Abstract
This study investigates seasonal, interannual, and short-term variability in mixed layer depth (MLD) and upper-ocean hydrography within the Florida Current using Conductivity, Temperature, Depth (CTD) data collected during 30 FLOTSUM (Florida Ocean Time Series by Undergraduates at the University of Miami) cruises between 2019 and 2025. Surface temperature, salinity, and density were calculated from the upper 20 m of the water column and analyzed alongside MLD, which was estimated using the Gibbs SeaWater Toolbox with a density threshold method. Seasonal regressions revealed strong Fall deepening of the MLD driven by cooling and increasing surface density, while Spring was characterized by MLD shoaling with relatively stable thermal and density structures. Interannual analysis showed no clear long-term trends, though elevated fall temperatures in 2022–2024 suggest possible shortterm warming episodes. Boxplot and statistical analyses showed that MLD exhibited the greatest relative spread across both seasons. At the same time Levene’s test identified salinity as the only parameter with a statistically significant difference in seasonal variability. These results highlight the importance of integrating current position and biogeochemical data in future cruises to better understand the variability in the Florida Current and its implications for climate and biogeochemistry.