Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • Problem Description
• Parameters
• Project Information
• Program Information
• Funding

Free floating, unpoisoned surface tethered sediment traps were used to quantify fluxes of sinking particles at St P2  (16.5ºN 107ºW) in January 2017, deployed from the R/V Sikuliaq on cruise SKQ201617S. Trap depths ranged between 69 m and 965 m, and trap deployments ranged between 21 and 91 hours with deeper traps deployed for longer. Traps were deployed in arrays of two traps per line. Two types of traps were deployed: 1) in shallow waters (<150 m), traps with a solid plastic cone top (0.46 m² opening area) were used, 2) in deep waters (>150 m), net traps (1.24 m² opening area) modeled from (Peterson et al., 2005) were used. For both types of trap, the cod end had bottoms that were open during deployment and during an 8 hour equilibration period at the target depth performed to remove oxygen contamination. Cod ends were closed with a gate valve, using a pre-programmed electronic dissolving link (burn wire) system controlled by an onboard Arduino microcontroller to start collection at the correct depth, and a second gate valve that closed the top of the cod end before retrieval. The aspect ratio, or height/trap mouth diameter, of the net traps was 2.5 while the aspect ratio of the cone traps was 0.6. These two types of traps have been shown to collect material with similar efficiency when normalized by opening area (Cram et al., 2022). No salt solution was used with these traps and no poisons were used in any chamber.

Some trap deployments functioned as simple sediment traps, and some deployments were combined trap and in situ incubators. The combined trap incubators consisted of upper and lower chambers. The material used to calculate fluxes reported here was collected from the upper chamber and was not incubated.  Sinking material was collected in the lower incubation chamber, then isolated by closed a gate valve and injected with ¹⁵N-NO₂^- . While the incubation occurred (in situ), sinking material was collected in an upper chamber that never encountered the spiked material. However, we do not report d¹⁵N natural stable isotopes for the sediment trap material here due to proximity to the incubation. 

After every deployment, sediment trap material was filtered onto pre-combusted GF-75 filters (0.3 µm nominal pore size). To conform to community standards, zooplankton carcasses were not included in the measurements of carbon and nitrogen flux. Filter samples (particles only) were wafted with HCl overnight to remove carbonate, dried at 40°C, packed into silver foil cups, and sent to the University of Washington Isolab facility in the Department of Earth and Space Sciences (Seattle, WA) for C and N analysis utilizing an Costech elemental analyzer  attached to an isotope ratio mass spectrometer (ThermoFinnegan MAT 253).

ug C and N were converted to fluxes in Microsoft Excel using the area of the trap opening and the duration of the deployment. 

Extracted from the NSF award abstract:

Marine oxygen deficient zones (ODZs) are waters that are functionally devoid of oxygen. Without oxygen, some microbes are capable of converting nitrogen in the water into N2 gas, which then leaves the ocean and enters the atmosphere. This loss of an important nutrient from the ocean has impacts on phytoplankton growth and marine food webs. While oxygen deficient zones occupy a very small percentage of the ocean, they account for as much as half of the oceanic loss of N as N2. Moreover, the size of these regions is predicted to expand during this century due to climate change. The microbes that are capable of producing N2 gas are extremely diverse, and use several different biochemical pathways to carry out this process. They may occur both free-floating in the water and attached to small particles that are suspended or sinking from the surface waters and providing them a carbon source. However the importance of these two lifestyles (free-living vs particle attached) in terms of contributions to N loss from the oceans is not well understood. This project will identify the major organisms that result in N2 gas production on both suspended and sinking particles, the chemical reactions they carry out, and the rates at which this occurs. This information will be used to improve global climate models to better predict rates of N loss in a future ocean. Elementary and middle school teachers enrolled in a Masters in Science for Science Teachers program will be involved in the project and the graduate students and post-doctoral researchers supported by the project will have opportunities to participate in their classrooms. Underserved populations will also be integrated into the research at the undergraduate and middle school level through a series of summer internships.

ODZs have very complex elemental cycles, implying great microbial diversity. Intertwined with the microbial complexity of ODZ regions is the relatively unexplored interplay between free-living bacteria and those living on either suspended or sinking particles. Determining how these communities and niches interact and relate is one of the most challenging components of ODZ system studies today. Current climate models portray the dynamics of particles in the ODZs and throughout the deep ocean through prescribed functions based on sparse data from the oxic ocean with microbes represented only by the net chemical reactions of the community. However, in reality a phylogenetically and metabolically diverse group of microbes, likely acting in consortia, are responsible for the nitrogen transformations that ultimately result in the production of N2. To explore the processes maintaining the genetic diversity and functional redundancy in N loss processes, four research areas will be integrated: the community phylogenetic diversity (both taxonomic and genomic diversity) the genetic diversity of the proteins that carry out key N transformation processes (as seen through quantitative proteomics), the resulting biogeochemical functions (15N labeled nitrogen transformation rate measurements) and predictions about how this diversity and corresponding function may change in response to climate change (biogeochemical modeling). The approach will be to assay both phylogenetic (16S rRNA tag sequencing) and functional genetic diversity (genomics) on sinking particles collected using large-volume sediment traps. Phylogenetic and genomic studies will be intimately tied to measurements of activity - who is doing key biogeochemical transformations (proteomics) and what are the in situ rates at which they are doing them (using novel incubation systems). Data will then be used to model how diversity and corresponding function change on a range of time and space scales, from the sinking of a single particle to seasonal cycles. To understand the relationship of community diversity and function on suspended and sinking particles, a series of three cruises will be conducted in the Eastern Tropical North Pacific ODZ.

(adapted from the NSF Synopsis of Program)
Dimensions of Biodiversity is a program solicitation from the NSF Directorate for Biological Sciences. FY 2010 was year one of the program.  [MORE from NSF]

The NSF Dimensions of Biodiversity program seeks to characterize biodiversity on Earth by using integrative, innovative approaches to fill rapidly the most substantial gaps in our understanding. The program will take a broad view of biodiversity, and in its initial phase will focus on the integration of genetic, taxonomic, and functional dimensions of biodiversity. Project investigators are encouraged to integrate these three dimensions to understand the interactions and feedbacks among them. While this focus complements several core NSF programs, it differs by requiring that multiple dimensions of biodiversity be addressed simultaneously, to understand the roles of biodiversity in critical ecological and evolutionary processes.