Paleoceanographic significance of deep-sea benthic foraminiferal species diversity at southeastern Indian Ocean Hole 752A during the Neogene Raj K. Singh ⁎, Anil K. Gupta 1 , Moumita Das 2 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur‐721302, India abstract article info Article history: Received 22 February 2012 Received in revised form 20 July 2012 Accepted 13 August 2012 Available online 23 August 2012 Keywords: Paleoceanography Neogene Benthic foraminifera Diversity Indian Ocean Oxygen Minimum Zone Diversity parameters of Neogene deep-sea benthic foraminifera were measured at Ocean Drilling Program (ODP) Hole 752A, southeastern Indian Ocean (water depth of 1086.3 m) using Information Function (H), Equitability (E), number of species (S) and Sander's rarefaction values. These parameters combined with population abundance of dominant benthic foraminifera (Bulimina macilenta, Nuttallides umbonifera, Cibicides wuellerstorfi, Cibicides lobatulus, Bolivina pusilla, Ehrenbergina carinata, Gavelinopsis lobatulus, Cassidulina laevigata, Globocassiulina subglobosa) reveal significant paleoceanographic changes in the southeastern Indian Ocean during the Neogene. The values of all the diversity parameters show a decrease from 25 to 23 Ma and thereafter an increase with peak values at ~13.5 Ma. The Late Oligocene to Earliest Miocene was an interval of more unstable conditions at Hole 752A dominated by species characteristic of low organic carbon, well-ventilated, carbonate corrosive high energy conditions. The highest values of diversity parameters coincide with the early Middle Miocene climatic optimum. All these parameters show a declining trend and gradual decrease from 13.5 to 4.5 Ma coinciding with the major build up of ice sheets in the Antarctic region. Major increase in B. pusilla and E. carinata population during this time suggests high nutrient levels and low oxygen conditions at Hole 752A. This interval corresponds with the so-called “biogenic bloom” and an intense Oxygen Minimum Zone as observed throughout the Indo-Pacific region. Deep waters were warmer from 4.5 to 3 Ma marked by an increase in species diversity values, coinciding with the early middle Pliocene warmth. The species diversity values abruptly decreased in the younger interval, contempo- raneous with the major Northern Hemisphere glaciation. During this time species characteristics of high-energy bot- tom currents and relatively cold deep water were dominant. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Deep-sea faunal diversity fluctuated considerably across major climatic and oceanic turnovers throughout the Neogene (Thomas and Gooday, 1996; Gupta et al., 2001; Rai and Singh, 2001; Singh and Gupta, 2005; Rai and Maurya, 2009; Yasuhara et al., 2012). Numerous studies on faunal diversity indicate relationship between species diversity and latitude (e.g., Fischer, 1960; Valentine, 1966; Rex et al., 1993; Thomas and Gooday, 1996; Culver and Buzas, 2000; Corliss et al., 2009; Yasuhara et al., 2009; Powell et al., 2012) and also with increasing depth in the marine environment (e.g., Gibson, 1966; Buzas and Gibson, 1969; Gibson and Hill, 1992; Rex et al., 2006; Larkin and Gooday, 2009). Availability of nutrients, heterogeneity of habitat and predation are other important factors bringing changes in deep-sea species diversity patterns (Gooday, 1988; Rai and Singh, 2001; Smart et al., 2007; Corliss et al., 2009; Gooday et al., 2010). In the northern Indian Ocean low species diversity values have been observed during intervals of environmental instability (Gupta and Srinivasan, 1992; Gupta et al., 2001). The oceanic surface productivity and oxygenation of deep waters had significant impact on ocean's faunal regime during the Cenozoic (Dickens and Owen, 1999; Zachos et al., 2001; Sun et al., 2006; Corliss et al., 2009; Kender et al., 2009; Ifrim et al., 2011). Changes in thermocline and thermohaline circulation of ocean basin have impacted the surface and deep-sea biota as well as regional and global climates (Cane and Molnar, 2001; Karas et al., 2009). The pro- ductivity increased significantly in all the oceans since the late middle Miocene (~13 Ma) coinciding with a major increase in Antarctic glacia- tion (Kennett and Barker, 1990) and reached its peak during 10–8 Ma (Dickens and Owen, 1999; Hermoyian and Owen, 2001; Gupta et al., 2004) during which time the Asian monsoons intensified (Quade et al., 1989; Kroon et al., 1991; Gupta and Srinivasan, 1992; An et al., 2001). These productivity-related events are believed to have triggered the so-called “biogenic bloom” and expansion of Oxygen Minimum Zone (OMZ) to large parts of the intermediate Indian Ocean in the late middle Miocene at about 13 Ma (Pisias et al., 1995; Filippelli, 1997; Dickens and Owen, 1999; Hermoyian and Owen, 2001). The expansion of OMZ during Palaeogeography, Palaeoclimatology, Palaeoecology 361-362 (2012) 94–103 ⁎ Corresponding author at: Wadia Institute of Himalayan Geology, 33 GMS Road, Dehradun‐248001, India. Tel.: +91 135 2525270; fax: +91 135 2625212. E-mail address: rajkursingh@yahoo.com (R.K. Singh). 1 Present address: Wadia Institute of Himalayan Geology, 33 GMS Road, Dehradun‐ 248001, India. 2 Present address: 5112 Adrian St, Rockville, MD 20853, USA. 0031-0182/$ – see front matter © 2012 Elsevier B.V. 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