Oceanography | Vol. 38, No. 3
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KUROSHIO INFLUENCE NORTH OF TAIWAN
By the time the Kuroshio, now influenced by the SCS, reaches the
region north of Taiwan, the S-max has a salinity of around 34.8
in the ORI-179 cross section east of 122.8°E (Figure 4, 25°N).
This cross section is perpendicular to the shelf break, which runs
from southwest to northeast. As a result, the Kuroshio is forced to
turn northeastward due to the topography (C.T.A. Chen, 2011).
Temperature, salinity, AOU, and nutrient contours indicate the
presence of high-nutrient waters (NO3 > 5 µM, PO4 > 0.2 µM, and
Si(OH)4 > 5 µM) along the shelf edge at depths as shallow as 60 m.
These subsurface nutrient-rich waters continue moving toward
the ECS shelf, making them available for photosynthesis. Current-
meter measurements and models confirm this onshore movement
of surface waters (Chuang and Liang, 1994; Matsuno et al., 2009;
D. Yang et al., 2011; Wu et al., 2017).
NUTRIENT ENRICHMENT IN THE MIDDLE
LATITUDE EAST CHINA SEA
Further north, in the TPS-24 cross section (Figure 5, 29°N), the
S-max core exhibits a salinity exceeding 34.8 between depths
of 100 m and 200 m in regions with water depths greater than
1,000 m, indicating a significant contribution from the orig-
inal Kuroshio. However, the salinity quickly drops to 34.6 west
of 126°E at depths of 100–200 m, where a salinity front appears
to exist (C.T.A. Chen, 2005). West of this front, the influence of
the SCS water is evident, with high-nutrient subsurface waters
moving further westward toward the shelf break. For instance,
the NO3 = 15 µM contour is approximately 100 m shallower
(Figure 5) compared to the area northeast of Taiwan (Figure 4).
The PO4 = 1 µM and Si(OH)4 = 20 µM contours also move up by
about 100 m.
NUTRIENT DYNAMICS IN THE NORTHERN
EAST CHINA SEA SHELF BREAK
Moving further north, the KEEP-MASS data reach a water depth
of approximately 80 m to the west (Figure 6, 32°N). While a lack of
data near the shelf break makes it challenging to demonstrate the
upwelling feature, the salinity, consistently lower than 34.6, sug-
gests that the upwelled waters are significantly influenced by the
SCS outflow or the ECS shelf waters. Notably, this region exhib-
its much higher nutrient concentrations, even in the surface layer,
compared to the surface waters at the Kuroshio’s origin (Figure 2).
While the Changjiang River outflow may play a role, it is likely
minimal in supporting productivity given its low phosphate con-
centration. Factors such as winter cooling, typhoons, and strong
winds could mix high-nutrient subsurface waters into the surface
euphotic layer on the shallow shelf. It is worth mentioning that this
area is some distance from the Kuroshio recirculation that contrib-
utes to nutrient supply in the entire Kuroshio region south of Japan
(X. Guo et al., 2019). Therefore, the higher nutrient concentra-
tions in this cross section likely originate from the SCS-influenced
Kuroshio coming from the southwest.
FIGURE 3. Zonal cross sections of temperature, salinity, σθ, AOU, nitrate, phosphate, and silicate southeast of Taiwan based on the ORI-462 data. Color shad-
ing and black contours represent the values of individual parameters.