Annually-resolved multi-parameter assessment of climate variability and solar activity during the 8.2 ka BP event

• Applicants: Professor Dr. Jan Esper; Dr. Ronny Friedrich; Dr. Gerhard Helle; Dr. Alexander Land; Professor Dr. Denis Scholz
• Subject Area: Physical Geography
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 471100574

8,200 years ago an abrupt climate fluctuation occurred and vast parts of the northern hemisphere suffered from this cooling event. This prominent climate relapse is known as the 8.2 ka BP event. Several drivers might played a role in forcing this climate event, such as a large single freshwater pulse into the Labrador Sea which altered ocean circulation by reducing sea surface salinity and heat transport into the North or a ~100-year long continuous pulse of freshwater into the North Atlantic. Some other triggers might also have played a significant role, including decreasing solar activity and internal climate system variability. A combination of several drivers is also plausible, however, the causes may be more complex than previously thought.In this project we will reconstruct central European climate variability (e.g. temperature, precipitation) and solar activity with an annual resolution prior to and during the 8.2 ka BP event. This will be achieved using several tree-ring climate proxies namely stable isotopes (δ13C, δ18O, δD) which are highly suitable for the investigation of paleoclimate. Additionally, radiocarbon (14C) measurements will be performed to modulate solar activity and thus the sun´s role prior to and during the event.MethodsTo achieve the project goals stable isotope (δ13C, δ18O, δD) and radiocarbon (14C) measurements from absolute dated oak tree rings will be performed with an annual resolution for the time period from 8600 to 7900 years ago. To reconstruct past climate variability from the developed stable isotope records, group detrending techniques (e.g. Signal-free Regional Curve Standardization) will be used to potentially retain low frequency variance. Modulation of solar variability will be done using a global carbon box model based on annual 14C data. To assess frequencies / periodicities in time and space within the different developed proxy records as well as coherencies between them, continuous and coherence wavelet transform techniques will be applied.Goals of the project- Reconstructing annually-resolved hydroclimate variability using oak tree-ring stable (δ13C, δ18O, δD) isotopes during 8.6 to 7.9 ka BP- Determining the onset, duration, end and temporal persistence of the 8.2 ka BP event and its pre-event for central Europe using stable (δ13C, δ18O, δD) and radioactive (14C) isotopes from tree rings- Disentangling temperature variability between warm-season and off-season- Estimating the solar activity during the 8.2 ka BP event and its pre-event from radiocarbon (14C) measurements and evaluating the sun´s role- Identifying solar production spikes from radiocarbon measurements, understanding the intensity and frequency of these solar events and their role prior to and during the 8.2 ka BP event- Improving the calibration dataset IntCal by contributing a large set of new high-resolution 14C data

• DFG Programme: Research Grants
• Co-Investigator: Dr. Bernd Kromer