Towards an improved organic carbon budget for the western Barents Sea shelf

Abstract

Abstract. There is generally a lack of knowledge on how marine organic carbon accumulation is linked to vertical export and primary productivity patterns in the Arctic Ocean. Despite the fact that annual primary production in the Arctic has increased as a consequence of shrinking sea ice, its effect on flux, preservation, and accumulation of organic carbon is still not well understood. In this study, a multi-proxy geochemical and organic-sedimentological approach is coupled with organic facies modelling, focusing on regional calculations of carbon cycling and carbon burial on the western Barents Shelf between northern Scandinavia and Svalbard. OF-Mod 3-D, an organic facies modelling software tool, is used to reconstruct and quantify the marine and terrestrial organic carbon fractions and to make inferences about marine primary productivity changes across the marginal ice zone (MIZ). By calibrating the model against an extensive set of sediment surface samples, we improve the Holocene organic carbon budget for ice-free and seasonally ice-covered areas in the western Barents Sea. The results show that higher organic carbon accumulation rates in the MIZ are best explained by enhanced surface water productivity compared to ice-free regions, implying that shrinking sea ice may reveal a significant effect on the overall organic carbon storage capacity of the western Barents Sea shelf.

Middle to late Holocene paleoproductivity reconstructions for the western Barents Sea: a model-data comparison

“…1) used here on the core data accounts for carbon flux through the water column and processes affecting burial in the sediments (see [28,35,40] for details on the equations).…”

“…Knies and Martinez [29] showed that the marine nitrogen endmember is represented by its organic fraction, i.e. %N org (of total) = 100 %, and a linear regression analysis of %N org and d 13 C org gives a marine d 13 C org endmember of -20.1 % at 100 % N org [29,40]. We interpret these endmembers (from the surface sample data set) as representative for the Barents Sea and use them to calculate the terrestrial (TOM) and marine (MOC) organic carbon fractions and to calibrate the organic facies model.…”

“…Marine organic carbon (MOC) and terrestrial organic matter (TOM) were distinguished in Barents Sea sediments using a mixing model based on total organic carbon (TOC), nitrogen content, and stable isotopes of organic matter (d 13 C org ) [29,40,76] to define the endmembers of the mixing model. For the purposes of this paper, the set of Barents Sea surface samples of Knies and Martinez [29] is used as the calibration data set and the endmembers determined therein are used here.…”

“…The Fig. 1 Map of the study area with surface circulation (red Atlantic Water (AW), blue Arctic Water (ArW)), Polar Front (after [32]), maximum winter ice extent for the past 250 years [40], modeled area (dash dot) and sample locations indicated Arktos (2015) 1:20 Page 3 of 17 20 northern part of the study region is partially covered by sea ice in the winter. Melting of the ice in spring and summer together with increased insolation and heat leads to a stratified water column in this marginal ice zone (MIZ) that induces a phytoplankton bloom that follows the receding ice edge northward [51].…”

“…Figure 1 and all following maps also show the maximum southernmost ice extent in the western Barents Sea over the last 250 years to distinguish between the ice-influenced northern and ice-free southern part of the study region. The ice edge is defined as the outer boundary for 30 % ice concentration based on Divine and Dick [9] (see [40], for details).…”