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

Abstract

Abstract. The Fram Strait is an area with a relatively low and irregular distribution of diatom microfossils in surface sediments, and thus microfossil records are scarce, rarely exceed the Holocene, and contain sparse information about past richness and taxonomic composition. These attributes make the Fram Strait an ideal study site to test the utility of sedimentary ancient DNA (sedaDNA) metabarcoding. Amplifying a short, partial rbcL marker from samples of sediment core MSM05/5-712-2 resulted in 95.7 % of our sequences being assigned to diatoms across 18 different families, with 38.6 % of them being resolved to species and 25.8 % to genus level. Independent replicates show a high similarity of PCR products, especially in the oldest samples. Diatom sedaDNA richness is highest in the Late Weichselian and lowest in Mid- and Late Holocene samples. Taxonomic composition is dominated by cold-water and sea-ice-associated diatoms and suggests several reorganisations – after the Last Glacial Maximum, after the Younger Dryas, and after the Early and after the Mid-Holocene. Different sequences assigned to, amongst others, Chaetoceros socialis indicate the detectability of intra-specific diversity using sedaDNA. We detect no clear pattern between our diatom sedaDNA record and the previously published IP25 record of this core, although proportions of pennate diatoms increase with higher IP25 concentrations and proportions of Nitzschia cf. frigida exceeding 2 % of the assemblage point towards past sea-ice presence.

Sedimentary ancient DNA (sedaDNA) as a new paleo proxy to investigate organismal responses to past environmental changes in Antarctica

“…In the Antarctic sea-ice environment, such organisms of interest may, for example, include various fragile diatoms that could be useful as sea-ice proxies (e.g. highly branched isoprenoid producing species; Zimmermann et al 2020) or other primary producers, such as chlorophytes and non-cyst forming/fragile dinoflagellates (De Schepper et al 2019). Antarctic krill are also highly abundant in sea-ice environments, though they are currently experiencing hardship due to ocean acidification, warming, and overfishing (Flores et al 2012).…”

From the Surface Ocean to the Seafloor: Linking Modern and Paleo‐Genetics at the Sabrina Coast, East Antarctica (IN2017_V01)

“…It is thought that sed aDNA is best preserved in organic‐rich, non‐UV exposed, anoxic, and cold environments (Armbrecht et al., 2019; Capo et al., 2022), hence, polar, deep ocean sediments are particularly suitable for sed aDNA‐based paleo‐ecosystem studies. Indeed, eukaryote sed aDNA has been recovered from up to ∼140,000‐year‐old sediments in the Arctic (De Schepper et al., 2019; Pawłowska et al., 2020; Zimmermann et al., 2020) and ∼1 million‐year‐old sediments in the Antarctic (Armbrecht et al., 2022). However, even in “ideal” cold and low‐oxygen conditions, genetic information is lost throughout the water column, for example, by postmortem DNA fragmentation, degradation, uptake of DNA by living organisms, and virus/bacteriophage activity (e.g., Corinaldesi et al., 2007; Thomsen & Willerslev, 2015; Wei et al., 2022).…”

Ancient marine sediment DNA reveals diatom transition in Antarctica

“…In polar marine ecosystems, eukaryote sed aDNA has been recovered from up to ~140,000-year-old sediments in the Arctic 14 – 16 and <25,000-year-old sediments in the Antarctic 7 . Deep polar marine environments are ideal locations for sed aDNA research because of favourable DNA preservation 14 , 15 . They feature constantly low temperatures (~0 °C) and low oxygen (~5 mL L −1 ), and UV radiation is absent 17 – 19 .…”