Oxygen and carbon stable isotope systematics in Porites coral near its latitudinal limit: The coral response to low-thermal temperature stress

We investigated oxygen and carbon isotopes (δ18O and δ13C, respectively) along the growth axis of a Porites coral living near the northern limit of hermatypic corals, off Ushibuka, Japan, where winter temperatures fall below the minimum required by most hermatypic corals. The coral's seasonal δ18O cycle depended mainly on seawater temperature, and the slope of the regression line between δ18O and sea-surface temperature for this coral was within reported values. The coral's growth was inhibited in 1968, and at around this time the annual growth rate was reduced. This growth inhibition began in winter 1967/1968, a period of extraordinarily low seawater temperature. Moreover, the amplitude of the annual δ18O fluctuation was small from winter 1967/1968 to winter 1969/1970. Although δ18O and δ13C fluctuations were out of phase most years, they were in phase some years. The in-phase fluctuations of δ18O and δ13C indicate that kinetic isotope effects may have been more important than metabolic isotope effects during those years. Sclerochronologic records thus reveal the coral response to low-temperature stress.