Frequency Analysis of Marine Heatwaves in the North Eastern Pacific Ocean

In the past decade, the North Eastern Pacific Ocean has had repeated severe marine heatwaves, causing damage to multiple fisheries and massive die-offs of many marine mammal and marine bird species. Here we investigate how unlikely these high duration and intensity events were and how likely they are to repeat. We focus on the Gulf of Alaska and Baja California as the two key locations where the most severe marine heatwaves were observed in 2013 and 2015, respectively. We use univariate and bivariate probability distributions to estimate the return periods of these events based on their duration, cumulative intensity, and peak intensity. We find that the observed peak intensities were significantly higher than average for both events. Both heatwaves are of unprecedented durations, lasting 194 days and 193 days at the Gulf of Alaska and Baja, respectively. The cumulative intensity of these events is of unparalleled severity and exacerbated due to both high peak temperatures and durations. Our results highlight that the cumulative intensity of these events is potentially important in the events' devastating influence over the region due to a prolonged duration of heightened warming.