Multi-proxy approach in tracking circulation change in the western North Atlantic during the Little Ice Age

Wai Ching Rachel Chu, Benoit Thibodeau

The Little Ice Age (LIA), a period from ~1400 CE to 1900 CE, was characterized by colder winter and more frequent extreme weather event, particularly in the Northern hemisphere. While the exact causes of the Little Ice Age remain a topic of ongoing research, evidence suggests that changes in ocean circulation patterns likely played a role in the observed global cooling, although the specific mechanisms and drivers of these changes are not yet fully understood. Here, we aim to generate new knowledge to help us better understand how ocean circulation changed before, during, and after this climatic event. To do this, we will investigate changes in the western North Atlantic circulation that can inform us on the relative strength of the Labrador current and Gulf stream. First, we established Mg/Ca-temperature calibration curve for Globobulimina auriculata in the Lower St. Lawrence Estuary, i.e. Mg/Ca (mmol/mol)=0.6341e^((0.3740t)) for bottom water temperature reconstruction. Coupling the temperature reconstruction with oxygen isotope data, we reconstructed the relative strength of the Labrador current and Gulf stream to infer regional oceanographical change. We discussed the oceanographic changes during the LIA in respect to volcanism, solar irradiance, and North Atlantic Oscillation. Additionally, we noted similarities between our records and previous proxy interpretations on the strength of Atlantic Meridional Overturning Circulation (AMOC), the Gulf Stream, and the Labrador Current. Our interpretation suggested a stepwise weakening of AMOC throughout the LIA followed by a sharp decrease of the oxygen isotope likely driven by a freshwater release.