Neogene history of the West Pacific Warm Pool, Kuroshio and Leeuwin currents

Abstract

Foraminiferal analysis of Miocene to recent strata of the Northwest Shelf of Australia is used to chart West Pacific Warm Pool (WPWP) influence. The assemblage is typified by “larger” foraminifera with ingressions of the Indo‐Pacific “smaller” taxa Asterorotalia and Pseudorotalia at around 4 Ma and from 1.6 to 0.8 Ma. A review of recent and fossil biogeography of these taxa suggests their stratigraphic distribution can be used to document WPWP evolution. From 10 to 4.4 Ma a lack of biogeographic connectivity between the Pacific and Indian Ocean suggests Indonesian Throughflow (ITF) restriction. During this period, the collision of Australia and Asia trapped warmer waters in the Pacific, creating a central WPWP biogeographic province from the equator to 26°N. By 3 Ma Indo‐Pacific species migrated to Japan with the initiation of the “modern” Kuroshio Current coinciding with the intensification of the North Pacific Gyre and Northern Hemisphere ice sheet expansion. Indo‐Pacific taxa migrated to the northwest Australia from 4.4 to 4 Ma possibly because of limited ITF. The absence of Indo‐Pacific taxa in northwest Australia indicates possible ITF restriction from 4 to 1.6 Ma. Full northwest Australian biogeographic connectivity with the WPWP from 1.6 to 0.8 Ma suggests an unrestricted stronger ITF (compared to today) and the initiation of the modern Leeuwin Current. The extinction of some Indo‐Pacific species in northwest Australia after 0.8 Ma may be related to the effects of large glacial/interglacial oscillations and uplift of the Indonesian Archipelago causing Indonesian seaway restriction.

Late Cenozoic history of deep water circulation in the western North Pacific: Evidence from Nd isotopes of ferromanganese crusts

“…It is likely that the similarity in Nd isotopic compositions between the studied two crusts in the Quaternary marked the full development of the modern deep circulation pattern near the Mariana arc. In the surface western North Pacific, the modern circulation pattern is characterized by the final formation of the west Pacific warm pool (WPWP) during ~3-4 Ma [68] and the intensification of Kuroshio Current at about 3 Ma [69,70]. Also noteworthy is the indistinguishable Nd isotopic composition of the equatorial and the Southwestern Pacific deep water over the Quaternary (Figure 3), as well as the convergent trends in Nd isotopic compositions of these crusts.…”

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“…They are abundant in all the facies of the West Tryal Rocks-1 Well (near Site U1461; Figure F8; see data and zonation in Gallagher et al, 2009). There are also a few useful dinoflagellate datums (McMinn, 1992(McMinn, , 2002 in the Pliocene-Pleistocene section to assist age calibration.…”

“…The benthic foraminifer δ 18 O curve is from Lisiecki and Raymo (2005). The NWS Indo-Pacific foraminiferal species distribution (from cuttings) is from Gallagher et al (2009) and unpublished results from the Fisher-1 Well (adjacent to Site U1462). Sea-surface temperature data are from Hole 763A (Karas et al, 2011) (Figure F1).…”

“…Kendrick et al (1991) used fossil mollusks to suggest that onset of the Leeuwin Current occurred more recently than 500 ka, whereas Sinha et al (2006) and Karas et al (2011) suggested onset at 2.5 Ma, and McGowran et al (1997) proposed a late Eocene (40 Ma) onset age. However, Gallagher et al (2009;2014b) used microfossil biogeographic indicators in subsurface petroleum well samples from the NWS to suggest that the "modern" Leeuwin Current is younger than 1 Ma. Spooner et al (2011) documented 500 ky of Leeuwin Current variability from a deep-sea core (MD002361, 1805 m water depth) ( Figure F1) using stable isotopes and planktonic foraminiferal proxies and suggested a weaker Leeuwin Current during glacial periods, when the West Australian Current was dominant, and a stronger Leeuwin Current during interglacials, especially marine isotope Stage (MIS) 11.…”

“…Oceanography and climate of the western Pacific (adapted from Gallagher et al, 2009). Currents (red = warm, blue = cold) are indicated.…”