Stable isotope paleoenvironmental record of a coral from Cabo Pulmo, entrance to the Gulf of California, Mexico

A 17-year-long record of delta O-18 and delta C-13 from a Cabo Pulmo coral (Pavona gigantea) was analyzed. Although the coral delta O-18 signal is mai nly temperature controlled (similar to 70%), the seasonal arrival of surfac e water masses to the Gulf of California produces an isotopic effect in the opposite direction to that produced by temperature. During summer and fall , the arrival of Equatorial water effectively reduces the annual range in t he delta O-18 Of the coral skeletons by increasing the delta O-18 value of water, even though this occurs during the rainy season. The incursion of Eq uatorial water masses to the entrance of the Gulf of California during El N ino years is so strong that even during the strongest ENSO years there is n o important isotopic shift in the skeleton, even though temperature records show significant positive temperature anomaly in the region. The same effe ct occurs for La Nina years, but in the opposite direction. By deconvolutin g the temperature signal from the isotopic record, the seasonal interplay o f the water masses from the California Current and the Costa Rica Coastal C urrent can be effectively deduced. Changes in the coral delta C-13 Seem to coincide with periods of upwelling events in the gulf, with the highest val ue coinciding with the annual maximum in pigment concentration for the regi on.