Search

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2008.11.010 Byline: M.A. Goni (a), H. Aceves (b), B. Benitez-Nelson (b), E. Tappa (b), R. Thunell (b), D.E. Black (c), F. Muller-Karger (d), Y. Astor (e), R. Varela (e) Keywords: Cariaco basin; Productivity; Biogeochemical fluxes; Holocene climate; Sediment traps; Sediment records; Organic matter Abstract: Materials collected by sediment traps over a 3-y period and sedimentary horizons from a gravity core covering the last 6000y were used to investigate the effects of climate-related processes such as wind-driven upwelling and regional rainfall on the production, export and burial of particulate organic matter in the Cariaco Basin. A variety of chemical analyses, including organic carbon and nitrogen, biogenic opal, calcite, lithogenic contents, stable carbon isotopic ratios of organic matter and the yields of CuO reaction products derived from distinct biochemicals such as amino acids, fatty acids and lignins, were carried out for this purpose. Principal component analyses were used to investigate the trends in this multivariate data set. These analyses reveal marked temporal differences in the composition of the materials sinking through the water column, which were related to distinct oceanographic and climatic forcings. For example, autochthonous fluxes, characterized by elevated contents of organic carbon and opal as well as high yields of amino acid and fatty acid reaction products, displayed peaks during periods of intense wind-driven upwelling. In contrast, allochthonous materials, characterized by elevated lithogenic contents and elevated yields of lignin-derived products, were more important during periods of high rainfall, low wind and enhanced stratification. In addition to the strong seasonal contrasts, there was significant temporal variability at both shorter (monthly) and longer (inter-annual) time scales. Hence, other factors, such as zooplankton grazing and El NiA[+ or -]o effects on local climatology, may also be important. Examination of the gravity core record yielded several significant trends. For example, there was a marked increase in sediment accumulation rates from 5000 to ca. 700y before present with concomitant increases in the concentrations of organic carbon, opal and most biomarkers. These results suggest that the Cariaco Basin experienced a marked increase in primary productivity and particle flux to the underlying sediments since the Holocene Thermal Maximum. Also within the sedimentary record, we observed distinct variations in the relative contributions of autochthonous and allochthonous organic matter. The frequency of these variations is roughly 1500y and appears to match ice-rafted debris records from the North Atlantic. Such coincidence indicates cold periods within the Holocene, which are related to minima in insolation, may have led to the southern migration of the inter-tropical convergence zone and the enhancement of wind-driven upwelling, primary productivity and autochthonous organic matter flux to the seabed in the Cariaco Basin. Alternatively, during warm periods, the opposite climatic conditions would have increased both the thermal stratification of the water column and average rainfall in the Cariaco Basin, leading to elevated inputs of allochthonous materials. Author Affiliation: (a) College of Oceanic & Atmospheric Sciences, Oregon State University, 104 Ocean Administration Building, COAS, Corvallis, OR 97331, USA (b) Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, USA (c) School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, USA (d) The School for Marine Science and Technology, University of Massachusetts Dartmouth, New Bedford, MA 02744-1221, USA (e) Estacion de Investigaciones Marinas de Margarita, Fundacion La Salle de Ciencias Naturales, Aptdo. 144, Porlamar 6301, Venezuela Article History: Received 12 June 2008; Revised 10 November 2008; Accepted 21 November 2008