Tropical storm-induced disturbance of deep-water porewater profiles, Gulf of Aqaba

Abstract

Storms have long been recognized as a force that agitates sediments, even in the deep-water. In shallow water depths (<40 m) sediments are affected dominantly by wave actions, while in deeper-water (>100 m) the impact is primarily due to suspended sediment flow. While such transport events have been studied sedimentologically extensively, their impact on porewater chemistry is yet poorly understood. The March 2020 tropical storm which impacted the Gulf of Aqaba (GoA) offered a unique opportunity to investigate this particular topic. Detailed sedimentological, mineralogical and porewater analyses were carried out on two sets of short cores collected along a transect from 270 m to 700 m water depths before and after the storm on the western margins of the GoA, which represents a steep slope with a potential for high energy transport events. The cores exhibited a decrease in grain size in the mid-slope water depth and an increase at the base of the slope after the storm, with the top of the core being enriched with terrestrial material. Both Fe2+ and NOx profiles exhibited a marked shift in the aftermath of the storm. NOx concentrations increased in the top 5 cm of all the cores and the ferruginous zone migrated upwards in both the top and bottom of the slope. We postulate that the storm event remixed the top of the sediment column and infused it with fine material. This filled burrows and decreased the diffusive coefficient across the sediment-water interface, limiting the exchange of ions. As a result, the porewater trapped in the sediment has developed along the terminal electron acceptor chain.