Abstract
Time-series sediment traps were deployed on the Chukchi Sea and East Siberian Sea slopes from August 2017 to August 2018 with the aim of elucidating the temporal and spatial variations in particle fluxes and identifying the main processes affecting those variations. Particle fluxes showed a typical seasonal pattern, with high values in summer and low values in other seasons, and a large inter-annual variation was observed only on the East Siberian Sea slope, where particle fluxes were one order of magnitude higher in early August 2018 than in late August 2017. This large inter-annual variation in particle flux resulted from the episodic intrusion of nutrient-enriched shelf water in the East Siberian Sea, which enhanced biological production at the surface and particle fluxes. The Chukchi Sea slope was influenced by the inflow of Anadyr Water, with high salinity and high nutrient concentrations, which had little annual variability. Therefore, particle flux showed little inter-annual variation on the Chukchi Sea slope. Under-ice phytoplankton blooms were observed in both the Chukchi Sea and East Siberian Sea slopes, and increases in particulate organic carbon (POC) flux and the C:N ratio under the sea ice were related to transparent exopolymer (TEP) production by ice algae. On the East Siberian Sea slope, particle fluxes increased slightly from 115 to 335 m, indicating lateral transport of suspended particulate matter; POC and lithogenic particles may be laterally transported to the slope as nutrient-rich shelf waters flowed from the East Siberian Sea to the Makarov Basin. Annual POC fluxes were 2.3 and 2.0 g C m–2 year–1 at 115 and 335 m, respectively, on the East Siberian Sea slope and was 2.1 g C m–2 year–1 at 325 m on the Chukchi Sea slope. Annual POC fluxes were higher on the Chukchi Sea and East Siberian Sea slopes than in Arctic basins, lower than on Arctic shelves, and generally similar to those on western Arctic slopes.
Highlights
In the Arctic Ocean, the extent of sea ice continues to decrease due to global warming, and it is predicted that ice-free conditions will occur during summer by 2040 (Rigor and Wallace, 2004; Müller-Karger et al, 2005; Serreze et al, 2007; Liu et al, 2013)
Particle fluxes at water depths of 115 and 335 m on the East Siberian Sea slope showed clear seasonal variations, with high values in summer and low values in other seasons (Figure 2)
particulate organic carbon (POC) flux ranged from n.d. to 83.3 mg m−2 day−1, and CaCO3 flux varied between n.d. and 19.0 mg m−2 day−1
Summary
In the Arctic Ocean, the extent of sea ice continues to decrease due to global warming, and it is predicted that ice-free conditions will occur during summer by 2040 (Rigor and Wallace, 2004; Müller-Karger et al, 2005; Serreze et al, 2007; Liu et al, 2013). The rapid decrease in sea-ice cover has lengthened the growing season in the Arctic Ocean, resulting in a marked increase in primary production (Sakshaug, 2004; Arrigo et al, 2008; Pabi et al, 2008; Brown and Arrigo, 2012). A rapid decrease in sea-ice cover has both positive and negative effects on primary production in the Arctic Ocean. Changes in primary production in the Arctic Ocean lead to variations in the biological pump, which is regarded as a long-term regulatory mechanism for climate change through control of atmospheric CO2 (Falkowski et al, 1998). Long-term monitoring of POC fluxes in the Arctic Ocean is essential to elucidating changes in the biological pump due to the decline in sea-ice cover
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