Geochemistry, fluxes and nitrogen isotopic composition data of traps LP1 and EBC2-1 and cores GeoB4242-4 and Geo4301-1

We compare total and biogenic particle fluxes and stable nitrogen isotope ratios (d15N) at three mooring sites along a productivity gradient in the Canary Islands region with surface sediment accumulation rates and sedimentary d15N. Higher particle fluxes and sediment accumulation rates, and lower d15N were observed in the upwelling influenced eastern boundary region (EBC) compared to the oligotrophic sites north of Gran Canaria [European Station for Time-Series in the Ocean, Canary Islands (ESTOC]] and north of La Palma (LP). The impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi-year flux record at the ESTOC. Remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0.8% and total nitrogen preservation of about 0.4% of the estimated export production. Higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50% of the particulate matter at the ESTOC was derived from allochthonous sources. Low d15N values in the lower traps of the ESTOC and LP point to a source region influenced by coastal upwelling. We conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources. This could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions.

Geochemistry of DSDP Hole 91-596

Geochemical analyses of sediments from the top 24.5 m of Deep Sea Drilling Project hole 596 (23°51.20'S, 169°39.27'W) show great variability in the composition of pelagic clays accumulated in the South Pacific since the late Cretaceous. Elemental associations indicate that most of this variability can be attributed to variations in abundances of six sediment end-member components: detrital (eolian), andesitic (volcanic), hydrothermal, hydrogenous, phosphate (fish debris), and biogenic silica. We develop a sedimentation model which is used to infer processes that might have influenced the accumulation rates of these components over the last 85 million years. The accumulation of eolian detritus in the South Pacific shows some similarities to that observed in the North Pacific and has been largely controlled by global climate trends in the Cenozoic. Much of the variation in the accumulation of other sediment components likely reflects the paleoceanographic evolution of the South Pacific. The most notable change in the sedimentary environment occurred at about the Paleogene/Neogene boundary. At that time, significant changes in the color, mineralogy, and chemistry of the sediment probably reflect major shifts in climate mode as well as oceanic circulation in the central South Pacific region.

Eolian accumulation rates of ODP Leg 121 holes

The late Cenozoic history of eolian sedimentation in the eastern Indian Ocean was developed from samples recovered during drilling of Sites 752, 754, and 756. Temporal changes in the mass accumulation rate of eolian material reflect major climatic shifts in the southern African source region. A significant drop in dust mass flux values occurs near the end of the lower Oligocene. Younger sediments are characterized by a gradual reduction in dust accumulation rates until the middle Miocene after which values remain consistently low throughout the late Cenozoic, although a slight increase in eolian accumulation rate occurs near 2.5 Ma. This pattern of dust mass flux appears related to the supply of dust-sized particles in the source region and represents a shift in the climatic regime of southern Africa to increasingly more arid conditions throughout the late Cenozoic.