Sea Ice Dynamics Drive Benthic Microbial Communities in McMurdo Sound, Antarctica.

Ashleigh A Currie,Vonda J Cummings,S Craig Cary,Sarah Seabrook,Alexis J Marshall,Andrew M Lohrer

doi:10.3389/fmicb.2021.745915

Abstract

Climate change is driving dramatic variability in sea ice dynamics, a key driver in polar marine ecosystems. Projected changes in Antarctica suggest that regional warming will force dramatic shifts in sea ice thickness and persistence, altering sea ice-associated primary production and deposition to the seafloor. To improve our understanding of the impacts of sea ice change on benthic ecosystems, we directly compared the benthic microbial communities underlying first-year sea ice (FYI) and multi-year sea ice (MYI). Using two tractable coastal habitats in McMurdo Sound, Antarctica, where FYI (Cape Evans) and MYI (New Harbour) prevail, we show that the structure and composition of the benthic microbial communities reflect the legacy of sea ice dynamics. At Cape Evans, an enrichment of known heterotrophic algal polysaccharide degrading taxa (e.g., Flavobacteriaceae, unclassified Gammaproteobacteria, and Rubritaleaceae) and sulfate-reducing bacteria (e.g., Desulfocapsaceae) correlated with comparatively higher chlorophyll a (14.2±0.8μgg−1) and total organic carbon content (0.33%±0.04), reflecting increased productivity and seafloor deposition beneath FYI. Conversely, at New Harbour, an enrichment of known archaeal (e.g., Nitrosopumilaceae) and bacterial (e.g., Woeseiaceae and Nitrospiraceae) chemoautotrophs was common in sediments with considerably lower chlorophyll a (1.0±0.24μgg−1) and total organic carbon content (0.17%±0.01), reflecting restricted productivity beneath MYI. We also report evidence of a submarine discharge of sub-permafrost brine from Taylor Valley into New Harbour. By comparing our two study sites, we show that under current climate-warming scenarios, changes to sea ice productivity and seafloor deposition are likely to initiate major shifts in benthic microbial communities, with heterotrophic organic matter degradation processes becoming increasingly important. This study provides the first assessment of how legacy sea ice conditions influence benthic microbial communities in Antarctica, contributing insight into sea ice–benthic coupling and ecosystem functioning in a polar environment.

Highlights

High-latitude polar oceans are covered in an extensive layer of sea ice, which grows and shrinks throughout seasonal cycles
Due to the proximity of the New Harbour sampling site to the Taylor Valley, it was important that we demonstrate that wind-blown terrestrial inputs were not influencing the marine sediment microbiomes so we could be confident that any differences between Cape Evans and New Harbour microbial communities would be in relation to the impact of local first-year sea ice (FYI) and multi-year sea ice (MYI) conditions
We show that there is a strong association between the legacy of sea ice dynamics and benthic microbial community structure and composition

Summary

Introduction

High-latitude polar oceans are covered in an extensive layer of sea ice, which grows and shrinks throughout seasonal cycles. Covering 3–6% of Earth’s surface area (Comiso, 2003), the high albedo of sea ice and snow cover reflects large fractions of incoming solar radiation, playing a crucial role in regulating Earth’s global climate system (Hall, 2004). Recent climate models have estimated that within the Arctic, an ice-free summer is likely to occur before the end of this century (Overland and Wang, 2013; Notz and Stroeve, 2018). Current climate models predict that substantial continental scale losses of sea ice will occur in the Antarctic before the end of this century (Bracegirdle et al, 2008; Collins et al, 2013; Smith et al, 2014)

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