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
• Program Information
• Funding

Seawater for five shipboard incubation experiments was collected using a surface towfish (Mellett and Buck 2020) at ~2 meters (m) depth on the RSS Discovery between 5 May 2021 and 26 May 2021. All experimental setup and sampling was conducted in a trace metal clean (TMC) lab using TMC methods. Water was prefiltered through a 150-micrometer (µm) mesh to remove large grazers. For all incubations, 20-liter (L) acid-cleaned carboys were filled in sets based on the replicate number (e.g. replicate 1 carboys for all treatments were filled in succession). For LT1, individual carboys were completely filled prior to filling the next. For all other experiments carboys were filled "round robin", filling each 1/3 at a time until all replicates in the set were full. Triplicate control and treatment carboys were amended for each experiment as indicated in Table 1 (see Supplemental File "EXPORTS_2021_dy131_table1.pdf"). In addition, triplicate T0 carboys were also collected. T0 carboys were sampled immediately after the experimental start. Control and treatment carboys were sampled at the end of each incubation. T0 carboys are shared between LT2 and ST2 experiments.

Short-term incubations were carried out for 24 (ST1A and ST2) and 42 hours (ST1B). Long-term incubations were carried out for 6 (LT1) and 5 (LT2) days (Table 1). Short-term nutrient amendment treatments were selected to alleviate potential in situ nutrient stress. The +Si and +N treatments were amended to final concentrations of 20 micromolar (µM) silicate and nitrate respectively, in addition to in situ nutrient concentrations. The +Fe treatment was amended to a final concentration of 0.005 µM ⁵⁷Fe. The long-term experiments were amended with all key macro and trace nutrients (N, P, Si, Fe) except one, with the aim of inducing a specified nutrient stress. For LT1 and LT2, we refer to the +20 μM nitrate +1.25 μM phosphate +20 μM silicic acid treatment as "AllButFe" and the +20 μM nitrate +1.25 μM phosphate +0.005 µM ⁵⁷Fe treatment as "AllButSi".

Nutrient samples were filtered through 0.2 μm polycarbonate filters and frozen at -20 degrees Celsius (°C). Samples for biogenic silica concentrations were size fractionated by serial filtration through 5 μm and 0.6 μm polycarbonate filters Filters were stored frozen at -20°C. Particulate organic carbon and nitrogen were measured on samples from experiments examining the effect of added Fe and Si on carbon fixation. These samples were filtered through precombusted GFF filters placed in glass scintillation vials and frozen at -20°C.

Biogenic silica concentrations were determined by NaOH digestion followed by colorimetric analysis of the resulting dissolved Si. Particulate organic carbon and nitrogen samples were analyzed by Dumas combustion. Nutrient concentrations were determined by flow injection using a Lachat Instruments QuikChem 8500 Series 2 analyzer.

Metatranscriptomes were sequenced for experiments LT1 and ST1B. Metatranscriptomic samples were collected on 5 μm 47-millimeter (mm) polyester (PETE) membrane filters using a peristaltic pump. Filters were then preserved in 2 milliliters (mL) of RLT buffer (RNeasy Mini Kit, Qiagen, Germantown, MD, USA), flash frozen in liquid nitrogen, and stored at -80°C until RNA extraction. PolyA selection was performed on sample libraries to enrich for eukaryotic sequences and libraries were sequenced on an Illumina NovaSeq 6000 platform.

For more information on nutrient, particulate, and chlorophyll measurements see the Protocol documents attached as Supplemental Files and https://msi.ucsb.edu/facilities-services/analytical-lab/services.

Values below detection limits are left blank and flagged in the quality columns, detection limits are as follows:

Nitrate (NO3) + Nitrite (NO2): 0.1 µM

Nitrite (NO2): 0.1 µM

Phosphate (PO4): 0.1 µM

Silicic Acid (Si(OH)4): 0.1 µM

- Imported original file "EXPORTS_dy131_experiments.xlsx" into the BCO-DMO system.
- Renamed fields to comply with BCO-DMO naming conventions.
- Saved the final file as "948590_v1_exports_dy131_experiments.csv".

NSF Award Abstract:
This project focuses on a group of microscopic single-celled photosynthetic organisms in the ocean called diatoms. Diatoms float in the surface ocean as part of a group of organisms collectively called phytoplankton. There are thousands of different species of diatoms distributed across the global ocean. A famous oceanographer Henry Bigelow once said "All fish is diatoms" reflecting the importance of diatoms as the base of the food chain that supports the world's largest fisheries. Despite their small size, diatom photosynthesis produces 20% of the oxygen on earth each year. That's more than all of the tropical rain forests on land. The major objective of the research is to understand how the metabolic differences among diatom species affects the amount of diatom organic carbon that is carried, or exported, from the surface ocean to the deep ocean. As diatoms are photo-synthesizers like green plants, their biological carbon comes from converting carbon dioxide dissolved in seawater from the atmosphere into organic forms. Diatoms also require a series of other nurtrients supplied by the ocean such as nitrogen and phosphorous and, uniquely for diatoms, the silicon used to construct their glass shells. This research will investigate how genetic and physiological differences among diatoms influence how each species react to changes in nutrient levels in the ocean and how those shifts affect the export of diatom carbon to the deep sea. The link between diatoms' physiological response and their carbon export comes about because shifts in physiology affect diatom attributes like how fast they sink and how tasty they are to predators. So if we can relate the physiological condition of different diatoms to the food-web pathways followed by different species, we can ultimately use knowledge of diatom physiological status and food web structure to predict how much diatom carbon gets to the deep sea. The research involves investigators with expertise in the physiology and genomics of diatoms and in the ocean's chemistry. The work will initially take place in the subarctic North Pacific in conjunction with the NASA Export Processes in the Ocean from RemoTe Sensing (EXPORTS) field program. The EXPORTS program is using a wide variety of methods to quantify the export and fate of photo-synthetically fixed carbon in the upper ocean. The research supports the training of undergraduate students, graduate students and a postdoctoral scholar. The research will also serve as the basis for activities aimed at K-12 and junior high school students.

The research will broadly impact our understanding of the biology of the biological pump (the transport of photo-synthetically fixed organic carbon to the deep sea) by forming a mechanistic basis for predicting the export of diatom carbon. It is hypothesized that the type and degree of diatom physiological stress are vital aspects of ecosystem state that drive export. To test this hypothesis, the genetic composition, rates of nutrient use and growth response of diatom communities will be evaluated and supported with measurements of silicon and iron stress to evaluate stress as a predictor of the path of diatom carbon export. The subarctic N. Pacific ecosystem is characterized as high nutrient low chlorophyll (HNLC) due to low iron (Fe) levels that are primary controllers constraining phytoplankton utilization of other nutrients. It has been a paradigm in low Fe, HNLC systems that diatoms grow at elevated Si:C and Si:N ratios and should be efficiently exported as particles significantly enriched in Si relative to C. However, Fe limitation also alters diatoms species composition and the high Si demand imposed by low Fe can drive HNLC regions to Si limitation or Si/Fe co-limitation. Thus, the degree of Si and/or Fe stress in HNLC waters can all alter diatom taxonomic composition, the elemental composition of diatom cells, and the path cells follow through the food web ultimately altering diatom carbon export.

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.