Latitudinal gradient consistency in carbon and nitrogen stable isotopes of particulate organic matter in the Southern Ocean

The Southern Ocean is characterized by strong latitudinal gradients that delimit areas which differ in terms of hydrological properties and production dynamics. Stable isotope values of carbon (delta C-13) and nitrogen (delta N-15) of surface particulate organic matter (POM) collected along a repeated transect between Cape Town and the Antarctic continent in the Atlantic sector of the Southern Ocean during summer 2005/06, fall 2004 and winter 2006 were analyzed to investigate their seasonal variability. In addition, published transect data collected in other sectors of the Southern Ocean were compiled for a wider spatio-temporal study of the POM stable isotope patterns. Combined delta C-13 and delta N-15 values of POM appeared to be an effective tool for identifying circum-Antarctic, latitudinally arranged areas with specific water mass characteristics and separated by the major frontal systems. Furthermore, POM delta C-13 values showed year-around consistency. We identified a few mechanisms that should be taken into account to effectively model carbon and nitrogen isoscapes in the studied area. The average level of primary productivity needs to be known to explain slightly higher delta C-13 values occurring in the Atlantic sector between the Subantarctic and Antarctic Polar Fronts. In addition, delta C-13 and delta N-15 values were highly variable in the marginal ice zone, especially at the ice edge and in the middle of the Weddell gyre. Processes linked to ice dynamics and upwelling explained some of the outlying values, especially for delta N-15. Improved comprehension of the main mechanisms driving changes in POM stable isotopes will enable satellite products to be used as predictors to model realistic isoscapes on the scale of the Southern Ocean over different temporal scales.