Marine heatwaves in the Humboldt current system: from 5-day localized warming to year-long El Ni\xf1os

Alice Pietri,Rodrigo Mogollon,François Colas,Dimitri Gutierrez,Jorge Tam

doi:10.1038/s41598-021-00340-4

Abstract

During the last 4 decades punctual occurrences of extreme ocean temperatures, known as marine heatwaves (MHWs), have been regularly disrupting the coastal ecosystem of the Peru-Chile eastern boundary upwelling system. In fact, this coastal system and biodiversity hot-spot is regularly impacted by El Niño events, whose variability has been related to the longest and most intense MHWs in the world ocean. However the intensively studied El Niños tend to overshadow the MHWs of shorter duration that are significantly more common in the region. Using sea surface temperature data from 1982 to 2019 we investigate the characteristics and evolution of MHWs, distinguishing events by duration. Results show that long duration MHWs (> 100 days) preferentially affect the coastal domain north of 15° S and have decreased in both occurrence and intensity in the last four decades. On the other hand, shorter events, which represent more than 90% of all the observed MHWs, are more common south of 15° S and show an increase in their thermal impact as well as on the number of affected days, particularly those spanning 30–100 days. We also show that long duration MHWs variability in the coastal domain is well correlated with the remote equatorial variability while the onset of short events (< 10 days) generally goes along with a relaxation of the local coastal wind.

Highlights

Marine heatwaves (MHWs) are characterized by prolonged extreme warming of the ocean and can have important effects on marine ecosystems
The number of marine heatwaves (MHWs) days in a year identified in the coastal domain ranges from 73 days in 1990 to almost the whole year when long duration MHWs are observed (Fig. 1d)
By removing the four years of the 38-year time series that correspond to the strongest El Niño (EN) conditions, the tendency for increased occurrence of MHWs shorter than 100 days in the Peru Chile Upwelling System (PCUS) might be the result of a higher sea surface temperatures (SST) variability

Summary

Introduction

Marine heatwaves (MHWs) are characterized by prolonged extreme warming of the ocean and can have important effects on marine ecosystems. Eastern Boundary Upwelling Systems (EBUS) are some of the most productive regions in the world ocean[16] and the dynamics that sustains such productivity is closely linked to the relatively cold coastal surface temperature rendering them sensitive to extreme warming events Among those regions, the Peru Chile Upwelling System (PCUS) is characterized by year-long coastal upwelling that makes it the most productive of all coastal upwelling systems[17]. In the southern part of the PCUS, interannual modes of variability have been discussed such as the South Pacific Meridional Mode ( SPMM19) or the “Chile Niño”[20] They are related to positive feedbacks between SST and wind forcing and could lead to warm SST anomalies that would favor the development of MHWs. Climate modes of variability significantly influence the occurrence of MHWs at interannual to decadal time scales, but the generation of MHWs is strongly related to teleconnections at intraseasonnal time scales, and regional air sea coupling[21]. It is sensitive to the variability of the alongshore wind, whether locally or through the generation of CTW at remote locations along the coast[25,26,27]

Methods

Results

Conclusion