Table of Contents

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

Water samples were collected via Niskin bottles mounted on a rosette, equipped with a CTD aboard R/V Endeavor cruise EN584 from Jun to Jul 2016 in the Northwest Atlantic. 

Seawater was transferred to 20 L carboys that were rinsed three times with water from the sampling depth and then filled with seawater from a single Niskin bottle, using silicone tubing that had been acid washed then rinsed with distilled water prior to use. From each carboy, water was dispensed into smaller glass containers that were cleaned and pre-rinsed three times with water from the carboy prior to dispensing. This water was used to measure cell counts, bacterial productivity, and the activities of polysaccharide hydrolases, peptidases, and glucosidases. A separate glass Duran bottle was filled with seawater from the carboy and sterilized in an autoclave for 20-30 minutes to serve as a killed control for various measurements.

For each substrate, three 15 mL falcon tubes were filled with bulk seawater and one 15 mL falcon tube was filled with autoclaved seawater to serve as a killed control. Experiments on (operationally defined) particles were carried out by gravity-filtering water through 3 µm pore size filters.  1/12th sections of the 3 µm pore-size filters were submerged in 15 mL artificial seawater.  Substrate was added at 3.5 μM monomer-equivalent concentrations, except for fucoidan, which was added at 5 μM concentrations (a higher concentration was necessary for sufficient fluorescence signal). Two 15 mL falcon tubes – one with seawater and one with autoclaved seawater – with no added substrate served as blank controls. Incubations were stored in the dark at as close to in situ temperature as possible.

Subsamples of the incubations were collected at time zero, and at a sequence of subsequent time points. At each time point, 2 mL of seawater was collected from the 15 mL falcon tube using a sterile syringe, filtered through a 0.2 μm pore size syringe filter, and stored frozen until analysis.

Molecular weight distributions were determined by sequential size-exclusion chromatography using a Bio-Rad Econo-Column packed with ~20 cm of Sephadex G-50 resin followed by ~18 cm of Sephadex G-75 resin, and quantified on Shimadzu 10ADvp HPLC systems equipped with Hitachi fluorescence detectors controlled by EZStart software. Hydrolysis rates were calculated based on the change in molecular weight distribution from higher molecular weight initially to lower molecular weight of the substrate over the course of the incubation time, as described in detail in Arnosti (2003). 

Data was processed using R software. Scripts to calculate hydrolysis rates are available in the associated Github repository (Hoarfrost, 2017).

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.