Haase-Schramm, Alexandra, Böhm, Florian, Eisenhauer, Anton , Dullo, Wolf-Christian , Joachimski, M. M., Hansen, B. and Reitner, J. (2003) Sr/Ca ratios and oxygen isotopes from sclerosponges: Temperature history of the Carribean mixed layer and thermocline during the Little Ice Age. Paleoceanography, 18 (3). p. 1073. DOI 10.1029/2002PA000830.

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Abstract

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.

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