Research Group Ocean Physics

The 'Ocean Physics' group aims at identifying and understanding the major processes and internal feedback loops relevant for the climate system. To consider potential feedbacks within the climate system, each individual component of the climate is simulated by a complex model and the individual models are coupled to each other.

In our studies, these complex model systems are used to perform long-term climate simulations with coarse spatial resolution and century-scale regional simulations with very high resolution.

In addition to physical modelling we also consider several tracers which are measured in sediment cores. These developments allow assessing model performances, elucidating past deep ocean circulation changes, and developing transfer functions linking the current ocean state and the sediment record.

 

Paleo climate modelling

For the long-term studies, emphasis is laid on investigating the mechanisms behind paleoclimate changes, which are preserved in natural climate archives. These kind of simulations also allow us to test and validate our models for parameter ranges which differ from present day. Our long-term goal is to perform transient simulations of the last glacial cycle (starting 135 000 years before present) in a coupled ice sheet-climate model framework. Our current focus is on simulations of the Last Glacial Maximum (21 000 years before present) and the last deglaciation. We apply the Max-Planck-Institute Earth System Model (MPI-ESM) in different setups together with the ice sheet model PISM.

Specifically, we are interested in the drivers of the massive ice sheet melt and the climate warming defining the deglaciation. Further, we aim to understand the processes behind the sudden climate swings during this period. We also investigate the dependence of the glacial Atlantic Meridional Overturning Circulation (AMOC) on greenhouse gas concentrations, ice sheet forcing and insolation, examining potential tipping points and thresholds.

Examples:

  • Simulation of Last Glacial Maximum ice sheets in a coupled ice sheet-climate model and the simulation of Heinrich event-like ice sheet surges (more)
  • Transient climate simulations from the Last Glacial Maximum to present day, using a coupled model setup with freely evolving ice sheets
  • Effect of greenhouse gas concentrations and ice sheets on the glacial AMOC (more)

Contacts: Marie Kapsch, Marlene Klockmann, Virna Meccia, Uwe Mikolajewicz, Florian Ziemen

Regional climate modelling

We also investigate ocean and atmosphere dynamics on regional scales, in particular in the Arctic and the Northwest European Shelf (NWES). For past and present-day simulations we focus on the understanding of natural variability in the climate system, while for future projections anthropogenic climate change impacts become important as well. We examine physical and biogeochemical exchange processes between shelf seas and the open ocean, and study air-sea interactions, including sea ice dynamics.

For modelling regional climate, the spatial resolution of global circulation models is insufficient to resolve small scale processes, such as slope convection and complex topography. To allow for higher horizontal resolution in the region of interest, we apply a regional model system, consisting of the global ocean-sea ice model MPIOM, the biogeochemistry model HAMOCC, the regional atmosphere model REMO and the hydrological discharge model HD.

Examples:

  • Patterns of natural variability in the North Sea physical conditions and their major driving mechanisms (more)
  • Potential future changes in the thermal stratification of the NWES and their effects on the distribution of nutrients, the shelf carbon pump and the trophic state of the ocean
  • The impact of large-scale climate and circulation changes on the future biogeochemical state of the NWES (more)
  • Potential future changes in the statistics of extreme events in the European Seas, such as storm surges
  • The interannual variability of the Arctic freshwater cycle and its driving mechanisms (more)
  • The variability of the Arctic Odden in the Nordic Seas (more),
  • Future changes in the Arctic sea ice

Contacts: Moritz Mathis, Uwe Mikolajewicz, Laura Niederdrenk

Proxy modelling

Marine sediments provide archives enabling reconstruction of past ocean states and variability. However, the relationship between observed quantities in sediment cores and ocean conditions is not straightforward. Another difficulty consists in obtaining an accurate chronology of events as recorded by proxies. These two aspects are investigated.

Regional scale: transfer function

At the regional scale, we focus on the Gulf of Taranto (Eastern Mediterranean Sea) where high resolution sediment records are available. Our goal is reconstructing climate variability and biogeochemical cycles over the late Holocene. In order to derive appropriate transfer functions, i.e., the relationships between sediment proxy data and environmental parameters, we perform model simulations under present-day conditions. We take advantage of the eddy-permitting physical model MPIOM and the biogeochemistry model HAMOCC which includes a sediment module. The very high resolution (approx. 9 km) of this version allows capturing small scale features in the region of interest.

More information is available here: TARANTO

Global scale: deep ocean chronologies

At the global scale, we are interested in the past deep ocean circulation changes in terms of transport pathways and transit times. We focus on Heinrich-like events to investigate to what extent the temporal evolution of the ocean circulation during abrupt climate transitions may be inferred from deep-sea sediment cores. A simplified biogeochemical cycle module is implemented in the physical model in order to reproduce the evolution of tracers recorded in sediment cores. An additional component including different age tracers allows deciphering patterns of ocean ventilation.

More information is available here: OCTANT

Contacts: Feifei Liu, Uwe Mikolajewicz, Anne Mouchet