Enhanced Microbial Respiration in the Open Melt Pond in the Arctic Ocean and its Implications for Carbon Cycles

Abstract

Sea ice melting driven by climate change-induced warming is continuously increasing in the Arctic Ocean. Although heterotrophic microbes play a pivotal role in biogeochemical processes, the impact of heterotrophic microbial respiration (HMR) on biogeochemical carbon cycles associated with the expansion of melt pond (MP) in the Arctic Ocean is understudied. We investigated variations of HMR across three distinct MP types (i.e., open MP, brackish MP, and closed MP) in the western Arctic Ocean. HMR was significantly higher in open MP (12.2±5.64 mmol O2 m？3 day？1) compared to closed MP (2.25±1.96 mmol O2 m？3 day？1), brackish MP (2.87±2.28 mmol O2 m？3 day？1), and ambient seawater (4.88±1.92 mmol O2 m？3 day？1). A strong correlation between dissolved organic carbon (DOC) and HMR suggests that sea-ice-derived DOC enhances heterotrophic microbial metabolism in open MPs. The prokaryotes carbon demand (27.8±26.8 mmol C m？3 day？1) required to sustain prokaryotes metabolism was greater than the organic carbon produced through primary production (PP; 0.05±0.02 mmol C m？3 day？1), suggesting that the remineralization of organic carbon supplied from the sea-ice communities to CO2 exceeds carbon fixation through PP. The high CO2 production in the open MPs (2.35 Tg C day？1), which is 20 times greater than the CO2 uptake by the MPs (0.12 Tg C day？1), suggests that warming-induced expansion of MPs stimulates microbial metabolisms, thereby serving as a positive CO2 feedback to the atmosphere. Our results provide new insights into carbon cycling driven by microbial responses to MP expansion under Arctic warming.