Abstract
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.
Highlights
The circulation and thermohaline structure of the Southern Ocean is of critical importance to global exchanges of heat, freshwater and biogeochemical constituents such as nutrients and CO2
A detailed understanding of the role of mesoscale eddy transport in these processes is still lacking. It has only fairly recently been established that mesoscale eddies contain most of the kinetic energy of ocean circulation (Fu et al, 2010; Ferrari and Wunsch, 2009) and that the global zonal eddy volume transport is comparable in magnitude to that of the large-scale wind- and thermohaline-driven circulation (Zhang et al, 2014)
The objective of this paper is to present an overview of in situ data that had been collected in the southern hemispheric autumn, across a number of distinct mesoscale features in the southwestern Indian sector of the Southern Ocean (Fig. 1), and to make this data set available to the scientific community
Summary
The circulation and thermohaline structure of the Southern Ocean is of critical importance to global exchanges of heat, freshwater and biogeochemical constituents such as nutrients and CO2. Our understanding of the global significance of coincident large-scale patterns of enhanced open-ocean productivity and mesoscale activity, as well as the importance of eddyinduced nutrient transport, is still in its infancy Progress in this field, including the incorporation of biogeochemical cycles into eddy-resolving general circulation models, is severely limited by scarce in situ data, collected with the specific aim of improving our understanding of the physical and biogeochemical processes associated with mesoscale features such as eddies (Joyce et al, 1981; Mahadevan and Archer, 2010; Ansorge et al, 2010; Lehahn et al, 2011; Stramma et al, 2013; Chen et al, 2015). This represents an important knowledge gap, with regards to understanding Southern Ocean nutrient transport processes and carbon cycling
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