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Abstract THE GROWTH AND PRODUCTIVITY OF ARCTIC KELP POPULATIONS: Kenneth H. Dunton Productivity of high latitude kelp is primarily regulated by distinct seasonal variations in temperature, light, and ambient inorganic-N. Of these factors, light exhibits the most pronounced variation in high latitude systems, where seasonal differences in underwater irradiance can range from nearly 0 to 6 mol/m2/day. High latitude benthic macroalgae are exposed to annual inputs of solar radiation that are 30-50% lower compared to north temperate and equatorial regions. Arctic kelp populations have adapted to these lower and variable light conditions by having a high efficiency for photon capture and significantly reduced rates of respiration at low temperatures as reflected by high photosynthesis to respiration (P:R) ratios. Consequently, arctic kelp are known to flourish at light levels equivalent to 0.2% of surface PAR, or 40-50 mol/m2/year, close to the estimated flux of 10 mol/m2/year for the lower limit of perennial benthic macroalgae. The Arctic continues to see large changes in climate as documented by the warmest air temperatures in four centuries, a shrinking ice cover, increasing river discharge, and accelerated rates of coastal erosion. The changes associated with these events could have a distinct effect on the amount of light available for photosynthesis which can be measured in annual increments of blade growth in kelp fronds. This paper examines a 30-yr record of kelp growth in the Beaufort Sea in relation to the profound environmental changes observed in the Arctic. An intensive study of the depth-integrated response of high latitude kelps to ambient levels of UV radiation is also presented.
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