Water quality impacts during Hurricane Irene (2011) in a large coastal-plain estuary

Embayments of North America’s east coast are positioned along the trajectory of Atlantic tropical cyclones (TCs) whose frequency and/or intensity are projected to increase over the century. Substantial water quality impacts of TCs have been documented over the years in some of those embayments, but large coastal plain estuaries remain an observational challenge that often confines water quality studies to sub-regions or to tributaries. The present study provides a ‘system-wide’ analysis of impacts on water properties during hurricane Irene (2011), reflecting the aggregate response of a large estuary (Chesapeake Bay) in terms of air/sea exchanges of CO 2 , O 2 , and other metrics. The study focuses on the days preceding/following the event and leverages an ensemble of atmospheric simulations of Irene (to quantify the sensitivity of its impacts on water properties to variations in the TC’s characteristics) and a 1985–2023 hindcast (to put Irene in perspective). The analysis indicates that the CO 2 outgassing during Irene was unprecedented over 1985–2023, and that TCs regularly cause CO 2 outgassing events of magnitude ∼ 25 % weaker than that of Irene (return period of 2–5 years). Based on the sensitivity analysis, most metrics worsen in proportion to an hypothetical intensification of Irene, but CO 2 outgassing exhibits a slightly superlinear response. These results emphasize the need to account for the contribution of large stochastic events in estuaries in order to derive global carbon budgets representative of reality. • The air/sea CO 2 outgassing during Irene was unprecedented over the period 1985–2023. • Similar outgassing events of smaller magnitude occur every 2–5 years in the estuary. • CO 2 outgassing scales superlinearly with intensified tropical cyclone winds.