Interannual climate variability in the Miocene: High resolution trace element and stable isotope ratios in giant clams

High resolution stable isotope and trace elemental ratios of a recent Tridacna squamosa from Vietnam and a Middle to Late Miocene (10-13 Ma) Tridacna gigas from Indonesia are presented. The seasonal pattern of modern sea surface temperature (SST) variability offshore Vietnam is faithfully recorded in the delta(18)O of the T. squamosa shell carbonate, confirming the potential of Tridacna shells as sub-annual resolution climate archives. Cultivation of the T. squamosa specimen in controlled conditions after recovery from the natural environment facilitated a quantitative calibration of the delta(18)O signal to ambient water temperatures. An age model for the Miocene T. gigas shell from Indonesia was therefore constructed on the basis of its delta(18)O profile, assuming a single-peak annual SST cycle. The magnitude of these oscillations was 5-7 degrees C. Mg/Ca and the growth-banding pattern in the Miocene T. gigas correlates well with shell delta(18)O during the later part of the organism's lifespan. Ba/Ca is negatively correlated to Mg/Ca, with a lag of several months, suggesting a different phasing of the annual primary productivity cycle from that of SST. Furthermore, delta(18)O and Mg/Ca show prominent deviations to warmer conditions with a periodicity of similar to 3 years. These shifts demonstrate the existence of substantial interannual sea surface temperature variability in the Miocene, a period with elevated global temperatures compared to the present day. (C) 2011 Elsevier B.V. All rights reserved.