And Antarctic Intermediate Water Research Articles

Water Mass Transformation in the Southern Ocean of a Global Isopycnal Coordinate GCM

Abstract A global isopycnal coordinate GCM is used to investigate the processes that drive the meridional circulation, transformation, and interocean exchange of water masses in the Southern Ocean. The noneddy-resolving model (mesh size 1.25°) includes an active mixed layer, parameterized bolus transport, and seasonally varying surface fluxes. The model gives a plausible picture of the formation and circulation of subantarctic mode water (SAMW) and Antarctic Intermediate Water (AAIW). Progressively denser versions of SAMW and AAIW form in the Indian and Pacific Oceans as the Antarctic Circumpolar Current drifts south and loses buoyancy. SAMW forms predominantly in the Indian Ocean, at a rate of 20 Sv (Sv ≡ 106 m3 s−1), while AAIW forms mainly in the Pacific sector, at a rate of 8.5 Sv. Throughout the circumpolar zone 25°–42.5°S, there is a net formation of 11 Sv of SAMW, largely by surface cooling. This SAMW is exported northward across 25°S into the subtropical gyres. The properties, distribution, and re...

Cadmium in the southwest Pacific Ocean two factors significantly affecting the CdPO4 relationship in the ocean

Vertical profiles of dissolved Cd were determined in the southwest Pacific Ocean, which includes the Tasman Sea, the Solomon Sea, and the Coral Sea. Cd shows a nutrient type distribution, but weakly correlates with phosphate compared to the North Pacific Ocean when all data are plotted. The CdPO4 ratio in surface layer is < 0.1 nMμM and the ratio in the intermediate and deep water shows an increase approaching the Pacific value of ~ 0.3 nMμM. The CdPO4 ratio in the regeneration process has been estimated using an AOU (apparent oxygen utilization) respiration model. This ratio is affected by that in surface layer, so deep water receives a regeneration flux with a low CdPO4 ratio. The preformed Cd and phosphate as estimated by the AOU relation are low in the surface layer and high in the deep layers. The intermediate water is a mixture of surface water and Antarctic Intermediate Water (AAIW). The characteristic CdPO4 relationship in this area would be a consequence of mixing with two water masses which have different original CdPO4 ratios. The factors affecting the CdPO4 relationship in the world ocean are physical mixing and biological cycling, based on the results of the southern Pacific Ocean.

Antarctic intermediate water intrusion into South Atlantic Bight shelf waters

Surface seawater samples were collected from seven stations on the coastline bordering the South Atlantic Bight and the southern Mid-Atlantic Bight in March 1986 and analysed for radiocarbon. Depletion in radiocarbon activity was observed in shelf water along the South Carolina coast at Myrtle Beach and Isle of Palms. If Sargasso Sea surface water withΔ 14C = 168‰ and Antarctic Intermediate Water (AAIW) withΔ 14C = −90‰ are two end members which supply water to this coastal region, a contribution of about 20–25% AAIW is required to produce theΔ 14C values observed.

The vertical thermohaline structure in the Argentine basin

The vertical thermohaline structure in the central Argentine basin is investigated on the basis of high‐resolution hydrographic data. Emphasis is placed on fronts, their horizontal gradients, vertical stability and associated fine structure. Horizontal thermohaline gradients vary strongly with depth, regions of strong gradients alternating with those of weak gradients. The strongest gradients occur often at depths below the upper mixed layer. The salinity gradient maximum occurs above the temperature gradient maximum. Enhanced gradients are found where warm, salty water moves over cooler, fresher water such as between the subtropical water (STW) and antarctic intermediate water (AAIW) and between the North Atlantic deep water (NADW) and the antarctic bottom water (AABW). Temperature, salinity, and density fronts do not always coexist. Density‐compensating temperature and salinity fronts occur in the surface layer of the subantarctic and at abyssal depth below 3500 m. Vertical profiles of the Väisälä frequency indicate much reduced hydrostatic stabilities in the Brazil current and subantarctic frontal zones. Potential vorticity minima indicate the formation of subantarctic mode water just north of the subantarctic front and its subsequent northward and upward spread across isopycnals. The thermohaline fine structure is vertically intermittent. The amplitude variances between the enhanced and quiet regions vary by almost 2 orders of magnitude. Enhanced fine structure amplitudes are found near the STW‐AAIW and NADW‐AABW interfaces, where large horizontal thermohaline gradients occur and the hydrostatic stability is low. The temperature and salinity fine structures are largely density compensating. The coherence between the temperature and salinity fine structure is strongly depth dependent and is highest in regions where warm, salty water moves over cooler, fresher water.

Mixing Trajectories of Intermediate Depth Waters of the South-East Indian Ocean as Determined by a Salinity Frequency Method

A new method for the detection of water masses and for the tracing of their mixing paths is described. Histograms of the salinity frequency distribution on 0.10 σt intervals from σt 26.90 to 27.70 contain modes which indicate the salinity characteristics of the intermediate water masses of the south-east Indian Ocean. These salinity characteristics are used to trace the extent of spreading of the water masses on these σt intervals and to determine trajectories of shallow and deep mixing. Comparison is made of the results obtained by the new method with those by the core method for the water masses and circulation in intermediate depth of the south-east Indian Ocean. The core method in this region has not been able to show the large extent of deep mixing associated with the spreading of the Banda and Antarctic Intermediate water masses. The core method has also failed to show the widespread distribution of patches of Banda water at about 400-500 m throughout the whole south-east Indian Ocean.