Browsing by Author "Tudhope, AW"

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    Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements
    (John Wiley & Sons, Inc, 2013-07-25) Hathorne, EC; Gagnon, A; Felis, T; Adkins, J; Asami, R; Boer, W; Caillon, N; Case, D; Cobb, KM; Douville, E; deMenocal, P; Eisenhauer, A; Garbe-Schönberg, D; Geibert, W; Goldstein, S; Hughen, K; Inoue, M; Kawahata, H; Kölling, M; Cornec, FL; Linsley, BK; McGregor, HV; Montagna, P; Nurhati, IS; Quinn, TM; Raddatz, J; Rebaubier, H; Robinson, L; Sadekov, A; Sherrell, R; Sinclair, D; Tudhope, AW; Wei, GJ; Wong, HKY; Wu, HC; You, CF
    The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1. ©2013 American Geophysical Union
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    Morphological variation, composition and age of submerged reefs on the Great Barrier Reef
    (Geological Society of Australia, 2010-07-04) Abbey, E; Webster, JM; Jacobsen, GE; Thomas, AL; Henderson, G; Reimer, PJ; Braga, JC; Tudhope, AW; Beaman, RJ; Bridge, T; George, N
    Coral reefs are powerful indicators of environmental changes, such as sea level, salinity and sea surface temperature fluctuations. Many sites within the Indo‐Pacific and the Caribbean have been investigated, yet the Great Barrier Reef (GBR) remains largely under‐represented in early deglacial, Late Pleistocene records. IODP Expedition 325 Site Survey (Proposal 519) returned with 4200 km2 of high‐resolution multibeam bathymetry of submerged reef features on the shelf edge, revealing extensive terraces, barrier reefs, lagoons, pinnacles and palaeo‐channels. Fossil coral reef specimens were collected from these features (in situ and loose) at depths ranging from 45–160 m and dated using 14C AMS and U‐Th. Preliminary results suggest the morphology of the features and the timing of drowning are influenced by a number of complex factors, possibly including, but not limited to variations in sea level, latitude, shelf width, local weather patterns and reef community composition.