Fig. 1: Map showing location of Marion Island and study site.

a Map showing location of Marion Island and the core belt of the Southern Hemisphere westerly winds. Arrows mark the direction of surface winds (see also Supplementary Fig. 3). Shaded annual sea surface-level (10 m) mean wind speeds are based on NOAA blended high resolution (0.25 degree grid) vector data downloaded from (https://www.ncdc.noaa.gov/data-access/marineocean-data/blended-global/blended-sea-winds), b the location of the lake coring site at La Grange Kop on Marion Island (satellite imagery courtesy of NASA Visible Earth, https://visibleearth.nasa.gov/). Numbered sites indicate places referred to in the text: (I) Verlorenvlei, in the winter rainfall zone (WRZ) of South Africa50, (II) Îles Kerguelen, (III) West Antarctic Ice Sheet (WAIS68).