The missing link to understand Plio-Pleistocene changes in southeast Pacific oceanography, productivity, and El Nino behavior - SE trade wind strength and its dust transport
Zusammenfassung der Projektergebnisse
The aim of this projecl was to reconstruct changes in tropical and subtropical S-American climate and southeast trade wind intensity at selected lime intervals of the last 5 Ma that were characterized by marked reorganizations in global climate and oceanography. We analysed ca. 2200 sediment samples from lODP Sites 1237 and 1239 and applied X-ray Fluorescence core scanning to determine a variety of different paleoclimate and paleoceanographic proxies including element concentrations, benthic and planktic oxygen isotopes, foraminiferal assemblages, biogenic opal concentrations, alkenone sea surface temperatures, grain sizes and organic biomarkers. In addition, a set of 170 surface samples covering mosl parts of the subtropical-tropical eastern Pacific was used to reconstruct the modern cross-equatorial distribution pattern of foraminiferal assemblages as well as spatial distribution patterns of clay mineral assemblages and siliciclastic grain-sizes. Major results from surface sediment samples are: (1.) The ratio between Globorotalia menardii cultrata and Neogloboquadrina dutertrei abundance in combination with the δ18O difference between G. ruber and G. tumida or between P. obliquiloculata and G. tumida are the most suitable tools for reconstructing changes in the latitudinal position of the Equatorial Front and changes in the thermal stratification of the upper water column in the eastern tropical Pacific. (2.) Siliciclastic grain-size distributions alone are insufficient to identify the eolian signal in marine sediments due to authigenic particle formation on the sub-oceanic ridges and abundant volcanic glass around the Galapagos Islands. Together with the clay-mineral compositions of the clay fraction, we have identified the dust lobe extending from the coasts of Pern and Chile onto Galapagos Rise as well as across the equator into the doldrums. Illite is a very useful parameter to identify source areas of dust in this smectite dominated study area. Major results from lODP sediment records 1237 and 1239 are: (1.) The input of terrigenous material over the past 5 million years is nicely reflected by the iron accumulation rates (Fe AR). However the evolution of the Fe AR is different at both sites. Site 1237 is marked by a long-term increase in Fe AR and a coarsening in siliciclastic modal grain sizes since 3.3 Ma. We interpret this to reflect a combination of aridification within the Atacama region and intensification in SE trade wind strength. (2.) At Site 1239, the siliciclastic sediment accumulation is dominated by fiuvial sediment supply from the paleo-Guayaquil river. An outstanding feature is the pronounced Fe-AR maximum from 4.2 Ma to 2.5 Ma. We ascribe the long-term increase in Fe AR from 4.2 to 3.0 Ma to a major uplift phase of the northern Andes, which led to enhanced river runoff from the Andes thereby increasing the fluvial sediment supply lo site 1239. The long-term decrease in Fe AR from 3.0 to 2.5 Ma has been related to a decrease in precipitation, which was triggered by the cooling of the cold tongue region. (3.) Our multiproxy reconstruction of riverine runoff at site 1239 indicates that interglacial periods experienced more humid conditions than the glacial periods. The north-south SST gradient is systematically steeper during glacial times, suggesting a mean background climatic state with a vigorous oceanic cold tongue during the last 0.5 Ma, resembling modern La Nina conditions. This enhanced north-south SST gradient would also imply a glacial northward shift of the Intertropical Convergence Zone at least in vicinity of the cold tongue: a pattern that has not yet been reproduced in climate models. (4). While findings from site 1239 (equatorial East Pacific) reveal enhanced fluvial input from northwestern South America during wetter interglacials, our results from site 1237 suggest increased eolian-derived terrigenous supply during drier glacials from the arid areas south of 3°S. Although the glacial dust fluxes are twice as high as during interglacials at Site 1237, grain-size characteristics do not vary on glacial-interglacial time scales, but remain rather constant, indicating no distinct changes in mean wind speed or direction.
Projektbezogene Publikationen (Auswahl)
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(2008). Eolian transport to the SE Pacific inferred from siliciclastic grain size variability, EGU General Assembly 13., 18.04.2008, Vienna
Saukel, C. , Stuut, J. B. , Rincon, D. , Lamy, F. and Tiedemann, R.
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(2009). Are Glacials (Interglacial) in the Easternmost Pacific Ocean Drier (Wetter) during the Last 300 000 Years? Goldschmidt Conference 2009, Davos
Rincon Martinez, D., Contreras, S., Lamy, F. and R. Tiedemann
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(2009). Plio-Pleistocene Changes in SE Trade Wind Strength and South American Rainfall - Implications for ITCZ Movements and Long-Term El Nino Behavior Goldschmidt Conference 2009, Davos
Lamy, F., Rincon-Martinez, D., Saukel, C , Steph, S., Sturm, A., Etourneau, J. and R. Tiedemann
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(2009). Pliocene changes in trade wind intensity in the SE Pacific inferred from grain-size variability. Workshop on Pliocene Climate Change. Workshop on Pliocene Climate, Bordeaux (France), 23-25 October 2009
Saukel, C , Stuut, J. B., Rincon Martinez, D., Lamy, F. and R. Tiedemann
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(2009). Reconstruction of changes in trade wind strength in the SE Pacific since the Pliocene - results from ODP site 1237, Department of Earth Sciences, University of Bristol
Saukel, C.
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(2009). The History of ENSO and ITCZ Variability, from the Holocene to the Pliocene Goldschmidt Conference 2009, Davos
Tiedemann, R. and G. Haug
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(2009). Tropical Pacific climate change during the Pliocene - causes and consequences. Workshop on Pliocene Climate, Bordeaux (France), 23-25 October 2009
Tiedemann R., Lamy, F., Rincon-Martinez, D., Steph, S., Saukel, Groeneveld, J. and J. Etourneau
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(2010) A rainy northern Atacama Desert during the last interglacial, Geophysical Research Letters
Contreras, S. S. Pantoja, C.B. Lange, G. Lavik, D. Rincón-Martinez and M.M.M. Kuypers
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(2010). Early Pliocene increase in thermohaline overturning preconditioned the development of the modem equatorial Pacific cold tonguge. Paleoceanography
Steph, S., Tiedemann, R., Prange, M., Groeneveld, J., Schulz, M., Timmermann, A., Nürnberg, D., Saukel, C. and G.H. Haug
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(2010). More humid interglacials in Ecuador during the past 500 kyr linked to latitudinal shifts of the Equatorial Front and the Intertropical Convergence Zone in the eastem tropical Pacific. Paleoceanography, 25, PA2210
Rincón-Martinez, D., Lamy, P., Contreras, S., Leduc, G., Bard, E., Saukel, C., Blanz, T., Mackensen, A. and Tiedemann, R.
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(2011). Distribution and provenance of windblown SE Pacific surface sediments. Marine Geology, 280 (1-4), 130-142
Saukel, C , Lamy, F., Stuut, J. B. W., Tiedemann, R. and C. Vogt
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(2011). Tracking the equatorial front in the eastem equatorial Pacific Ocean by the isotopic and faunal composition of planktonic foraminifera. Marine Micropaieontology, 79 (1), 24-40
Rincón-Martinez, D., Steph, S., Lamy, F., Mix, A. and R. Tiedemann
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2011. Tropical Southeast Pacific Continent-Ocean-Atmosphere Linkages Since the Pliocene Inferred from Eolian Dust. Dissertation, University Bremen
Saukel, C.
