Antarctic Circumpolar Deep Water; a Quaternary paleoflow record from the northern Scotia Sea, South Atlantic Ocean

• Published in: Journal of Sedimentary Research
• Main Authors: Howe, J. A., Pudsey, C. J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Society for Sedimentary Geology 1999
• Subjects: Antarctic; Drake Passage; Scotia Sea; North Scotia Ridge; Falkland Trough; Antarc*; Neogloboquadrina pachyderma; South Atlantic Ocean
• Online Access: http://nora.nerc.ac.uk/id/eprint/503526/; https://doi.org/10.2110/jsr.69.847

In the northern Scotia Sea, the main pathway of Circumpolar Deep Water (CPDW) flows north to pass through a deep gap in the North Scotia Ridge before turning east into the Falkland Trough. A sediment drift has developed on the seabed since the early-middle Miocene, coincident with the opening of Drake Passage and the inception of deep-water flow. Seismic and acoustic surveys show that the drift covers an area of 10,500 km 2 and forms a broadly asymmetrical mound up to 800 m thick. There is a zone of sediment thinning along the northwestern margin, the result of accentuated CPDW flow around rough ocean floor topography. Small debris flows originating around the margins of the drift suggest localized instability and high sediment supply. Four cores 3-9 m long have been recovered from the crest and margins of the drift in water depths of 3900-4300 m. Biostratigraphy and chemostratigraphy reveal that the longest core extends down to oxygen isotope stage 10 (approx. 370 ka). The sediments are predominantly fine-grained contourites and diatom-rich hemipelagites, capped by sandy-silty contourites rich in the planktonic foraminifer Neogloboquadrina pachyderma. Grain-size analysis of the fine fraction, finer than 4 phi (63 mm), combined with radiocarbon (AMS) dating and magnetic susceptibility, provide an indication of relative CPDW strength over the last 18 ka. Shortly after the last glacial maximum (LGM), at approximately 17 ka, silt modes fluctuated from 5.5 phi to up to 6.25 phi; this increased current winnowing is indicative of an unstable CPDW, with stormier glacial benthic conditions producing sporadic, high-energy currents across the drift crest and flanks. At approximately 12,280 ka, an increase in sediment sorting is noted, indicative of a strong flow of CPDW over the drift crest, suggesting an unstable and fluctuating deep-water flow. During deglaciation and into the Holocene, at approximately 10 ka, CPDW flow stabilized, becoming less vigorous across the drift crest and flanks with silt modes from 6 phi to ...