A Link between Kuroshio Extension Variations, Northeast Pacific Marine Heatwaves, and Marine Ecosystems in the Gulf of Alaska

Recent Marine Heatwave (MHW) events in the Northeast Pacific Ocean during the periods 2014-2016 and 2019-present have substantially impacted ocean life and livelihoods in the region. Initial analysis has found that the observed evolution of the 2012-2015 marine heatwave in the Gulf of Alaska (GOA) (i.e., the "Pacific Blob") best correlates with the evolution of historical SSTs in response to large-scale variations in the Kuroshio Extension (KE) region. Here we examine the physical and biogeochemical changes during this MHW and their relation to these same KE variations. For this work we used multiple data sets from Multi Observation Global Ocean ARMOR3D L4 analysis (1993-2018), Global Ocean biogeochemistry hindcasts (1993-2018), global ocean Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) SST reprocessed data (1981-2018), and ERA5 atmospheric data (1981-2018). It is well known that SST variations in the KE region result in higher-than-normal sea level pressures (SLP) and weaker wind stress over the GOA. Our results show that this lower wind stress results in a reduction of ocean mixed layer thickness (MLT) both intra-seasonally and with a one-year lag. While this reduction in MLT influences the heat content in the northeast Pacific and results in the MHW during this time (i.e. the "Blob"), it also results in depleted nutrient availability (nitrates and phosphates). We find that it is the latter influence that in turn reduced the primary production in the GOA during the period 2014-2016. These findings will provide baseline guidance for the understanding of the biological and fisheries implications of MHWs in the GOA further supporting the formulation of climate-related ocean and fisheries policies on local, regional, and global scales.