The effects of irradiance and nutrient supply onthe productivity of Arctic waters: a perspectiveon climate change

摘要

A previous analysis of published data suggested that annual, pelagic primaryproduction in the Arctic Ocean is related linearly to the duration of the ice-freeperiod, presumably through cumulative exposure to solar irradiance. However, theregions with the longest ice-free periods are located in peripheral seas andpolynyas where nutrient supply by advection or the vertical mixing induced bywinds and convection can be extensive. The ensuing replenishment of nutrientsdrives primary production to levels unattained in the strongly stratified interior(e.g. the Beaufort Sea), with the exception of upwelling areas. A reanalysis ofpublished data showed no relation between cumulative production and incidentsolar radiation during the growth season. We propose that changes in annualprimary production per unit area in seasonally ice-free waters are controlledprimarily by the environmental forcing of nitrogen supply. Incidental changes inlight regime should mostly affect the timing and, possibly, the species compositionof the main production pulse(s) in the upper mixed layer and, underneath, theability of phytoplankton to exploit nutrients in the lower euphotic zone. While theongoing rise in the supply of heat and freshwater to the Arctic Ocean shouldbolster vertical stratification and further impede the mean upward supply ofnutrients, episodic yet direct atmospheric forcing of the upper ocean may act insynergy with a prolonged exposure to light and greatly augment pelagicproductivity.