Seasonal Changes in the North Atlantic Subtropical Gyre

The eastern part of the North Atlantic subtropical gyre is found in the region between the Azores and the Cape Verde Islands. A study of the gyre structure in the area east of 35°W between 8°N and 41°N is presented. The geostrophic flow field determined from historical temperature-salinity data sets by objective analysis indicates seasonal variations in shape but no significant changes in the magnitude of volume transports. The eastern part of the gyre has a larger east-west and smaller north-south extension in summer compared with the winter season. The center shifts by about 2° latitude to the south from winter to summer. Long-term temperature time series (6.5 years) from a mooring near the Azores are consistent with these results, showing always a consistent temperature increase at the beginning of the year which is apparently due to the displacement of the northeastern part of the gyre. A comparison between the mean flow fields and fields obtained from individual zonal sections indicates large deviations north and south of the gyre but small deviations within the gyre

Nitrous oxide emissions from theupwelling area off Mauritania (NW Africa)

Nitrous oxide (N2O) flux densities across the ocean/atmosphere interface from the Mauritanian upwelling (16°–18.5°W, 16°–21°N) were computed with a simple upwelling model using N2O measurements from four cruises between 2006 and 2008 as well as wind data from the QuikSCAT satellite. The resulting N2O flux densities show a strong seasonality reflecting the wind-driven seasonality of the upwelling: N2O flux densities are highest in the northern part (19.5°–21°N) and show a decreasing trend towards the south. The summer periods with no upwelling (and thus associated with no or negligible N2O flux densities) are most pronounced in the southern part (16°–17°N). The mean seasonally and regionally weighted annual N2O emissions from the Mauritanian upwelling were estimated to 1.0 Gg N. This is low compared to other major upwelling areas (Arabian Sea, off Chile) indicating that N2O emissions from the Mauritanian upwelling are a minor source of atmospheric N2O

On the zonal distribution of South Atlantic Central Water (SACW) along a section off Cape Blanc, Northwest Africa

The hypothesis of isopycnal mixing was used in order to calculate the percentages of South Atlantic Central Water (SACW) in proportion to North Atlantic Central Water (NACW) in the intermediate layer between the density surfaces of sigma sub(t) = 26.5 and sigma sub(t) = 27.2 along a zonal section at 20 degree 10'N. In this profile the SACW distribution was "conserved" within an offshore distance of about 370 km from the African coast during two observation periods with a time lag of ten months. The SACW distribution along the section follows from the zonal energy structure of the geostrophic meridional flow within this layer. It is concluded that the intermediate geostrophic meridional motions are adjusted to the local profile of the continental slope H(x)