Intrusion of Kuroshio water onto the continental shelf in the East China

Sea and its influences on the ecosystem

○Xinyu Guo (CMES, Ehime University/FRCGC)Yasumasa Miyazawa (FRCGC)

Toshio Yamagata (The University of Tokyo/FRCGC)

Volume transport from

50 m to 0 m

Changjiang

Chen and Wang, JGR,1999

SW: Kuroshio Surface Water; TW: Kuroshio Tropical Water

IW: Kuroshio Intermediate Water; p: precipitation

Chen and Wang, JGR,1999

SW: Kuroshio Surface Water; TW: Kuroshio Tropical Water

IW: Kuroshio Intermediate Water; p: precipitation

b. Winter

Yellow Sea NO3

-: 0.053 NH4

+: 0.013 PO4

3-: 0.006 SiO3

2-: 0.111

Outflow NO3

-: 17.1 NH4

+: 0.98 PO4

3-: 1.34 SiO3

2-: 33.6

Kuroshio NO3

-: 12.6 NH4

+: 0.97 PO4

3-: 0.92 SiO3

2-: 23.7

River NO3

-: 0.765 NH4

+: 0.195 PO4

3-: 0.006 SiO3

2-: 1.37 Bottom Sediment

NO3-: 0.11

NH4+: 1.01

PO43-: 0.025

SiO32-: 2.51

Taiwan Strait NO3

-: 5.73 NH4

+: 0.69 PO4

3-: 0.46 SiO3

2-: 17.9

Atmosphere NO3

-: 0.71 NH4

+: 1.27 PO4

3-: 0.003 SiO3

2-: 0.017

East China Sea Shelf

unit: ×103 mol/sZhang et al., 2004

Taiwan Strait NO3

-: 7.10 NH4

+: 1.35 PO4

3-: 0.359 SiO3

2-: 14.7

Bottom SedimentNO3

-: 0.11 NH4

+: 1.01 PO4

3-: 0.025 SiO3

2-: 2.51

River NO3

-: 2.76 NH4

+: 0.182 PO4

3-: 0.013 SiO3

2-: 3.94

Kuroshio NO3

-: 5.43 NH4

+: 0.47 PO4

3-: 0.384 SiO3

2-: 6.20

Outflow NO3

-: 11.8 NH4

+: 2.38 PO4

3-: 0.57 SiO3

2-: 20.1

Yellow Sea NO3

-: 0.027 NH4

+: 0.008 PO4

3-: 0.004 SiO3

2-: 0.107

Atmosphere NO3

-: 0.37 NH4

+: 0.80 PO4

3-: 0.002 SiO3

2-: 0.047

East China Sea Shelf

a. Summer

unit: ×103 mol/sZhang et al., 2004

We need an onshore flux from the Kuroshio to support the above results

1.2 Sv in Chen and Wang(1999), estimated by

a box model

Teague et al, CSR, 2003Fig.2

Fig.3

Teague et al, CSR, 2003

Oct.-Dec.,1999

1) What is the seasonal variation of Kuroshio onshore flux?

2) What is the spatial distribution of Kuroshio onshore flux?

3) What is the role of Kuroshio onshore flux in the material transport in the ECS?

As a annual mean,

Tsushima St.: ~2.7 Sv

Taiwan St.:1~2 Sv

Kuroshio onshore flux: ~1 Sv

(Autumn: ~3 Sv)

→ Examining results of numerical model

Guo et al., JPO, 2003.

TAS:Taiwan Strait

ET: East of Taiwan

RK-1~4:four sections

TOS: Tokara Strait

OS: Osumi Strait

EC: East of Cheju

CS: Cheju Strait

TUS: Tsushima Strait

200m-isobath (black dots--every 30 grids). Kuroshioonshore flux:the VT through this line.

Observed data at PN-line (upper panels) for along-shelf geostrophic velocity referred to 100 m ADCP current data, potential temperature and salinity, and the corresponding model results of NEST3 (lower panels). The observed potential temperature and salinity data are averaged from 1973 to 1993; the model results are from 1994 to 1998. Regions with negative values of along-shelf velocity are shaded.

Time series of daily volume transport (thin line) and 90-day running mean (thick line). The first and second numbers in the bracket of each panel are the time average and standard deviation, respectively.

Thin line: daily KOF; upper thick line: 90-day running mean of daily KOF; Broken thin line: difference between daily VTs through Tsushima Strait and Taiwan Strait; lower thick line: difference between daily KOF and its 90-day running mean.

1.46 1.17 Sv± 1.39 0.90 Sv±

0.01 0.37 Sv− ±

Minimum in Jun.~Jul.: ~0.5 Sv

Maximum in Oct.~Nov. :~3Sv(consistent with Teague et al.,2003).

The water budgets in the ECS and in the continental shelf of ECS as a mean state. The number shows volume transport (Sv) through each section; the arrow indicates the direction of volume transport.

What is the spatial distribution of KOF (1.46Sv)?

VOL: mean KOF (0.2 Sv); IVOL: spatial integration (1 Sv); SD-D: standard deviation of daily KOF at each grid point (0.02 Sv); SD-L: standard deviation of 90-day running mean (0.02 Sv); SD-S: standard deviation of the difference between daily KOFand its 90-day running mean (-0.02 Sv). The positive value of KOF is defined as that onto the continental shelf of the ECS.

SD-D: all the variations SD-L: seasonal variationsSD-S: short-term variations

Monthly anomaly of KOF at each grid point of the 200m-isobath (Jan-Dec, unit is 0.1 Sv, origin is shifted to the corresponding number of the month); the temporal average of KOF is also presented for reference (Ann, unit is 0.2 Sv).

Time series of daily KOF(thin line) and its 90-day running mean (thick line) through the upper layer (a), two middle layers (b and c), and lower layer (d).

Depth dependence of KOF and its variation

Passive tracer experiments

The calculation starts from 1993 with zero initial value over entire model domain and ends in 1998. During the calculation, the value of three tracers is fixed to 1.0 at three places denoted by Taiwan Strait, east of Taiwan and Yellow Sea and fixed to 0 at other places.

Summary• KOF has a strong seasonal variation: ~0.5

Sv in summer and ~3 Sv in winter• KOF has two major sources: northeast of

Taiwan and southwest of Kyushu• KOF has vertical structure: 0.68 Sv for 0-50

m, 0.27 Sv for 50 –150 m, 0.52 for 150 m –bottom

• KOF has strong effects on material transport• Mechanism: local effects (wind, rivers

runoff, heating and cooling) and remote effects (variations in the Kuroshio)

1

0 0

( , )

z

a bz z z z

M fcurl M

H H

D AJ H curl curl curl curl

H H H H

tτ τ

χρ ρ

−

• ∇ =

+ − + −

∂ ⎛ ⎞ ⎛ ⎞+ ⎜ ⎟⎜ ⎟∂ ⎝ ⎠⎝ ⎠⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎛ ⎞

⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠⎝ ⎠ ⎝ ⎠

rr

rrr v

1

0 0

( , ) a bz z

fM J H curl curl

H H H

τ τχ

ρ ρ−• ∇ = + −

⎛ ⎞ ⎛ ⎞⎛ ⎞⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠

r vr

Vol ume Tr anspor t acr oss i sobat hs

Anomaly of four terms

DIN → DINC, DINT, DINK

DIP → DIPC, DIPT, DIPK

C: Changjiang, T: Taiwan Strait, K: Kuroshio

DIN=100DINC=17.5

DINT=28.8

DINK=53.7

DIP=100DIPC=0.6

DIPT=28

DIPK=71.4

Thanks