Publication Date:
2023-06-27
Description:
Planktic foraminifera data from three cores of the Angola-Zaire margin are used to reconstruct palaeopositions of the Angola-Benguela Front (ABF) between the warm Angola Current and cold Benguela Current for the last 180,000 years. Strong northward shifts occurred in stages 4 and 3.3-3.1, but not in stages 6 and 2. The Benguela Current did not penetrate into the Gulf of Guinea. The southernmost positions, not far from the present one, were occupied in stages 5.5 and 1, but also in stage 6.3. The record of the shifts contains significant variance in the 23 ky**-1 orbital frequency band and there are indications for a strong 100-ky**-1 frequency component. There is also much variance at 15 ky1, the sum frequency of the 23-ky**-l and the absent 41-ky**-1 cycles. This cyclicity is a real feature in the records.
The Benguela Current system performs a combination of two types of precessional (23 ky**-1) movements: shifts of the ABF to the south and north precede swings between more zonal and more meridional directions respectively of the Benguela Oceanic Current by 6.6 ky. The extreme positions of the ABF may be described by the 100-ky**-1 eccentricity component which is also documented in cores from Walvis Ridge and Cape Basin. Both the 23-ky and 100-ky shifts of the ABF are in phase with the meridional movements of the Subtropical Convergence zone (STC) in the southern Indian Ocean, and with advection variations in the equatorial Atlantic. The movements of the STC are probably driven by meridional displacements of the belt of westerly winds over the southern hemisphere. These caused displacements of the circumpolar fronts, the SE trades and the Benguela Current system, and made the cool advection at the equator fluctuate.
The northernmost positions of the ABF coincide with strong sea-surface temperature minima in the Arabian Sea and the equatorial Pacific Ocean. These minima are probably the result of increased advection of relatively cool surface water from the south which is also caused by the northward eccentricity-driven movement of the westerlies and the associated oceanic polar fronts.
Keywords:
Age, 14C AMS; Age, dated; Age, dated, range, minimum; Age, dated standard deviation; DEPTH, sediment/rock; NIOZ89; PC; Piston corer; Sample code/label; SFB261; South Atlantic in Late Quaternary: Reconstruction of Budget and Currents; Southeast Atlantic; T89-24; T89-24-PC; Tyro; δ13C
Type:
Dataset
Format:
text/tab-separated-values, 38 data points
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