The variability of sea surface temperature in the Patagonian Shelf Argentina, from 35 years of satellite information

Abstract

The aim of the present work is to analyse the variations of Sea Surface Temperature (SST) and Anomaly of Sea Surface Temperature (ASST) using more than thirty years of satellite data. We studied if these variations have possible ocean-atmosphere connections with the Southern Annular Mode (SAM), the Southern Oscillation Index (SOI), and the Oceanic Niño Index (ONI) in a crucial region for fisheries off the Patagonian Shelf. For the analysis, we used SST data collected from 1985 to 2019 with Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments. The two databases were merged to obtain 35 years of continuous SST data. The study area was divided into three zones to present different oceanographic and bathymetric characteristics. These zones are located in the gulf, in the middle of the continental shelf, and at the shelf break. For each of the zones, the monthly SST climatology and the ASST series are shown. To define their periodicity, monthly ASST data were analysed spectrally by Fast Fourier Transform (FFT) and Wavelet Transform. Cross-Wavelet Transform (XWT) was applied to analyse the co-variance of ASST with respect to climate indices. Our results show that the isotherm distribution seems to be separated by the 64º W meridian. To the east of 64º W, it follows an oblique direction from southwest to northeast; to the west of 64º W, a more complex behaviour of the SST field seems to be associated with the coastal dynamics. The ASST series shows that the values of negative anomalies are higher than those of the positive ones. Nevertheless, positive ASSTs are more extreme and persistent in time than the negative ones. The ASST wavelet diagrams denote a common and non-stationary periodicity in the three zones, with statistically significant power spectra in the intra-seasonal (9-month) and inter-annual (24-month and 4-year) time scales. There are clearly common features in the wavelet power of the time series related to ASST and climate forcing. The SAM exhibited the closest relationship with ASST in the three zones. The SAM and ASST indices denote significant power peaks in the 2-year and 4- to 6-year bands.