Tracking seasonal changes in sea ice over millennia can give scientists a better understanding of just how much variation is natural, as well as how these yearly variations interact with long-term climate patterns. Although annual fields of reflective ice are carefully monitored today, it is difficult to accurately discern the extent of summer or winter sea ice from times before satellite imagery. Therefore, the question remains, How can scientists follow these data back tens of thousands of years?
In a new study, Winski et al. track sea salt levels in the South Pole Ice Core to follow sea ice patterns over more than 11,000 years. According to a chemical transport model, storms carry sea salt from sea ice inland to the core’s location. Although most of the sea ice itself melts away each year, the core’s chemical profiles can indicate how much sea ice existed from season to season across an entire epoch.
The researchers discovered an increase in wintertime sea ice between 8,000 and 10,000 years ago, followed by an abrupt decrease 5,000 to 6,000 years ago. The sudden decrease, concentrated in the South Atlantic region, accompanied an increase in sea ice in the Northern Hemisphere. According to the authors, this moment likely marks a change in sea currents affecting local and global climate.
Changes in sea ice can lead to rapid climate change, which affects the entire planet. This study fills in the details on this ephemeral, but vital, indicator, the authors say. (Geophysical Research Letters, https://doi.org/10.1029/2020GL091602, 2021)
—Elizabeth Thompson, Science Writer