Late Pleistocene palaeoproductivity patterns during the last climatic cycle in the Guyana Basin as revealed by calcareous nannoplankton G.-E. López-Otálvaro1, J. A. Flores1, F. J. Sierro1, I. Cacho2, J.-O. Grimalt3, E. Michel4, E. Cortijo4, and L. Labeyrie4 1Dept. of Geology, Univ. of Salamanca, Plaza de la Merced s/n, 37008 Salamanca, Spain 2Dept. of Stratigraphy, Palaeontology and Marine Geosciences, Univ. of Barcelona, Martí i Franquès, 08028 Barcelona, Spain 3Dept. of Environmental Chemistry, Institute of Chemical and Environmental Research (IIQAB-CSIC), Jordi Girona 18, 08034 Barcelona, Spain 4Laboratoire des Sciences du Climat et de l'Environnement, IPSL, Laboratoire Mixte, CEA-CNRS-UVSQ, Parc du CNRS, 91198 Gif-sur-Yvette Cedex, France
Received: 06 Feb 2008 – Published in eEarth Discuss.: 17 Mar 2008 – Published: 02 Apr 2009
Abstract. Variations in the assemblage and abundance of coccoliths reveal changes in
oceanic and atmospheric dynamics in the Guyana Basin over the last climatic
cycle, mainly linked to latitudinal variations in the ITCZ (Intertropical
Convergence Zone). Records of the N ratio (a palaeoproductivity index of
coccolithophores) allowed us to monitor nutri-thermocline fluctuations.
Nannofossil accumulation rates (NAR) vary closely with the N ratio,
indicating a strong correlation between these two palaeoproductivity proxies.
Decreases in the N ratio and NAR values suggest lower palaeoproductivity
during glacial substages, indicating a deep nutri-thermocline (deep
stratification of the mixed layer) as a consequence of the piling up of warm
water dragged by the NEC. This setting was favoured by the southern shift of
the ITCZ and Trade winds which blew perpendicular to the Guyana coast. By
contrast, increases in the N ratio and NAR values revealed higher
palaeoproductivity during interglacial substages, suggesting a shoaling of
the nutri-thermocline. This scenario is favoured by a northward displacement
of the ITCZ with the southeast Trade winds blowing alongshore. Additionally,
palaeoproductivity changes during substages of Marine Isotope Stage (MIS) 6-5
are of much higher amplitude than those recorded in substages of MIS 4-2 and
the early Holocene. Similarities between the palaeoproductivity and the
65° N summer insolation records, suggest a link between the depth
of nutri-thermocline, the latitudinal migration of the ITCZ and ice-sheet
changes in the Northern Hemisphere.
Citation: López-Otálvaro, G.-E., Flores, J. A., Sierro, F. J., Cacho, I., Grimalt, J.-O., Michel, E., Cortijo, E., and Labeyrie, L.: Late Pleistocene palaeoproductivity patterns during the last climatic cycle in the Guyana Basin as revealed by calcareous nannoplankton, eEarth, 4, 1-13, doi:10.5194/ee-4-1-2009, 2009.