DOI: 10.5061/dryad.b8gtht7c3
title: Size normalized shell weights and measurements for Neogloboquadrina pachyderma and Uvigerina peregrina from the Gulf of Alaska (IODP Exp 341) and associated environmental proxy data

description: Here we use volume density (ρV) measurements as a metric of
 size-normalized weights for Neogloboquadrina pachyderma, a planktonic
 foraminifer, from upper OMZ and abyssal depth sites in the Gulf of Alaska
 over the past ~20,000 years to test for covariation between carbonate
 preservation and OMZ intensity. We find that dissolution of N. pachyderma
 is most intense at the upper OMZ site where oxygenation is generally lower
 than at the abyssal site. We also examine Uvigerina peregrina, a benthic
 foraminifer, at the upper OMZ site and find that the lowest ρV
 measurements in both taxa occur during deglacial and early Holocene
 dysoxic events. We use computed tomography images to confirm that changes
 in ρV are related to shell thickness, observe dissolution features, and
 test for growth influences on ρV. Further, we use stepwise selection of
 multiple regression models in which co-registered environmental proxies
 are potential predictors of ρV and find that the best supported models
 retain negative associations between ρV and the concentration of redox
 sensitive metals and the relative abundance of dysoxia-tolerant and
 opportunistic benthic foraminifera, indicating that low ρV is associated
 with low-oxygen conditions and pulsed availability of organic matter at
 the seafloor.  Taken together, our results suggest the primary
 driver of carbonate dissolution here is related to organic carbon
 respiration at the seafloor. This highlights the importance of metabolic
 dissolution in understanding the inorganic carbon cycle and the role
 regions with high organic carbon export, such as OMZs, can have as CO2
 sources as metabolic dissolution intensifies.
description: Data are derived from marine seidment cores from IODP Expedition
 341 Site U1419 and the co-located EW0408-85JC, IODP Expedition 341 Site
 U1418 and the co-located core EW0408-87JC. We weighed
 specimens of each species from each sample in aggregate to the nearest 0.1
 μg using a Sartorius Ultramicro Balance to determine the total weight.
 Individual shell dimensions were digitally measured from 2D images of
 these same specimens using a Nikon SMZ 1500 stereoscope at 30x and the
 software program NIS Elements BR 2.10. To calculate shell volume, we
 approximated <i>N. pachyderm</i>a as a sphere using the
 average of the semi-major axis and semi-minor axis of a hypothetical 2D
 ellipse that encapsulates the shell as the radius of that sphere
 and <i>U. peregrina</i> was approximated as a cylinder. 
 Sample weight was then size normalized to volume by dividing total weight
 by the total volume of the individuals.  Computed
 tomography scans were completed at the University of Texas High-Resolution
 X-ray Computed Tomography Facility (UTCT). Twenty-one samples were imaged
 in 2019 using a Xradia MicroXCT 400 scanner at a resolution of ~1.5 mm. In
 2020, an additional 15 samples were imaged at the UTCT facility using
 Zeiss Versa 620 scanner; these were scanned at a resolution of ~0.04 µm. We then
 measured the shell thickness of each specimen using the thickness mesh
 tool in Dragonfly. This tool calculates thickness as the diameter of a
 hypothetical sphere that fits within the boundary of the shell. The number
 of points measured on each shell varies
 (median=1.36x10<sup>7</sup>; interquartile range (IQR) =
 7.56x10<sup>6</sup> – 2.42x10<sup>7</sup>)
 depending upon the size of the shell and is determined by the Lapalacian
 algorithm that converts the voxel-based shell volume to a triangle-based
 &gt;mesh. This thickness mesh tool produced a minimum measurement
 value of ~4.48 µm for samples scanned
 in 2019 and ~4.32 µm for samples scanned
 in 2020. Chamber volume measurments for <em>U.
 peregrina</em> were done within the CT imaging processing software
 3D Slicer 4.10.2 using the segmentation editor with thresholding, level
 tracing, painting, grow-from-seed, fill between slices, and quantification
 tools. The environmental proxy data associated with
 these measurements and the associated methods were previously published
 in Belanger, C. L., Du, J., Payne, C. R., & Mix, A. C. (2020).
 North Pacific deep-sea ecosystem responses reflect post-glacial switch to
 pulsed export productivity, deoxygenation, and destratification.
 <i>Deep Sea Research Part I: Oceanographic Research
 Papers</i>, 103341. doi.org/10.1016/j.dsr.2020.103341. SST
 values were interpoled 85JC from Praetorius, S. K., Mix, A. C., Walczak,
 M. H., Wolhowe, M. D., Addison, J. A., & Prahl, F. G. (2015).
 North Pacific deglacial hypoxic events linked to abrupt ocean warming.
 <i>Nature</i>, <i>527</i>, 362–366. https://doi.org/10.1038/nature15753. Ages provided are based upon Walczak, M. H., Mix, A. C., Cowan, E. A., Fallon, S., Fifield, L. K., Du, J., et al. (2020). Phasing of millennial-scale climate variability in the Pacific and Atlantic Oceans. <i>Science. </i>https://doi.org/10.1126/science.aba7096 and Du, J., Haley, B. A., Mix, A. C., Walczak, M. H., & Praetorius, S. K. (2018). Flushing of the deep Pacific Ocean and the deglacial rise of atmospheric CO<sub>2</sub> concentrations. <i>Nature Geoscience</i>, <i>11</i>(10), 749–755. https://doi.org/10.1038/s41561-018-0205-6.