Seasonal patterns of urea regeneration by size-fractionated microheterotrophs in well-mixed temperate coastal waters

Urea regeneration by size-fractionated plankton was measured over an annual cycle at a coastal station in the permanently well-mixed waters of the western English Channel. Rates of urea regeneration in the <200 μm fraction varied from 0.6 to 20.6 nmol N L−1 h−1. Regeneration rates were lowest in winter and highest in summer. The ratio of the rates of regeneration to uptake of urea was close to 1 on all time (seasonal and nycthemeral), and space...