Ocean Circulation and Climate Dynamics

Paleoclimate modelling

Figure 1a.: Upper panel; A mid-Cretaceous palegeography as basis for the model-ling. 1b.: Lower panel; Results from a coupled Atmospheric-Oceanic-General-Circulation-Model (AOGCM) predict a strong thermohaline circulation and intense ventilation in the Late Cretaceous under high pCO2 – contrary to previous sugges-tions of a stagnant greenhouse ocean.
Figure 2a: Upper panel; Onset of OAE1a and OAE2 in the two selected key locali-ties that allow high resolution (centennial to millennial scale) studies of the onset of Cretaceous anoxic events (from Kuhnt et al., 2000 and 2004) and database of Cre-taceous OAE2 sites with material available for the proposed reconstruction of lati-tudinal extension of enhanced OM accumulation and anoxia (Holbourn & Kuhnt, unpublished). Figure 2b: Lower panel; Modelled (red line) versus measured δ13Ccarb data.

During Earths history, the climate system has experienced tremendous amplitudes of global climate change, such as transitions from icehouse to greenhouse states and back again or sea-level changes, regional changes such as glaciation, desertification, or tectonic uplift, and local changes in land cover or changes in freshwater discharge. 
Spanning millions of years or just decades, the geologic record is a vital, but incomplete (e.g. by subduction or erosion) report of Earth's climate history. Therefore, efforts to understand past climate change apply and rely on numeric climate models that include the relevant physical and biogeochemical processes of the climate system. This includes modelling of the ocean and atmospheric circulation, as well as past pCO2 levels or biogeochemical nutrient cycling. Better understanding of feedback processes in and between the various compartments of Earth’s climate are a prerequisite for an improved view on past dynamics and anticipated future global change. 
The Paleoclimate Modelling Group within the Paleoceanography research unit uses a hierarchy of climate and biogeochemical models to investigate the underlying mechanisms of past climate states. Numeric models help us to gain insights into the mechanisms and processes controlling and linking the various compartments of Earth’s climate system. In turn, the comparison between the output from these simulations and the paleoclimate proxy data provides the only way to validate current state-of-the-art climate models commonly used for future climate change scenarios. Currently, we use models of different complexity such as General Circulation Models (GCMs), models of intermediate complexity, and biogeochemical box models to investigate the longterm evolution of climate.   

 Research topics and associated projects:  

 ·      Cretaceous (~118 Ma and ~94 Ma) climate variability and anoxia  
SFB 754 - Unraveling the Onset and Spread of Cretaceous Anoxia   

·      Interglacial (~15 ka) hydrodynamics in the Gulf of Mexico   
 SPP Interdynamics – LOOP current variability – its relation to meridional overturning circulation and the impact of Mississippi discharge   

 ·      Lena River freshwater plume in the Laptev Sea   
Changing Eurasian shelf seas – oceanic frontal systems and polynyas in the Laptev Sea


Unraveling the Onset and Spread of Cretaceous Anoxia
Evolving carbon sinks in the young South Atlantic: Drivers of global climate in the early Cretaceous Greenhouse?


Dr. Sascha Flögel
email: sfloegel(at)geomar.de