Reef Core Data from the Hawaiian Islands for Analysis of El Nino control of Holocene Reef Accretion, 2000-2002 (NODC Accession 0000901)

Drill cores were collected at all locations except Mana Reef, Kauai, using a diver operated Tech 2000 submersible, hydraulic rotary coring drill with a 7.6 cm diameter diamond-studded drill bit. Wireline (NQ2) drill system components were added and the entire system attached to the seafloor using a tripod and center mast for stability. This configuration was utilized at the Kailua site to recover 6 cm diameter cores up to 18 m in length. Cores were collected at water depths from +2 to -34 m and sampled for petrographic, mineralogic, and radiometric analysis. Accuracy of sample depths within cores varied depending on the drilling method used and porosity of reef material. Kailua sample depth uncertainties averaged 0.03-0.1 m but were as high as ~1 m for two highly porous sections. Those from Punaluu averaged ? 0.3 m, with higher uncertainties from unconsolidated reef flat cores. The reef in Molokai, particularly at the Hikauhi site, is more porous than those at the Oahu sites, yielding a mean depth of certainty of ? 0.6 m. Limestones from core samples were classified according to Dunham's (1962) scheme, as modified by Embry and Klovan (1971). Logistical considerations precluded drilling at Mana, Kauai. However, vertical faces ~10 m high expose fossil reef growth. Hand samples were collected at a range of depths and locations along exposed faces by divers using hammers and chisels. Sample depths, recorded from digital depth gauges, have an uncertainty of 0.3 m. Radiocarbon and X-ray diffraction (XRD) sample material was cleaned with ddH2O in an ultrasonic cleaner until the supernatant was clear. Organic material was removed in a 15% H2O2 bath, followed by a second series of ddH2O baths. A 15% HCl acid etch was performed in house or at the radiocarbon analysis facility to eliminate any final contamination, typically removing 10%-40% of the material. Oven drying at 38 C and weighing of samples completed the preparations. Carbonate mineralogy was determined using a Scintag Pad Vpowder X-ray diffractometer using Cu K radiation. Calcite-to-aragonite composition ratios were determined using a standard curve generated from the peak area ratios (111 aragonite peak, 104 calcite peak) of known mixtures of aragonite and calcite (Sabine, 1992). Mole percentages of MgCO3 of calcite phases were determined using the offset of the d spacing of the 104 calcite peak from that of pure calcite (Bischoff et al., 1983). Radiocarbon ages were determined at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) at Woods Hole, on samples with >97.5% aragonite (corals) or >12 mole % MgCO3(coralline algae). Ages were corrected for isotopic fractionation by NOSAMS using ?13C values. Calibration to calendar years for Kailua and Mana samples was done with the INTCAL Calibration data set (Stuiveret al., 1998) and Calib 4.12 program (Stuiver and Reimer, 1993). A regional marine reservoir correction of 115 calendar years for regional Hawaiian marine waters was used (Stuiver and Braziuman, 1993). Samples from Molokai and Punaluu were calibrated with Calib version 4.3 and a regional marine reservoir correction of 220 +- 100 (Dye, 1994) was applied for Punaluu samples. Benthic community structure was surveyed at the Molokai and Oahu sites using a modification of the line intercept technique. Dominant substrate types and descriptions along replicate transect lines were recorded on preprinted survey forms by scuba divers, at increments of 0.1 m. Corals and coralline algae encountered were identified to the species level and described in terms of colony size and morphology. Surveys were conducted across a range of depths and habitats to gain an understanding of present day patterns of reef building organism recruitment and growth.