promoting a thicker sea ice cover than found in
the Southern Ocean, where the temperature and
salinity profiles coincide.
The Bering Strait water, boosted by an additional 0.13–0.18 Sv of river inflow and excess
precipitation, ultimately passes into the North
Atlantic, where it provides the fresh water to offset
the net evaporation over the Atlantic Ocean and
input of salt from the Indian Ocean, conceivably
playing a vital role in the susceptibility of the
Atlantic Ocean to convection (Rahmstorf, 1995,
1996; Weijer et al., 2001a; see Section 4.7.5).
4.7.3 Indonesian Seas
4.7.3.1 Introduction
A pathway for more massive export of Pacific upper
ocean water to an adjacent ocean than afforded
by Bering Strait occurs within the Indonesian
Seas (Fig. 4.7.1d, see Plate 4.7.1d, p. 300; see also
Godfrey, 1996; Lukas et al., 1996). Large-scale
observation-based studies (including inverse solutions) reveal significant Pacific export of fresh water
and heat into the Indian Ocean (Piola and Gordon,
1984, 1986; Toole and Raymer, 1985; Wijffels
et al., 1992; Toole and Warren, 1993; MacDonald,
1993; MacDonald and Wunsch, 1996; Ganachaud,
1999). Shriver and Hurlburt (1997; also see
Goodman, 1998) find profound effects on the
Indonesian ThroughFlow (ITF) if model NADW
formation is shut down, implying that even the faroff Atlantic thermohaline budgets may be related
to ITF (Gordon, 1986). Increased oceanic heat and
freshwater flux into the Indian Ocean at the
expense of the Pacific affect atmosphere–ocean
coupling with potential impacts on the ENSO and
monsoon phenomena. Webster et al. (1998) state
that the ITF heat flux ‘… is comparable to the net
surface flux over the northern Indian Ocean and a
substantial fraction of the heat flux into the western Pacific warm pool … it would appear that
the throughflow is an integral part of the heat
balances of both the Pacific and Indian Oceans.’
Model research reveals dependence of Pacific
and Indian Ocean SST and upper-layer heat storage on the throughflow (Hirst and Godfrey, 1993;
Verschell et al., 1995; Murtugudde et al., 1998).
The Indian and Pacific Oceans would be very different if the ITF were zero (MacDonald, 1993). Maes
(1998) finds that the effect of a zero ITF would
raise sea level in the Pacific and lower sea level in
the Indian by 2–10 cm. Schneider (1998) shows
that the presence of the throughflow shifts the
warmest SST and associated atmospheric convective region towards the west, relative to a nothroughflow condition.
The ITF waters are drawn from the Mindanao
(North Pacific thermocline) and Halmahera (South
Pacific thermocline) eddies at the Pacific entrance
to the Indonesian Seas, between the Philippines and
New Guinea. Models show that the ITF source
water (North Pacific versus South Pacific) depends
upon land geometry and the tropical Pacific wind
fields (Nof, 1996; Morey et al., 1999; Wajsowicz,
1999). Observations show that the ITF is composed mostly of North Pacific thermocline and
intermediate water flowing through Makassar
Strait (Fine, 1985; Ffield and Gordon, 1992;
Gordon, 1995; Gordon and Fine, 1996). Traces
of what may be low-salinity Sulu Sea water are
found in the Makassar Strait thermocline in the
boreal winter season (Ilahude and Gordon, 1996).
Wajsowicz’s (1996) model shows that the westernmost deep channel, Makassar Strait, carries the
bulk of ITF. While some Makassar throughflow
exits the Indonesian Sea within Lombok Channel
(Murray and Arief, 1988), most turns eastward
within the Flores Sea to enter the Banda Sea before
entering the Indian Ocean (Gordon and Fine, 1996).
In the deep channels east of Sulawesi, South Pacific
water infiltrates (isopycnally) into the lower thermocline of the Banda Sea and dominates the deeper
layers through density-driven overflow (Van Aken
et al., 1988; Gordon and Fine, 1996; Hautala et al.,
1996; Ilahude and Gordon, 1996).
The Indonesian Seas are not a passive channel
linking the two oceans: within the seas the ITF
thermal and salinity stratification and the SST are
significantly modified by tidal and wind-induced
mixing and by sea–air fluxes (Ffield and Gordon,
1992, 1996). The various Pacific water masses
composing the ITF are altered, so that the thermohaline profile of ITF entering the Indian Ocean is
quite different from that of the source Pacific
water masses.
4.7.3.2 Transport
ITF transport estimates based on observations
(Fig. 4.7.1d, see Plate 4.7.1d, p. 300), models and
conjecture range from near zero to 30 Sv (Wyrtki,
1961a; Godfrey and Golding, 1981; Murray and
Arief, 1988; Godfrey, 1989; Kindle et al., 1989;
4.7 Interocean Exchange
307
Gordon
the Southern Ocean, where the temperature and
salinity profiles coincide.
The Bering Strait water, boosted by an additional 0.13–0.18 Sv of river inflow and excess
precipitation, ultimately passes into the North
Atlantic, where it provides the fresh water to offset
the net evaporation over the Atlantic Ocean and
input of salt from the Indian Ocean, conceivably
playing a vital role in the susceptibility of the
Atlantic Ocean to convection (Rahmstorf, 1995,
1996; Weijer et al., 2001a; see Section 4.7.5).
4.7.3 Indonesian Seas
4.7.3.1 Introduction
A pathway for more massive export of Pacific upper
ocean water to an adjacent ocean than afforded
by Bering Strait occurs within the Indonesian
Seas (Fig. 4.7.1d, see Plate 4.7.1d, p. 300; see also
Godfrey, 1996; Lukas et al., 1996). Large-scale
observation-based studies (including inverse solutions) reveal significant Pacific export of fresh water
and heat into the Indian Ocean (Piola and Gordon,
1984, 1986; Toole and Raymer, 1985; Wijffels
et al., 1992; Toole and Warren, 1993; MacDonald,
1993; MacDonald and Wunsch, 1996; Ganachaud,
1999). Shriver and Hurlburt (1997; also see
Goodman, 1998) find profound effects on the
Indonesian ThroughFlow (ITF) if model NADW
formation is shut down, implying that even the faroff Atlantic thermohaline budgets may be related
to ITF (Gordon, 1986). Increased oceanic heat and
freshwater flux into the Indian Ocean at the
expense of the Pacific affect atmosphere–ocean
coupling with potential impacts on the ENSO and
monsoon phenomena. Webster et al. (1998) state
that the ITF heat flux ‘… is comparable to the net
surface flux over the northern Indian Ocean and a
substantial fraction of the heat flux into the western Pacific warm pool … it would appear that
the throughflow is an integral part of the heat
balances of both the Pacific and Indian Oceans.’
Model research reveals dependence of Pacific
and Indian Ocean SST and upper-layer heat storage on the throughflow (Hirst and Godfrey, 1993;
Verschell et al., 1995; Murtugudde et al., 1998).
The Indian and Pacific Oceans would be very different if the ITF were zero (MacDonald, 1993). Maes
(1998) finds that the effect of a zero ITF would
raise sea level in the Pacific and lower sea level in
the Indian by 2–10 cm. Schneider (1998) shows
that the presence of the throughflow shifts the
warmest SST and associated atmospheric convective region towards the west, relative to a nothroughflow condition.
The ITF waters are drawn from the Mindanao
(North Pacific thermocline) and Halmahera (South
Pacific thermocline) eddies at the Pacific entrance
to the Indonesian Seas, between the Philippines and
New Guinea. Models show that the ITF source
water (North Pacific versus South Pacific) depends
upon land geometry and the tropical Pacific wind
fields (Nof, 1996; Morey et al., 1999; Wajsowicz,
1999). Observations show that the ITF is composed mostly of North Pacific thermocline and
intermediate water flowing through Makassar
Strait (Fine, 1985; Ffield and Gordon, 1992;
Gordon, 1995; Gordon and Fine, 1996). Traces
of what may be low-salinity Sulu Sea water are
found in the Makassar Strait thermocline in the
boreal winter season (Ilahude and Gordon, 1996).
Wajsowicz’s (1996) model shows that the westernmost deep channel, Makassar Strait, carries the
bulk of ITF. While some Makassar throughflow
exits the Indonesian Sea within Lombok Channel
(Murray and Arief, 1988), most turns eastward
within the Flores Sea to enter the Banda Sea before
entering the Indian Ocean (Gordon and Fine, 1996).
In the deep channels east of Sulawesi, South Pacific
water infiltrates (isopycnally) into the lower thermocline of the Banda Sea and dominates the deeper
layers through density-driven overflow (Van Aken
et al., 1988; Gordon and Fine, 1996; Hautala et al.,
1996; Ilahude and Gordon, 1996).
The Indonesian Seas are not a passive channel
linking the two oceans: within the seas the ITF
thermal and salinity stratification and the SST are
significantly modified by tidal and wind-induced
mixing and by sea–air fluxes (Ffield and Gordon,
1992, 1996). The various Pacific water masses
composing the ITF are altered, so that the thermohaline profile of ITF entering the Indian Ocean is
quite different from that of the source Pacific
water masses.
4.7.3.2 Transport
ITF transport estimates based on observations
(Fig. 4.7.1d, see Plate 4.7.1d, p. 300), models and
conjecture range from near zero to 30 Sv (Wyrtki,
1961a; Godfrey and Golding, 1981; Murray and
Arief, 1988; Godfrey, 1989; Kindle et al., 1989;
4.7 Interocean Exchange
307
Gordon