Browsing by Author "Kölling, M"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    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
  • Thumbnail Image
    Item
    Millennial to seasonal scale views of El Niño-Southern Oscillation from central Pacific corals
    (Australasian Quaternary Association, 2022-12-06) McGregor, HV; Wilcox, P; Fischer, MJ; Phipps, SJ; Gagan, MK; Wittenberg, A; Felis, T; Kölling, M; Wong, HKY; Devriendt, L; Woodroffe, CD; Zhao, JX; Fink, D; Gaudry, JJ; Chivas, AR
    El Niño-Southern Oscillation (ENSO) is naturally highly variable on interannual to decadal scales making it difficult to detect a possible response to climate forcing. Despite the high variability, several lines of evidence from tropical corals, mollusc, lake sediments, and foraminifera suggest that 5,000-3,000 years ago ENSO variance was on average reduced by 60-80% compared to the present day. We investigate the seasonal-to-centennial variation in ENSO amplitude and tropical climate during this ENSO ‘quiet period’ 5,000-3,000 years ago using a new Sr/Ca SST record from a 175-year-long 4,300-year-old coral, and new d18O and Sr/Ca results from a similar-aged ~180-year-long Porites sp. coral. Both corals were discovered on Kiritimati (Christmas) Island, an optimal ENSO ‘centre of action’ in the central tropical Pacific. Together, these corals confirm a reduction in ENSO amplitude and that ENSO amplitude is modulated on multi-decadal scales. Composites of month-by-month changes in Sr/Ca-SST show an unprecedented view of ENSO and detail which seasonal-scale features of ENSO are an inherent part of the system, and which are subject to change under altered climate states. We also investigate the millennial timescale changes in ENSO variance using combine coral oxygen isotope (18O) data from central Pacific corals and a suite of forced and unforced simulations conducted using the CSIRO Mk3L and GFDL CM2.1 climate system models. On millennial timescales, the coral data reveal a statistically significant increase in ENSO variance over the past 6,000 years. This trend is not reproduced by the unforced model simulations but can be reproduced once orbital forcing is accounted for. Together these views of past ENSO may contribute to advances in understanding the response of ENSO to future changes in climate forcings.
  • Thumbnail Image
    Item
    Millennial to seasonal scale views of El Niño-Southern Oscillation from central Pacific corals
    (2022-12-06) McGregor, HV; Wilcox, P; Fischer, MJ; Phipps, SJ; Gagan, MK; Wittenberg, A; Felis, T; Kölling, M; Wong, HKY; Devriendt, L; Woodroffe, CD; Zhao, JX; Fink, D; Gaudry, JJ; Chivas, AR
    El Niño-Southern Oscillation (ENSO) is naturally highly variable on interannual to decadal scales making it difficult to detect a possible response to climate forcing. Despite the high variability, several lines of evidence from tropical corals, mollusc, lake sediments, and foraminifera suggest that 5,000-3,000 years ago ENSO variance was on average reduced by 60-80% compared to the present day. We investigate the seasonal-to-centennial variation in ENSO amplitude and tropical climate during this ENSO ‘quiet period’ 5,000-3,000 years ago using a new Sr/Ca SST record from a 175-year-long 4,300-year-old coral, and new d18O and Sr/Ca results from a similar-aged ~180-year-long Porites sp. coral. Both corals were discovered on Kiritimati (Christmas) Island, an optimal ENSO ‘centre of action’ in the central tropical Pacific. Together, these corals confirm a reduction in ENSO amplitude and that ENSO amplitude is modulated on multi-decadal scales. Composites of month-by-month changes in Sr/Ca-SST show an unprecedented view of ENSO and detail which seasonal-scale features of ENSO are an inherent part of the system, and which are subject to change under altered climate states. We also investigate the millennial timescale changes in ENSO variance using combine coral oxygen isotope (18O) data from central Pacific corals and a suite of forced and unforced simulations conducted using the CSIRO Mk3L and GFDL CM2.1 climate system models. On millennial timescales, the coral data reveal a statistically significant increase in ENSO variance over the past 6,000 years. This trend is not reproduced by the unforced model simulations but can be reproduced once orbital forcing is accounted for. Together these views of past ENSO may contribute to advances in understanding the response of ENSO to future changes in climate forcings.