Work by George Mason University post-doc Mingsong Li (now at Penn State University), his advisor AOES faculty member Linda Hinnov, and international collaborators, has been published in Nature Communications (Li et al, 2018) and received notice in AAAS Eureka Alert, ScienceDaily and elsewhere.
Today there is great concern that global warming will melt Greenland and Antarctic icecaps and the resulting meltwater will raise sea level, inundating coastal cities. Geological evidence shows that over the past million years, sea level rose and fell several times by over 100 m due to changes between ice ages and warmer climates such as we have had for the last 10,000 years.
Back in the Triassic Period (250 – 200 million years ago), sea level also oscillated by about 100 m at million-year timescales. At that time, however, the Earth was much warmer than today and there were no ice caps to affect sea level. What was responsible for the Triassic sea level changes if it wasn’t the ice?
Groundwater is another reservoir which can potentially hold a large volume. By analyzing sedimentary records, Li, Hinnov, and collaborators were able to find evidence that sea level and groundwater formed a kind of seesaw, in which rises in sea level occurred during reductions in groundwater and sea level falls occurred when groundwater was expanding. They argue that in considering how sea level will behave in the future, groundwater may play a larger role than previously thought.