[M-IS02] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS02-09] Contrasting vertical distributions of recent planktic foraminifera off Indonesia during the southeast monsoon: implications for paleoceanographic reconstructions

*Raul Tapia¹, Sze Ling Ho¹, Hui-Yu Wang², Jeroen Groeneveld¹, Mahyar Mohtadi³ (1.Institute of Oceanography, National Taiwan University, Taipei, Taiwan, 2.Biodiversity Research Center, Academia Sinica, Taipei, Taiwan, 3.MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany)

Keywords:Planktic foraminifera, Plankton net, Vertical distribution, Census counts

The accuracy of paleoceanographic and paleoclimatic reconstructions based on planktic foraminifera is as good as our understanding of the ecology of the organisms. Here we present field observations of planktic foraminiferal abundances (>150 µm) from 5 depth intervals between 0-500 m in 37 sites off Indonesian islands. The total planktic foraminiferal assemblage comprises 29 morphospecies, with 11 morphospecies accounting for ~90% of the total assemblage. The species composition and dominance in the net samples are broadly consistent with surface sediment observations. The abundance and vertical distribution of planktic foraminifera are low offshore west Sumatra and increase toward offshore south Java and the Lesser Sunda Islands (LSI). The average living depth of Trilobatus trilobus, Globigerinoides ruber, and Globigerina bulloides increases eastward, while Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii remains constant. We interpret the overall zonal and vertical distribution patterns in planktic foraminiferal abundances as a response to the contrasting upper water column conditions during the southeast monsoon, i.e., oligotrophic and stratified offshore Sumatra (non-upwelling) vs. eutrophic and well-mixed offshore Java-LSI (upwelling). Overall, the inferred habitat depths of selected planktic foraminifera species agree with those from sediment trap samples and surface sediments off Sumatra, but not with those from surface sediments off Java-LSI. The discrepancy might arise from the different temporal coverage of these sample types. Our findings highlight the need to consider how foraminiferal assemblages and ecology vary on shorter timescales, i.e., from “snapshots” of the water column captured by plankton net to seasonal and interannual variability recorded in sediment traps, and how these changes are transferred and preserved in deep-sea sediments.