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PAGES Indonesia
national science highlight
 1. Coral Proxy Records - The Indian Ocean Dipole Event
Geochemical records from living and fossil corals from off western Sumatra document repeated events of anomalously strong upwelling in the eastern Indian Ocean during the last two centuries and the mid-Holocene.
The upwelling events and resulting cooler surface waters were associated with the Indian Ocean Dipole (IOD) oscillation. During the last of these IOD anomalies in 1997, coral reefs in the area died, whereas they survived all the earlier anomalies recorded. Detailed analysis reveals that iron fertilization by wildfires in Indonesia in 1997 produced an unusual red tide that led to the death of the corals. While wildfires in Indonesia can result from drought in response to IOD (and ENSO) oscillations, they seem to become more severe with ongoing land-use changes, posing an increasing threat also to coastal ecosystems.
Figure 1. Coral Sr/Ca (red), ∂18O (blue) records, grid-SST anomaly (black) from Mentawai, western Sumatra shows cooling SST during IOD events. (figure modified from Abram et al., 2003).
References:
Abram, N.J., M.K. Gagan, M.T. McCulloch, J. Chappell and W.S. Hantoro (2003), Coral reef death during the 1997 Indian Ocean Dipole linked to Indonesian wildfires, Science, 301, 952-955.
2. Tree Rings
 The Palmer Drought Severity Index (PDSI) reconstruction based on nine individual tree ring records from Java shows past monsoon drought variability back to the 18th century. The Java PDSI reconstruction (1787-1988) correlated significantly with the El Niño Southern Oscillation (ENSO)-related SST for the calibration period of 1870-1988 and 1896-1988, reflecting the strong coupling between the regional climate of Indonesia and the large-scale tropical Indo-Pacific climate system (D'Arrigo et al., 2006).
References:
D'Arrigo, R., R. Wilson, J. Palmer, P. Krusic, A. Curtis, J. Sakulich, S. Bijaksana, S. Zulaikah and L.O. Ngkoimani (2006), Monsoon drought over Java, Indonesia, during the past two centuries, Geophysical Research Letters, 33, doi: 10.1029/2005GL025465.
Figure 2.(a) Coherency spectrum between Javanese reconstructed and instrumental PDSI. (b) Multi-taper method spectral analysis of instrumental (1870-2003) and (c) of reconstructed (1787-1988) Javanese PDSI (from D'Arrigo et al., 2006).
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3. Sediment Core Records
A high-resolution (~1-2 kyr) multi-proxy record from the Timor Sea (International Marine Global Change (IMAGES) Program core MD01-2378, 1783 depth) tracks changes in the intermediate water ventilation and paleoproductivity over the last 460 kyr within the main exit pathways of the Indonesian throughflow (ITF). Spectral analysis of the flux-base productivity proxies shows power concentrate at the 100 kyr period (glacial-interglacial period) and the periods of 23 kyr and 19 kyr (precessional). In the Timor Sea, productivity fluctuations over the last 460 kyr were strongly influenced by the monsoonal wind pattern offshore NW Australia, varying at 23 and 19 kyr. In addition, productivity was modulated by sea-level-related variations in the intensity of the Indonesia throughflow (100 kyr) (Holbourn et al., 2005).
Figure 3. Benthic and planktonic foraminifera ∂18O and ∂13C versus depth in core MD01-2378 (from Holbourn et al., 2005.)
References:
Holbourn, A., W. Kuhnt, H. Kawamura, Z. Jian, P. Grootes, H. Erlenkeuser and J. Xu (2005), Orbitally paced paleoproductivity variations in Timor sea and Indonesian throughflow variability during 460 kyr, Paleoceanography, doi: 10.1029/2004PA001094.
4. Molluskan Studies of Milankovitch Sea Level
The analyses of lithofacies and the molluskan fossil association from the lower part of the Nyalindung Formation (Sukabumi, West Java Province Indonesia; age Middle Miocene ~12 Myr) provide reconstructions from tropical deposits of glacio-eustatic sea-level cycles in the Middle Miocene. The reconstructions suggest significant sea-level fluctuations between non-marine, supratidal, intertidal, subtidal and open, shallow marine conditions. These cycles have a short time range and represent Milankovich scale cycles of 41 kyr. This appears to be the first time Milankovich sea levels have been reported from tropical regions (Aswan and Ozawa, 2006).
References:
Aswan, T. Ozawa (2006), Milankovitch 41000-year cycles in lithofacies and molluscan content in the tropical Middle Miocene Nyalindung Formation, Jawa, Indonesia, Palaeogeography, Palaeoclimatology, Palaeoecology, 235:382-405.
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