Table of Contents

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

Particle sampling was conducted onboard RRS Discovery (size-fractionated particles) and James Cook (sinking particles) in the Northeast Atlantic (around 49°N, 15°W) during a declining spring phytoplankton bloom in May 2021 as part of the EXPORTS campaign. Particles were collected by in situ pump filtration using large volume pumps (WTS-LV; McLane Research Laboratories, Inc) outfitted with mini-MULVFS (Multiple Unit Large Volume in situ Filtration System) filter holders (Bishop et al., 2012). At 30 meters (m) and 340 m, sequentially stacked filters were loaded on pumps of 5 filter pore sizes: 0.3-1 micrometers (μm) particles (combusted GF75 glass fiber filters), 1-6 μm particles (combusted quartz fiber filters), 6-51 μm particles, 51-335 μm particles, and >335 μm particles (acid-washed Nitex mesh). At 20, 50, 75 or 95, 125 or 145, 175 or 195, 330, and 500 m, filter stacks of two filter pore sizes were loaded onto pumps: 0.8-51 μm particles (Supor polyethersulfone filters) and >51 μm particles (acid-washed polyester mesh). Filters containing particles were stored in combusted foil and kept frozen at -80 degrees Celsius (°C) until further processing on land. Large particles were resuspended off Nitex mesh filters using low-nutrient, 0.2 µm- filtered seawater, and subsequently collected onto 47-mm diameter combusted glass fiber filters, which were then re-frozen, and lyophilized. Lyophilized, large particles (≥6 µm) were examined under a dissecting microscope, and materials that should be excluded from the passively sinking POM pool were removed. Sinking particles were collected using sediment traps, either surface tethered sediment traps (STT) or neutrally buoyant sediment traps (NBST). Sinking particles were collected in polycarbonate tubes with a collection area of 0.0113 square meters (m²). Sinking particles were kept frozen at -80°C until further processing on land, then particles were lyophilized. Lyophilized particles were quantitatively split by weight for bulk isotope analysis and compound-specific isotope analysis of amino acids (CSIA-AA).

Bulk nitrogen concentrations and δ¹⁵N values were determined using standard methods in the Close Laboratory (University of Miami). Subsamples from filters for bulk nitrogen analysis were quantitatively split by weight and packed directly into tin capsules for elemental and isotopic composition.

CSIA-AA preparation was guided by methods of Hannides et al. (2013), Hannides et al. (2020), and Popp et al. (2007) and were identical to those of Wojtal et al. (2023). Samples were hydrolyzed using 6N HCl at 110°C for 20 hours, filtered using disc filters, purified using cation exchange resin (50W-X8, 100-200 mesh, 1 milliliter (mL) bed volume), eluting in 2N ammonium hydroxide, followed by reprotonation using 0.2N HCl at 110°C for 5 minutes, and derivatized to trifluoroacetyl/isopropyl esters in a two-step process (isopropyl esterification and trifluoroacetylation; Popp et al., 2007). Excess salts were removed after derivatization using liquid-liquid extraction (phosphate buffer/chloroform), and samples were put through a second acetylation before storage at -20°C prior to analysis. Immediately before analysis, sample aliquots were dried under N₂ gas and reconstituted in ethyl acetate. All glassware was acid washed (10% HCl) and combusted at 500°C overnight before use.

Bulk nitrogen concentrations and δ¹⁵N values were determined using a Costech Elemental Analyzer (EA) interfaced with a MAT 253 Plus Isotope Ratio Mass Spectrometer (IRMS) via a Conflo IV open split interface. The EA oxidation reactor was held at 980°C, the reduction reactor held at 650°C, and the oven housing the gas chromatography column was held at 65°C. CSIA-AA samples were analyzed using a Thermo Fisher Scientific Trace 1310 Gas Chromatograph (GC) coupled to a MAT 253 Plus IRMS via a Thermo Fisher GC Isolink II system with a combined oxidation/reduction reactor held at 1000 °C, a liquid nitrogen trap, and a Conflo IV open split interface.

δ¹⁵N values (‰ vs. AIR) were calculated by the Thermo Isodat 3.0 software, using reference nitrogen gas peaks. Instrument accuracy was determined by analyzing a mixture of amino acids of known δ¹⁵N values that was prepared alongside samples. Individual amino acid δ¹⁵N values were calculated as the average across replicates, if applicable. The 1σ uncertainty was calculated as the standard deviation across samples replicates, if no replicates were possible (low sample concentration) a 1‰ error was applied. Amino acid concentrations were determined from the IRMS peak area response of individual amino acid standards and the amount of sample injected.

Data were processed through Thermo Fisher Isodat 3.0 and Microsoft Excel. 

- Imported original file "particulate_bulk_AA_d15N.csv" into the BCO-DMO system.
- Flagged "nd" as a missing data value (missing data are empty/blank in the final CSV file).
- Created separate columns for the standard deviation values.
- Converted all date fields to ISO 8601 format or YYYY-MM-DD.
- Saved the final file as "986932_v1_exports_particulate_bulk_aa_d15n.csv".

NSF Award Abstract:
The downward settling of organic material transports carbon out of the ocean surface, as part of a process called the biological pump. However, only a small fraction of organic material produced by organisms in surface waters makes it to the deep ocean. The rest can be fragmented or consumed (respired) by bacteria or larger organisms; the role of each process remains in question. Guided by recent results from the Pacific Ocean, the investigators will use the stable isotopes of carbon and nitrogen in amino acids to identify the input of fresh algal material, zooplankton feces, and bacteria to the biological pump in the North Atlantic spring bloom. With data from contrasting locations, the investigators will test and develop their isotopic models so they can be used to help predict global patterns in carbon transport. The work will be part of a large oceanographic field program (NASA EXPORTS). The tremendous amount of data collected in this program will aid the development and interpretation of the isotopic models. To share results broadly, the investigators will produce and distribute several episodes of Voice of the Sea, a local television program that will air in Hawaii and the Pacific islands. Episodes will be posted online and publicized through social media to the south Florida community. The project will support a Ph.D. student and an undergraduate student at University of Miami, which serves a 25% Hispanic population, and a Ph.D. student and an undergraduate student at University of Hawaii, a designated minority-serving institution.

The proposed work will assess the relative importance of packaging organic matter in fecal material, particle disaggregation, microbial reworking, and zooplankton dietary usage on vertical patterns of particle flux across contrasting oceanic provinces, using empirical methods independent of incubation techniques or metabolic rate measurements. From their existing work in relatively low-flux environments of the Pacific Ocean, the investigators have developed two nascent models: (1) a mixing model that uses the compound-specific isotope analysis of amino acids (AA-CSIA) to estimate the phytodetritus, fecal pellet, and microbially degraded composition of particles, such that the vertical alteration mechanisms and size distribution of these materials can be detected; and (2) an inverse relationship between carbon flux into the deep ocean and the reliance of mesopelagic food webs on small, degraded particles. In this project, the investigators will test these two models by applying the same methods to the recent NASA EXPORTS field study in a high productivity, high flux regime, the North Atlantic spring bloom. The first EXPORTS field study in the subarctic Pacific provided some of the materials from which the models were developed. Application and refinement of the investigators’ newly developed isotopic indicators will enable development of a globally generalized isotopic framework for assessing the degradative history of particulate organic matter and its relationship to mesopelagic dietary resources, including small, microbially degraded particles that are often not accounted for as a metazoan dietary resource. This work capitalizes on existing, comprehensive field programs specifically focused on building a predictive framework relating surface ocean properties to the vertical flux of organic carbon. The proposed work directly addresses EXPORTS Science Question 2: What controls the efficiency of vertical transfer of organic matter below the well-lit surface ocean? The results of this work additionally will provide observational comparisons to global models of carbon flux composition and pelagic food web resources.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

EXport Processes in the Ocean from Remote Sensing (EXPORTS) is a large-scale NASA-led field campaign that will provide critical information for quantifying the export and fate of upper ocean net primary production (NPP) using satellite observations and state of the art ocean technologies.

Ocean ecosystems play a critical role in the Earth’s carbon cycle and the quantification of their impacts for both present conditions and for predictions into the future remains one of the greatest challenges in oceanography. The goal of the EXport Processes in the Ocean from Remote Sensing (EXPORTS) Science Plan is to develop a predictive understanding of the export and fate of global ocean net primary production (NPP) and its implications for present and future climates. The achievement of this goal requires a quantification of the mechanisms that control the export of carbon from the euphotic zone as well as its fate in the underlying "twilight zone" where some fraction of exported carbon will be sequestered in the ocean’s interior on time scales of months to millennia. In particular, EXPORTS will advance satellite diagnostic and numerical prognostic models by comparing relationships among the ecological, biogeochemical and physical oceanographic processes that control carbon cycling across a range of ecosystem and carbon cycling states. EXPORTS will achieve this through a combination of ship and robotic field sampling, satellite remote sensing and numerical modeling. Through a coordinated, process-oriented approach, EXPORTS will foster new insights on ocean carbon cycling that maximizes its societal relevance through the achievement of U.S. and International research agency goals and will be a key step towards our understanding of the Earth as an integrated system.