Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Seawater for six shipboard incubation experiments was collected using a surface towfish (Mellett and Buck 2020) at ~2 meters (m) depth on the R/V Roger Revelle between 15 August 2018 and 29 August 2018. Water was prefiltered through a 150-µm mesh to remove large grazers. For incubations (Inc) 1-2 and 4-5, water was homogenized into 20-liter (L) carboys, and three carboys were amended for each treatment indicated in Table 1 (see Supplemental Files), yielding triplicates for each treatment and timepoint sampled. Each carboy was sampled once at the indicated timepoints. Control carboys sampled at the beginning and end of each incubation were unique to the timepoint (i.e., no carboy was resampled over time). For Incs 3 and 6, water was first homogenized into two 20-L carboys, from which 4-L bottles were filled and amended with the treatments indicated in Table 1. Three 4-L bottles were amended for each treatment, and each 4-L bottle was sampled once at the indicated timepoints, yielding triplicates.

Incubations 1 and 4 were carried out for 24 hours, Inc 2 and 3 for 6 days, and Inc 5 and 6 for 8 days (Table 1). The nutrient amendments for each experiment were selected to induce nutrient stress. For Inc 2 and Inc 5, 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 +5 nM ⁵⁷FeCl₃ treatment as "AllButSi".

Dissolved (<0.4 μm) trace metal samples were collected in acid-cleaned 125-milliliter (mL) low-density polyethylene (LDPE, Nalgene) bottles, and acidified to 0.024 M hydrochloric acid (HCl, Fisher Optima). Dissolved trace metal (Fe, Cu, Mn, Co, Ni, Cu, Zn, Cd, Pb) concentrations were determined by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) at the University of South Florida (USF) on an Element XR (Hollister et al. 2020; Burns et al. 2023).

Leachable particulate trace metals were collected on 0.4-μm and 5-μm polycarbonate track etch (PCTE) filters, transferred into 1.5-mL high-density polyethylene (HDPE) snap-cap vials, and frozen at -20 degrees Celsius until processed. Filters were leached in a heated 25% acetic acid leach with a reducing step, "Berger Leach", at National High Magnetic Field Laboratory (NHMFL) to extract the leachable particulate trace metals (Berger et al. 2008). Leachable particulate elemental (P, V, Fe, Cu, Mn, Co, Ni, Cu, Zn, Cd, Pb) concentrations were determined by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) on an Element 2 with the assistance of Dr. Peter Morton of Florida State University (FSU).

Sample analyses for dissolved trace metals and leachable particulate trace metals were performed by Shannon Burns (USF). Detection limits and quality control results are presented in Table 2 (see Supplemental Files).

Data Processing:
Data were processed using ESI SC version 2.9.0.380.

Data Quality Flags:
The standard Ocean Data View (ODV) / SeaDataNet qualifying flags were used (reference all flags at http://vocab.nerc.ac.uk/collection/L20/current/). The notation 'na' = 'not applicable' was used for samples not analyzed.

1: Good Value: Good quality data value that is not part of any identified malfunction and has been verified as consistent with real phenomena during the quality control process. [Used when replicates were in good agreement and/or when dataset agreed with previously published results].
2: Probably Good Value: Data value that is probably consistent with real phenomena but this is unconfirmed. [Used when no replicates or published datasets to compare.]
3: Probably Bad Value: Data value recognized as unusual during quality control that forms part of a feature that is probably inconsistent with real phenomena. [Used when data not oceanographically consistent but replicate analyses agreed.]
4: Bad Value: An obviously erroneous data value. [Used when replicates did not agree].
5: Changed Value: Data value adjusted during quality control. [Not used.]
6: Value Below Detection Limit: The level of the measured phenomenon was too small to be quantified by the technique employed to measure it. Values are replaced with 'nd' for 'not detectable'. [See Table 2 for detection limits.]
7: Value in Excess: The level of the measured phenomenon was too large to be quantified by the technique employed to measure it. The accompanying value is the measurement limit for the technique. [Not used.]

BCO-DMO Processing:
- converted SAMPLE_DATE column to YYYY-MM-DD format;
- renamed fields to comply with BCO-DMO naming conventions.

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.