Project Outline

CorClim aims at reconstructing North Atlantic climate variability on interannual to multidecadal time scales over the last centuries beyond the period that is covered by instrumental data. The approach is twofold employing proxy data and numerical modelling. Proxy records are primarily derived from Bermuda corals and include annual growth rates as well as monthly geochemical parameters (i.e., skeletal stable isotopic and trace elemental compositions). The key parameter we focus on in our reconstructions is sea surface temperature (SST). The advantage of the coral proxies is that they reflect oceanic climate signals and therefore fill in an important gap in proxy-based reconstructions of North Atlantic climate variability. Most existing high-resolution records, such as tree-ring and speleothem chronologies, basically reflect atmospheric conditions. In combination with proxies from other sources the coral data are used in Global Circulation Models (GCMs) to simulate large-scale climate variability. In order to solve the problem of using local, spatially limited data the DATUN-technique (Data Assimilation Through Upscaling and Nudging; von Storch et al., 2000) is applied, where a DATUN model is placed between the proxy time series and the GCM. DATUN models connect local time series with the large-scale circulation through statistical relationships.