Journal Article

Distribution, Mixing, and Transformation of a Loop Current Ring Waters: The Case of Gulf of Mexico

Middleton, Leo, Tenreiro, Miguel, Ruiz‐Angulo, Angel, Gentil, Mathieu, Pallàs‐Sanz, Enric, Durante, Giovanni, Allis Estrada, Sheila N., Sheinbaum, Julio, Meunier, Thomas

2024

Overview

Mesoscale warm‐core rings, known as Loop Current rings (LCRs) reshape the Gulf of Mexico water masses by redistributing large amounts of heat and salt laterally. LCRs also transform water masses via diapycnal mixing, but the mechanisms by which this occurs are poorly measured. Here, we present glider‐MicroPod turbulence observations that reveal enhanced mixing below the mixed layer, along the eddy edges, driving the LCR's heat, salt, and oxygen exchanges. Interleavings of adjacent water masses may be interpreted mainly as a manifestation of submesoscale processes through stirring of the spice gradients, which facilitates double‐diffusive mixing that transforms Subtropical Underwater into Gulf Common Water. Our findings highlight the need for ocean models to parameterize double‐diffusive mixing processes directly resulting from submesoscale tracer stirring, which may be important at basin scale in the presence of LCRs in the Gulf of Mexico. Plain Language Summary In the Gulf of Mexico (GoM), anticyclonic eddies, known as Loop Current rings (LCRs) carrying warm and salty water shape the basin's water mass properties, which in turn, affects the regional climate and marine life. The water mass properties are altered by turbulent mixing. However, the mechanisms leading to the mixing of GoM waters are still under debate due to a lack of observations. Here, we use an autonomous underwater vehicle (glider) equipped with a turbulence sensor to assess the nature of LCR mixing and its impact on water properties. The breaking of internal waves in the ocean is often thought to be responsible for turbulent mixing in the ocean interior. However, our findings demonstrate that a process called double‐diffusive convection is responsible, where turbulence is forced by differences between the temperature and salinity of adjacent water parcels. We found that double‐diffusive convection was the main driver in mixing heat, salt, and oxygen along the eddy edges, producing Gulf Common Water. These findings highlight the need to include double diffusive processes in ocean models for more accurate simulations. Key Points Direct observations of turbulence reveal the distribution of mixing across a Gulf of Mexico Loop Current Ring Subtropical Underwater is transformed into Gulf Common Water through double‐diffusive convection on the edges of the eddy

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Autonomous underwater vehicles / Convection / Current rings / Diapycnal mixing / Double diffusion / double‐diffusive convection / Eddies / eddy / Heat / Heat exchange / Internal waves / Loop Current / Mixed layer / Mixing / Mixing processes / Ocean models / Oceanic convection / Oceanic turbulence / Oceans / Oxygen / Regional climates / Salinity / Salts / Stirring / Tracers / Turbulence / Turbulent mixing / Underwater vehicles / Water / Water mass properties / Water masses / Water properties