Abram, N.J., J.M. Webster, P.J. Davies & W.C. Dullo, 2001. Biological response of coral reefs to sea surface temperature variation: evidence from the raised Holocene reefs of Kikai-jima (Ryuku Islands, Japan). Coral Reefs, 20: 221-234. The island of Kikai-jima (central Ryuku Islands, Japan) provides a rare opportunity to define both environmental and biological variations within a reef ecosystem over a geological time frame. This paper documents the palaeo-environmental records archived in the δ¹⁸O composition of four Holocene Porites cores collected from the raised reef terraces of Kikai-jima. These coral samples record mean sea surface temperatures of 23.5^oC at 4,200 years B.P., falling to 22.2^oC at 3,790 years B.P. and to a minimum of 21.4^oC at 3,400 years B.P. After this time mean sea surface temperatures rose to 23.5^oC at 1,860 years B.P. before reaching modern-day conditions of 24.9^oC. During the cool water period between 3,790 and 3,400 years B.P., the coral isotope data indicate that sea surface temperatures were below the currently accepted 18^oC minimum temperature for reef development approximately 14% of the time. Biological changes (total coral abundance, colony size, individual coral coverage, genera diversity and evenness) preserved in the raised reef terraces of Kikai-jima can be explained by these variations in Holocene sea surface temperature. The biological data indicate that the coral community at Kikai-jima was ecologically stresses during the cool water period from 3,790 to 3,400 years B.P.; however, in the gross morphological sense the coral community did still constitute a coral reef.

Allison, N., A.A. Finch, S.R. Sutton & M. Newville, 2001. Strontium heterogeneity and speciation in coral aragonite: implications for the strontium paleothermometer. Geochimica Cosmochimica Acta, 65: 2669-2676. Sea surface temperatures (SSTs) have been inferred previously from the Sr/Ca ratios of coral aragonite. However, microanalytical studies have indicated that Sr on some coral skeletons is more heterogeneously distributed than expected from SST data. Strontium may exist in two skeletal phases, as Sr substituted for Ca in aragonite and as separate SrCO₃ (strontianite) domains. Variations in the size, quantity, or both of these domains may account for small-scale Sr heterogeneity. Here, we use synchrotron X-ray fluorescence to map Sr/Ca variations in a Porites lobata skeleton at a 5 μm scale. Variations are large and unrelated to changes in local seawater temperature or composition. Selected area extended X-ray absorption fine structure (EXAFS) spectroscopy of low- and high-Sr areas indicates that Sr is present as a substitute ion in aragonite i.e., domains of Sr carbonate (strontianite) are absent or in minor abundance. Variations in strontianite abundance are not responsible for the Sr/Ca fluctuations observed in this sample. The Sr microdistribution is systematic and appears to correlate with the crystalline fabric of the coral skeleton, suggesting Sr heterogeneity may reflect nonequilibrium processes. Nonequilibrium incorporation of Sr complicates the interpretation of Sr/Ca ratios in terms of SST, particularly in attempts to extend the temporal resolution of the technique. The micro-EXAFS technique may prove to be valuable, allowing the selection of coral microvolumes for Sr/Ca measurement where strontium is incorporated in a known structural environment.

Barnes, D.J. & R.B. Taylor, 2001. On the nature and causes of luminescent lines and bands in coral skeletons. Coral Reefs, 19: 221-230. Holes pushed into the surface of laboratory grade CaCO₃ powder reproduced visible and measurable luminescence similar to that seen and measured in coral skeletons. Heating such powder to 450^oC for 2 h did not destroy the luminescence although it did destroy luminescence in powdered coral skeleton. The effect in coral skeletal powder was probably due to carbonisation of contained organics because addition of small and increasing amounts of powdered charcoal to laboratory grade CaCO₃ increasingly attenuated luminescence. Luminescent lines and bands in coral skeletons have previously been ascribed to incorporation of humic substances. However, coating laboratory grade powder with humic acid attenuates rather than enhances luminescence. Ultra-violet lamps used to display coral luminescent lines and bands emit significant amounts of violet and blue visible light. Reflection of these visible wavelengths from the surface of laboratory grade CaCO₃ powder obscured luminescence of the powder. Multiple reflections within a hole in the powder resulted in absorption of the short wavelengths of visible light, including violet and blue light that would otherwise mask luminescence, and their re-emission at longer wavelengths. Luminescent bands in offshore corals were associated with the low-density regions of the annual density banding pattern. Luminescent lines in skeletons of inshore corals were in narrow regions of low-density skeleton, probably resulting from altered growth during periods of lowered salinity.

Barnes, D.J. & R.B. Taylor, 2001. Natural and artificial luminescence in a skeletal slice of Porites. Reef Sites, Coral Reefs, 10: 270.

Bessat, F. & D. Buigues, 2001. Two centuries of variation in coral growth in a massive Porites colony from Moorea (French Polynesia): a response of ocean-atmosphere variability from south central Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology, 2749: 1-12. Long-lived massive corals can contribute to the monitoring of coral reef environments through measurable growth records in the annual density patterns; these can provide an historical perspective against which to assess environmental changes, and can help to establish limits of coral growth. Furthermore, proxy records from corals may provide information about long-term variability in the performance of coral reefs, allowing unnatural changes to be distinguished from natural variability. A measurement of two centuries (1800-1990) coral growth, using computerized tomography, has led to a refined record of skeletal extension, density and calcification rates in a massive coral head from Moorea Island (French Polynesia). Correlation analysis of coral-growth characteristics with climatic instrumental data indicates a link between variations in average annual calcification and variations in annual air temperature. Linear regression of temperature versus calcification shows a trend in which a rise of 1^oC in temperature would increase the calcification rate by about 4.5%. Moreover, these data suggest that calcification has increased over recent decades, which differs notable from the 6-14% decline in calcification over the past 100 yr predicted by certain researchers. Spectral analysis of annual calcification record indicates a strong concentration of variance at the quasi-biennial (~2.5 yr), El Nino/Southern Oscillation (~ 4-7 yr) and decadal-scale variability (~21.9 yr) frequency bands.

Cardinal, D., B. Hamelin, D. Bard & J. Patzold, 2001. Sr/Ca, U/Ca and δ¹⁸O records in recent massive corals from Bermuda: relationships with sea surface temperatures. Chemical Geology, 176: 213-233. High-resolution records of Sr/Ca, U/Ca ratios and δ¹⁸O have been obtained in two recent colonies of massive corals (Diploria labryinthiformis) from Bermuda. The three geochemical proxies display regular seasonal variations and are well correlated with each other. However, some important discrepancies are observed between the two colonies: the average seasonal variations of the three geochemical proxies are lower by almost 50% in one of the profiles, where the seasonal oscillation also displays a strong asymmetry, with narrower summer maxima. Different calculations are discussed for calibrating Sr/Ca and δ¹⁸O with sea surface temperatures (SST). We show that the method using only temperature minima and maxima is slightly more accurate and is also more reliable. Our results from Bermuda corals confirm the temperature dependency of Sr/Ca, U/Ca and δ¹⁸O is species-dependent, as previously shown by others and that "vital effects" are clearly involved in the geochemical incorporation of trace elements in the coral skeleton. Finally, a simple model involving seasonal variation of the growth rate and a kinetic fractionation related to growth rate is presented to explain the differences between the two Bermuda colonies. It is shown that these factors may prevent corals from recording the complete temperature seasonality and could be the cause for the discrepancies observed between profiles, resulting in significant biases of the SST reconstructions.

Carricart-Ganivet, J.P. & M. Merino, 2001. Growth responses of the reef-building coral Montastrea annularis along a gradient of continental influence in the southern Gulf of Mexico. Bull. Mar. Sci., 68: 133-146. Skeletal growth variables [density g cm^-3), extension (cm yr^-1), and calcification rate (g cm^-2 yr^-1)] were determined for annual density bands in skeletal slabs of the reef building coral Montastrea annularis. Colonies growing at the same depth (10 m) were collected from six coral reefs distributed along an environmental gradient of continental influence within the southern Gulf of Mexico. No significant differences in growth variables were evident within each reef for the period of time represented by the slabs. Variations in calcification rate are most closely linked with variations in extension rate than with variations in density. Differences among reefs were significant for the three growth variables and appeared to relate to the environmental gradient dominated by turbidity and sediment load. Density and calcification rate increased from high to low turbidity and sediment load, while extension rate followed an inverse trend. The data suggest that, as corals experience a harsher environment, they respond by extending their skeleton more with the same or less calcium carbonate, with a concomitant reduction of skeletal density. This ‘stretching’ modulation of skeletal growth may be a wide-spread phenomenon.

Chen-Tung, C., W. Chung-Ho, S. Ker-Yea & W. Bing-Jye, 2001. Water temperature records from corals near the nuclear power plant in southern Taiwan. Science in China, 44: 356-362. Coral samples collected at the outlet and the inlet of the Third Nuclear Power Plant were measured for the δ¹⁸O and δ¹³C, indicating the surrounding seawater temperature and physiological/biochemical reactions during coral skeletal growth. The results show that with higher seawater temperature in summer, the values of δ¹⁸O are lower but those for δ¹³C are higher; however the δ¹⁸O extremes lag six weeks behind the δ¹³C extremes because the highest water temperature lags the maximum number of sunshine hours. Records of the extreme high temperature observed in the northern South China Sea between Oct. 1987 and Sep. 1988, and the extraordinary low temperature from Oct. 1992 to Feb. 1993 are also preserved in the coralline isotope signals. However, when the water temperature becomes too high the coral growth seems to stop.

Cobb, K.M., C.D. Charles & D.E. Hunter, 2001. A central tropical Pacific coral demonstrates Pacific, Indian and Atlantic decadal climate connections. Geophysical Research Letters, 28: 2209-2212. While instrumental and proxy-based climate records describe significant decadal-scale climate variability through the tropical Pacific, Indian, and Atlantic Oceans, the processes responsible for these variations and their interactions are not readily apparent from the observations. A new 112-yr coral-based sea surface temperature (SST) reconstruction from Palmyra Island in the central tropical Pacific (CTP) exhibits strong decadal variability with an amplitude of roughly 0.3^oC. A 12-13yr-period signal in this coral record is highly coherent with long equatorial Atlantic and Indian Ocean climate records, implying a unified phenomenon. The Atlantic pattern suggests that it may fall under direct influence of anomalous SST in the CTP, as it does over interannual timescales, while the Indian Ocean pattern exhibits maximum response during the switch between warm/cold states in the tropical Pacific. The results demonstrate that the CTP has played a significant role in determining the expression of global decadal climate variability over the twentieth century.

Cohen, A.L., G.D. Layne, S.R. Hart & P.S. Lobel, 2001. Kinetic control of skeletal Sr/Ca in a symbiotic coral: implications for the paleotemperature proxy. Paleoceanography, 16: 20-26. Modeling of past climates is critically dependent on estimates of past sea surface temperatures (SSTs), for which one of the principal techniques used is the measurement of Sr/Ca ratios in corals. The link between coral Sr/Ca and SST is not well-understood and there have been a number of discrepant observations. Corals with symbiotic zooxanthellae are known to show large diurnal fluctuations in calcification rate associated with the photosynthetic activity of their symbionts. Using detailed measurements with the ion microprobe, we compared the Sr/Ca content of discrete daytime and nighttime skeletal structures in the massive hermatypic coral Porites lutea over the course of 1 year and a seasonal temperature range of 4^oC. The Sr/Ca content of daytime skeleton is always lower than that of adjacent nighttime skeleton. While the slope of the nighttime Sr/Ca-SST correlation is close to that seen in inorganic aragonite precipitates, that of the daytime correlation is >4 times as steep. We attribute these differences to the role of photosynthesis in calcification and conclude that bulk Sr/Ca is related principally to daytime calcification rate rather than directly to SST. More reliable estimates of past SST may be arrived at through selective analysis of nighttime skeleton.

Goldstein, S.J., D.W. Lea, S. Chakraborty, M. Kashgarian & M.T. Murrell, 2001. Uranium-series and radiocarbon geochronology of deep-sea corals: implications for Southern Ocean ventilation rates and the oceanic carbon cycle. Earth and Planetary Science Letters 193: 167-182. We present new uranium-series and radiocarbon measurements for deep-sea corals from the Southern Ocean. These data are used to reconstruct ventilation ages, both at present and at the end of the last glacial period approximately 16,500 years ago. We apply an improved two-component mixing approach to correct uranium-series dates for contaminant thorium and protactinium present in oxide coatings. Calculated sweater radiocarbon values for contemporary samples decrease with depth in the water column and agree with direct sweater radiocarbon measurements for this area. This indicates that deep-sea corals can accurately record seawater radiocarbon distributions. Two of three glacial samples experience open-system uranium-series systematics, however, a third sample from the Drake Passage yields concordant thorium and protactinium dates as well as sweater values for initial ²³⁴U/²³⁸U. This coral yields a ventilation age that is approximately 20-40% greater than modern values for its location. This increase is consistent with published deep-sea coral and calibrated planktonic-benthic foraminifera radiocarbon data, suggesting that the glacial oceans as a whole may have been substantially less ventilated, presumably due to decreased formation of North Atlantic Deep Water. An overall decrease in oceanic mixing rates could have contributed to lower dissolved carbon in surface ocean water and lower atmospheric pCO₂ during the last glacial period.

Correge, T., T. Quinn, T. Delcroix, F. Le Cornec, J. Recy & G. Cabioch, 2001. Little Ice Age sea surface temperature variability in the southwest tropical Pacific. Geophysical Research Letters, 28: 3477-3480. We present a 60-year near-monthly record of tropical sea surface temperature (SST) during the Little Ice Age derived from coupled Sr/Ca and U/Ca analysis of a massive corals from New Caledonia (southwest tropical Pacific). The record indicates that, from 1701 to 1761, surface temperatures were on average 1.4^oC cooler than during the past 30 years. This cooling was accompanied by strong interannual to interdecadal oscillations that changed the background state. Correlations between SST changes and the Southern Oscillation and the Pacific Decadal Oscillation are evolutive and appear to depend on the background state.

Druffel, E.R.M., S. Griffin, T.P. Guilderson, M. Kashgarian, J. Southon & D.P. Schrag, 2001. Changes of subtropical North Pacific radiocarbon and correlation with climate variability. Radiocarbon, 43: 15-25. We show that high-precision radiocarbon (Δ¹⁴C) measurements from annual bands of a Hawaiian surface coral decreased by 7‰ from AD 1893 to 1952. This decrease is coincident with the Suess Effect, which is mostly due to the dilution of natural levels of ¹⁴C by ¹⁴C-free fossil fuel CO₂. This decrease is equal to that expected in surface waters of the subtropical gyres, and indicates that the surface waters of the North Pacific were in steady state with respect to long term mixing of CO₂ during the past century. Correlation between Δ¹⁴C and North Pacific gyre sea surface temperatures indicates that vertical mixing local to Hawaii and the North Pacific gyre as a whole is the likely physical mechanism to result in variable Δ¹⁴C. Prior to 1920, this correlation starts to break down: this may be related to the non-correlation between biennial Δ¹⁴C values in corals from the southwest Pacific and El Niño events observed during this period as well.

Evans, M.N., M.A. Cane, D.P. Schrag, A. Kaplan, B.K. Linsley, R. Villalba & G.M. Wellington, 2001. Support for tropically-driven Pacific decadal variability based on paleoproxy evidence. Geophysical Research Letters, 28: 3689-3692. Two independent proxy reconstructions of sea surface temperature relect a common pattern of Pacific decadal sea surface temperature variability over the past two centuries. Since the pattern extends to both the northern and southern hemispheres, this result supports the idea that Pacific decadal variability is a basin-wide phenomenon originating in the tropics.

Guilderson, T.P., R.G. Fairbanks & J.L. Rubenstone, 2001. Tropical Atlantic coral oxygen isotopes: glacial-interglacial sea surface temperatures and climate change. Marine Geology, 172: 75-89. We have generated a detailed oxygen isotope time-series from the fossil coral reefs from offshore Barbados. The Barbados coral-based record is a unique paleoceanographic data set with an equivalent sedimentation rate in excess of 600 cm/kyr where not only is the annual signal uniquely preserved but seasonality as well. Oxygen isotope values during the late glacial and LGM (16-20 ¹⁴C kyrs; 19-24 calendar kyrs) are ~ 2.3 ‰ heavier than corresponding living specimens, and indicate a regional cooling on the order of 4.5^oC. There is also an isotopic expression of the Bolling-Pre-Boreal climate oscillation, with values reflecting a cooling during the Younger Dryas, a key diagnostic of the state of the climate system, remained the same or slightly less than present and indicates that the observed coolings were a change in the mean state of the western tropical Atlantic. Pan-tropic cooling during the last glaciation is best explained by a change in the radiative balance of the tropics. Variable tropical sea surface temperatures during climate oscillations such as the Younger Dryas challenges the paradigm that climate change only cascades from variations in North Atlantic deep water production.

Juillet-Leclerc, A. & G. Schmidt, 2001. A calibration of the oxygen isotope paleothermometer of coral aragonite from Porites. Geophysical Research Letters, 28: 4135-4138. The oxygen isotopic composition _σ (δ¹⁸O_aragonite) of coral aragonite is dependent upon two parameters, temperature and water oxygen isotopic composition. This tracer allows temperature reconstruction in tropical zones. Different published δ¹⁸O: temperature relationships show a slope derived from the regression δ¹⁸O against T (^oC) which varies between –0.16 and –0.23 for Porites genus. This implies greater uncertainty for paleoclimatic reconstruction. The calibrations were generated differently. They were obtained from several colonies, collected in different locations or the formula was derived from the same coral head following seasonal variations of temperature. The relationships took into account of δ¹⁸O_SW fluctuation or δ¹⁸O_SW were estimated from salinity or were not considered. We show by using isotopic data from Weber and Woodhead (1972) and assessing the δ¹⁸O_SW value by two different methods that a thermodynamically significant formula is generated.

Marshall, J.F. & M.T. McCulloch, 2001. Evidence of El Niño and the Indian Ocean Dipole from Sr/Ca derived SSTs for modern corals at Christmas Island, eastern Indian Ocean. Geophysical Research Letters, 28: 3453-3456. While the El Niño/Southern Oscillation (ENSO) has been regarded as an almost exclusively Pacific Ocean phenomenon, there is a growing amount of evidence that there are interannual events in other ocean basins which are possibly related to ENSO. Here we describe results from Sr/Ca analysis of a 24 year coral record from Christmas Island in the tropical eastern Indian Ocean. The Sr/Ca data was matched with blended ship and satellite data from the region to produce the Sr/Ca-SST calibration. There is evidence of both warm and cool SST anomalies in the Sr/Ca derived SSTs, with an extreme cooling event of 1994 relating to the unusual oceanographic conditions set up by the Indian Ocean Dipole (IOD) and warmer than normal SSTs corresponding with ENSO events in the Pacific.

Mitsuguchi, T., T. Uchida, E. Matsumoto, P.J. Isdale & T. Kawana, 2001. Variations in Mg/Ca, Na/Ca, and Sr/Ca ratios of coral skeletons with chemical treatments: implications for carbonate geochemistry. Geochimica Cosmochimca Acta, 65: 2865-2874. We made a systematic examination into the effects of chemical treatments on Mg/Ca, Na/Ca, and Sr/Ca ratios of coral skeletons. Five skeletal samples were cut from modern and fossil corals of the genus Porites. Each sample was ground into powder, and replicate subsamples were taken and spilt into four groups. One group was left untreated as the control group. The other three groups were treated cumulatively with distilled/deionised water (DDW), 30% H₂O₂ and weak HNO₃, with one group separated after each treatment step. The H₂O₂ and HNO₃ treatments incurred partial dissolution of the skeletal powder and thus resulted in considerable sample loss. All the groups were determined for the elemental ratios. The Mg/Ca and Na/Ca ratios showed decreases or little changes with the DDW treatment, and then increased with the H₂O₂ and HNO₃ treatments. The Mg/Ca and Na/Ca variations were closely parallel throughout the treatment sequence. The Sr/Ca ratio showed slight or little variation through the treatment sequence. These results reflect fine-scale elemental distribution in the skeletons. The Mg/Ca and Na/Ca decreases with the DDW treatment can be ascribed to removal of adsorptive Mg and Na from the skeletal surface. The Mg/Ca and Na/Ca increases with the latter treatments reflect enrichments in Mg and Na at the innermost portion of the skeletons (i.e. around the center of calcification). The Mg/Na ratio of the adsorptive phase is approximately the same as that of the skeletons. The covariation of Mg and Na in the adsorptive and skeletal phases indicates that Mg and Na behave similarly both in adsorption onto the skeletal surface and in the skeletogenesis. Sulfate ion (SO²₄^-) may participate in the Mg and Na behaviors. The Sr/Ca variation indicates that Sr is distributed almost homogeneously in the skeletons with little adsorptive fraction. Attention should be paid to the effects of chemical treatments associated with the fine-scale elemental heterogeneity, especially if coral Mg/Ca and Na/Ca ratios are used for paleoenvironmental analysis.

Nyberg, J., J. Csapo, B.A. Malmgren & A. Winter, 2001. Changes in the D- and L-content of aspartic acid, glutamic acid, and alanine in a scleractinian coral over the last 300 years. Organic Geochemistry, 32: 623-632. The D- and L-contents of aspartic acid (Asp), glutamic acid (Glu), and alanine (Ala) together with absolute and relative concentrations of 17 amino acids (Aas) were determined in samples of aragonite skeletons of a scleractinian coral from the Caribbean through the last 308 years. Regular patterns of increasing D/L ratios with increasing age are seen from the last 300 years. High and linear racemization rates occur through the first 250 years in Asp, the first 150 years in Glu, and the first 250 years in Ala. An evaluation of the utility of the D/L ratios of these amino acids as a chronological tool through the last 250 years yields standard errors for individual age estimates ranging between 1.7 and 6.4 years. Thereafter the racemizations slow down and in the 308-years old terminal sample the D/L values are discordant. A rapid increase in the total amino acid concentration of 33%% over approximately the last hundred years is identified. The rapid rate of decrease in Asp and Glu may be responsible for this decrease in the total AA concentration. The relative concentrations of Asp, Glu, and Ala (g AA/100 g protein) show a general pattern of decrease, although not significant, through the time interval analysed. A regularity of the decrease in L-contents and an irregularity of the decrease in D-contents are observed. This may imply that, in addition to possible diagentic alterations and/or leaching of amino acids, contamination of D-amino acids explains the discordant D/L values. The D-amino acids could originate from peptidoglycans in bacterial cell walls.

Reynaud-Vaganay, S., A. Juillet-Leclerc, J. Jaubert & J.-P.Gattuso, 2001. Effect of light on skeletal δ¹³C and δ¹⁸O, and interaction with photosynthesis, respiration and calcification in two zooxanthellate scleractinian corals. Palaeogeography, Palaeoclimatology, Palaeoecology, 175: 393-404. The respective role of environmental and physiological controls on the isotopic composition of coral skeletons is a matter of debate. It has been shown that δ¹³C can be affected by light, seawater δ¹³C_DIC, nutrition, respiration, spawning, pH and temperature. We investigated the effect of light on photosynthesis, respiration, calcification, and stable isotope composition (δ¹³C and δ¹⁸O) of the skeleton in zooxanthellate scleractinian corals Acropora sp. and Stylophora pistillata. Colonies were grown on glass slides under controlled conditions in the laboratory at low and high light (LL and HL: 132 and 258 μmol photons m^-2 s^-1). The average net photosynthesis of Acropora sp. was significantly higher under HL than under LL. The difference was not statistically significant for Stylophora pistillata. The respiration rate did not change significantly in both species under the two light conditions. The calcification rate of S. pistillata under HL was 17-fold higher than under LL and 2.5-fold higher for Acropora sp. The average skeletal δ¹³C and δ¹⁸O of Acropora sp. were significantly more negative under LL than under HL. For S. pistillata, skeletal δ¹⁸O was significantly more negative in the LL than in the HL condition. The δ¹³C value of the skeleton deposited under LL was also more negative than under HL, although the difference was not statistically significant. The skeletal δ¹³C was significantly correlated with the rate of calcification, both in LL and HL. No correlation was found between skeletal δ¹³C and the following physiological parameters: net and gross photosynthesis (P_n and P_g), respiration (R), and the P_g/R ratio. The increase of skeletal δ¹³C with increasing light seems to support the model of Goreau (1977). Zooxanthellae mostly fix ¹²C under HL, leading to an increased concentration of ¹³C in the common carbon pool which supplies dissolved inorganic carbon (DIC) for calcification. Hence, the skeleton deposited is isotopically enriched in ¹³C. This general model needs revision to accommodate the recent finding that calcification and photosynthesis draw carbon from two reservoirs (seawater and metabolic DIC), and that respiratory CO₂ is the major source of DIC for calcification. It is suggested that zooxanthellae mostly fix ¹²C[DIC] in LL; the organic matter respired, the CO₂ released, and the CaCO₃ deposited being therefore isotopically light. Under HL condition, zooxanthellar photosynthesis uses both [¹²C]- and [¹³C]DIC. The photosynthetic products catabolized by the coral, as well the respiratory CO₂ and the CaCO₃ precipitated are therefore heavier.

Ribaud-Laurenti, A., B. Hamelin, L. Montaggioni & D. Cardinal, 2001. Diagenesis and its impact on Sr/Ca ratio in Holocene Acropora corals. International J Earth Sciences, 90: 438-451. The effect of early diagenesis on Sr/Ca ratios encapsulated in coral skeletons was evaluated by comparing mineralogical, structural and geochemical characteristics of modern and Holocene, branching Acropora colonies. The modern specimens (Acropora danai, Acropora Formosa) come from Reunion Island (Western Indian Ocean) and the Great Barrier Reef of Australia, respectively. The Sr/Ca ratios of modern specimens ranged from 9.08 to 9.37 nmol/mol. The fossil acroporids (Acropora group danai-robusta) were collected from a 50-m core drilled through a barrier reef in Tahiti island; their C-14 ages range from 3,200 to 10,200 calendar years B.P. Fossil skeletons are 100% aragonite. Earlier diagenesis has occurred in the marine environment; it is expressed by growth of secondary aragonite over primary skeletal aragonite needles, development of syntaxial aragonite cements within intraskeletal cavities and decrease in size of original 1-1,050-μm-wide pores (residual porosity ranges from 25 to 28%), which results in a volume reduction by 34 to 49%. Cementation increases with increasing age of the corals. Later diagenesis has occurred in a mixed marine-freshwater environment. It includes partial dissolution of skeletal and growth of cement aragonite fibres in the form of spherolites, irregular meshes of large squarely terminated laths; this results in an increase in porosity from 30 to 59%. By reference to modern well-preserved acroporids, this diagentic alteration has led to an increase of Sr/Ca values (from 9.08-9.37 to 8.89-10.55 nmol/mol). This variation in Sr/Ca ratio can be linked to the increase in the amount of Sr-enriched cements relative to the volume of the skeletal aragonite and to a more homogeneous distribution of these cements throughout the skeleton. The uncritical use of Sr/Ca ratios as paleothermometers from diagenetically altered skeletons may cause serious misinterpretations. Accordingly, estimate of the degree of diagentic alteration in skeletons is a prerequisite to any paleoclimatic reconstruction based on coral records.

Rimbu, N., G. Lohmann, T. Felis & J. Patzold, 2001. Arctic Oscillation signature in a Red Sea Coral. Geophysical Research Letters, 28: 2959-2962. We show that the winter time series of the Ras Umm Sidd coral oxygen isotope record from the northern Red Sea (approximately 28^oN) is linked to the Arctic Oscillation phenomenon, the Northern Hemisphere’s dominant mode of atmospheric variability. Until now, the detection of this mode, which is most prominent in winter, in proxy climate records was difficult due to the lack of a clear seasonality in most paleoclimatic archives. The results suggest that northern Red Sea corals can provide information about the low-frequency variability of the Northern Hemisphere winter circulation during the pre-instrumental period.

Smithers, S.G. & C.D. Woodroffe, 2001. Coral microatolls and 20^th century sea level in the eastern Indian Ocean. Earth & Planetary Science Letters, 191: 173-184. Coral microatolls are discoid intertidal corals that are limited in their upward growth by subaerial exposure during low tides. Microatoll upper surface morphology preserves a filtered record of changes in the height of living coral (HLC), the upper limit to which corals can grow, and by proxy a historical record of former constraining water levels. Chronologies for these variations in HLC were established in this study using annual skeletal density bands revealed when skeletal slices were X-radiographed, supplemented by annual fluorescent bands visible when samples were illuminated with ultra-violet light. The upper surface morphologies of two large microatolls from separate reef-flat sites on the Cocos (Keeling) Islands are well correlated and indicate that the upper limit to coral growth has fluctuated by more than 5 cm since the early 1900s. The upper surface of these microatolls also indicate that there has been little net rise in sea level in the eastern Indian Ocean during the 20^th century. Microatoll surface morphology suggests that average rates of sea-level rise in the eastern Indian Ocean over this period were less than 0.35 mm.yr^-1, a rate considerably lower that the rate of average global sea-level change determined from aggregated tide-gauge data. The broad surface undulations do not appear to correlate directly with either El Niño-Southern Oscillation events or occurrence of the Indian Ocean dipole mode of ocean-atmosphere circulation. Microatolls provide a simple and effective method for extrapolating broad variations in sea level beyond the tide-gauge record in remote mid-oceanic settings.

Suzuki, A., M.K. Gagan, P. de Deccker, A. Omura, I. Yukino & H. Kawahata, 2001. Last interglacial coral record of enhanced insolation seasonality and seawater ¹⁸O enrichment in the Ryuku Islands, northwest Pacific. Geophysical Research Letters, 28: 3685-3688. We present a calibrated, high-resolution ¹⁸O/¹⁶O and ¹³C/¹²C record for a well-preserved Last Interglacial Porites spp. coral (U-Th age of 127 ± 6 ka) from the sea-level high-stand terrace of Yonaguni Island, Japan. Seasonal variations in the δ¹⁸O and δ¹³C values for the fossil coral are greater than those observed in modern coral records from the same reef setting and appear to be driven by the enhanced insolation seasonality in the northern hemisphere during the Last Interglacial maximum. The ¹⁸O enrichment of 1.1 ‰ in the fossil coral compared to the modern analogue cannot be due entirely to a reduction in sea-surface temperature because corals in this region are already growing at their lower thermal limit. Instead, most of the ¹⁸O enrichment must be due to a change in the δ¹⁸O of the surface seawater, probably in response to enhanced evaporation of the ocean or a higher volume flux of the Kuroshio Current.

Tudhope, A.W., C.P. Chilcott, M.T. McCulloch, E.R. Cook, J. Chappell, R.M. Ellam, D.W. Lea, J.M. Lough & G.B. Shimmield, 2001. Variability in the El Nino-Southern Oscillation through a glacial-interglacial cycle. Science, 291: 1511-1517. The El Nino-Southern Oscillation (ENSO) is the most potent source of interannual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to develop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for the past 130,000 years, operating even during "glacial" times of substantially reduced regional and global temperature and changed solar forcing. However, we also find that during the 20^th century ENSO has been strong compared with ENSO of previous cool (glacial) and warm (interglacial) times. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations.

Watanabe, T., M. Minagawa, T. Oba & A. Winter, 2001. Pretreatment of coral aragonite for Mg and Sr analysis: implications for coral thermometers. Geochemical Journal, 35: 265-269. Trace elements (e.g. Sr, Mg and U) in coral skeletons are widely used as a potential robust paleothermometers. However, there is little consensus among workers on the chemical pre-treatment of skeletal samples, which contain small amounts of organic materials and inorganic detritus enriched in many metals compared to the skeleton. We tested the analytical effects of chemical treatment on coral aragonite by comparing several chemical treatments for Mg/Ca and Sr/Ca as well as oxygen and carbon isotopic rations. Our results suggested that the Sr/Ca ratio and stable isotopic ratios are resistant to chemical treatments. However, organic matter or crystal surfaces in corals could absorb more than 40% of magnesium although 60% of magnesium in coral aragonite substitutes for calcium. Our results suggest that it is expedient to remove impurities by the method outlined here, especially before determining Mg/Ca ratios in corals for paleoenvironmental reconstruction.

Watanabe, T., A. Winter & T. Oba, 2001. Seasonal changes in sea surface temperature and salinity during the Little Ice Age in the Caribbean Sea deduced from Mg/Ca and ¹⁸O/¹⁶O ratios in corals. Marine Geology, 173: 21-35. The oxygen isotopic composition (δ¹⁸O) of coral skeletons reflects a combination of sea surface temperature (SST) and the δ¹⁸O of seawater, which is related to sea surface salinity (SSS). In contrast the magnesium/calcium (Mg/Ca) ratio of a coral skeleton reflects SST independent of salinity. By using the relationships among coral Mg/Ca ratios, coral δ¹⁸O, seawater δ¹⁸O and SST, it is possible to determine past SST and SSS uniquely. Such determinations were made and calibrated using Mg/Ca ratio and the δ¹⁸O of the modern part of a 3 m long coral core (Montastrea faveolata), collected from the southwest coast of Puerto Rico in the Caribbean Sea where both SST and SSS changes seasonally and the seawater δ¹⁸O measured at the coral site. Our results yielded three relationships: 

(coral Mg/Ca – SST, δ¹⁸O_coral - δ¹⁸O_water – SST, and δ¹⁸O_water – SSS) 

With these calibration equations seasonal changes in SST and SSS during the little ice age (LIA) in the Caribbean Sea were reconstructed. The δ¹⁸O and Mg/Ca ratio of the coral skeleton between 1699 and 1703 suggests that the SST during the LIA was approximately 2^oC cooler than present with the SSS showing greater seasonal changes as well. These results are in good agreement with climate-based reconstruction from corals based on oxygen isotopes, although the possibility of some uncertainty remain in our estimation including long-term decadal scale trends in climate.

Yu, K-F, T. Chen, D. Huang, H. Zhao, J. Zhong & T-S Liu, 2001. The high-resolution climate recorded in the δ¹⁸O of Porites lutea from the Nansha Islands of China. Chinese Science Bulletin 46: 2097-2102. A Porites lutea core from Yongshu Reef of Nansha Islands covering 50 years growth history was analysed for oxygen isotopic composition with monthly and seasonally resolution. The calibration of the δ¹⁸O with the instrumental temperature indicated that the coral δ¹⁸O is a good indicator for sea surface temperature (SST) and air temperature (t). It can be used to reconstruct the SST and air temperature of the Yongshu Reef sea area. In addition, the coral δ¹⁸O provides signatures for the intensity of the East Asia monsoon and it is a record for the activities of El Nino events. With the calibrated SST and air temperature formulas, the most recent fifty years SST and air temperature were reconstructed based on the coral δ¹⁸O, thus back up the understanding of the climate of Nansha Islands to 1950, far beyond the limit of the instrumental recording since September 1988. It was found that, in general, increasing 1^oC air temperature results in 0.24‰ decrease in skeletal δ¹⁸O.