In general, the early Pliocene interval (up to ∼ 3.5 Ma) was characterized by the development of the Cibicides lobatulus and Cibicides wuellerstorfi assemblages, reflecting the low influx of organic carbon to the sea floor due to decreased rates of surface water productivity. This interval also corresponds with the increase in faunal diversity, and the relative abundance of C. lobatulus and C. wuellerstorfi, along with a low percentage of total infaunal taxa, high productivity
taxa and suboxic taxa. Thus, during most of the early Pliocene the eastern Indian Ocean was characterized by relatively warm and stable bottom waters at bathyal depths with low organic carbon influx and better ventilation. The early Pliocene was a period of prolonged global warming find more (Dowsett et al., 1996 and Haywood et al., 2000) with relatively less developed Northern Hemisphere ice sheets and a higher CO2 concentration (pCO2) (Raymo et al. 1996). The low occurrence of the C. lobatulus assemblage along with the distinct occurrence of the C. wuellerstorfi assemblage at ∼ 5 Ma could have been due to active bottom
currents with a low-moderate organic flux in the deep sea. There is much evidence to suggest that up to the early Pliocene the Indonesian seaway was better open, which links the Indian Ocean and Pacific ( Srinivasan and Sinha, 1998 and Cane and Molnar, 2001) and most of the Indonesian Throughflow (ITF) was probably fed from warm south Pacific waters. Thus, PTC124 cost up to ∼ 3.5 Ma warm water from the southern Pacific should have been flowing into the Indian Ocean. Cane & Molnar (2001) proposed that a permanent El Niño-like condition
during Phosphoglycerate kinase early the Pliocene increased the temperature at high latitudes and prevented the growth of Northern Hemisphere ice sheets. Thus, the inflow of warm southern Pacific waters in the eastern Indian Ocean during the early Pliocene increased the strength of the southward-flowing warm Leeuwin Current (LC), whose pressure gradient exceeds the offshore Ekman transport ( Smith 1992), supplying tropical heat towards the pole. Ravelo et al. (2004) also explained that the lack of a δ18O gradient across the tropical Pacific during the early Pliocene warm period strongly supports a persistent El Niño-like condition increasing the eastern Indian Ocean temperature due to the intense Leeuwin Current. This, in turn, suppressed the intensity of the relatively deep and cold northward-flowing Western Australian Current (WAC), which may have been responsible for reduced upwelling and surface water productivity, as in modern times. Also during most of the early Pliocene (before ∼ 3.5 Ma) the temperature of the deep ocean was significantly high and the thermocline was so deep that winds were unable to upwell deep, cold and nutrient-rich water to the surface ( Fedorov & Philander 2000).
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