Reconstructing hypoxia of the southeastern Gulf of California over the last 18,000 years: sediments of Pescadero Basin

Abstract:

We present the first high-resolution multiproxy reconstruction of the past 18,000 years of oceanic redox variability in the southeastern Gulf of California (GC) and eastern Pacific. The variation in oxygen content prove to be a crucial regulator responsible for changes in biota distribution, water chemistry, physicochemical transformations of dissolved and particulate phases for trace elements in the water column, and formation of authigenic minerals, among other effects. The gravity core DIPAL-III T2 collected aboard the R/V “El Puma” (UNAM) from Pescadero Basin, located within the oxygen minimum zone (OMZ) of the southern GC, was thoroughly studied in terms of C, S, trace element and Fe speciation. After establishing the age-model of the marine sediments, the produced data revealed two clear episodes of peleoceanographic variability, associated with changes in hypoxia. The first period (18.0 - 11.6 cal kyr BP), represented by massive sediments, points to a time with an oxygenated water column and moderate productivity, elucidated by low C_org, high S and a relatively low redox sensitive trace element content (Mo and U). The second (11.6 cal kyr BP - present), easily perceived by a clear lamination pattern, indicates a suboxic/anoxic episode, evidenced by higher C_org, Mo and U, among others. A clear dramatic shift is distinctly observable between these periods for most of the redox-proxies. This shift is related to the changes in sea-level that immediately followed the Last Glacial Maximum, when the ice sheets began to melt. This transitioned Pescadero hydrochemistry from a shallow well-ventilated basin (prior to 11.6 cal kyr BP) to a deep OMZ system. When compared to renowned marine sedimentary records, such as Cariaco and Guaymas basins, some events became more eminent than others. In the particular case of the Younger Dryas (YD) stadial and Bolling Allerod (BA) interstadial, the C_org, S and some trace element patterns were similar among basins even from different climatic and oceanographic settings. The latter provides evidence that the mentioned paleoceanographic events had a wider influence than previously reported.