Effect of the continental shelf in seasonal oceanographic conditions at the Northern edge of the Eastern Tropical Pacific

The continental shelf in front of Nayarit is located in the northern limit of the tropical Eastern Pacific, characterized by constituting a convergence zone of different masses of water, forming an area of significant hydrographic variability. Based on satellite remote sensing data and reanalysis between 2003 and 2019 of sea surface temperature (SST), wind stress, Ekman velocity, and geostrophic velocity, the contribution of the seasonal cycle to the variability of the study area were analyzed through climatological means, Hovmohler diagrams, and Empirical Orthogonal Functions. The results show that in the zone in front of Matanche ' n Bay (21.5 degrees N) and the adjacent continen-tal shelf, there is a core of warm surface water. The distribution of the SST is explained by the seasonal pattern of meridional/zonal variability in the thermal gradient, where the EOFs show the influence of the annual scale in both modes, with the only difference being that the first describes the meridional gradient as the dominant signal (66.2%), and the second shows the zonal behavior of the thermal gradient (16.6%). The summer weakening of the wind stress and Ekman speed is the product of the irregular shape of the coastline, the extension of the continental shelf, and the divergence of the North American monsoon around 21 degrees N, whereas during the rest of the year an intensification of these parameters prevailed in front of Cabo Corrientes. On the other hand, the intense geostrophic flow in summer does not contribute to the increase in SST on the continental shelf because it diverges around 22.5 degrees N. Likewise, during the winter, the formation of a cyclonic geostrophic gyre located inside the continental shelf, between the coast and the Marias Islands, stands out. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

Automated summary

The study analyzed the contribution of the seasonal cycle to the variability of the study area using satellite remote sensing data and reanalysis of sea surface temperature, wind stress, Ekman velocity, and geostrophic velocity from 2003 to 2019. The results showed the presence of a core of warm surface water in front of Matanche'n Bay and the adjacent continental shelf. The weakening of wind stress and Ekman velocity in summer is attributed to the irregular coastline shape, the extension of the continental shelf, and the divergence of the North American monsoon around 21 degrees N.