Soledad Basin, Baja California: a Twin to Cariaco Basin for Monitoring the Eastern Tropical Pacific Today and the Past?

Soledad Basin, a semi-enclosed basin on the Pacific margin of southern Baja California at 25oN, is ideally located to document past variations of ocean/atmosphere interactions responding to the Pacific Decadal Oscillation (PDO) and the El Nino-Southern Oscillation (ENSO). This presentation focuses on the hydrography and geochemistry of the basin in the context of a potential monitoring program that could reach the scale of current activities in Cariaco Basin. Soledad Basin (sometimes referred to as Magdalena Basin or San Lazaro Basin) has been studied intermittently since the 1970's although detailed studies to exploit its paleoceanographic potential have started only recently. A very flat bottom with a maximum depth of 540 m was mapped with SeaBeam. A comparison of hydrographic profiles collected inside and outside the basin indicates a sill depth of 290 m. Bioturbation is currently inhibited within the basin primarily because of low oxygen concentration in adjacent source waters, rather than oxygen consumption within the basin as is the case for Cariaco and Santa Barbara Basins. Radiocarbon dating of planktonic foraminifera indicates a very high sedimentation rates of ~108 cm/kyr up through the end of the Bolling/Allerod 13 kyr ago (van Geen et al., Paleoceanography, v. 8, no. 4, 2003). A non-bioturbated section, characterized by sub-cm dark brown to black, coarse, mm- to cm-scale laminations rather than by mm-scale fine laminations, extends almost continuously from the top of a piston core to ~9 m depth, an interval dated at 10.0 ka. In addition, thin white mm-scale laminae composed almost entirely of coccoliths packed in faecal pellets extend to a depth of ~11 m (11.3 ka). A selection of promising results based on diffuse spectral reflectance records obtained at 1-cm resolution, planktonic Mg/Ca data, and the acccumulation of authigenic Mo will be presented.