Middle Holocene SST record (7,518±46 to 5,944±28 ybp) based on corals from the Enriquillo Valley, Dominican Republic

Abstract

Corals are important paleo-climatological tools because as they accrete their aragonite skeletons they also store a record of fluctuations in the chemical and physical conditions that existed in the sea water surrounding them. The Cañada Honda outcrop located in Enriquillo Valley in southwestern Dominican Republic is a rare and excellently preserved fossil coral reef which allows for the collection of paleo-climate information from the early Holocene. Orbicella species complex coral samples were collected from this outcrop ranging in age from 7,518 ±46 to 5,944 ±28 years before present. Slabs from these corals were x-rayed to show annual growth bands which were analyzed for annual growth rates. Powdered samples were taken at millimeter intervals across the maximum growth axis of each coral slab. The powders were analyzed for δ 18O and Sr/Ca ratios which were used to calculate sea surface temperatures (SST) and estimate residual δ18O which is correlated to sea surface salinity. Results from these mid-Holocene corals show that annual growth rates range from 2.5 to 5.3±0.2 mm/yr, which is expected for corals growing at 17 to 20±1 meters depth. Sr/Ca derived SST range on average from 21.95 to 20.28°C. δ 18O derived SST range from 11.09 to 16.79°C which are temperatures outside the tolerance of corals (18-30 C). Residual δ 18O suggest that the corals grew in an environment with high variability in sea surface salinity. δ 18O derived salinity values suggest that that the coral reefs accreted in the mid-Holocene Enriquillo paleo-embayment were subject to the upper limit of coral salinity tolerance. Sr/Ca-SST from Cañada Honda corals are 5.5 to 8°C cooler than other Caribbean SST proxies suggesting that the Sr/Ca-SSTs from this study do not show absolute temperature. Regardless, Sr/Ca-SSTs do capture a warming trend in the mid-Holocene also seen other Caribbean SST proxies.