Plio- und Pleistozäne Umwelt- und Klimabedingungen im Golf von Alaska
Zusammenfassung der Projektergebnisse
The main objectives of the PECA project targeted at the reconstruction of the environmental conditions in the Gulf of Alaska (subpolar NE Pacific) across the Plio-Pleistocene time interval using sediment samples recovered during IODP Expedition 341. The main focus was on the Mid Pleistocene Climate Transition and late Pleistocene climate shifts recorded at distal Site U1417 and proximal Site U1419, respectively. Biomarker analyses provided data on sea surface temperature, sea ice variability, and the input of terrigenous organic matter. For a comprehensive and more detailed assessment of land-ocean feedback mechanisms, a multi-proxy approach has been pursued in close cooperation with IODP 341 shipboard scientists to complement the U1417 biomarker records by micropalaeontological, sedimentological and geochemical (XRF) data. A major outcome of this approach is the identification of hitherto unconsidered iron fertilisation mechanisms that promoted Mid Pleistocene diatom productivity events in the study area. These mechanisms potentially also stimulated primary productivity in other Northern Hemisphere glacio-marine environments and could have affected the sequestration of atmospheric CO2 during the Mid Pleistocene Transition and beyond. A further finding of the PECA project is the observation of similar Mid Pleistocene sea surface temperature changes in the study area, the Northwest Pacific, and the North Atlantic, which support hypotheses of a synchronous evolution (and cooling) in Northern Hemisphere subpolar ocean areas as a prerequisite for Pleistocene continental ice-sheet growth. While the identification of the sea ice biomarker IP25 failed for U1417 sediments, trace amounts of this proxy were detected in sediments recovered at Site U1419 and, supported by C37:4 alkenone data, permitted the assessment of sea ice conditions at the South Alaskan continental slope during the past ca. 50 ka BP. Though specific research questions relating to the role of sea ice coverage for e.g. ocean-atmosphere interactions, primary productivity, or as transport agent for sediments could not be fully addressed, the PECA project provided valuable insight into the palaeoceanographic development in the subpolar Northeast Pacific in response to the evolving (and waning) Northwestern Cordilleran Ice Sheet. Over different time scales, marine productivity in the Gulf of Alaska, a classical high nutrient, low chlorophyll region, was mainly steered by the addition of bioavailable iron through different transport pathways. The iron availability, however, was significantly controlled by ice-sheet dynamics affecting the erosion and the subsequent dispersal of glacigenic silt. These processes reflect important land-ocean interactions, which are best assessed by a multiproxy approach. The testing and evaluation of specific tri-unsaturated C25 highly branched isoprenoids as potential SST proxy in subpolar environments could not be carried out with full confidence due to analytical uncertainties. Preliminary data obtained at Site U1419, however, strengthen an ocean temperature dependence in the isomerisation of these compounds, which is supported by the observation of similar trends in the UK37-based SST record and the C25 HBI triene data. The PI will pursue the further evaluation of this approach in another project.
Projektbezogene Publikationen (Auswahl)
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2015. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska. Proceedings of the National Academy of Sciences, 112, pp. 15042-15047
Gulick, S.P.S., J.M. Jaeger, A.C. Mix, H. Asahi, H. Bahlburg, C.L. Belanger, G.B.B. Berbel, L. Childress, E. Cowan, L. Drab, M. Forwick, A. Fukumura, S. Ge, S. Gupta, A. Kioka, S. Konno, L. J. LeVay, C. März, K.M. Matsuzaki, E.L. McClymont, C. Moy, J. Müller, A. Nakamura, T. Ojima, F.R. Ribeiro, K.D. Ridgway, O.E. Romero, A.L. Slagle, J.S. Stoner, G. St-Onge, I. Suto, M. D. Walczak, L.L. Worthington, I. Bailey, E. Enkelmann, R. Reece, J.M. Swartz
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(2014). Late Pleistocene biogenic sedimentation in the Gulf of Alaska: A biogeochemical perspective from IODP Expedition 341, AGU Fall Meeting 2014, San Francisco, USA
Moy, C., Addison, J., Finney, B., Bahlburg, H., Childress, L., Cowan, E., Forwick, M., Müller, J., Ribeiro, F. and Ridgway, K.
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(2016). Climate-Ocean-Ice sheet interactions across the Pliocene and Pleistocene: Preliminary Results from IODP 341 Exp (Gulf of Alaska), Geophysical Research Abstracts, EGU General Assembly 2016, Vienna, Austria
Sanchez Montes, M., McClymont, E.L., Müller, J., Cowan, E.A., Romero, O. E., Moy, C. and Lloyd, J. M.
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(2016). Evolution of sea surface temperatures and primary productivity in the Gulf of Alaska since the Last Glacial Maximum, International Conference on Paleoceanography 2016, Utrecht, Netherlands
McClymont, E.L., Müller, J., Mix, A., LeVay, L., Romero, O.
