Breif ITF review; Pacific inflow into the Indonesian Seas
Arnold L. Gordon, CLIVAR ITF Task Team, Ancol, Indonesia, 12-13 March 2012
Indonesian Throughflow [ITF]
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
Corrected from Gordon et al, 2010
INSTANT: 2004-2006 simultaneous ITF array
overflow
1.1
2.3
Imbalance ~ 2-3 Sv: uncertainty;
and/or missing links,
e.g. Karimata, wide-eastern
Halmahera/Maluku portal?
Mak
11.6
0.3
1.4
1.6
2.4
2.3
2.7
1.9
Lifa
1
Ombai, 4.9
Lombok
2.6
Timor, 7.5
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
Inflow
Pacific
Outflow
Interior Indonesians Seas
Heating of upwelled thermocline water (upper 500 m)
~80 W/m2
sea surface
Indian
0- 100 m: 5.5 Sv
0-100 m 4.1 Sv
Isotherm shallowing
100-500 m: 8.7 Sv
Upwelling: 1.4 Sv
Thermocline upwelling cell
100-500 m: 7.3 Sv
Null level upwelling <10-6 m/sec 500-600 m layer
<0.6 Sv net upwelling
Lifamatola Passage
>600 m 2.9 Sv
1940 m
600 m to Sunda sill depth: 2.3 Sv
Deep ‘overflow’ upwelling cell
~1300-1500 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?]
SST intraseasonal variance to total SST
variance
?
>1250 m overflow
200-2000 m
Tides; M2
Karimata
1 Sv ?
15
The italics numbers in black represent transport values based
on pre-INSTANT data. The red numbers are the 2004-2006 3year 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
part of coral triangle
m/sec
Negative values denote flow towards
the south
More about the ‘ENSO factor’, in Makassar Strait
Along channel speeds m/sec,
upper 300 m at 2°51' S; 118°28'
E
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]
Mak obs
Observation:model comparison
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.
HYCOM full depth Luzon Strait transport scales to nino4
HYCOM upper ~ 100 m
seasonal cycle removed
Mindanao Leakage
Makassar Strait
Sibutu Passage
Sibutu transport: strong ENSO dependence
Luzon Strait
Sibutu Passage
Karimata Strait
Karimata transport: noisy; weak ENSO dependence
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.
HYCOM
2008
La Niña
‘salty’
C
vvB
Low SSS
Low salinity surface layer produces an
eastward pressure gradient in upper
100 m
A
HYCOM
2004
El Niño
SCS/Suluthroughflow
freshening
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
The Hypothesis, ENSO connection
Strong Luzon throughflow
El Niño
Weak Luzon throughflow
~100 m
~100 m
Blocked:
upper ~100 m
40 m
40 m
Blocked:
upper ~40 m
local monsoonal wind
[stronger in la nina]
Mindanao surface layer
blocked upper ~100 m
WPWP low leakage to ITF
Mindanao surface layer
blocked upper ~40 m
WPWP high leakage to ITF
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.
Mindanao Current
Mindanao Current
La Niña
In revision GRL
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 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).
Maybe More?
Anomaly of Luzon transport is out-of-phase with total ITF anomaly
[sum of Lombok + Ombai + Timor]
Increased Luzon Throughflow may reduce export to Indian Ocean?
ITF export to Indian Ocean
This happens during El Niño
This happens during La Niña
Increase SCS throughflow during El Niño
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
C
B
Maluku Sea
Halmahera Sea
1986-1999 gray
Tropical Pacific GATEWAY
How to determine the retroflection leakage?
Go here
A
C
B
Maluku Sea
Halmahera Sea
Go here
Go here
Tropical Pacific GATEWAY
How to determine the retroflection leakage?
I propose that GATEWAY has a component covering exchange of
Maluku/Halmahera with Seram Sea
x
x
?
x
Seram Sea inflowx