Evolution of the Oligotrophic West Pacific Warm Pool During the Pliocene‐Pleistocene Boundary

Abstract

This study investigates the development of oligotrophic conditions, thickening, and zonal and meridional contraction of the West Pacific Warm Pool (WPWP) during the Pliocene. It has been hypothesized that the evolution of the WPWP and the establishment of strong equatorial Pacific zonal gradients are closely related to the narrowing of the Indonesian Gateway (IG) as well as the closure of the Central American Seaway (CAS). However, the timing of the development of these events remains unclear. Here we report Pliocene-to-Recent relative abundances of planktic foraminifera at Deep Sea Drilling Project (DSDP) Site 214 in the eastern Indian Ocean and at Ocean Drilling Program (ODP) Site 807, in the western Pacific. A comparison of the abundance of mixed-layer species (MLS) from both sites indicates a pronounced increase in their population between~3.15 and 1.6 Ma. There is a contemporaneous decrease in the Globigerinita glutinata population during this time, which together with the MLS data suggest the development of oligotrophic conditions in the western tropical Pacific. Our data suggest that the oligotrophic WPWP, resembling present-day conditions, developed around 3.15 Ma and was closely linked to the gradual constriction of the IG.

Aridification of Northwest Australia and Nutrient Decline in the Timor Sea During the 40 Kyr World

“…It has been reported that the increasing zonal SST gradient across the equatorial Pacific is tightly linked to increasing meridional SST gradient via the wind‐driven circulation and upper‐ocean stratification (Fedorov et al., 2015), which affects precipitation changes, including reduced rainfall in northwest Australia (Brierley et al., 2009; Burls & Fedorov, 2017). The IPWP underwent a steplike transition between 1,800 and 1,600 ka (Bali et al., 2020; Martínez‐Garcia et al., 2010) from an expanded tropical warm pool which persisted in the Pliocene to a reduced warm pool, due to the expansion of the subpolar water masses (Martínez‐Garcia et al., 2010). To investigate the connection between the warm pool change and the transition observed at Site U1483, we evaluate changes in SST gradients between the IPWP center and its edge (Figure 2d and Figure S13 in Supporting Information ).…”

Pliocene to Earliest Pleistocene (5–2.5 Ma) Reconstruction of the Kuroshio Current Extension Reveals a Dynamic Current

“…Today, the WPWP is characterized by a very thick mixed layer that depresses the thermocline in the western Pacific to more than 200 m water depth (Locarnini et al., 2013). The development of the WPWP through the late Neogene has been hypothesized to be related to the constriction of the Indonesian Throughflow and restriction of the CAS, as shown through geochemical and planktic foraminiferal assemblage data (Bali et al., 2020; Chaisson, 1995; Chaisson & Ravelo, 2000; Jian et al., 2006; Keller, 1985; Q. Li et al., 2006; Nathan & Leckie, 2009; Sato et al., 2008; Srinivasan & Sinha, 1998; Wara et al., 2005). The formation and expansion of the WPWP had critical effects on the Neogene climate system (Clement et al., 2005) likely including the continued intensification and development of the KC system and North Pacific Subtropical Gyre through the Miocene and Pliocene (Keller, 1985; Kennett et al., 1985).…”

“…Today, the WPWP is characterized by a very thick mixed layer that depresses the thermocline in the western Pacific to more than 200 m water depth (Locarnini et al, 2013). The development of the WPWP through the late Neogene has been hypothesized to be related to the constriction of the Indonesian Throughflow and restriction of the CAS, as shown through geochemical and planktic foraminiferal assemblage data (Bali et al, 2020;Chaisson, 1995;Chaisson & Ravelo, 2000;Jian et al, 2006;Keller, 1985;Q. Li et al, 2006;Nathan & Leckie, 2009;Sato et al, 2008;Srinivasan & Sinha, 1998;Wara et al, 2005).…”

Aridification of northwest Australia and nutrient decline in the Timor Sea during the 40 kyr world

“…It has been reported that that the increasing zonal SST gradient across the equatorial Pacific is tightly linked to increasing meridional SST gradient via the wind-driven circulation and upper-ocean stratification (Fedorov et al, 2015), which affects precipitation changes, including reduced rainfall in northwest Australia (Brierley et al, 2009;Burls & Fedorov, 2017). The IPWP underwent a steplike transition between 1800 and 1600 ka (Bali et al, 2020;Martínez-Garcia et al, 2010) from an expanded tropical warm pool which persisted in the Pliocene to a reduced warm pool, due to the expansion of the subpolar water masses (Martínez-Garcia et al, 2010). To investigate the connection between the warm pool change and the transition observed at U1483, we evaluate changes in SST gradients between the IPWP center and its edge (Figures 2 and S13).…”