Assessment of Coral Sr/Ca Variations in Orbicella faveolata Colonies in Veracruz, Mexico

Kristine L DeLong1, Robin Cobb1, Amy J Wagner2, J Harold Hudson3, Gilman Ouellette Jr4 and Achim Dirk Herrmann5, (1)Louisiana State University, Geography and Anthropology, Baton Rouge, LA, United States, (2)UNC - Wilmington, Wilmington, NC, United States, (3)Reef Tech, Inc., Miami, FL, United States, (4)Louisiana State University, Geography & Anthropology, Baton Rouge, LA, United States, (5)Louisiana State University, Geology and Geophysics, Baton Rouge, LA, United States
Abstract:
Orbicella (formerly Montastraea) faveolata is an Atlantic massive coral species used by paleoclimatologists to reconstruct monthly- and annually-resolved sea surface temperature (SST) variations. Previous studies found discrepancies in coral strontium-to-calcium ratios (Sr/Ca) among colonies separated by meters to kilometers possibly attributed to either biological processes inherent to each colony, environmental differences at each coral site, and/or sampling-analytical methods. Here we examine coral Sr/Ca variations in five O. faveolata colonies offshore from Veracruz, Mexico (19.06ºN, 96.93ºW), two colonies from different water depths (3 and 6 m) in the same local reef environment (Santiaguillo) and three colonies in nearby reefs closer to the mainland (water depth of 4, 6, and 12 m); all colonies were cored in 1993. We control for sampling-analytical methods by using a refined sampling protocol that follows a corallite thecal wall that is parallel to the coral slab surface (i.e., optimal alignment) and we use the same analytical method and instrument for all colonies. Coral annual growth rates decrease by 44% for colonies in deeper water (12 m) with no significant correlation in annual growth rates among the colonies. Monthly coral Sr/Ca determinations co-vary among colonies up to 16 km apart suggesting a common environmental signal. Means in coral Sr/Ca among the colonies is similar until 1986 when a divergence occurs that does not follow the expected differences due to water depth and growth rate. The two colonies farthest from the mainland (Santiaguillo) have similar means and coral Sr/Ca variations from 1986–1993. In the mid-1980s, Veracruz experienced changes in land use with increased river runoff delivering more sediment to the ocean that could shift seawater chemistry in coastal waters causing the observed coral Sr/Ca divergence in the near shore colonies. Increased sedimentation could stress coral colonies causes different biological responses evident in the coral Sr/Ca records.
Back to: High-Resolution Geochemical Proxies of Global Change: Progress, Problems, and Utility I