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PAPOCA: Production and Preservation of organic carbon in relationship to dust input and nepheloid layers in the upwelling area off NW Africa


PD. Dr. Karin Zonneveld


+49 421 218-65797


+49 421 218-9865974



MARUM II, Raum 1010

Fig 1. Map of working areas and planned study sites.

Cruise track of P398

The region off NW Africa is one of the most productive regions on Earth as result of the presence of coastal upwelling and the year round terrestrial dust input. Both upwelling and dust input fertilize the ocean by nutrient and trace elements such as iron and phosphorus. However, the relationship between upper ocean fertilization, marine bioproduction and transport and burial of the upper ocean produced marine carbon is far from being completely understood. Notably the early diagenetic induced alteration of the total organic carbon flux as well as the modification of the chemical, organic geochemical, isotopic and elemental character of the organic matter (OM) and marine carbonate during transport though the water column and at the sediment/water interface is far from clear.

A factor that largely affects OM preservation is oxygen availability. Oxygen availability determines the respiratory types of benthic micro and macro organisms, with anaerobic consortia of micro-organisms being less efficient than aerobic micro-organisms and micro- and macrofauna. It has been suggested that redox oscillations, may enhance degradation by promoting symbiosis of aerobes and anaerobes. The residence time of organic matter in the water column strongly influences the exposure time of OM to aerobic conditions. For high productivity areas it has been suggested that some organic components can remain for several thousand years in suspension in the water column related to the existence of nepheloid layers at intermediate water depths. Within nepheloid layers individual organic matter compounds appear to show a difference in resistance to early sedimentary diagenesis during vertical transport.

During cruise P398 we intended to obtained more insight
(1) the effects of early diagenetic processes within intermediate depth nepheloid layers on the flux and character of the organic matter flux.

(2) the effects of the bottom water oxygen concentrations on the fixation or cycling of major elements and organic matter in the Benthic Boundary Layer and in surface sediments.

(3) the stable isotopic and elemental composition of the fossilisable calcareous remains of coccolithophorids and calcareous dinoflagellate cysts in relation to the environmental conditions and physical and chemical composition of the water column in which they are being formed.

For this we intent to investigate the atmosphere, water column and upper ocean sediments along two transects. Along a first W-E transect that crosses the lower shelf and upper slope off Cap Blanc, the atmospheric dust content will be sampled with two dust collectors. The suspension load in the water column will be collected using in-situ pumps and a CTD-rosette system. For detailed investigations on processes that take place within and near the bottom-boundary nepheloid layer in both oxic and anoxic environments, stations are planned above, within and below the here existing oxygen minimum zone (OMZ). To study the fate of different types of particulate organic matter and of nutrients, N, P, and Fe in the bottom-boundary-layer, bottom waters and sediment will be sampled with a Bottom Water Sampler, a Bottom Water Profiler and a Multicorer.

The second transect runs parallel the Moroccan coast. It crosses the area of maximal Saharan dust input. Here a continuous sampling of dust particles is planned. Furthermore, the CTD-rosette system and in-situ pumps will be deployed for sampling of the water column with focus on nepheloid layers in the upper part of the water column.

Cross section of the water column in 2008 along transect 1; oxygen concentration