Enhanced productivity on the Iberian margin during glacial/interglacial transitions revealed by barium and diatoms

Thomson, J., Nixon, S., Summerhayes, C.P., Rohling, E.J., Schonfeld, J., Zahn, R., Grootes, P., Abrantes, F., Gaspar, L. and Vaqueiro, S. (2000) Enhanced productivity on the Iberian margin during glacial/interglacial transitions revealed by barium and diatoms. Journal of the Geological Society, 157 (3), 667-677.

Abstract

The Portuguese margin is at a critical location for studies of the ocean's behaviour during glacial/interglacial climatic changes, and the rapid accumulation rates of the sediments enable high-resolution palaeoclimatic investigation. The sedimentary record of the past 350 ka has been investigated in a 35 m long core from 3.5 km water depth on the slope at 40°N by geochemical, isotopic and micropalaeontological techniques. The CaCO3 content of this core as a function of time contains significant Milankovitch orbital frequencies of 18.8, 23.7, 38.0 and 100.6 ka, but these are driven primarily by dilution by clay-flux variations rather than by CaCO3 productivity variations. The largest signals in the productivity indicators Corg, Ba/Al and diatom abundance are all observed as simultaneous peaks at the oxygen isotope stage boundaries 10/9 and 6/5, with the signal magnitude in the order 10/9>6/5 for all three indicators. Smaller coincident signals in Corg, Ba/Al but not diatoms are also observed at the oxygen isotope stage 2/1 boundary. Other less prominent peaks in the Corg and Ba/Al profiles occur elsewhere, including Heinrich Event horizons, but these are not always simultaneous and none contain evidence of the dissolution-prone diatom microfossils. The 10/9, 6/5 and 2/1 oxygen isotope stage transitions represent the three most extreme glacial/interglacial sea level rises in the past 350 ky, possibly in the same sequence of magnitude, when sea level rose rapidly by 120+m from glacial low stands to interglacial high stands. The productivity signals at these transitions are contained within <5 ka (including bioturbation).

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Contributors

Author: E.J. Rohling

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