Circulation and Mixing in the Core and Oxycline of the Tropical North Atlantic Oxygen Minimum Zone as inferred from two TREs.
Circulation and Mixing in the Core and Oxycline of the Tropical North Atlantic Oxygen Minimum Zone as inferred from two TREs.
Abstract:
The Guinea dome Upwelling Tracer Release Experiment (GUTRE) began in April 2008 and the final large scale survey took place in November 2010. A total of 92 kg of SF5CF3 were injected at 8°N, 23°W in the upper part of the oxygen minimum zone (OMZ). Three subsequent survey cruises measured the tracer distribution approximately 7, 20 and 30 months after the tracer release. The experiment was designed to estimate the time-mean diapycnal mixing rate at the upper boundary of the OMZ and some first estimates for the horizontal mixing and exchange. We found that the best estimate of time and space integrated diapycnal mixing over the region covered by the tracer was 1.19 ± 0.18 × 10-5 m2 s-1 (Banyte et al., 2012). A second TRE, the Oxygen Supply Tracer Release Experiment (OSTRE) began in December 2012. A total of 88.5 kg of CF3SF5 (tracer) was released in the center of the oxygen minimum zone at roughly 10° 30’ N and 21° 00’ W at the depth of the lowest oxygen values on the potential density anomaly surface 27.035 kg m-3. Three subsequent survey cruises measured the tracer distribution approximately 7, 15 and 29 months after the tracer release. Even though the OSTRE experiment was designed to quantify the horizontal diffusion, it also offers the opportunity to quantify the vertical diffusivity at the center of the OMZ, and compare that with the estimates from GUTRE that measured the vertical diffusivity in the oxycline. The mean di- apycnal diffusivity in Cartesian coordinates was found to be only insignificantly smaller with 1.06 ± 0.22 × 10-5 m2 s-1 in the OMZ core. The role of seamounts and a comparison with mixing across density layers will be discussed.
The horizontal spreading of the tracer was qualitatively and quantitatively compared to a tracer release in a high resolution ocean circulation model and showed some rather striking similarities. Estimation of the strength of zonally alternating jets using a simple jet dispersion model will be presented.