Abstract
Hurricanes passing over the ocean can mix the water column down to great depths and resuspend massive volumes of sediments on the continental shelves. Consequently, organic carbon and reduced inorganic compounds associated with these sediments can be resuspended from anaerobic portions of the seabed and re-exposed to dissolved oxygen (DO) in the water column. This process can drive DO consumption as sediments become oxidized. Previous studies have investigated the effect of hurricanes on DO in different coastal regions of the world, highlighting the alleviation of hypoxic conditions by extreme winds, which drive vertical mixing and re-aeration of the water column. However, the effect of hurricane-induced resuspended sediments on DO has been neglected. Here, using a diverse suite of datasets for the northern Gulf of Mexico, we find that in the few days after a hurricane passage, decomposition of resuspended shelf sediments consumes up to a fifth of the DO added to the bottom of the water column during vertical mixing. Despite uncertainty in this value, we highlight the potential significance of this mechanism for DO dynamics. Overall, sediment resuspension likely occurs over all continental shelves affected by tropical cyclones, potentially impacting global cycles of marine DO and carbon.
Highlights
Hurricanes, generically known as tropical cyclones (TCs), impact many coastal regions of the world by bringing strong winds and rain to both the land and sea
As a large portion of the terrestrial organic carbon is remineralized after it reaches the coastal ocean, the region changes from a net sink to a net source of carbon dioxide to the atmosphere during these events[16]
While our focus is on the northern Gulf of Mexico, we argue that this process occurs on other continental shelves affected by extreme wind events and could be important for dissolved oxygen (DO) and carbon budgets of the global coastal ocean
Summary
As a measure of sediments resuspended from the ocean floor when hurricanes pass through the shelf, we used weekly satellite-derived Total Suspended Matter (TSM) concentrations (see Methods). SSS and rainfall in late summer/ early fall 2005 showed two freshening events after each of the hurricanes Katrina and Rita: the first one was an immediate response to rainfall and the second lagged for ~5–7 days, indicating the arrival of the river plume (Supplementary Fig. S1) To generalize these findings to all hurricanes, we followed a similar approach as for TSM and created composites of SSS and rainfall from two days before the arrival of hurricanes to 14 days after (Fig. 2c for rainfall and Fig. 2d for ΔSSS, which is SSS minus SSS two days before the hurricanes). Based on the above and given that the ΔSSS composites represent an average response of SSS to hurricanes at a location close to the Mississippi River mouth (i.e., the plume will take longer to arrive to the northwestern shelf, even if winds and other factors affect the plume location), we assumed that riverine delivery has minimal effect on the shelf TSM in surface waters within the first ~5–7 days after the storms
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