Organic C, N, and stable isotopic composition of particulate matter collected on glass‐fiber and aluminum oxide filters

There is recent evidence that commonly used glass‐fiber filters do not quantitatively sample suspended particles in the open ocean. To test for potential artifacts, I compared the quantity and composition of particles retained on glass‐fiber (Whatman GF/F, QM‐A, and GF/D) and aluminum oxide filters (Anotec Anopore, 0.2‐ µ m pore size). At a site off Bermuda, most of the particles passed GF/D and QM‐A filters. At both this site and the site of the JGOFS North Atlantic bloom experiment, the majority was retained on GF/F filters but a significant fraction passed through to be retained by Anopore filters (∼30% of total). This fraction increased at and below the base of the euphotic zone. For the North Atlantic experiment, particles passing GF/F filters also accounted for up to 60% of the NH 4 + and 80% of the NO 3 − uptake into particle uptake. Uptake integrated over the upper 60 m, however, was not significantly underestimated by the GF/F filters. At the Bermuda site, significant and consistent variations in C: N, δ 15 N, and δ 13 C values occurred among the various filter fractions. GF/F filters, however, did not appear to produce significant artifacts in these quantities relative to particles collected by Anopore filters.