GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 6, 1329, doi:10.1029/2002GL016564, 2003
Freshwater teleconnections and ocean thermohaline circulation Dan Seidov and Bernd J. Haupt Environment Institute, Pennsylvania State University, University Park, Pennsylvania, USA Received 5 November 2002; accepted 16 January 2003; published 27 March 2003.
[1] Asymmetry of the Atlantic and Pacific sea surface salinity (SSS) is recognized as an important element of the global ocean thermohaline circulation. However, a threshold of such asymmetry that may trigger a true global deepocean conveyor has not yet been examined. A combined effect of the Atlantic-Pacific and the Southern Ocean surface salinity asymmetries also has not yet been clearly shown. We address these issues and conclude that AtlanticPacific SSS asymmetry is one of the most critical elements for maintaining the global ocean conveyor. Our experiments suggest, albeit preliminary, that high-latitudinal freshwater impacts, as a mechanism of altering global ocean thermohaline circulation, may be less effective than interINDEX TERMS: 1655 basin freshwater communications. Global Change: Water cycles (1836); 4512 Oceanography: Physical: Currents; 4255 Oceanography: General: Numerical modeling. Citation: Seidov, D., and B. J. Haupt, Freshwater teleconnections and ocean thermohaline circulation, Geophys. Res. Lett., 30(6), 1329, doi:10.1029/2002GL016564, 2003.
[2] Although there is still a great deal of dispute of how the global ocean thermohaline circulation (THC) really works (or even how it should be correctly defined; a useful recent discussion can be found in Wunsch [2002]), a number of abyssal circulation schemes have been designed during several past decades, of which two schemes are most widely cited. One scheme emphasizes the role of deep-ocean western boundary currents [Stommel, 1958] and is supported by the Stommel-Arons theory of abyssal circulation [Stommel and Arons, 1960]. Another scheme endorses the inter-ocean salinity contrasts as the key control of the THC [e.g., Broecker, 1991; Gordon, 1996, 2001; Schmitz, 1995] and is pictured in a popular salinity conveyor belt metaphor [Broecker, 1991]. Both schemes agree, however, that the global THC is driven by deepwater production in few highlatitudinal convection sites, although the exact nature of impacting this production is still under debate [e.g., Nilsson and Walin, 2001]. [3] The idea of high-latitudinal density control of THC received a lot of attention and has been thoroughly examined in various models [e.g., Bryan, 1986; Ganopolski et al., 1998; Hughes and Weaver, 1994; Manabe and Stouffer, 1988; Rahmstorf, 1996; Renssen et al., 2002; Schmittner and Clement, 2002; Wang and Mysak, 2002]. (see most references in Clark et al. [2002], Haupt et al. [2001], and Rahmstorf [2002]). [4] However, the significance of inter-basin sea surface salinity (SSS) contrasts, especially between Atlantic and Pacific Oceans, has never been disputed (though receiving Copyright 2003 by the American Geophysical Union. 0094-8276/03/2002GL016564$05.00
62
less attention). The inter-basin SSS contrasts are our main focus in this work. [5] Inter-basin SSS asymmetry can develop for a variety of reasons (see a review in Weaver et al. [1999]), which we do not discuss here. Instead, we consider only the consequences of the build up of these contrasts for the global THC. Seidov and Haupt [2002] have shown that SSS zonally averaged within individual basins, i.e. retaining only basin-scale inter-basin SSS contrasts, can yield reasonable global THC. Building on those results, we now introduce a stronger hypothesis that inter-basin SSS gradients, regardless of their genesis and without detailed latitudinal distributions of SSS in different basins, can be accountable for the global THC structure. To test this hypothesis, we use the GFDL ocean model [Pacanowski, 1996] with realistic geography and bottom topography bounded by Antarctica in the south and 80°N in the north. Horizontal resolution is 6° 4° at 12 levels. The GentMcWilliams isopycnal mixing scheme is used as implemented in Pacanowski [1996] (more details and references can be found in Haupt et al. [2001]). [6] We discuss only six sensitivity experiments: (i) the control run (Exp. 1) with annual mean sea surface temperature (SST) and SSS from the Levitus and others’ World Ocean Atlas and Hellerman-Rosenstein wind stress (see all appropriate references in Seidov and Haupt [2002]); (ii) Exp. 2, with constant SSS = 34.25 psu everywhere; (iii) three experiments (Exp. 3 – 5) with idealized SSS contrasts between the North Atlantic (NA) and the North Pacific (NP) with (a) low (about 50% smaller than observed; Exp. 3), (b) moderate (matching observations; Exp. 4), and (c) strong (about 50% larger than observed; Exp. 5); and (iv) Exp. 6 with the Southern Ocean (SO) inter-basin SSS contrasts added to those in Exp. 4 (by increasing SSS to the north of 50°S in all three oceans, and reducing SSS between 50° and 60°S). [7] Inter-basin SSS contrasts in Exp. 3 – 5 are simulated by increasing SSS in the subtropical NA, and decreasing SSS in the NP in the areas shown in Figure 1 and keeping SSS = 34.25 everywhere else. Since the NP area is larger than that in the NA, SSS has been reduced in the NP to preserve globally averaged SSS at 34.25 psu. In Exp. 3, the SSS in the North Atlantic (NA) has been increased by 1.5 psu and decreased in the NP by 1.35 psu; in Exp. 4 and Exp. 5 these numbers are 2.5 psu and 3.5 psu in NA, and 2.25 and 3.15 psu in NP, respectively. The Atlantic-Pacific SSS differences in Exp. 4 match the differences of about 2.5 psu given in the World Ocean Atlas (see references in Seidov and Haupt [2002]), making this scenario the most realistic in representing the NA-NP SS contrasts. It is easy to convert the SSS differences to a freshwater flux equivalent. However, in a study with prescribed SSS, such an estimate may be misleading because the conveyor itself contributes to - 1
62 - 2
SEIDOV AND HAUPT: FRESHWATER TELECONNECTIONS
oceans to the north of 40°N is introduced to mimic a freshwater strip around Antarctica (Exp. 6). The cartoon in Figure 1 does not depict actual fluxes of water vapor; it just indicates that freshwater redistribution between major ocean basins leads, at least partially, to the build-up of inter-basin SSS contrasts. [9] To save space, we depict only the results of Exp. 1, 2 and 4. The Exp. 3 and 5 yield either too weak or too strong global THC relative to the control case. Conversely, meridional overturning in Exp. 6 is an almost perfect match to the control case. Salinity cannot match the control case exactly simply because of the oversimplified SSS distribution in all experiments, except for Exp. 1. However, salinity sections in Exp. 4 mimics the results of the control case fairly well and they show some improvement in Exp. 6 over those in Exp. 4. Figure 2 depicts the meridional overturning streamfunction in the Atlantic (left panel) and Pacific (right panel) sectors of the world ocean (in Sv; 1 Sv = 106 m3/s). Figure 3 represents Meridional sections of salinity in the Atlantic Ocean at 32°W and Pacific Ocean at 170°W, and only in Exp. 1 and 4 (salinity is 34.25 psu everywhere in Exp. 2; the NADW southward incursion is too weak in Exp. 3, too strong in Exp. 5, and in Exp. 6 it is close to those in Exp. 4). [10] In the homogeneous salinity case of the Exp. 2, there is a fairly reasonable overturning and temperature structure in the Atlantic Ocean (temperature is not shown here). This confirms Stommel’s concept [Stommel, 1961] of the North Atlantic Deep Water (NADW) formation being mainly thermally driven, with no need for the NA to be a net evaporative basin. However, there is a catch: despite acceptable Atlantic branch of THC, the global conveyor is not running correctly in this experiment. Although some amount of NADW is still formed (about 10 Sv vs. 15 Sv in Exp. 1; compare Figures 2a and 2c), this water is not dense enough to maintain the
0
a)
5000
0 0
4000
depth [m]
15
4
8
0
0
4000
10
8
4
3000 -4
0
-4
e)
5000 -20
S
-10
0
10
N
20
30
Latitude [o]
5
0
0 0
40
50
60
-35
1000 2000
5 -1
4000
-8
5000
70
0 -4 -8 -10 -15 -20 -25 -30 -2-52-105 0 -3 - 15
-1
0
d)
15 04-4 -8 -1 0
Latitude [o] 4 8 10 15 4 0 -4
108
-10
0
0
0
-8
-4
-4
f)
0
0
5
N
30 14 12 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -10
10 15 20 25 30 35 40 45 50 55 60
-8
0
-25 -20 -15 -10 -5
S
5
N
0
3000
108
-4
-4
-25 -20 -15 -10 -5 30 14 12 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -10
0
-20
-1 -8 1 0
-2 5
0
5000
-8
-10
-20
10
-8
70
8
4 0
S 4 8 10
8
4 0
0
60
stream function [Sv]
8
4
2000
84 10 10
8
1000
50
4 0 1
0 4
40
Latitude [o]
N
0
30
8
-4
4 10 8
20
4000 -15
-1 5
0
S
10
3000
-8
0
4
-4
-10
4
-20
0
4 10 8
0
c)
5000
-4
-1 -8 0
2000
0
1084 10
-4
0
3000
4 8 15 20 10 10 8
0
-8
8 4
30 14 12 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -10
Latitude [o]
0 -25 -4 -8 -10 -15 0 -20 -15 -20-1 -80-4 108 15 -25
30 14 12 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -10
10 15 20 25 30 35 40 45 50 55 60
N
0 1000
5
-4
0
0
b) 0
- 10
10
4 0
0
30 14 12 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -10
-8
4
8
4
8
0
0
-25 -20 -15 -10 -5
-15
depth [m]
4
10
0
2000
-1 0 8 -
70
stream function [Sv]
0
60
4
-4
1000
50
0
0
-4
S
4
4 8
0
40
5000
Latitude [o]
N 0
0
30
-4
-20
S
20
4000
-20
10
-15
-15
0
4 8 10 10 15 8 4 0
-10
-10 -8
-25
-10
3000
-30
-20
-15
2000
-2 5 -2 0
-4
-4
0
4000
0
-35 5 -2
- 30
-4
-4
depth [m]
3000
0 -30 -4 -8 -10 -15 -20 -25 15 4 0 -1-40 0 -8 -15 -2-25 30
1000
-2
4
4
0
depth [m]
4
8
10
8
30 14 12 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 -10
depth [m]
0
0
10
8 4
10
10
8
stream function [Sv]
4
0 0
0
depth [m]
4
8 10
stream function [Sv]
4 0
8
15
8
4
2000
4
stream function [Sv]
8
stream function [Sv]
4 10 8
-4
-4 0 0 4
0 1000
4
build-up and sustain of the SSS contrast; see below and also in Manabe and Stouffer [1988]. [8] An analogy of a ‘‘freshwater air teleconnection’’ or ‘‘effective salt teleconnection’’ is invoked to illustrate the build-up of the Atlantic-Pacific SSS asymmetry in Exp. 2– 5, as shown in Figure 1. Similarly, an effective salt teleconnection between the Southern Ocean (SO) and all three
0
Figure 1. In Exp. 2 (see text) SSS is 34.25 psu everywhere in the world ocean. Areas where SSS has been changed: In Exp. 3, SSS has been increased by 1.5 psu in the NA, and decreased by 1.35 psu in the NP; In Exp. 4, SSS has been increased by 2.5 psu in the NA, and decreased by 2.25 psu in the NP; In Exp. 5, SSS has been increased by 3.5 psu in the NA, and decreased by 3.15 psu in the NP; In Exp. 6 (with the same SSS in the NA and NP as in Exp. 4), SSS in the subtropics of the Southern Hemisphere has been increased by 0.1 psu, and decreased by 0.2 psu between 50°S and the Antarctica.
0
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0
/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
-1 0
/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
-4
................................................. ......................................................................... ................................................. ......................... ......................................................................... ................................................. .........................
10 15 20 25 30 35 40 45 50 55 60
Latitude [o]
Figure 2. Meridional overturning in the Atlantic Ocean (left panel; a, c, and e) and Pacific Ocean (right panel; b, d, f ) in Exp. 1, 2, and 4 (see text). Streamfunction is shown in Sv (1 Sv = 106 m3/s).
62 - 3
SEIDOV AND HAUPT: FRESHWATER TELECONNECTIONS
a)
34.4
section at 32.50 oW
5000
-80 -70 -60 -50 -40 -30 -20 -10
0
30
40
50
35
.2
34.8
34.4
c)
4000
section at 32.50 oW -80 -70 -60 -50 -40 -30 -20 -10
0
10
Latitude [o]
20
30
40
50
60
70
34.4
34
.4
b)
section at 170.50 oW
5000
0
10
34
N
30
40
50
33.6
34
34.2
34.2
2000
34.2
34.2
33.4 33.2 33.8 33.6 34
32.2 4 32. 32.6 32.8 33 33.4 33.8
34.2
d)
34.2
section at 170.50 oW
5000
-80 -70 -60 -50 -40 -30 -20 -10
0
10
20
30
40
Latitude [o]
S
38.0 37.5 37.0 36.5 36.0 35.5 35.0 34.5 34.0 33.5 33.0 32.5 32.0 31.5 31.0 30.5 30.0 29.5 29.0
60
3000 4000
38.0 37.5 37.0 36.5 36.0 35.5 35.0 34.5 34.0 33.5 33.0 32.5 32.0 31.5 31.0 30.5 30.0 29.5 29.0
N 34
.2
1000
80
20
Latitude [o]
S 0
salinity [psu]
34.8
33.8
34 34.2
34.4
-80 -70 -60 -50 -40 -30 -20 -10 38.0 37.5 37.0 36.5 36.0 35.5 35.0 34.5 34.0 33.5 33.0 32.5 32.0 31.5 31.0 30.5 30.0 29.5 29.0
.4
34.4
3000
80
34.8
.4
.8
34 34
S
70
2000
N
36 35.2 35.6
34
1000
5000
60
34 34.4 .2
.8 33
.8 345.2 .6 35 3
34.4
3000
20
Latitude [o]
S 0
2000
10
35.2 35 .8 34 .6 34
34.6
4000
depth [m]
34.4
depth [m]
.4
36.4
depth [m]
34
35 34.8
.4 34
3000
0 1000
salinity [psu]
34.8
4000
depth [m]
35.2
34.4
3
34.4
2000
38.0 37.5 37.0 36.5 36.0 35.5 35.0 34.5 34.0 33.5 33.0 32.5 32.0 31.5 31.0 30.5 30.0 29.5 29.0
36 35.235.6
4.8
salinity [psu]
35. 35.6 34.8 2
salinity [psu]
.235.6
.4 34
1000
.6 34
35
0
50
60
N
Figure 3. Meridional salinity sections in the Atlantic Ocean at 32°W (left panel; a and c) and the Pacific Ocean at 170°W (right panel; b and d) in Exp. 1 and 4. NADW-driven global conveyor. Moreover, the meridional overturning in the Pacific Ocean is unrealistic: A strong overturning cell has developed in the northern NP (Figure 2d). Thus, although the THC is indeed thermally driven, it is the inter-basin salinity contrasts that are responsible for a true global NADW-driven conveyor. [11] Despite only rudimentary NA-NP SSS contrasts are prescribed in Exp. 3 –5, the THC tends to return to a more realistic mode, especially in Exp. 4. The overall picture in Exp. 4 (Figures 2e and 2f ) is acceptable - the NADW outflow across 30°S is almost twice as high as in Exp. 3 (not shown), and a tongue of salty and relatively warm NADW is easily seen in the Atlantic salinity section (Figure 3c). If the amplitude of the NA-NP SSS is too small (Exp. 3; not shown), the global conveyor and observed salinity structure cannot develop. Conversely, if this amplitude is too large (Exp. 5; not shown), an exaggerated overturning and vertical salinity structure develops in the Atlantic Ocean. [12] Although Exp. 4 produced a fairly acceptable thermohaline and overturning structure, it failed to match the control case closely enough. Thus, additional controls may be needed to improve the larger picture. The THC dynamics is known to be sensitive to deepwater sources in the northern NA and in the SO. There is an increasing line of argument indicating that surface freshening in SO can be at least as an important THC control, as in the NA [Goosse and Fichefet, 1999; Seidov et al., 2001; Sto¨ssel et al., 1998]. The SO impact can induce a strong bi-polar seesaw behavior - the reduction of NADW leads to increased role of Antarctic Bottom Water (AABW), whereas lessening AABW causes stronger NADW [e.g., Broecker, 1998; Stocker, 1998; Seidov et al., 2001]. [13] To mimic the southern control (Exp. 6), a SO ‘‘freshwater teleconnection’’ has been added to the NANP bridge as shown in Figure 1. This freshwater bridge is much weaker than between NA and NP in Exp. 4 - the SO SSS has been reduced only by 0.2 psu. Nonetheless, it appeared to be sufficient for establishing an almost perfect global THC rivaling the conveyor in the control case, without any need to exceed the observed NA-NP SSS asymmetry (as in Exp. 5). Similarity between overturning in Exp. 1 and Exp. 6 is so strong that we opted not to show the plots of overturning in Exp. 6.
[14] Combined with our recent work [Seidov and Haupt, 2002], the new experiments here show that if the AtlanticPacific SSS contrasts are absent or strongly reduced, a global THC connecting northern Atlantic and Pacific Oceans cannot develop, even if realistic SST are retained. (In one of the runs in Seidov and Haupt [2002], realistic SST were combined with zonally averaged SSS, i.e., without longitudinal SSS gradients anywhere; in that run a global conveyor had not developed either.) [15] Even a moderate and rudimentary NA-NP SSS asymmetry may be sufficient for running a NADW-driven global ocean conveyor. A decrease or increase of this asymmetry can slow down or speed up the conveyor. A threshold in NA-NP SSS difference, after which a true global conveyor emerges, is less than 50% of the observed NA-NP SSS amplitude. A relatively small leveling of the NA-NP asymmetry below that threshold can even allow a competitive NP overturning. The role of THC in sustaining inter-basin salinity contrasts is not yet completely understood. Some studies imply that the conveyor ‘‘on’’ and ‘‘off’’ regimes depend on NA-NP water vapor exchange (e.g. Wang and Birchfield [1992]). On the other hand, Manabe and Stouffer suggest that the conveyor itself, if started, can sustain the NA-NP SSS contrast [Manabe and Stouffer, 1988] (see also Stouffer and Manabe [1999]). Our experiments represent a different line of work, and cannot prove, or disprove results of coupled ocean-atmosphere models. Yet, we show below that they suggest that these opinions may, in fact, converge. [16] To comment on the conveyor capacity to sustain inter-basin SSS contrasts, we analyzed meridional salinity transport by ocean currents. In Atlantic Ocean (Table 1), a stronger conveyor transports salinity into the northern NA, thus effectively removing freshwater from the middle lat-
Table 1. Northward Salt Flux in 1010g/s Across 30°S and 60°N in the Atlantic Ocean Exp. #/Latitude 30°S 60°N
1
3
4
5
6
3.6 0.6
0.4 0.2
2.1 0.6
8.0 1.1
2.7 0.6
62 - 4
SEIDOV AND HAUPT: FRESHWATER TELECONNECTIONS
itudes, rather than compensating for its catchments. Quite opposite, a weaker conveyor fails to transport salt northward into the northern NA and Nordic Seas, and a negative feedback may establish that would further hamper the conveyor operation. This agrees well with Rahmstorf [1996] (see above) and with the results in Manabe and Stouffer [1988]. However, a northward compensatory freshwater influx (i.e., negative salt transport) occurs in the South Atlantic, rather than a southward outflux suggested in Rahmstorf [1996]. There is a negative northward salt transport (or effectively northward freshwater transport) across 30°S in the Atlantic (compare Figures 2 and 3, and Table 1), in agreement with recent results in Saenko et al [2002]. It is also worth while to mention how well salt transports in Exp. 4 and 6 agree with those in Exp. 1 (Table 1). [17] Based on these experiments combined with the results in Seidov and Haupt [2002], we suggest, albeit still preliminary, that high-latitudinal freshwater impacts, as a mechanism of altering global THC, may be less effective than inter-basin freshwater communications. However, more work is needed to resolve this issue. [18] Diagnosing the present-day ocean circulation relies heavily on extensive observations. However, as soon as we head off from the present-day situation to the past or to the future, the ground is lost in having reliable sea surface conditions, especially the hydrological cycle. Our simulations suggest that exact knowledge of the spatial distribution of sea surface salinity may not be critical for THC sensitivity studies, as long as the basin-wide inter-basin SSS contrasts can be specified. Therefore, assessing past and future ocean climates can be done with more confidence, even if simulations employ limited sea surface data. [19] Acknowledgments. The comments of two anonymous reviewers were very useful and are greatly appreciated. This study was supported in part by NSF (NSF projects #9975107 and ATM 00-00545). Acknowledgment is also made to the donors of the American Chemical Society Petroleum Research Fund for partial support of this research (ACS Petroleum Research Fund PRF #36812-AC8). Assistance from Eric Brozefsky is very much appreciated.
References Broecker, W., The great ocean conveyor, Oceanography, 1, 79 – 89, 1991. Broecker, W. S., Paleocean circulation during the last deglaciation: A bipolar seesaw?, Paleoceanography, 13, 119 – 121, 1998. Bryan, F., High-latitude salinity effects and interhemispheric thermohaline circulations, Science, 323, 301 – 304, 1986. Clark, P. U., N. Pisias, T. F. Stocker, and A. J. Weaver, The role of thermohaline circulation in abrupt climate change, Nature, 415, 863 – 869, 2002. Ganopolski, A., S. Rahmstorf, V. Petoukhov, and M. Claussen, Simulation of modern and glacial climates with a coupled global model of intermediate complexity, Nature, 391, 351 – 356, 1998. Goosse, H., and T. Fichefet, Importance of ice-ocean interactions for the global ocean circulation: A model study, J. Geophys. Res., 104, 23,337 – 23,355, 1999. Gordon, A. L., Communication between oceans, Nature, 382, 399 – 400, 1996.
Gordon, A. L., Interocean exchange, in Ocean Circulation and Climate: Observing and Modelling the Global Ocean, edited by G. Siedler, J. Church, and J. Gould, pp. 303 – 314, Academic, San Diego, Calif., 2001. Haupt, B. J., D. Seidov, and E. J. Barron, Glacial-to-interglacial changes of the ocean circulation and eolian sediment transport, in The Oceans and Rapid Climate Change: Past, Present, and Future, Geophys. Monogr. Ser., vol. 126, edited by D. Seidov, B. J. Haupt, and M. Maslin, pp. 169 – 197, AGU, Washington, D. C., 2001. Hughes, C. W., and A. Weaver, Multiple equilibria of an asymmetric twobasin ocean model, J. Phys. Oceanogr., 24, 619 – 637, 1994. Manabe, S., and R. J. Stouffer, Two stable equilibria of a coupled oceanatmosphere model, J. Clim., 1, 841 – 866, 1988. Nilsson, J., and G. Walin, Freshwater forcing as a booster of thermohaline circulation, Tellus, Ser. A, 53, 628 – 641, 2001. Pacanowski, R. C., (Ed.), MOM-2, Documentation, in User’s Guide and Reference Manual, GFDL Ocean Tech. Rep. 3.2, 329 pp., Geophys. Fluid Dyn. Lab., Princeton, N. J., 1996. Rahmstorf, S., On the freshwater forcing and transport of the Atlantic thermohaline circulation, Clim. Dyn., 12, 799 – 811, 1996. Rahmstorf, S., Ocean circulation and climate during the past 120,000 years, Nature, 419, 207 – 214, 2002. Renssen, H., H. Goosse, and T. Fichefet, Modeling the effect of freshwater pulses on the early Holocene climate: The influence of high-frequency climate variability, Paleoceanography, 17(2), 1020, doi:10.1029/ 2001PA000649, 2002. Saenko, O. A., J. M. Gregory, A. J. Weaver, and M. Eby, Distinguishing the influences of heat, freshwater and momentum fluxes on ocean circulation and climate, J., Clim., 15, 3686 – 3697, 2002. Schmittner, A., and A. C. Clement, Sensitivity of the thermohaline circulation to tropical and high latitude freshwater forcing during the last glacial-interglacial cycle, Paleoceanography, 17(2), 1017, doi:10.1029/ 2000PA000591, 2002. Schmitz, W. J., Jr., On the interbasin-scale thermohaline circulation, Rev. Geophys., 33, 151 – 173, 1995. Seidov, D., and B. J. Haupt, On the role of inter-basin surface salinity contrasts in global ocean circulation, Geophys. Res. Lett., 29(16), 1800, doi:10.1029/2002GL014813, 2002. Seidov, D., E. J. Barron, and B. J. Haupt, Meltwater and the global ocean conveyor: Northern versus southern connections, Global Planet. Change, 30, 253 – 266, 2001. Stocker, T. F., The seesaw effect, Science, 282, 61 – 62, 1998. Stommel, H., The abyssal circulation, Deep Sea Res, 5, 80 – 82, 1958. Stommel, H., Thermohaline convection with two stable regimes of flow, Tellus, 13, 224 – 230, 1961. Stommel, H., and A. B. Arons, On the abyssal circulation of the world ocean, I, Stationary planetary flow patterns on a sphere, Deep Sea Res., 6, 140 – 154, 1960. Sto¨ssel, A., S.-J. Kim, and S. S. Drijfhout, The impact of Southern Ocean sea ice in global ocean model, J. Phys. Oceanogr., 28, 1999 – 2018, 1998. Stouffer, R. J., and S. Manabe, Response of a coupled ocean-atmosphere model to increasing atmospheric carbon dioxide: Sensitivity to the rate of increase, J. Clim., 12, 2224 – 2236, 1999. Wang, H. X., and G. E. Birchfield, An energy-salinity balance climate model: Water vapor transport as a cause of changes in the global thermohaline circulation, J. Geophys. Res., 97, 2335 – 2346, 1992. Wang, Z., and L. A. Mysak, Response of the thermohaline circulation to cold climates, Paleoceanography, 17(1), 1006, doi:10.1029/2000PA000587, 2002. Weaver, A. J., C. M. Bitz, A. F. Fanning, and M. M. Holland, Thermohaline circulation: High latitude phenomena and the difference between the Pacific and Atlantic, Annu. Rev. Earth Planet. Sci., 27, 231 – 285, 1999. Wunsch, C., What is the thermohaline circulation?, Science, 298, 1179 – 1181, 2002.
B. J. Haupt and D. Seidov, Environment Institute, Pennsylvania State University, University Park, PA 16802-2711, USA. (
[email protected])
