Warming substantially amplifies Antarctic coastal polynyas as key carbon sinks

[Geoengineering News]

‎https://www.pnas.org/doi/10.1073/pnas.2511585122

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‎Authors: 

Chengzhen Zhou, Maodian Liu, Brad E. Rosenheim, Thomas S. Bianchi, Nikki H. Zhang, Xingrui Cai, Qianru Zhang, and Xuejun Wang

08 December 2025

https://doi.org/10.1073/pnas.2511585122

Significance

Antarctic coastal polynyas, small open-water areas within sea ice, are revealed in this study to be unexpectedly powerful carbon sinks. Despite covering just ~3% of the Southern Ocean, they bury 42% of its organic carbon, making them the region’s most efficient carbon sequestration hotspots. Importantly, warming over the past 12 kyr amplifies this process ninefold by extending ice-free seasons, boosting phytoplankton growth, and accelerating carbon export to the seafloor. This counterintuitive finding reveals a natural brake on climate change: As global warming progresses, these polar carbon sinks grow stronger, partially offsetting rising CO2. This work transforms understanding of the Southern Ocean’s role in the global carbon cycle and highlights the need to incorporate these dynamics into climate models and policy.

Abstract

The Southern Ocean plays an important role in the global carbon cycle by absorbing atmospheric CO2, aiding climate change mitigation. Antarctic coastal polynyas (ACPs) are key CO2 uptake areas, yet whether this CO2 is effectively sequestered as organic carbon (OC) in marine sediments, and the spatiotemporal dynamics and drivers of this process, remains unclear. Here, we reconstruct a high-resolution record of Holocene (~12,000 y BP) to present-day OC accumulation fluxes and sources in ACP sediments using existing data as well as our measurements. We find that despite covering only 3% of the Southern Ocean, ACPs account for approximately 42% of the modern OC accumulation across the Southern Ocean. Since the Holocene, OC accumulation has increased ninefold due to climate warming, largely driven by marine primary production. Structural equation modeling reveals that warming enhances the biological carbon pump and OC accumulation efficiency by expanding and prolonging open water areas in ACPs, with larger ACPs showing stronger feedback. Furthermore, basal melt from ice shelves releases fine particulate matter, further boosting OC accumulation. Our findings highlight that climate warming has greatly amplified ACPs’ carbon-sequestration efficiency, making them rapidly expanding and crucial carbon sinks in the Southern Ocean, with the potential to provide strong negative feedback in future climate change.

Source: PNAS