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.

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 N. pachyderma 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 U. peregrina 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=1.36x10⁷; interquartile range (IQR) = 7.56x10⁶ – 2.42x10⁷) 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 >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 U. peregrina 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. Deep Sea Research Part I: Oceanographic Research Papers, 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. Nature, 527, 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. Science. 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 CO₂ concentrations. Nature Geoscience, 11(10), 749–755. https://doi.org/10.1038/s41561-018-0205-6.