Extreme South Pacific Phytoplankton Blooms Induced by Tropical Cyclones

Wind-driven mixing and Ekman pumping driven by slow-moving tropical cyclones (TCs) can bring nutrients to the euphotic zone, promoting phytoplankton blooms (TC-PBs) observable by satellite remote sensing. We examine an exceptional (z-score = 18-48) TC-PB induced by category-1 Cyclone Oma near the South Pacific island of Vanuatu in February 2019, the most extreme event in the observed satellite record of South Pacific surface Chlorophyll-a (Chl-a). Examining all 156 South Pacific TC since 1997, we identify a hover parameter derivable from storm track data correlated with post-TC surface Chl-a (r = 0.84). Using a data set of synthetic storm tracks, we show revisit times for South Pacific TC-PBs are O(250) years and O(1,500) years for Oma-scale TC-PBs. The episodic, extreme, but consistent nature of such events means they may imprint on sediment records. If so, we show their signature could be used to reconstruct past TC variability assuming near-stationarity of TC statistics.

Automated summary

Wind-driven mixing and Ekman pumping by slow-moving tropical cyclones can promote phytoplankton blooms in the euphotic zone. We examine an exceptional TC-induced phytoplankton bloom near Vanuatu in February 2019 and identify a parameter correlated with post-TC surface chlorophyll-a. Using synthetic storm tracks, we show the revisit times for TC-induced phytoplankton blooms in the South Pacific are on the order of hundreds to thousands of years.