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Southeastern Atlantic Deep-Water Evolution During the Late-Middle Eocene to Earliest Oligocene (Ocean Drilling Program Site 1263 and GEOSPHERE; V

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Southeastern Atlantic Deep-Water Evolution During the Late-Middle Eocene to Earliest Oligocene (Ocean Drilling Program Site 1263 and GEOSPHERE; V Research Paper GEOSPHERE Southeastern Atlantic deep-water evolution during the late-middle Eocene to earliest Oligocene (Ocean Drilling Program Site 1263 and GEOSPHERE; v. 12, no. 3 Deep Sea Drilling Project Site 366) doi:10.1130/GES01268.1 Samantha J. Langton1,*, Nathan M. Rabideaux1,†, Chiara Borrelli2, and Miriam E. Katz1 6 figures; 3 tables; 2 supplemental files 1Department of Earth & Environmental Sciences, Rensselaer Polytechnic Institute, Jonsson-Rowland Science Center, 1W19 110 8th Street, Troy, New York 12180, USA 2Department of Earth & Environmental Sciences, University of Rochester, 227 Hutchison Hall, P.O. Box 270221, Rochester, New York 14627, USA CORRESPONDENCE: katzm@ rpi .edu CITATION: Langton, S.J., Rabideaux, N.M., Borrelli, ABSTRACT Miller et al., 1992, 2005, 2008a, 2008b, 2009; Diester-Haass and Zahn, 1996; C., and Katz, M.E., 2016, Southeastern Atlantic deep-water evolution during the late-middle Eo- Zachos et al., 1996; Lear et al., 2004, 2008; Coxall et al., 2005; Katz et al., 2008; cene to earliest Oligocene (Ocean Drilling Program Comparison of new benthic foraminiferal δ18O and δ13C records from Ocean Wade and Pearson, 2008; Pusz et al., 2011; Wade et al., 2012; Bijl et al., 2013). The Site 1263 and Deep Sea Drilling Project Site 366): Drilling Program (ODP) Site 1263 (Walvis Ridge, southeast Atlantic, 2100 m transition from warmer to colder high-latitude ocean temperatures from the Geosphere, v. 12, no. 3, p. 1032–1047, doi:10.1130 /GES01268.1. paleodepth) and Deep Sea Drilling Project (DSDP) Site 366 (Sierra Leone Rise, early Eocene to the Oligocene (ca. 50–33 Ma) is evident in many paleoceano- eastern equatorial Atlantic, 2200–2800 m paleodepth) with published data graphic records (e.g., Browning et al., 1996; Diester-Haass et al., 1996; see Received 18 September 2015 from Atlantic and Southern Ocean sites provides the means to reconstruct the compi la tions of Cramer et al., 2009, 2011). Southern Ocean deep- water tem- Revision received 2 February 2016 development of deep-water circulation in the southeastern Atlantic from the peratures peaked during the early Eocene and subsequently cooled during the Accepted 7 April 2016 late-middle Eocene to the earliest Oligocene. Our comparison shows that in middle Eocene to the early Oligocene by as much as 5–10 °C (e.g., Mackensen Published online 5 May 2016 the late-middle Eocene (ca. 40 Ma), the South Atlantic was characterized by a and Ehrmann, 1992; Zachos et al., 2001; Diekmann et al., 2004; Cramer et al., homogeneous thermal structure. Thermal differentiation began ca. 38 Ma. By 2011; Bohaty et al., 2012). The earliest documented ephemeral Antarctic glacia- 37.6 Ma, Site 1263 was dominated by Southern Component Water; at the same tion occurred in the late-middle Eocene (ca. 37.3 Ma; Scher et al., 2014), followed time, warm saline deep water filled the deeper South Atlantic (recorded at by additional ephemeral glaciations and warming and cooling cycles leading southwest Atlantic ODP Site 699, paleodepth 3400 m, and southeast Atlantic into continental-scale Antarctic glaciation in the early Oligocene (e.g., Miller ODP Site 1090, paleodepth 3200 m). The deep-water source to eastern equa- et al., 1991; Zachos et al., 1992; Thomas, 1992; Cramer et al., 2011). torial Site 366 transitioned to Northern Component Water ca. 35.6–35 Ma. Pro- Deep-water circulation patterns during this transition changed as key tec- gressive cooling at Site 1263 during the middle to late Eocene and deep-water tonic gateway configurations changed (Exon et al., 2004; Stickley et al., 2004; thermal stratification in the South Atlantic may be attributed at least in part to Scher and Martin, 2006; Livermore et al., 2007; Cramer et al., 2009; Katz et al., the gradual deepening and strengthening of the proto–Antarctic Circumpolar 2011; Borrelli et al., 2014; Borrelli and Katz, 2015), including the progressive Current from the late-middle Eocene to the earliest Oligocene, as the Drake openings of the Drake (Cox, 1989; England, 1992; Toggweiler and Bjornsson, and Tasman gateways opened. Our isotopic comparisons across depth and 2000; Livermore et al., 2004, 2007; Sijp and England, 2004; Eagles et al., 2006) latitude provide evidence of the development of deep-water circulation simi- and Tasman (Exon et al., 2004; Stickley et al., 2004; Sijp et al., 2011, Bijl et al., lar to modern-day Atlantic Meridional Overturning Circulation. 2013) passages that ultimately resulted in the development of the Antarctic Circumpolar Current (ACC). Initial opening of the Drake Passage began in the middle Eocene (ca. 50 Ma; Livermore et al., 2007), with circulation as deep as INTRODUCTION 1000 m by ca. 41 Ma (Scher and Martin, 2006; Livermore et al., 2007). Onset of spreading at the West Scotia Ridge in the latest Eocene–early Oligocene al- The late-middle Eocene to earliest Oligocene (ca. 38–33 Ma) was a period of lowed the development of eastward-flowing deep currents through the Drake transition to large-scale glaciation on Antarctica and cooling of the oceans (e.g., Passage (Livermore et al., 2007). Shallow westward flow through the Tasman Miller and Fairbanks, 1985; Barron et al., 1991; Ehrmann and Mackensen, 1992; gateway began in the middle Eocene (Bijl et al., 2013), progressing to deep flow by the latest Eocene–earliest Oligocene (Scher et al., 2015); deep eastward *Now at Environmental Products and Services of Vermont, 210 Wembly Road, New Windsor, flow through the Tasman gateway began ca. 30 Ma (Scher et al., 2015). New York 12553, USA For permission to copy, contact Copyright †Now at Department of Geosciences, Georgia State University, 24 Peachtree Center Ave., NE, The cooling of Southern Component Water (SCW; deep-water mass origi- Permissions, GSA, or [email protected]. Atlanta, Georgia 30302, USA nating in the Southern Ocean) coincided with the progressively developing © 2016 Geological Society of America GEOSPHERE | Volume 12 | Number 3 Langton et al. | Southeastern Atlantic deep-water evolution Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/3/1032/4092597/1032.pdf 1032 by guest on 29 September 2021 Research Paper ACC in response to the gradual opening of the Drake and Tasman Passages Drilling Project (DSDP) Site 366 (eastern equatorial Atlantic, 2853 m present (e.g., Livermore et al., 2007; Cramer et al., 2009; Sijp et al., 2011; Bijl et al., depth, 2200–2800 m paleodepth) to published data sets from the Atlantic and 2013); this is consistent with models that show the formation of cold SCW Southern Oceans (Table 1; Figs. 1 and 2). We compare the circulation changes with the progressive deepening of the Drake and Tasman Passages (e.g., to gateway changes in order to examine how the development of the proto- Toggweiler and Samuels, 1995; Toggweiler and Bjornsson, 2000; Nong et al., ACC affected deep-water circulation in the southeastern Atlantic, as has been 2000; Sijp and England, 2004, 2005). The opening of the Drake Passage and suggested for other regions including the Southern Ocean, northern Atlantic, developing proto-ACC (defined as the precursor to the modern ACC; the and northwestern Pacific (e.g., Diester-Haass and Zahn, 1996; Diekmann et al., proto- ACC was shallower than the modern current because of the more con- 2004; Scher and Martin, 2006; Via and Thomas, 2006; Cramer et al., 2009; Katz stricted Drake and Tasman gateways; e.g., Borrelli et al., 2014) also has been et al., 2011; Borrelli et al., 2014; Borrelli and Katz, 2015). linked to the production of Northern Component Water (NCW; deep-water mass originating in the northern North Atlantic; e.g., Scher and Martin, 2008; Katz et al., 2011; Borrelli et al., 2014) that originated in the late-middle Eocene MODERN SOUTH ATLANTIC OCEAN CIRCULATION from the Labrador Sea (Borrelli et al., 2014). In addition, the Tethys closed to the North Atlantic during the middle Eocene, which prohibited export of The modern ocean is driven by thermohaline circulation (e.g., Gordon, low-latitude warm saline deep water to the Atlantic Ocean from the western 1986; Broecker, 1991; Jayne and Marotzke, 2001), wind-driven surface mix- Tethys (Oberhänsli, 1992). ing (Wyrtki, 1961; Schmitz, 1995; Rahmstorf, 2003), and eddy diffusivity (e.g., In the marine record, d18O values of foraminifera are used to interpret paleo- Holzer and Primeau, 2006). The Meridional Overturning Circulation (MOC) in temperature and global ice volume (e.g., Miller and Fairbanks, 1987; Cramer the present-day ocean is driven primarily by wind-induced upwelling that is et al., 2009), while d13C values are indicative of paleoproductivity, water-mass most intense along the ACC and causes the displacement of deep water to aging, and the oceanic carbon cycle (e.g., Kroopnick, 1985; Lynch-Stieglitz the surface, allowing formation of new deep water through downwelling in et al., 1995). The analysis of benthic foraminifera that record isotopic changes the North Atlantic and Southern Ocean (e.g., Toggweiler and Samuels, 1998). provides a snapshot of global climate and deep-water circulation from the time The South Atlantic plays an important role in the global balance of the modern they formed their tests. Intersite comparisons between benthic foraminiferal Atlantic Meridional Overturning Circulation (AMOC) through mixing, advec- d18O and d13C records are used to interpret the source region of deep-water tion, and subduction of water masses that enter this basin from all depths and production and the flow path of deep-water masses (e.g., Curry and
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