Impact of Submesoscale in the Primary Production of a Loop Current Eddy

The importance of submesoscale circulation structures for biological systems is still subject of debate in the oceanographic research community. The challenge is mainly linked to the lack of observations that are able to resolve such high-resolution and short-living processes. Therefore, physical-biogeochemical coupled models have been proposed as suitable alternatives to explore the consequences of submesoscale structures on the Primary Production (PP) and trophic structure in the ocean.

Two processes are involved in the uplift of nutrients to the euphotic layer by submesoscale structures: (i) The increase of vertical velocities (w) due to ageostrophic circulation cells that can enhance the vertical nutrient transport; and (ii) changes in the mixed layer depths (MLD), which becomes shallower or deeper depending on the dyapicnal mixing levels and restratification effects. The impact of these two processes leads to the increase or decrease of the PP and changes in the structure of the marine ecosystems.

Based on a physical-biogeochemical coupled model (ROMS-Fennel), two model setups are configured to study the consequences of these processes in terms of PP inside a Loop Current anticyclonic eddy in the Gulf of Mexico (GoM). A 5 km horizontal resolution configuration for the whole GoM (LR), and a nested 1 km horizontal resolution domain centered in the Loop Current eddy (HR).

The results show submesoscale filaments around the eddy as the most productive areas. There is 15% increase of the PP during winter in the HR in relation to the LR simulation. This relates to the wintertime enhancement of w and diapycnal mixing. Contrary to recent studies, the MLD is deeper in the HR than in the LR configuration. This leads to the wintertime enhancement of PP in the oligotrophic GoM.