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CRP El Niño member

Mr. David Fink

ANSTO
Sydney, Australia

Scientific Background

The Australian Nuclear Science and Technology Organisation in Sydney Australia has established a comprehensive Project to study natural archives and records of paleo-climates based on the role of cosmogenic and stable isotopic signatures as tracers and chronometers of earth system processes. This project titled CcASH - Cosmogenic Climate Archives in the Southern Hemisphere - is an ANSTO initiative to establish a working group of Australasian researchers active in aspects of Quaternary-Holocene climate and environmental change in the Southern Hemisphere. Our focus is to increase our knowledge of regional and hemispheric differences in past climate change in order to better predict future change and its impact on Australia such as from ENSO and sea-level rise. The Project has 3 major Tasks (Glacial and sedimentary systems, Ocean and atmospheric systems, radiocarbon signatures of greenhouse gases). Project Objectives are:

  1. To challenge the accepted paradigm that millennial-scale glacial climate changes are globally synchronised and quantify the timescales of Antarctic ice sheet behavior over the past 2 Ma.

  2. Study the variations in atmospheric transport and ocean circulation over the last glacial-interglacial transition and thru the Holocene to determine the character of paleo-ENSO and impacts on human migrations across the Pacific in the past.
  3. Better understand the role of naturally occurring carbonaceous gasses, particularly methane, in global warming by analysing radiocarbon in air bubbles of pre-industrial Antarctic ice and ancient Greenland ice.

Understanding paleoclimate change on a global, let alone a regional scale, can only be accomplished by the comparison between different paleoarchives over a range in temporal and spatial scales. CcASH will focus on applications of cosmogenic and stable isotopes in (a) glacial deposits from New Guinea, Tasmania, New Zealand and Antarctica, (b) sediment cores from the Indian and Pacific Oceans, (c) tree-rings from Tasmania, Indonesia and Thailand and (d) ice and trapped air in Greenland and Antarctic ice-cores.

With respect to this IAEA Cooperative Research Program, our modern and paleo ENSO studies are centered on corals (from China Sea, Indonesia, Cocos (Keeling) and Kirabati Islands), on speleothems (China and Australia) and from ocean sediments (off-shore Peru and eastern Indian Ocean).

Current Research

  1. Modern ENSO Variability, Ocean circulation in the Indian Ocean

    Most coral 14C data in the Indian Ocean are available for the western side, and only one record has recently published for the eastern side (Indonesia). The Cocos (Keeling) Islands is an isolated Australian atoll in the eastern Indian Ocean. An annual band chronology has recently been established for the corals from this atoll, which covers most of the 20th century. Based on pre-bomb D14C coral values of surface water in the western Indian Ocean and one 14C data point from the Cocos (Keeling) Islands in the eastern Indian Ocean, Southon et al. (2002) suggested that upwelled 14C-depleted waters in the northwestern Indian Ocean is carried to Cocos through the southeasterly flow from the Arabian Sea. However, based on sub-annual D14C data from corals from Kenya in western equatorial Indian Ocean for the past 50 yrs, Grumet et al. (2002) found that the Kenyan site is partly supplied by water from the southwestern Indian Ocean during the southwest monsoon, which is not influenced by 14C-depleted water as suggested by Southon et al. (2002).

    We have completed a survey of reservoir ages ( 1830-1990) from known age corals and have produced a 14C bomb curve 1950 to 1995 for annual samples in Cocos coral. This compilation of D14C supports that finding and suggests that surface waters that reach the Cocos (Keeling) Islands might be partly derived from the far western and southwestern Pacific, flowing through Torres Strait and the Indonesian through-flow and might not be as influenced by the southeast flow from the Arabian Sea as originally thought.

    Although the influence of ENSO in the Indian Ocean is still a matter of debate, there is a growing amount of evidence in the literature documenting a possible link between changes in the tropical Pacific and those in the Indian Ocean during major ENSO events. Cole et al. (2000) presented a strong correlation between a 194-year long d18O coral record in the western Indian Ocean and the SSTs variability in the tropical Pacific Ocean. For the eastern Indian Ocean, Grumet et al. (2004) reported the dominance of a ~3 year ENSO like periodicity for their del-14C coral record from the Mentawai Islands, Sumatra, indicating that the interannual variability in the record may be related to ENSO-like teleconnections over the Indo-Pacific basin. What is now tantalizsing is to re-analyse the Cocos 14C bomb curve at sub-annual resolution to look for ENSO-like variability.

  2. Holocene ENSO Variability - comparisons between the Indian an Pacific Oceans

    Previous work from our collaborators from University of Wollongong and ANU have identified mid-late Holocene fossil micro-atoll coral sections located on Kiritibati Island in the central Pacific. These data sets indicated ENSO variability over the past 1-3 ka compared to similar modern records on the island. We now are expanding this work to a new set of micro-atoll coral samples that based on our pilot 14C measurements appear to extend the record back to 5ka. Our preliminary survey indicates that each of these coral specimens spans upto 50-100 years of growth. Similarly, a recent field trip to Cocos (keeling) Is has also retrieved late-mid Holocene coral sections. A more long-term (and challenging) extension of this work is to attempt to match these sub-centennial coral records with overlapping time periods (based on U-Th dating) between Cocos and Kiritibati and compare isotopic signatures.

  3. Peruvian continental margin laminated sediments

    This work is being carried out in conjunction with Prof Geg Skilbeck from the Univ of Technology in Sydney and is described in that section.

  4. ENSO modes during the last glacial in the Timor sea

    The first 20 ka of a long sediment core (~360ka) from the northern Timor Trough of the north western coast of Australia is being studied using d18O, d-N and 14C (benthic, planktonic forams) and other geochemical proxies (for SST, terrigenous supply, aridity periods). New data of enhanced upwelling, productivity and increased aridity off northwest Australia during the LGM may suggest a long term mean ENSO state prevailed. This may mean a shallower thermocline in the eastern Indian ocean giving rise to easterly wind anomalies that resembles an ENSO like condition.

  5. Coral and speleothem records: South China Sea

    1. We feel that little is understood with regards to the spatial and temporal shifts in reservoir ages. We have commenced a survey to investigate the variations of marine 14C reservoir ages using coral samples (n=13) from the South China Sea (Leizhou Peninsula) which have been dated precisely using U-Th ages over the period covering broadly the period from the mid to late Holocene. Our initial results show a remarkable pattern in reservoir offsets from the predicted modelled marine reservoir ages based on ocean-atmospheric exchange. Such larger than expected reservoir ages have strong implications on short term variations in ocean-atmospheric circulations and may well assist in understanding linkages from tropical to high-latitude regions.

    2. A 60 cm speleothem record covering the time scale from 15-33 ka is being used to obtain a high precision 14C calibration linked to U-Th dating. Although not directly related to a paleo-ENSO study, we plan to use this speleothem to test the applicability of a high(er) latitude, speleothem-based C-14 calibration curve. Published curves with good internal precision and coherence, such as Lake Suigetsu sediment (Japan) and Bahama stalagmite strongly disagree (>5 ka) and have generated considerable debate. These two records actually represent two extremes of all calibration curves. We believe this speleothem has superior qualities to those previously used for calibration - a) it has a remarkable uniform growth rate of 49.8 mm/ka (based on U-Th) over its entire length implying unchanged hydrological conditions and thus (hopefully!) a constant DCF, b) it is of high-purity carbonate with a 230Th/232Th ratio > 4000, minimising detrital corrections. We have completed the first phase of 30 spot 14C measurements across the 20 ka age range with additional paired U-Th dates. Our next challenge is to obtain sub 1% 14C measurements to allow a calibration curve to enable resolution of the discrepancy amongst other calibration curves.

  6. Latitudinal tree ring studies and 14C offsets

    This aspect of our work, although not directly related to ENSO, is relevant in the study of regional atmospheric 14C offsets and their temporal variations in association with climate changes. There are two sections to this study:

    1. Comparing 14C variations between absolute dendro-matched tree-rings from different latitudes (such as from Thailand and Indonesia to Tasmania and New Zealand). The research will focus on the southern tropics and provide atmospheric 14C records over Indonesia and their relationship to the northeast Asian monsoon for the past 400 years - particularly over the Little Ice Age.

    2. Huon Pine chronologies during the Younger Dryas and the Little Ice Age. In a collaboration with the Univ of Sydney, we have located unique samples from the Huon Pine collection from Tasmania which belong to the Younger Dryas cold episode (~11,000 years ago) and the Little Ice Age (~300 years ago). Our aim is to determine the contributions of solar variability and changes in ocean circulation that occurred during this period of abrupt climate change by comparing the Huon (atmospheric) 14C tree ring data with that from the northern hemisphere. This represents the first ever atmospheric signal in the southern hemisphere during the Younger Dryas chronozone.

All the above listed activities are supported by collaborations with Universities of Sydney (Barbetti), Wollongong (Woodroffe), James Cook (Smithers), ANU (Gagan) and Queensland (Zhao, Collerson, Mueller).