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Woods Hole Oceanographic Institution

Heather Benway

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Projects
» EPWP Paleosalinity

» North Atlantic temperature reconstruction

» Oxygen isotope tracers in rainwater and seawater


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Annual average salinity (PSU) for the Eastern Pacific Warm Pool (EPWP) region and the western Caribbean [World Ocean Atlas, 1998]. Pacific sites (ME0005A-43JC: 7? 51.35?N, 83? 36.50?W, 1368 m and ODP Site 1242: 7? 51.35?N, 83? 36.42?W, 1364 m) used in this study are indicated. Inset: T-S diagram [World Ocean Atlas, 1998] of the EPWP region with isopycnals (dashed) and predicted δ18Oc isolines (solid) calculated from temperature and salinity [Bemis et al., 1998] assuming modern regional δ18Osw-S [Benway and Mix, 2004].


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Data from ME0005A-43JC (filled symbols) and ODP Site 1242 (unfilled symbols). Ages reported in calendar ky before present. AMS 14C dates for ME0005A-43JC are indicated by filled circles on age axis with 2-sigma error bars. A. δ18Oc for G. ruber (white) and N. dutertrei. B. δ18Oc difference between G. ruber and N. dutertrei, indicating upper ocean contrast above the pycnocline. C. Mg/Ca-based temperature for G. ruber. Mg/Ca was converted to temperature using Mg/Ca = 0.38Exp(0.090T) [Anand et al., 2003]. Modern annual average surface temperature [World Ocean Atlas, 1998] is indicated on the y-axis. D. δ18Osw estimates calculated from G. ruber Mg/Ca and δ18Oc [Bemis et al., 1998; Thunell et al., 1999] and corrected for ice volume changes [Clark and Mix, 2002; Waelbroeck et al., 2002]. The potential range of δ18Osw uncertainty associated with ice volume change is indicated by two curves. The solid curve indicates a scaling of 0.01? m-1 while the dashed curve indicates a scaling of 0.0075? m-1 decrease in relative sea level (RSL). The resulting range of uncertainty in the corrected δ18Osw is indicated by the corresponding solid and dashed smoothed δ18Osw records. The modern measured δ18Osw [World Ocean Atlas, 1998] is indicated on the y-axis. For the combined records of the two sites a Gaussian smoothing function (time step = 0.2 ky; filter width = 0.8 ky) was applied.


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A. Sea-surface temperature (SST) reconstructions from Cariaco Basin core PL07-39PC [Lea et al., 2003] based on Mg/Ca and subtropical northeast Atlantic core SU8118 [Bard, 2002] based on alkenones. B. Measured color reflectance (550 nm) [Peterson et al., 2000] and % Ti [Haug et al., 2001] of Cariaco Basin sediments, ODP Site 1002. Lower reflectance (darker, clay-rich sediment) and higher % Ti (increased terrigenous sediment) imply wetter conditions in northern South America. C. δ18Osw and estimated paleosalinity from the EPWP (ME0005A-43JC and ODP Site 1242) [Benway and Mix, 2004] and the Caribbean [Schmidt et al., 2004]. The same ice volume correction is applied to both records (see solid curve, Fig. 3d), and two separate salinity scales are shown, based on regional δ18O-S [Benway and Mix, 2004; Schmidt et al., 2004]. Circles indicate Caribbean radiocarbon age control points with 2-sigma error bars. Pacific radiocarbon age control points are shown in Fig. 3D. D. Estimates of interbasin salinity average based on averaging Pacific and Caribbean [Schmidt et al., 2004] δ18Osw. Upward arrow indicates southward ITCZ position. The higher resolution Pacific record was first placed on the Caribbean time scale using Gaussian interpolation, the records were differenced, and the result was smoothed (0.2 ky time step, filter width = 0.8 ky). Dashed curves show maximum age model error in the interbasin contrast calculation, based on 2-sigma ranges in Pacific and Caribbean radiocarbon dates. E. Estimates of interbasin salinity contrast based on differencing Pacific and Caribbean [Schmidt et al., 2004] δ18Osw. Upward arrow indicates increased water vapor transport. See above (4D) for details on calculations. F. 231Pa/230Th ratios (calculated from measured 238U activity) from Bermuda rise [McManus et al., 2004], indicating strength of Atlantic meridional overturning circulation (MOC). Circles indicate Bermuda Rise radiocarbon age control points with 2-sigma error bars. Benthic δ13C records from MD95-2042 [Shackleton et al., 2000], V30-51K [Mix, 1985], and ODP Site 980 [McManus et al., 1999; Oppo et al., 2003] also indicate changes in deep ocean circulation. G. GISP2 δ18Oice [Grootes and Stuiver, 1997], indicating high latitude air temperatures. Shaded bars indicate key climate events of the last 30 ky. 8 ka = 8.2 ka event; YD = Younger Dryas; HE-1, 2, 3 = Heinrich events; 19 ka = earliest postglacial sealevel rise; T-1A = Termination or meltwater pulse (MWP)-1A; T-1B = Termination or MWP-1B.


Eastern Pacific Warm Pool paleosalinity and climate variability: 0-30 ky

Collaborators:
Alan Mix, Brian Haley, Gary Klinkhammer

Multi-proxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 ky. Although evident in the paleotemperature record, there is no glacial-interglacial difference in paleosalinity, suggesting that tropical hydrologic changes do not respond passively to high-latitude ice sheets and oceans. Millennial variations in paleosalinity with amplitudes as high as ~4 PSU occur with a dominant period of ~3-5 ky during the glacial/deglacial interval and ~1.0-1.5 ky during the Holocene. The amplitude of the EPWP paleosalinity changes greatly exceeds that of published Caribbean and western tropical Pacific paleosalinity records. EPWP paleosalinity changes correspond to millennial-scale climate changes in the surface and deep Atlantic and the high northern latitudes, with generally higher (lower) paleosalinity during cold (warm) events. In addition to Intertropical Convergence Zone (ITCZ) dynamics, which play an important role in tropical hydrologic variability, changes in Atlantic-Pacific moisture transport, which is closely linked to ITCZ dynamics, may also contribute to hydrologic variations in the EPWP. Calculations of interbasin salinity average and interbasin salinity contrast between the EPWP and the Caribbean help differentiate long-term changes in mean ITCZ position and Atlantic-Pacific moisture transport, respectively.

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