Abstract
Abstract. The main goal of this study is to reconstruct the paleoceanographic development of Storfjorden during the Neoglacial (∼4 cal ka BP). Storfjorden is one of the most important brine factories in the European Arctic and is responsible for deepwater production. Moreover, it is a climate-sensitive area influenced by two contrasting water masses: warm and saline Atlantic Water (AW) and cold and fresh Arctic Water (ArW). Herein, a multiproxy approach was applied to provide evidence for existing interactions between the inflow of AW and sea ice coverage, which are the major drivers of environmental changes in Storfjorden. The sedimentary and microfossil records indicate that a major reorganization of oceanographic conditions in Storfjorden occurred at ∼2.7 cal ka BP. The cold conditions and the less pronounced presence of AW in Storfjorden during the early phase of the Neoglacial were the prerequisite conditions for the formation of extensive sea ice cover. The period after ∼2.7 cal ka BP was characterized by alternating short-term cooling and warming intervals. Warming was associated with pulsed inflows of AW and sea ice melting that stimulated phytoplankton blooms and organic matter supply to the bottom. The cold phases were characterized by heavy and densely packed sea ice, resulting in decreased productivity. The ancient environmental DNA (aDNA) records of foraminifera and diatoms support the occurrence of the major pulses of AW (∼2.3 and ∼1.7 cal ka BP) and the variations in sea ice cover. The episodes of enhanced AW inflow were marked by an increase in the percentage of DNA sequences of monothalamous foraminifera associated with the presence of fresh phytodetritus. Cold and less productive intervals were marked by an increased proportion of monothalamous taxa known only from environmental sequencing. The diatom aDNA record indicates that primary production was continuous during the Neoglacial, regardless of the sea ice conditions. However, the colder periods were characterized by the presence of diatom taxa associated with sea ice, whereas the present-day diatom assemblage is dominated by open-water taxa.
Highlights
The northward flow of Atlantic Water (AW) is one of the major contributors of heat to the Arctic Ocean (Polyakov et al, 2017)
Six radiocarbon dates were obtained, all of which were recorded in chronological order
Prior to ∼ 2.7 cal ka BP, the ST_1.5 sedimentary record displayed relatively higher ice-rafted debris (IRD) delivery and a relatively lower 0–63 μm sediment fraction than in the following period (Fig. 4). These results are in agreement with the record from Storfjordrenna (Łacka et al, 2015), where peaks in IRD were noted during the Neoglacial and were attributed to increased iceberg rafting due to fluctuations in the glacial fronts (e.g., Forwick et al, 2010).The coarser 0–63 μm fraction may suggest the winnowing of fine-grained sediment; foraminiferal fauna showed no clear response to sediment removal
Summary
The northward flow of Atlantic Water (AW) is one of the major contributors of heat to the Arctic Ocean (Polyakov et al, 2017). A distinct cooling and freshening of the west Spitsbergen shelf bottom-water masses occurred during the middle to late Holocene (6.8–1 cal ka BP) and were accompanied by glacier readvances in Svalbard, leading to the present-day conditions (Slubowska-Woldengen et al, 2007; Telesinski et al, 2018). The paleoceanographic conditions in the Svalbard margins correlate closely with the sea surface temperature (SST) variations in the Nordic Seas and confirm that the Svalbard area is highly sensitive to fluctuations in the inflow of AW (Slubowska-Woldengen et al, 2007; Werner et al, 2013). Until the 1990s eastern Svalbard was recognized as an area exclusively influenced by the East Spitsbergen Current (ESC), which carries cold, less saline
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