A 35,000 year record of changes in the eastern Indian Ocean offshore Sumatra (original) (raw)
Related papers
Journal of Asian Earth Sciences, 1998
ÐDeep sea cores from sites 214 and 758 A (Ninetyeast Ridge, northeast Indian Ocean), 761 B (Wombat Plateau, northeast Indian Ocean) and 586 B (Ontong Java Plateau, Tropical Paci®c) are ideally located for comparison of late Neogene planktic foraminiferal biogeography and paleoceanographic records of tropical Indian and Paci®c oceans to infer the timing of closing of the Indonesian Seaway. A consistent stratigraphy was developed between sites 214 and 586 B using graphic correlation and was integrated with the paleomagnetic time scale of Berggren et al. (1985) to provide an accurate chronology to compare interocean stratigraphic ranges of late Neogene planktic foraminifera. Tropical planktic foraminifera occur throughout each sequence at all sites. At each site the Miocene±Pliocene boundary is de®ned by the ®rst appearance of Globorotalia tumida (5.2 Ma), the early/late Pliocene boundary by the ®rst appearance of Globigerinoides ®stulosus (3.2 Ma) and the Pliocene±Pleistocene boundary by the last appearance of G. ®stulosus (1.6 Ma). Neogene planktic foraminiferal assemblages at sites 214, 758A, 761 B and 586B are generally similar until the beginning of the Pliocene (5.2 Ma) when the faunal record indicates divergence. A notable dierence is complete absence of early Pliocene taxon Pulleniatina spectabilis from all the Indian Ocean sites. This dierence suggests that the Indonesian Seaway became an eective biogeographic barrier to planktic foraminifera at the beginning of the Pliocene. However, there is still exchange of surface waters through this Seaway. Earlier studies suggested a Middle to Late Miocene occurrence for this biogeographic barrier. P. spectabilis evolved from P. primalis in the equatorial Paci®c at about 5.2 Ma. It is a short-ranging early Pliocene species spanning about 1.3 my and occurred only in Paci®c, unlike earlier suggestions of a broader distribution into the Indian Ocean.
The western margin of Australia is unique in being the only eastern boundary region undergoing no upwelling as the poleward flowing Leeuwin Current (LC) nullifies the equatorward-driven wind-induced circulation. The principal forcing mechanism of the Leeuwin Current is the alongshore pressure gradients and associated zonal geostrophic flows along the West Australian margin. Based on planktic foraminiferal census counts and stable isotopic analysis of a surfacedwelling planktic foraminifera, Globigerinoides sacculifer, we show that during the Quaternary there have been five intervals when this eastern boundary region behaved in an opposite manner and the margin experienced extensive upwelling due to weakening of the LC and dominance of equatorward wind-driven circulation, causing offshore Ekman transport. These events occurred at 2.22, 1.83, 0.68, 0.45 and 0.04 Ma and have been named here as PL-1 to PL-5 in ascending stratigraphic order. We demonstrate here that the previous two events, PL-1 and PL-2, occurred due to ENSO-induced changes in the Western Pacific Warm Pool, while the last three events, PL-3, PL-4, and PL-5, occurred due to reduced Indonesian throughflow as a result of lowered sea level caused by ice volume expansion. We envisage here that these periods must be those of reduced net heat input to the Indian Ocean from the Pacific via Indonesian Seaway and thus should have an effect on sea surface temperature of the Indian Ocean and Indian monsoon.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2007
Benthic foraminifera and carbon isotopes from closely spaced samples taken from three deep-sea cores were analysed to reconstruct the palaeoceanographic evolution of the eastern Indian Ocean for the last 30 kyrs, with an extension back to 60 kyrs based on one core. Benthic foraminifera were studied by means of Q-mode Factor Analysis. The benthic foraminifera accumulation rate (BFAR) and the accumulation rates (AR) of Bulimina aculeata, Epistominella exigua and Uvigerina proboscidea were calculated for determining episodes of increased organic matter supply to the sea floor. The δ 18 O and δ 13 C records of Cibicidoides wuellerstorfi were measured from all 3 cores to gather information about past intermediate-and deep-water circulation and changes in seasurface palaeoproductivity. The co-variance of the organic matter supply and dissolved-oxygen levels affected the distribution of benthic foraminifera. Below a depth of 1800 m, reduced deep-water circulation was recognised by a low δ 13 C of C. wuellerstorfi and increased carbonflux rate by a high BFAR and B. aculeata, E. exigua and U. proboscidea AR, as well as by a B. aculeata faunal dominance. A more oligotrophic environment was characterised by a low BFAR and B. aculeata, E. exigua and U. proboscidea AR. Active deep-water circulation was postulated with high δ 13 C values for C. wuellerstorfi and by a faunal dominance by C. wuellerstorfi. At intermediate depths (∼ 1000 m) and south of 20°S, the presence of strong bottom currents and the lateral advection of small amounts of organic matter, favoured the suspension feeder C. wuellerstorfi. Under extremely high dissolved-oxygen levels, determined by the increased influence of the Antarctic Intermediate Water (seen through high δ 13 C of C. wuellerstorfi) and a reduced supply of organic matter, Nummoloculina irregularis and Globocassidulina subglobosa dominated the benthic foraminifera assemblage. The reduction of oxygen levels, a more stratified water column and the Leeuwin Current flow, along its present pattern, favoured the species U. proboscidea and Bolivina robusta. Based on these observations, the following palaeoceanographic evolution of the eastern Indian Ocean is proposed:
Journal of Asian Earth Science, 1998
ÐDeep sea cores from sites 214 and 758 A (Ninetyeast Ridge, northeast Indian Ocean), 761 B (Wombat Plateau, northeast Indian Ocean) and 586 B (Ontong Java Plateau, Tropical Paci®c) are ideally located for comparison of late Neogene planktic foraminiferal bio-geography and paleoceanographic records of tropical Indian and Paci®c oceans to infer the timing of closing of the Indonesian Seaway. A consistent stratigraphy was developed between sites 214 and 586 B using graphic correlation and was integrated with the paleomagnetic time scale of Berggren et al. (1985) to provide an accurate chronology to compare interocean stratigraphic ranges of late Neogene planktic foraminifera. Tropical planktic foraminifera occur throughout each sequence at all sites. At each site the Miocene±Pliocene boundary is de®ned by the ®rst appearance of Globorotalia tumida (5.2 Ma), the early/late Pliocene boundary by the ®rst appearance of Globigerinoides ®stulosus (3.2 Ma) and the Pliocene±Pleistocene boundary by the last appearance of G. ®stulosus (1.6 Ma). Neogene planktic foraminiferal assemblages at sites 214, 758A, 761 B and 586B are generally similar until the beginning of the Pliocene (5.2 Ma) when the faunal record indicates divergence. A notable dierence is complete absence of early Pliocene taxon Pulleniatina spectabilis from all the Indian Ocean sites. This dierence suggests that the Indonesian Seaway became an eective biogeographic barrier to planktic foraminifera at the beginning of the Pliocene. However, there is still exchange of surface waters through this Seaway. Earlier studies suggested a Middle to Late Miocene occurrence for this biogeographic barrier. P. spectabilis evolved from P. primalis in the equatorial Paci®c at about 5.2 Ma. It is a short-ranging early Pliocene species spanning about 1.3 my and occurred only in Paci®c, unlike earlier suggestions of a broader distribution into the Indian Ocean. #
Journal of Asian Earth Sciences, 2019
Here we present the first detailed planktonic and benthic 13 C records and benthic foraminiferal assemblage records from the northeastern Indian Ocean to decipher the palaeoceanographic changes during the last 56 kyr. We identified three different palaeoceanographic stages, clearly differentiated by significant variations in the benthic foraminiferal assemblages and 13 C records. The results of this study indicate that productivity was generally higher during the glacial periods than during the Holocene. Comparison of the benthic foraminiferal assemblage distributions and planktonic and benthic 13 C records show a significant correlation between productivity and the bottom water oxygenation on glacial-interglacial timescales. Productivity gradually increased during the period between 56-27.5 kyr. During this period, the dominance of Melonis spp. and Oridosalis umbonatus were correlated with conditions of intermediate to high surface productivity and moderate bottom water oxygenation. Increased higher equatorial productivity and low bottom water oxygenation during the period between 27.5-15 kyr are supported by planktonic 13 C and faunal records. During this period, the dominance of benthic foraminifera assemblages characterised by Uvigerina peregrina indicates sustained continuous phytodetritus flux to the seafloor from enhanced surface water productivity and relatively low bottom water oxygenation. The absence or minimal occurrences of high productivity indicating U. peregrina, the dominance of intermediate to low productivity indicating fauna, and relatively low planktonic 13 C records suggest low productivity and active deep-water oxygenation after 15 kyr. Concurrent river discharge and rising sea levels during this period are indicated by negative 18 O of G. ruber at the site.
Paleoceanography, 2008
Historically, the Holocene has been considered an interval of relatively stable climate. However, recent studies from the northern Arabian Sea (Netherlands Indian Ocean Program 905) suggested high-amplitude climate shifts in the early and middle Holocene based on faunal and benthic isotopic proxy records. We examined benthic foraminiferal faunal and stable isotopic data from Ocean Drilling Program (ODP) Site 723 and total organic carbon data from ODP Site 724, Oman Margin (808 and 593 m water depths, respectively). At Site 723 the mid-Holocene shift in δ18O values of infaunal benthic species Uvigerina peregrina (1.4‰) is 3 times larger than that of epifaunal benthic species Cibicides kullenbergi recorded at Site NIOP 905 off Somalia. However, none of the five other benthic species we measured at Hole 723A exhibits such a shift in δ18O. We speculate that the late Holocene δ18O decrease in U. peregrina represents species-specific changes in ecological habitat or food preference in response to changes in surface and deep ocean circulation. While the stable isotopic data do not appear to indicate a middle Holocene climatic shift, our total organic carbon and benthic faunal assemblage data do indicate that the early Holocene deep Arabian Sea was influenced by increased ventilation perhaps by North Atlantic Deep Water and/or Circumpolar Deep Water incursions into the Indian Ocean, leading to remineralization of organic matter and a relatively weak early Holocene oxygen minimum zone in the northwest Arabian Sea in spite of strong summer monsoon circulation.
Mid-Pliocene climate change amplified by a switch in Indonesian subsurface throughflow
Nature Geoscience, 2009
The tectonically driven closure of tropical seaways during the Pliocene epoch (∼5-2 million years (Myr) ago) altered ocean circulation and affected the evolution of climate. Plate tectonic reconstructions show that the main reorganization of one such seaway, the Indonesian Gateway, occurred between 4 and 3 Myr ago. Model simulations have suggested that this would have triggered a switch in the source of waters feeding the Indonesian throughflow into the Indian Ocean, from the warm salty waters of the South Pacific Ocean to the cool and relatively fresh waters of the North Pacific Ocean. Here we use paired measurements of the δ 18 O and Mg/Ca ratios of planktonic foraminifera to reconstruct the thermal structure of the eastern tropical Indian Ocean from 5.5 to 2 Myr ago. We find that sea surface conditions remained relatively stable throughout the interval, whereas subsurface waters freshened and cooled by about 4 • C between 3.5 and 2.95 Myr ago. We suggest that the restriction of the Indonesian Gateway led to the cooling and shoaling of the thermocline in the tropical Indian Ocean. We conclude that this tectonic reorganization contributed to the global shoaling of the thermocline recorded during the Pliocene epoch, possibly contributing to the development of the equatorial eastern Pacific cold tongue.
OCEANOLOGIA, 2012
Pliocene-Pleistocene deep sea benthic foraminifera from ODP Site 762B in the eastern Indian Ocean were examined to understand the tectonically/climatically induced palaeoceanographic changes. In addition to already published data on this site by Rai & Singh (2001), some more faunal parameters were considered in the present work. Characteristic benthic foraminiferal assemblages as well as more diverse fauna during the early Pliocene (before 3.5 Ma) reflected relatively oligotrophic and warm bottom water conditions. At the beginning of the late Pliocene (i.e. ∼ 3 ± 0.5 Ma) relative abundances of Uvigerina proboscidea, infaunal taxa and high productivity taxa increased, whereas faunal diversity showed a distinct decline, suggesting the development of pronounced upwelling resulting in higher surface water productivity. The strongly reduced inflow of warm and oligotrophic water masses as the South Equatorial Current (SEC) from the South Pacific to the eastern Indian Ocean due to the effective closure of the Indonesian seaway increased the surface water productivity. The closing of the Indonesian seaway during the late Pliocene was also responsible for the cessation of the warm, southward-flowing Leeuwin Current (LC) and the greater influence of the cold, deep The complete text of the paper is available at http://www.iopan.gda.pl/oceanologia/ Open access under CC BY-NC-ND license.