The carbon cycle during the Mid Pleistocene Transition: the Southern Ocean Decoupling Hypothesis

• Main Authors: P. Köhler, R. Bintanja
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2008
• Subjects: Environmental pollution; TD172-193.5; Environmental protection; TD169-171.8; Environmental sciences; GE1-350; Southern Ocean; Pacific
• Online Access: https://doaj.org/article/a5997cc198b54094973fd329cf924e8a

Various hypotheses were proposed within recent years for the interpretation of the Mid Pleistocene Transition (MPT), which occurred during past 2 000 000 years (2 Myr). We here add to already existing theories on the MPT some data and model-based aspects focusing on the dynamics of the carbon cycle. We find that the average glacial/interglacial (G/IG) amplitudes in benthic δ 13 C derived from sediment cores in the deep Pacific ocean increased across the MPT by ~40%, while similar amplitudes in the global benthic δ 18 C stack LR04 increased by a factor of two over the same time interval. The global carbon cycle box model BICYCLE is used for the interpretation of these observed changes in the carbon cycle. Our simulation approach is based on regression analyses of various paleo-climatic proxies with the LR04 benthic δ 18 C stack over the last 740 kyr, which are then used to extrapolate changing climatic boundary conditions over the whole 2 Myr time window. The observed dynamics in benthic δ 13 C cannot be explained if similar relations between LR04 and the individual climate variables are assumed prior and after the MPT. According to our analysis a model-based reconstruction of G/IG amplitudes in deep Pacific δ 13 C before the MPT is possible if we assume a different response to the applied forcings in the Southern Ocean prior and after the MPT. This behaviour is what we call the "Southern Ocean Decoupling Hypothesis". This decoupling might potentially be caused by a different cryosphere/ocean interaction and thus changes in the deep and bottom water formation rates in the Southern Ocean before the MPT, however an understanding from first principles remains elusive. Our hypothesis is also proposing dynamics in atmospheric p CO 2 over the past 2 Myr. Simulated p CO 2 is varying between 180 and 260 μatm before the MPT. The consequence of our Southern Ocean Decoupling Hypothesis is that the slope in the relationship between Southern Ocean SST and atmospheric p CO 2 is different before and after the MPT, something for ...