Latitudinal impacts of Hurricane Lorenzo on North Atlantic physics and biology

Sergio Muacho , Andre Valente, Manoa Postec

Hurricane Lorenzo was the easternmost Category 5 Atlantic hurricane on record. The impact of this exceptional storm on North Atlantic sea surface temperature, mixed layer depth and chlorophyll-a concentrations is investigated in this study using high-resolution daily interpolated satellite, historical in-situ vertical profiles, and model-derived datasets. Results show that Lorenzo induced strong sea surface cooling up to –2.5 °C, modest increases in the MLD (5 to 30 m on average), and a significant increase in chlorophyll-a from 100 up to 250% relative to pre-storm conditions. Impacts were observed over a ~200 km-wide band along the right-hand side of the track and persisted for more than 10 days. Chlorophyll-a from different phytoplankton functional types were also examined. All major groups showed increased chlorophyll-a levels. Prokaryotes and Haptophytes dominated across the region both before and after the storm, though their relative dominance shifted at higher latitudes (35–40°N), where Haptophytes surpassed Prokaryotes as the leading community. Results highlight the distinctive imprint of this anomalous hurricane on the upper ocean, provide insights into alterations in phytoplankton communities and enable future comparisons for extreme atmospheric events in subtropical to midlatitude ocean.