In order to evaluate the variability in surface water masses in the Western Pacific Warm Pool, we report highprecision radiocarbon measurements in annual and seasonal bands from Porites lutea corals collected from the Palau Archipelago (7N, 134E). Annual coral bands from 1945 to 2008 and seasonal samples from 1953 to 1957 were analyzed to capture the initial early input of bomb 14 C from surface thermonuclear weapons testing in the Marshall Islands. Results show a pre-bomb average  14 C value of-54.9‰ between 1945 and early 1953. Beginning early in 1954, there is a rapid increase to a maximum of-23.1‰ at the start of 1955. Values continued to rise after 1957 to a post-bomb peak of 141‰ by 1976. The large initial rise in  14 C cannot be accounted for by air-sea CO 2 exchange. Results therefore suggest that the primary cause of this increase is the lateral advection of fallout-contaminated water from the Marshall Islands to Palau via the North Equatorial Current and then to the North Equatorial Countercurrent.

In order to evaluate the variability in surface water masses in the Western Pacific Warm Pool, we report high-precision radiocarbon measurements in annual and seasonal bands from Pontes lutea corals collected from the Palau Archipelago (7°N, 134°E). Annual coral bands from 1945 to 2008 and seasonal samples from 1953 to 1957 were analyzed to capture the initial early input of bomb 14C from surface thermonuclear weapons testing in the Marshall Islands. Results show a pre-bomb average δ14C value of-54.9% between 1945 and early 1953. Beginning early in 1954, there is a rapid increase to a maximum of-23.1% at the start of 1955. Values continued to rise after 1957 to a post-bomb peak of 141% by 1976. The large initial rise in δ14C cannot be accounted for by air-sea CO2 exchange. Results therefore suggest that the primary cause of this increase is the lateral advection of fallout-contaminated water from the Marshall Islands to Palau via the North Equatorial Current and then to the North Equatorial Countercurrent.

The growth rate and composition of cave calcite deposits (speleothems) are often used as proxies for past environmental change. There is, however, the potential for bias in the speleothem record due to seasonal fluctuations in calcite growth and dripwater chemistry. It has been proposed that the growth rate of speleothem calcite in Texas caves varies seasonally in response to density-driven fluctuations in cave-air CO 2 , with lower growth rates in the warmer months when cave-air CO 2 is highest. We monitored CO 2 in three undeveloped caves and three tourist caves spread over 130 km in central Texas to determine whether seasonal CO 2 fluctuations are confined to tourist caves, which have been modified from their natural states, and the extent to which cave-air CO 2 is controlled by variations in cave geometry, host rocks, cave volume, and soils. Nearly 150 lateral transects into six caves over three years show that CO 2 concentrations vary seasonally in five of the caves monitored, with peak concentrations in the warmer months and lower concentrations in the cooler months. The caves occur in six stratigraphic units of lower Cretaceous marine platform carbonate rocks and vary in volume (from 100 to .100,000 m 3 ) and geometry. Seasonal CO 2 fluctuations are regional in extent and unlikely due to human activity. Seasonal fluctuations are independent of cave geometry, volume, depth, soil thickness, and the hosting stratigraphic unit. Our findings indicate that seasonal variations in calcite deposition may introduce bias in the speleothem record, and should be considered when reconstructing paleoclimate using speleothem proxies.

Stable isotopic and trace element records from corals collected within the West Pacific Warm Pool (WPWP) are well suited to examine interannual to decadal climate variability associated with the El Niño-Southern Oscillation (ENSO) phenomenon. The most commonly used climate recorder in corals is δ 18 O (δ 18 O CRL), a parameter subject to multiple regional and local environmental influences. Location-specific calibration of δ 18 O CRL is a necessary first step for developing long-term paleoceanographic reconstructions. Here we present four new coral δ 18 O stratigraphies from the Republic of Palau (7.5°N 134.5°E), and compare our records with instrumental measurements for the period 1950-2008. We also compare our results with a previously published coral record from Palau. We employ a new sea surface salinity (SSS) product and validate its utility for coral-based paleoclimate calibrations. We not only examine differences among the records but also identify strong and regionally coherent environmental signals. We find that SSS variability is the dominant influence on δ 18 O CRL in Palau, while sea surface temperature (SST) is of secondary importance. Our results show that time-averaging multiple δ 18 O CRL records into a single composite series produce greater correlations with instrumental data and indices than individual stratigraphies alone. Our results are consistent with observations of a strengthening of the hydrological cycle in the WPWP region over the past 50 years, though the magnitudes of long term linear trends differ among the different Palau δ 18 O CRL records. Interannual and interdecadal variabilities between the Palau δ 18 O CRL records are more consistent than the long term linear trends. Monthly Palauan δ 18 O CRL anomalies capture strong El Niño events with high fidelity over the calibration period. This study provides constraints for future paleoenvironmental investigations in Palau using longer coral records.

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