽  
Daniel S. F. Jorge ◽  
Claudio C. F. Barbosa
Keyword(s):  
Remote Sensing ◽  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Seasonal Variability ◽  
Large Scale ◽  
River Bank ◽  
In Situ Data ◽  
Amazon Floodplain ◽  
Significant Difference

Abstract. Given the importance of DOM in the carbon cycling of aquatic ecosystems, information on its seasonal variability is crucial. This study assesses the use of available absorption optical indices based on in situ data to both characterize the seasonal variability of the DOM dynamics in a highly complex environment and their viability of being used for satellite remote sensing on large scale studies. The study area comprises four lakes located at the Mamirauá Sustainable Development Reserve (MSDR). Samples for the determination of coloured dissolved organic matter (CDOM) and remote sensing reflectance (Rrs) were acquired in situ. The Rrs was applied to simulate MSI visible bands and used in the proposed models. Differences between lakes were tested regarding CDOM indices. Significant difference in the average of aCDOM (440), aCDOM spectra and S275–295 were found between lakes located inside the flood forest and those near the river bank. The proposed model showed that aCDOM can be used as proxy of S275–295 during rising water with good validation results, demonstrating the potential of Sentinel/MSI imagery data in large scale studies on the dynamics of DOM.

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 Use of optical absorption indices to assess seasonal variability of dissolved organic matter in Amazon floodplain lakes

2020 ◽  
Vol 17 (21) ◽  
pp. 5355-5364
Author(s):  
Maria Paula da Silva ◽  
Lino A. Sander de Carvalho ◽  
Evlyn Novo ◽  
Daniel S. F. Jorge ◽  
Claudio C. F. Barbosa
Keyword(s):  
Remote Sensing ◽  
Organic Matter ◽  
Optical Absorption ◽  
Dissolved Organic Matter ◽  
Seasonal Variability ◽  
Large Scale ◽  
Remote Sensing Data ◽  
Floodplain Lakes ◽  
Sentinel 2

Abstract. Given the importance of dissolved organic matter (DOM) in the carbon cycling of aquatic ecosystems, information on its seasonal variability is crucial. In this study we assess the use of optical absorption indices available in the literature based on in situ data to both characterize the seasonal variability of DOM in a highly complex environment and for application in large-scale studies using remote sensing data. The study area comprises four lakes located in the Mamirauá Sustainable Development Reserve (MSDR). Samples for the determination of colored dissolved organic matter (CDOM) and measurements of remote sensing reflectance (Rrs) were acquired in situ. The Rrs was used to simulate the response of the visible bands of the Sentinel-2 MultiSpectral Instrument (MSI), which was used in the proposed models. Differences between lakes were tested using the CDOM indices. The results highlight the role of the flood pulse in the DOM dynamics at the floodplain lakes. The validation results show that the use of the absorption coefficient of CDOM (aCDOM) as a proxy of the spectral slope between 275 and 295 nm (S275–295) during rising water is worthwhile, demonstrating its potential application to Sentinel-2 MSI imagery data for studying DOM dynamics on the large scale.

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 Tracing the transport of colored dissolved organic matter in water masses of the Southern Beaufort Sea: relationship with hydrographic characteristics

2012 ◽  
Vol 9 (3) ◽  
pp. 925-940 ◽  
Author(s):  
A. Matsuoka ◽  
A. Bricaud ◽  
R. Benner ◽  
J. Para ◽  
R. Sempéré ◽  
...  
Keyword(s):  
Organic Matter ◽  
Surface Layer ◽  
Dissolved Organic Matter ◽  
Heat Budget ◽  
Ocean Color ◽  
Beaufort Sea ◽  
The Arctic ◽  
Strongly Correlated ◽  
Colored Dissolved Organic Matter ◽  
Color Data

Abstract. Light absorption by colored dissolved organic matter (CDOM) [aCDOM(λ)] plays an important role in the heat budget of the Arctic Ocean, contributing to the recent decline in sea ice, as well as in biogeochemical processes. We investigated aCDOM(λ) in the Southern Beaufort Sea where a significant amount of CDOM is delivered by the Mackenzie River. In the surface layer, aCDOM(440) showed a strong and negative correlation with salinity, indicating strong river influence and conservative transport in the river plume. Below the mixed layer, a weak but positive correlation between aCDOM(440) and salinity was observed above the upper halocline, resulting from the effect of removal of CDOM due to brine rejection and lateral intrusion of Pacific summer waters into these layers. In contrast, the relationship was negative in the upper and the lower haloclines, suggesting these waters originated from Arctic coastal waters. DOC concentrations in the surface layer were strongly correlated with aCDOM(440) (r2 = 0.97), suggesting that this value can be estimated in this area, using aCDOM(440) that is retrieved using satellite ocean color data. Implications for estimation of DOC concentrations in surface waters using ocean color remote sensing are discussed.

Evaluating Dissolved Organic Carbon Retrieval in the Lena River Delta using Sentinel 3 OLCI Data

2021 ◽  
Author(s):  
Rene Preusker ◽  
Jan El Kassar ◽  
Bennet Juhls
Keyword(s):  
Remote Sensing ◽  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Arctic Ocean ◽  
The Arctic ◽  
Lena River ◽  
The Arctic Ocean ◽  
Arctic Rivers

<p>As air temperatures in the Arctic continue to rise, permafrost thaw intensifies, and discharge from the Arctic rivers increases. These drastic changes are likely to accelerate mobilization of organic matter and its export through rivers into the Arctic Ocean. Therefore, thorough monitoring of these processes becomes increasingly important. The Lena River with its large catchment area is one of the major sources of the organic carbon in the Arctic Ocean and, therefore, plays a crucial role in the Arctic carbon cycle. <br>To observe current and future changes of carbon transport via the Lena River, a new monitoring program has been initiated in 2018. In situ water samples are collected from the one of the Lena Delta branches every several days. Since generally the in situ sampling in the Arctic is challenging and costly, in this study, we test the potential of remote sensing to complement the field observations. Remote sensing provides synoptic spatial coverages and high temporal resolution at high latitudes. <br>We test the retrieval of dissolved organic carbon (DOC) from satellite-derived chromophoric dissolved organic matter (CDOM). For this, we use measurements of the Ocean & Land Colour Instrument (OLCI) on board the Sentinel-3 satellites in combination with beforehand tested atmospheric correction algorithms and CDOM retrieval algorithms. The quality of the satellite retrieved DOC of the Lena River water is assessed by DOC, measured in the in situ samples. Remotely sensed DOC contributes to an improvement of DOC fluxes monitoring, which can potentially be extended to all big Arctic rivers.</p>

Characteristics of organic carbon in surface sediments of Laptev Sea shelf

2020 ◽  
Author(s):  
Irina Oberemok ◽  
Elena Gershelis ◽  
Andrey Grin’ko ◽  
Alexey Ruban ◽  
Elizaveta Klevantseva ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Coastal Erosion ◽  
Surface Sediments ◽  
Oxygen Index ◽  
Outer Shelf ◽  
The Arctic ◽  
Laptev Sea ◽  
Shelf Sediments ◽  
The Laptev Sea

<p>Accelerating coastal erosion and enhancing river sediment discharge are expected to greatly increase the delivery of terrestrial organic carbon (terrOC) to the Arctic Ocean. Remobilized terrOC may be buried in shallow or outer shelf sediments, degraded and translocated to the deeper basins, or remineralized in the water column causing a positive feedback to amplified global warming. The East Siberian Arctic Shelf (ESAS), represented by the Laptev Sea, the East Siberian Sea, and the Russian part of the Chukchi Sea, is the widest and shallowest continental shelf of the World Ocean. In the current study, we investigated surface sediment samples collected across the Laptev Sea shelf (from the coastline to the outer shelf) during the Arctic expedition onboard the Russian <em>R/V Academician M. Keldysh</em> during fall 2018.</p><p>We analyzed 16 samples for bulk (TOC, <em>δ</em>13C) and molecular (distribution and concentration of n-alkanes and PAHs) parameters. We also performed Rock-Eval (RE) analysis in order to compare its results with the signatures provided by traditional geochemical tracers and thereby to gain new insights into the sources of organic matter in modern surface sediments. In addition, a grain-size analysis was carried out to reveal hydrodynamic control on the organic carbon transport across the studied transect. Using a combination of traditional molecular interpretations (performed in this study and published earlier) and RE parameters (Hydrogen index, Oxygen index and T<sub>peak</sub>) we attempted to distinguish riverine input and coastal erosion and disentangle processes of terrOC degradation and its replacement with fresh/marine OC during cross-shelf transport. Overall, a strong decrease of terrigenous contribution to the sedimentary organic carbon was observed on molecular level with increasing distance from the coast. According to the RE data, intensive terrOC degradation takes place in the shallow and mid-shelf sediments which is traced by sharply increasing oxygen index. The clear correlation between OI and the clay content points toward the perception that mineral matrix do not seem to be such good protector as expected, and intensive microbial degradation of the sedimentary organic matter contained in fine particles occurs during repeated resuspension.</p><p>This research is supported by Russian Science Foundation, project # 19-77-00067.</p>

Molecular Geochemistry of the Dispersed Organic Matter in the Late Cenozoic Sediments of the Laptev Sea Continental Margin and Adjacent Part of the Arctic Ocean

2021 ◽  
Vol 62 (4) ◽  
pp. 460-473
Author(s):  
V.I. Petrova ◽  
G.I. Batova ◽  
A.V. Kursheva ◽  
I.V. Litvinenko ◽  
I.P. Morgunova
Keyword(s):  
Organic Matter ◽  
Continental Margin ◽  
Depositional Environments ◽  
The Arctic ◽  
Geochemical Data ◽  
Laptev Sea ◽  
Lomonosov Ridge ◽  
Late Cenozoic ◽  
Cenozoic Sediments ◽  
The Laptev Sea

Abstract ––The main factors controlling the bulk sedimentation in the Siberian segment of the Lomonosov Ridge (axial part and western slope) and the Laptev Sea continental margin during the late Cenozoic were studied using a complex of geomorphological, lithological, and organic geochemical data. Samples for the study were collected during the cruises of R/V Akademik Fedorov in 2005 and 2007 and nuclear icebreaker Rossiya in 2007. Analysis of the group and molecular composition of the dispersed organic matter (DOM) in bottom sediments has shown that the input of terrigenous sediments enriched in the products of abrasion of lithified rocks determines sedimentation process on the continental slope of the Laptev Sea and in the Amundsen Basin. The individual characteristics of the DOM of the late Cenozoic sediments from the Lomonosov Ridge reflect the wide diversity of sedimentary sources and depositional environments. Subaqueous erosion of edaphogenic products and pre-Holocene sediments plays an important part in sedimentation together with terrigenous flow and ice transport.

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