Hydrographic characteristics of the Indian sector of the Southern Ocean

Citation
Pv. Shirodkar et al., Hydrographic characteristics of the Indian sector of the Southern Ocean, CURRENT SCI, 77(10), 1999, pp. 1273-1282
Citations number
21
Categorie Soggetti
Multidisciplinary,Multidisciplinary
Journal title
CURRENT SCIENCE
ISSN journal
00113891 → ACNP
Volume
77
Issue
10
Year of publication
1999
Pages
1273 - 1282
Database
ISI
SICI code
0011-3891(19991125)77:10<1273:HCOTIS>2.0.ZU;2-C
Abstract
Oceanographic studies in the Indian sector of the Southern Ocean (58-61 deg rees S; and 30-40 degrees E) carried out during December 1995 and March 199 6 indicate a 3-layer structure typical of summer in the oceanic domain sout h of the Antarctic Polar Front. The upper 300 m water column consists of th ree distinctive thermohaline characteristics. The surface layer (50 m) of s ummer surface water formed by seasonal warming with temperatures (0-2 degre es C) and low salinity (< 33.8 PSU), the intermediate layer (50-150 m) of w inter reminiscent water with negative temperatures (0 to -2 degrees C) and moderate salinity (33.8-34.3 PSU) and the deeper layer (below 150 m) of Cir cumpolar Deep Watermass (CDW) with positive temperatures (0-2 degrees C) an d higher salinity (34.3-34.8PSU). The influence of the strong Antarctic Div ergence between the east and west drifts is noticed at 61 degrees S, 34 deg rees E marked by phytoplankton and zooplankton patches. The dissolved oxygen (DO) shows high concentrations (7.6 to >8.0 ml l(-1)) in the upper layer, These higher levels of DO sometimes extend down to the intermediate layer and gradually decrease further downwards. The observed l ow temperature and high DO in the subsurface water (50-75 m) are typical si gnatures of Antarctic Winter Watermass (AWW) formed during winter, Calcium, magnesium and boron show significant spatial variations with higher values of Ca and Mg along 59 degrees S and 60 degrees S relative to 61 degrees S, Ca exhibits large variations (398-421 mg kg(-1) while Mg shows least varia tions with concentrations close to the average value for normal sea water ( 1294 mg kg(-1)). Boron depicts high values along 59 degrees S and 61 degree s S compared to 60 degrees S, with higher values in the subsurface layer (2 5-75 m) which are attributed to biological characteristics and the frontal systems in the region. Phytoplankton cell counts remain high (between 1.92 and 22.9 x 10(4) per li tre) while zooplankton biomass shows variations from 9.8 to 303.62 ml 100 m (-3). A marked drop of both phytoplankton and zooplankton in the region of krill swarm (between 60 degrees 40'-61 degrees 13'S and 33 degrees 34'-34 d egrees 14'E), however, indicates active feeding by the latter on the plankt onic communities.