Long-term annual primary production in the Ulleung Basin as a biological hot spot in the East/Japan Sea

Abstract

Although the Ulleung Basin is an important biological ''hot spot'' in East/Japan Sea (hereafter the East Sea), very limited knowledge for seasonal and annual variations in the primary productivity exists. In this study, a recent decadal trend of primary production in the Ulleung Basin was analyzed based on MODIS-derived monthly primary production for a better annual production budget. Based on the MODISderived primary production, the mean daily primary productivity was 766. the Ulleung Basin during the study period. The monthly contributions of primary production were not largely variable among different months, and a relatively small interannual production variability was also observed in the Ulleung Basin, which indicates that the Ulleung Basin is a sustaining biologically productive region called as ''hot spot'' in the East Sea. However, a significant recent decline in the annual primary production was observed in the Ulleung Basin after 2006. Although no strong possibilities were found in this study, the current warming sea surface temperature and a negative phase PDO index were suggested for the recent declining primary production. For a better understanding of subsequent effects on marine ecosystems, more intensive interdisciplinary field studies will be required in the Ulleung Basin.

Long-Term Pattern of Primary Productivity in the East/Japan Sea Based on Ocean Color Data Derived from MODIS-Aqua

“…Recently, Jo et al [40] reported that the rate of the SST increase was 0.041˝C¨y´1 in the east coast of Korea, which was much faster than the global average (0.005˝C¨y´1). However, no substantial increased SST was observed in this study during our investigation period (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012), most likely because the observation period was not long enough to detect any small changes in the SST [13]. Gregg et al [39] argued that increased temperature and shallower mixed layers via surface stratification could result in increased Chl-a concentrations in early spring and that more severe nutrient exhaustion in late spring and summer could reduce the Chl-a concentrations and, consequently, annual primary production [41].…”

“…Gregg et al [39] argued that increased temperature and shallower mixed layers via surface stratification could result in increased Chl-a concentrations in early spring and that more severe nutrient exhaustion in late spring and summer could reduce the Chl-a concentrations and, consequently, annual primary production [41]. In fact, the concentrations of major inorganic nutrients decreased in euphotic water layers (0-50 m water depth) in the Ulleung Basin (located in the middle of the East Sea) during our observation period [13]. The decrease in nitrate concentrations was also distinct during both the summer time and the winter season in the study region from 2003 to 2012 [13].…”

“…A recent study reported that the MODIS-derived primary productivity using the regional primary productivity algorithm [19] was strongly correlated with in situ primary productivity measurements in the Ulleung Basin of the East Sea [13]. …”

“…However, shipboard measurements with a continuous sampling limitation and relatively small area coverage could cause a temporal and spatial under or overestimation of overall primary productivity [13][14][15]. Over the past several decades, estimates of primary productivity were attempted in various regions using satellite ocean color data to overcome the lack of in situ spatial and temporal data e.g., [16][17][18][19].…”

“…Global time series of satellite-measured data allow the monitoring of intra-annual, inter-annual, multi-annual, and long-term changes in phytoplankton productivity [20]. The remote sensing program of ocean color measurements from satellite data was applied to estimate Chl-a concentrations and primary productivity based on a regional productivity model [13]. Chl-a is a photosynthetic pigment that is common to all microscopic algae (i.e., phytoplankton), which are the main primary producers that comprise the base of most oceanic food webs.…”