Executive Summary Project Title: Character and Timing of a Reef Give-Up Event on the Southwest Puerto Rico Shelf Date: 23 April 2012 Project Number: R-111-1-08 Investigators: Clark Sherman, UPRM Department of Marine Sciences Wilson Ramírez, UPRM Department of Geology Project Period: 1 February 2008 – 30 April 2012
Summary of Impacts and Contributions Objectives Objective 1 – Document the Chronology and Paleoecologic Character of Reef Accretion This objective has been met. Five separate outer-shelf hummock reefs were cored to determine their age and accretion history. Radiocarbon ages of corals indicate that the upper 1-2 m of these reefs are recent (<1200 yr BP; yr BP = years before present) and actively accreting upward. This is contrary to our original hypothesis that these reefs were largely relict features formed prior to ~6 ka (ka = “kilo-annum”, thousands of years before present). The primary frame builder of these reefs is the Montastraea annularis species complex, with secondary contributions from Acropora cervicornis and Acropora palmata. These are all common reef builders in the Caribbean, though the depth of the reefs (~14-19 m) is somewhat deeper than typically expected for A. palmata (Aronson et al., 2002; Montaggioni and Braithwaite, 2009). Internally, the reefs are poorly cemented and unconsolidated coral rubble is a major constituent within the framework. Objective 2 – Establish Coral-Based Oxygen and Carbon Isotopic Records of Paleoenvironmental Conditions This objective has not yet been met. Meaningful coral-based stable isotope records typically require larger corals with massive growth morphology so that records of several years to decades may be established. Isolated measurements are generally not as useful. While the M. annularis complex is the primary frame builder in these reefs, coral rubble is also a major component. Thus, recovery of large, intact massive corals was problematic due to the nature of the reefs. Additionally, larger corals were often heavily bioeroded disrupting the resultant record. Still, over the course of the coring several larger, massive coral samples suitable for paleoenvironmental work were eventually recovered. These samples range in age from ~200 to 1200 yr BP and are now being analyzed for Sr/Ca and stable oxygen isotope composition to establish seasonal paleotemperature records. Objective 3 – Correlate Reef-Accretion and Isotopic Records with Other Paleoclimatic Records Thus far, this objective cannot be met due to the nature of the record recovered. An overriding hypothesis of the stated objectives was that the outer shelf reefs to be studied were relict give-up reefs. This was based on previous coring studies in the area (Hubbard et al., 1997). Our research shows that the reefs are not relict, but, rather, are recent features that are actively accreting. Their recent upward accretion is consistent with the availability of accommodation space and minimal sea-level changes over the last millennia. Upon completion of Objective 2 described above, seasonal paleotemperature records from recovered corals will allow for a 1