Table of Contents

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

This dataset contains size fractionated rates of 14C-bicarbonate assimilation and the “group-specific” rates of 14C-bicarbonate assimilation.  The group-specific rates were derived from flow cytometrically sorting radiolabeled cells (post-incubation) including Prochlorococcus, Synechococcus, and photosynthetic picoeukaryotes.

These results were published in the following publication:

Rii YM, Karl DM, Church MJ (2016) Temporal and vertical variability in picophytoplankton primary productivity in the North Pacific Subtropical Gyre. Mar Ecol Prog Ser 562:1-18. https://doi.org/10.3354/meps11954 

Seawater was collected in 12-L polyvinylchloride bottles affixed to a 24-bottle rosette sampler, equipped with a Sea-Bird 911+ conductivity, temperature, and pressure profiler. Rates of size-fractionated (>3 μm and 0.2-3 um) and group-specific particulate 14C-based primary production were measured at six discrete depths (5, 25, 45, 75, 100, and 125 m) throughout the euphotic zone.  Seawater samples from each depth were subsampled into triplicate 30-mL polycarbonate centrifuge tubes (Nalgene (TM) Oak Ridge) from a pre-dawn cast, inoculated under subdued light with 70 uL of NaH14CO3- (final activity = ~0.14 MBq/mL; MP Biomedicals 17441H), then incubated over the full photoperiod (~12-14 hours) in white mesh bags affixed to a floating in situ array at the corresponding depths where the water was collected.  At the end of the incubation period (after sundown), each polycarbonate tube was sampled for size-fractionated and group-specific rates of 14C primary productivity. Aliquots (25 µl) were subsampled from each tube and stored in 20-mL glass scintillation vials containing 500 µL of B–phenylethylamine to determine the total activity of 14C added to each sample. Next, 5 mL of each sample was preserved in cryotubes containing 30 uL of 16% (final concentration 0.24% w/v) microscopy-grade paraformaldehyde (PFA, Alfa Aesar 43368), flash-frozen in liquid nitrogen, and stored at -80C for subsequent flow cytometric sorting. The remaining sample volume (~25 mL) was vacuum-filtered first onto a 25-mm diameter 3-μm pore size polycarbonate membrane (Millipore IsoporeTM), then the filtrate was vacuum-filtered onto a 25-mm diameter 0.2-um pore size polycarbonate membrane filter (GE Osmonics). After filtration, each filter was placed into a 20-mL glass scintillation vial and stored at -20C until analyzed back at the shore-based laboratory. Upon return to shore, vials were uncapped, 1 mL of 2 M hydrochloric acid was added to each filter, and vials were vented for at least 24 hours to remove remaining inorganic 14C. After venting, 10 mL of Ultima Gold liquid scintillation cocktail was added to each vial, and vials were placed in a liquid scintillation counter (Packard TRI-Carb 4640) for the determination of 14C activities.  Group-specific rates of 14C-assimilation by Prochlorococcus, Synechococcus, and PPE were determined by measuring the amount of 14C assimilated into populations sorted using the BD InfluxTM (100-μm nozzle tip, 1X BioSure® sheath solution). Calibration of the # of cells sorted was conducted at the beginning of each sorting session; a known number of fluorescent microspherical beads (1 um, Fluoresbrite, Polysciences) were gated through the data acquisition software Spigot, sorted onto a slide, and checked for accuracy under the microscope. The ‘1.0 drop purity’ setting in the Spigot software was utilized as a conservative way of ensuring accuracy of the types of cells sorted into two 6.5-mL HDPE scintillation vials with the ‘two tube sort’ setting. Beads were included with the samples for size reference, and 0.2 x 103 to 4 x 103 beads were sorted for the determination of background levels of radioactivity (both organic 14C in the seawater and 14C absorbed to the beads). Picophytoplankton cells were triggered on forward scatter (FSC) and enumerated based on FSC and side scatter, chlorophyll-based red fluorescence (692 +- 20 nm), and phycoerythrin-based orange fluorescence (585 +- 20 nm) following excitation with two lasers, 488 nm (200 mW) and 457 nm (300 mW). 

BCO-DMO Data Manager Processing Notes:
* added a conventional header with dataset name, PI name, version date
* modified parameter names to conform with BCO-DMO naming conventions
* "na" values changed to "nd" for no data.
* split location column into two columns (lat,lon) in decimal degree format.
* removed the directional (N|W) and made longitude negative for west.
* changed comma delimited bottle list in one column to ; delimited
* added ISO_DateTime_UTC timestamp from date and time columns

(Extracted from NSF award abstract)

Marine phytoplankton are a diverse group of Prokaryotic and Eukaryotic unicellular organisms that account for approximately 50% of global carbon fixation. Nitrogen (N) is an essential element for microbial growth, but concentrations of bioavailable nitrogen in vast regions of subtropical ocean gyres are extremely low (submicromolar to nanomolar concentrations), and generally limit phytoplankton growth. Phytoplankton taxa differ in their genetic capabilities to take up and assimilate nutrients, and thus competition for different chemical forms of N (NH4+, NO3- and urea) and supply of these N-containing compounds are important controls on phytoplankton growth, productivity, and ultimately ecosystem function. The form and supply of N to phytoplankton have already been altered by anthropogenic activities, and with increasing environmental perturbations the effects will accelerate. To date however, there is limited information on how the N forms and fluxes impact the marine phytoplankton community composition and primary production. Similarly, determining the mechanisms of the response are crucial to assessing how ocean ecosystem function will respond to global climate change.

This project seeks to determine how taxonomic, genetic and functional dimensions of phytoplankton diversity are linked with community-level responses to the availability of different N substrates (NH4+, NO3-, and urea) in one of Earth's largest aquatic habitats, the North Pacific Subtropical Gyre. The project will characterize phytoplankton community composition change and gene expression, photosynthetic performance, carbon fixation, and single-cell level N and C uptake in different taxa within the phytoplankton assemblage in response to different N compounds. The research project is unique in investigating community-to-single-cell level function and species (strain)-specific gene expression patterns using state-of-the-art methods including fast repetition rate fluorometry, nanoscale secondary ion mass spectrometry and a comprehensive marine microbial community microarray. The results will provide predictive understanding of how changes in the availability of key nitrogen pools (N) may impact phytoplankton dynamics and function in the ocean.

References:

Karl, D. M., Bjorkman, K. M., Dore, J. E., Fujieki, L., Hebel, D. V., Houlihan, T., Letelier, R. M., Tupas, L. M. 2001. Ecological nitrogen-to-phosphorus stoichiometry at station ALOHA. Deep-Sea Research II. 48:1529 - 1566.

Karl, D. M., Letelier, R., Tupas, L., Dore, J., Christian, J. & Hebel, D. 1997. The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean. Nature. 388:533-538.

McCarthy, J., Taylor, W. R., Taft, J. 1997.  Nitrogenous nutrition of the plankton in the Chesapeake Bay. Limnology and Oceanography. 35:822 - 829.

Letelier, R., Karl, D. M. 1996.  Role of Trichodesmium spp. in the productivity of the subtropical North Pacific Ocean. Marine Ecology Progress Series. 133:263 - 273.

Lipschultz, F. 1995.  Nitrogen-specific uptake rates of marine phytoplankton isolated from natura populations of particles by flow cytometry. Marine Ecology Progress Series. 123:245-258.

(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.