Particles were collected using in situ McLane pumps equipped with mini-MULVFS (Bishop et al. 2012) 2-tiered filter holders. Particle collection captured sequentially large (>53 µm) particulates on acid-cleaned Nitex mesh filters and small particles (<53 µm) on pre-combusted GFF or QMA filters at discrete depths for amino acid compound-specific isotope analysis (AA CSIA) and for particulate carbon and nitrogen. This method is designed to exclude motile metazoans but include all other ambient, non-swimming particulate matter (see Bishop et al. 2012). Immediately after collection, large particles were rinsed off of the Nitex screens and onto pre-combusted 25-mm QMA filters using 0.2 µm filtered seawater. All filters were frozen at -20°C or -80°C as soon as possible after collection.
Zooplankton were collected using a 1-m² MOCNESS net during the day (~09:00-15:00) and at night (~20:00-03:00). Night and day tows were repeated to obtain replicate samples for biomass and isotopic analyses. Upon collection, each sample was size-fractionated using 0.2, 0.5, 1.0, 2.0 and 5.0 mm mesh sieves, filtered onto pre-weighed 47 mm filters of 0.2 mm Nitex mesh and stored frozen at -80ºC.
For nitrogen isotope composition of the amino acids, particles and zooplankton samples were freeze dried and analyzed following the methods Hannides et al. (2013). δ¹⁵N values of source amino acids ( δ¹⁵NSrc₋AA ) for both particles and zooplankton were calculated as the average δ¹⁵N of: serine, phenylalanine, lysine and glycine. Freeze-dried zooplankton filters for all size fractions were weighed to calculate zooplankton biomass (mg in dry weight/m³) at each depth during the day and at nighttime.
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