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

Abstract

Climate warming is transforming arctic and subarctic ecosystems by a reduction in the duration, extent, and thickness of sea ice (Parkinson et al., 1999;Walsh et al., 2017)-a key variable of the global climate system whose disappearance is resulting in a positive temperature feedback from a reduction of the surface albedo (Pistone et al., 2014). Rapidly melting glaciers and increased riverine runoff resulting from thawing permafrost and augmented precipitation over the adjacent continents are expected to decrease sea-surface salinities, for example, by about 1.5 ± 1.1 psu on average in the Arctic Ocean (Shu et al., 2018). As a consequence, the fresher, less dense water masses are expected to enhance vertical water-column stratification, which could result in a reduced supply of nutrients to the euphotic zone (Tremblay & Gagnon, 2009). On top of the regionally expected loss of sea ice-associated organisms, such a scenario could potentially affect the distribution, composition, and diversity of primary producers which are limited by the availability of nutrients, amongst others, with unknown consequences for food-web structure, biochemical cycles, and the biological carbon pump (Coupel et al., 2015;Li et al., 2009). The subarctic northwest (NW) Pacific and its adjacent seas have experienced pronounced environmental changes since the Last Glacial Maximum (LGM). The variability of previously reconstructed sea-surface temperatures and sea-ice coverage has been connected to the millennial-scale climatic changes recorded in sediment cores from the North Atlantic and in Greenland ice cores (Max et al., 2012a;Méheust et al., 2016).

Tracking mineral and geochemical characteristics of Holocene lake sediments: the case of Hotagen, west-central Sweden

“…The similarity in the categorization of the sediments strongly suggests that the mineral and organic evolution occurred conjointly as a result of ecosystem development that had occurred in the late glaciation, deglaciation, and post-glaciation periods. Indeed, natural environmental changes that occurred during these periods can lead to such changes (e.g., Snowball et al 2002;Voldstad et al 2020;Zimmermann et al 2021).…”

“…6d). This OM might have been preserved in ice-sheets, possibly in interglacial soils that deposited during deglaciation and post-glaciation, or might have come from organisms that formed during the Late Pleistocene (late glaciation or deglaciation periods) or Early Holocene (e.g., Zale et al 2018;Zimmermann et al 2021). Indeed, it was shown that vegetation was able to penetrate thin ice sheets during Late glaciation 14,000-11,000 years ago (Kullman 2002).…”

“…However, the OM IR peak at 2960 cm −1 was only detected in the till, and not in the other sediments. This suggests that the unique OM IR band belongs to material(s) that was stored in ice-sheets that thawed in the vicinity of lake Hotagen, was present pre-deglaciation and discontinued post-glaciation (e.g., Clarke et al 2019;Zimmermann et al 2021), or originated from another watershed (e.g., Sadori 2013). Radiocarbon dating, organic identification, pollen records, and sedimentary ancient DNA can give more information in this regard (e.g., Öberg and Kullman 2011;Swärd et al 2018).…”

“…The last glacial period in the northern hemisphere ended approximately 10,000 years ago. Subsequently, ecosystem evolution prevailed during the late glaciation, deglaciation, and post-glaciation periods (e.g., Gibbard and Van Kolfschoten 2004;Öberg and Kullman 2011;Zimmermann et al 2021). These changes are chronologically stored in undisturbed (intact) lacustrine sediments.…”

“…These changes are chronologically stored in undisturbed (intact) lacustrine sediments. The developments of the ecosystem during those periods have been recently recorded through sedimentary ancient DNA (sedaDNA) and organic proxies (e.g., Snowball et al 2002;Zale et al 2018;Zimmermann et al 2021). Nonetheless, the mineral and geochemical composition of sediments that accompanied ecosystem development in Sweden, especially during the deglaciation and post-glacial periods, have not been reported.…”