Ocean Circulation and Climate Dynamics

PREFACE - Enhancing PREdiction oF tropical Atlanbtic ClimatE and its impacts

PREFACE aims at a better understanding of the physical processes driving today's climate in the Tropical Atlantic. Understanding the interaction of the atmosphere and ocean in the Tropical Atlantic region is key to accurately project the future climate for the Tropical Atlantic region as well as the global climate. In the framework of PREFACE a quantification of the cumulative effects of climate variability, greenhouse-induced climate change and fisheries on marine ecosystems and functional diversity is aspired. Furthermore, one objective is to assess socio-economic vulnerabilities of the West-African fishing communities and evaluate their resilience to climate-driven ecosystem shifts and global markets.
 

WP4: Circulation and wave response

WP4 aims at improving our understanding of the role of local and remote forcings, such as circulation variability or wave propagation along the equatorial and coastal wave-guide, in setting the mean sea surface temperature pattern and in driving sea surface temperature variability in the eastern boundary coastal upwelling regions of both hemispheres. The sea surface temperature variability in the eastern equatorial Atlantic is forced by different processes: Year-to-year variations are associated with air-sea interactions (including the positive Bjerknes feedback) similar to processes resulting in the El Niño phenomenon of the equatorial Pacific (the so-called Atlantic Niño), by advection and wave dynamics as well as by internal variability associated with stochastic processes due to variations in the intensity of tropical instability waves or basin-mode oscillations associated with the generation of equatorial deep jets. The equatorial variability was found to be strongly related to the generation of Benguela Niños, warm oceanic events in the southeastern tropical and subtropical Atlantic (Rouault, 2012).
However, local forcing of sea surface temperature variability in the coastal upwelling regimes of both hemispheres might be as important. In the southern hemisphere south of about 13°S, coastal upwelling is strongly related to variations in along-shore winds, north of it upwelling also occurs during periods of calm winds possibly induced by coastal Kelvin wave propagation.
 
The specific objectives of WP4 are as follows:

  1. Extend the existing observational network by installing new time series stations to allow evaluation of changes in the advection of anomalous water masses and wave propagation along the equatorial and coastal wave guides.
     
  2. Using historical and new observational data to characterize the local circulation system near the coastal upwelling regions including the Gabon and Angola Currents, the upwelling undercurrents, and the Angola Dome.
     
  3. Identify and understand differences in the connection of coastal upwelling systems of both hemispheres with the equatorial region.
     
  4. Understand the generation and evolution of warm and cold events in the coastal upwelling regions of both hemispheres.
Fig. 1: Ship-sections of a) alongshore (-34˚TN) velocity [m/s], b) Temperature [˚C], and c) Oxygen content [µmol/kg] during R.V. Meteor cruise M98 in July 2013. Dashed black contours denote isopycnals [kg/m3-1000]. In a) the configuration of the boundary current array, that was deployed during M98, is sketched.

 

For a list of observations to be used in PREFACE, please follow this link: Observations

Team:
Dr. Marcus Dengler
Prof. Dr. Peter Brandt
Dr. Willi Rath
Msc. Robert Kopte