Dataset: Coral calcification histories
Deployment: Palau_reefs_2011-13

Coral skeletal core collection: We collected 101 skeletal cores from massive Porites coral colonies at ten reef sites representing two major reef environments, barrier reef and lagoon, the latter including fringing reefs around the uplifted karst Rock Islands. The two environments are broadly distinguishable in both physical (flow, temperature, and light regimes) and chemical (carbon system parameters, salinity) characteristics with generally higher flow, light, pH, and salinity and lower SST on the barrier reefs (Shamberger et al. 2014; Barkley et al. 2015).

Skeletal cores (20-40 cm in length) were collected in April 2011, September 2011, April 2012, August 2014, and January 2015 vertically from live coral colonies at 1-6 m depth using pneumatic drills with 3.8 cm diameter diamond drill bits. Core holes were filled with cement plugs hammered flush with the colony surface and sealed with underwater epoxy. Visual inspections of colonies 6-12 months after coring revealed significant overgrowth of plugs and no long-term impacts to the corals. Coral cores were oven-dried and scanned with a Siemens Volume Zoom Helical Computerized Tomography (CT) Scanner at Woods Hole Oceanographic Institution. 3-D CT scans of coral cores were analyzed using OsiriX freeware to visualize the 3-D image (Cantin et al. 2010; Crook et al. 2013) and an automated MATLAB code to quantify skeletal growth parameters and stress banding (DeCarlo et al. 2015). 

Coral calcification histories: Annual calcification rates were calculated as the product of annual linear extension and density following the automated procedure described in DeCarlo et al. (2015), which traces density variations along individual corallites identified within the entire 3-D core. Extension rates (upward linear growth) were measured between the successive low-density bands of annual high-low density couplets. Annual density banding was clearly represented in all cores, with low density bands formed at the beginning of each year (c. February) and high-density bands accreted toward the mid-to-late months of the year (c. September). Band identifications were verified using cross-dating, a dendrochronology technique in which shared years of lower growth rates are identified and matched across core records (Fritts 1976; Yamaguchi 1991). Annual skeletal densities were calculated from CT scan intensities converted to calcium carbonate density values using nine coral standards (0.81-1.54 g cm-3), where independent measurements of weight and volume for each standard were used to derive a linear relationship between CT scan intensity values (in Hounsfield units) and calcium carbonate density (in g cm-3) (DeCarlo et al. 2015).