Hobart

Seminar abstract

Wednesday 31 October 2007, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Stewart J Fallon
Research School of Earth Sciences
The Australian National University

Surface Water Processes in the Indonesian Seas from Coral Radiocarbon Records

Radiocarbon has been used as a tracer of ocean circulation and marine geochemistry since the discovery of carbon-14 dating. ∆14C has been used to study global ocean circulation through the distribution of natural and bomb-derived 14C.  Two expeditions, GEOSECS (1970s) and WOCE (1990s) identified spatial gradients in both the surface and deep-water ∆14C, which define large-scale ocean circulation.  The main limitation of these studies is that they provide only a “snap shot” of 14C variability.  In order to get a complete picture of the temporal variation of 14C, proxy records, such as those provided by corals are needed.  Corals can provide time series of seasonal and interannual 14C variations of the surface ocean over time scales of hundreds of years.  Bi-monthly radiocarbon values have been recovered from corals in the Indonesian Seaway (Makassar Strait) and the outflow to the Indian Ocean (Lombok Strait) in order to better understand seasonal, interannual and decadal variability in the surface water masses that contribute to the Indonesian Throughflow (ITF). Both coral records have a pre-bomb (<1950) ∆14C of ~ -65‰. After 1954 the radiocarbon record increases rapidly, a response to the increased atmospheric 14C caused by nuclear weapons testing. From 1954 to 1986 the Makassar St. coral record displays clear seasonal variability from 15 to 60‰.  The quick response to the increased atmospheric 14C and the high post-bomb peak (+160‰) indicate a North Pacific source to the waters entering the Indonesian Throughflow. The Lombok St. coral ∆14C data exhibits strong seasonal and interannual variability although the magnitude and amplitude of the ∆14C variability is quite different from the Makassar St. coral. Although there is a suggestion that the peaks of the Makassar St. and Lombok St. records may be correlated, there is clearly at least one source of low 14C water to the Lombok St.  There are low radiocarbon excursions that can be linked with the El Niño years 1982 and 1987 indicating a reversal of waters from the Indian Ocean back into the Indonesian Seas.

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Karen Wild-Allen, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5010
Thomas Kunz, (Biological seminars) CSIRO Marine and Atmospheric Research
(03) 6232 5076
Jillian Enraght-Moony (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5456
Sandra Zicus, Antarctic Climate and Ecosystems CRC (03) 6226 7888
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 21/12/07