ABSTRACT
The ENSO (El Nino and the Southern Oscillation) is a fundamental
ocean-atmosphere
phenomenon that dominates interannual global climate variability.
Reconstructing
past ENSO events is therefore important for documenting and
understanding
the past behavior of the global climate system and enabling us to
predict
future climate change. However, the present understanding of ENSO
events
has been mainly based on the instrumental record of Pacific
climate which
provides detailed data only for the past few decades. Recent
studies have
shown that the stable isotope record in coral skeletons can be
used as
a valuable indicator of paleoclimatic changes in tropical regions,
and
therefore can potentially be used as a tool for reconstructing
past ENSO
events. This study presents a complete 88-year oxygen and carbon
isotopic
record in corals from Clipperton Atoll in the eastern Pacific for
the period
1906-1994. The data were analyzed using time-series statistical
methods
and discussed in terms of the varying extent to which they reflect
the
past ENSO events as well as other climatic changes. Although both
sea surface
temperature (SST) and precipitation have influenced coral d18O at
Clipperton,
multisample analysis suggests that the effect of SST on coral d18O
appears
to have played a more important role than that of
precipitation/salinity.
Growth rate does not appear to have much effect on coral d18O. In
the case
of d13C in these corals, there is a negative correlation between
SST and
d13C, although not as apparent as with skeletal d18O. Solar
radiation intensity
also shows weak negative correlation with d13C, which suggests a
view contrary
to what is generally held. To identify possible ENSO events and
other possible
climate changes in this region, the 88-year d18O record was
analyzed using
singular spectrum analysis (SSA) which revealed pronounced
interannual
cycles, interpreted as reflecting past ENSO events, as well as
other interdecadal
cycles and a long term trend. Comparison of the ENSO components
(period
between 3 and 5 years) with the historic records of ENSO and SST
shows
that at Clipperton coral d18O is generally sensitive to ENSO
variability,
although it also shows some local characteristics. Comparison with
coral
isotopic records from other regions in the Pacific and Indian
Oceans further
corroborates other studies which indicate that ENSO has occurred
persistently
for at least 100 years over the entire tropical ocean and that it
has oscillated
in the same characteristic 3- to 6-year frequency band. The
interdecadal
cycles in the d18O record may also be related to ENSO events,
while the
long-term trend maybe related to the global temperature rise as
the result
of the CO2 "greenhouse effects". Coral d13C also has a long-term
trend.
Comparison with a model of variation of d13C in dissolved
inorganic carbon
(DIC) at Clipperton based on measurements of atmospheric O2 and
CO2 concentration
shows that this trend may be due to the input of 13C depleted CO2
and the
"Suess" effect.
Ren, L., 1998. Identification of past climate variability of the
eastern
Pacific Ocean using both d13C and d18O records in corals from
Clipperton
Atoll (1994-1906). Unpublished MSc. thesis, State University of
New York
at Albany. 105 pp., +xi
University at Albany Science Library call number: SCIENCE
Oversize
(*) QC 869 Z899 1998 R46
thesis (scanned
text) - 5.6MB pdf file
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