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

摘要

The Ulleung Basin (UB), located in the southwestern part of the East/JapanSea (EJS), is considered having an unusually high productivity for a deepbasin. Recently changes have been reported in physical, chemical, andbiological properties. Here we measured the primary and new productivitiesin the UB using a 13C-15N dual isotope tracer technique.Measurements took place every month for the first time throughout a year fora better estimate of the annual primary production in the EJS. Temporalvariations of temperature, salinity, and density (σ_t) in thestudy area were highly seasonal as expected for an ocean in the temperatezone. Nutrient distributions reflected these seasonal fluctuations in thevertical structure of the water column. Diatoms were in general the mostdominant phytoplankton ranging from 15.5 to 82.2% with an average of42.0% (S.D. = ±9.9%). Based on those average dailyproductivities from our monthly measurements, the annual primary, new, andregenerated production in the UB were 273.0 g C m?2 yr?1,62.6 g N m?2 yr?1, and 48.7 g N m?2 yr?1, respectively. Ourestimated high f ratio (0.59) in the UB, indicated that the predominantnitrogen source for primary production was nitrate. This is comparable withthe nitrogen source in a productive coastal-upwelling region. New carbonproduction by phytoplankton is estimated as 145.6 g C m?2 yr?1(S.D. = ±40.8 g C m?2 yr−1) which indicates that a largeportion (53.9%) of the total annual primary production might potentially beexported from the diatom-dominated euphotic zone to a deeper zone in the UB.Further intense integrated field observations will be necessary to improveour understanding of the current marine ecosystem in the UB as an importantbiological production area in the EJS.