Editorial: Sea ice in the polar regions

This special volume highlights advances in sea-ice reconstruction and reflects the efforts of two PAGES working groups: Arctic Cryosphere Change and Coastal Marine Ecosystems (ACME; pastglobalchanges.org/acme) and Cycles of Sea-Ice Dynamics in the Earth System (C-SIDE; pastglobalchanges.org/c-side). This joint effort recognizes the large-scale and rapid changes happening in the high latitude oceans, where changes in sea-ice extent are central to a wide range of cascading and interconnected impacts. Both working groups address paleo sea-ice reconstruction as a tool for understanding broad ecosystem changes that have occurred in the past. This research provides a longer-term perspective on modern changes, and these data can be used to constrain models used to understand today's evolving cryosphere. Our articles are dedicated to overviewing the proxies we have to reconstruct past sea-ice conditions, their different use between the Northern and Southern hemispheres, and across different timescales.