Search

Abstract: Short-lived radionuclides (210Pb and 137Cs) were used to document sedimentation regime changes over the last ∼100 years, from analysis of a single sedimentary sequence collected in the coastal zone of the Gulf of Tehuantepec, South Pacific of Mexico. Sedimentation rates found in the core Tehua II-21 varied from 0.03 to 0.21cmyr−1, whereas mass accumulation rates ranged from 0.05 to 0.29gcm−2 yr−1. 137Cs data validate results obtained from 210Pb measurements and confirm significant changes in the sedimentation regime between 1950 and 1970. We associate these alterations to land use changes, including deforestation for agriculture development and industrialization, as well as the regimentation of the Tehuantepec River from the early 1960s to the late 1970s. This interval has been marked by a major demographic expansion that followed the industrial development of the area. [Copyright &y& Elsevier]

Abstract: Three marine sediment cores from the Gulf of Tehuantepec (Eastern Tropical North Pacific) were used to determine variations in upwelling intensity and surface circulation patterns over the last 26kyrBP. Changes in foraminiferal assemblages at glacial-interglacial timescale indicate a sequence of three major palaeoceanographic events in the study area: (1) The Late Pleistocene (including the Last Glacial Maximum, LGM), dominated by a Neogloboquadrina dutertrei–Globorotalia menardii assemblage, indicative of a stable thermocline, stratified water column and greater persistence of warm equatorial waters in the region. (2) The Termination 1, dominated by a Globigerinita glutinata assemblage, which indicates mixed surface water and transitional conditions between upwelling and stratified water column episodes. Changes in sedimentation rates and a clear reduction of the faunal abundances at this time, could be the result of eustatic sea level change. (3) The Holocene, dominated by a Globigerina bulloides–Globigerinoides ruber assemblage, indicates periods of elevated productivity, intense upwelling and the establishment of the modern ocean conditions. These findings are consistent with climate model results that suggest that regional surface ocean and upwelling conditions are mostly linked to changes in atmospheric circulation over the Laurentide Ice Sheet and shifts in the latitudinal position of the Intertropical Convergence Zone. [Copyright &y& Elsevier]