Hurricanes enhance the ocean’s biological carbon pump

Hurricanes have well-established physical and biogeochemical impacts on the surface ocean, generating intense upper ocean mixing and upwelling of nutrient-rich waters that induces transient phytoplankton blooms. However, how hurricanes impact the deep ocean remains unknown. Using elemental and molecular tools to trace particle flux processes, we present direct evidence that hurricanes impact the ocean’s biological pump by enhancing labile carbon export to the deep ocean. This presentation focuses on the coupled physical and biological responses in surface waters and the resultant carbon export flux during passage of three hurricanes in the northern Sargasso Sea offshore Bermuda: Fabian (Sept. 2003, Cat. 3), Igor (Sep. 2010, Cat. 1) and Nicole (Oct. 2016, Cat. 3). Fabian and Igor had similar tracks and translational speeds and generated similar ocean responses. They were particularly noteworthy in that they resulted in both a transient phytoplankton bloom/flux event and in extensive resuspension of deep Bermuda platform sediments which were subsequently advected offshore, reaching the Bermuda Time Series site 75 km distant. The deep flux of advected platform carbonates, measured by the Oceanic Flux Program sediment traps at 1500 m and 3200 m depths, following Fabian and Igor was comparable to the annual open ocean carbonate flux for this region. Nicole induced a transient phytoplankton bloom, but no sediment resuspension. After the passage of each hurricane, deep fluxes of lipids diagnostic of labile and fresh phytodetritus increased by 200-400%. These observations indicate that hurricanes impact the carbon cycle in the oligotrophic ocean by generating transient blooms and pulsed export of fresh organic material (and associated bioreactive elements) to the deep ocean interior which, in turn, significantly affects deep ocean ecosystems. Hurricane-induced sediment resuspension also may play an important role in the injection of carbon to the ocean interior.