Marine Heatwaves Modulate Food Webs and Carbon Transport Processes

Abstract The impact of marine heatwaves (MHWs) on ecosystem functions and services remains poorly constrained due in part to the limited availability of time-resolved datasets integrating physical, chemical and biological parameters at relevant operating scales. Here we paired over a decade of autonomous Biogeochemical (BGC)-Argo profiling float data with water column plankton community composition profiles to investigate the impacts of MHWs on carbon cycling dynamics in the Northeastern subarctic Pacific Ocean (NESAP), resolving temperature-induced changes in production and transport of particulate organic carbon (POC) within the water column. POC concentrations were extremely high during MHWs in Spring 2015 and 2019, associated with detritus enhancement and changes in plankton community structure. Instead of sinking, particles < 100 µm accumulated in mesopelagic waters where remineralization happened slowly over the year, thus decreasing the rapid deep particle export and carbon sequestration potential of thermally-impacted waters.