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

Abstract

With ongoing climate change, research into the biological changes occurring in particularly vulnerable ecosystems, such as Antarctica, is critical. The Totten Glacier region, Sabrina Coast, is currently experiencing some of the highest rates of thinning across all East Antarctica. An assessment of the microscopic organisms supporting the ecosystem of the marginal sea-ice zone over the continental rise is important, yet there is a lack of knowledge about the diversity and distribution of these organisms throughout the water column, and their occurrence and/or preservation in the underlying sediments. Here, we provide a taxonomic overview of the modern and ancient marine bacterial and eukaryotic communities of the Totten Glacier region, using a combination of 16S and 18S rRNA amplicon sequencing (modern DNA) and shotgun metagenomics (sedimentary ancient DNA, sedaDNA). Our data show considerable differences between eukaryote and bacterial signals in the water column versus the sediments. Proteobacteria and diatoms dominate the bacterial and eukaryote composition in the upper water column, while diatoms, dinoflagellates, and haptophytes notably decrease in relative abundance with increasing water depth. Little diatom sedaDNA is preserved in the sediments, which are instead dominated by Proteobacteria and Retaria. We compare the diatom microfossil and sedaDNA record and link the weak preservation of diatom sedaDNA to DNA degradation while sinking through the water column to the seafloor. This study provides the first assessment of DNA transfer from ocean waters to sediments and an overview of the microscopic communities occurring in the climatically important Totten Glacier region.Plain Language Summary Antarctica is highly vulnerable to climate change and research into how marine organisms around the continent will respond to warming conditions is important. Microscopic organism, such as bacteria and phytoplankton, are key in the marine ecosystems because they support the entire marine food web. In this study, we investigated the composition of these microorganisms in the climatically important East Antarctic Totten Glacier region. We profiled compositional changes throughout the water column and into underlying subseafloor sediments, which provided information on both actively living and long dead organisms, and thus modern and past environmental conditions, respectively. We used genetic techniques to compare these marine communities, focusing on the taxonomically informative small subunit ribosomal ribonucleic acid (SSU rRNA) gene. Our study provides an overview about the microorganisms that live in the modern ocean in the Totten Glacier region, and how well their genetic signatures preserve in the underlying sediments. This knowledge is important both for assessments of presentday marine ecosystem health and functioning, and when reconstructing past ocean environments as analogs to ongoing climate change.