Climate and Ocean Dynamics
The world ocean forms a crucial component of the earth's climate system. Our group investigates the dynamics of the oceans and its interaction with other climate system components like the atmosphere, cryosphere and biosphere to provide a better understanding of the ocean's role in the variability of the world's climate.
Our studies cover a wide range of spacial and temporal scales from mesoscale eddies or a small island, like Moorea, to the whole Southern Ocean or the Pacific and from intra-seasonal to millennial time scales. In all cases we keep the interaction of ocean dynamics with biogeochemistry in mind linking us the other groups at UP.
Mesoscale Eddies
The atmosphere and ocean consist of a broadband spectrum of differing scales of motion, varying from meters up to thousands of kilometers in size. While these scales interact internally in each system, the atmosphere and ocean are strongly coupled and communicate on a variety of differing spatial and time scales. While we understand quite well how the atmosphere and the ocean interact at large scales, we are only just beginning to understand the role of smaller scale interactions both internally in each system and between the two. What is becoming increasingly apparent is that mesoscales, that range from 10’s to a few 100’s of kilometres can have a profound impact on the dynamics and climate sensitivity of the entire system. Particularly in the Southern-Ocean where mesoscale processes are largely responsible for the insensitivity of the Antarctic Circumpolar Current to increased winds. Moreover they therefore provide a regulation of the Southern Ocean carbon and heat uptake. The degree to which they compensate the MOC largely depends upon the energy contained in the ocean mesoscale eddy field.
While the main energy pathway via which mesoscale ocean eddies are generated and powered is well known (wind generated potential energy, followed by baroclinic instability), however, during their lifetime the temperature anomalies associated with eddies change the atmosphere above them, increasing/decreasing heat fluxes, which changes the overlying wind, evaporation which in turn affects cloud formation and even rain. How and if these small scale changes have strong implications for short and long term variability of the atmosphere and if the ocean responds in turn to the eddy induced changes to the wind forcing remains largely unknown. Our research aims to answer such questions.
In particular our research group has quantified the magnitude and physical mechanism responsible of the atmospheric response above small-scale ocean eddies and how these change depending upon the atmospheric conditions. This has allowed us to develop a bulk flux parameterization for the eddy-induced effects upon the atmosphere. While a simulation of the entire Southern Ocean on climatic timescales, using our full high resolution Coupled Atmosphere-Ocean model is not feasible, the use of this parameterization to mimic our coupled Atmosphere-Ocean model allows us to begin to understand the long term integrated effects of this small scale coupling on the Southern Ocean dynamics and climate sensitivity.
Large-scale ocean dynamics and climate
In our research group, we focus on the interaction of ocean dynamics with the climate system in the Southern Ocean and in the tropical Pacific.
The Southern Ocean provides a major return pathway of deep ocean water masses to the surface and is, thus, a key component of the global meridional overturning circulation. Next to the upwelling, in this region around the Antarctic continent, also important new water masses are formed, feeding the global thermocline waters and the ocean's abyss. Through this interaction of the deep and surface ocean, the Southern Ocean plays a key role for the global carbon cycle and ocean heat uptake (e.g. Frölicher et al., 2015) and thus for the global climate. In particular, we (Alexander Haumann, Matthias Münnich, Samuel Eberenz) study the impact of changing surface freshwater fluxes on the Southern Ocean stratification, water mass formation and overturning circulation. Based on satellite data from recent decades, we derived estimates of freshwater fluxes associated with sea ice melting and freezing, which is a key component of the high-latitude freshwater budget (Haumann et al., in prep.). Performing high-resolution simulations with a coupled biogeochemistry-ocean model (ROMS-BEC), we investigate the impact of the different components in the surface freshwater budget on the ocean. Moreover, we investigate and contrast the role of these components in determining Southern Ocean stratification during cold (LGM) and warm (present, 21st century) climates, as their influence on the ocean stratification is potentially much stronger in a colder climate with substantial biogeochemical consequences.
A further research area within our group (Matthias Münnich, Martin Frischknecht) are the ocean dynamics of the tropical Pacific, which have through the El Niño Southern Oscillation (ENSO) a profound influence on the global and regional climate (e.g. Münnich et al., 2005). We perform high-resolution simulations with ROMS to for example investigate the influence of ENSO dynamics on the eastern boundary upwelling systems (e.g. Frischknecht et al., 2015).
Key publications
Frenger, I., Gruber, N., Knutti, R. & Münnich, M. Imprint of Southern Ocean eddies on winds, clouds and rainfall. Nat. Geosci. 1–14 (2013). doi:10.1038/NGEO1863
Byrne, D., Papritz, L., and Frenger, I., and Münnich, M. and Gruber, N. Atmospheric response to mesoscale sea surface temperature anomalies: assessment of mechanisms and coupling strength in a high resolution coupled model over the South Atlantic. Journal of the Atmospheric Sciences (2014). doi: 10.1175/JAS-D-14-0195.1
Haumann, F. A., N. Gruber, M. Münnich, I. Frenger, and S. Kern (2016): Sea-ice transport driving Southern Ocean salinity and its recent trends. Nature, 537, 89–92. doi:10.1038/nature19101.
Frischknecht, M., M. Münnich, and N. Gruber (2015), Remote versus local influence of ENSO on the California Current System, J. Geophys. Res. Oceans, 120, doi:10.1002/2014JC010531.
Frölicher, T. L., J. L. Sarmiento, D. J. Paynter, J. P. Dunne, J. P. Krasting, and M. Winton, (2015), Dominance of the Southern Ocean in anthropogenic carbon and heat uptake in CMIP5 models. J. Climate, 28, 862-886.
Münnich, M., and J. D. Neelin (2005), Seasonal influence of ENSO on the Atlantic ITCZ and equatorial South America, Geophys. Res. Lett., 32, L21709, doi:10.1029/2005GL023900.