Assessing the paleoclimatic utility
of
the Indo-Pacific coral genus Diploastrea in a 225-year oxygen
isotope
record from Fiji
Stefan Bagnato 2003
A thesis presented to the Faculty of the University at Albany, State
University of New York in partial fulfillment of the requirements
for
the degree of Master of Science
College of Arts & Sciences, Department of Earth and Atmospheric
Sciences
Advisor: B.K. Linsley
Abstract
In the Western Pacific there remains, both spatially and temporally,
a
sparse record of surface ocean conditions and very few long
paleoclimate records able to extend our understanding of this
important
region. The coral genus Porites is the common coral currently
used for Pacific paleoclimate studies and has proven to be very
useful. The massive coral Diploastrea, due to its slow growth
rate and dense structure, may preserve temporally longer geochemical
proxy records than Porites colonies of the same length. Its
long
lifespan and fossil history give this genus great potential; however
no
assessment has been made of the paleoclimatic utility of Diploastrea
skeletons.
Presented here are Diploastrea d18O time series from Savusavu, Fiji,
a
region sensitive to combined SST and precipitation changes due to
activity of the El Niño Southern Oscillation (ENSO) and the
South Pacific Convergence Zone (SPCZ). Sampling of a single
skeletal element and/or a narrow sample track results in annual
variations with the least amount of time averaging and greatest
amplitude. Higher winter growth rates coupled with a constant
sampling interval have preferentially captured winter conditions in
the
geochemical composition of Diploastrea's skeleton. These
winter-biased d18O time series illustrate that Diploastrea is as
effective as Porites in recording the interannual environmental
history
of the region, dominated by both sea surface temperature (SST) and
SPCZ-related rainfall. Examination of SST and
precipitation
data suggests that the trend component in Porites d18O at this site
is
amplified relative to observed trends in SST and expected trends in
d18Oseawater, and that Diploastrea-generated d18O time series more
closely reflects variability on this time scale. Utilizing
Singular Spectrum Analysis (SSA) analysis, it is demonstrated that
Diploastrea captures climate variability related to the Interdecadal
Pacific Oscillation (IPO) as faithfully or more so than
Porites.
Wavelet analysis reveals a splitting of ENSO spectral power around
1880
to include lower frequencies, indicating that this interdecadal mode
of
variability may be fundamentally linked to ENSO, although it is
observed to operate independently. The results presented here
suggest that Diploastrea skeletal d18O reliably records both high
and
low frequency climate signals with some notable improvements over
the
genus Porites, and has enormous future potential for reconstructing
tropical climate over the past 600-800 years.
Bagnato, S., 2003. Assessing the paleoclimatic utility of the
Indo-Pacific coral genus Diploastrea in a 225-year oxygen isotope
record from Fiji.
Unpublished MSc. thesis, State University of New York at Albany. 128
pp., +viii
University at Albany Science Library call number: SCIENCE
Oversize (*) QC 869 Z899 2003 B34
thesis (text
pdf) - 1.7MB pdf file
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