Table of Contents

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

Bacterial activity as measured by hydrolysis rates from unfiltered seawater and particle-associated communities collected near shore in northeastern Greenland in August 2015.

Using a small boat, samples were collected in 20L carboys in Tylerfjord-Young Sound. Three rivers that feed into Tyrolerfjord-Young Sound (Tyroler River, Lerbugten River and Zackenberg River) were sampled; surface and subsurface water samples were also collected at transition sites where the rivers feed into the fjord (Tyro_01, Zac_30, Ler_30, altogether referred to as ‘river transition sites’). Enzyme activities were measured in unfiltered water. In addition, water was size-fractionated using gravity filtration through a GF/A filter to capture ≥1.6 µm particles.

Two substrates, a-glucose and b-glucose linked to a 4-methylumbelliferyl (MUF) fluorophore, were used to measure glucosidase activities. Five substrates linked to a 7-amido-4-methyl coumarin (MCA) fluorophore, one amino acid – leucine – and four oligopeptides – the chymotrypsin substrates alanine-alanine-phenylalanine (AAF) and alanine-alanine-proline-phenylalanine (AAPF), and the trypsin substrates glutamine-alanine-arginine (QAR) and phenylalanine-serine-arginine (FSR) – were used to measure exo- and endo-acting peptidase activities, respectively. Hydrolysis rates of the substrates were measured as an increase in fluorescence as the fluorophore was hydrolyzed from the substrate over time [as in Hoppe, 1993; Obayashi and Suzuki, 2005].  All substrates were used to measure enzyme activities in unfiltered water, as well as particle-associated (≥1.6 µm) enzymatic activities.

In unfiltered water, enzyme activities were measured by adding 4 mL of water to triplicate cuvettes. One incubation containing autoclaved water served as the killed control. This procedure was applied to each of the 7 substrates and one live blank and autoclave blank (no substrate addition). Each cuvette containing either live or autoclaved water was amended with one substrate to a concentration of 100 µM. Fluroescence was measured using a Promega Quantifluor solid-state single-cuvette fluorimeter; excitation and emission maxima were 365 nm and 410–450 nm, respectively,

To measure particle-associated enzyme assays, 1/12th piece of a GF/A filter through which water had been gravity filtered was put into a cuvette containing 4 mL of cooled, autoclaved water from the same station/depth as the live samples. In addition, killed controls were set up using sterile GF/A filters cut into 1/12th pieces. Bulk water and particle-associated enzyme assays were incubated for up to 24 and 16 hours, respectively; timepoints were taken at specific intervals. Incubations were kept in the dark either at 0°C, 5°C, or 8°C, depending on in situ water temperature at the time of sampling.

Activities of polysaccharide hydrolases were measured using fluorescently labeled polysaccharides (Arnosti 2003). Activities of enzymes that hydrolyze pullulan, laminarin, xylan, fucoidan, arabinogalactan, and chondroitin sulfate were measured in unfiltered water, and using GF/A filters through which water had been gravity-filtered. For these measurements, substrate was added (of 3.5 µM monomer equivalent) to 15 mL of water; autoclaved ambient water served as the killed control. Particle-associated activities were measured by submerging 1/12th of a GF/A filter in 15 ml autoclaved seawater. Samples were incubated in the dark at near in situ temperature (0°C, 5°C, or 8°C), and sub-sampled at specific time intervals—t0 (0h, upon substrate addition), t1 (120 h), t2 (240 h), t3 (360 h) and t4 (600 h). Sub-samples from each timepoint were filtered using 0.2 µM pore size SFCA (surfactant-free cellulose acetate) syringe filters, and the filtrate was collected in tubes and frozen at -20°C until processing in the lab. Sub-samples were processed using gel permeation chromatography (Arnosti, 2003). 

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- added trip_id, bulk_or_not, FLA_MCAMUF columns
- reduced the decimal precision of time_elapsed_hr and the rates columns to 3.
- sorted by sample_type, fluorophore, station, cast, depth_id

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.