Water Of Southern Origin Research Articles

Water masses in the Gulf of Aden

Hydrographic data collected from Gulf of Aden since 1920 have been compiled to identify and refine the definitions of water masses in the Gulf of Aden (GA) and to describe their spatio-temporal variability. Four water masses have been identified based on their θ-S characteristics. The Red Sea Water (RSW) that flows from the Red Sea is the most prominent water in the GA; this occupies about 37% of the total volume of Gulf of Aden. The Gulf of Aden Surface Water (∼3%) forms as a mixture of local water and the water from western Arabian Sea during winter and Red Sea surface water during summer. The intermediate water, identified as Gulf of Aden Intermediate Water (GAIW), occupies about 9% of the total volume of GA; a characteristic salinity minimum is associated with it at σθ=26.50 kg m−3. The northward spread of sub-tropical subsurface water from the south appears to be the major source of GAIW. The bottom water, named Gulf of Aden Bottom Water, showed the least variability. It was formed due to the mixing of Red Sea Water and water of southern origin. Mixing triangles have been used to analyze the composition of water in the GA.

Seasonal uptake of anthropogenic CO2 in an ocean general circulation model

A model of the inorganic carbon cycle, embedded within an ocean general circulation model is described, and results from a seasonal simulation of the present-day ocean carbon cycle are presented. Whilst the circulation characteristics of the model appear reasonable, the model gives North Atlantic Deep Water rates that are too low compared with deep water of southern origin, which may result in an overestimate of the southern hemisphere uptake. A comparison of the model results with available observations of dissolved inorganic carbon and partial pressure of carbon dioxide reveals that a defect in the present model is the neglect of ocean biology, which causes the phase of seasonal variations in partial pressure in high latitudes to be incorrectly simulated. A series of experiments were performed in which CO 2 was added to the atmosphere at a specific rate to simulate anthropogenic emissions. The model predicts an oceanic uptake of 44 % of atmospheric emissions at the end of a 50-year run. The largest sinks in the model occur in the southern hemisphere and equatorial regions. A comparison between parallel runs made under conditions of seasonally varying and annual-mean forcing reveals that the use of seasonal forcing in the present model makes little difference to the estimate of global oceanic uptake of anthropogenic CO 2 . Varying the background coefficient of vertical diffusion, within commonly accepted limits, is found to have a much greater impact on CO 2 uptake estimates

A chlorofluoromethane and hydrographic section across Drake Passage: Deep water ventilation and meridional property transport

New hydrographic and nutrient data obtained on a section across Drake Passage (F/S Meteor January 1990, World Ocean Circulation Experiment Hydrographic Program section S1) are in close agreement with property sections reported previously. The chlorofluoromethanes CFM 11 and CFM 12 were measured in Drake Passage for the first time. CFM concentrations are found to decrease from the surface down into the Upper Circumpolar Deep Water, for which they confirm water renewal from the south. For the Lower Circumpolar Deep Water, in which CFM concentrations were above detection limit only south of the Polar Front, very little water renewal on the CFM time scale is implied. Nonvanishing CFM is again found in the Weddell Sea Deep Water and the Southeast Pacific Deep Water toward the bottom in the south, but recent ventilation for the latter water mass is rejected. CFM 11 and CFM 12 concentrations vary essentially in constant proportion down to very low concentrations, questioning the possibility of using CFM ratios as “age” markers. The observed ratios are shown to be a natural feature of the upwelling regime of the southern ocean. Property concentrations on isopycnal surfaces display large undulations, reaching down into the Upper Circumpolar Deep Water. Their extrema, due to varying contribution of young water of southern origin, are situated at the boundaries of the current bands of the Antarctic Circumpolar Current The feature is ascribed to property advection by rings and is taken to support previous claims that rings are an important transport mechanism across the Antarctic Circumpolar Current and that they might assist in maintaining its fronts.

Hydrography of the central Atlantic—I. The two-degree discontinuity

A discontinuity in the slope of the property-property relationships for the deep water in the central Atlantic is clearly confirmed by the Geochemical Ocean Sections (GEOSECS) data. The potential temperature and salinity of the discontinuity water lie within the limits 2.08 ± 0.15°Cand 34.90 ± 0.01‰ from 40°N to 30°S. The horizon slopes up from a depth of 4.0 km (σθ = 27.92) at the northern to 3.2 km (σθ = 27.90) at the southern end of this region. The discontinuity water consists of 89% water of northern and 11% water of southern origin. It is proposed that this water represents the outflow from the topographically confined abyssal Atlantic. If so, the ratio of the input rate to the northern end member to that of the southern end member is about 8. The changes in abundance of the nutrient elements along the discontinuity horizon are best explained if respiration and opal dissolution take place primarily in the eastern basin. An alternate hypothesis for the origin of the discontinuity involves the active erosion of a previously more extensive mixing zone between North Atlantic Deep Water and Antarctic Bottom Water.