Table of Contents

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

Macrofauna and megafauna were collected in May and October 2019 using the HOV Alvin and the ROV Doc Ricketts, respectively, at Station M; and in July 2019, January 2020, and July 2020 using ROV Lu'ukai at Station Aloha. Macrofauna at Station M were collected using HOV-operated Ekman cores (20x20 centimeters (cm)). Macrofauna at Station Aloha were collected using a Brenke epibenthic sled towed across the seafloor due to the considerably lower macrofaunal densities at this oligotrophic site. Megafauna were collected using the submersible vehicle's manipulator arm and/or slurp gun. Upon retrieval to the surface, samples were placed in a cool room (5 degrees Celsius (ºC)) for further processing. Specimens of megafauna were weighed and measured, then they were dissected using a scalpel. All tissue samples were placed in cryovials and frozen in liquid nitrogen, and subsequently stored at -80ºC. Sieved (300 micrometers (um)) macrofauna samples were preserved in 10% buffered formalin. In the laboratory, macrofauna were further sorted by taxon. Samples of megafauna body tissues or macrofauna were freeze dried and ground to a homogenous powder using mortar and pestle.

Sediment samples were taken with ROV-operated push cores and sliced into 1 cm sections. Frozen samples were freeze dried, acidified, and then used for isotopic analysis. Sediment traps were McLane Parflux traps using formalin fixed collection cups varying from 10 to 30 day sample integration. Swimmers were removed from the samples under a dissecting microscope prior to concentration, freeze drying, and acidification for isotopic analysis.

Compound specific isotopic analysis of amino acids followed the protocols outlined in Hannides et al 2013.

- Imported original file "Abyssal food web AACSIA.xlsx" into the BCO-DMO data system.
- Flagged "NA" as a missing data value. Missing data are empty/blank in the final CSV file.
- Converted date fields to YYYY-MM-DD format.
- Converted positive Longitude values to negative (to indicate the direction is west).
- Renamed fields to comply with BCO-DMO naming conventions.
- PI provided updated copy of file named as "922789_v1_compound_specific_isotope_dataV2.csv".
- Imported the new file, "922789_v1_compound_specific_isotope_dataV2.csv", into the BCO-DMO system; converted dates and renamed fields as described above.
- Saved the final file as "922789_v1_compound_specific_isotope_data.csv".

NSF Award Abstract:
The abyssal plains of the oceans cover roughly half of the earth's surface, host enormous reservoirs of biodiversity and mineral resources, and play important roles in nutrient recycling and carbon sequestration. The most important process controlling the structure and function of these ecosystems is the quantity and quality of food (mostly sinking organic particles) that reaches the deep-sea floor. However, we do not fully understand the processes provisioning this vast ecosystem. We propose to evaluate the relative importance of small and larger "marine snow" particles that sink to deep-sea benthic communities by using the stable isotope signature of amino acids within various food sources and trace their consumption by fauna on the seafloor. This project compares ecosystems from the productive waters off California with the nutrient poor central Pacific, north of Hawaii. This project provides novel insights into how surface ocean processes are coupled to food-webs at the deep ocean seafloor and how changes in food sources potentially impact deep-sea communities. This project also provides excellent training opportunities for graduate students, a postdoctoral researcher, and undergraduates at UH and USC, particularly underrepresented minorities who pursue majors in the geosciences. The project will sponsor an annual G6-12 teacher workshop to inform Hawaii educators about the deep sea and broadly disseminate knowledge to the community. All results are communicated broadly to inform the public as concerns regarding abyssal ecosystems are rising due to interests in deep-sea mining.

The most important process controlling the structure and function of abyssal ecosystems is the quantity and quality of organic material that ultimately reaches the deep-sea floor. Despite the strong relationship between euphotic zone export flux and benthic ecology, studies of abyssal ecosystems have observed a deficit between food supply and benthic community demand. Additional work is therefore needed, particularly with regards to understanding the sources of nutrition to the deep-sea benthos. Recent evidence suggests that small particles may be significant contributors to carbon export, increasing in relative importance with depth in the mesopelagic and reaching the abyssal seafloor. This project is to evaluate the relative importance of small and larger "marine snow" particles to deep-sea benthic communities using a combination of particle flux measurements and state of the art compound specific stable isotope analysis of amino acids (AA-CSIA) at two abyssal locations that contrast in overlying productivity, seasonality, and export magnitude. Time series measurements at these locations (Sta. M off California and Sta. Aloha off Hawaii) provide a rich context for the work. In the mesopelagic central North Pacific larger particles (>53 um) can be resolved from microbially reworked, smaller (0.7-53 um) particles using AA-CSIA. This project is characterizing the isotopic compositions of key individual compounds in a continuum of particle sizes (< 1.0 um suspended particles to large sinking particles >53 um) collected using in situ filtration near the seafloor and bottom-moored sediment traps, thereby defining source-specific isotopic signatures that can be traced into benthic fauna and sediments (that are collected by ROVs and epibenthic sleds). This research to understand pelagic-benthic coupling from particles to megafauna using isotopic measurements at the compound-level will yield novel insights into the importance of small microbially reworked particles to deep-sea benthic food webs. This will more precisely couple surface ocean processes to food-webs at the deep ocean seafloor with implications for understanding climate change effects and the efficiency of energy transfer to higher trophic levels. Furthermore, isotopic measurements can also be used to further parameterize ecosystem models by quantifying trophic position across size classes and thus estimate predator-prey mass ratios in relation to variation in body size spectra, functional type, and ultimately to carbon flux and remineralization. Finally, the results will help refine interpretations of deep-sea paleorecords of past nitrogen dynamics by calibrating potential changes in organic matter isotope values between the surface and seafloor archives.

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.