Abstract The Western Antarctic Peninsula (WAP) has experienced significant changes in seawater temperature over the past 50?years. This warming affects seawater and sea ice microbial cycling of organic matter, where viral features could play a crucial role in sympagic sea ice melting environments. However, there is a lack of information about the sea ice viral abundances and processes (e.g. lysis rates and carbon release from microorganisms). To gain knowledge of sea ice viral, microbial, and chemical characteristics, we collected four different sea ice samples and their surrounding surface seawater during the Austral summer of 2019 north of the WAP. In each sample, we assessed viral and microbial abundances and environmental parameters. In the sea ice, we also measured viral-driven mortality rates on prokaryotes and protists and the consequent release of organic carbon. The viral and microorganism abundances in the sea ice were higher (4.5?±?1.9?×?106 viruses mL?1; 1.5?±?0.7?×?106 prokaryotes mL?1, 9.4?±?5.0?×?102 protists mL?1) than in the surrounding surface seawater (1.7?×?106 viruses mL?1, 0.4?×?106 prokaryotes mL?1, 7.1?×?102 protists mL?1). Furthermore, viral lytic production on prokaryotes (4.5?±?0.8?×?105?mL?1day?1) and protists (1.9?±?1.0?×?104?mL?1 day?1) in sympagic environments had a higher viral impact on carbon release by protist (1.5?±?1.1 μg C L?1 day?1) than by prokaryotes (0.3?±?0.1 μg C L?1 day?1). Our results suggest that, after sea ice melting, viral abundances and activities may influence the functioning of the microbial food web by increasing the release of dissolved organic matter, affecting biogeochemical cycles and microbial communities in the underlying surface waters.
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