This paper examines the relationship between spectral reflectance and CaCO3 measurements. There are two objectives for doing this. First, to see if spectral reflectance values can be used as a proxy for CaCO3 measurements, and second, to see if paleoceanographic changes can be identified and studied using spectral measurement which are both quicker and cheaper to obtain than CaCO3 measurements. This investigation was carried out on sediments from Site 1090.
Site 1090 (42°54.8´S, 8°55.2´E) is located on the southern flank of the Agulhas Ridge in the central part of the Subantarctic Zone (Fig. F1). Although deep (3702 m of water), the site lies above the CaCO3 compensation depth. It is near the present-day boundary between North Atlantic Deep Water (NADW, above) and Circumpolar Deep Water (CDW, below) (Fig. F2). Site 1090 is part of a three-site depth transect to intersect all of the major South Atlantic water masses. The other sites in this transect are Sites 1088 (2082 m) also on the Agulhas Ridge and Site 1089 (4620 m) in the Cape Basin.
Site 1090 was drilled to recover upper Miocene to Pleistocene sediments to investigate changes in the location of the Polar Front Zone, investigate changes in the mixing ratios of CDW and NADW, and investigate the response of the Southern Ocean to orbital forcing. In particular, it was hoped that this site would provide sediments that would allow the examination of phase relationships to climatic changes identified in the Northern Hemisphere.
Five holes were drilled, reaching a maximum depth of 397.5 meters below seafloor (mbsf) and middle Eocene age (~46 Ma). The Quaternary sediments consist of alternating foraminifer nannofossil ooze, diatom-bearing nannofossil ooze, and mud-bearing nannofossil ooze with several short hiatuses. A Miocene through early Pliocene hiatus, extending over 10 m.y. is marked by a lithologic change with white nannofossil ooze above and reddish, mud-rich nannofossil ooze below. Miocene and Oligocene sediments consist of mud-bearing diatom ooze and mud- and diatom-bearing nannofossil ooze and chalk. Opal-rich sediments dominate the upper Eocene interval, whereas calcareous sediments predominate in the middle Eocene sediments (Fig. F2). Here we present data comparing spectral reflectance and percent CaCO3.