DOI: 10.25921/cwb8-6d95
title: NOAA/WDS Paleoclimatology - Chukchi Sea Holocene Rock Magnetic Data

description: We present a high-resolution Holocene sedimentary record of environmental variability from the eastern Chukchi Sea. An ice-rafted debris bearing silty-clay marks the deglacial to post-glacial Holocene transition at this site and is dated at 9.7 ka. An interval of oscillating magnetic parameters from 9.5 to 8.7 ka coincides with the Holocene Thermal Maximum in the western Arctic, and is manifested at the study area as pulses of fine-grained magnetite input every 180-230 years, possibly from increased river discharge or stronger currents flowing over the core site.  The magnetic mineral assemblage is very uniform over the last 8.2 ka and consists of a mixture of magnetite, titanomagnetite, and a magnetic phase that we tentatively identify as the magnetic iron sulfide greigite.  The amount of magnetic iron sulfides increases up through the Holocene, a trend that is controlled by the amount of marine organic matter available to fuel bacterial sulfate reduction.  The median destructive field of the Natural Remanent Magnetization (MDFNRM) displays centennial to millennial scale cycles with significant variance at periods of 900–1300 and 1700–2700 years, with intervals of high MDFNRM values coinciding with indicators of greater sea ice cover [McKay, J., de Vernal, A., Hillaire-Marcel, C., Not, C., Polyak, L., Darby, D., 2008. Holocene fluctuations in Arctic sea-ice cover: Dinocyst-based reconstructions for the eastern Chukchi Sea. Can. J. Earth Sci. 45, 1399–1415]. The MDFNRM is controlled by the variable abundance of iron sulfides formed during early diagenesis. We interpret intervals of high MDFNRM values as times of stronger water column stratification, during which the pyritization process was interrupted by the lack of marine organic matter and lack of reactive iron. Intervals of low MDFNRM values, which coincide with indicators of reduced sea ice cover, are interpreted as times of stronger vertical mixing of the water column, which allows fresh marine organic matter and reactive iron to reach the seafloor, driving the pyritization process to completion.
description: The dataset consists of rock magnetic parameters, 
which are sensitive to sea ice cover, paleoproductivity, 
and post depositional diagenesis along the Chukchi-Alaska 
margin. Piston Core HLY05-01 JPC5 and its trigger core TC5 
were collected from the eastern Chukchi Sea, North of Barrow, 
Alaska during cruise 05–01 of the USCGC Healy. The parameters 
include low-field magnetic susceptibility (X-LH), 
coercivity (Hc), saturation remanence (Mr), saturation 
magnetization (Ms), saturation remanence normalized by 
saturation magnetization (Mr/Ms), high-field magnetic 
susceptibility (Xhf), ferromagnetic susceptibility (Xf), 
coercivity of remanence (Hcr), coercivity of remanence 
normalized by coercivity (Hcr/Hc), S-ratio, saturation 
remanence normalized by low-field susceptibility (Mr/X), 
median destruction field of the natural remanent 
magnetization (MDF-NRM), anhysteretic remanent 
magnetization (ARM), median destructive field of the 
anhysteretic remanent magnetization (ARM-MDF), 
saturation isothermal remanent magnetization (SIRM), 
and anhysteretic remanent magnetization normalized 
by saturation isothermal remanent magnetization (ARM/SIRM). 
The parameters MDF-NRM, ARM, MDF-ARM, and SIRM were measured 
on U-channel subsamples on 2G-Enterprises Model 760R u-channel 
magnetometer at the University of Florida, Gainesville, FL. 
Low-field mass-normalized magnetic susceptibility (XLF) 
of dry samples was measured on an AGICO KLY-4 Kappabridge 
in an applied field of 300 A/m. Ferromagnetic susceptibility (XF) 
was calculated by subtracting the high-field slope (XHF) 
of the magnetization (M) vs. applied field (H) curve 
measured on a vibrating sample magnetometer from XLF. 
Magnetic hysteresis measurements were made on a Princeton 
Measurements Corp. micro-Vibrating Sample Magnetometer 
model 3900-04 at Montclair State University, NJ. 
Hysteresis loops were measured in a peak field of 1 T 
and field increments of 5 mT. Raw data were processed 
by using XHF, calculated from 0.7 to 1 T, to remove the 
paramagnetic contribution to the induced magnetization, 
and then normalized by dry mass. The hysteresis parameters 
saturation magnetization (Ms), saturation remanence (Mr) 
and coercivity (Hc) were determined from the paramagnetic- 
corrected data. The coercivity of remanence (Hcr) was 
determined through the DC-demagnetization of a saturation 
isothermal remanent magnetization imparted in a 1 T field. 
The S-ratio was measured by imparting a 1 T isothermal 
remanent magnetization, followed by the application of 
a 300 mT backfield, and calculating Mr(300mT)/MR(1T). 

A combination of 210Pb dating and Accelerator Mass Spectrometer (AMS) 
radiocarbon dating of calcareous shells was used to construct the 
depth-age model for TC5 and JPC5.