Browsing by Author "Linsley, BK"

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    Has nitrogen supply to coral reefs in the south Pacific Ocean changed over the past 50 thousand years?
    (John Wiley & Sons, Inc, 2019-03-28) Erler, DV; Shepherd, BO; Linsley, BK; Nothdurft, LD; Hua, Q; Lough, JM
    Tropical islands can facilitate surface ocean biological productivity by enhancing the supply of nitrogen to the euphotic zone. Yet in the world's most oligotrophic oceanic region, the South Pacific Subtropical Gyre (SPSG), this “island mass effect” appears diminished. If this is the case, where did island coral reefs in the SPSG get their nitrogen from, and has this changed over time? Here we use coral skeleton isotopes (δ15N and δ18O) and element/Ca ratios to identify the sources of nitrogen to a late Pleistocene coral reef in the SPSG (Cook Islands); we then compare these results to modern corals in the same region. The supply of nitrogen to the late Pleistocene reef appears dominated by upwelling of subsurface nitrogen during cool dry events, supplemented with nitrogen from island-induced N2 fixation (27 ± 3%) during warm wet periods. For the modern corals, N2 fixation supplies nitrogen to the island reefs during cool dry periods with groundwater providing nitrogen during wet periods. We propose that the subsurface supply of nitrogen to the modern reefs has declined as a result of reduced upwelling but this supply has been replaced with increasing nitrogen discharge from groundwater and an increase in island-induced N2 fixation. ©2019 American Geophysical Union
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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