Transfer of organic carbon on the Moroccan Atlantic continental margin (NW Africa): productivity and lateral advection

• Published in: Geo-marine letters 2009-10, Vol.29 (5), p.277-289
• Main Authors: Bozzano, Graziella, Alonso, Belén
• Format: Article
• Language: English
• Subjects: Advection; Bottom water; Carbon; Continental margins; Earth and Environmental Science; Earth Sciences; Eutrophic environments; Eutrophication; Foraminifera; Geochemistry; Geology; Globigerina bulloides; Marine; Marine environment; Oceans; Organic carbon; Organic matter; Original; Primary production; Sea level; Sediment transport; Sedimentary geology; Upwelling
• ISSN: 0276-0460; 1432-1157
• DOI: 10.1007/s00367-009-0141-y

Land—ocean transfer of sediment and organic matter along the Moroccan Atlantic margin (NW Africa) seems to have been very effective during the last 130 ka. In a marine core from this region, we found total organic carbon (TOC) values ranging from 0.3 to 1.7 dry wt% of bulk sediments. These relatively high values are fairly unusual, as the core was recovered from an open-ocean environment that is currently oligotrophic. In order to explain this trend, more typical of an upwelling eutrophic setting, three processes were evaluated: (1) in situ primary production associated with the extension of the Cape Ghir upwelling filament, (2) bottom water conditions that may favour organic carbon preservation and (3) lateral organic carbon advection. The site occasionally experienced more eutrophic conditions, especially during termination I; here, we recorded a relative high abundance of the planktonic foraminifer Globigerina bulloides , suggesting high primary production. However, given the absence of correlation between TOC and G. bulloides records, high TOC storage cannot be attributed exclusively to primary production. Preservation factors such as bottom water ventilation are also ruled out. Lateral TOC advection seems to be the most plausible process. Today, lateral advection and offshore transport of nutrients and organic matter characterize the study region. However, the triggering mechanisms deserve further investigation. Different controlling factors influencing the mobilization and advection of organic carbon from coastal upwelling sites to the deep basin are discussed. The correlation found between down-core TOC and sea-level changes suggests sea-level fluctuations as the most effective mechanism driving nepheloid layer detachment and seaward material transport.