Table of Contents

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

This data was used in Viviani et al (2018). For related research of experimental work done on some of the same cruises and drawn from some of the same experiments but reporting different parameters, see Bottjer et al (2014).

Rates of primary production were assessed using the 14C-bicarbonate incorporation technique. Rates of bacterial production were assessed using incorporation of 3H-leucine. Whole seawater samples from six discrete depths (5, 25, 45, 75, 100, and 125 m) were collected into duplicate acid-washed 20 L carboys. Control carboys were unamended; 43 mL of 1.0 N HCl and 4 mmol sodium bicarbonate were added to a treatment carboy at each depth, to increase the pCO2 to ~750 µatm, while minimizing changes to total alkalinity. Water from control and treatment carboys were then each subsampled into acid washed 500 mL polycarbonate bottles, with triplicate bottles per depth and treatment. To each bottle, was then added ~1.85 MBq 14C-bicarbonate. Water from each depth and treatment was also added to acid-cleaned 40 mL polycarbonate centrifuge tubes, each tube was then inoculated with 3H-leucine to a final concentration of 20 nmol L-1. For each depth and treatment, there was a dark (in a opaque cloth bag) and light incubation. Time zero blanks were immediately subsampled from each tube, by aliquoting 1.5 mL of seawater into 2 mL microcentrifuge tubes each containing 100 µL of 100% TCA. Following addition of radioactive substrates, the bottles and tubes were affixed to a free-drifting array and incubated in situ at the original depth of sample collection from dawn to dusk.

Upon recovery of the array, the total radioactivity added to each primary production sample bottle was determined by subsampling 250 µL aliquots of seawater into scintillation vials containing 500 µL of β-phenylethylamine. 400 mL from each 500 mL sample bottle was filtered at low vacuum (<50 mm Hg) onto 25 mm diameter, 10 µm porosity polycarbonate membrane filters. The filtrate was collected and filtered onto 25 mm diameter 2 µm porosity polycarbonate membrane filters. 100 mL of that filtrate was then filtered onto 25 mm diameter 0.2 µm porosity polycarbonate membrane filters.  Filters were stored frozen in 20 mL scintillation vials until analysis. Analysis consisted of acidification via addition of 1 mL of 2 N hydrochloric acid, and passively venting at least 24 hours in a fume hood to remove all inorganic 14C. Addition of 10 mL Ultima Gold LLT liquid scintillation cocktail and counting on a Perkin Elmer 2600 liquid scintillation counter completed the primary production analysis.

Upon recovery of the array, triplicate 1.5 mL subsamples were removed from each polycarbonate tube for bacterial production rate measurements, and aliquoted into 2 mL microcentrifuge tubes containing 100 µL of 100% TCA. The microcentrifuge tubes were frozen (-20°C) for subsequent processing, following the procedures described in Smith and Azam 1992.

Samples for the determination of dissolved inorganic carbon and total alkalinity were collected from each carboy and analyzed according to the protocols of the Hawaii Ocean Time-series (Dore et al. 2009; Winn et al. 1998). DIC and TA samples were collected into precombusted 300 mL borosilicate bottles. Care was taken to avoid introduction of air bubbles into samples during filling; bottles were allowed to overflow three times during filling. Once filled, samples were immediately fixed with 100 µL of a saturated solution of mercuric chloride; bottles were capped with a grease seal, and stored in the dark for later analysis.

Samples for measurement of fluorometric chlorophyll a were collected according to the protocols of the Hawaii Ocean Time-series; analysis was performed following Letelier et al. (1996).

The North Pacific Subtropical Gyre (NPSG) is the largest ocean ecosystem on Earth, playing a prominent role in global carbon cycling and forming an important reservoir of marine biodiversity. Nitrogen (N2) fixing bacteria (termed diazotrophs) provide a major source of new nitrogen to the oligotrophic waters of the NPSG, thereby exerting direct control on the carbon cycle. Oceanic uptake of CO2 causes long-term changes in the partial pressure of CO2 (pCO2) in the seawater of this ecosystem. Therefore, understanding how carbon system perturbations may influence ocean biogeochemistry is an important and timely undertaking.

In this project, the investigators will examine how natural assemblages of N2 fixing microorganisms respond to perturbations in seawater carbon chemistry. Laboratory and field-based experiments will be placed in the context of monthly time series measurements on the activities and abundances of N2 fixing microorganism abundances. Together, the project will provide insight into the dependence of N2 fixing microorganism physiology on variations in CO2. The broad objectives of the research are: (1) Quantify the responses and consequences of changes in seawater pCO2 on the growth and community structure of naturally-occurring assemblages of ocean diazotrophs; (2) Identify why and how changes in seawater pCO2 influence the growth and carbon acquisition strategies of two model marine diazotrophs (Trichodesmium and Crocosphaera); and (3) Quantify temporal variability in diazotroph community structure and activities at Station ALOHA.

This is a Collaborative Research award.

The Ocean Carbon and Biogeochemistry (OCB) program focuses on the ocean's role as a component of the global Earth system, bringing together research in geochemistry, ocean physics, and ecology that inform on and advance our understanding of ocean biogeochemistry. The overall program goals are to promote, plan, and coordinate collaborative, multidisciplinary research opportunities within the U.S. research community and with international partners. Important OCB-related activities currently include: the Ocean Carbon and Climate Change (OCCC) and the North American Carbon Program (NACP); U.S. contributions to IMBER, SOLAS, CARBOOCEAN; and numerous U.S. single-investigator and medium-size research projects funded by U.S. federal agencies including NASA, NOAA, and NSF.

The scientific mission of OCB is to study the evolving role of the ocean in the global carbon cycle, in the face of environmental variability and change through studies of marine biogeochemical cycles and associated ecosystems.

The overarching OCB science themes include improved understanding and prediction of: 1) oceanic uptake and release of atmospheric CO2 and other greenhouse gases and 2) environmental sensitivities of biogeochemical cycles, marine ecosystems, and interactions between the two.

The OCB Research Priorities (updated January 2012) include: ocean acidification; terrestrial/coastal carbon fluxes and exchanges; climate sensitivities of and change in ecosystem structure and associated impacts on biogeochemical cycles; mesopelagic ecological and biogeochemical interactions; benthic-pelagic feedbacks on biogeochemical cycles; ocean carbon uptake and storage; and expanding low-oxygen conditions in the coastal and open oceans.