Quaternary CaCO3 Input and Preservation within Antarctic Intermediate Water Mineralogic and Isotopic Results from Holes 818B and 817A, Townsville Trough (Northeast Australian Margin)

• Main Authors: Haddad, G. A., Droxler, A. W., Kroon, D., Müller, D. W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Texas A&M University 1993
• Subjects: Antarctic; Queensland; Antarc*
• Online Access: https://oceanrep.geomar.de/id/eprint/34668/; https://oceanrep.geomar.de/id/eprint/34668/1/sr133_16.pdf; https://doi.org/10.2973/odp.proc.sr.133.229.1993

The Quaternary history of metastable CaCO3 input and preservation within Antarctic Intermediate Water (AAIW) was examined by studying sediments from ODP Holes 818B (745 mbsl) and 817A (1015 mbsl) drilled in the Townsville Trough on the southern slope of the Queensland Plateau. These sites lie within the core of modern AAIW, and near the aragonite saturation depth (-1000 m). Thus, they are well positioned to monitor chemical changes that may have occurred within this watermass during the past 1.6 m.y. The percent of fine aragonite content, percent of fine magnesian calcite content, and percent of whole pteropods (>355 μm) were used to separate the fine aragonite input signal from the CaCO3 preservation signal. Stable δ 1 8 θ and δ13C isotopic ratios were determined for the planktonic foraminifer Globigerinoides sacculifer and, in Hole 818B, for the benthic foraminifer Cibicidoides spp. to establish the oxygen isotope stratigraphy and to study the relationship between intermediate and shallow water δ13C of Σ C O 2 and the relationship between benthic foraminiferal δ13C and CaCO3 preservation within intermediate waters of the Townsville Trough. Data were converted from depth to age using oxygen isotope stratigraphy, nannostratigraphy, and foraminiferal biostratigraphy. Several long hiatuses and the absence of magnetostratigraphy did not permit time series analysis. The principal results of the CaCO3 preservation study include the following (1) a general increase in CaCO3 preservation between 0.9 and 1.6 Ma; (2) a CaCO3 dissolution maximum near 0.9 Ma, primarily expressed in the Hole 818B fine aragonite record; (3) an abrupt and permanent increase of fine aragonite content between 0.86 and 0.875 Ma in both Holes 818B and 817A probably reflecting a dramatic increase of fine carbonate sediment production on the Queensland Plateau; (4) an improvement in CaCO3 preservation near 0.87 Ma, which accompanied the increase of sediment input, indicated by the first appearance of whole pteropods in the deeper Hole 817A and a ...