A large volume in situ filtration system has been developed for the extraction of material greater than one micron in diameter from several cubic meters of water. The system has worked reliably to 400 meters. The particulate matter concentrations determined in profile compare well with those found using conventional Niskin-Nuclepore techniques. By using 53µm Nitex and 1µm glass fiber filters in series, the samples are separated into two size fractions....