Articles | Volume 7, issue 2
Earth Syst. Sci. Data, 7, 415–422, 2015
Earth Syst. Sci. Data, 7, 415–422, 2015

Brief communication 10 Dec 2015

Brief communication | 10 Dec 2015

In situ measurement of the biogeochemical properties of Southern Ocean mesoscale eddies in the Southwest Indian Ocean, April 2014

S. de Villiers, K. Siswana, and K. Vena S. de Villiers et al.
  • Oceans and Coastal Research, Department of Environmental Affairs, Cape Town, South Africa

Abstract. Several open-ocean mesoscale features – a "young" warm-core (anti-cyclonic) eddy at 52° S, an "older" warm-core eddy at 57.5° S and an adjacent cold-core (cyclonic) eddy at 56° S – were surveyed during a R/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, which will be suitable for comparative study and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards. The major result is that the older warm-core eddy at 57.5° S is, at its core, 2.7 °C colder than a younger eddy at 52° S, while its dissolved silicate levels are almost 500 % higher and accompanied by chlorophyll a levels that are more than 200 % higher than that in the younger eddy. A total of 18 CTD stations were occupied in a sector south of the Southwest Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise. The CTD data, as well as chlorophyll a and dissolved nutrient data (for NO3, NO2, PO43− and SiO2), have been processed, quality controlled and made available via the PANGAEA Data Archiving and Publication database at doi:10.1594/PANGAEA.848875.

Short summary
A "young" warm-core eddy and an "older" warm-core eddy further south were surveyed in the Southern Ocean to study differences in their heat, salt and nutrient characteristics. Results show that warm eddies that migrate from the polar front further south lose heat but gain dissolved silicate and exhibit much higher levels of chlorophyll-a. This demonstrates important heat and nutrient exchange processes associated with eddy transport in the ocean.