Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Detailed methodology for MOCNESS tows can be found in Wishner et al. (2018). Briefly,  a 1 m² MOCNESS fitted with 222 micron nets was used to collect vertically stratified environmental data and plankton samples (9 nets per tow, 0-1000 m, 25-100 m intervals).  Some tows also targeted oxygen minimum zone features. Nets were rinsed with filtered seawater and whole samples were preserved in 4% sodium-borate buffered formaldehyde. 

Detailed methodology for sample preparation and analysis can be found in Davis et al. (2023). Foraminifera with intact cytoplasm were isolated from tow material to ensure samples were living at the time of collection. Shells of G. hexagonus were subjected to oxidative cleaning: shells were bathed individually in a 1:1 mixture of NaOH and H₂O₂ for 10 minutes, then rinsed in deionized water. Shells were then mounted on carbon conductive tape on a glass slide. Trace element analysis was completed at the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University using a laser ablation system (Photon Machines 193 nm ArF laser with an ANU HelEx dual-volume laser ablation cell, 65 mm spot size, a 4 Hz rep rate, and a fluence of 0.85 J cm^-2) coupled to an iCAP quadrupole ICP-MS. Standards NIST 610 and NIST 612 were ablated every 10 samples. 

Ablation data were processed using LATools software (Branson et al. 2019).

* Table "all_ablations.csv" was imported into the BCO-DMO data system with values "NA" as missing data values. 
** Missing data values are displayed differently based on the file format you download.  They are blank in csv files, "NaN" in MatLab files, etc.

* Column names adjusted to conform to BCO-DMO naming conventions designed to support broad re-use by a variety of research tools and scripting languages. [Only numbers, letters, and underscores.  Can not start with a number]

* decimal places rounded from 18 to 8 places.

* Columns added from dataset supplemental metadata table.
* Columns added from supplemental table: date_time_UTC, Lat_In, Lat_Out
* Columns added to this dataset by joining column "MOCNESS_cast" and string "tow" "net" and "foram" with supplemental metadata table "MOCNESS_cast" "net" and "foram".

NSF abstract: 

Oxygen minimum zones (OMZs) are naturally occurring regions of low oxygen found across large swaths of the ocean at depths of 100 to 1000 meters below the surface. OMZs play an important role in biogeochemical cycling and ecosystem function and any change in the expanse of their low oxygen waters can have far reaching implications for marine life and valuable fisheries resources. Marine oxygenation is variable on multiple timescales in response to global climate change, with recent observations showing that OMZs have expanded over the past half century. This project will explore promising new geochemical and morphologic proxies applicable to low-oxygen environments in the planktic foraminifer Globorotaloides hexagonus, a unicellular calcifying organism whose fossil record in seafloor sediments is well suited to reconstructing past low-oxygen environments in the water column. The project will focus on the extensive OMZ of the eastern tropical Pacific. The first goal is to evaluate and calibrate the targeted measurements for modern G. hexagonus collected live in plankton tows. The second goal is to apply these proxies to fossil specimens in sediment cores to generate records of glacial-Holocene change. The outcomes will be useable proxies for generating records of the OMZ environment, and a better understanding of how a major regional OMZ changed during the most recent period of rapid climate change. Both outcomes represent important progress towards understanding natural oscillations in the OMZ as well as modeling and planning for a changing OMZ in the face of global climate perturbations. The project will provide opportunities for undergraduate researchers as well as support a female early career researcher. 

The marine sedimentary record is the most promising archive from which to reconstruct long term marine oxygenation. However, significant limitations exist in the available proxies for low oxygen marine environments. This project aims to address this need by evaluating and applying a range of promising geochemical (trace element and stable isotope) and morphologic (area-density and porosity) proxies relevant to low oxygen environments in the planktic foraminifer Globorotaloides hexagonus. The project will develop viable proxies based on the morphology and geochemistry of G. hexagonus shells previously collected in depth-distributed MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System) tows from the eastern Pacific. The results from this proxy development in modern shells will then be ground-truthed and applied to two already well characterized sediment cores from the Mexican Margin and Panama Basin that span from the Last Glacial Maximum through the Holocene. The sediment records will be used to reconstruct past conditions in the eastern tropical Pacific OMZ, where significant questions about glacial-interglacial oxygenation persist. This research will lead to a more mechanistic understanding of how OMZs respond to climate more broadly.