Lamont-Doherty Earth Observatory, United States

We studied cores from ODP sites 1089 and 1090 in the subantarctic South Atlantic to reconstruct paleoceanographic changes during the mid-Brunhes in the context of climate evolution of the Pleistocene. The "mid-Brunhes event" is marked by an abrupt shift toward lower delta (super 18) O values during interglacial stages beginning with MIS 11, consistent with Jansen et al. [1986] who first proposed a mid-Brunhes transition to more humid, interglacial conditions in the southern hemisphere. In addition, we identified the "mid-Brunhes dissolution cycle" as part of a long-period oscillation that is expressed in dissolution indices and planktic delta (super 13) C, which reach maximum values during interglacial stages 13 and 11. Taking advantage of the high sedimentation rates at site 1089 (15 cm/kyr), we enumerate the sequence of events that occurred during Termination V and MIS 11 and speculate about their cause(s). A comparison between site 1089 and the Vostok ice core suggests that peak conditions of stage 11 are accurately captured in the ice core record, and that temperatures in the high-latitude southern hemisphere and global pCO (sub 2) levels during stage 11 were similar to the Holocene. Furthermore, a remarkable correlation between Vostok pCO (sub 2) and % foraminiferal fragmentation at site 1089 suggests a strong coupling of the marine carbonate system and atmospheric pCO (sub 2) during the mid-Brunhes. Although stage 11 and the Holocene share some similarities (e.g., orbital configuration, pCO (sub 2) etc.), caution is advised in using stage 11 as an analog for the Holocene because the maximum in dissolution and delta (super 13) C during the mid-Brunhes indicate that the marine carbonate-carbon cycle was fundamentally different than today.