DOI: 10.25921/2wvj-j882
title: NOAA/WDS Paleoclimatology - Line Islands Survey and Coring Cruise Multi-sensor Track, Isotope and Radiocarbon Data

description: Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).
description:  Cruise MGL1208 data to characterize the sediments on the Line Islands Ridge and collect sediment cores suitable for paleoceanographic research.
 
 ISOTOPE METHODS:
  Cores 15GC, 18GC, 20BB, 28BB, 31BB, 34BB, 35BB, 37BB (Georgia Tech):
 Samples were dried overnight at 65°C, weighed, washed through 63 µm sieve with dionized water, and the washed samples were then dried overnight at 65°C.  Fifteen specimens of G. ruber (white) were picked from the 250-355 µm size fraction and analyzed on a Thermo MAT253 with Kiel IV individual acid bath device.  Values were converted to PDB via NBS-19 and an in-house standard, and NBS-18 values were monitored in each run.  Replicate analyses of the in-house standard mixed in the sample runs yielded a 1-sigma standard deviation of .05‰ for d18O and 0.01‰ for d13C.

 Cores 6BB, 10GC, 11GC, 12GC, 17PC, 17TC, 19GC, 30BB (LDEO):
 Samples were processed and analyzed at LDEO by Allison Jacobel with oversight by Polissar.  Samples were freeze-dried, washed through a 63 µm sieve and the >63µm fraction dried at 45 °C overnight.  Seven or eight specimens of G. ruber (white) were picked from the 250-355 µm size fraction, weighed and analyzed on a Thermo Delta V with Kiel IV individual acid bath device.  Values were calibrated to the VPDB isotope scale with NBS-19 and NBS-18.  Reproducibility of the in-house standard (1-sigma) is ±0.06 ‰ (d18O) and ±0.04 ‰ (d13C).

 Use and Attribution
 These data are provided for the development of age models and as preliminary data for developing research projects on the MGL12-08 cores.  The data and plots provided here may be freely used in funding proposals with appropriate attribution.   Isotope data should be attributed as unpublished data, with this web site as the reference.  Before using these data in a publication, please contact Jean Lynch-Stieglitz or Pratigya Polissar for further details and updates.
 Isotope Analysis Strategy
 Given the limited amount of time and number of analyses possible we strove to maximize the available stratigraphic information from the cores collected during MGL1208 as follows.

 1)    We used the very abundant planktonic foraminifera G. ruber to minimize picking time.  However, this foraminifera can be more susceptible to dissolution effects than more robust foraminifera and the timing of surface water changes limits the precision to which these isotope records can be matched to a global benthic stack. 
 2)    We established 2 benchmark cores at the northern and southern portions of the transect (17PC, 37BB).  As measured using the MST, these cores had density changes with depth that were typical for the cores taken during the cruise.  For these cores we measured the oxygen isotopic composition from top to bottom of the core.
 3)    All cores that had a clear match in MST density with the benchmark cores were not sampled and analyzed for oxygen isotopes. 
 4)    For the remaining cores that did not have a clear match in MST density with the benchmark cores, we analyzed the top 240cm of the core.   We did not analyze cores that contained sediments at the top or near the top that were late Pleistocene in age based on the biostratigraphy performed on board (see cruise report for details).

  Radiocarbon Data:
  Measurements were made at NOSAMS.  Please consult their website for details on methods.
  
  Use and Attribution: Radiocarbon data are provided for the development of age models and as preliminary data for developing research projects on the MGL12-08 cores.  The data and plots provided here may be freely used in funding proposals with appropriate attribution.   Radiocarbon dates should be attributed as unpublished data, with this web site as the reference.  Before using these data in a publication, please contact Jean Lynch-Stieglitz or Pratigya Polissar for further details and updates.