Downflow of the Antarctic shelf water at the shelf and continental slope of the Commonwealth Sea in the summer season and its effect on the bottom water formation in the Southern Ocean

Abstract

In the summer seasons of 2004–2007, the intensive runoff (cascading) of the Antarctic shelf water (ASW) down the shelf and continental slope was revealed thanks to the recording of numerous thermohaline profiles across the shelf and continental slope of the Commonwealth Sea and Prydz Bay. The quickly executed profiles (4–10 h) with submesoscale resolution (near the shelf’s edge, the scale was even eddy-determinative, i.e., within 1.9–5.6 km), in combination with the fine-structure sounding and fine vertical resolution of the near-bottom boundary layer, provided a qualitatively new level of understanding the natural data. The detailed analysis of the temperature, salinity, and density patterns revealed the regularities and peculiarities of the ASW shelf and slope cascading. The intensive ASW cascading near the shelf break and lower part of the slope can be forced (appearing as discrete frontal meanders) or free (appearing as discrete plumes) and often has a wave-eddy character. The field observational data confirmed the obtained representative estimates of the elements of the ASW slope cascading. The basic area of the ASW formation is near the Amery Shelf Ice, from where the ASW spreads to the northwest, goes around the Fram Bank, and flows down the continental slope. The evaluative contribution of the ASW slope cascading to the ventilation of the deep and slope water of the Southern Ocean (near the shelf break 70 km long where the ASW cascading was observed) is QK = 0.04–0.24 Sv, which agrees well with the analogous estimates obtained in other regions of the Antarctic.