Kvartære geosystemer

North Atlantic east-west synchronization of abrupt climate change events during the last glacial period using distinct tephra horizons

PhD Candidate: Sunniva Rutledal

Supervision: Prof. Dr. Eystein Jansen (UiB), Dr. Sarah M. P. Berben (UiB), Dr. Trond M. Dokken (NORCE).

Project period: September 2017 – September 2020

This PhD project is part of the ERC Synergy project Ice2Ice (http://ice2ice.b.uib.no)

My PhD project focuses on using tephra markers to better understand the timing of abrupt climate change events in the North Atlantic during the last glacial period.

The last glacial period is characterized by abrupt climate change events, such as Dansgaard- Oeschger (D-O) and Heinrich (H) events. However, a major challenge affecting our understanding of the key physical processes during such rapid climatic transitions, is the establishment of a precise chronological control when comparing different climate archives (e.g. ice cores and marine sediment cores). The instantaneous deposition of geochemically unique volcanic ash shards (tephra markers) provides the opportunity to act as an independent time-synchronous marker. Therefore, tephra horizons open the possibility to firmly link and synchronize the time scales of marine sediment cores from the North Atlantic with the annual layers counted in Greenland ice core records, particularly after the discovery of cryptotephras (i.e. tephra layers not visible to the naked eye). Thus, within integrated studies of paleoclimatic records from disparate climate archives, using tephrochronology to constrain the timing of several D-O events will contribute to the understanding of leads and lags issues of such events.

The PhD project consists of three parts: Developing a tephra framework, building on existing frameworks in the literature. This part will focus on identifying two tephra isochrones found in the Greenland Ice cores (FMAZ II and NAAZ II) in marine sediment cores along the east-Greenland coast and in the Nordic Seas. The second part will be to use the tephra framework to synchronize marine sediment cores from North Atlantic and Nordic Seas with the Greenland ice cores to constrain the timing of abrupt climate change events. The third part of my project aims to reconstruct last glacial iceberg trajectories and surface ocean circulation patterns using the deposition of ice-rafted tephra.