Eastern Pacific sea surface temperature since 1600 A.D.: The δ¹⁸O record of climate variability in Galápagos Corals

Abstract

We measured stable oxygen isotope ratios and skeletal growth rates in the massive corals Pavona clavus and P. gigantea from the west coast of Isabela Island, Galápagos, to assess interannual to decadal climate variability in the eastern Pacific. Comparisons of instrumental data sets show that sea surface temperatures (SST) in the Galápagos region are representative of a broad portion of the eastern equatorial Pacific. The site is especially well‐suited for long‐term studies of the El Niño/Southern Oscillation (ENSO) phenomenon, as it lies within the eastern 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 Galápagos instrumental SST record (r = −0.90 for annual averages). Cross‐spectral analysis shows that SST can explain greater than 80% of the variance in δ18O at both the annual cycle and within the high‐frequency portion of the ENSO band (3‐5 years). The P. clavus record is annual in resolution, extends from 1587 to 1953 A.D., and was obtained from a 10‐m diameter colony preserved within the Urvina Bay uplift. Because seawater δ18O variations in the region are very small, we interpret the Urvina Bay coral δ18O 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 historical ENSO reconstruction of Quinn et al. (1987). A number of low δ18O excursions that we observe during the 17th and 18th centuries very likely represent ENSO events that are missing from the historical tabulations. Most interannual δ18O variations between 1607 and 1953 A.D. represent annual average temperature excursions of 1° to 2.5°C. During the Little Ice Age, the annual δ18O series correlates well with many North American tree ring records and shows low temperatures during the early 1600s and early 1800s, and relatively warmer conditions during the 1700s. Unlike most northern hemisphere tree ring and instrumental records, we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling (<1°C). Oscillatory modes within the ENSO frequency band dominate the 347‐year δ18O 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 δ18O show variance at periods equivalent to the solar and solar magnetic periods (e.g., 11 and 22 years, respectively). In addition, the amplitude of the 11‐year δ18O cycle generally varies with the amplitude of the solar cycle, supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability 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 lat...

Stochastically induced climate shift of El Niño‐Southern Oscillation

“…A similar conclusion was obtained from analysis of a long temperature time series fi'om central England [Allen and Smith, 1996]. It may turn out that other cited significant decadal peaks [Dunbar et al, 1994] will also not meet this more stringent criteria. All of the above leads us to propose that the stochastic mechanism should be taken as a null hypothesis for decadal ENSO modulation against which competing mechanisms must be compared.…”

Evaluation of annual resolution coral geochemical records as climate proxies in the Great Barrier Reef of Australia

“…It is notable that while the geochemical records from 10AR2 are closely correlated with annual growth rates, they still record climatic change well, which suggests that the climatic significance of faster and steadier growing coral is independent of skeletal growth rate (Mitsuguchi et al 2003;Jones et al 2009). Therefore, such annual resolution coral records offer a potential approach to reconstructing past climate change (Dunbar et al 1994;Cole et al 2000;Zinke et al 2014). This is especially the case for research into climate change (2002) and Wei et al (2007) over long timescales, in which annual resolution sampling can save much time and expense, but still provides similar information to studies based on high-resolution sampling.…”

“…Nevertheless, relative to the large quantity of high-resolution studies, annual to multi-year resolution coral-based studies are still relatively rare. In addition, of those coral-based studies undertaken at annual to pent-annual resolutions (Dunbar et al 1994;Cole et al 2000;Hendy et al 2002;Pelejero et al 2005;Calvo et al 2007;Linsley et al 2008;Abram et al 2009;Wei et al 2009;Deng et al 2013;Zinke et al 2014), few have focused on the replication of the lowresolution geochemical records of multiple coral cores. Some studies have evaluated the climatic significance of annual coral records averaged using monthly or sub-annual values from each year (Lough 2004;Smith et al 2006;Pfeiffer et al 2009).…”

Century-scale records of land-based activities recorded in Mesoamerican coral cores

“…Scleractinian corals can live for hundreds of years and continuously record changes in the marine environment in their aragonitic skeletons. Annual density banding in corals allows accurate time control on reconstructions (Knutson et al, 1972), and many studies have utilized corals for paleoclimatic and paleoenvironmental reconstruction, measuring stable isotopes (Dunbar et al, 1994;Cobb et al, 2003, Marion et al, 2005 and metals that substitute into the CaCO 3 matrix (Smith et al, 1979;Hanna and Muir, 1990;Bastidas and Garcia, 1999;Fallon et al, 2002;David, 2003;McCulloch et al, 2003;Ramos et al, 2004;Fleitmann et al, 2007;Lewis et al, 2007;Prouty et al, 2008). Although the coral calcification mechanism and therefore the exact pathway of metal substitution in the aragonite matrix are still under debate (Cohen and McConnaughey, 2003), empirical studies have shown that corals appear to faithfully record relative metal concentrations in the surrounding seawater (Runnalls and Coleman, 2003;Correge, 2006).…”