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Gerhardt, Sabine; Henrich, Rüdiger (2001): Shell preservation of Limacina inflata in surface sediments of the Central and South Atlantic. PANGAEA,, Supplement to: Gerhardt, S; Henrich, R (2001): Shell preservation of Limacina inflata (Pteropoda) in surface sediments from the Central and South Atlantic Ocean: a new proxy to determine the aragonite saturation state of water masses. Deep Sea Research Part I: Oceanographic Research Papers, 48(9), 2051-2071,

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Over 300 surface sediment samples from the Central and South Atlantic Ocean and the Caribbean Sea were investigated for the preservation state of the aragonitic test of Limacina inflata. Results are displayed in spatial distribution maps and are plotted against cross-sections of vertical water mass configurations, illustrating the relationship between preservation state, saturation state of the overlying waters, and overall water mass distribution. The microscopic investigation of L. inflata (adults) yielded the Limacina dissolution index (LDX), and revealed three regional dissolution patterns. In the western Atlantic Ocean, sedimentary preservation states correspond to saturation states in the overlying waters. Poor preservation is found within intermediate water masses of southern origin (i.e. Antarctic intermediate water (AAIW), upper circumpolar water (UCDW)), which are distinctly aragonite-corrosive, whereas good preservation is observed within the surface waters above and within the upper North Atlantic deep water (UNADW) beneath the AAIW. In the eastern Atlantic Ocean, in particular along the African continental margin, the LDX fails in most cases (i.e. less than 10 tests of L. inflata per sample were found). This is most probably due to extensive “metabolic” aragonite dissolution at the sediment-water interface combined with a reduced abundance of L. inflata in the surface waters. In the Caribbean Sea, a more complex preservation pattern is observed because of the interaction between different water masses, which invade the Caribbean basins through several channels, and varying input of bank-derived fine aragonite and magnesian calcite material. The solubility of aragonite increases with increasing pressure, but aragonite dissolution in the sediments does not simply increase with water depth. Worse preservation is found in intermediate water depths following an S-shaped curve. As a result, two aragonite lysoclines are observed, one above the other. In four depth transects, we show that the western Atlantic and Caribbean LDX records resemble surficial calcium carbonate data and delta13C and carbonate ion concentration profiles in the water column. Moreover, preservation of L. inflata within AAIW and UCDW improves significantly to the north, whereas carbonate corrosiveness diminishes due to increased mixing of AAIW and UNADW. The close relationship between LDX values and aragonite contents in the sediments shows much promise for the quantification of the aragonite loss under the influence of different water masses. LDX failure and uncertainties may be attributed to (1) aragonite dissolution due to bottom water corrosiveness, (2) aragonite dissolution due to additional CO2 release into the bottom water by the degradation of organic matter based on an enhanced supply of organic matter into the sediment, (3) variations in the distribution of L. inflata and hence a lack of supply into the sediment, (4) dilution of the sediments and hence a lack of tests of L. inflata, or (5) redeposition of sediment particles.
Related to:
Gerhardt, Sabine (2001): Late Quaternary water mass variability derived from the pteropod preservation state in sediments of the western South Atlantic Ocean and the Caribbean Sea. Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen, 171, 109 pp, urn:nbn:de:gbv:46-ep000102968
South Atlantic in Late Quaternary: Reconstruction of Budget and Currents (SFB261)
Median Latitude: -7.217291 * Median Longitude: -37.590747 * South-bound Latitude: -38.468300 * West-bound Longitude: -79.145000 * North-bound Latitude: 20.920000 * East-bound Longitude: 15.480000
Date/Time Start: 1959-04-21T00:00:00 * Date/Time End: 1998-05-25T02:43:00
A240-ML * Latitude: 15.433300 * Longitude: -68.500000 * Elevation: -4180.0 m
AT_II-107_65 * Latitude: -32.030000 * Longitude: -36.180000 * Elevation: -2795.0 m * Campaign: ATII_USA * Basis: Atlantis II (1963)
GeoB1000-1 * Latitude: -5.698833 * Longitude: 11.709333 * Date/Time: 1988-02-20T00:00:00 * Elevation: -106.0 m * Recovery: 0.5 m * Location: Walvis Ridge * Campaign: M6/6 * Basis: Meteor (1986) * Method/Device: Giant box corer (GKG) * Comment: Ton, feinsandig, olivgrau
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