Monthly measured primary and new productivities in the Ulleung Basin as a biological "hot spot" in the East/Japan Sea

Abstract

The Ulleung Basin (UB), located in the southwestern part of the East/Japan Sea (EJS), is considered having an unusually high productivity for a~deep basin. Recently changes have been reported in physical, chemical, and in biological properties. Here we measured the primary and new productivities in the UB using a <sup>13</sup>C-<sup>15</sup>N dual isotope tracer technique. Measurements took place every month for the first time throughout a year for a~better estimate of the annual primary production in the EJS. Temporal variations of temperature, salinity and density (σ<sub>t</sub>) in the study area were highly seasonal as expected for an ocean in the temperate zone. Nutrient distributions reflected these seasonal fluctuations in the vertical structure of the water column. Diatoms were in general the most dominant phytoplankton ranging from 15.5 to 82.2% with an average of 42.0% (S.D. = ± 9.9%). Based on those average daily productivities from our monthly measurements, the annual primary, new, and regenerated production in the UB were 273.0 g C m<sup>−2</sup> yr<sup>−1</sup>, 62.6 g N m<sup>−2</sup> yr<sup>−1</sup>, and 48.7 g N m<sup>−2</sup> yr<sup>−1</sup>, respectively. Our estimated high <i>f</i>-ratio (0.59) in the UB, indicated that the predominant nitrogen source for primary production was nitrate. This is comparable with the nitrogen source in a productive coastal-upwelling region. New carbon production by phytoplankton is estimated as 212.8 g C m<sup>−2</sup> yr<sup>−1</sup> (S.D. = ± 9.7 g C m<sup>−2</sup> yr<sup>−1</sup>) which indicates that a large portion (78%) of total annual primary production might potentially be exported from the diatom-dominated euphotic zone to a deeper zone in the UB. Further intense integrated field observations will be necessary to improve our understanding of the current marine ecosystem in the UB as an important biological production area in the EJS

Evidence for ontogenetic feeding strategies in four calanoid copepods in the East Sea (Japan Sea) in summer, revealed by stable isotope analysis

“…In the East Sea, the abundance of diazotrophic picocyanobacteria belonging to the genera Synechococcus and Prochlorococcus was extremely low in February and then drastically increased and peaked between late spring and autumn (Choi et al 2013;Park et al 2014). Moreover, Kwak et al (2013) reported that the contributions of picoplankton to chlorophyll a and primary production in summer were 38 ± 16 and 35 ± 2%, respectively. Therefore, our results indicate that the energy flow from the microbial loop to the top consumers may supplement the insufficient energy of the classical food web in the summer.…”

“…This caused a subsequent limitation in nutrient supply and the relatively low primary productivity in the surface mixed layer. Thus, during the period when stratification prevailed, cyanobacteria contributions increased at the surface layer with depleted dissolved inorganic nutrients (Kwak et al 2013). In the present study, we found an increase in the δ 13 C values of pico-to microplankton from -28.45 to -23.63‰ (Table 1).…”

Summer primary productivity and phytoplankton community composition driven by different hydrographic structures in the East/Japan Sea and the Western Subarctic Pacific

“…Although nutrient concentrations in the euphotic zone (<75 m) were higher in the WSP than in the EJS, the integrated primary productivity was higher in the EJS than in the WSP [Shiomoto, 2000;Yamada et al, 2005;Kwak et al, 2013aKwak et al, , 2013b [Lozier et al, 2011]. Iron limitation may be another cause as suggested by Nishioka et al [2003] and Harrison et al [2004].…”

“…For example, the vertical position of the SCM layer in relation to light and nutrient availability can control phytoplankton biomass and productivity [Martin et al, 2010]. Kwak et al [2013b] observed that the generation and destruction of the SCM layer and the associated shift in phytoplankton assemblages are related to the nature of the water column structure in the UB. Phytoplankton size and community composition directly reflect the response of phytoplankton assemblages to environmental variations [Margalef, 1978;Malone, 1980;Elser et al, 1986;Piontkovski et al, 1995;Iriarte et al, 2000].…”

Biogeochemistry and ecosystems of continental margins in the western North Pacific Ocean and their interactions and responses to external forcing – an overview and synthesis

“…The maintenance of high primary production in the Ulleung Basin of the JES has been explained by wind-driven coastal upwelling (Hyun et al, 2009;Yoo and Park, 2009), mesoscale eddies, which are often associated with the branch currents of the Kuroshio (Hyun et al, 2009;Kim et al, 2012;Lim et al, 2012), and hydrographic conditions (Kwak et al, 2013a). Kwak et al (2013b) measured the primary and new productivities in the UB throughout a year. The vertical structure of the water column in the basin is characterized by two distinct features: well-stratified in summer-autumn and wellmixed in winter-spring.…”