Intermediate water circulation changes in the western equatorial Atlantic over the past 20,000 years
Oceanography
Final Report Abstract
The DFG project focused on the reconstruction of natural deglacial climate variability at intermediate water depths in the western equatorial Atlantic. The main tools used for paleoceanographic reconstructions were the stable carbon/oxygen isotope, bulk sedimentary 231Pa/230Th as well as the concentrations of redox-sensitive metals. Important results of the DFG project include (1) the reconstruction of changes in the meridional gradients in δ13C that occurred over the past 20 000 years in the mid-depth western Atlantic, (2) the observation that a greater amount of respired carbon must have been stored in the mid-depth Atlantic during Heinrich Stadial 1 (HS1: ~17.5 to 14.7 ka BP) and the Younger Dryas (YD: ~12.8 to 11.7 ka BP) and (3) the description of the dominant role of ocean circulation over the negative carbon excursions that occurred throughout much of the mid-depth Atlantic (~1000 - 3000m) during HS1 and YD in which a reduced ventilation due to Atlantic meridional overturning circulation (AMOC) slowdown markedly increased the residence time of Northern Component Water during HS1 and the YD, favoring the accumulation of 13C-depleted respired carbon in the Atlantic interior. Accordingly, the multiproxy approach of the DFG project revealed that the negative δ13C excursions in the western Atlantic mid-depths during HS1 and the YD originate from a weaker AMOC, which partly reduced ventilation by NCW. As NCW aged it became increasingly enriched in nutrients and depleted in oxygen, resulting in a highnutrient, low-oxygen water mass. A reduced ventilation rate of NCW during HS1 and the YD therefore caused the Atlantic mid-depth to more effectively trap respired carbon within its interior. We proposed in the DFG proposal to use neodymium isotope ratios (143Nd/144Nd, expressed in ƐNd notation as a powerful palaeoceanographic water-mass tracer. Due to absence of fish teeth and debris in the sediment samples we used planktonic foraminifera, as a reliable archive of the mid-depth Nd isotope composition, yielding information on the strength of the export of NCW (SCW) from the North Atlantic (South Atlantic) over the past 20,000 years (in co-operation with Prof. Dr. Katharina Pahnke-May). However, a test series of sediment samples (i.e. GeoB16206-1) show very low, unradiogenic ƐNd values in comparison to the seawater which indicates that the foraminifera shells have already been overprinted in the sediment by local lithogenic signals. We therfore decided for reconstructing changes in the AMOC strength to investigate in concentrations of sedimentary 231Pa/230Th (in co-operation with Prof. Dr. Jörg Lippold).
Publications
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(2015). Holocene shifts of the Southern Westerlies across the South Atlantic. Paleoceanography 30, 39-51
Voigt, I., Chiessi, C.M., Prange, M., Mulitza, S., Groeneveld, J., Varma, V., Henrich, R.
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(2015): Response of the Tropical Atlantic Ocean-Atmosphere System to Deglacial Changes in Atlantic Meridional Overturning , Nova Acta Leopoldina NF, 121 (408), pp. 167-169
Mulitza, S., Chiessi, C. M., Lippold, J., Lynch-Stieglitz, J., Mackensen, A., Paul, A., Prange, M., Ramos, R. P., Cruz, A.P.S., Schefuss, E., Schwenk, T., Schulz, Michael, Tiedemann, R., Voigt, I., Werner, M., and Zhang, Y.
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(2016). Holocene changes in Antarctic Intermediate Water flow strength in the Southwest Atlantic. Palaeogeography, Palaeoclimatology, Palaeoecology 463, 60-67
Voigt, I., Chiessi, C.M., Piola, A.R., Henrich, R.
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(2017). Deglacial changes in the strength of deep southern component water and sediment supply at the Argentine continental margin. Paleoceanography 32 (8), 796-812
Warratz, G., Henrich, R., Voigt, I., Chiessi, C.M., Kuhn, G., Lantzsch, H.
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(2017). δ13C decreases in the upper western South Atlantic during Heinrich Stadials 3 and 2. Clim. Past, 13, 345-358
Campos, M. C., Chiessi, C.M., Voigt, I., Piola, A. R., Kuhnert, H., and Mulitza, S.
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(2017): Variability in mid-depth ventilation of the western Atlantic Ocean during the last deglaciation. Paleoceanography, 32(9), 948-965
Voigt, I, Cruz, A. P. S., Mulitza S., Chiessi, C. M., Mackensen, A., Lippold, J., Antz, B., Zabel, M., Zhang Y., Barbosa, C. F., Tisserand, A. A.
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(2018). Intermittent development of forest corridors in northeastern Brazil during the last deglaciation: Climatic and ecologic evidence. Quaternary Science Reviews, Volume 192, 86-96
Bouimetarhana, I., Chiessi, C.M., González-Arango, C., Dupont, L., Voigt, I., Prange, M. und Zonnevelda, K.
