Glacial‐interglacial changes in central tropical Pacific surface seawater property gradients

Abstract

Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).

Constraining foraminiferal calcification depths in the western Pacific warm pool

“…Relative ACDs within a foraminifera assemblage point to G. ruber as the shallowest dweller, followed with increasing depth by G. sacculifer, N. dutertrei, P. obliquiloculata and G. hexagonus being the deepest dwelling species. The ACDs of these species are similar to that shown for other ocean basins (e.g., Ravelo and Fairbanks, 1992;Dekens et al, 2002;Steph et al, 2009;Regenberg et al, 2009;Rincón-Martínez et al, 2011;Birch et al, 2013;Lynch-Stieglitz et al, 2015). However, absolute values differ between and within ocean basins.…”

“…4, Table 3). This mirrors the thick SML in the WPWP and supports the notion of these species being surface-dwellers (Fairbanks et al, 1982;Bé et al, 1985;Ravelo and Fairbanks, 1992;Watkins et al, 1996;Steph et al, 2009;Rincón-Martínez et al, 2011;Lynch-Stieglitz et al, 2015;Nürnberg et al, 2015).…”

“…O values and thus, a generally deeper ACD for G. sacculifer in comparison to G. ruber (Lynch-Stieglitz et al, 2015). Furthermore, a plankton tow study from the South Atlantic revealed that in areas with a thick mixed layer, G. sacculifer often exhibits deeper ACDs than G. ruber, whereas in areas with a shallow thermocline, both species dwell at similar depths (Kemle-von Mücke and Oberhänsli, 1999).…”

“…Despite the importance of the WPWP in the climate system, only little information about foraminiferal ACDs are available. To-date, the limited number of studies from the WPWP have concentrated on reconstructing upper ocean conditions with known ACDs from different regions (e.g., Wara et al, 2005;Russon et al, 2010) or focused on foraminiferal assemblages from the center of the WPWP near New Guinea (Kawahata et al, 2002;Yamasaki et al, 2008), or on plankton tows and surface sediments from the central equatorial Pacific Lynch-Stieglitz et al, 2015).…”

Assessing the reliability of foraminiferal Mg/Ca thermometry by comparing field-samples and culture experiments: a review

“…Mg/Ca palaeothermometry has the po ten tial of re cord ing rel a tively small ocean T changes, which is par tic u larly use ful when study ing high-fre quency cli mate changes dur ing the Pleis to cene (Lea et al, 2000;Me dina-Elizalde and Lea, 2005;Rodríguez-Sanz et al, 2012;Regoli et al, 2015;Lynch-Stieglitz et al, 2015;Lear et al, 2015), and is based on the prem ise that sea wa ter tem per a ture is the pri mary con trol on Mg 2+ in cor po ration into foraminiferal tests dur ing cal ci fi ca tion. The un der ly ing ba sis for Mg/Ca ther mom e try, as cor rob o rated by both ther mody nam ics and phys i o log i cal pro cesses, is that the sub sti tu tion of Mg in cal cite is en do ther mic and there fore is fa voured at higher tem per a tures Erez, 2003;Bentov and Erez, 2006;Lea, 2014).…”