Carbon export and drivers in the southeastern Levantine Basin

In this paper, we present C export data from the southeastern Levantine Basin, 50 km west of Haifa, at water depth of 1500 m. Particulate organic carbon (POC) fluxes were measured for 18 months by automated and single bottle sediment traps at the recently-deployed DeepLev observatory and compared with water column profiles of ²³⁴Th. Calculations, based on POC/²³⁴Th ratios, result in water column-integrated export of 18 mmolC m⁻² d⁻¹ at the end of summer (Dec 2017) and remineralization during spring (e.g. 14.4 mmolC m⁻² d⁻¹, Apr, 2018). Based on the sediment traps POC export in the basin was generally low (0.05–1 mmolC m⁻² d⁻¹ at the base of the photic zone during Dec 2017–May 2018). Fluxes were quite variable, and the export pattern was mainly controlled by coastal discharge or shelf-resuspension (winter peaks) rather than by marine primary production. This was demonstrated by: i) larger POC fluxes measured by deep water (1300 m) and twilight zone (280 m) traps compared to fluxes measured at the base of euphotic zone, ii) tight correlation of POC with total mass flux, iii) decrease of the POC percentage during winter peak events and iv) imbalance (large integrated deficit or excess) of water column ²³⁴Th. Both deficit and excess are evidence of lateral flux, where the first probably results from wave-induced shelf resuspension of organic-poor material, which underwent minimal remineralization and induced scavenging, while the latter derives from the conveyance of large amount of land-derived organic matter, which undergoes remineralization, therefore input of ²³⁴Th to the water column.