DOI: 10.25921/axwt-t745
title: NOAA/WDS Paleoclimatology - Healy-Oden Trans Arctic Expedition(HOTRAX) Grain Size, XRF, and Reflectance Data

description: Sediment clay and silt mineral assemblages provide an excellent means of assessing the provenance of fine-grained Arctic sediment especially when a unique mineral assemblage can be tied to specific source areas. The diffuse spectral reflectance (DSR) first derivative measurements and quantitative X-Ray Diffraction (qXRD) on a high-resolution sediment core from the continental slope north of Alaska constrain the sediment mineralogy. DSR results are augmented by measurements on several adjacent cores and compared to surface sediment samples from the northern Alaskan shelf and slope. Using Principal Component Analysis (PCA), we infer that the three leading DSR modes relate to mixtures of smectite + dolomite, illite + goethite, and chlorite + muscovite. This interpretation is consistent with the down core qXRD results. While the smectite + dolomite, and illite + goethite factors show increased variability down core, the chlorite + muscovite factor had highest positive loadings in the middle Holocene, between ca. 6.0 and 3.6 ka. Because the most likely source of the chlorite + muscovite suite in this vicinity lies in the North Pacific, we argue that the oscillations in chlorite + muscovite values likely reflect an increase in the inflow of Pacific water to the Arctic through the Bering Strait. The time interval of this event is associated in other parts of the globe with a non-linear response of the climate system to the decrease in insolation, which may be related to changes in water exchange between the Pacific and Arctic Ocean.
description: The Grainsize measurements were generated as follows: Dried sample measured with a Malvern Mastersizer 200 equipped with an MU; Size fraction = <63um. Samples were pre-sieved with a #18 screen mesh to prevent larger particles from becoming stuck in the instrument. Sample were run in triplicate and averaged for each sample, with each measurement set to integrate for 5 minutes. Irregular particle shape model; Mie theory; index of Refraction = quartz; Opacity =1.
 
Header information is as follows: expedition name and number core number, core device (TC = trigger core; PC = piston core), section number, depth in core in cm. Thus the header for the HOTRAX Leg 1 expedition sample from Core 7PC section 1, 1 cm is as follows: HLY 0501 7JPC 1 1

The reflectance measurements were generated as follows: Dried sample measured with an ASD labspec Pro FR UV-VIS -NIR analyzer; Size fraction = <63um; sample integration = 250 spectra per measurement; Sample size: >250 mg sediment wet filtered onto a 0.4 um GF/F filter, oven dried at 60 deg C overnight. Comparison of sample and blank values indicated that the sediment sample was sufficiently thick to block absorption of reflectance from the GF/F filter and thus required no blank correction. Reflectance values are stored in files labeled by core name, samples are identified by depth in core (columns) and wavelength (rows).

The XRF elements measurements were generated as follows: Measurements were conducted at Ohio State University or Kent State University using the Kent State University Innov-X alpha series Handheld XRF scanner. Measurements were conducted in soils mode with concentration determined by the default Compton scattering mode with a 60-90 second integration time merging standard and light element mode measurements. All values are reported as ppm
 
The reported values are the raw average value +/- 1 sigma. When the internal variability was greater than 3 sigma, the mean value is reported in the 1-sigma error column and flagged as below the limit of detection in the raw column. Values listed as "adjusted" include the best estimate of the <LOD values as the mean value in the adjusted column. The 1-sigma error is identical for these samples and is listed in the 1-sigma error column. The data was post-processed at Kent State to extract signal from the adjusted values using a varimax rotated, principle component analysis (VPCA). VPCA was used to extract the coherent part of all measurements from the data by partitioning measurement from noise. Information on these methods are reported in the MS thesis by Siriwardana cited below. The values used as input for the VPCA are tabulated as adjusted values in the data table. Additional information about sample collection can be found from the data report, cruise website and thesis work by Chandawimal H.E.R. Siriwardana at KSU