Cruises

The region off NW Africa is one of the most productive regions on Earth as result of the presence of coastal upwelling and 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.

During cruise P398 we intend to obtain more insight into the relationship between dust input, upper ocean bioproduction and the alteration of the isotopic, elemental, chemical and organic-geochemical character of the organic matter and marine carbonates that are exported out of the photic zone into the deep ocean. Special focus become processes that occur in the water column and at the sediment/water inter-phase in and around nepheloid layers.

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.

Figure 2. Cross section of the water column in 2008 along transect 1; oxygen concentration.