Seasonal and interannual variability in the East Sea ecosystem: effects of nutrient

transport through the Korea Strait

Chan Joo Jang, and Yuri OhKorea Institute of Ocean Science & Technology

2014 ROMS/TOMS User WorkshopRovinj, Croatia, 26-29 May

“Why do we care about Biology as physical oceanographers?Because of Physics!”

Courtesy: Francesco

2012.4-5 composite

GOCI CHL

The East Sea (Japan Sea)Talley et al 2002

Korea

Cascading sites around the world…

not so many, but powerful drivers of the overall circulation, heat/salt /carbon transfer, and rele-

vant for climate dynamics

Courtesy: Sandro Carniel

From Ivanov et al., PIO (2004) & Durrieu de Madron et al., PIO (2005))

Deep ConvectionTalley et al 2002

Korea

Long-Term Mean Chlorophyll-aEast Sea (Japan Sea)

Log (CHL) mg m-3

LC

NKCC SPF

JB

YRYB

SS

TS

UB

NB

OB

EKWC

KS

EKWC: East Korean Warm Cur-rentJB: Japan BasinKS: Korea StraitLC: Liman CurrentNB: Nearshore BranchNKCC: North Korea Cold Cur-rentOB: Offshore BranchSPF: Subpolar FrontSS: Soya StraitTS: Tsugarn StraitUB: Ulleung BasinYB: Yamato BasinYR: Yamato Rise

CHL variability

Yoon et al (2013)

Gallisai et al. 2012 (Biogeosciences Discus-sions)

1. Coastal Upwelling(You & Park, 2009)

KOREA

Japan

2. Nutrient transport through the KS

Nutrient transport through the KS

DIN : Dissolved inorganic NitrogenDIP : Dissolved inorganic phosphorus

◀ The annual mean fluxes of DIN and DIP transported through the KS are rela-tively large compare to other nutrient sources.

Morimoto et al. (2009)

Total 3.59 kmol/s Total 0.29 kmol/s

Vertical cross sections of fluorescence (Aug 2008)

Roh et al. (2012)

▲ The Tsushima intermediate water with high nutrient may contribute to maintain-ing the SCM.

SCM (subsurface chloro-phyll maximum layer)

Yoo and Kim (2004)

S V

Objective

• To investigate how the nutrient transport through the Korea Strait affect the ecosystem in the East Sea (considering higher primary production in the southern basin)

Numerical experiments

Hypothesis: Nutrient transport through the KS contributes to the ES ecosystem, mainly to southwestern area.

Two numerical experiments with different nutrient transports:

1)Seasonally varying nutrient flux2)No nutrient flux

Methodology: 3D circulation-biological coupled model

3D circulation - biologicalcoupled model

Circulation model

Initial condi-tion

Circulation only-modelSpin-up (10 years)

Bound-ary condi-tion(at KS)

T, S : observation2D-U,V : Kim (1996)3D-U,V : observation

ROMS

Biological modelSeasonally varying N flux no N flux

N : WOA2005 P, Z, D : 1.0 mmolN/m3

N : WOA2009 P : 50% of seaWiFS (roms_agrif) Z, D : 20% of seaWiFS

No N flux (bry value = inner value)

1. domain: 126.5˚E-142.5˚E, 33˚N-52˚N

3. Horizontal resolution: 1/6˚4. Vertical layers: 30 layers

2. Topography : ETOPO5

5. forcing: ERA40 (bulk formula)6. Integration: 10 years

+Low trophic biolog-

ical modelNPZD model

N cycle, 7 biochemical processes

Powell et al. (2006)

Coastal upwelling

Korea

Japan

(You & Park, 2009)

Idealized Ecosystem model for coastal upwelling

• grid:41x80x16(41km x 80km x 150m)

• IC: T- 22oC at 0m, 14oC at the bottom, S-uniform(35psu)

• Wind stress: southly (0.02, 0.05, 0.1 Pa)

• OBC: Radiation

Wind = 0.02, 0.05, 0.1 Pa

IC

Upwelling Case (Day 20)wind change effects

0.1 Pa

T P Z D DIN

0.02 Pa

Model Validation I

Model MLD (m)

0.5 m/s

Model SST ( ℃ ) & surface current (m/s)

Feb

Aug

Model Validation II

Spring bloom

Fall bloom

Model

Chlorophyll-a concentration (mg/m3)Spring bloom

Fall bloom

SeaWiFS+MODIS (1998-2012)

Exp 2) No fluxExp 1) Seasonally varying flux

Experiment ResultsChlorophyll-a

Exp 2) No flux

Exp 1) Seasonally varying flux

nutrientnutrient Chlorophyll-aChlorophyll-a

Exp 2) - Exp1)

nutrient

134 °E

Experiment Results134 °E Chlorophyll-a &

nutrient

4-5 mmol N/m3 1-2

mmol N/m3

Exp 1) Seasonally varying flux

Exp 2) No flux

MLD

Exp 2) No flux

Exp 1) Seasonally varying

Nutrient

Phyto P

Zoo P

Apr Apr

Apr Apr

Apr Apr

Exp 1) Seasonally varying

Nov Nov

Nov Nov

Nov Nov

Exp 2) No flux

130°E

Experiment ResultsNutrient & phytoplankton &

Zooplankton

130°E

Conclusion

When there was no nutrient flux through the Korea Strait, the southern East

Sea shows (within limited model resolution & simple NPZD model) :

– Spring bloom considerably weakened

– Fall bloom almost disappeared

– The Subsurface Chlorophyll Maximum layer was not distinct

But, the northern basin shows insignificant changes.

The Nutrient transport through the Korea Strait contributes

to higher primary production in the southern East Sea.

Challenges & Limitations

• Resolution-1/6 deg (10 km)– EKWC overshooting– UWE, upwelling

• NPZD– Only one compartment of PP & ZP– T dependency (photosynthesis, grazing etc.)

ignored– BC & parameters poorly known

Future Work

• Nutrient budget analysis• Experiments with yearly- varying nutrient

transport through the KS (with climatologi-cal forcing)

HVALA THANK YOU

RCM nestingfor Climate Change Projection

25

North Pacific(Ocean only) → Western N. Pacific (ocean only) → East Sea (Coupled Model)

1/6 x 1/6 deg.

1/12 x 1/12 deg.

1/24 x 1/24 deg.

Projected Ocean Warmingwinter (2081~2100 – 1981~2000)

26

Color shading: SST changeContours: SSH (red-future)

Relative smaller warm-ing: southward shift of Kuroshio

Ocean projection with a GCM(CanESM2) atmospheric forcing (pseudo global warming)

Integrated RCM

Nutrient Supplythrough the Korea Strait

(Kawk et al 2013)

Nitracline

Euphotic depth