Colin WOODROFFE - Research Information

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Coral paleoclimatology and ocean circulation

Colin Woodroffe is studying palaeoenvironmental conditions in several tropical ocean settings using fossil coral, including:

 Microatolls as proxy indicators
 Ocean circulation indicated by fossil corals

Microatolls as proxy indicators

Coral microatolls are discoid corals that grow up to a level in the lower intertidal zone at which they are limited by exposure at the lowest tides. They are dead on top, but living around the margin and grow laterally. Their upper surface is generally constrained by water level making them suitable as indicators of former sea levels. Colin Woodroffe has undertaken several projects examining the potential of these corals to extend the historical record of sea-level changes. He has studied this, in particular, with former PhD student Scott Smithers, in the Cocos (Keeling) Islands in the Indian Ocean (Smithers and Woodroffe, 2000, 2001).

More recently, he has demonstrated the use of oxygen isotope measurements from the skeletal bands in microatolls to extract palaeoceanographic proxy data. Stable isotope analyses of coral microatolls from Christmas Island in the mid-Pacific provide an insight into El Niño-Southern Oscillation (ENSO) variability. This work, undertaken in conjunction with Mike Gagan at the Australian National University, is being continued by Helen McGregor who is an AINSE postdoctoral fellow at the University of Wollongong.  Preliminary results have shown that the isotope record in modern microatolls correlates well with sea surface temperatures determined from satellites (Woodroffe and Gagan, 2000; McGregor et al., 2011), and studies of fossil corals indicate that there have been significant variations in the intensity of ENSO during the Holcoene (Woodroffe et al., 2003).

References

Smithers, S.G. and Woodroffe, C.D. (2000) Microatolls as sea-level indicators on a mid-ocean atoll: Cocos (Keeling) Islands, Indian Ocean. Marine Geology 168, 61-78.

Smithers, S.G. and Woodroffe, C.D. (2001) Coral microatolls and 20th century sea level in the eastern Indian Ocean. Earth and Planetary Science Letters 191, 173-184.

Woodroffe, C.D. and Gagan, M.K. (2000) Coral microatolls from the central Pacific record late Holocene El Nino. Geophysical Research Letters 27, 1511-1514.

Woodroffe, C.D., Beech, M.R. and Gagan, M.K. (2003) Mid-late Holocene El Nino variability in the equatorial Pacific from coral microatolls. Geophysical Research Letters 30, 1358-1361.

McGregor, H.V., Fishcer, M.J., Gagan, M.K., Fink, D. and Woodroffe, C.D. (2011) Environmental control of the oxygen isotope composition of Porites coral microatolls. Geochimica et Cosmochimica Acta 75, 3930-3944.

Ocean circulation indicated by fossil corals

Other geochemical records can also be extracted from corals, and detailed analyses of radiocarbon determined in collaboration with Quan Hua and David Fink at ANSTO have revealed a pattern of increase in post-bomb radiocarbon that can be used to track ocean circulation in the Indian Ocean. Our analyses reveal that surface waters in the northwestern Indian Ocean do not extend across to influence the Cocos (Keeling) Islands (Hua et al., 2004, 2005).

References

Hua, Q., Woodroffe, C.D., Barbetti, M., Smithers, S.G. and Fink, D. (2004) Marine reservoir correction for the Cocos (Keeling) Islands, Indian Ocean. Radiocarbon, 46, 603-610.

Hua, Q., Woodroffe, C.D., Smithers, S. G., Barbetti, M. and Fink, D. (2005) Radiocarbon in corals from the Cocos (Keeling) Islands and implications for Indian Ocean circulation. Geophysical Research Letters, in press.

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