ORIGINAL PAPER Optical gradients and phytoplankton production in the Mackenzie River and the coastal

• Main Authors: Beaufort Sea, Leira Retamal, Æ Sylvia, Bonilla Æ Warwick, F. Vincent
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; Mackenzie River; Climate change; Mackenzie river; Phytoplankton
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.474.5112; http://132.203.57.253/warwickvincent/PDFfiles/220.pdf

Abstract We sampled a 300-km transect along the Mackenzie River and its associated coastal shelf system (western Canadian Arctic) in July–August of 2004 to evaluate the gradients in optical, phytoplankton and photosynthetic characteristics. The attenuation of photo-synthetically available radiation (PAR) was best explained by coloured dissolved organic matter (CDOM) and tur-bidity (non-algal particles), while UV attenuation correlated most strongly with CDOM. Bacillariophyceae and Chlorophyceae dominated in the river, and shifted to Cryptophyceae and Prasinophyceae in the estuarine tran-sition zone. In the coastal shelf waters, picoplanktonic cells dominated the surface autotrophic communities while both large and small cells occurred in the deep chlorophyll maximum. High PAR attenuation reduced the integral primary production rate in the river, while at an offshore marine site, 55 % of integral production was at or below the pycnocline, under low PAR. Climate change is likely to increase the sediment and CDOM loading to these waters, which would exacerbate light limitation of photosynthesis throughout the system.