Monitoring in the ITF InflowRegion

A.M. Thurnherr with input from A. Gordon & T. Kanzow

ant@ldeo.columbia.edu

Lamont-Doherty Earth Observatory

ITF Inflow Region Monitoring – p.1/16

The Indonesian Throughflow

A. Gordon (pers. comm.)

ITF pathways are complex (topography, forcing)

ITF pathways vary with time (ENSO, Monsoon)

⇒ an interesting monitoring challenge ITF Inflow Region Monitoring – p.2/16

The INSTANT Program

http://www.ldeo.columbia.edu/res/div/ocp/projects/instant/projectDescription.html

monitor up- and downstream choke points

very successful but no direct connection with tropical Pacific sourcewaters (required to understand variability of pathways and its drivers)

⇒ GATEWAYITF Inflow Region Monitoring – p.3/16

Pathways: Makassar Strait

118˚E 120˚E 122˚E 124˚E 126˚E 128˚E 130˚E 132˚E 134˚E4˚S

2˚S

0˚

2˚N

4˚N

6˚N

8˚N

Sulawesi

Mindanao

ObiH

almah

era

S. Utara

Sulu Sea

New G

uinea

BuruSeram

S. Utara

Banda S.

Seram SeaLifam

atola P.

Mak

assa

r S

trai

tCelebes Sea

Mol

ucca

Sea

Sib

utu

P.

main pathway for warm, shallow ITF water

GATEWAY monitoring like INSTANT

Celebes sea is connected to Molukka & Sulu seas, not to the tropicalPacific

ITF Inflow Region Monitoring – p.4/16

Pathways: Sibutu Passage

118˚E 120˚E 122˚E 124˚E 126˚E 128˚E 130˚E 132˚E 134˚E4˚S

2˚S

0˚

2˚N

4˚N

6˚N

8˚N

Sulawesi

Mindanao

ObiH

almah

era

S. Utara

Sulu Sea

New G

uinea

BuruSeram

S. Utara

Banda S.

Seram SeaLifam

atola P.

Mak

assa

r S

trai

tCelebes Sea

Mol

ucca

Sea

Sib

utu

P.

deep Sulu sea likely ventilated via Sibutu passage (Gordon et al., 2011)

significant contribution to Makassar from SCS via Sulu and Sibutupassage (“SCS Throughflow”) during El Niños (Gordon et al., in review)

piracy ⇒ monitor Luzon strait and/or Panay Sill insteadITF Inflow Region Monitoring – p.5/16

Molukka Sea

118˚E 120˚E 122˚E 124˚E 126˚E 128˚E 130˚E 132˚E 134˚E4˚S

2˚S

0˚

2˚N

4˚N

6˚N

8˚N

Sulawesi

Mindanao

ObiH

almah

era

S. Utara

Sulu Sea

New G

uinea

BuruSeram

S. Utara

Banda S.

Seram SeaLifam

atola P.

Mak

assa

r S

trai

tCelebes Sea

Mol

ucca

Sea

Sib

utu

P.

both shallow and deep ITF waters, heading for Makassar strait andLifamatola passage, respectively, pass through the Molukka sea

topographically complex ⇒ pathways are not obvious

low latitude ⇒ monitoring based on geostrophy may not workaccurately and will be hard to defend in proposals

ITF Inflow Region Monitoring – p.6/16

2005–2007 Drifter Tracks

2006

115°E

115°E

120°E

120°E

125°E

125°E

130°E

130°E

135°E

135°E

0° 0°

5°N 5°N

10°N 10°NFig. by P. Mele

2005 20072006

Mindanao current bifurcates in Molukka sea with one branch flowingaround Sulawesi Utara before returning to the Pacific and the otherflowing into the Celebes sea

ITF Inflow Region Monitoring – p.7/16

GATEWAY Region

118˚E

118˚E

119˚E

119˚E

120˚E

120˚E

121˚E

121˚E

122˚E

122˚E

123˚E

123˚E

124˚E

124˚E

125˚E

125˚E

126˚E

126˚E

127˚E

127˚E

128˚E

128˚E

129˚E

129˚E

130˚E

130˚E

131˚E

131˚E

132˚E

132˚E

133˚E

133˚E

134˚E

134˚E

135˚E

135˚E

4˚S

4˚S

3˚S

3˚S

2˚S

2˚S

1˚S

1˚S

0˚

0˚

1˚N

1˚N

2˚N

2˚N

3˚N

3˚N

4˚N

4˚N

5˚N

5˚N

6˚N

6˚N

7˚N

7˚N

8˚N

8˚N

ITF Inflow Region Monitoring – p.8/16

Molukka Sea

124˚E

124˚E

125˚E

125˚E

126˚E

126˚E

127˚E

127˚E

128˚E

128˚E

129˚E

129˚E

2˚S

2˚S

1˚S

1˚S

0˚

0˚

1˚N

1˚N

2˚N

2˚N

3˚N

3˚N

4˚N

4˚N

5˚N

5˚N

6˚N

6˚N

7˚N

7˚N

How can one monitor the circulation in this region effectively?

ITF Inflow Region Monitoring – p.9/16

Molukka Sea Monitoring Sections

118˚E 120˚E 122˚E 124˚E 126˚E 128˚E 130˚E 132˚E 134˚E4˚S

2˚S

0˚

2˚N

4˚N

6˚N

8˚N

B

A

C

D

exchange between Celebes and Molukka seas can only be monitoredalong section C

Mindanao retroflection can be monitored along sections A & B

exchange through Lifamatola passage can potentially be monitoredalong section D

ITF Inflow Region Monitoring – p.10/16

Section C (Mindanao-Sulawesi)

-500

0

500

1000

1500

2000 0 50 100 150 200 250 300 350 400 450

Dep

th [m

]

Distance from Northern End [km]

N channel: 50 km wide, 1500 m deep; min. 2 velocity moorings;sufficiently north (≈5

◦N) to be suitable for monitoring with PIEs?

central region: <500 m deep; 1–2 short moorings

S channels: 2 narrow deep channels >1500 m; 1 channel ≈1000 m; 3moorings

ITF Inflow Region Monitoring – p.11/16

Secs A & B (Mindanao-Halmahera)-500

0

500

1000

1500

2000

2500

3000

3500 0 50 100 150 200

Dep

th [m

]

Distance from Northern End [km]

-500

0

500

1000

1500

2000

2500

3000

3500 0 20 40 60 80 100 120 140 160 180

Dep

th [m

]Distance from Northern End [km]

A: min. 3–4 moorings, leaving significant side gaps; cross-section notwell suited for geostrophic moorings(?)

B: 3 moorings; too close to equator for geostrophic method

in addition to or instead of section A, the Mindanao current canpotentially be monitored further north (with PIEs?)

ITF Inflow Region Monitoring – p.12/16

Secs A & B (Mindanao-Halmahera)-500

0

500

1000

1500

2000

2500

3000

3500 0 50 100 150 200

Dep

th [m

]

Distance from Northern End [km]

-500

0

500

1000

1500

2000

2500

3000

3500 0 20 40 60 80 100 120 140 160 180

Dep

th [m

]Distance from Northern End [km]

the available float trajectories suggest that inflow into the Celebes seais ≈ residual between sections A and B

however, this ignores any exchange across southern part of section C(both shallow and deep) ⇒ hard to defend in proposals

ITF Inflow Region Monitoring – p.13/16

Section D (Sulawesi-Halmahera)

-500

0

500

1000

1500

2000

2500

3000

3500 0 50 100 150 200 250 300

Dep

th [m

]

Distance from Western End [km]

entire deep ITF flows south through Molukka sea and over the sill inLifamatola passage

4 separate deep channels in Molukka sea; min. 4 moorings required(low latitude precludes use of geostrophic moorings)

ITF Inflow Region Monitoring – p.14/16

Lifamatola Passage

118˚E 120˚E 122˚E 124˚E 126˚E 128˚E 130˚E 132˚E 134˚E4˚S

2˚S

0˚

2˚N

4˚N

6˚N

8˚N

Sulawesi

Mindanao

ObiH

almah

era

S. Utara

Sulu Sea

New G

uinea

BuruSeram

S. Utara

Banda S.

Seram SeaLifam

atola P.

Mak

assa

r S

trai

tCelebes Sea

Mol

ucca

Sea

Sib

utu

P.

Lifamatola passage is “natural” location for monitoring (much bettersignal-to-noise ratio than section D with much fewer instruments)

strong bottom-intensified flows make mooring design difficult; andupper-ocean moored hydrographic measurements perhaps impossible

ITF Inflow Region Monitoring – p.15/16

Conclusions

118˚E 120˚E 122˚E 124˚E 126˚E 128˚E 130˚E 132˚E 134˚E4˚S

2˚S

0˚

2˚N

4˚N

6˚N

8˚N

B

A

C

D

clear science goals are required for a detailed monitoring plan

personal preferences: (i) because of low latitude, direct velocitymeasurements, rather than geostrophy-based methods; (ii) section C, ifexchange btw. Celebes and Molukka seas is important; (iii) Lifamatolapassage rather than section D, if monitoring of deep ITF is important.

ITF Inflow Region Monitoring – p.16/16