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Changes in Ocean Circulation: Approach
In the framework of the junior research group climate models of different complexity are applied to questions of past, present and future climate change. The most important tool is a complex prognostic climate model (Kiel Climate Model System, KCMS) developed at the GEOMAR. The model has already been shown to realistically reproduce present day ocean circulation, while its performance under past climate conditions has not been tested yet.
In order to assess the performance of the KCMS for past climates, the model is adapted to boundary conditions of the present and last interglacial (Holocene: ≈ 0-10 kyr BP; Eemian: ≈ 115-130 kyr BP). The application of boundary conditions from the Holocene and the Eemian is largely a test of the sensitivity of the model to changes in solar radiation, as induced by changes in the configuration of the orbital parameters eccentricity, obliquity and precession. Six 1000 year long quasi steady-state simulations are performed for distinct time periods in the past. In particular, these are preindustrial (0 kyr BP), mid Holocene (6 kyr BP), early Holocene (9.5 kyr BP), late Eemian (115 kyr BP) mid Eemian (122 kyr BP), and early Eemian (126 kyr BP). The Eemian often serves as an analogue for the Holocene as it experienced similar climatic conditions. Additionally, trends in orbital forcing over both periods have some similarities with a gradual decrease in obliquity and an increase in the precessional index, although the Eemian has overall higher eccentricity and lower obliquity and the amplitude of insolation change is much more pronounced than during the Holocene (see figure).
The experiments result in three dimensional data sets of ocean and atmosphere characteristics covering full annual cycles as well as interannual climate variability. Analyses are carried out with respect to e.g. sea surface temperatures, precipitation patterns, ocean currents and marine biogeochemical cycles. After the analysis of model data, the results are compared to paleo proxy data from marine sediment cores or other reservoirs representing the same processes and features of the climate system.
