Pliocene development of the east‐west hydrographic gradient in the equatorial Pacific

Abstract

Abstract. Foraminifer count and multispecies isotopic data from

Pliocene Changes in Tropical East Pacific Upper Ocean Stratification: Response to Tropical Gateways?

“…This finding contradicts the general assumption that variations in δ 18 O salinity play a minor role for interpreting TEP planktonic δ 18 O records (Cannariato and Ravelo, 1997;Chaisson and Ravelo, 2000).…”

“…Past studies demonstrate that the isotopic offset between different species of planktonic foraminifers reflects the temperature range within the photic zone in the tropics (e.g., Ravelo and Fairbanks, 1992;Ravelo and Shackleton, 1995;Cannariato and Ravelo, 1997;Ravelo and Andreasen, 1999;Chaisson and Ravelo, 2000;Faul et al, 2000). The temperature range and thus the isotopic differences in δ 18 O between species are assumed to be large when the thermocline is shallow and small when the thermocline is deep.…”

“…Such overprints especially affected the δ 18 O records of G. sacculifer and N. dutertrei. As salinity changes have exerted a more important control on Pliocene TEP upper ocean hydrography than previously assumed (Cannariato and Ravelo, 1997;Chaisson and Ravelo, 2000), we based our interpretations on depth-stratified Mg/Ca temperature and δ 18 O seawater records to assess temporal changes in vertical temperature and salinity gradients.…”

“…According to Farrell et al (1995), carbonate and opal accumulation in the tropical east Pacific (TEP) decreased significantly and the maximum of opal accumulation shifted toward the east at ~4.4 Ma. Based on eolian grain size and flux studies, Hovan (1995) (Chaisson and Ravelo, 2000). This change is characterized by shoaling of the thermocline in the TEP, which was also recorded in multispecies planktonic stable isotope records from TEP Site 851 as documented by Cannariato and Ravelo (1997).…”

History of upwelling in the Tropical Eastern Pacific and the paleogeography of the Isthmus of Panama

“…Uplift rates based on paleobathymetries of marine sediments from across the Isthmus suggest that the majority of the volcanic arc was submerged up until very recently with bathyal sediments of latest Miocene age present in the Caribbean and Pacific of western Panama, the Caribbean of central Panama and eastern Panama (Coates et al, 1992;Collins, 1992Collins, , 1993Collins, , 1996Coates, 1999;Coates et al, 2000Coates et al, , 2003Coates et al, , 2004Coates et al, , 2005. Strong similarities between Pacific and Caribbean Mio-Pliocene biota (Chaisson and Ravelo, 2000;O'Dea et al, 2007b) and near-identical environmental conditions on either side of the Isthmus (Keigwin, 1978(Keigwin, , 1982Keller et al, 1989;Haug and Tiedemann, 1998;Haug et al, 2001) in the Early Pliocene imply the CAS was maintained in some form until the mid-Pliocene. Nevertheless, well-studied and extensive lacustrine sediments, shallow water reefs and mangroves, plus a continental-like mammal fauna in the Canal Zone of Panama demonstrate the presence of substantial subaerial land(s) in the middle Miocene (Whitmore and Stewart, 1965;Kirby and MacFadden, 2005;Johnson and Kirby, 2006;Retallack and Kirby, 2007;Kirby et al, 2008).…”