In contrast to other coastal regions of the world, the giant kelp (Macrocystis pyrifera)  ecosystem in southwestern Patagonia has been persistent in area and associated biodiversity in the last decades. In this ecoregion, Sea Surface Temperature (SST) records have consistently remained below the upper thermal threshold for kelp survival, however no studies have analysed the spatiotemporal variability of SSTs and their anomalies across the geographical diversity of the southwestern Patagonian coastline. We explored the geographical distribution of extreme warm and cold events in this region from latitudes 47° to 56° S in a range of 1,000 km, identifying the dates and spatial distribution of Marine Heatwaves (MHWs) and Marine Cold-Spells (MCSs) from 1982 to 2020. Results show that a peak in the number of MHWs occurred in the great El Nino year of 1998. Additionally, the 2014-2019 period has had more severe and extreme MCSs than the previous decades. We discuss the origin of these events with a focus on three main processes: 1) geographically constrained cold events caused by glacier melting, 2) regional cold events caused by extreme winds linked to the position of the polar front, and 3) extensive SST anomalies linked to planetary-scale events such as El Nino and La Nina.  Overall, those processes were conductive to counteract global warming trends locally/regionally, highlighting southwestern Patagonia as a possible climatic refugium for the giant kelp ecosystem. Despite this, the effects of freshwater inputs and storm turbulence on the exposed coasts facing the Southern Ocean may cause new kinds of stress on this ecosystem.

This dataset comprises a list of MCS and MCS per marine ecosystem in Southwestern Patagonia, derived from daily SST measurements. The list includes events categories II, III and IV. 

The original daily SST measurements were extracted from the NOAA CDR OISST v02r01: Optimum Interpolation Sea Surface Temperature product (Reynolds et al., 2008; Gorelick et al., 2017). This dataset was selected per marine ecosystem through zonal statistics, with a spatial resolution of 0.25 arc degrees, using a Google Earth Engine script. 

Files in this dataset: 

• Table S1 (SM_MHW_MCS_March2022.xlsx): List of MCSs (Categories II, III and IV); list of MHWs (Categories II, III and IV); Combined list of MCSs and MHWs, Categories III and IV.
• MCS per ecoregion; the complete series is in MCS_category_March2022.csv
• MHW  per ecoregion; the complete series is in MHW_category_March2022.csv
• SST per ecoregion. 

We found a gap of data between 31-Dec-1984 to 01-Sep-1985, and 31-Dec-2020, not included in the analysis.

The original shapefile with the marine ecosystems used in this study is from Rovira, J., & Herreros, J.    (2016).    Clasificacion de ecosistemas marinos chilenos de la zona economica exclusiva [Report]. Departamento de Planificacion y Polıticas en Biodiversidad. Division de Recursos Naturales y Biodiversidad. Ministerio del Medio Ambiente.

The MHW and MCS method has been developed by: Robert W. Schlegel and Albertus J. Smit (2018). heatwaveR: A central algorithm for the detection of heatwaves and cold-spells. Journal of Open Source Software, 3(27), 821, https://doi.org/10.21105/joss.00821.

The heatwaveR package used in this study is explained here: https://robwschlegel.github.io/heatwaveR/index.html