Transport of airborne lithogenic material down through the water column intwo contrasting regions of the eastern subtropical North Atlantic Ocean

Downward particle fluxes were measured using deep-moored sediment traps dep loyed in two regions of contrasting primary productivity levels (mesotrophi c and oligotrophic) of the eastern subtropical North Atlantic Ocean. The hi gh percentage of lithogenic material (similar to 20-30% on average) in the particulate matter collected shows the regional significance of the atmosph eric dust inputs originating from West Africa. The magnitudes of lithogenic and biogenic fluxes decrease similar to 5-6 and similar to 8-9 fold, respe ctively, from near the African margin (mesotrophic region) to the remote op en ocean (oligotrophic region). These trophic differences seem to give rise to differences in the characteristics of the downward transport of lithoge nic material. At the oligotrophic site, the relatively low and slow export of biogenic matter apparently limits and delays the removal of lithogenic p articles delivered to surface waters from the atmosphere. In contrast, the higher biological activity in the mesotrophic region seems to provide persi stent conditions for an efficient and faster downward transport of the depo sited lithogenic particles, and the temporal variability of lithogenic flux es largely reflects that of the atmospheric dust inputs. Thus whether the t emporal variability of the exported lithogenic flux in the water column fol lows that of the atmospheric deposition appears to depend on the trophic st atus. In the mesotrophic region the oft-observed linear relationship betwee n lithogenic and particulate organic matter (hereinafter POM) fluxes breaks down at high POM fluxes. This observation adds weight to the idea that lin ear relationships between POM fluxes and some candidate proxies for POM tra nsfer cannot be assumed when POM export is large. A high mesoscale variabil ity of biogenic, but not lithogenic, fluxes in the water column of the meso trophic region underscores the relevance of mesoscale studies for regional estimates of export of biogenic material.