Drivers and impacts of the most extreme marine heatwaves events
July 09,2021

Alex Sen Gupta, Mads Thomsen, Jessica A. Benthuysen, Alistair J. Hobday, Eric Oliver, Lisa V. Alexander, Michael T. Burrows, Markus G. Donat, Ming Feng, Neil J. Holbrook, Sarah Perkins-Kirkpatrick, Pippa J. Moore, Regina R. Rodrigues, Hillary A. Scannell, Andréa S. Taschetto, Caroline C. Ummenhofer, Thomas Wernberg & Dan A. Smale

Published in Scientific Reports, NOV 2020

Prolonged high-temperature extreme events in the ocean, marine heatwaves, can have severe and long-lasting impacts on marine ecosystems, fisheries and associated services. This study applies a marine heatwave framework to analyse a global sea surface temperature product and identify the most extreme events, based on their intensity, duration and spatial extent. Many of these events have yet to be described in terms of their physical attributes, generation mechanisms, or ecological impacts. Our synthesis identifies commonalities between marine heatwave characteristics and seasonality, links to the El Niño-Southern Oscillation, triggering processes and impacts on ocean productivity. The most intense events preferentially occur in summer, when climatological oceanic mixed layers are shallow and winds are weak, but at a time preceding climatological maximum sea surface temperatures. Most subtropical extreme marine heatwaves were triggered by persistent atmospheric high-pressure systems and anomalously weak wind speeds, associated with increased insolation, and reduced ocean heat losses. Furthermore, the most extreme events tended to coincide with reduced chlorophyll-a concentration at low and mid-latitudes. Understanding the importance of the oceanic background state, local and remote drivers and the ocean productivity response from past events are critical steps toward improving predictions of future marine heatwaves and their impacts.

Fig.3 Characteristics of MHW duration. (a) Duration of longest recorded MHWs and associated zonal mean (black) and median (red) (b). (c) Proportion of ocean experiencing maximum MHW duration for all MHW categories (blue) and for strong or greater MHW categories (red); coloured lines show associated cumulative totals), (d) central year of longest MHW; (e) proportion of ocean experiencing its longest (red) and largest cumulative intensity (dashed) MHW by month.

Sen Gupta, A., Thomsen, M., Benthuysen, J.A. et al. Drivers and impacts of the most extreme marine heatwave events. Sci Rep 10, 19359 (2020).

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