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Volbers, Andrea N A; Henrich, Rüdiger (2002): Planktic foraminifera of sediment core GeoB1710-3. PANGAEA,, Supplement to: Volbers, ANA; Henrich, R (2002): Late Quaternary variations in calcium carbonate preservation of deep-sea sediments in the northern Cape Basin: results from a multiproxy approach. Marine Geology, 180(1-4), 203-220,

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In this study, we test various parameters in deep-sea sediments (bulk sediment parameters and changes in microfossil abundances and preservation character) which are generally accepted as indicators of calcium carbonate dissolution. We investigate sediment material from station GeoB 1710-3 in the northern Cape Basin (eastern South Atlantic), 280 km away from the Namibian coast, well outside today's coastal upwelling. As northern Benguela upwelling cells were displaced westward and periodically preceded the core location during the past 245 kyr (Volbers et al., submitted), GeoB 1710-3 sediments reflect these changes in upwelling productivity. Results of the most commonly used calcium carbonate dissolution proxies do not only monitor dissolution within these calcareous sediments but also reflect changes in upwelling intensity. Accordingly, these conventional proxy parameters misrepresent, to some extent, the extent of calcium carbonate dissolution. These results were verified by an independent dissolution proxy, the Globigerina bulloides dissolution index (BDX') (Volbers and Henrich, 2002, doi:10.1016/S0025-3227(02)00333-X). The BDX' is based on scanning electronic microscope ultrastructural investigation of planktonic foraminiferal tests and indicates persistent good carbonate preservation throughout the past 245 kyr, with the exception of one pronounced dissolution event at early oxygen isotopic stage (OIS) 6.
The early OIS 6 is characterized by calcium carbonate contents, sand contents, and planktonic foraminiferal concentrations all at their lowest levels for the last 245 kyr. At the same time, the ratio of radiolarian to planktonic foraminiferal abundances and the ratio of benthic to planktonic foraminiferal tests are strongly increased, as are the rain ratio, the fragmentation index, and the BDX'. The sedimentary calcite lysocline rose above the core position and GeoB 1710-3 sediments were heavily altered, as attested to by the unusual accumulation of pellets, aggregates, sponge spicules, radiolaria, benthic foraminifera, and planktonic foraminiferal assemblages.
Solely the early OIS 6 dissolution event altered the coarse fraction intensely, and is therefore reflected by all conventional calcium carbonate preservation proxies and the BDX'. We attribute the more than 1000 m rise of the sedimentary calcite lysocline to the combination of two processes: (a) a prominent change in the deep-water mass distribution within the South Atlantic and (b) intense degradation of organic material within the sediment (preserved as maximum total organic carbon content) creating microenvironments favorable for calcium carbonate dissolution.
Related to:
Volbers, Andrea N A (2001): Planktic foraminifera as paleoceangraphic indicators: Production, preservation, and reconstruction of upwelling intensity. Implications from late quarternary South Atlantic sediments. Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen, 184, 114 pp, urn:nbn:de:gbv:46-00101382-15
Latitude: -23.431667 * Longitude: 11.698333
Date/Time Start: 1992-01-11T00:00:00 * Date/Time End: 1992-01-11T00:00:00
Minimum DEPTH, sediment/rock: 0.03 m * Maximum DEPTH, sediment/rock: 10.58 m
GeoB1710-3 * Latitude: -23.431667 * Longitude: 11.698333 * Date/Time: 1992-01-11T00:00:00 * Elevation: -2987.0 m * Recovery: 10.45 m * Location: Namibia continental slope * Campaign: M20/2 * Basis: Meteor (1986) * Method/Device: Gravity corer (Kiel type) (SL) * Comment: CC: Karbonatschl., weißgrün
#NameShort NameUnitPrincipal InvestigatorMethod/DeviceComment
1DEPTH, sediment/rockDepthmGeocode
2Orbulina universaO. universa%Volbers, Andrea N ACounting >125 µm fraction
3Globorotalia minutaG. minuta%Volbers, Andrea N ACounting >125 µm fraction
4Neogloboquadrina pachydermaN. pachyderma%Volbers, Andrea N ACounting >125 µm fraction
5Globorotalia truncatulinoidesG. truncatulinoides%Volbers, Andrea N ACounting >125 µm fraction
6Globorotalia inflataG. inflata%Volbers, Andrea N ACounting >125 µm fraction
7Globigerina bulloides dissolution index (Volbers)BDX´Volbers, Andrea N ACalculated, see reference(s)
8Fragmentation index, planktic foraminiferaFragm plankt foram%Volbers, Andrea N ACalculated, see reference(s)
9Foraminifera, planktic, fragmentsForam plankt fragm%Volbers, Andrea N ACounting >125 µm fraction
10Benthic foraminifera/planktic foraminifera indexbF/pFVolbers, Andrea N ACalculated, see reference(s)
11Radiolaria/planktic foraminifera indexr/pFVolbers, Andrea N ACalculated, see reference(s)
12Foraminifera, plankticForam plankt%Volbers, Andrea N ACounting >125 µm fraction
13Foraminifera, planktic indeterminataForam plankt indet#/gVolbers, Andrea N ACounting >125 µm fraction
648 data points

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