Geochemical and isotopic data from the Mendeleev Ridge core HLYHLY0503-11MC8

The data are from samples of core HLYHLY0503-11MC8, which was collected onboard the American research vessel Healy on the Mendeleev Ridge during the Healy-Oden Trans Arctic Expedition (HOTRAX) in summer 2005 (Darby et al., 2005). The core site is located at 83°07.7300N, 174°41.5700W (water depth = 2570 m). The data include dolomite and total carbonate, stable isotope data in planktic foraminifers and bulk (18O and 13C), sand and clay content, in addition to 230Thxs and 231Paxs. Data are reported vs. depth (cm). Methods : The multicore was sampled at half-centimeter intervals. The sediment was dried and ground in an agate mortar. Particle-size analyses were performed from wet sieved sediment in the < 2 mm fraction after disaggregating in an ultrasonic bath for 90 seconds. The disaggregated sediment was analyzed with a laser-diffraction particle-size analyzer (LS13320, Beckman-Coulter™). Laser calibration was verified before and after analyses using three standards Latran 300-0.3 mm, G15-15 mm, and GB500-500 mm). The particle-size data and granulometric statistics were processed with the Gradistat program of Blott and Pye (2001). Percentages of sand and clay data are reported here. The foraminifer samples used for isotopic investigation consist of sieved then hand-picked ~ 80 mg sub-assemblages of Neogloboquadrina pachyderma, i.e., about 10 to 12 shells. Samples were analyzed with a Micromass Isoprime™ isotope ratio mass spectrometer in dual inlet mode coupled to a MultiCarb™ preparation system. CO2 was extracted at 90°C by acidification with 100% concentration H3P04. Measurements were made with an internal reference carbonate material calibrated against the VPDB scale. The analytical reproducibility determined by replicate measurements of the internal carbonate material (UQ6a; dl3C= 2.25‰; d18O = -1.4‰) was routinely better than 0.05 ‰ for both isotopes. Mineralogical assemblages were determined by X-ray diffraction using a Siemens D5000 with CoKa2 radiation and Si detector. Aliquots of dry bulk sediment were dispersed in distilled water and then sieved on a 63 mm mesh. Following this sieving, the samples were then sieved on a 10 mm mesh. Each sample was placed on an X-ray diffractometer three times, one with no specific treatment, one heated, and one with an ethylene-glycol treatment. Semi¬ quantitative estimations N (s ~ 5%) of the main mineral species were based on the area of the diffraction peak for each mineral corrected for quartz. The carbonate fraction reported here is defined as the sum of calcite and dolomite contents. The methods for 230Th measurements, 230Th excess, and 231Pa excess calculations are described in Not and Hillaire-Marcel (2010). The 230Th excess data are already archived in PANGAEA (https://doi.org/10.1594/PANGAEA.914619). Blott, S.J., Pye, K., (2001) Gradistat: a grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth Surface Processes and Landforms 26, 1237-1248. Darby, D.A., Jakobsson, M., Polyak, L. (2005). Ice breaker expedition collects key Arctic seafloor and ice data. EOS Transactions American Geophysical Union 86, 549-552. Not, C., Hillaire-Marcel, C. (2010) Time constraints from 230Th and 231Pa data in late Quaternary, low sedimentation rate sequences from the Arctic Ocean: an example from the northern Mendeleev Ridge. Quat. Sci. Rev. 29, 3665–3675.