Nutrient and diatom dynamics during late winter and spring in the Oyashio region of the western subarctic Pacific Ocean

Abstract

We investigated the nutrient and diatom dynamics during late winter and spring These results suggest that the spring bloom in the cold water system with high macronutrients and iron concentrations would progress rapidly and intensely, and then be terminated by nitrogenous nutrient depletion. However, the diatom bloom in warmer waters with lower macronutrients and iron concentrations would be terminated by Si-and/or iron-limitation of heavily-silicified diatoms. In the OECOS study, variation of macronutrients and iron due to the surface intrusions of several water masses and modification from different chemical conditions during winter were the most important factors regulating the progression, magnitude and probably fate of the spring phytoplankton bloom in the Oyashio region.2

Responses of phytoplankton assemblages to iron availability and mixing water masses during the spring bloom in the Oyashio region, NW Pacific

“…Hydrographic condition, satellite images of SST and Chl a concentration, and both macronutrient and iron concentrations during the OECOS cruise are detailed in Kono and Sato (), Nakayama et al (), and Sugie et al () and therefore are only briefly mentioned here. The hydrography observed at the fixed station (Stn) A5 of the A‐Line during OECOS was not a consistent water mass (Table ; Fig.…”

Effects of pCO2 and iron on the elemental composition and cell geometry of the marine diatom Pseudo‐nitzschia pseudodelicatissima (Bacillariophyceae)1

“…In addition, the iron concentration varies spatiotemporally by one to two orders of magnitude due to water mass exchange and biological uptake in the western subarctic Pacific (Sugie et al. , Nishioka et al. ).…”

“…Therefore, the phytoplankton, particularly diatoms, in the oceanic regions located far from iron sources are iron limited (de Baar 1994). In addition, the iron concentration varies spatiotemporally by one to two orders of magnitude due to water mass exchange and biological uptake in the western subarctic Pacific (Sugie et al 2010a, Nishioka et al 2011. Therefore, phytoplankton need to adapt and survive in a fluctuating iron environment Kuma 2008, Sugie et al 2011).…”

“…Moutin et al 2008), the rate of which is significantly enhanced by an increase in pCO 2 , Levitan et al 2007). However, the new production will decrease in N-limiting environments, where the iron concentration is sufficiently high to allow exhaustion of nutrients (e.g., Sugie et al 2010a). These N-limiting environments are high productivity regions, including the majority of the coastal regions (Tyrrell andLaw 1997, Wong et al 2002).…”

Size of Dominant Diatom Species Can Alter Their Evenness

“…One of the other possible reasons for the dominance of intermediate-sized diatoms is chain- and mucilaginous colony-formation. It has been well documented that chain-forming diatom species often produce massive blooms in coastal waters e.g., [ 49 , 50 ]. Thingstad et al [ 26 ] hypothesized that diatoms, in general, simultaneously achieved high affinity for nutrient uptake and predator defense, with their Si cell walls serving as a survival strategy, i.e., large yet small strategy, which may lead them to success in modern seas.…”