2004 年 38 巻 4 号 p. 241-254
Although tropical oceans are a key component of the global climate system, their behavior in the past - even only a few decades ago - remains poorly characterized. Coral skeletons can provide several centuries of continuous paleoclimatic records with weekly to annual resolution. The skeletal oxygen isotope ratio (δ18O) is one of the most commonly used coral-based paleoclimatic proxies. The skeletal δ18O values reflect a combination of temperature and the δ18O of ambient surface seawater, and seawater δ18O and sea surface salinity are affected by similar factors. Many calibration studies have sought to validate skeletal δ18O as a paleoclimatic tracer and to define the relationship between skeletal δ18O, temperature, seawater δ18O and salinity. The time resolution of this calibration is increasing; it currently occurs biweekly in the Palau Islands in the tropical Western Pacific. Generally, changes in sea surface temperature and seawater δ18O have almost the same effect on changes in skeletal δ18O, both temporally and spatially. Local contribution rates of these two factors to skeletal δ18O differ owing to regional climatic conditions. Parallel studies of detailed calibrations and an expansion of coral skeletal δ18O datasets over the next decade are anticipated to lead to many developments in paleoclimatic understanding.
