GEO-01 Present and past ocean-atmosphere-climate interactions
Rainfall and vegetation changes in the Western Pacific Warm Pool during the last 15.000 years
Lázár B.* , Department of Geology, Babeș-Bolyai University, Cluj-Napoca, Romania, Department of Geological Oceanography and State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
M. Mohtadi, MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
E. Schefuß, MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
Z. Jian, State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
S. Steinke, Department of Geological Oceanography and State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China

The Western Pacific Warm Pool (WPWP) is the largest reservoir of warm surface water on earth with a permanent sea surface temperature (SST) of >28°C and it is considered to be the heat engine of the globe. Hence, it represents a significant source of heat for the global atmosphere and a location of deep atmospheric convection and heavy rainfall. Small SST variations in the WPWP influence the area and strength of convection in the rising limb of the Hadley and Walker circulations, perturbing planetary scale atmospheric circulation, atmospheric heating globally, and tropical hydrology. Rainfall varies seasonally due to the Intertropical Convergence Zone (ITCZ) migration and inter-annually because of El Niño Southern Oscillation (ENSO). Generally, El Niño years are characterized by dry conditions in the WPWP, since deep atmospheric convection moves eastward towards the central Pacific and the Pacific Walker circulation weakens. The opposite scenario occurs during La Niña years with higher rainfall due to strong atmospheric convection, and a strong Pacific Walker circulation. Thus, variability in rainfall in the WPWP is a sensitive diagnostic variable to track changes in the state of ENSO and the strength of the Pacific Walker circulation. To this end, we measured the δD and δ13C composition in plant waxes from core GeoB17429-2 off the northern coast of Papua New Guinea to reconstruct the rainfall and vegetation (C3- versus C4-plants) during the last ~15.000 years.

Our δ13Cwax data indicate a clear dominance in C3, rainforest-type vegetation throughout the studied section without a major contribution from C4-type plants. Changes can be observed at the longer chain, C33n-alkanes during the Younger Dryas, showing an accentuated presence of grass-type plants. Also, our δD analyses reveal that rainfall was relatively lower during the Younger Dryas. Furthermore, the δD data based on the long chain (C29, C31, and C33) n-alkanes show a relatively high rainfall amount, which is reflected and confirms our findings on the vegetation types. Besides this, changes can be observed in the intensity of the rainfall signals expressing a cyclicity in the data.