The Gulf of Maine has experienced rapid ocean warming in recent times. However, a lack of long-term instrumental records has hindered the contextualization of these hydrographic changes. This study presents 300-year geochemical records (oxygen, nitrogen, and radiocarbon isotopes) from *Arctica islandica* shells, combined with climate model simulations. The findings suggest a long-term cooling trend in the Gulf of Maine over the past 1000 years, primarily due to volcanic forcing and North Atlantic ocean dynamics. This cooling trend reversed in the late 1800s due to increased atmospheric greenhouse gas concentrations and changes in western North Atlantic circulation. The climate model simulations indicate that the warming of the last century was exceptionally rapid compared to other 100-year periods in the last millennium.

Nina M. Whitney, Alan D. Wanamaker, Caroline C. Ummenhofer, Beverly J. Johnson, Nathaniel Cresswell-Clay, Karl J. Kreutz