Evaluation of sampling resolution in coral stable isotope records: A case study using records from New Caledonia and Tarawa

We have generated a 40‐year‐long, monthly stable isotope record from a Porites lutea coral collected offshore of Amedee, New Caledonia (22°S, 167°E) to investigate the relation between sampling resolution in coral isotope studies and retrieval of sea‐surface environmental information. We interpret the high correlation between our oxygen isotope record and a twenty‐year long sea‐surface temperature record at the monthly timescale ( r =0.88) to indicate that our coral isotope record is an accurate monitor of environmental conditions offshore of Amedee. The character of the signal and the percent variance explained in the record at the annual band, at the quasi‐biennial oscillation band ((QBO) 2.0‐2.4 years), and at the El Nino‐Southern Oscillation band ((ENSO) 3–8 years) changes little in response to a reduction in sampling density from monthly to bimonthly to quarterly. Similar results have been obtained in a reanalysis of a coral isotope record from Tarawa, Kiribati. Our results indicate that a significant amount of the information obtained from high‐density sampling can also be retrieved from lower‐density sampling. In particular, bimonthly sampling yields virtually no drop‐off in variance explained, and quarterly sampling is satisfactory for resolving interannual and decadal‐scale trends in time series. The proposed sampling approach may enable a more rapid filling in of numerous spatial holes in coral sampling sites needed for reconstruction of long‐term decadal‐scale variations in climate.