ORIGINAL PAPER Spatial and temporal variation of photosynthetic parameters in natural phytoplankton assemblages in the Beaufort Sea, Canadian Arctic Molly A. Palmer • Kevin R. Arrigo • C. J. Mundy • Jens K. Ehn • Michel Gosselin • David G. Barber • Johannie Martin • Eva Alou • Suzanne Roy • Jean-E ´ ric Tremblay Received: 17 February 2011 / Revised: 6 June 2011 / Accepted: 10 June 2011 / Published online: 2 July 2011 Ó Springer-Verlag 2011 Abstract During summer 2008, as part of the Circum- polar Flaw Lead system study, we measured phytoplankton photosynthetic parameters to understand regional patterns in primary productivity, including the degree and timescale of photoacclimation and how variability in environmental conditions influences this response. Photosynthesis–irradi- ance measurements were taken at 15 sites primarily from the depth of the subsurface chlorophyll a (Chl a) maximum (SCM) within the Beaufort Sea flaw lead polynya. The physiological response of phytoplankton to a range of light levels was used to assess maximum rates of carbon (C) fixation (P m * ), photosynthetic efficiency (a * ), photo- acclimation (E k ), and photoinhibition (b * ). SCM samples taken along a transect from under ice into open water exhibited a [ 3-fold increase in a * and P m * , showing these parameters can vary substantially over relatively small spatial scales, primarily in response to changes in the ambient light field. Algae were able to maintain relatively high rates of C fixation despite low light at the SCM, particularly in the large ( [ 5 lm) size fraction at open water sites. This may substantially impact biogenic C drawdown if species composition shifts in response to future climate change. Our results suggest that phytoplankton in this region are well acclimated to existing environmental con- ditions, including sea ice cover, low light, and nutrient pulses. Furthermore, this photoacclimatory response can be rapid and keep pace with a developing SCM, as phyto- plankton maintain photosynthetic rates and efficiencies in a narrow ‘‘shade-acclimated’’ range. Keywords Phytoplankton  Photosynthesis–irradiance measurements  Subsurface chlorophyll maximum  Beaufort Sea  Polynya Introduction The Arctic sea ice cover will be subject to large reductions in future years due to climate warming and the associated complex feedbacks (Stroeve et al. 2008; Wang and Overland 2009). It has been suggested that the reduction in ice cover, through the increase in nutrient supply from wind-induced upwelling and greater number of open water days, may increase primary productivity (PP) in the Arctic by as much as 3-fold (Arrigo et al. 2008; Pabi et al. 2008; Zhang et al. 2010). In contrast, a freshening of polar sur- face waters in the Canada Basin due to increases in melt- water and river runoff has been suggested to limit the This article belongs to the special issue ‘‘Circumpolar Flaw Lead Study (CFL)’’, coordinated by J. Deming and L. Fortier. M. A. Palmer (&)  K. R. Arrigo Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305, USA e-mail: mapalmer@stanford.edu C. J. Mundy  M. Gosselin  E. Alou  S. Roy Institut des sciences de la mer, Universite ´ du Que ´bec a ` Rimouski, Rimouski, QC G5L 3A1, Canada J. K. Ehn Marine Physical Laboratory, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA, USA D. G. Barber Centre for Earth Observation Science, Faculty of Environment, Earth and Resources, University of Manitoba, Winnipeg, MB R3T 2N2, Canada J. Martin  J.-E ´ . Tremblay Que ´bec-Oce ´an, De ´partement de biologie, Universite ´ Laval, Que ´bec, QC G1V OA6, Canada 123 Polar Biol (2011) 34:1915–1928 DOI 10.1007/s00300-011-1050-x