Western Pacific thermocline variability in orbital- and millennial-timescale

Abstract:

The western tropical Pacific is a region where sea surface temperature (SST) is warmest in the world ocean. Thickness of surface warm water as well as SST is expected to have an influence on regulating global climate because of its potential to provide heat to atmosphere. A number of paleoceanographic studies have reconstructed SST in this region and revealed that changes in SST is very similar to atmospheric CO2 in glacial-interglacial timescale. However, little is known about changes surface warm water thickness, i.e. thermocline depth, in the past. For better understanding the heat content of ocean surface, changes in depth of thermocline is investigated. Here, we reconstruct sub-surface water temperature in the western tropical Pacific for the last 380 kyr. The sub-surface temperature reconstruction is done by Mg/Ca-thermometry of thermocline dweller planktonic foraminifer, Pulleniatina obliquiloculata. This species dwells around the depth of thermocline, and its temperature record is expected to reflect vertical migration of thermocline. The glacial-interglacial amplitude of sub-surface temperature is larger than that of SST. The precessional cycle is dominant in the sub-surface temperature variability. Such features are well consistent with model output by EMIC LOVECLIM although amplitudes are much smaller in model. Concomitant changes of sub-surface temperature and terrestrial input suggests that thermocline change is closely related to precessional controlled ITCZ movement. The high frequent variability during the MIS3 implies D-O oscillation related thermocline change in the millennial timescale.