EASTERN PACIFIC SEA-SURFACE TEMPERATURE SINCE 1600-AD - THE DELTA-O-18 RECORD OF CLIMATE VARIABILITY IN GALAPAGOS CORALS

Citation
Rb. Dunbar et al., EASTERN PACIFIC SEA-SURFACE TEMPERATURE SINCE 1600-AD - THE DELTA-O-18 RECORD OF CLIMATE VARIABILITY IN GALAPAGOS CORALS, Paleoceanography, 9(2), 1994, pp. 291-315
Citations number
90
Categorie Soggetti
Paleontology,Oceanografhy,Geology
Journal title
ISSN journal
08838305
Volume
9
Issue
2
Year of publication
1994
Pages
291 - 315
Database
ISI
SICI code
0883-8305(1994)9:2<291:EPSTS1>2.0.ZU;2-E
Abstract
We measured stable oxygen isotope ratios and skeletal growth rates in the massive corals Pavona clavus and P. gigantea from the west coast o f Isabela Island, Galapagos, to assess interannual to decadal climate variability in the eastern Pacific. Comparisons of instrumental data s ets show that sea surface temperatures (SST) in the Galapagos region a re representative of a broad portion of the eastern equatorial Pacific . The site is especially well-suited for long-term studies of the El N ino/Southern Oscillation (ENSO) phenomenon, as it lies within the east ern Pacific ''center of action'' for thermal anomalies associated with ENSO. The P. gigantea isotope record is nearly monthly in resolution, spans the period 1961-1982, and shows strong correlation with a Galap agos instrumental SST record (r = -0.90 for annual averages). Cross-sp ectral analysis shows that SST can explain greater than 80% of the var iance in deltaO-18 at both the annual cycle and within the high-freque ncy portion of the ENSO band (3-5 years). The P. clavus record is annu al in resolution, extends from 1587 to 1953 A.D., and was obtained fro m a 10-m diameter colony preserved within the Urvina Bay uplift. Becau se seawater deltaO-18 variations in the region are very small, we inte rpret the Urvina Bay coral deltaO-18 record in terms of annual average SST. The isotopic record appears to be a very good, but not perfect, indicator of ENSO events and shows good correspondence with the histor ical ENSO reconstruction of Quinn et al. (1987). A number of low delta O-18 excursions that we observe during the 17th and 18th centuries ver y likely represent ENSO events that are missing from the historical ta bulations. Most interannual deltaO-18 variations between 1607 and 1953 A.D. represent annual average temperature excursions of 1-degrees to 2.5-degrees-C. During the Little Ice Age, the annual deltaO-18 series correlates well with many North American tree ring records and shows l ow temperatures during the early 1600s and early 1800s, and relatively warmer conditions during the 1700s. Unlike most northern hemisphere t ree ring and instrumental records, we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling (<1 -degrees-C). Oscillatory modes within the ENSO frequency band dominate the 347-year deltaO-18 time series, accounting for >28% of the total variance. The main ENSO mode is centered at 4.6 years and accounts for 12% of the total variance. Additional significant oscillations occur at periods of 3.3, 6, 8, 11, 17, 22, and 34 years. Both annual growth rate and deltaO-18 show variance at periods equivalent to the solar an d solar magnetic periods (e.g., 11 and 22 years, respectively). In add ition, the amplitude of the 11-year deltaO-18 cycle generally varies w ith the amplitude of the solar cycle, supporting previous suggestions that the solar cycle may modulate interannual to decadal climate varia bility in the tropics. The dominant oscillatory modes, both within the ENSO and interdecadal frequency bands, shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s. Thi s may reflect major reorganizations within the tropical ocean-atmosphe re system and suggests that tropical Pacific climate variability is li nked across timescales ranging from years to decades.