The structure and drivers of oxygen minimum zone (OMZ) evolution in the Eastern Tropical North Pacific (ETNP) are investigated from ~20.7-10 ka using planktic foraminiferal assemblages alongside multiple other proxies from core MAZ-1E-04 (22°54.29’N, 106°54.59’W; 1463 m depth). Understanding how OMZ vertical structure changed during past glacial/interglacial cycles will help elucidate the drivers and patterns of OMZ expansion/contraction on longer timescales. Planktic foraminifera assemblage counts from core MAZ-1E-04, collected on cruise MAZ-I aboard the R/V El Puma in April 2015, are used here to explore any composition shifts driven by environmental changes. Universidad Nacional Autónoma de México financed ship time and M. Alejandro Rodríguez Ramírez directed the oceanographic campaign to retrieve the core.

Table of Contents

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

Please see Alcorn et al. (2026) for a more detailed methodology.

Core MAZ-1E-04 (MAZ-I E04G) was collected on the oceanographic cruise MAZ-I aboard the R/V "El Puma" on April 28, 2015 using a gravity corer.

Sediments from core MAZ-1E-04 had previously been sampled at 1 cm intervals and washed over a 63 µm sieve. A total of 15 planktic foraminifera assemblages with n > 300 individuals from the > 150 µm size fraction were completed spanning 140.5-51.5 cm (~20.5 to 10 ka). Samples were split using a microfossil splitter into fractions ranging from 1/128 to 3/8. Samples contained between 315 to 762 planktic individuals, and all planktic foraminifera within a given fraction were identified to the species level (Brummer and Kučera, 2022). Relative abundances were calculated for each planktic species by dividing species abundance over total planktic foraminiferal abundance. Some Globorotaloides hexagonus were removed before completing assemblages. The number removed from an entire sample was multiplied by the split picked and added to G. hexagonus counts. 

Species identified and counted in dataset are as follows: 

• Globigerina bulloides (urn:lsid:marinespecies.org:taxname:113434)
• Globigerinoides ruber (white) (urn:lsid:marinespecies.org:taxname:113444)
• Trilobatus sacculifer (urn:lsid:marinespecies.org:taxname:1026286)
• Globigerinita glutinata (urn:lsid:marinespecies.org:taxname:113464)
• Neogloboquadrina dutertrei (urn:lsid:marinespecies.org:taxname:113473)
• Neogloboquadrina incompta (urn:lsid:marinespecies.org:taxname:113474)
• Globorotalia cultrata (urn:lsid:marinespecies.org:taxname:1417053)
• Globorotalia tumida (urn:lsid:marinespecies.org:taxname:418114)
• Globigerinella siphonifera (urn:lsid:marinespecies.org:taxname:113440)
• Orbulina universa (urn:lsid:marinespecies.org:taxname:113460)
• Globoturborotalita rubescens (urn:lsid:marinespecies.org:taxname:113454)
• Globigerinoides tenellus (urn:lsid:marinespecies.org:taxname:418107)
• Neogloboquadrina pachyderma (urn:lsid:marinespecies.org:taxname:113458)
• Turborotalita quinqueloba (urn:lsid:marinespecies.org:taxname:113462)
• Globigerinella radians (urn:lsid:marinespecies.org:taxname:993793)
• Globorotaloides hexagonus (urn:lsid:marinespecies.org:taxname:1026605)
• Globorotalia inflata (urn:lsid:marinespecies.org:taxname:113449)
• Tenuitellita iota (urn:lsid:marinespecies.org:taxname:1567956)
• Pulleniatina obliquiloculata (urn:lsid:marinespecies.org:taxname:221331)
• Globorotalia truncatulinoides (urn:lsid:marinespecies.org:taxname:113453)
• Globorotalia crassaformis (urn:lsid:marinespecies.org:taxname:418113)
• Globigerinoides conglobatus (urn:lsid:marinespecies.org:taxname:113441)
• Globorotalia scitula (urn:lsid:marinespecies.org:taxname:113452) 

- Loaded sheet 1 from "Supplementary Table S2.xlsx" (xlsx format) using the filename as the resource name, treating empty strings and "nd" as missing values
- Renamed 29 fields to remove spaces, parentheses, and taxonomic punctuation (e.g., "Depth (cm)" to "Depth_core", "Age (ybp)" to "Age", "G. bulloides" to "G_bulloides", etc.)
- Exported file as "991444_v1_planktic_foraminifera_assemblages.csv"

- Species and Genus names listed in the Methods section verified as current accepted form on 2026-04-08, using the WoRMs World Registry of Marine Species database with two exceptions:
*Globorotalia crassaformis is unaccepted. The accepted term is Globorotalia (Truncorotalia) crassaformis (urn:lsid:marinespecies.org:taxname:1455327)
*Globorotalia inflata is unaccepted. The accepted term is Globoconella inflata (urn:lsid:marinespecies.org:taxname:1026410)

Our radiocarbon results allow us to identify the presence of mixing or reworking at 37.5 and 39.5 cm. Allochthonous wood fragments observed at 50.5 and 86.5 cm (9.8 and 14.5 ka) support sedimentary disturbances in other areas of the core, potentially contributing to the observed non-linear radiocarbon results. Thus, results from these periods are cautiously interpreted. 

Coverage: eastern Pacific

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.