Breif ITF review; Pacific inflow into the Indonesian SeasArnold L. Gordon, CLIVAR ITF Task Team, Ancol, Indonesia, 12-13 March 2012

Pacific Ocean Entry Portals:• South China Sea via Luzon Strait to Karimata and Sibutu;• Tropical Pacific via Mindanao & Halmahera Eddies [Retroflections];[Torrie Strait]

Indian Ocean Exit Portals:Sunda Archpeligo passages:Lombok, Ombai, Timor, [Sunda Strait, Malacca Strait]

Interior Seas [the mix-master]:Makassar Strait: western boundary, primary inflow pathway;Eastern seas: Banda ‘cyclonic gyre’,Seram/Halmahera/Maluku Seas puzzle

I n d o n e s i a n T h r o u g h fl o w [ I T F ]

Imbalance ~ 2-3 Sv: uncertainty; and/or missing links, e.g. Karimata, wide-eastern Halmahera/Maluku portal?

Mak11.6

Lombok2.6

Ombai, 4.9

Timor, 7.5

Lifa1

INSTANT: 2004-2006 simultaneous ITF array

1.1 0.3 1.4 1.6

overflow

2.3 2.3

Corrected from Gordon et al, 2010

2.4 2.7 1.9

Schematic of approximate inflow/outflow and upwelling pattern during the 3 year observational period of INSTANT

Strong upwelling and air-sea heat flux- a tidal dissipation driven mix-master acting on a ~15 Sv stream

Inflo

w

Outf

lowPacific Indian

sea surface

Upwelling: 1.4 Sv

Heating of upwelled thermocline water (upper 500 m)~80 W/m2

0- 100 m: 5.5 Sv0-100 m 4.1 Sv

Isotherm shallowing

Thermocline upwelling cell

Deep ‘overflow’ upwelling cell

Null level upwelling <10-6 m/sec 500-600 m layer<0.6 Sv net upwelling

100-500 m: 7.3 Sv100-500 m: 8.7 Sv

Interior Indonesians Seas

Lifamatola Passage>600 m 2.9 Sv

600 m to Sunda sill depth: 2.3 Sv

~1300-1500 m1940 m

Gordon, A.L.; Sprintall, J.; Van Aken, H.M.; Susanto, D.; Wijffels, S.; Molcard, R.; Ffield, A.; Pranowo, W.; Wirasantosa, S. (in press) “The Indonesian Throughflow during 2004-2006 as observed by the INSTANT program.” Dynamics of Atmosphere and Ocean: “Modeling and Observing the Indonesian Throughflow”.

Indonesian Throughflow ~15 Sv [INSTANT: 2004-2006] but ~11 Sv from non-simultaneous obs of 1990s [ENSO Factor?]

15

>1250 m overflow200-2000 m

Karimata1 Sv ?

The italics numbers in black represent transport values based on pre-INSTANT data. The red numbers are the 2004-2006 3-year mean transports measured by INSTANT.

In Lifamatola Passage the green number is the INSTANT overflow transport >1250 m, representing the overflow into the deep Seram and Banda Sea

?

Tides; M2

SST intraseasonal variance to total SSTvariance

part of coral triangle

Along channel speeds m/sec, upper 300 m at 2°51' S; 118°28'

E

m/s

ecN

egati

ve v

alue

s de

note

flow

tow

ards

th

e so

uth

V-max ~140 m at 0.65 m/s to ~70 m at 0.95 m/s

~20°C at 140 m; ~25°C at 70 m

[ENSO thermocline heaving is much smaller]

More about the ‘ENSO factor’, in Makassar Strait

Mak obs

HYCOM

Monthly mean anomaly of along-channel velocity at 60 m from the 2004-2011 mean. The seasonal signal has been removed; data smoothed with a 7-month running mean. The gray dashed curve is a 3rd order polynomial fit to the Makassar time series. The apparent regime change in 2007, roughly coincides with a shift from prolonged El Niño to a period of more frequent El Niño/La Niña transitions.

Observation:model comparison

HYCOM upper ~ 100 mseasonal cycle removed

HYCOM full depth Luzon Strait transport scales to nino4

Sibutu transport: strong ENSO dependence

Karimata transport: noisy; weak ENSO dependence

Luzon Strait

Sibutu Passage

Karimata Strait

Sibutu Passage

Mindanao Leakage

Makassar Strait

vvB

A

C

Low salinity surface layer produces an eastward pressure gradient in upper

100 m

Low SSS

The freshwater plug: the low salinity Sulu Sea surface layer (upper 100 m) injected into western

Sulawesi Sea via Sibutu Passage imposes an eastward pressure gradient [relative to 1000 db]

within the Sulawesi Sea.

2004El Niño

2008La Niña

A hybrid water column [composed from archive obs] in western Sulawesi: Sulu upper 100 m replacing average upper 100 of the Sulawesi Sea Imposes increased eastward pressure gradient in

upper 100 m

HYCOM

HYCOM

‘salty’

SCS/Suluthroughflow freshening

El Niño La NiñaStrong Luzon throughflow Weak Luzon throughflow

40 m40 m

~100 m ~100 m

Mindanao surface layer blocked upper ~100 mWPWP low leakage to ITF

Mindanao surface layer blocked upper ~40 mWPWP high leakage to ITF

Min

da

na

o C

urr

en

t

Min

da

na

o C

urr

en

t

Blocked: upper ~100 m

Blocked: upper ~40 m

local monsoonal wind [stronger in la nina]

Karimata throughflow, responds to local wind [stronger in la nina] rather than the Luzon Strait throughflow, as does Sibutu, leading to the patterns proposed above.

The Hypothesis, ENSO connection

• In 2008-2009, the Makassar throughflow profile dramatically changed, with the characteristic thermocline velocity maximum increasing from 0.7 to 0.9 m/sec and shifted from 140 m to 70 m, amounting to a 47% increase in warm water transport between 50 and 150 m during the boreal summer.

• HYCOM output indicates that ENSO related changes of the South China Sea (SCS) throughflow into the Indonesian seas are the likely cause. Increased SCS throughflow during El Niño with a commensurate increase in the southward flow of buoyant SCS surface water through the Sulu Sea into the northern Makassar Strait inhibits tropical Pacific surface water injection into Makassar Strait.

• During La Niña SCS throughflow is reduced or reversed allowing tropical Pacific surface flow into the ITF, increasing the flux of warm water available to spread into the Indian Ocean, affecting regional sea surface temperature and climate (with 2-3 year lag, Song et al. 2004).

South China Sea Throughflow Impact on the Indonesian Throughflow

Arnold L. Gordon, Bruce A. Huber, E. Joseph Metzger, R. Dwi Susanto, Harley E. Hurlburt, T. Rameyo Adi

In revision GRL

Maybe More?Anomaly of Luzon transport is out-of-phase with total ITF anomaly

[sum of Lombok + Ombai + Timor]

This happens during El Niño This happens during La Niña

Increased Luzon Throughflow may reduce export to Indian Ocean?

Increase SCS throughflow during El Niño

ITF export to Indian Ocean

2004-2006: agrees with INSTANT, Gordon et al, 2010, Table 1

Pacific Ocean Entry Portals:• South China Sea via Luzon Strait to Karimata and Sibutu;• Tropical Pacific via Mindanao & Halmahera Eddies [Retroflections];[Torrie Strait]

Indian Ocean Exit Portals:Sunda Archpeligo passages:Lombok, Ombai, Timor, [Sunda Strait, Malacca Strait]

Interior Seas [the mix-master]:Makassar Strait: western boundary, primary inflow pathway;Eastern seas: Banda ‘cyclonic gyre’,Seram/Halmahera/Maluku Seas puzzle

A

BC

1986-1999 gray

Mindanao Retroflection

North Pacific

Halmahera Retroflection

South Pacific

Mak

assa

r

Tropical Pacific GATEWAYHow to determine the retroflection leakage?

Halmahera SeaMaluku Sea

A

BC

Mindanao Retroflection

North Pacific

Halmahera Retroflection

South Pacific

Mak

assa

r tim

eser

ie

Tropical Pacific GATEWAYHow to determine the retroflection leakage?

Halmahera SeaMaluku Sea

Too co

mplicated

Blackbox it

Go here

Go here

Go here

xx

x

?

x

Seram Sea inflow

I propose that GATEWAY has a component covering exchange of Maluku/Halmahera with Seram Sea