Effects of dust deposition on iron cycle in the surface Mediterranean Sea: results from a mesocosm seeding experiment

[摘要] Soil dust deposition is recognized as a major source of iron to the openocean at global and regional scales. However, the processes that control thespeciation and cycle of iron in the surface ocean after dust deposition arepoorly documented mainly due to the logistical difficulties to investigatein-situ, natural dust events. The development of clean mesocosms in the frame of theDUNE project (a DUst experiment in a low Nutrient low chlorophyll Ecosystem)was a unique opportunity to investigate these processes at the unexploredscale of one dust deposition event. During the DUNE-1-P mesocosm seedingexperiment, iron stocks (dissolved and particulate concentrations in thewater column) and fluxes (export of particulate iron in sediment traps) werefollowed during 8 days after an artificial dust seeding mimicking a wetdeposition of 10 g m⁻². The addition of dust at the surface of themesocosms was immediately followed by a decrease of dissolved iron [dFe]concentration in the 0–10 m water column. This decrease was likely due todFe scavenging on settling dust particles and mineral organic aggregates.The scavenging ratio of dissolved iron on dust particles averaged 0.37 ± 0.12 nmol mg⁻¹. Batch dissolution experiments conducted in parallelto the mesocosm experiment showed a increase (up to 600%) in dust irondissolution capacity in dust-fertilized waters compared to controlconditions. This study gives evidences of complex and unexpected effects ofdust deposition on surface ocean biogeochemistry: (1) large dust depositionevents may be a sink for surface ocean dissolved iron and (2) successivedust deposition events may induce different biogeochemical responses in thesurface ocean.

[学科分类] 地球化学与岩石