Molecular biogeochemistry of dissolved organic matter in the permafrost-influenced Lena Delta and the coastal Laptev Sea

Dissolved organic matter (DOM) is a ubiquitous complex mixture of organic compounds in aquatic systems. DOM is an important contributor to the global carbon cycle. The global inventory of permafrost carbon represents half of the global belowground soil carbon. The mobilization and degradation of this carbon pool would have critical implications in the Arctic. The ultra-complex mixture of organic compounds in DOM is a proxy of ecosystem metabolism and represents an imprint of past and ongoing biogeochemical processes. Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and statistical analyses were performed on DOM samples obtained in various expeditions to the Lena Delta and Laptev Sea. The DOM composition, reactivity and properties in the permafrost-influenced Lena Delta and coastal Laptev Sea, Siberia were characterized. The systematics of the molecular DOM composition with respect to source of natural waters, reactivity during the Lena River - Laptev Sea transition, mobilization, mineralization and turnover of permafrost-derived DOM were addressed

CHARACTERIZATION AND FATE OF DISSOLVED ORGANIC MATTER IN THE LENA DELTA REGION, SIBERIA

Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased towards the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation

FROM FRESH- TO MARINE WATERS: THE FATE OF DISSOLVED ORGANIC MATTER IN THE LENA DELTA REGION, SIBERIA

The connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change. This is influencing both freshwater budgets and the supply of carbon to sea. This study characterizes the composition of dissolved organic matter (DOM) within the Lena Delta region across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis, with a clear dominance of humic-like signals in fresh waters. At higher salinities there was an increased autochthonous contribution. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and, as a response to the hydrographical forcing, the region displayed a pseudo-conservative behavior of DOM in relation to salinity at marine-influenced sites; and a non-conservative behavior with evidence of considerable removal of DOM (up to 54%), likely driven by photodegradation and sorption/flocculation, at sites influenced by the Lena River plume. The latter mixing curve was split into three mixing regimes with regard to different amount and reactivity degree of DOM and to the factors driving DOM variability: 1) the low salinity regime (salinity>10) with high concentrations of DOM, dominated by highly reactive terrigenous contribution and characterized by rapid removal; 2) the intermediate regime (1025) showing the lowest DOM and an increased contribution of less reactive compounds, displaying a pseudo-conservative behavior, with relatively low removal/addition processes controlling the dilution of DOM

Molekulare Biogeochemie von gelöstem organischen Material im von Permafrost beeinflussten Lena Delta und der küstennahen Laptev See

Dissolved organic matter (DOM) is a ubiquitous complex mixture of organic compounds in aquatic systems. DOM is an important contributor to the global carbon cycle. The global inventory of permafrost carbon represents half of the global belowground soil carbon. The mobilization and degradation of this carbon pool would have critical implications in the Arctic. The ultra-complex mixture of organic compounds in DOM is a proxy of ecosystem metabolism and represents an imprint of past and ongoing biogeochemical processes. Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and statistical analyses were performed on DOM samples obtained in various expeditions to the Lena Delta and Laptev Sea. The DOM composition, reactivity and properties in the permafrost-influenced Lena Delta and coastal Laptev Sea, Siberia were characterized. The systematics of the molecular DOM composition with respect to source of natural waters, reactivity during the Lena River - Laptev Sea transition, mobilization, mineralization and turnover of permafrost-derived DOM were addressed

Biogeochemistry of dissolved organic matter in the Arctic permafrost and the Lena delta

Permafrost soils have accumulated vast stores of organic carbon recently estimated to be ~1600 Pg C. During the next century, near-surface permafrost across the circumpolar Arctic is expected to degrade significantly. Large amounts, especially of dissolved organic matter (DOM), may be released, transported to the oceans and either mineralized or convected down to the deep Arctic Ocean. Although DOC in Arctic rivers often shows relatively conservative characteristics, it has been recently shown that terrestrial DOC removal is an active but probably slow process. The major discharge of freshwater to the Arctic Ocean occurs within a very short period of time when ice is melting in late spring /early summer. All involved processes are characterized by high spatial and temporal variability but in their entirety they are likely to have critical implications for primary production and carbon cycling on Arctic shelves and in the Arctic Ocean. DOC in the Lena River has quite similar concentrations over long distances with a high carbon to nitrogen ratio. The classical relation between DOC and salinity in the coastal regions implies a conservative mixing, however, a strong modification of DOM must occur during transition from freshwater to seawater. C:N ratio strongly decrease in the estuarine and near shore regions. The discharge of nutrients is low except for silicate. The major aim is to identify and quantify the flux of soil-derived DOM and nutrients from the permafrost into the Lena estuary and the Arctic shelf-ocean system. Field sampling and experiments were carried out in August 2009 and 2010. Samples were taken from the main channels in the Lena delta and some near-shore coastal stations in the Buor-Khaya Bay as well as from run-off water from different ice complexes and permafrost lakes and soils. These samples with very different characteristics had highly variable DOC concentrations that are in the range from 450 to 650 µM for Lena River water, 800 to 10,800 µM for ice complex meltwater and of about 800 µM for the ice of ice complexes. Most of the freshwater and DOM is discharged via the eastern and north-eastern channels of the Lena River. Bacterial and photo-degradation batch experiments have shown that a considerable amount of terrestrial DOM of ice complex meltwater is mineralized or degraded. Ultra high resolution mass spectrometry is used to identify markers to trace the fate of DOM. Our goal is to implement a molecular classification system for the bioavailability of permafrost-derived DOM

From fresh to marine waters: characterization and fate of dissolved organic matter in the Lena River Delta region, Siberia

Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets, and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased toward the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation

Dissolved organic matter in the Lena Delta in 2009

Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into the Arctic Ocean. We sampled natural waters of the Lena River, the Buor-Khaya Bay (Laptev Sea), permafrost melt water creeks, ice complex melt water creeks and a lake. The goal of this study was to characterize the molecular DOM composition with respect to different water bodies within the Lena Delta. We aimed at an identification of source-specific DOM molecular markers and their relative contribution to DOM of different origin. The molecular characterization was performed for solid-phase extracted DOM by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Average dissolved organic carbon concentrations in the original samples were 490±75 µmol C/L for riverine and bay samples and 399±115 µmol C/L for permafrost melt water creeks. Average TDN concentrations were elevated in the permafrost melt waters (19.7±7.1 µmol N/L) in comparison to the river and the bay (both 13.2±2.6 µmol N/L). FT-ICR MS and statistical tools demonstrated that the origin of DOM in the Lena Delta was systematically reflected in its molecular composition. Magnitude weighted parameters calculated from MS data (O/Cwa, H/Cwa, C/Nwa) highlighted preliminary sample discrimination. The highest H/Cwa of 1.315 was found for DOM in melt water creeks in comparison to 1.281 for river and 1.230 for the bay samples. In the bay samples we observed a higher fraction of oxygen-rich components which was reflected in an O/Cwa ratio of 0.445 in comparison to 0.425 and 0.427 in the river and creeks, respectively. From the southernmost location to the bay a relative depletion of nitrogenous molecular markers and an enrichment of oxidized DOM components occurred. The highest contribution of nitrogenous components was indicative for creeks reflected in a C/Nwa of 104 in comparison to 143 and 176 in the river and bay, respectively. These observations were studied on a molecular formula level using principal component and indicator value analyses. The results showed systematic differences with respect to water origin and constitute an important basis for a better mechanistic understanding of DOM transformations in the changing Arctic rivers

Dissolved organic matter in the Lena River Delta Region, Siberia, Russia

Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased towards the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation