Abstract

Upwelling events over the Yucatan shelf are physical phenomena of importance for the region. In July 2018, based on oceanographic sampling, we detected the presence of upwelled waters on the west side of the shelf. These events have been widely studied on the northern Yucatecan coast but little has been said about their existence off Campeche, although they are known to the fishing communities of the region. Back-in-time Lagrangian simulations identify the origin of the subsurface Caribbean water; this particular event came from the northeast of Yucatan, over 500 km away from the sampling site. It took over a month to arrive at the study region, traveling alongshelf with an average velocity of 14.5 cm/s along the region with the most intense upwelling of the Yucatan shelf. This phenomenon separated the water column into two layers with differentiable thermohaline characteristics.  These trajectories are also observed with climatological Lagrangian Coherent Structures suggesting recurrence. Monthly-averaged SST anomalies also show that advected upwelling waters off Campeche occur mainly during summer (from July to August each year).

Introduction

Located on the southeast Gulf of Mexico (GoM), the Yucatan Peninsula continental shelf (hereafter Yucatan Shelf), is an important economic area rich in fishing resources,  gas, and oil deposits. It is a wide shallow marine region where the ocean floor frictions the ocean currents and detriments the height of the waves, characterized by low speeds (mean -20 cm/s, \citealp*{Mart_inez_Lopez_1998}\citealp{r2016}) and low significant wave heights (0.63 m on average), respectively.  Wind stress forcing and bottom friction are the main drivers of the ocean currents over the shelf, but also the water column stratification has been found to be an important factor (\citealp{r2016}\citealp{jl2016},  \citealt{Jouanno_2018}). Winds blow preferentially towards the west all year-round (also known as easterlies or trade winds), forcing the ocean to produce a westward circulation (\citealp*{Mart_inez_Lopez_1998} and \citealp{Zavala_Hidalgo_2003}). But from September to June atmospheric cold fronts coming from continental North America motivate wind burst episodes affecting the region with northwesterly winds blowing over the hole GoM (events locally known as "Nortes")\citep{g2020}.