Multiproxy evidence of the Neoglacial expansion of Atlantic Water to eastern Svalbard

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.

Sedimentary Ancient DNA From the Subarctic North Pacific: How Sea Ice, Salinity, and Insolation Dynamics Have Shaped Diatom Composition and Richness Over the Past 20,000 Years

“…When we know more about the biogeography and environmental preferences of these variants (e.g., nutrient limitation, temperature constraints), their presence in sedaDNA records could help to reconstruct past seasonal environmental conditions. This is supported by a recent study in which ASVs of the foraminifer N. pachyderma were traced in a 140,000-year spanning sedaDNA record and correlated with oceanographic changes (Pawłowska, Łącka, et al, 2020;Pawłowska, Wollenburg, et al, 2020). This is further proof of the potential of sedaDNA to trace responses of microbial eukaryotes to environmental changes on population level (Pawłowska, Łącka, et al, 2020;Pawłowska, Wollenburg, et al, 2020).…”

“…This is supported by a recent study in which ASVs of the foraminifer N. pachyderma were traced in a 140,000-year spanning sedaDNA record and correlated with oceanographic changes (Pawłowska, Łącka, et al, 2020;Pawłowska, Wollenburg, et al, 2020). This is further proof of the potential of sedaDNA to trace responses of microbial eukaryotes to environmental changes on population level (Pawłowska, Łącka, et al, 2020;Pawłowska, Wollenburg, et al, 2020).…”

“…In this regard, the analysis of sedaD-NA is an advantage. Recently, sedaDNA was used as a proxy for sea-ice reconstructions by targeting diatom sedaDNA composition in Fram Strait (Zimmermann et al, 2019), for tracing a sea-ice dinoflagellate east of Greenland (De Schepper et al, 2019) and to identify changes of ocean circulation patterns by targeting diatoms and non-fossilized foraminifers east of Svalbard (Pawłowska, Łącka, et al, 2020). Ancient DNA has profound advantages.…”

The maturing relationship between Quaternary paleoecology and ancient sedimentary DNA

“…For example, Palowska et al . (2020) use diatom DNA in a reconstruction of the history of Stjorfjorden (Svalbard), a critical site for deep-water production, and Giosan et al . (2018) similarly track changes in the planktonic composition of the water column for an Indian Ocean core in a reconstruction of winter monsoon dynamics.…”

Changes in the composition of marine and sea-ice diatoms derived from sedimentary ancient DNA of the eastern Fram Strait over the past 30 000 years

“…The marine environment is a complex ecosystem in which the distribution of organisms is controlled significantly by abiotic constraints such as sea-surface temperatures (SSTs), salinity, nutrient distribution, light conditions, and sea-ice cover (Cherkasheva et al, 2014;Ibarbalz et al, 2019;Nöthig et al, 2015;Pierella Karlusich et al, 2020). Over the past 30 000 years the subarctic North Atlantic Ocean has been subject to frequent sea-ice expansions and contractions (Müller et al, 2009;Müller and Stein, 2014;Syring et al, 2020;Werner et al, 2013), which are expected to have affected the composition of the regional species pool.…”