Primary production in the Chukchi Sea with potential effects of freshwatercontent

[摘要]

The in situ primary production rates and various environmental variableswere investigated in the Chukchi Sea during the RUSALCA expedition, which wasconducted in 2012, to identify the current status of primary production. A¹³C–¹⁵N dual-tracer technique was used to measure the daily primaryproduction rates, which ranged from 0.02 to 1.61 g C m⁻² d⁻¹(mean ±SD  =  0.42 ± 0.52 g C m⁻² d⁻¹). The primaryproduction rates showed large regional differences, with the southern region(0.66 ± 0.62 g C m⁻² d⁻¹) producing approximately 5times as much as the northern region(0.14 ± 0.10 g C m⁻² d⁻¹), which was primarily due to thedifferences in phytoplankton biomasses induced by regional nutrientconditions. The primary production rates in the Chukchi Sea were averagedusing data acquired during the three different RUSALCA expeditions (2004,2009, and 2012) as 0.33 g C m⁻² d⁻¹(SD  =  0.40 g C m⁻² d⁻¹), which was significantly lower thanpreviously reported rates. In addition to strong seasonal and interannualvariations in primary production, recent decreases in the concentrations ofmajor inorganic nutrients and chlorophyll a could be among the reasons forthe recent low primary production in the Chukchi Sea because the primaryproduction is mainly affected by nutrient concentration and phytoplanktonbiomass. The nutrient inventory and primary production appear to be largelyinfluenced by the freshwater content (FWC) variability in the region due tothe significant relationships between FWC, nitrate inventory (r  =  0.54,p < 0.05), and primary production rates (r  =  0.56, p< 0.05). Moreover, we found highly significant relationships betweenthe nutrient inventory and the primary production rates (r  =  0.75, p< 0.001). In conclusion, the primary production in the Chukchi Seais primarily controlled by nutrient availability, which is strongly related tothe FWC variability. Our results imply that the predicted increase infreshwater accumulation might cause a decrease in primary production bylowering the nutrient inventory in the euphotic zone of the Chukchi Sea.

[学科分类] 地球化学与岩石