ALBERT

Description: 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.

Description: In this dataset we present a global compilation of over 1000 sedimentary records of 230Th from across the global ocean at two time slices, the Late Holocene (0-5000 years ago, or 0-5 ka) and the Last Glacial Maximum (18.5-23.5 ka). Data have been screened for age control, errors, and lithogenic corrections. Overall quality levels were computed by summing each record's scores on the individual criteria. A record is optimal if it is based on a chronology that is constrained by δ18O or 14C and it provides both the raw nuclide concentrations and the associated errors. About one quarter of the records in the database achieved this highest quality level. The large majority of the records in the database are good, passing two of the three criteria, while the remaining quarter are of fair or poor quality.

Description: Ocean acidification (OA) is the decline in seawater pH and saturation levels of calcium carbonate (CaCO3) minerals that has led to concerns for calcifying organisms such as corals, oysters and mussels because of the adverse effects of OA on their biomineralisation, shells and skeletons. A range of cellular biology, geochemistry and materials science approaches have been used to explore biomineralisation. These techniques have revealed that responses to seawater acidification can be highly variable among species, yet the underlying mechanisms remain largely unresolved. To assess the impacts of global OA, researchers will need to apply a range of tools developed across disciplines, many of which are emerging and have not yet been used in this context. This review outlines techniques that could be applied to study OA-induced alterations in the mechanisms of biomineralisation and their ultimate effects on shells and skeletons. We illustrate how to characterise, quantify and monitor the process of biomineralisation in the context of global climate change and OA. We highlight the basic principles, as well as the advantages and disadvantages, of established, emerging and future techniques for OA researchers. A combination of these techniques will enable a holistic approach and better understanding of the potential impact of OA on biomineralisation and its consequences for marine calcifiers and associated ecosystems.

Description: Abstract Since the 1980s-1990s, international research efforts have augmented our knowledge of the physical and chemical properties of the Arctic Ocean water masses, and recent studies have documented changes. Understanding the processes responsible for these changes is necessary to be able to forecast the local and global consequences of these property evolutions on climate. The present work investigates the distributions of geochemical tracers of particle fluxes and circulation in the Amerasian Basin and their temporal evolution over the last three decades (from stations visited between 1983 and 2015). Profiles of 230-thorium (230Th) and 231-protactinium (231Pa) concentrations and neodymium isotopes (expressed as εNd) measured in the Amerasian Basin prior to 2000 are compared to a new, post-2000s data set. The comparison shows a large scale decrease in dissolved 230Th and 231Pa concentrations, suggesting intensification of scavenging by particle flux, especially in coastal areas. Higher productivity and sediment resuspension from the shelves appear responsible for the concentration decrease along the margins. In the basin interior, increased lateral exchanges with the boundary circulation also contribute to the decrease in concentration. This study illustrates how dissolved 230Th and 231Pa, with εNd support, can provide unique insights not only into changes in particle flux but also into the evolution of ocean circulation and mixing.