PP31B-2246
Changes in productivity and redox conditions during the Last Glacial Maximum as recorded in high-resolution geochemical records from Alfonso Basin, Gulf of California
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Konstantin Choumiline, University of California Riverside, Department of Earth Sciences, Riverside, CA, United States, Timothy W Lyons, University of California, Department of Earth Sciences, Riverside, CA, United States, Jose D. Carriquiry, Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanologicas, Ensenada, Mexico, Ligia L Perez-Cruz, Universidad Nacional Autónoma de Mexico, Instituto de Geofísica, Mexico D.F., Mexico and Luc Beaufort, Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement, Aix-en-Provence, France
Abstract:
The Last Glacial Maximum represents the most recent major sea level low stand in Earth history. Such changes in eustatic sea level impacted the oxygenation of marine basins, yet the characteristics and mechanisms of those impacts remain poorly known. Specific basin conditions are needed to develop, record, and preserve those paleoredox changes through time most effectively, including rapid sedimentation rates and silled basin morphologies. The anoxic Alfonso Basin, partially separated from the Gulf of California by a bathymetric sill, is such a place. The basin is located in a dry semiarid region dominated by dust inputs and only occasional tropical cyclone-induced fluvial contributions. We present the first multi-proxy reconstruction of southern Gulf of California paleoredox that covers an uninterrupted timespan from the Late Pleistocene to the present, with an emphasis on the Last Glacial Maximum. In this research we contrast geochemical data from a 47-meter-long sediment core (collected with the giant CALYPSO corer aboard the R/V Marion Dufresne) with the solid phase and pore water chemical data from a shorter but very detailed box core (collected on the R/V El Puma), both from Alfonso Basin. Our results show that during the Late Pleistocene and throughout the Holocene several paleoredox shifts occurred, often accompanied by differences in lamination (laminated/massive alternations) and trace element (Mo, V, U) compositions; detailed Fe chemistry (FeHR/FeTand Fe/Al ratios); as well as carbon and sulfur concentrations and isotope ratios. For example, FeHR/FeT ratios indicate values of roughly 0.15 during the Last Glacial Maximum (lower than theoretic threshold of 0.2 between oxic and anoxic), suggesting more oxic conditions, in comparison to 0.25 and higher in the Holocene. Most of the variability seen in these proxies is related to global sea level change, while some variability is instead related to local variations in paleoproductivity, often connected to varying aeolian supply of micronutrients through mineral dust. Our results also provide insights into microbially mediated diagenetic processes in Alfonso Basin and related impacts on paleoenvironmental proxies revealed by dissolved Fe and Mn in pore waters, as well as labile (oxyhydroxide) Fe fractions in the solid phase, among other indicators.
