An observational study of oceanic eddy generation mechanisms by tall deep-water islands (Gran Canaria)

[EN]Oceanic eddy generation by tall deep-water islands is common phenomenon. It is recognized that these eddies may have a significant impact on the marine system and related biogeochemical fluxes. Hence, it is important to establish favourable conditions for their generation. With this objective, we present an observational study on eddy generation mechanisms by tall deep-water islands, using as a case study the island of Gran Canaria. Observations show that the main generation mechanism is topographic forcing, which leads to eddy generation when the incident oceanic flow is sufficiently intense. Wind shear at the island wake may acts only as an additional eddy-generation trigger mechanism when the impinging oceanic flow is not sufficiently intense. For the case of the island of Gran Canaria we have observed a mean of ten generated cyclonic eddies per year. Eddies are more frequently generated in summer coinciding with intense Trade winds and Canary Current.

Krill as a central node for iron cycling in the Southern Ocean

[EN] In order to establish the potential role of Antarctic krill (Euphausia superba) in the recycling of bioactive elements, we have quantified the release of iron, phosphate, and ammonia by these organisms along the Antarctic Peninsula sector of the Southern Ocean. The experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations, as large amounts of this trace element were released by the krill (22–689 nmol Fe g Dry Weight−1 h−1, equivalent to 0.2 to 4.3 nmol Fe L−1 d−1). Half of this iron release occurred within the first hour of the experiment, and differences in iron and phosphate release rates (3.1 to 14.0 μmol PO43− g DW−1 h−1) seemed to reflect differences in food availability. These results identify krill as a major node in iron cycling in the Southern Ocean, potentially influencing iron residence time in the upper water column of this region.