Variability of the Mediterranean Outflow on glacial-interglacial and millennial time scales
Final Report Abstract
This study focuses on a reconstruction of the late Quaternary hydrographic variability of the flow path of the Mediterranean Outflow Water (MOW) and the changing weathering contributions of the detrital clay-size fraction to the SW Iberian shelf. MOW spreads at water depths between 500 and 1500 m from the Strait of Gibraltar into the eastern North Atlantic and has been a source of salinity for the Atlantic Meridional Overturning Circulation in the North Atlantic. In order to evaluate the hydrographic changes of MOW since the Last Glacial Maximum (LGM) highresolution Nd and Pb isotope records of past ambient seawater obtained from authigenic ferromanganese oxyhydroxide coatings of bulk marine sediments from three gravity cores in the Gulf of Cadiz (577 m water depth) and along the Portuguese margin (1745 m and 1974 m water depth) were produced. The surface and downcore Nd isotope data from all water depths exhibit only a very small variability close to the present day composition of MOW but do not reflect the present day Nd isotopic stratification of the water column as determined from a nearby open ocean hydrographic station due to downslope sediment redistribution processes. In contrast, the Pb isotope records show significant and systematic variations, which provide evidence for a pattern of the MOW pathways between 20,000 and 12,000 years ago significantly different from subsequent periods of time. The assemblages of marine sediments on the SW Iberian shelf consist of the various regional particulate sources that comprise North African dust, river transported particles from the Iberian Peninsula and suspended particulate matter (SPM) carried by MOW. In order to reconstruct climate and circulation driven changes in the supply of sediments from these sources over the past ~23000 years, radiogenic Nd, Sr and Pb isotope records of the clay-size sediment fraction of the same core locations as above were produced. Clay mineral abundances and clay mineral ratios from the same set of samples were obtained. Contrary to expectations, the transition from the LGM to the Holocene was not marked by very strong environmental changes but Heinrich stadial 1 and the African Humid Period (AHP; ~5500-12000 B.P.) are reflected by significantly different isotopic records. The mineralogical time series vary significantly out-of-phase to the isotope records. This suggests that due to the sensitivity of secondary clay formation to climate conditions, the clay mineral assemblages allow insights into the prevailing chemical weathering regime over time in addition to information about changes in detrital source areas.
Publications
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2009. Late Quaternary variability of Mediterranean Outflow Water based on neodymium and lead isotopes. Cioppino Workshop 2009, Urbino, Italy
Stumpf, R., Frank, M., Haley, B. A. und Schönfeld, J.
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2009. Late Quaternary variability of Mediterranean Outflow Water based on neodymium and lead isotopes. Goldschmidt Conference 2009, Davos, Switzerland
Stumpf, R., Frank, M., Haley, B. A. und Schönfeld, J.
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2009. Radiogenic isotopes in the Mediterranean Outflow Water (MOW): Late Quaternary to Holocene variability of neodymium and lead. 4th MedCLIVAR Workshop 2009, Sesimbra, Portugal
Stumpf, R., Frank, M., Haley, B. A. und Schönfeld, J.
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2010. A reconstruction of late Quaternary Mediterranean Outflow Water from radiogenic Nd, Sr and Pb isotopes. 10th International Conference on Paleoceanography, La Jolla, Kalifornien, USA
Stumpf, R., Frank, M., Schönfeld, J. und Haley, B. A.
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2010. Late Quaternary Mediterranean Outflow Water: implications from radiogenic Nd, Sr, Pb isotopes and clay minerals. AGU Fall Meeting 2010, San Francisco, California, USA
Stumpf, R., Frank, M. und Haley, B. A.
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2010. Late Quaternary variability of Mediterranean Outflow Water from radiogenic Nd and Pb isotopes. Quaternary Science Reviews 29 (19/20), 2462-2472
Stumpf, R., Frank, M., Schönfeld, J., and Haley, B.A.
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2011. Climatically driven changes in sediment supply on the SW Iberian shelf since the Last Glacial Maximum. Earth and Planetary Science Letters
Stumpf, R., Frank, M., Schönfeld, J., and Haley, B.A.
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2011. Climatically driven changes in sediment supply on the SW Iberian shelf since the Last Glacial Maximum. Goldschmidt Conference 2011, Prag, Tschechische Republik
Stumpf, R., Frank, M., Schönfeld, J. und Haley, B. A.
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2011. Late Quaternary variability of hydrography and weathering inputs on the SW Iberian shelf from clay minerals and the radiogenic isotopes of neodymium, strontium and lead. Dissertation, Christian-Albrechts-Universität, Kiel, Germany, 122 pp.
Stumpf, R.
