Sedimetological, geochemical and isotopic evidence from of the Bering and Chukchi Seas during the last deglaciation.

Summary Description 
This dataset was used to aid interpretations of past productivity, terrestrial input and circulation , based on d13Corg, %TOC, bulk d15N, %Norg, Corg/Norg, elemental X-ray fluorescence (XRF) data, grain size analysis, bulk density and magnetic susceptibility data.  Also included are color data.

Contacts 
Ben M. Pelto, Research Assistant, UMass Amherst, investigator who collected the data, peltoglacier@gmail.com, bpelto@umass.edu (will expire before 2015) 
Julie Brigham-Grette, Principal Investigator, UMass Amherst, juliebg@geo.umass.edu
Steven Petsch, Co-PI, UMass Amherst, spetsch@geo.edu

Background 
This data was collected in addition to sea ice data and biomarker data collected by Jim Kocis, UMass Amherst. 
  
Detailed Data Description 
There are four types of data, isotope, grain size, GEOTEK core scanner, and XRF elemental data, as well as core images.  Each type of data has a file for each core, i.e. there are 5 grain size files, each labelled for a specific core.  Some data, like isotopic data, have only four files, as no isotopic data was collected from 28JPC.  Gaps in the GEOTEK data file are a result of gaps in sediment recovery, or major cracks within the core.  Data files are in .csv format. 

Data Acquisition and Processing 
Age Models: The 14C ages were calibrated using Clam version 2.2 [Blaauw, 2010] operated in the free open-source statistical software R (version 3.0.2; R Development Core Team, 2013) using the Marine13 calibration curve [Reimer et al., 2013].  All age-depth models were created in Clam using linear interpolation for minimal investigator bias.  While dated sedimentary units such as laminations match well with regional studies, we present our data with the caveat that reservoir age could have fluctuated by a few hundred years at certain points of the record, particularly around what we define as 18 ka.

Non-destructive Analysis: All archive-half sections of our cores were logged at UMass on both a Multi-Sensor Core Logger (MSCL, GEOTEK), and an XRF core scanner (ITRAX, COX Analytical Systems).

		Elemental XRF: The ITRAX XRF core scanner provides high-resolution elemental composition and X-Radiograph images [Löwemark et al., 2008].  ITRAX (high-resolution continuous micro fluorescence-X core scanner) uses an intense non-destructive micro X-ray beam that irradiates the sample to collect positive X-ray images (contact author if interested in the radiograph images), and detects the energy of fluorescent radiation in order to provide high-resolution relative concentration of elemental profiles (from Al to U).   ITRAX analyses are measured on a 4 mm-wide and 0.1 mm-thick area.  The XRF output data is an intensity given in counts per second (cps) with an average value around 19 kcps for our cores.  Any measurement point with fewer than 10 kcps, was not considered, and any points with Validity=0 were also not considered (Validity generally is zero when kcps was below 10k).  Radiograph images were taken with an exposure time of 1600 ms at a voltage of 60 kV, and a 50 mA current.  XRF exposure time was 10 s at a voltage of 30 kV and a 55 mA current.  XRF data were analyzed at 1000 micron scale, and though data was taken at 200 micron in laminated sections, 1000 micron scale was chosen for consistent analysis and interpretation.  Without quantitative mineralogy [Viscosi-Shirley et al., 2003; Eberl, 2004], we do not interpret XRF elemental count data as quantitative or exact, merely as a general descriptor of relative changes in sediment composition. (For a detailed description of the ITRAX core scanner see Croudace et al. [2006])  There is a hiatus in data in 3JPC from 856.7-893.2 cm due to an unknown error that went unnoticed. 

		MSCL Data: The MSCL obtained magnetic susceptibility (MS), gamma ray attenuation density, spectral properties, and high-resolution images.  Magnetic susceptibility was measured using a point sensor (MS2E, Bartington) mounted on an arm that allows the sensor to be placed on the core surface for each measurement. The point sensor has a field of influence of about 1 cm in diameter.  The bulk density for the GEOTEK is GRAPE bulk density (gamma ray attenuation porosity evaluator); obtained using a Cesium 137 gamma source which emits a narrow beam of collimated gamma rays with energies at 0.662 MeV.  A color spectrophotometer (CM-2600d, Konica Minolta) measured reflectance in the near UV through the visible spectrum and just into the near IR range (wavelengths 360–740 µm).  MS, density, and color data were all recorded at 0.5 cm resolution.

Destructive Analysis–Sampling: The sediment cores were sampled for biogeochemical and isotopic data, as well as grain size analysis using 1 cm diameter sediment plugs.  3JPC was sampled at 10 cm resolution in massive sections and 5 cm resolution in both laminated intervals and the top meter of the core for isotopic and grain size analyses.  24JPC was sampled at 5 cm resolution in the upper two meters of the core (1 m for grain size) and 10 cm throughout the remainder.  51JPC was sampled at 10 cm resolution for grain size, and 2 cm resolution from 124–242 cm and 4 cm from 242–420 cm, only for d13Corg and %TOC.  17JPC was sampled at 10 cm resolution.  
		
		Elemental Isotopic Analyses: Bulk biogeochemical properties include d13Corg, d15N, %TOC, %Norg and C/N ratios measured on an Isotope Ratio Mass Spectrometer (IRMS) with a Sercon GSL and Gilson gas auto-sampler prep unit (PDZ-Europa 20/20). The isotopic data were measured by the Stable Isotope Research Unit of the Department of Crop and Soil Sciences at Oregon State University, Corvallis, OR.  Samples were freeze-dried and then ground to a fine powder before being treated with 1 M HCl to remove carbonate for samples used to measure d13Corg and %TOC [Ramnarine et al., 2011].  The samples were then mixed with deionized water, centrifuged and excess water was removed by pipette.  This process was repeated five or more times, until reaching a neutral pH, after which the samples were left to air dry.  Samples were then heated in an oven at 50°C and placed in a container with desiccant to keep moisture from contaminating the samples.  The samples were encapsulated in tin capsules (Elemental Microanalysis D1008 or D1010). For all four cores we used ~150µg total C (15 mg of sample) for d13Corg, and %TOC.  Replicate analyses indicated a standard deviation of 0.91 wt% for %TOC, and 0.09‰ for d13Corg.  For d15N, %N and %TC, each sample had about 75 µg total N (55 mg sample).  Replicate analyses indicated a standard deviation of 0.24‰ for d15N, and 0.26 wt% for %N.  
	
		Organic Carbon Isotopes (d13Corg): The d13Corg of marine sediments is often used to estimate the relative amounts of terrigenous and marine organic carbon in sediment organic matter (OM) using a linear mixing model of terrigenous and marine OM [Hedges and Parker, 1976; Shultz and Calder, 1976; Prahl et al., 1994; Addison et al., 2012; Trefry et al., 2014], according to the following equation: %OC_terr(fraction) = (d13C_sample - d13C_mar) / (d13C_terr-d13C_mar) The value obtained from this equation (OCterr) is then used to calculate the %TOCterr:  %TOC_terr = %TOC_sample - (%OC_terr × %TOC_sample)	Depleted d13Corg values (-26 to -28) are typical of terrigenous OM using the C3 pathway of photosynthesis [Stein and Macdonald, 2004], as seen in the following regions: Mackenzie Beaufort terrigenous end-member: -26.5 to -27‰ [Naidu et al., 2000], Russian Rivers draining taiga/tundra: -26.5‰ [Lobbes et al., 2000], Yukon: -26 to -28‰ [Guo and Macdonald, 2006], Gulf of Alaska: -26‰.  Marine d13Corg is generally assumed to be <-25‰ [Grebmeier et al., 1988], with average marine phytoplankton values of -19 to -22‰ [Fontugne and Jouanneau, 1987; Meyers, 1994].  We chose -27‰ for terrigenous OC and -21‰ from marine OM based on the above cited values, and for consistency with studies from the Bering and Chukchi Seas [Walsh et al., 1989; Naidu et al., 1993, 2000, 2004; Trefry et al., 2014], and the Gulf of Alaska [Addison et al., 2012].
	
		C/N Ratios and %Norg: We calculated C/N ratios for 3JPC 17JPC, and 24JPC, as no nitrogen analyses were performed on 51JPC.  Arctic sediments have been known to have relatively high amounts of inorganic nitrogen bound to clay minerals (Nbou) [Stein and Macdonald, 2004], which can bias C/N ratios which are interpreted as "Corg/Norg".  To better represent source materials, we plotted %TOC (x) versus %TN (y), where the y-intercept represents Nbou (Figure 2.4) [Schubert and Calvert, 2001; Stein and Macdonald, 2004]. We estimated %Norg using the following equation: %N_org = %N - %N_bou  Where %Nbou is the intercept from Figure 2.4.  
	
		Grain Size Analysis: Grain Size (GS) analyses were performed at the Marine Sediments Lab of Iowa State University, using laser diffraction (Malvern Mastersizer 3000) to measure particle size from 0.01–3500 µm.  Prior to running the samples, a 3M solution of sodium hexametaphosphate (SHMP) was added to the dry material to deflocculate the clay, and then the vial was agitated.  Sodium carbonate (0.05 moles) was added when making the SHMP to increase the pH to 8.  Samples for grain size analysis were not treated to remove carbonates, organics, or siliceous organisms [Aiello and Ravelo, 2012], and are thus representative of bulk grain size. 

Data Files List:
	GEOTEK data: 3JPC_Geotek.csv, 24JPC_Geotek.csv, 17JPC_Geotek.csv, 51JPC_Geotek.csv, 28JPC_Geotek.csv
	Isotopes data: 3JPC_iso.csv, 24JPC_iso.csv, 17JPC_iso.csv, 51JPC_iso.csv
	XRF elemental data: 3JPC_XRF.csv, 24JPC_XRF.csv, 17JPC_XRF.csv, 51JPC_XRF.csv, 28JPC_XRF.csv
	Grain size data: 3JPC_GS.csv, 24JPC_GS.csv, 17JPC_GS.csv, 51JPC_GS.csv, 28JPC_GS.csv
	Images: JPC3_Sec1_R_1350-1441cm...total of 25 core images
	
Headers List by File
	Isotopes_Pelto.csv
		Depth(cm):core depth, Age(ka):cal ky BP, Weight(mg):sample weight after carbonate removal, total C(ug):total C in micrograms,	%Corg:organic carbon percent weight, d13Corg: per mill carbon isotope using PBD standard, %OCterr: estimated terrestrial organic carbon, %OCmar:estimated marine organic carbon,...gap delineates a separate isotope run on samples without carbonate removal...%TN:Total nitrogen percent weight, %Norg:organic nitrogen (explanation above), total N(ug):weight total nitrogen, d15N: Nitrogen isotope using air standard, C/N:organic carbon to organic nitrogen ratio
	XRF_data_Pelto.csv
		Elements in counts per second, a measured intensity.
	Grainsize_all_Pelto.csv
		Median Grain Size(µm),	Clay(%):0-4µm,	Silt(%):4-62µm,	Sand(%):63-3100µm
	GEOTEKdata_all_Pelto.csv
		MS: Magnetic Susceptibility (( x 10-6) SI), Density: GRAPE bulk density (gcm^3), X Y Z:XYZ color, L* a* b*: CIE color (L*, a*, b*), Red Green Blue:Spectra summed over each default bin, 360 370...:spectrophotometer bin e.g.(0-360) (360-370)
	Images i.e...JPC3_Sec1_R_1350-1441cm, where JPC3 is the core, Sec1 = section 1, and the depth is the core depth, thought to be depth below sea floor.  R indicates a ruler
		was included next to the image.

References and Related Publications 
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Acknowledgements 
This work was funded by the National Science Foundation Arctic Natural Sciences ARC 1023537 grant, "Late Quaternary Sea Ice history of the Beringian Arctic Gateway".
Document Information 

Author: Ben M. Pelto 6/28/2014