Table of Contents

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

Experiments on (operationally defined) particles were carried out by gravity-filtering water through 3 um pore size filters. Bacterial protein production was measured from ³H-leucine incorporation by heterotrophic bacteria.

See Niskin Bottle and Cast List EN556 to link specific casts and bottles to each experiment: https://www.bco-dmo.org/dataset/717427.

Seawater was transferred to 20 L carboys that were rinsed three times with water from the sampling depth. Experiments on (operationally defined) particles were carried out by gravity-filtering water through 3 um pore size filters. Fractions of the filters (1/8 of each filter) was incubated in autoclaved seawater from the same depth/station; bacterial protein production was calculated to account for the volume of seawater that had passed through the filter.

Bacterial protein production was measured from 3H-leucine incorporation by heterotrophic bacteria using the cold trichloroacetic acid (TCA) and microcentrifuge extraction method [as in Kirchman, 2001]. All work was performed aboard ship. In brief, triplicate live samples of 1.5 mL seawater as well as one 100% (w/v) TCA-killed control were incubated with 23 uL of L-[3,4,5-3H(N)]-Leucine (PerkinElmer, NET460250UC) for between 4 and 24 hours in the dark at as close to in situ temperature as possible. Live samples were then killed with 89 uL of 100% (w/v) TCA and centrifuged (10,000 rpm at 4°C for 10 min) to pelletize cell material.  The supernatant liquid was removed and 1 mL of 5% (w/v) TCA solution was added, followed by vortex mixing and centrifugation. Supernatant removal, mixing, and centrifugation were repeated using 1 mL of 80% ethanol solution.  Finally, the supernatant liquid was removed and each sample was dried overnight.  After drying, 1 mL of scintillation cocktail (ScintiSafe 30% Cocktail, Fisher SX23-5) was added and incorporated radioactivity was measured using an LSA scintillation counter (PerkinElmer Tri-Carb 2910TR). Leucine incorporation rate was calculated from the incorporated radioactivity, compared to 1 mL of scintillation cocktail spiked with 23 uL of L-[3,4,5-3H(N)]-Leucine radioactivity, divided by incubation time.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- converted lat and lon to decimal degrees
- added cruise_id column
- replaced 'NA' and blank cells with 'nd' (no data)
- removed from display the following columns with no data: NO2_NO3_uM, NH4_uM, PO4_uM, DOC_uM, cells_per_mL

NSF Award Abstract:
Heterotrophic microbial communities are key players in the marine carbon cycle, transforming and respiring organic carbon, regenerating nutrients, and acting as the final filter in sediments through which organic matter passes before long-term burial. Microbially-driven carbon cycling in the ocean profoundly affects the global carbon cycle, but key factors determining rates and locations of organic matter remineralization are unclear. In this study, researchers from the University of North Carolina at Chapel Hill will investigate the ability of pelagic microbial communities to initiate the remineralization of polysaccharides and proteins, which together constitute a major pool of organic matter in the ocean. Results from this study will be predictive on a large scale regarding the nature of the microbial response to organic matter input, and will provide a mechanistic framework for interpreting organic matter reactivity in the ocean.

Broader Impacts: This study will provide scientific training for undergraduate and graduate students from underrepresented groups. The project will also involve German colleagues, thus strengthening international scientific collaboration.