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

Abstract

In this study we focus on late Holocene primary productivity (PP) variability in the western Barents Sea and its response to variable sea ice coverage by combining PP reconstructed from several sediment cores with regional PP trends simulated with a well-constrained organic facies model, OF-Mod 3D. We find that modern production rates reconstructed from buried marine organic matter (''bottomup'') resemble simulated export production at 50 m water depth inferred from numerical simulations of surface water PP in a 3D ocean model, SINMOD (''top-down''). Paleoproductivity rates in the northern Barents Sea are more variable and generally higher (30-150 gC m -2 year -1 ) than in the SW Barents Sea region (\75 gC m -2 year -1 ) throughout the last 6000 years BP. In the SW Barents Sea, PP rates and terrestrial organic matter (TOM) supply remain constantly low indicating present-day-like oceanographic conditions with only marginal influence of sea ice related processes during the last 6000 years BP. PP rates in the northern Barents Sea indicate a shift from stable modern-like conditions prior to 2800 BP to denser, more permanent sea ice coverage along the marginal ice zone (MIZ) between 2800 and 1000 years BP and low PP rates. PP rates increase around 1000 years BP indicating a northward shift of the MIZ and accelerated export towards the seabed. During the last 500 years a pronounced decline in PP rates towards the present day indicates reduced annual duration of the MIZ in the area due to global warming. Our results suggest that a combination of first-year ice and higher PP in a warming pan-Arctic may point to a potential Arctic carbon sink while sea ice is still present.

The last two millennia: climate, ocean circulation and palaeoproductivity inferred from planktic foraminifera, south-western Svalbard margin

“…At 1400-ca. 1500 AD, the moderate to high flux of planktic foraminifera agrees with the high surface productivity recorded by a high flux of cold-water dinocyst assemblages in core JM06-04MC from the western Svalbard margin (Bonnet et al 2010), but contrasts with a decrease in primary productivity around 1450 AD in the nearby core St20 from the Kveithola Trough on the shelf (Pathirana et al 2015; Fig. 1; Supplementary Table S1).…”

“…They found these intervals to correlate with pronounced changes in the planktic foraminiferal fauna compositions and low planktic foraminiferal flux. The low subsurface and near-surface to surface productivity at Storfjorden Fan during the cold period at 400-900 AD correspond to low primary productivity and low content of phytoplankton biomarkers recorded in northern Storfjorden in core JM10-010GC (Pathirana et al 2015;Knies et al 2017), and low concentrations of benthic foraminifera (Rasmussen & Thomsen 2015;Fig. 7a, f;Supplementary Table S1).…”

“…The interval is referred to as the first half of the Little Ice Age (Bonnet et al 2010;Pathirana et al 2015). We speculate that the differences in productivity between the St20 and our site were caused by a highly fluctuating sea-ice margin, with strong seasonal gradients and intense melting at the sea-ice edge due to influence of the warm Atlantic Water, as is observed in the western Barents Sea (e.g., Pathirana et al 2015). The minimum productivity, but relatively warm surface conditions at ca.…”

“…The two water masses The flow of warm Atlantic Water via the WSC into the Arctic Ocean is considered a major controlling factor of climate and the location of the sea-ice margin and therefore of the surface water productivity in Fram Strait (e.g., Walczowski & Piechura 2011;Beszczynska-Möller et al 2012;Walczowski et al 2017). Numerous studies have examined changes in circulation, productivity and properties of the Atlantic Water in the Nordic seas during the Holocene and the past glacial period (e.g., Rasmussen et al 2003;Ellingsen et al 2008;Müller et al 2012;Pathirana et al 2015;Hoff et al 2016;Berben et al 2017). As only a few high-resolution studies in the Arctic areas have been undertaken (Wollenburg et al 2004;Majewski et al 2009;Spielhagen et al 2011;Werner et al 2011;Pawłowska et al 2016), knowledge regarding the natural variability in ocean surface conditions and surface productivity for the last two millennia before the last 150 years is still scarce.…”

“…As only a few high-resolution studies in the Arctic areas have been undertaken (Wollenburg et al 2004;Majewski et al 2009;Spielhagen et al 2011;Werner et al 2011;Pawłowska et al 2016), knowledge regarding the natural variability in ocean surface conditions and surface productivity for the last two millennia before the last 150 years is still scarce. Variations in the inflow of warm Atlantic Water, its mixing with cold Polar Water and the resulting changes in productivity were probably controlled by natural climate anomalies before human impact became a dominant factor (e.g., Spielhagen et al 2011;Pathirana et al 2015;Pawłowska et al 2016).…”