Growth of Pleistocene massive corals in south Florida: low skeletal extension-rates and possible ENSO, decadal, and multi-decadal cyclicities

Abstract

Skeletal extension-rates and their variability are significantly lower in Pleistocene massive reef-building corals (Montastraea annularis group) in south Florida as compared with modern corals of the same taxa in the same study area. We analyzed 1,429 annual increments in 18 cores of Montastraea colonies from Windley Key and the Key Largo Waterway in the late Pleistocene Key Largo Limestone, which was deposited during marine isotope stage 5e (ca. 125 kyrs BP). The average extension-rate is 5.2 mm/year, which is about half the value known for modern Montastraea in shallow water reef environments. With an average standard deviation (SD) of 1.01, the variability of extension-rates is at the lower range limit of modern Montastraea in south Florida (SD = 1–3.6). Due to the higher sea level, the Pleistocene Key Largo patch reef trend was located on a large carbonate platform. Unlike today, the island chain of the Florida Keys, which function as a shelter for the Florida Reef Tract from inimical bank water, was not in existence. Corals probably grew under higher-than-present sea surface temperatures, which resulted in comparably low skeletal extension-rates. The detection of 3–7 year, decadal, and multi-decadal cyclicities in extension-rate time series suggests that the major modes of modern tropical climate variability such as the El Nino-Southern Oscillation (ENSO) and possibly the Atlantic Multidecadal Oscillation (AMO) were in effect during the last interglacial.