Middle to Late Miocene integrated biostratigraphy and biozonation for the mid-latitude Indian Ocean (ODP Site 752)

Deep sea Cenozoic paleoceanographic evolution was studied using quantitative analysis of benthic foraminifera from ODP Sites 757 and 758 (Ninetyeast Ridge) and Site 747 (Kerguelen Plateau), on the south-north transect of the Indian Ocean. Bathyal Site 747 records high latitude paleoceanography and Sites 757 and 758 record midto lowlatitude bathyal and abyssal paleoceanography respectively. Benthic foraminiferal assemblages reflect global paleoceanographic changes, but the faunal changes are not all coeval, due to the different paleodepths and paleolatitudes. At Site 747, Southern Component Water (SCW) developed in the Oligocene and middle Miocene; Northern Component Water (NCW) and SCW developed in the Oligocene and the late Miocene. At bathyal Site 757, the following periods of paleoceanographic change were recognized: early to middle Eocene (-52 Ma), late middle Eocene (-42 Ma), latest Eocene (-38 Ma), early Oligocene (-32 Ma), middle Miocene (-12 Ma), and late Miocene (-8 Ma). At abyssal Site 758, the paleoceanographic changes are complex, with both NCWand SCW-allied assemblages occurring in the Oligocene and the middle Miocene to Pliocene (-33-29, -26-24, -9, -6-4, -3 Ma). Comparison of the benthic foraminiferal assemblages with the modern distribution of foraminiferal species and with oxygen and carbon isotopic data suggests the following paleoecological conditions at Sites 757 and 758: Cold water and high organic matter-exploiting assemblages appeared from the late Miocene to Pleistocene; warm water and lower organic matter-exploiting assemblages occurred from the early Eocene to middle Miocene. Resistant to high carbonate corrosion-type assemblages developed during the Oligocene and from the late Miocene to Pliocene at Site 747. Temperature decrease and changes in the food resource (phytodetritus) level of deep water are important factors for the benthic faunal changes throughout the Cenozoic. Faunal changes at bathyal depths before the middle Miocene occurred during a lower food resource level and those from the middle Miocene onward occurred in an enriched phytodetritus flux in deep water. The modern deep water is formed at -2 Ma in the Indian Ocean at Sites 757 and 758. The cold-water and carbonate corrosion-type assemblages are more dominant at Subantarctic Site 747.

Late Miocene and mid-Pliocene enhancement of the East Asian monsoon as viewed from the land and sea

Distribution of diatoms in sediments of the northern Indian Ocean: Relationship to physical oceanography

The exchange of water between the Pacific and Indian Oceans is important in regulating planetary climate. North of Australia, this exchange plays a key role in regulating the Indo-Pacific Warm Pool with far-reaching effects via Indonesian Throughflow (ITF). The exchange south of Australia is far less understood, and much of the exchange occurs at intermediate depths through Tasman Leakage (TL). Here, we investigate Ocean Drilling Program (ODP) Site 752 which was drilled on Broken Ridge. The Site is located within the path of TL, and thus, can provide a paleoceanographic history of TL. Benthic foraminiferal (BF) assemblage is a useful tool to reconstruct paleoceanographic patterns. At ODP Site 752, BF assemblages vary over time but at no point exhibit evidence of extreme stress or oxygen deficiency. Benthic foraminiferal diversity measured with the Fischer Alpha diversity index remains between 5 and 10, indicating moderate diversity throughout the last 9 million years. Furthermore, the high abundance of epiphytic species Cibicidoides wuellerstorfi and Lobatula lobatula likely reflects a high current energy environment over Broken Ridge during this time. Based on our comprehensive benthic foraminiferal assemblage study, we suggest that the driving factor behind the benthic ecological changes on Broken Ridge since the Late Miocene has been TL intensity, distinguished by its kinetic energy. In addition, we present a ~13 Myr neodymium (Nd) isotopic record, suggesting that TL onset likely occurred sometime in the late Middle Miocene, advecting isotopically older Pacific-sourced waters into the Indian Ocean. The latter findings challenge the previously presumed onset of TL at ~7 Ma and indicate a much earlier initiation of TL between 14 – 10 Ma, that intensified during the Late Miocene when the modern-like TL was established.

Nd isotope systematics on ODP Sites 756 and 762 sediments reveal major volcanic, oceanic and climatic changes in South Indian Ocean over the last 35 Ma

Surface paleoceanography of the eastern equatorial Indian Ocean since the latest Miocene: Foraminiferal census and isotope records from ODP Hole 758A

Linking the oxygen isotope record of late Neogene eustasy to sequence stratigraphic patterns along the Bahamas margin: results from a paleoceanographic study of ODP Leg 166, Site 1006 sediments

Sonostratigraphy of tropical Indian Ocean giant piston cores: toward a rapid and high-resolution tool for tracking dissolution cycles in Pleistocene carbonate sediments

Timing of rifting in the Alboran Sea basin — correlation of borehole (ODP Leg 161 and Andalucia A-1) to seismic reflection data: implications for basin formation

The last major turnover in deep-sea benthic foraminifera (the Stilostomella extinction) is documented in detail in six DSDP and ODP sites around New Zealand, South-west Pacific. This was the final phase in the progressive decline of elongate, cylindrical taxa (mostly stilostomellids, pleurostomellids and uniserial nodosariids), which reached their greatest relative abundance in the late Eocene, and exhibited major declines during periods of global cooling around the Eocene-Oligocene boundary, in late middle Miocene, and through the late Pliocene to middle Pleistocene. The Stilostomella extinction includes the extinction of all elongate species with cribrate ( Chrysalogonium, Cribronodosaria ), slit lunate, hooded with two teeth (Pleurostomellidae), or secondarily toothed, necked (Stilostomellidae) apertures. Elongate and uniserial benthic foraminifera are separated into: an Extinction Group (53 taxa, including several elongate agglutinated and uvigerine forms, that became extinct in the South-west Pacific during the late Pliocene-middle Pleistocene); a Die-back Group (8 species that dramatically declined in abundance but survived to the Recent); and a Survivor Group (88 mostly rare species of uniserial nodosariids with little recognised decline). In the South-west Pacific, the absolute abundance of the Extinction and Die-back groups began to decline in the late Pliocene. The decline became more dramatic during the late early and middle Pleistocene (1.2–0.7 Ma). The rate of decline was pulsed, with major declines usually associated with the onset of cold intervals, and partial recoveries in intervening warm intervals. The pulses varied in timing between sites. The highest occurrences (HOs or local disappearances) of individual Extinction Group species are variable and mostly diachronous between sites. There was a progressively increasing overall rate of local disappearances per time through the late Pliocene (onset of northern hemisphere glaciation) to the middle Pleistocene climatic revolution, with the peak period of local disappearances (mostly 0.9–0.7 Ma) up to 0.5 Ma earlier at deeper and cooler water locations. The youngest occurrence of any member of the Extinction Group ( Stilostomella extinction datum) is remarkably consistent in all sites (0.65–0.57 Ma). The timing of these abundance declines, highest occurrences (or withdrawals) and extinctions was essentially the same as in the Atlantic Ocean. The precise mechanistic cause of the Stilostomella extinction (cooling, increased oxygenation of bottom waters, food supply changes) is yet to be resolved. This study reveals a much larger extinction of taxa than previously recorded (middle Pleistocene extinction rate of 23% of the bathyal-upper abyssal fauna/myr). Becoming extinct, or virtually so, during this period were at least two families (Stilostomellidae, Pleurostomellidae), one subfamily (Plectofrondiculariinae), at least 17 genera ( Awhea, Chrysalogonium, Cribronodosaria, Ellipsoglandulina, Ellipsopleurostomella, Ellipsopolymorphina, Haeuslerella, Mucronina, Myllostomella, Nodosarella, Orthomorphina, Parafrondicularia, Pleurostomella, ? Rectuvigerina, Siphonodosaria, Stilostomella, Strictocostella ) and 53 species. Their taxonomy is reviewed, revealing many synonymies, often going back to Schwager’s (1866) pioneering study of Pliocene deep-sea foraminifera of Car Nicobar, Indian Ocean. A revised generic subdivision of the Stilostomellidae is proposed based primarily on apertural features, and Myllostomella n.gen. described.

Concerning climatic conditions during the Miocene Climate Optimum (MCO), global temperatures were about 3-4°C warmer than modern, and characterized by globally lower ice volume. Indian Ocean Sub-Antarctic Mode Water (SAMW) is primarily formed south of 30°S and is the primary return path for deep waters to the surface, migrating and intermixing northwards at Intermediate Water (IW) depths. Today, the SAMW carries access nutrients into the lower latitudes, strongly impacting latitude productivity. During warmer climates, decreasing sea ice may increase nutrient trapping in the Southern Ocean, reducing the nutrient flux through SAMW into the lower latitudes. Thus, the MCO may indicate future climate, nutrient transport, and SAMW formation by exploring differences between cooler (modern) and warmer (MCO) climates.Ocean Drilling Project (ODP) Site 752, located on Broken Ridge in the southeastern Indian Ocean at a water depth of 1086.3 m, is a key location for investigating changes in IW conditions in the Indian Ocean after the MCO and the Middle Miocene Climatic Transition (MMCT). In particular, the reactions to global warming and the reorganization of oceanic and atmospheric circulation following the MCO and MMCT can be detected. This also includes the analysis of SAMW, Antarctic Intermediate Water (AAIW), and Tasman Leakage (TL).The present study aims to reconstruct paleoenvironmental conditions and bottom-water oxygenation at Site 752 during the Middle to Late Miocene (15-8 Myrs). To achieve this, we apply benthic foraminifera assemblages as proxies for bottom water oxygenation, for example, enhanced Benthic Foraminifera Oxygen Index (eBFOI), paleoproductivity, and stable carbon and oxygen isotopes.Initial results in the Middle to Late Miocene show an occurrence of oxic benthic foraminifera at a relatively constant abundance, especially in the early Late Miocene. In addition, in a relatively high oxic environment, an increase of dysoxic conditions occurred during the early Late Miocene, with peaks of abundance in dysoxic and deep infaunal benthic foraminifera. A co-occurrence of infaunal dysoxic and epifaunal oxygen-rich species is accompanied by enhanced current winnowing and an increase of nutrient flux during the Late Miocene (Lyu et al., 2023; DOI: 10.1029/2023PA004761). These data indicate that during the Late Miocene, since approximately 10 Ma, the strengthening of SAMW and AAIW formation resulted in notable changes in bottom-water conditions at Broken Ridge, such as increased current winnowing. The observed changes in IW are potentially linked to the shift of the southern hemisphere westerlies towards the north and the subsequent northward migration of the frontal system in the southern hemisphere around Antarctica after 12 Ma.

In the early-to-mid Cenozoic (66-34 Ma), Southern Ocean circulation was dominated by two subpolar gyres in the Atlantic-Indian and Pacific Oceans. These gyres transported surface water from the subtropics towards Antarctica. The Drake Passage and Tasmanian Gateway opening and widening during the late Cenozoic (34–0 Ma) gradually allowed circumpolar flow of the Antarctic Circumpolar Current (ACC) and the onset of complex oceanic frontal systems, which broke down the earlier subpolar gyres. Questions remain about the precise timing and nature of the onset of the ACC-system and the consequence for climate, ocean circulation and Antarctic ice volume. We hereby provide new insights into the Late Eocene-Miocene (37–5 Ma) oceanographic development by reconstructing surface ocean environment combining remains of organic walled dinoflagellate cysts (dinocysts) and organic biomarker (TEX86and Uk’37) sea surface temperature (SST) estimates from marine sedimentary drill cores from the southwestern South Atlantic (IODP Site U1536, ODP Site 696 and piston cores from Maurice Ewing Bank), southeastern Indian Ocean (ODP Site 1168) and southwestern Pacific (ODP Site 1172). We compare our results, together with available Southern Ocean records, with model experiments and tectonic reconstructions to deconvolve the effects of climate, ice volume and tectonic changes on Southern Ocean oceanography.Late Eocene – Early Oligocene SSTs (37­–27 Ma) were broadly similar across the Southern Ocean (4–8°C latitudinal temperature difference), which we ascribe to persistent, strong subpolar gyral circulation influencing the sites. In the Late Oligocene (~26 Ma), progressive Antarctic-proximal cooling increased the SST gradient in the Australian-Antarctic gulf (>9°C). The timing of this Antarctic-proximal cooling coincided with sedimentary and kinematic reconstructions of Drake Passage deepening after 26 Ma, thus matching with ocean model experiments demonstrating that Drake Passage deepening weakened gyral circulation, enhanced thermal isolation and cooled Antarctic proximal waters. Throughout the Late Oligocene–Late Miocene (26–5 Ma) we record a continued contraction of the sub-polar gyre and southward migration of the subtropical gyre in the South Atlantic, with strengthening frontal systems and progressive cooling that first started in the southern South Atlantic. Although geographic coverage is sparse, our data shows for the first time the stepwise breakdown of subpolar gyres into the modern-like oceanographic regime with the development of strong frontal systems, latitudinal gradients and deep-water formation. We demonstrate, with modelling and geological data, that while climate and ice volume changes determine the strength of latitudinal SST gradients and position of ocean fronts on orbital time scales, gateway configurations play a large role in long-term trends.

Paleoproductivity of the Indian Ocean during the Tertiary Period

The Latest Miocene–Early Pliocene biogenic bloom: a revised Indian Ocean perspective

New Sr- Nd- and Pb-isotopic and trace element data are presented on basalts from the Sulu and Celebes Basins, and the submerged Cagayan Ridge Arc (Western Pacific), recently sampled during Ocean Drilling Program Leg 124. Drilling has shown that the Sulu Basin developed about 18 Ma ago as a backarc basin, associated with the now submerged Cagayan Ridge Arc, whereas the Celebes Basin was generated about 43 Ma ago, contemporaneous with a general plate reorganisation in the Western Pacific, subsequently developing as an open ocean receiving pelagic sediments until the middle Miocene. In both basins, a late middle Miocene collision phase and the onset of volcanic activity on adjacent arcs in the late Miocene are recorded. Covariations between 87Sr/86Sr and 143Nd/144Nd show that the seafloor basalts from both the Sulu and Celebes Basins are isotopically similar to depleted Indian mid-ocean ridge basalts (MORB), and distinct from East Pacific Rise MORB, defining a single negative correlation. The Cagayan Arc volcanics are different, in that they have distinctly lower ɛNd(T) for a given ɛSr(T), compared to Sulu and Celebes basalts. In the 207Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, the Celebes, Sulu and Cagayan rocks all plot distinctly above the Northern Hemisphere Reference Line, with high Δ7/4 Pb (5.3–9.3) and D8/4 Pb (46.3–68.1) values. They define a single trend of radiogenic lead enrichment from Celebes through Sulu to Cagayan Ridge, within the Indian Ocean MORB data field. The data suggest that the overall chemical and isotopic features of the Sulu, Cagayan and Celebes rocks may be explained by partial melting of a depleted asthenospheric N-MORB-type (“normal”) mantle source with isotopic characteristics similar to those of the Indian Ocean MORB source. This asthenospheric source was slightly heterogeneous, giving rise to the Sr-Nd isotopic differences between the Celebes and Sulu basalts, and the Cagayan Ridge volcanics. In addition, a probably slab-derived component enriched in LILE and LREE is required to generate the elemental characteristics and low Nd(T) of the Cagayan Ridge island arc tholeiitic and calcalkaline lavas, and to contribute to a small extent in the backarc basalts of the Sulu Sea. The results of this study confirm and extend the widespread Indian Ocean MORB signature in the Western Pacific region. This signature could have been inherited by the Indian Ocean mantle itself during the rupture of Gondwanaland, when fragments of this mantle could have migrated towards the present position of the Celebes, Sulu and Cagayan sources.