Cold-core eddy

Low, but measurable N2 fixation rates were recently reported by Needoba et al. (2007), from the inter-convergence zone, 200 km off the coast of Northern California, where sea surface temperatures were >19°C. In addition, they reported the temporal dynamics of mRNA abundance for nijH down to 80 m, where temperatures ranged 14-19°C, and expression was dominated by a unicellular Group A phylotype, and to a lesser extent by Group B. Similarly, HoU et al. (2007) reported N2 fixation in the upper water column of warm core and cold core eddies at temperatures at or below 19C in the Leeuwin Current off the west coast of Australia. 

Yilmaz, A. and Tugral, S. (1998) The effect of cold- and warm-core eddies on the distribution and stoichiometry of dissolved nutrients in the northeastern Mediterranean. Journal of Marine Systems, 16, 253-268. 

Fig. 1.36 (Chern and Wang, 2003) depicts the horizontal distribution of temperature in the second layer, 25 50 m, averaged over a year. The 25 °C isotherm separates the SCS into two regions. The cold water, <25 °C, occurs in the northwestern part of the basin, corresponding to the main cyclonic eddy. The core of the eddy, to the west of Luzon, has a mean temperature lower than 24 °C. The warm water, >25 °C, occurs in the southern SCS, including the Gulf of Thailand, the Luzon Strait, and the region of the anticyclonic eddy to the southwest of Taiwan region.

Mixing phenomena between cold and hot fluids at the core exit, investigated in simulation experiments with air (AIRJECO) and sodium (NAJECO, were already presented [Ref. 1-2]. Simulations were obtained with Large Eddies Simulations (LES). The LES filtered Navier-Stokes equations were solved using the TRIO-VF code. 

In the mixed core, illustrated in Fig. 8-1, the inlet and outlet are concentric at the top of the sphere. The inlet jet coincides with the vertical axis of the sphere and is broken up when it hits the bottom surface. Except for the cold central jet, the bulk of the core is at outlet temperature. The velocity of eddies is great enough so that the gas bubbles travel along with the liciuid. The pressure drop is about 1.0 to 1.5 inlet-velocity heads. The core-tank surface is maintained at a temperature very close to that of the core fluid l)y the high turbulence. 

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