Sr/Ca ratios and oxygen isotopes from sclerosponges

We investigate aragonitic skeletons of the Caribbean sclerosponge Ceratoporella nicholsoni from Jamaica, 20 m below sea level (mbsl), and Pedro Bank, 125 mbsl. We use d18O and Sr/Ca ratios as temperature proxies to reconstruct the Caribbean mixed layer and thermocline temperature history since 1400 A.D. with a decadal time resolution. Our age models are based on U/Th dating and locating of the radiocarbon bomb spike. The modern temperature difference between the two sites is used to tentatively calibrate the C. nicholsoni Sr/Ca thermometer. The resulting calibration points to a temperature sensitivity of Sr/Ca in C. nicholsoni aragonite of about -0.1 mmol/mol/K. Our Sr/Ca records reveal a pronounced warming from the early 19th to the late 20th century, both at 20 and 125 mbsl. Two temperature minima in the shallow water record during the late 17th and early 19th century correspond to the Maunder and Dalton sunspot minima, respectively. Another major cooling occurred in the late 16th century and is not correlatable with a sunspot minimum. The temperature contrast between the two sites decreased from the 14th century to a minimum in the late 17th century and subsequently increased to modern values in the early 19th century. This is interpreted as a long-term deepening and subsequent shoaling of the Caribbean thermocline. The major trends of the Sr/Ca records are reproduced in both specimens but hardly reflected in the d18O records.

Ogasawara winter Sr/Ca and U/Ca data of coral core OGA-02-1 and PDO reconstruction (coral-geoduck index)

The Pacific Decadal Oscillation (PDO), the leading mode of sea surface temperature (SST) anomalies in the extratropical North Pacific Ocean, has widespread impacts on precipitation in the Americas and marine fisheries in the North Pacific. However, marine proxy records with a temporal resolution that resolves interannual to interdecadal SST variability in the extratropical North Pacific are extremely rare. Here we demonstrate that the winter Sr/Ca and U/Ca records of an annually-banded reef coral from the Ogasawara Islands in the western subtropical North Pacific are significantly correlated with the instrumental winter PDO index over the last century. The reconstruction of the PDO is further improved by combining the coral data with an existing eastern mid-latitude North Pacific growth ring record of geoduck clams. The spatial correlations of this combined index with global climate fields suggest that SST proxy records from these locations provide potential for PDO reconstructions further back in time.