Multiproxy probing of rainwater dissolved organic matter (DOM) composition in coastal storms as a function of trajectory

• Rainwater provenance affects its DOM composition.
• Coastal rainwater DOM is not derived exclusively from aerosol scavenging.
• Marine-derived DOM may be found in Atlantic hurricane rain.
• This recycled marine rainwater may subsidize the carbon cycle in coastal aquatic ecosystems.

Rainwater dissolved organic matter (DOM) was characterized in two sequential coastal rainstorms of different geographic origins: an Atlantic hurricane (Hurricane Irene [2011]) and a terrestrial squall. Using a multiproxy approach incorporating electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR), stable carbon isotope analysis, and excitation–emission fluorescence spectroscopy, we demonstrate the unique composition of marine-derived organic matter in Atlantic hurricane rainwater. Hurricane Irene rainwater DOM (DOMIrene) was molecularly distinct from that of the terrestrial squall (DOMsquall). For example, δ13CDOC of Irene rainwater was − 19.2 ± 0.13‰ while that of the squall was − 26.3 ± 0.01‰. Peaks assigned using FTICR which were unique to DOMIrene contained a greater relative number of molecular formulas containing nitrogen (representing any of several isomeric CHON, CHONS, CHONP compounds) relative to those unique to the DOMsquall. Although there was insufficient rainwater available to test DOMsquall for its bioavailability, a simple room-temperature incubation of Irene rainwater over 30 days in the dark resulted in its dissolved organic carbon decreasing from 2.3 to 1.5 mg L− 1. When coupled with the abundant precipitation generally-associated with hurricanes, these results suggest that marine DOM in rainwater may exert unique but substantial impacts to organic matter in coastal aquatic ecosystems.