Corals offer an invaluable source of palaeoclimate
information. Physiological, isotopic and elemental
tracers in aragonitic coral skeletons provide a suite
of information on sea surface temperature,
salinity, river runoff and seawater chemistry. An
important goal of this thesis was to demonstrate
the reliability of palaeo-environmental records
obtained from Porites coral colonies from the Great
Barrier Reef over decadal-to-centennial time-
scales. Stable isotopes (delta-18O and delta-13C),
Sr/Ca, U/Ca and Ba/Ca ratios were measured over
common 5-year periods from 1565-70 to 1980-85
in eight Porites cores, spanning 120 to 420 years
of continuous growth. Ages were determined by
rigorous cross-dating between the cores using
characteristic UV fluorescent banding. The
resulting fluorescence chronology also provides a
history of regional rainfall and insights into the
variability of ENSO teleconnection patterns over
the past several centuries.

Confidence estimates for each of the composite
reconstructions provide the first quantitative
analysis of coral tracer reliability for the tracers
delta-18O, delta-13C, U/Ca, Sr/Ca, and Ba/Ca,
over multi-decadal to centennial time-scales. The
question of tracer variability was examined further
in a comparative study of 26 Porites colonies from
four reefs in the central Great Barrier Reef
sampled for the common 5-year periods 1980-85
and 1975-80. In terms of absolute values, delta-
18O, Sr/Ca and U/Ca are consistent between
inshore and midshelf reefs, however, delta-13C
and Ba/Ca do show significant cross-shelf
gradients that can be explained by proximity to
land and riverine influences. Causes of tracer
variability over pentannual to multi-century time-
scales within and between coral colonies include
physiology, skeletal diagenesis and endolithic
infestations. The influence of coral physiology
through skeletal extension rate, density and
calcification rate over the life of the colony, and
differences due to colony age and species, were
also examined. The results demonstrate that
reliable coral palaeoclimate reconstructions
revealing the common environmental signal are
achievable by combining information replicated
between multiple coral records.

The composite coral Sr/Ca and U/Ca records
reconstruct sea surface temperatures consistently
higher in the 18th and early 19th centuries than
the 20th century (until 1985 when the records
end). This result is in conflict with global proxy-
temperature reconstructions, which show that the
20th century was significantly warmer than the
four preceding centuries, although few tropical and
Southern Hemisphere records exist to confirm that
this is a global signal. Changes in the evaporation-
precipitation balance dominate the delta-18O
record, and a striking 0.2‰ shift in delta-18O
from the 1850s to modern values in the 1870s
indicates an abrupt freshening of the ocean
surface. Ba/Ca ratios in the inshore corals
strongly correlate with the delta-18O record,
including the abrupt shift in the 1870s, which is
also observed in coral delta-18O records
throughout the tropical southwest Pacific. Greater
wind-induced evaporation, altered precipitation
patterns, increased poleward water vapour
transport and altered surface-ocean circulation
combine to influence stable isotope and Ba/Ca
variability prior to 1870 AD. Such a scenario is
consistent with a stronger latitudinal temperature
gradient, as suggested by the Sr/Ca and U/Ca SST
reconstructions, and an intensified Hadley
circulation during the ‘Little Ice Age’.