Relationships between Baltic Sea level variations and periods of rapid climate change in the Holocene as analogues for future changes

• Applicant: Dr. Eduardo Zorita
• Subject Area: Oceanography
• Term: from 2006 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 23633144

Variations of Baltic Sea level caused by rapid climate change within the last 8000 years will be estimated from joint analysis of long instrumental series, proxy data and simulations with global climate models. The overall goal is to find analogues for rapid sea-level changes in the past record that can be used to estimate changes in the next centuries. 1) The output of global climate simulations with the global climate model ECHO-G for the Holocene will be regionalized with standard statistical downscaling methods, which relate meteorological forcing (wind, temperature, rainfall) and sea-level variations yielding - together with the simulated steric sea-level variationsestimations of the past and future variations of sea-level for each individual sea-level gauge. These statistical models have been already designed and validated in the project SINCOS. The simulations would allow to identify periods in the past where the climate forcing may have produced sea-level changes as rapid as those expected in this century. 2) The estimations of past climate-related sea-level changes will be validated by the analysis of tree-ring data from living oaks along the southern coast of the Baltic Sea. After calibration with the well-known climate during the recent century, the climatic signal can be expected to be also retrievable from the long-term oak chronology along the southern coast of the Baltic Sea composed of several absolutely dated as well as some floating parts over the last 8.000 years. Statistical models may be designed that describe the indirect relationship proxy data - climate forcing - sea level in a similar manner as meteorological data and sea-level data (project SINCOS). The statistical models can be then applied to the long time series of climatic proxy data, such as tree-ring series, to obtain a second and independent estimation of the climate-related sea-level variability. Particular attention will be posed on decadal cold periods in the past millennium, the Late Maunder Minimum around 1700 and specially the Dalton Minimum around 1800. In the latter period a direct analysis of climate change and instrumental sea-level change may be possible for a number of gauges. The analysis of tree-ring data will be performed and the results put at our disposal by a contract for scientific services. 3) The North Atlantic Holocene climate has undergone periods of abrupt climate change at decadal and centennial timescales, e.g. the so-called 8.2k event. Temperatures in Greenland may have dropped by as much as 5 degrees and those in Northern Europe by 2 degrees in a period as short as a few decades, with a slower recovery to normal values along a few centuries. This sudden and strong climate change, probably caused by reorganizations of the Meridional Overturning Circulation in the North Atlantic, could be seen as an analogue for future changes, since global climate models also predict a future weakening of the Meridional Overturning Circulation. The global climate model ECHO-G, together with the regional model REMO, will be used to simulate the 8.2K event and its possible consequences for Baltic Sea level. The analysis of long time series of dendroclimatological data will deliver clues about regional climate impacts in this area. These results can be compared to proxy indicators of sea level from the literature or obtained by other projects of the present cluster.

• DFG Programme: Research Grants