Summary
Sea ice is a critical but poorly understood component of Earth’s climate system. A rapid decline in Arctic sea ice over recent decades has been documented using historical ship charts and satellite images. However, almost nothing is known about the behaviour of sea ice around Antarctica before routine satellite monitoring began, and proxy reconstructions of Antarctica’s sea ice history are urgently needed to improve predictions of how Antarctic sea ice will respond to, and influence, future global climate change. Ice cores from the Antarctic continent provide a potentially powerful archive for reconstructing sea ice changes. Our research uses an array of high-resolution ice core records from near-coastal sites around Antarctica, examining changes in the concentration of methanesulphonic acid (MSA) – a chemical species derived from plankton found at the sea ice margin. Using this network of MSA records we are able to develop an understanding of which ice core sites are most suited to provide reliable reconstructions of sea ice. This new network of ice core MSA records also suggests that there have been substantial regional differences in the variability and timing of sea ice decline around Antarctica during the 20th century. Comparison with sparse historical whaling records and sea ice charts supports these regional differences, suggesting that networks of ice core MSA records have the potential to improve our understanding of the characteristics and drivers of past sea ice changes around Antarctica.