THE EFFECTS OF LIGHT AND NUTRIENT ENRICHMENT ON THE PRIMARY PRODUCTIVITY IN THE CANADA BASIN

Abstract

The Joint Ocean Ice Study (JOIS) was conducted in the Canada Basin from mid September to mid October in 2009. During the period, the primary productivity of phytoplankton was measured at six different light depths of 11 stations in the Canada Basin, using a 13C-15N dual isotope tracer. In addition, we identified the effects of light and nutrient enrichments on the primary production of phytoplankton in the chlorophyll a maximum layer. The temperature and salinity at surface were -2~ 1℃ and 24-27, respectively in the Canada Basin. In contrast, the very salty water (>31) was existed below 60m water depth and the strong stratification was developed at the depth. In general, the NO3- concentration was depleted from surface to 60m over the North of 720. The primary productivity of phytoplankton was somewhat lower in the Canada Basin during the cruise period in 2009 compared to other regions in the Arctic Ocean. The averaged hourly primary production rate vertically integrated from 100% to 1% light depth was 1 mg C m-2 h-1 from this cruise. The light and nutrient enrichments induced higher primary productivity of the phytoplankton in the chlorophyll a maximum layer. The increases of primary productivity at the stations with <50% ice cover were much higher than those from other stations with >50% ice cover. This is probably because the phytoplankton at the stations with the higher ice cover was more shade-adapted and thus slower response on the light enrichments.