ALBERT

Description: 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.

Description: 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.

Description: 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 (10〈salinity〈25) exhibiting lower concentrations of DOM and a decreased contribution and reactivity of terrigenous compounds; and 3) the high salinity regime (salinity〉25) 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.

Description: 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 (10〈salinity〈25) exhibiting lower concentrations of DOM and a decreased contribution and reactivity of terrigenous compounds; and 3) the high salinity regime (salinity〉25) 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.

Description: 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.