δ18O and Mg/Ca Analysis on Mid-Pleistocene Foraminifera from the Bay of Bengal

Abstract:

The Mid-Pleistocene Transition (MPT) (0.7-1.2 Ma) marks a change in the Earth’s climate system response to orbital forcing from the 40 kyr obliquity cycle to the 100 kyr eccentricity cycle. Although many records of the MPT exist, particularly at high latitudes, our understanding of how this transition affected the tropics, and the east-Asian monsoon in particular, is limited. The International Ocean Discovery Program (IODP) Expedition 354 drilled 7 sites in the Bay of Bengal in the Indian Ocean, which contain hemipelagic calcareous clay, sand, and turbidite deposits. All sites have a ~1 Ma hemipelagic Mid-Pleistocene layer, providing a unique opportunity to gain insight into how the strength of the east-Asian monsoon was affected by the MPT.

The 1 Ma layer contains the Cobb Mountain (1.173-1.185 Ma) and Jaramillo (0.988-1.072 Ma) subchrons of the Matuyama Chron (2.58-0.78 Ma). This, along with biostratigraphic datums, indicates that the layer is Mid-Pleistocene in age and likely contains the MPT. We will present δ¹⁸O and Mg/Ca analyses on surface planktonic foraminifera from this Mid-Pleistocene layer at IODP site U1452B (8.0°N, 87.2°E, 3670 mbsl). We will present data from ~185 -186 mbsf at 2 cm resolution (~1kyr age resolution). The δ¹⁸O in foraminifera shells reflects the temperature and δ¹⁸O of the seawater from which the foraminifera formed their shells, while Mg/Ca is a proxy for sea surface temperature (SST). Therefore paired foraminifera δ¹⁸O and Mg/Ca measurements will allow us to reconstruct SST and δ¹⁸O of seawater. This preliminary work aims to assess the feasibility of these paleoceanographic proxies in this hemipelagic layer found in the complex depositional environment of the Bay of Bengal. Future work aims to reconstruct the full MPT, and along with other proxies generated by collaborators, will improve our understanding of response of the monsoon of the MPT.