Reconstructing the biogeochemical response of Indonesian coastal ecosystems to environmental change during the late Quaternary as recorded by marine sediment cores along the Sumatra - Java - Flores transect (BIORESICO)
Final Report Abstract
Global climate change is and had been in the past a mosaic of regional changes to a large extent determined by region-specific feedbacks between climate and ecosystems. Therefore, the temporal/causal relationships between regional climates and ecosystems need to be investigated in order to further our process understanding related to global change. Tropical regions play an important role in global climate change and the Indonesian archipelago is a key region in this respect. The overall goal of this project was to investigate the response of terrestrial and marine ecosystems to past climate change in a tropical region which is of global relevance and governed by a complex interplay of atmospheric and oceanographic phenomena. Recent studies found past hydroclimate in the region extremely complex. Taking this and the fact that the investigated area stretches over 4,000 km into account, the originally not planned analysis of plant wax n-alkanes and their stable hydrogen and carbon isotope composition was added to the suite of parameters to be measured. It can provide additional information on past precipitation and vegetation composition. We found distinct spatio-temporal variations of precipitation, vegetation composition and organic matter production and deposition in marine sediments from the Indonesian continental margin along the transect Sumatra – Java – Flores. The Australian-Indonesian Winter Monsoon (AIWM) and exposure of the Sunda shelf during sea level lowstand appear to be the major overall controls of precipitation and upwelling intensity. During the Last Glacial Maximum (LGM) and the Deglacial (DG) a large gradient in plant wax n-alkane isotopes and pollen composition indicate a dominance of C3 plants in Sumatra and a mixed C3/C4 plant composition in Java and Flores which, in turn, reflects a gradient in precipitation with more dryness towards the east. During the Holocene this gradient became much less pronounced with only a slightly higher, but generally low portion of C4 plants in Java and Flores. During the LGM and the DG organic matter accumulation was similar off Sumatra and Java and much lower off Sunda Strait and Flores. While it decreased slightly off Sumatra it increased off Java and Flores during the Holocene. Despite these variations surprisingly similar δ15N profiles in all sites indicate an almost uniform development of upwelling-related denitrification intensity which was strongest during the AIWM maximum in the mid Holocene. In general, OM burial off Indonesia was much lower than in major upwelling regions which, however, are located in arid regions. Monsoon-controlled seasonality of upwelling appears to be responsible for the lower OM accumulation off Indonesia. Terrestrial and marine ecosystems in the study area appear to have responded almost synchronously to millennial scale climate changes.
Publications
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2012. Reconstructing hydrologic changes in Indonesia by deuterium isotope compositions of plant waxes. Abstract PP41A-1980 presented at 2012 Fall Meeting, AGU, San Francisco, Calif., 3-7 Dec.
Karin Gesierich, Enno Schefuss, Dierk Hebbeln, Mahyar Mohtadi, Hermann Behling, Tim C Jennerjahn
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2014. Variations in organic matter burial and composition in sediments from the Indian Ocean continental margin off SW Indonesia (Sumatra – Java – Flores) since the Last Glacial Maximum. Abstract PP53B-1228 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.
T.C. Jennerjahn, K. Gesierich, E. Schefuß, M. Mohtadi
