Climate Change and Earth-Ocean-Atmosphere Systems
Nature and pacing of past climate change in the sub-Antarctic Atlantic in relation to variations in atmospheric CO2
Nowadays, the ocean acts as a major sink of anthropogenic CO2. Based on enclosed air in ice cores from Antarctica we have a good reference of past atmospheric CO2 concentrations. It is assumed that ocean processes are substantially involved in shaping the observed variability of past atmospheric CO2. Particularly, the potential influence of the Southern Ocean on atmospheric CO2 via changes in upwelling of CO2 - rich, deep waters and productivity drawing down CO2 from surface waters via photosynthesis is considered to be high.
The stability of the meridional overturning circulation and ice sheets on Greenland and Antarctica calving into the Atlantic Ocean appears to be crucial in triggering rapid climate transitions that have a distinct but opposing expression in the northern and southern hemisphere. The concept of a "(thermal) bipolar seesaw" is often used to explain this asymmetric temperature pattern in both hemispheres. It still remains unclear which conditions and tipping elements lead to rapid climate shifts and which mechanisms lead to their global propagation.
The influence of the "bipolar seesaw"-phenomenon on surface ocean productivity, the extent of sea ice and vertical mixing in the Southern Ocean and to what extent these factors govern atmospheric greenhouse gas concentrations is insufficiently understood.
Past oceanographic and hydrological conditions and changes in the carbon cycle recorded in the high-resolution sediment core MD07-3076CQ are investigated in order to unravel the forcing, pacing and feedback mechanisms of characteristic millennial-scale climate variability in the sub-Antarctic Atlantic. Past southern high latitude changes are analysed in the light of global atmospheric CO2 variations. The reconstructions are based on stable isotopic and trace element composition of planktonic and benthic foraminifera tests. The focus is put on Marine Isotope Stage (MIS) 3 (60 - 30 ka before present) as well as MIS 6 (190 - 140 ka before present) to understand the significance of the background state of the climate system in rapid climate change. A major goal is to establish chronostratigraphic links between Antarctic and North Atlantic climate events to elucidate the involvement of the "bipolar seesaw".
In addition, numerical model simulations of the interhemispheric behavior of climate variability in the Atlantic will be applied to constrain the physical dynamics behind abrupt climate transitions. They will focus on the role of vertical mixing, wind and heat transport, complementing sediment-based analyses.
The research is conducted in collaboration with the University of Bremen (Germany) and the Laboratoire des Sciences du Climat et de l'Environnment (LSCE) in Gif-sur-Yvette (France).
Location of sediment core MD07-3076CQ in the South Atlantic; modern surface currents (in red) and deep water currents (North Atlantic Deep Water (NADW) in orange, Antarctic Bottom Water (AABW) in black) show the pronounced influence of ocean currents from both, the northern and southern hemisphere, at the study site; redrawn from Peterson & Stramma, 1991 and Stramma & England, 1999 with a basis map created with Generic Mapping Tool (Wessel & Smith, 1991)
The focus of my research is the pacing and nature of abruptness in past climate change on millennial time scales. The mechanisms that lead to their operation, the involvement of thresholds and feedbacks as well as their potential to lead the climate system into either full glacial or interglacial conditions are of particular interest. The research is based on a synthesis of various climate archives including ice cores and speleothems with a strong focus on marine sediments and aims in investigating:
- the global signature and trigger mechanisms of abrupt climate change
- the contribution of the ocean and the atmosphere in connecting remote regions in terms of their climate (i.e. the operation of the "bipolar seesaw")
- the representation of abrupt climate change depending on boundary conditions of the climate system
- the role of the Southern Ocean in millennial, atmospheric CO2 variations.
Gottschalk, J.; Max, L.; Tiedemann, R.; Schulz, M.; Merkel, U. (2011) Linkage of annual laminae formation in the Bering Sea and the Bølling-Allerød and Preboreal warm periods in the North Atlantic, Poster, AGU Fall Meeting, San Francisco
Gottschalk, J.; Schulz, M.; Merkel, U.; Tiedemann, R.; Max, L. (2011) Proxy and model-based implications of the operation of the North Atlantic - North Pacific teleconnection since Heinrich Stadial 1, Poster, EGU General Assembly, Vienna
Gottschalk, J.; Kopf, A.J.; Goldhammer, T.M.; Melles, M; El'gygytgyn Scientific Party (2010), School project about paleoclimate research: ICDP expedition at Lake El'gygytgyn enters the class room, Invited talk, German IODP/ICDP colloquium, Frankfurt/Main
Gottschalk, J.; Taldenkova, E.; Bauch, H.A. (2009), Environmental history of the western Laptev Sea since the Late Pleistocene, Invited talk, 9th Russian - German Workshop 'Laptev Sea System', Saint Petersburg
Taldenkova, E.; Nikolaev, S.; Bauch, H.A.; Gottschalk, J.; Rostovtseva, Y. (2008) Records of Iceberg Rafting at the North Siberian Margin Linked to Regional ice cap History, AGU Fall Meeting, San Francisco.