Discussion
The geochemical composition of coral skeletons
currently offers the only means of recovering multicentury records of seasonal-to-centennial timescale
variation in tropical climate. d
18
O-derived SST and
SSS records are the workhorse of coral-based
paleoclimate reconstructions to date. Improved
methodologies are now making high resolution,
multicentury Sr/Ca records feasible. Since Sr/Ca is
potentially a less ambiguous SST recorder, coupling
Sr/Ca with d
18
O records could yield more reliable
SST and SSS reconstructions. d
13 C as a paleorecorder
of seasonal variation in cloud cover and upwelling is
also gaining credibility. However, more experimental
research needs to be done before d
13
C records can be
used more widely for paleoclimate reconstructions.
Coral D
14
C records are highly valued as an ocean
circulation/ventilation proxy. Increasing numbers of
high-resolution D
14
C coral records are being published shedding invaluable new light on links between climate and ocean circulation processes. Coral
trace and minor element records are also becoming
more common and can add critical information
about past upwelling regimes, wind patterns, pH,
river discharge patterns, and SST.
The growing number of multicentury coral
oxygen isotope records is yielding new information
on the natural variability in tropical climate. Eastern
equatorial Pacific corals track ENSO-related
changes in SST and upwelling. Further west, coral
records track ENSO-related changes in SST and
SSS related to the displacement of rainfall associated
with the Indonesian Low. Decadal timescale changes
in ENSO frequency and in ocean circulation
and water mass movement detected in d
18 O and
D
14 C records, respectively, indicate a major reorganization in Pacific climate at various intervals
over time. Long-term trends in coral oxygen isotope
records point to a gradual warming/freshening of
the oceans over the past century suggesting that the
tropics are responding to global forcings.
Although the coral-based paleoclimate records
reconstructed to date are impressive, much work
remains to be done. It is necessary to develop
multiple tracer records from each coral record in
order to establish a more comprehensive reconstruction of several concurrent climatic features. In
addition, replication of long isotopic and elemental
records from multiple sites is invaluable for establishing better signal precision and reproducibility.
Coupled with fossil and deep-sea coral records,
coral proxy records offer a comprehensive and
effective means of reconstructing tropical paleoclimates.
Acknowledgments
I thank B Linsley, E Druffel, T Guilderson, J Adkins
and an anonymous reviewer for their comments on
the manuscript. I thank the Henry and Camille
Dreyfus Foundation for financial support.
Further Reading
Beck JW, Recy J, Taylor F, Edwards RL, and Cabioch G
(1997) Abrupt changes in early Holocene tropical sea
surface temperature derived from coral records. Nature
385: 705--707.
Druffel ERM (1997) Geochemistry of corals: proxies of
past ocean chemistry, ocean circulation, and climate.
Proceedings of the National Academy of Sciences of the
USA 94: 8354--8361.
Druffel ERM, Dunbar RB, Wellington GM, and Minnis SS
(1990) Reef-building corals and identification of ENSO
warming episodes. In: Glynn PW (ed.) Global Ecological
Consequences of the 1982–83 El Nin ˜ o – Southern
Oscillation pp. 233–253 Elsevier Oceanography, Series
52. New York: Elsevier.
Dunbar RB and Cole JE (1993) Coral records of oceanatmosphere variability. NOAA Climate and Global
Change Program Special Report No. 10, Boulder, CO:
UCAR.
Dunbar RB and Cole JE (1999) Annual Records of
Tropical Systems (ARTS). Kauai ARTS Workshop,
September 1996. Pages workshop report series 99–1.
Fairbanks RG, Evans MN, Rubenstone JL et al. (1997)
Evaluating climate indices and their geochemical
proxies measured in corals. Coral Reefs 16 suppl.: s93–
s100.
Felis T, Pa ¨ tzold J, Loya Y, and Wefer G (1998) Vertical
water mass mixing and plankton blooms recorded
in skeletal stable carbon isotopes of a Red Sea
coral. Journal of Geophysical Research 103: 30731-30739.
Gagan MK, Ayliffe LK, Beck JW, et al. (2000) New views
of tropical paleoclimates from corals. Quaternary
Science Reviews 19: 45--64.
Grottoli AG (2000) Stable carbon isotopes (d
13
C) in coral
skeletons. Oceanography 13: 93--97.
Linsley BK, Ren L, Dunbar RB, and Howe SS (2000)
El Nin ˜ o Southern Oscillation (ENSO) and decadal-scale
climate variability at 101N in the eastern Pacific from
1893 to 1994: a coral-based reconstruction from
Clipperton Atoll. Paleoceanography 15: 322--335. http://
pangea. stanford. edu/Oceans/ARTS/arts_report/arts_
report_ home. html
Hudson JH, Shinn EA, Halley RB, and Lidz B (1981)
Sclerochronology: a tool for interpreting past environments. Geology 4: 361--364.
NOAA/NGCD Paleoclimatology Program http://www.ngdc.
noaa.gov/paleo/corals.thml
Shen GT (1993) Reconstruction of El Nin ˜ o history
from reef corals. Bull. Inst. fr. e ´tudes andines 22(1):
125--158.
PAST CLIMATE FROM CORALS 431
The geochemical composition of coral skeletons
currently offers the only means of recovering multicentury records of seasonal-to-centennial timescale
variation in tropical climate. d
18
O-derived SST and
SSS records are the workhorse of coral-based
paleoclimate reconstructions to date. Improved
methodologies are now making high resolution,
multicentury Sr/Ca records feasible. Since Sr/Ca is
potentially a less ambiguous SST recorder, coupling
Sr/Ca with d
18
O records could yield more reliable
SST and SSS reconstructions. d
13 C as a paleorecorder
of seasonal variation in cloud cover and upwelling is
also gaining credibility. However, more experimental
research needs to be done before d
13
C records can be
used more widely for paleoclimate reconstructions.
Coral D
14
C records are highly valued as an ocean
circulation/ventilation proxy. Increasing numbers of
high-resolution D
14
C coral records are being published shedding invaluable new light on links between climate and ocean circulation processes. Coral
trace and minor element records are also becoming
more common and can add critical information
about past upwelling regimes, wind patterns, pH,
river discharge patterns, and SST.
The growing number of multicentury coral
oxygen isotope records is yielding new information
on the natural variability in tropical climate. Eastern
equatorial Pacific corals track ENSO-related
changes in SST and upwelling. Further west, coral
records track ENSO-related changes in SST and
SSS related to the displacement of rainfall associated
with the Indonesian Low. Decadal timescale changes
in ENSO frequency and in ocean circulation
and water mass movement detected in d
18 O and
D
14 C records, respectively, indicate a major reorganization in Pacific climate at various intervals
over time. Long-term trends in coral oxygen isotope
records point to a gradual warming/freshening of
the oceans over the past century suggesting that the
tropics are responding to global forcings.
Although the coral-based paleoclimate records
reconstructed to date are impressive, much work
remains to be done. It is necessary to develop
multiple tracer records from each coral record in
order to establish a more comprehensive reconstruction of several concurrent climatic features. In
addition, replication of long isotopic and elemental
records from multiple sites is invaluable for establishing better signal precision and reproducibility.
Coupled with fossil and deep-sea coral records,
coral proxy records offer a comprehensive and
effective means of reconstructing tropical paleoclimates.
Acknowledgments
I thank B Linsley, E Druffel, T Guilderson, J Adkins
and an anonymous reviewer for their comments on
the manuscript. I thank the Henry and Camille
Dreyfus Foundation for financial support.
Further Reading
Beck JW, Recy J, Taylor F, Edwards RL, and Cabioch G
(1997) Abrupt changes in early Holocene tropical sea
surface temperature derived from coral records. Nature
385: 705--707.
Druffel ERM (1997) Geochemistry of corals: proxies of
past ocean chemistry, ocean circulation, and climate.
Proceedings of the National Academy of Sciences of the
USA 94: 8354--8361.
Druffel ERM, Dunbar RB, Wellington GM, and Minnis SS
(1990) Reef-building corals and identification of ENSO
warming episodes. In: Glynn PW (ed.) Global Ecological
Consequences of the 1982–83 El Nin ˜ o – Southern
Oscillation pp. 233–253 Elsevier Oceanography, Series
52. New York: Elsevier.
Dunbar RB and Cole JE (1993) Coral records of oceanatmosphere variability. NOAA Climate and Global
Change Program Special Report No. 10, Boulder, CO:
UCAR.
Dunbar RB and Cole JE (1999) Annual Records of
Tropical Systems (ARTS). Kauai ARTS Workshop,
September 1996. Pages workshop report series 99–1.
Fairbanks RG, Evans MN, Rubenstone JL et al. (1997)
Evaluating climate indices and their geochemical
proxies measured in corals. Coral Reefs 16 suppl.: s93–
s100.
Felis T, Pa ¨ tzold J, Loya Y, and Wefer G (1998) Vertical
water mass mixing and plankton blooms recorded
in skeletal stable carbon isotopes of a Red Sea
coral. Journal of Geophysical Research 103: 30731-30739.
Gagan MK, Ayliffe LK, Beck JW, et al. (2000) New views
of tropical paleoclimates from corals. Quaternary
Science Reviews 19: 45--64.
Grottoli AG (2000) Stable carbon isotopes (d
13
C) in coral
skeletons. Oceanography 13: 93--97.
Linsley BK, Ren L, Dunbar RB, and Howe SS (2000)
El Nin ˜ o Southern Oscillation (ENSO) and decadal-scale
climate variability at 101N in the eastern Pacific from
1893 to 1994: a coral-based reconstruction from
Clipperton Atoll. Paleoceanography 15: 322--335. http://
pangea. stanford. edu/Oceans/ARTS/arts_report/arts_
report_ home. html
Hudson JH, Shinn EA, Halley RB, and Lidz B (1981)
Sclerochronology: a tool for interpreting past environments. Geology 4: 361--364.
NOAA/NGCD Paleoclimatology Program http://www.ngdc.
noaa.gov/paleo/corals.thml
Shen GT (1993) Reconstruction of El Nin ˜ o history
from reef corals. Bull. Inst. fr. e ´tudes andines 22(1):
125--158.
PAST CLIMATE FROM CORALS 431