Nutrient and pigment distributions in the southern Tyrrhenian Sea during mid-summer and late fall 2005

Nutrient, dissolved oxygen and pigment distributions measured in two cruises conducted during mid-summer and late fall 2005 in the southern Tyrrhenian Sea were analyzed to address specific questions on the biogeochemical dynamics of the region in the context of Mediterranean biogeochemistry. The sampled area was characterized by a homogeneous spatial distribution of most properties, including the relative abundance in chemotaxonomic pigment groups in both seasons. The only evident structure was a persistent anticyclonic eddy, which did not play a relevant role in differentiating phytoplankton communities at least during these two seasons. An interesting feature was the presence of a summer deep nitracline, well below the pycnocline, which is likely the result of an already depleted Modified Atlantic Water reaching the area. This implies less effective refueling of nutrients in the mixed layer and, possibly, a low primary production rate. Oxygen and nutrient concentrations in the subsurface layer supported the view of the area being oligotrophic. In deeper layers, there was no specific feature that suggested that the significant double diffusive processes occurring in the region played a role in the vertical distributions of nutrients; on the other, the temporal trend in the nutrient pool showed the impact of the Eastern Mediterranean Transient on the basin.