Picophytoplankton and nanophytoplankton abundance and distribution in the southeastern Beaufort Sea (Mackenzie Shelf and Amundsen Gulf) during Fall 2002

IRENE R. SCHLOSS, CHRISTIAN NOZAIS, SÉBASTIEN MAS, BON VAN HARDENBERG, EDDY CARMACK , JEAN-ÉRIC TREMBLAY, SONIA BRUGEL, SERGE DEMERS

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Año: 2008

0924-7963

The distribution of picophytoplankton (0.2?2 µm) and nanophytoplankton (2?20 µm) in the Beaufort Sea?Mackenzie Shelf and Amundsen Gulf regions during autumn, 2002 is examined relative to their ambient water mass properties (salinity, temperature and nutrients: nitrate + nitrite, phosphate, and silicate) and to the ratio of variable to maximum fluorescence, Fv/Fm. Total phytoplankton and cell abundances (b20 µm) were mainly correlated with salinity. Significant differences in picophytoplankton cell numbers were found among waters near the mouth of the Mackenzie River, ice melt waters and the underlying halocline watermasses of Pacific origin. Picophytoplankton was the most abundant phytoplankton fraction during the autumnal season, probably reflecting low nitrate concentrations (surface waters average ~0.65 µM). The ratio Fv/Fm averaged 0.44, indicating that cells were still physiologically active, even though their concentrations were low (max Chla= 0.9 mg m−3). No significant differences in Fv/Fm were evident in the different water masses, indicating that rate limiting conditions for photosynthesis and growth were uniform across the whole system, which was in a pre-winter stage, and was probably already experiencing light limitation as a result of shortening day lengths.