Site 1239 (proposed Site CAR-1C) is located at 0°40.32´S, 82°4.86´W, ~120 km off the coast of Ecuador (Fig. F1). Near the eastern crest of Carnegie Ridge at 1414 m water depth, the site is situated roughly in the middle of a bench that slopes gently to the south (Fig. F2). Just to the east, Carnegie Ridge slopes downward into the Peru-Chile Trench, where subduction is consuming the volcanic seamounts produced by the Galapagos hotspot. Basement at Site 1239 likely consists of basalt formed at the Galapagos hotspot ~11-13 m.y. ago (Lonsdale and Klitgord, 1978). From the southwest, where Site 1238 is found on a sedimented ramp near 2200 m depth, the seafloor steps up a basement scarp of Carnegie Ridge to another gently sloping platform on which Site 1239 is located. Farther to the north, the basement rises again to a series of partially eroded seamounts with peaks from 500 to 1000 m below sea level. These bathymetric highs may have been above sea level early in their history as part of an archipelago similar to the modern Galapagos Islands.
The region of Site 1239 is heavily sedimented, with likely pelagic sediments of variable thickness covering rough basement topography. Seismic profiles (Fig. F3) reveal stratified reflective sediments that drape the underlying bathymetry and fill basement lows. Dominant sediments in the region are foraminifer-bearing diatom nannofossil ooze, with some intervals of diatom ooze (Kemp et al., 1995) and occasional ash layers (Ledbetter, 1985). The steep basaltic flanks of Carnegie Ridge are mostly bare rock, so some downslope transport of sediment is possible (Fig. F2).
A tectonic backtrack path on the Nazca plate (Pisias et al., 1995) moves Site 1239 about 600 km westward and slightly to the south relative to a fixed South America (and probably to shallower depths, which would account for the possible erosion features on the volcanic highs) (Fig. F2) to a position southeast of the Galapagos hotspot about 12 m.y. ago (Fig. F4).
Today, Site 1239 is situated under the eastern reaches of the equatorial cool tongue, in an open-ocean upwelling system near the equator (Fig. F5). The site is close to the equatorial front that separates cool, relatively high salinity surface waters south of the equator from the warm, low-salinity waters of Panama Basin (Strub et al., 1998). Nutrient-rich waters of the Equatorial Undercurrent (EUC) surface here and along the coast of Peru and Ecuador (Levitus et al., 1993), but nitrate and phosphate are not fully utilized by the phytoplankton in spite of high production (Fig. F6). Here, a limited supply of micronutrients such as iron, for which the EUC is a major source, may play an important role as a regulator of production (Murray et al., 1994).
Site 1239 is likely to record changes in upwelling and biological production, as well as long-term changes in upper-ocean temperature and pycnocline depth. The surface-ocean properties of the eastern equatorial Pacific are sensitive to interannual to decadal oscillations such as those of the well-known El Niņo Southern Oscillations (ENSO) (Cane, 1986) as well as during the Pleistocene ice ages (Pisias and Mix, 1997; Mix et al., 1999; Lea et al., 2000; Beaufort et al., 2001).
Plate tectonic backtrack locations can be used to predict general features of oceanographic change at Site 1239, under the assumptions that overall conditions in the region remain constant and that the only change in the system is drift of the site location relative to this fixed oceanographic background (Fig. F7). In this analysis we ignore changes in the position of the continental margin through time, which may be significant in the region of northern South America and the Central American Isthmus. Sampling of modern oceanographic atlas values at the paleosite locations suggests that from 3 to 4 Ma, sea-surface temperatures at Site 1238 may have been slightly (~1°C) cooler than today. At greater ages, the site was within the core of the South Equatorial Current (SEC), where temperatures are roughly constant along the backtrack path. Salinities increase slightly at greater ages, as the site backtracks gradually away from the equator and the eastern boundary. Pycnocline depth is stable along the backtrack path, at values of 20 m. Sea-surface nutrient concentrations of silicate, phosphate, and nitrate all increase significantly from 2 to 4 Ma, likely because utilization of nutrients is greater in the equatorial band, where the EUC surfaces and supplies micronutrients such as iron. Nutrients are relatively stable on the Site 1239 backtrack path prior to 4 Ma. In contrast to nutrients, primary productivity is predicted to be highest from 4 to 6 Ma, when the site was under the modern edge of the SEC. Productivity declines gradually at greater ages as the site backtracks away from the eastern margin. In the absence of other regional changes in ocean circulation or tectonics, we would expect that biogenic sediment accumulation rates at Site 1239 would be relatively high from 4 to 6 Ma, when the site was under the modern zone of highest production, but that terrigenous sediment accumulation rates associated with continental runoff would be higher at younger ages, when the site was located closer to both the eastern boundary and the equator, although eolian sediment components may be more prevalent at greater ages, when Site 1239 backtracks across the northern edge of the Atacama dust plume (Molina-Cruz, 1977). Significant deviations from these general trends, if detected in the sediment cores, would imply changes in regional oceanographic or climatic conditions, or errors in the tectonic backtrack model.
The modern water depth of Site 1239 is within the range of Pacific Central Water (PCW) south of Carnegie Ridge, but shallow enough that some mixing with remnants of Antarctic Intermediate Water (AAIW) can be detected here, especially by its relatively low salinities (Tsuchiya and Talley, 1998). AAIW is not easily detected with water column oxygen data because of the high rates of biological productivity in the region and the accompanying organic rain that consumes oxygen in the upper water column (Fig. F8). However, the comparison between a benthic foraminiferal 
13C record from the top of the Carnegie Ridge (~1400 m) with records from deeper water depths (~3100 m) indicates a stronger glacial difference in nutrient concentrations than during interglacials, suggesting some change in ventilation of shallow subsurface water masses at least for the last 400 k.y. (Mix et al., 1991). North Pacific Intermediate Waters are limited to the Northern Hemisphere and are not detected in the modern water column at Site 1239.
The primary objectives at Site 1239 were to provide a continuous sedimentary sequence of Neogene age (as old as 11-12 Ma) to
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