Water was collected via Niskin bottles mounted on a rosette, equipped with a CTD.

From the Niskin bottle, water was dispensed into smaller glass containers that were cleaned and pre-rinsed three times with water from the Niskin bottle prior to dispensing. This water was used to measure the activities of peptidases and glucosidases. A separate glass Duran bottle was filled with seawater from the Niskin bottle and sterilized in an autoclave for 20-30 minutes to serve as a killed control for microbial activity measurements.

Two substrates, alpha-glucose and beta-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. Incubations with the seven low molecular weight substrates were set up in a 96-well plate. For each substrate, triplicate wells were filled with a total volume of 200 uL seawater for experimental incubations; triplicate wells were filled with 200 uL autoclaved seawater for killed control incubations. Substrate was added at saturating concentrations. A saturation curve was determined with surface water from each station to determine saturating concentrations of substrate. The saturating concentration was identified as the lowest tested concentration of substrate at which additional substrate did not yield higher rates of hydrolysis. Fluorescence was measured over 0-72 hours incubation time with a plate reader (TECAN infiniteF200; 360 nm excitation, 460 emission), with timepoints taken every 4-6 hours.