Low primary production in the Chukchi Sea shelf, 2009

• Low primary production was observed in the Chukchi Sea shelf in 2009.
• These lower rates were induced by less widespread Anadyr Water.
• High amounts of freshwater accumulated from Siberian Coastal Current affected negatively production rates.
• More abundant small phytoplankton existed in the Chukchi Sea shelf in 2009.
• Our study area covered less studied Russian Chukchi Sea.

Using a 13C–15N dual tracer technique, phytoplankton production measurements were conducted along the entire Chukchi Sea shelf during the 2nd RUSALCA cruise from September 1 to 31, 2009, as a part of long-term ecosystem monitoring. The daily total nitrogen production rates ranged from 6.3 to 126.1 mg N m−2 d−1 in this study, which were significantly lower than those of previous studies in the region. The large difference in nitrate production rate between the northern and southern regions could be explained by different ambient nitrogen concentrations during the cruise period. Consistently, the overall daily carbon production rate in 2009 was low with a mean of 0.3 g C m−2 d−1 (SD=±0.2 g C m−2 d−1). These lower rates of phytoplankton production were induced by a decrease in chlorophyll a concentration resulting from less widespread Anadyr Water, which is normally high in nutrients and phytoplankton biomass. In addition, high amounts of freshwater accumulated from the Siberian Coastal Current negatively affected phytoplankton production rates. Under the low nutrient and freshening conditions during this study, small phytoplankton were more abundant than those reported previously on the Chukchi Sea shelf. Because of large variations in production rates of phytoplankton caused by strong seasonal/interannual variations of environmental conditions, various long-term monitoring programs are important to understand marine ecosystem responding to ongoing environmental changes in the Chukchi Sea.