Quantitative Evaluations of Turbulent Mixing and Double-Diffusive Convection Around Adelie Depression
Abstract
Adelie Land Bottom Water is thought to be mixture of Shelf Water from Adelie Depression and Circumpolar Deep Water (Gordon and Tchernia, 1972; Williams et al., 2008). To evaluate mixing strengths of turbulence and double-diffusive convection around the Adelie Depression, hydrographic observations using Sea-Bird Electronics SBE911plus with Lowered Acoustic Doppler Current Profiler (LADCP, RDI) were carried out off Adelie Land including Adelie Depression by TR/V Umitaka-Maru in austral summer of 2008. This observation was conducted as a part of CEAMARC project (Collaborative East Antarctic Marine Census, URL: http://www.caml.aq). Shelf Water (θ<-1.7°C, σ2>37.16) was only found in the depression. Temperature inversions due to intrusions of warmer offshore waters of Circumpolar Deep Water origin were found from 250 to 350 dbar at some stations in the depression. Velocity field around the depression obtained by LADCP indicated that the intrusions were related to inflow of southward current. Turbulent eddy diffusivity Kv were estimated from vertical overturning scale of density inversions. Relatively large values of Kv (10-4~10-3m2s-1) were found at continental shelf and slope regions, and in the Adelie Depression. On the other hand, Kv in the open ocean showed one or two order smaller than that in the boundary region and Adelie Depression. These results showed the possibility of boundary mixing in these regions. Next, activities of double-diffusive convection were examined from Turner angle Tu. Values of Tu in the upper part of the intrusions in the depression were up to about -80°, indicating active diffusive convection, and the values were about 60° in the lower part of the intrusions, indicating weak salt finger convection. While there were few active double-diffusive convection layers in the shelf and the depression, many active double-diffusive convection layers (75°<|Tu|<90°) distributed on the continental slope region. In this region, diffusivities of heat due to diffusive convection were O(10-5)m2s-1 above 500 dbar, whereas diffusivities of salt due to salt finger convection were up to about 10-4m2s-1 below the depth. Therefore double-diffusive convection may play an important role on the formation of bottom water which sinks along the continental slope.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMOS13C1204H
- Keywords:
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- 1626 Global climate models (3337;
- 4928);
- 1635 Oceans (1616;
- 3305;
- 4215;
- 4513);
- 4283 Water masses;
- 4532 General circulation (1218;
- 1222);
- 4540 Ice mechanics and air/sea/ice exchange processes (0700;
- 0750;
- 0752;
- 0754)