HR: 0830h
AN: PP51B-0925    [PDF]
TI: Trans-Mediterranean Paleoclimate Connections Evident From Carbon and Nitrogen Stable Isotope Patterns in Late Pliocene Sapropels
AU: * Arnaboldi, M
EM: marna@umich.edu
AF: Department of Geological Sciences, The University of Michigan, 425 East University Avenue, Ann Arbor, MI 48109-1063 United States
AU: Meyers, P A
EM: pameyers@umich.edu
AF: Department of Geological Sciences, The University of Michigan, 425 East University Avenue, Ann Arbor, MI 48109-1063 United States
AB: Variations in the Earth's orbital parameters cause fluctuations in the global climate. In particular precession is important at low latitude locations, such as the Mediterranean Sea. Here 21 kyr periodic precessional forcing drives dramatic oceanographic and environmental changes over the whole region. Precessional minima coincide with intensifications of the monsoonal system. As a result, the Mediterranean area experiences enhanced seasonality, increased precipitation, and greater fluvial discharge. Primary productivity has cyclically increased at the sea surface while dysoxic/anoxic conditions has developed at the sea floor. Such perturbations of the Mediterranean system have resulted in the deposition of sapropels, dark layers of organic-carbon-rich sediment, since the late Miocene. Sapropels represent an exceptional natural laboratory for investigating the mechanisms and dynamics of paleoclimate and paleoceanographic cycles and their local impacts over an entire basin. Our study is focused on complete and continuous sequences containing two sapropels corresponding to insolation cycles 180 (1.851 Ma) and 178 (1.829 Ma) and intervening "normal" sediment from the Vrica Plio-Pleistocene type section and ODP Sites 964, 967, 969, 974, and 975. These locations represent a spectrum of different sub-basins, distances from land, proximities to fluvial input, influences of different water masses and differences in water depths. Sapropels appear to be consistently characterized by higher del13C and generally lower del15N values, suggesting a widespread pattern of higher marine productivity with a major contribution from nitrogen fixation during their deposition. The presence of the same isotopic patterns in hydrologically separated parts of the Mediterranean suggests a strong paleoclimatic connection between the major sub-basins. Furthermore, the nitrogen isotopic evidence for a switch from algal to bacterial modes of primary production implies strong trans-Mediterranean near-surface stratification during sapropel times.
DE: 1055 Organic geochemistry
DE: 4267 Paleoceanography
DE: 4802 Anoxic environments
DE: 4805 Biogeochemical cycles (1615)
DE: 4870 Stable isotopes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting