Vertical Variability of Primary Production and Features of the Subsurface Chlorophyll Maximum in the Laptev Sea in August–September, 2015, 2017, and 2018
“…The East Siberian Sea was characterized by low chlorophyll values decreasing in the south-north direction from 0.44 to 0.03 μg l -1 at the Kolyma transect and from 0.48 to 0.04 μg l -1 at the Indigirka transect. The obtained results on chl-a distribution are consistent with the data reported for the Laptev Sea (Demidov et al, 2019;Demidov et al, 2020) and the East Siberian Sea (Ershova and Kosobokova, 2019) in autumn season.…”
The East Siberian Sea is an area of high biogeochemical activity caused by multiple factors, such as an influence of river runoff, Atlantic, and Pacific waters, formation and melting of sea ice, and internal circulation. Extensive amounts of carbon are accumulated in sub-sea permafrost within the Arctic shelf in East Siberia. Thawing permafrost and resulting microbial decomposition of frozen carbon pool is a potential feedback process affected global climate dynamics. Several studies of dissolved organic carbon (DOC) distribution in the East Siberian Sea have demonstrated untypical for other Arctic shelf seas pronounced non-conservative DOC behavior. Using seawater samples from the 69th cruise of R/V Akademik Mstislav Keldysh conducted in the Laptev and East Siberian seas in September 2017, this study examines the distribution of fluorescent dissolved organic matter (FDOM) along the shelf-crossing transects including the areas affected by the Khatanga, Lena, Indigirka, and Kolyma river runoff. The set of 137 excitation-emission matrices (EEMs), analyzed with Parallel Factor analysis (PARAFAC), was described by a 4-component model demonstrating Tucker’s congruence coefficient above the 0.95 threshold. Spectral characteristics of the resulting components allowed identifying them as well-known humic-like A and C, protein-like B/T, and marine humic-like M fluorophores. Component C1 (A fluorophore) showed a good correlation with salinity for different river plume influenced regions. As well as chromophoric DOM (CDOM) absorption, it can be used as marker of input of terrestrial DOM to the Arctic Ocean. A distinctive feature of the East Siberian Sea shelf waters in comparison with the Laptev Sea is the higher content of the C2 and C4 components, exhibiting protein-like and marine humic-like fluorescence. Component C3 (C fluorophore) which is usually identified as terrestrial-derived material, was found to be produced locally on the East Siberian Sea shelf and in the continental slope region of the Khatanga transect. Destruction of dead algae cells, production of marine biota and dissolved organic matter (DOM) reworking are considered as possible autochthonous FDOM sources in the Siberian shelf seas.
“…The East Siberian Sea was characterized by low chlorophyll values decreasing in the south-north direction from 0.44 to 0.03 μg l -1 at the Kolyma transect and from 0.48 to 0.04 μg l -1 at the Indigirka transect. The obtained results on chl-a distribution are consistent with the data reported for the Laptev Sea (Demidov et al, 2019;Demidov et al, 2020) and the East Siberian Sea (Ershova and Kosobokova, 2019) in autumn season.…”
The East Siberian Sea is an area of high biogeochemical activity caused by multiple factors, such as an influence of river runoff, Atlantic, and Pacific waters, formation and melting of sea ice, and internal circulation. Extensive amounts of carbon are accumulated in sub-sea permafrost within the Arctic shelf in East Siberia. Thawing permafrost and resulting microbial decomposition of frozen carbon pool is a potential feedback process affected global climate dynamics. Several studies of dissolved organic carbon (DOC) distribution in the East Siberian Sea have demonstrated untypical for other Arctic shelf seas pronounced non-conservative DOC behavior. Using seawater samples from the 69th cruise of R/V Akademik Mstislav Keldysh conducted in the Laptev and East Siberian seas in September 2017, this study examines the distribution of fluorescent dissolved organic matter (FDOM) along the shelf-crossing transects including the areas affected by the Khatanga, Lena, Indigirka, and Kolyma river runoff. The set of 137 excitation-emission matrices (EEMs), analyzed with Parallel Factor analysis (PARAFAC), was described by a 4-component model demonstrating Tucker’s congruence coefficient above the 0.95 threshold. Spectral characteristics of the resulting components allowed identifying them as well-known humic-like A and C, protein-like B/T, and marine humic-like M fluorophores. Component C1 (A fluorophore) showed a good correlation with salinity for different river plume influenced regions. As well as chromophoric DOM (CDOM) absorption, it can be used as marker of input of terrestrial DOM to the Arctic Ocean. A distinctive feature of the East Siberian Sea shelf waters in comparison with the Laptev Sea is the higher content of the C2 and C4 components, exhibiting protein-like and marine humic-like fluorescence. Component C3 (C fluorophore) which is usually identified as terrestrial-derived material, was found to be produced locally on the East Siberian Sea shelf and in the continental slope region of the Khatanga transect. Destruction of dead algae cells, production of marine biota and dissolved organic matter (DOM) reworking are considered as possible autochthonous FDOM sources in the Siberian shelf seas.
“…Because the depths of the euphotic zone and the upper mixed layer in Khatanga Bay were markedly lower than on the shelf, the average integral total Chl a concentrations under 1 m 2 in the layers were similar in both domains. Figure 3 Distribution of total chlorophyll a (total Chl a ) (according to Demidov et al., 2020 ) (a) and relative contribution of pico chlorophyll a (pico Chl a , %) (b) in the transect. Black dots: sampling depths.…”
Section: Resultsmentioning
confidence: 99%
“… Distribution of total chlorophyll a (total Chl a ) (according to Demidov et al., 2020 ) (a) and relative contribution of pico chlorophyll a (pico Chl a , %) (b) in the transect. Black dots: sampling depths.…”
The spatial variations of photosynthetic picoplankton abundance and biomass and the picoplankton's contribution to chlorophyll
a
concentration along the transect from Khatanga Bay to the continental slope in the western part of the Laptev Sea were studied in September 2017. Picoeukaryotes dominated in the picophytoplankton communities. Picophytoplankton in Khatanga Bay showed more variability than those over the Laptev shelf and continental slope: abundance and biomass were the highest in the southern part of the bay and markedly decreased with increasing salinity in its northern part. Picocyanobacteria were found over the shelf and slope at temperatures of +2.4 to -1.6°С and salinity from 22 to 34. Picophytoplankton contribution to total chlorophyll
a
on the shelf was higher than in Khatanga Bay. The study of picophytoplankton of Khatanga Bay and in the western Laptev Sea can serve as a baseline for future assessment of the Laptev Sea ecosystem response to interannual and climate changes.
The export of organic carbon from the surface to deep-sea layers, resulting from sedimentation of particulate organic matter, is one of the main processes of the global carbon cycle in the ocean and a key factor in regulating the level of CO 2 in the atmosphere (Archer et al., 2000;Siegenthaler et al., 2005). Recently, the processes of sedimentation of matter and the functioning of the "biological pump" in the Arctic have attracted great attention, since in this region the current climate changes are most pronounced (Walsh, 2008). The dynamics of the vertical flux of sedimentary matter and, to a lesser extent, its composition, have been studied in various marine ecosystems of the Arctic Basin over the past decades (
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