Antje Buß

PhD project:

Upwelling in the Southern Ocean

Upwelling is the vertical advective movement of water towards the ocean surface and is driven by a divergence in the Ekman transport. It is an important process, as it changes the characteristics of the mixed layer and closes the mass balance of the meridional overturning circulation. Upwelling also provides a pathway for nutrients, gases and other components from the ocean‘s interior to the mixed layer and hence into the atmosphere. It may thus counteract the CO2 uptake of the ocean. However, estimates of upwelling velocities are rare, particularly in the Southern Ocean. Since upwelling velocities are too small to be measured directly - approximately a few meters per day - Rhein et al. (2010) introduced an indirect method to infer upwelling velocities from a helium isotope disequilibrium. Hydrothermal venting is the main source of 3He in the ocean and thus a disequilibrium in the mixed layer can only be caused by upwelling of 3He-enriched water from the ocean‘s interior.

During my Ph.D. project, I will calculate upwelling velocities, upwelling rates and heat fluxes in the Weddell Sea and in selected areas of the Antarctic Circumpolar Current (ACC). A historical helium isotope data set - measured from 1986 to 2009 - shows a significant excess of 3He in the mixed layer, but the horizontal and vertical resolution of the data sets is too low to calculate 3He gradients, which are necessary for the calculation of the upwelling velocities, upwelling rates and vertical heat fluxes. A new helium data set was collected, with a sufficient spatial resolution to calculate horizontal and vertical 3He gradients and from this upwelling velocities, rates and vertical heat fluxes, in November 2010 to February 2011 (Polarstern cruise ANT 27/2) and in January/February 2012 (Polarstern cruise ANT 28/3). For my Ph.D. project I will use the new data set as well as the historical data set to investigate upwelling in the Weddell Sea and in the ACC. I will also regard the role of the concurrent vertical mixing, the prevailing wind field and ice coverage. Furthermore, I will compare the helium based results with estimates based on estimates of Ekman pumping derived from wind field divergences.

Rhein, M., M. Dengler, J. Sültenfuß, R. Hummels, S. Hüttel-Kabus and B. Bourles (2010), Upwelling and associated heat flux in the equatorial Atlantic inferred from helium isotope disequilibrium. J. Geophys. Res., 115, C08021, doi:10.1029/2009JC005772

Research Area: A "Ocean and Climate"