Department Seminar: Branwen Williams

Title: Using climate archives to understand impacts of carbon on our Earth system: a case study in the Gulf of Maine

Abstract: Coastal regions like the Gulf of Maine face amplified impacts from ocean warming and acidification due to local environmental variability superimposed on top of global ocean changes. This threatens vital coastal economies, including the shellfish industry. However, long-term data to contextualize recent trends are limited and the multi-stressor impacts of the rapid changes on coastal species are sometimes unknown. Here, we use annually banded coralline algae as environmental archives to reconstruct historical seawater pH, revealing generally low pH over the past century and an increase of +0.2 pH units in the last 40 years—likely due to reduced low-alkalinity input from the Labrador Sea. Experimental work shows species-specific responses of marine calcifiers to future warming and acidification, highlighting that some species will fare better than others in a higher-carbon world. Our findings underscore the disconnect between policy tools and underlying ocean processes, and we suggest potential strategies for improved coastal resilience.