Tudhope, A.W.; Chilcott, C.P.; McCulloch, M.T.; Cook, E.R.; Chappell, J.; Ellam, R.M.; Lea, D.W.; Lough, J.M.; Shimmield, G.B.

Tudhope, A. W.: Variability in the El Nino-Southern Oscillation Through a Glacial-Interglacial Cycle, Science, 291(5508), 1511–1517, doi:10.1126/science.1057969, 2001.

Variability in the El Nino-Southern Oscillation Through a Glacial-Interglacial Cycle

Note: floating fossil coral sections have greater uncertainty in absolute temperature for palaeoclimate reconstructions (NJA)

The d18O of the samples was measured at the Fachbereich Geowissenschaften, Universita�t Bremen, on a Finnigan MAT 251 mass spectrometer, calibrated against the NBS-19 standard. Data are corrected for the usual isobaric interferences and are reported in x versus V-PDB.

X-ray diffraction (XRD) and measurements of Mg/Ca. Additional investigations were carried out on thin sections ratios.

; climateInterpretation_seasonality changed - was originally monthly; archiveType changed - was originally Coral (CO)

The top and base of the core section were U/Th-dated (measured at the Institut fur Umweltphysik, Heidelberg, Germany), with a precision of i¿½15 yr. The midpoint of the top dated sample is 14 density band couplets above the profile for geochemical measurements, and the midpoint of the bottom dated sample is seven band couplets below the profile (Fig. 2). In other words, the age model within the chronology is based on the annual banding. According to band couplet counts and the number of annual cycles in the d18O, the U/Th-dated sections differ in age by 104 yr, while the difference is 130 yr according to their radiometric dates (base: 1499, top: 1629 AD). To remove the surplus of 26 yr we adjusted the radiometric ages by adding 13 yr to the bottom and subtracting 13 yr from the top sample age. Therefore, individual years in our record are correct with respect to their positions within the time series, but they do not necessarily match calendar years. Years in the isotopic record are defined by cyclic variations in d18O, which are assumed to be annual, with each cycle spanning ca. 2.5-4 mm core length. Subannual dating is based on the annual d18O cycles, where the most positive d18O value in each cycle is assigned to the coldest average month, which, for Bermuda, is March. This introduces a non-cumulative error of approximately i¿½1 month. The ages of other sampling points were linearly interpolated according to their spatial distances along the sampling profile.