Deepening of the ocean mixed layer at the northern Patagonian continental shelf: a numerical study

TL;DR

This study uses a numerical model to show that increasing wind speeds are causing the ocean mixed layer to deepen and slightly cool at the northern Patagonian shelf, with potential climate implications.

Contribution

It demonstrates that wind speed increase is the primary driver of mixed layer deepening in this region, supported by long-term numerical simulations.

Findings

Mixed layer thickness increased by approximately 10.1 cm/yr.

Wind speed increase is the main factor influencing deepening.

Sea surface temperature shows a slight cooling trend.

Abstract

A possible deepening of the ocean mixed layer was investigated at a selected point of the Patagonian continental shelf where a significant positive wind speed trend was estimated. Using a 1-dimensional vertical numerical model (S2P3) forced by atmospheric data from NCEP/NCAR I reanalysis and tidal constituents from TPXO 7.2 global model on a long term simulation (1979-2011), it was found that the mixed layer thickness presents a significant and positive trend of 10.1 +/- 1.4 cm/yr. Several numerical experiments were carried out in order to evaluate the impact of the different atmospheric variables (surface zonal and latitudinal wind components, air temperature, atmospheric pressure, specific humidity and cloud coverage) considered in this study. As a result it was found that an increase in the wind speed can be considered as the main responsible of the ocean mixed layer deepening at the selected location of the Patagonian continental shelf. A possible increasing in the mixed layer thickness could be directly impacting on the sea surface temperature. Preliminary results obtained in this paper show that a slight but significant cooling in the temperature of the sea upper layer (of the order of 1 C every 50 years) could be happening since some decades ago at the northern Patagonian continental shelf waters.