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Photo: Bruno Marty / IRD
Chapter 3 Observed and expected changes to the tropical Pacific Ocean Alexandre S Ganachaud, Alex Sen Gupta, James C Orr, Susan E Wijffels, Ken R Ridgway, Mark A Hemer, Christophe Maes, Craig R Steinberg, Aline D Tribollet, Bo Qiu and Jens C Kruger
‘The oceans are warming.’ (Bindoff et al. 2007)i
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140°E
160°E
180°
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140°W
120°W
100°W
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3.2.7.2 Effect of waves coming ashore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ÁDWVZKLFKLVDERXWRIWKHRIIVKRUH6:+7KLVLQFUHDVHLV NQRZQ DV ¶ZDYH VHWXS· )LJXUH )RU HQFORVHG ODJRRQV DQG DWROOV WKH ODJRRQ ZDWHUOHYHOFDQUHPDLQDERYHWKHDYHUDJHRFHDQKHLJKWWKURXJKRXWWKHWLGDOF\FOHDQG ULVHVLJQLÀFDQWO\GXULQJODUJHZDYHHYHQWV :DYHVHWXSFDQFUHDWHDGGLWLRQDOKDELWDW VSDFHHQDEOLQJWKHYHUWLFDOJURZWKRIDUHHIDERYHWKHPHDQKHLJKWRIOLYLQJFRUDOV :DYH VHWXS DOVR FUHDWHV D ZDWHU OHYHO JUDGLHQW VORSLQJ WRZDUGV WKH OHVV HQHUJHWLF VLGH RI DQ DWROO UHVXOWLQJ LQ ZDYHGULYHQ ÁXVKLQJ RI ODJRRQV )RU H[DPSOH D VZHOO HYHQWLQ$LWXWDNL&RRN,VODQGVZLWKD6:+RIPDQGDZDYHSHULRGRIVHFRQGV UHVXOWHGLQDZDWHUOHYHOJUDGLHQWRIFPDFURVVWKHODJRRQ7KLVFDXVHGDWULSOLQJRI FXUUHQWVSHHGVLQVLGHWKHODJRRQ 7KHUHIRUHERWKDYHUDJHZDYHFRQGLWLRQVDVZHOODV LQGLYLGXDOHYHQWVFDQKDYHLPSRUWDQWLPSOLFDWLRQVIRUWKHUHQHZDORIODJRRQDOZDWHU
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3.2.7.3 Variability in wave height 7KHUHDUHODUJHQDWXUDOYDULDWLRQVLQWKHZDYHFRQGLWLRQVRIWKHWURSLFDO3DFLÀF2FHDQ $VWKHIRUPDWLRQRIZDYHVLVGULYHQE\ZLQG6:+DQGZDYHSHULRGLQWKHUHJLRQ FDQ EH UHODWHG WR ODUJHVFDOH FOLPDWH SDWWHUQV &KDSWHU (162 HYHQWV DUH D PDMRU VRXUFHRIWKLVYDULDELOLW\$Q(O1LxRHYHQWLVDVVRFLDWHGZLWKKLJKHUZDYHVHDVWRI DERXW(GXULQJWKHDXVWUDOVXPPHU )LJXUH :HVWRI(ZDYHVJHQHUDOO\ GHFUHDVHGXULQJ(O1LxR7KHRSSRVLWHRFFXUVGXULQJ/D1LxDHYHQWV7KHODUJHU(O 1LxRZDYHVLQWKHFHQWUDOVRXWKHUQ3DFLÀFDOVRWHQGWRFRPHIURPDPRUHVRXWKHUO\ GLUHFWLRQWKDQQRUPDO'XULQJWKHUHVWRIWKH\HDUWKHSDWWHUQRILQFUHDVHLQWKHHDVW DQGGHFUHDVHLQWKHZHVWLVVKLIWHGWRZDUGVWKHZHVW )LJXUH
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Sea level (cm)
20 0 -20 1950
1960
1970
1980
1990
2000
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1
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CHAPTER 3
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139
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163°E
165°E
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169°E
171°E
16°S
18°S
20°S
22°S
24°S
26°S
20
21
22
23
24
25
26
27
28
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20°N 10°N 0° 10°S 20°S
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30
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:LWKLQRIWKHHTXDWRUWKHZHVWZDUGÁRZLQJ6(&DOVRGHFUHDVHVLQVWUHQJWKZLWK JOREDOZDUPLQJ,WVLQLWLDOÁRZZKLFKDYHUDJHVEHWZHHQDQGFPSHUVHFRQGLQ WKHXSSHUPLVSURMHFWHGWRGHFUHDVHE\RQO\WRFPSHUVHFRQGLQXQGHU ERWKVFHQDULRVDQGWKHQE\DERXWFPSHUVHFRQGXQGHU%DQGFPSHUVHFRQG XQGHU$LQ7KHFRUUHVSRQGLQJSURMHFWHGUHGXFWLRQVLQ6(&WUDQVSRUW YROXPH RI ZDWHU PRYHG FRPSDUHG ZLWK LWV DYHUDJH SUHVHQW YDOXH EHWZHHQ ( WR :
142
CHAPTER 3
(~ 28 Sv, Figure 3.27) (1 Sv = 1 Sverdrup = 106 m3 per second) are -0.5 to -1 Sv (3–5%) in 2035, -2 Sv (9%) under B1 in 2100 and -4.5 Sv (18%) under A2 in 2100. A vertical section along the equator shows that just below the SEC the eastward EUC is projected to move progressively upwards by about 10 m under B1 and A2 in 2035 and B1 in 2100, and then by 20 m under A2 in 2100 (Figure 3.27). The eastward EUC is also expected to increase in strength and transport over the 21st century (Figure 3.27), reducing the depth to which the SEC penetrates. &KDQJHVLQFXUUHQWVWUHQJWKVDUHOLNHO\WRDIIHFWELRORJLFDOSURGXFWLRQDQGÀVKHULHV through the various processes that supply nutrients discussed below. They will also affect the dispersal of larvae and connectivity among populations123. Changes to the EUC may have consequences because of the important role of this undercurrent in the transport of iron, sourced from the New Guinea Coastal Undercurrent, to the HDVWHUQ DQG FHQWUDO 3DFLÀF124, where iron concentrations limit primary productivity (Chapter 4). Therefore, changes to the depth and strength of the EUC may also have LPSRUWDQWHIIHFWVRQÀVKHULHVLQWKHUHJLRQ
3.3.2 Ocean temperature 3.3.2.1 Observed changes As a result of its large heat capacity, the ocean has absorbed most of the additional heat due to recent global warming – about 30 times more anthropogenic heat has entered the ocean than the atmosphere since the 1960s125. Globally, SST is estimated to have warmed ~ 0.67°C from 1901 to 2005126,QWKH3DFLÀFEDVLQZDUPLQJRI667RI 1 to 1.5°C has occurred at the western coastal boundary south of the equator and in the east, north of the equator, during the past 50 years127,128. 6HSDUDWLQJORQJWHUPZDUPLQJRI667IURPWKHQDWXUDOYDULDELOLW\RIWKHWURSLFDO3DFLÀF Ocean has not been straightforward. For example, ENSO has accounted for ~ 30% of the variability (excluding the seasonal cycle) during the past 100 years, with ~ 10% attributable to global warming127,129, and the remaining ~ 60% being due to decadal and other modes of variability. But the warming trend is conspicuous, even below the surface – it has been detected in all oceans and at increasing depths since the 1950s125,130–132. Over the past 50 years, the water column between the surface and about 200 m in WKHWURSLFDODQGVXEWURSLFDO3DFLÀFKDVZDUPHGE\XSWR& )LJXUH &RXQWHU intuitively, south of 8°N, a consistent and broad-scale cooling has occurred in the central and lower thermocline that extends south to at least 25°S (Figure 3.28), which is most pronounced at around 200 m in the equatorial region. This cooling appears to be related to changes in the surface winds that can raise the thermocline. Despite the addition of heat to the system, the upward displacement of the strongest vertical temperature gradient associated with the thermocline leads to net cooling133.
143
CHAPTER 3
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143
160°E
Transport (Sv)
a)
b)
180°
160°W
140°W
120°W
100°W
180°
160°W
140°W
120°W
100°W
-15 -20 -25 -30
Transport (Sv)
50 40 30 20
Depth (m)
c) 140 160 180 200 160°E 0
d)
20 40
Depth (m)
60 80 100 120 140 160 180 200
-10
-5
0
5
10
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CHAPTER 3
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a)
20°S
10°S
0°
10°N
20°N
b)
20°S
10°S
0°
10°N
20°N
0
Depth (m)
200
400
600
800
1
0.8 0.6 0.4 0.2
0 -0.2 -0.4 -0.6 -0.8 -1
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3.3.2.2 Projected changes 6HDVXUIDFHWHPSHUDWXUHRIWKHWURSLFDO3DFLÀF2FHDQLVSURMHFWHGWRLQFUHDVHXQGHU WKH%DQG$HPLVVLRQVVFHQDULRV)RUERWKVFHQDULRVDQQXDOO\DYHUDJHGZDUPLQJ DFURVVWKHUHJLRQUHODWLYHWRWKH WR DYHUDJHLVSURMHFWHGWRLQFUHDVHZLWKLQ DUDQJHRIWR&E\,QWKHLQFUHDVHLQ667LVH[SHFWHGWREHZLWKLQ WKHUDQJHRIWR&JUHDWHUXQGHU%DQGWRLQFUHDVHE\WR&XQGHU$ 7DEOH 7KH JUHDWHVW ZDUPLQJ LV SURMHFWHG WR RFFXU LQ WKH 3DFLÀF (TXDWRULDO 'LYHUJHQFH 3URYLQFH DQG WKH OHDVW ZDUPLQJ DW WKH HDVWHUQ ERXQGDU\ RI WKH 6RXWK 3DFLÀF6XEWURSLFDO*\UH 6HFWLRQ %RWK VFHQDULRV DQG WLPH SHULRGV VKRZ D VLPLODU VSDWLDO DQG YHUWLFDO SDWWHUQ RI ZDUPLQJ7KHLQFUHDVHLVJUHDWHVWQHDUWKHHTXDWRUZLWKZDUPLQJGHFUHDVLQJZLWK GHSWK0D[LPXPZDUPLQJLVH[SHFWHGWRDSSURDFK&DWWKHVXUIDFHDQG&DW PE\LQERWKVFHQDULRV )LJXUH 8QGHU%LQWKHPXOWLPRGHOPHDQ 145
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CHAPTER 3
a)
140°E 0
160°E
180°
160°W
140°W
Depth (m)
100
200
300
400
b)
20°S
10°S
0°
10°N
20°N
0
c)
20°S
1.5
2
10°S
0°
10°N
20°N
Depth (m)
100
200
300
400
-1
-0.5
0
0.5
1
2.5
3
Warming (oC) )LJXUH 3URMHFWHG ZDUPLQJ LQ WKH XSSHU P RI WKH WURSLFDO 3DFLÀF 2FHDQ XQGHU WKH$HPLVVLRQVVFHQDULRLQ D DORQJWKHHTXDWRU DYHUDJHGEHWZHHQ6DQG1 E DORQJ ( DYHUDJHG EHWZHHQ ( DQG ( DQG F DORQJ : DYHUDJHG EHWZHHQ : DQG : &RORXU VKDGLQJ VKRZV WKH PXOWLPRGHO PHDQ SURMHFWHG ZDUPLQJLQIRUWKH$VFHQDULRUHODWLYHWR ² *UH\PRWWOLQJLQGLFDWHVDUHDV ZKHUHZDUPLQJLVQRWVLJQLÀFDQWDWWKH FRQÀGHQFHOHYHO%ODFNFRQWRXUVVKRZPHDQ SUHVHQWGD\WHPSHUDWXUHV EDVHGRQWKH&$56&6,52FOLPDWRORJ\ DQGWKHEOXHOLQH UHSUHVHQWV WKH PHDQ WHPSHUDWXUHV SURMHFWHG IRU FDOFXODWHG UHODWLYH WR WKH &$56 GDWD ZLWK WKH & LVRWKHUPV WKLFNHQHG 7KH UHG OLQHV LQ D LQGLFDWH WKH GHSWK RI WKH WKHUPRFOLQH GXULQJ ² VROLG DQG WKH GHSWK SURMHFWHG IRU GDVKHG 7KHUPRFOLQH GHSWK LV HVWLPDWHG DV WKH GHSWK ZKHUH WHPSHUDWXUH LV & EHORZ WKH WHPSHUDWXUHDWWKHVXUIDFH
147
RI WKH DUHD FRPSULVLQJ WKH :DUP 3RRO LV H[SHFWHG WR KDYH DQ HDVWHUQ ERXQGDU\ DURXQG : LQ XQGHU ERWK HPLVVLRQV VFHQDULRV 7KLV DUHD LV SURMHFWHG WR LQFUHDVHE\DIDFWRURIHLJKWDQGWKHHDVWHUQOLPLWRIWKH &LVRWKHUPLVH[SHFWHGWR EHDURXQG:IRUWKH%VFHQDULRLQ)RU$LQWKHDUHDLQFUHDVHVE\D IDFWRURIQLQHUHDFKLQJPLOOLRQNP%\WKDWWLPHWKH &ZDWHUVDUHSURMHFWHGWR VSUHDGDFURVVWKH3DFLÀFEDVLQDWWKHHTXDWRUUHDFKLQJWKHFRDVWRIFHQWUDO$PHULFD 7DEOH3URMHFWHGFKDQJHVWRVHOHFWHGNH\IHDWXUHVRIWKHWURSLFDO3DFLÀF2FHDQUHODWLYH WR ² IRU ² DQG ² XQGHUWKH%DQG$HPLVVLRQV VFHQDULRV EDVHG RQ D PXOWLPRGHO PHDQ 7KH FRQÀGHQFH LQWHUYDOV SURYLGHG DW FRQÀGHQFH IRU HDFK SURMHFWLRQ VHH NH\ EHORZ SHUFHQWDJH FKDQJH IRU WKH PXOWLPRGHO PHDQLVLQGLFDWHG Ocean feature
1980–1999
Mean equatorial SEC transport (Sv) (160°E–130°W) Strength of SECC in upper 50 m* (cm.s-1) SECC zonal component isotach* 5 cm per second
2035
2100
28
B1 26–28 (-5%)
A2 26–29 (-3%)
B1 25–27 (-9%)
A2 22–25 (-18%)
6.20
4.9–6.5 (-8%)
3.9–6.2 (-18%)
3.2–5.7 (-28%)
0–5.1 (-60%)
186°E (2°W)
184°E (3°W)
181°E (6°W)
174°E (13°W)
187°E
-3.26 to -3.06 -3.24 to -3.08 (-5%) (-5%)
-3.23 to -2.91 -3.20 to -2.73 (-8%) (-10%)
Zonally averaged zonal windstress* (10 -2 Nm-2) (2oS to 2oN)
-3.3
Pacific basin SST (°C)**
27.4
28.0–28.2 (+0.7)
28.0–28.2 (+0.7)
28.6–29.0 (+1.4)
29.6–30.1 (+2.5)
29.6
30.3–30.5 (+0.7)
30.4–30.6 (+0.8)
30.9–31.3 (+1.5)
32.0–32.5 (+2.6)
29°C Warm Pool area*** (x 106 km2)b
7
20–26 (+230%)
22–27 (+250%)
36–46 (+480%)
58–65 (+770%)
Warm Pool salinity frontc
~ 166°E
Maximum Warm Pool temperatures (°C)a,**
166°E–172°E 166°E–169°E
167°E–172°E 170°E–179°E
$YHUDJHHDVWZDUGYHORFLW\EHWZHHQ&DQG:DQG6WR6ZKLFKFRUUHVSRQGVWRWKH PD[LPXP RI WKH PXOWLPRGHOPHDQ FRQWRXU OLQH RI FRQVWDQW YHORFLW\
IRU UHJLRQ (²: 6²1
IRU UHJLRQ (²: 6²1 D WHPSHUDWXUH EDVHG RQ WKH PD[LPXP ORQJWHUP PRQWKO\ PHDQ VHD VXUIDFH WHPSHUDWXUHV LQ WKH ZDUPHVW RI WKH UHJLRQ KLJKHU WHPSHUDWXUHV FDQ EH H[SHFWHG LQ LQGLYLGXDO \HDUV ² SDUWLFXODUO\ WKRVH DVVRFLDWHG ZLWK (162 E ¶ &SRRO·GHÀQHGDVDUHDZLWKWHPSHUDWXUHDERYH & F GHÀQHGDVWKHSRVLWLRQRIWKH VDOLQLW\DWWKHHTXDWRU 6(& 6RXWK(TXDWRULDO&XUUHQW 6(&& 6RXWK(TXDWRULDO&RXQWHU&XUUHQW 667 VHDVXUIDFHWHPSHUDWXUH Unlikely 0%
148
Somewhat likely 29%
66%
Likely
Very likely 90% 100%
CHAPTER 3
7KHSRVLWLRQRIWKH:DUP3RROLVLQWLPDWHO\WLHGWR(162G\QDPLFVDQGWKHERXQGDU\ RI LQWHQVH FRQYHFWLYH UDLQIDOO +RZHYHU EHFDXVH ZDUPLQJ RFFXUV DFURVV WKH ZKROH EDVLQ FKDQJHV LQ WKH & LVRWKHUP PD\ QRW EH WKH EHVW ZD\ WR LGHQWLI\ WKH HGJH RI WKH :DUP 3RRO LQ WKH IXWXUH $ PRUH UHOHYDQW ERXQGDU\ PD\ EH WKH SRVLWLRQ RI WKHVDOLQLW\IURQWWKDWKLJKOLJKWVWKHDUHDRIVWURQJUDLQIDOORFFXUULQJRYHUWKH:DUP 3RRO$WWKHHTXDWRUWKLVIURQWLVSURMHFWHGWRPRYHHDVWE\aNPXQGHUWKH$ VFHQDULRE\ 7DEOH)LJXUH ZKLFKLVOLNHO\WRDOWHUWKHGLVWULEXWLRQRI WXQD &KDSWHU 120°E
140°E
160°E
180°
160°W
140°W
120°W
20°N
10°N
0°
10°S
20°S
30°S 33.5
34
34.5
35
35.5
36
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3.3.3 Ocean eddies 3.3.3.1 Observed changes (QHUJ\ LV JHQHUDWHG IRU HGGLHV ZKHQ WKHUH DUH VWURQJ KRUL]RQWDO GHQVLW\ JUDGLHQWV HJ ZKHQ WKH WKHUPRFOLQH LV WLOWHG &RQVHTXHQWO\ HGG\ DFWLYLW\ FKDQJHV RQ VHDVRQDOGHFDGDODQGORQJHUWLPHVFDOHVDVWKHGHQVLW\VWUXFWXUHRIWKHRFHDQYDULHV 6HFWLRQ &KDQJHVLQZDWHUGHQVLW\DUHPLUURUHGE\WKRVHIRUVHDOHYHO HJKLJK GHQVLW\FROGSDWFKHVRIZDWHUDUHDVVRFLDWHGZLWKGHSUHVVHGVHDOHYHO $VDUHVXOW REVHUYDWLRQRIODUJHVFDOHSDWWHUQVRIHGG\DFWLYLW\FDQEHPDGHIURPVDWHOOLWHGDWD
149
IRU VHD VXUIDFH KHLJKW 7KHVH DOWLPHWULF GDWD KDYH EHHQ XVHG WR UHYHDO LPSRUWDQW VHDVRQDODQGLQWHUDQQXDOYDULDWLRQVLQHGG\DFWLYLW\%HWZHHQ DQGHGG\ DFWLYLW\YDULHGE\²LQWKHWURSLFDO3DFLÀF2FHDQ$QH[WHQVLRQRIWKHVDWHOOLWH WLPHVHULHV XQWLO UHYHDOHG HYHQ ODUJHU LQWHUDQQXDO YDULDELOLW\ LQ VWUHQJWK DQG GLVWULEXWLRQ RI HGGLHV )LJXUH ZLWK VRPH RI WKH ¶KLJKHQHUJ\· UHJLRQV GXULQJ WR GLVDSSHDULQJ EHWZHHQ DQG 7KH OLPLWHG SHULRG WKDW VDWHOOLWH REVHUYDWLRQV KDYH EHHQ DYDLODEOH GRHV QRW DOORZ XV WR GHWHUPLQH ZKHWKHU WKLV UHSUHVHQWVQDWXUDOLQWHUDQQXDOFKDQJHVLQHGGLHVRUDORQJWHUPWUHQG
3.3.3.2 Projected changes 7KH FRDUVH VSDWLDO VFDOHV RI WKH &0,3 FOLPDWH PRGHOV GR QRW UHVROYH RFHDQLF HGGLHV 7KHUHIRUH SURMHFWLRQV RI IXWXUH HGG\ DFWLYLW\ FDQ RQO\ EH TXDOLWDWLYH $V HGGLHV DUH JHQHUDWHG DW WKHUPDO IURQWV ZKHUH WKHUH DUH VWURQJ RFHDQLF FXUUHQWV 6HFWLRQ IXWXUH HGG\ DFWLYLW\ PD\ DOVR EH OLQNHG WR SURMHFWHG FKDQJHV LQ RFHDQFXUUHQWV 6HFWLRQ 7KHPXOWLPRGHODYHUDJHVXJJHVWVWKDWOLWWOHFKDQJHLQ FLUFXODWLRQ LV OLNHO\ SROHZDUG RI 1²6 6HFWLRQ 1HYHUWKHOHVV VLJQLÀFDQW FKDQJHVDUHSURMHFWHGZLWKLQRIWKHHTXDWRULQ )LJXUH (DVWRI6RORPRQ ,VODQGVWKH6(&&LVSURMHFWHGWRGHFUHDVH 6HFWLRQ ZKLFKPD\FDXVHDGHFOLQH LQ HGG\ DFWLYLW\ $W 6 WKH 6(& LV SURMHFWHG WR LQFUHDVH LQ D WKLQ ]RQDO EDQG ,QWKH1RUWKHUQ+HPLVSKHUHHGG\DFWLYLW\FDQEHH[SHFWHGWRLQFUHDVHRUGHFUHDVH LQ DVVRFLDWLRQ ZLWK SURMHFWHG FKDQJHV LQ VWUHQJWK LQ SDUWV RI WKH 1(& DQG 1(&& 6HFWLRQ LIWKHVDPHG\QDPLFDOOLQNEHWZHHQÁ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
3.3.4 Nutrient supply 3.3.4.1 Observed changes 7KH DYDLODELOLW\ RI QXWULHQWV LQ WKH SKRWLF ]RQH DQG FRQVHTXHQWO\ WKH ELRORJLFDO SURGXFWLYLW\ WKDW VXVWDLQV ÀVKHULHV LV VHQVLWLYH WR FKDQJHV LQ WKH FLUFXODWLRQ DQG VWUDWLÀFDWLRQRIWKHRFHDQ 6HFWLRQ 6WURQJYDULDWLRQVLQWKHVXSSO\RIQXWULHQWV KDYH EHHQ REVHUYHG DV D UHVXOW RI FOLPDWH YDULDELOLW\ RQ GHFDGDO WLPH VFDOHV 2QH RI WKH WZR H[LVWLQJ ORQJWHUP WLPHVHULHV RI QXWULHQW OHYHOV FROOHFWHG RYHU WKH SDVW \HDUV LQGLFDWHV VPDOO QHW GHFUHDVHV LQ QXWULHQW VXSSO\ WR WKH SKRWLF ]RQH RI WKH WURSLFDO3DFLÀF2FHDQ+RZHYHUSRRUVSDWLDODQGWHPSRUDOGDWDFRYHUDJHEHIRUHWKH VDWHOOLWHHUDPHDQVWKDWDQ\DVVHVVPHQWDFURVVWKHUHJLRQLVXQFHUWDLQ
150
CHAPTER 3
a)
120°E
140°E
160°E
180°
160°W
140°W
20°N
10°N
0°
10°S
20°S
1992–1997
b) 20°N
10°N
0°
10°S
20°S
1998–2002
c) 20°N
10°N
0°
10°S
20°S
2003–2008
0
5
10
15
Sea surface height, cm (RMS) )LJXUH 'HFDGDOFKDQJHVLQHGG\DFWLYLW\PHDVXUHGIURPYDULDELOLW\LQVHDVXUIDFH KHLJKW 66+ DQRPDO\IRU D ² E ² DQG F ²(DFKPDSZDV REWDLQHGXVLQJWKHVDPHSURFHGXUHVDVGHVFULEHGIRU)LJXUH
151
7KH REVHUYHG GHFUHDVHV LQ QXWULHQW VXSSO\ DSSHDU WR EH UHODWHG WR WKH LQFUHDVHG VWUDWLÀFDWLRQ RI WURSLFDO VXUIDFH ZDWHUV 6HFWLRQ RYHU WKH SDVW \HDUV )LJXUH /RZQXWULHQW VXUIDFH ZDWHUV DUH ZDUPLQJ DQG KLJKQXWULHQW GHHSHU ZDWHUV DUH FRROLQJ VRXWK RI 1 7KLV PD\ KDYH UHGXFHG WKH HIÀFLHQF\ RI QXWULHQW WUDQVIHU LQWR WKH SKRWLF ]RQH %R[ RYHU EURDG UHJLRQV RI WKH WURSLFDO 3DFLÀF 2FHDQ1RUWKRI1LQFUHDVHGVWUDWLÀFDWLRQLVDOVRDSSDUHQWDVWKHXSSHUZDWHUVDUH ZDUPLQJIDVWHUWKDQWKHZDWHUVQHDUDQGEHORZWKHS\FQRFOLQH )UHTXHQWO\UHSHDWHGREVHUYDWLRQVLQWKHZHVWHUQSDUWRIWKH1RUWK3DFLÀF6XEWURSLFDO *\UH3URYLQFHDOVRGHPRQVWUDWHDGHFOLQHLQQXWULHQWFRQFHQWUDWLRQLQWKHPL[HGOD\HU RYHUWKHSDVW\HDUV7KLVGHFOLQHKDVDOVREHHQDWWULEXWHGWRHQKDQFHGVWUDWLÀFDWLRQ DFWLQJ DV D EDUULHU WR WKH WUDQVIHU RI QXWULHQWV IURP WKH GHHSHU RFHDQ %HORZ WKH PL[HGOD\HUDQGGRZQWRDGHSWKRIPDFRPSDULVRQRIK\GURJUDSKLFGDWDWDNHQ a\HDUVDSDUWLQWKHQRUWKHUQ3DFLÀFVKRZVDQLQFUHDVHLQQLWUDWH7KLVLVDWWULEXWHG WR YDULDWLRQV LQ DGYHFWLYH WUDQVSRUW RI QXWULHQWV IURP UHPRWH ORFDWLRQV UDWKHU WKDQ FKDQJHVLQWKHORFDOLQWHQVLW\RIUHPLQHUDOLVDWLRQ
a)
b) 25°S
0°
25°N
25°S
0°
25°N
0
Depth (m)
100 200 300 400 500 600
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Linear density trend (kg per m3 per 50 years)
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7KH+DZDLL2FHDQ7LPH6HULHV +27 VWDWLRQSURYLGHVWKHORQJHVWFRQWLQXRXVUHFRUGV RISK\VLFDODQGELRJHRFKHPLFDOGDWDWKURXJKRXWWKHZDWHUFROXPQIRUWKH1RUWK3DFLÀF 6XEWURSLFDO*\UH$OWKRXJKDVWURQJXSZDUGWUHQGLQSULPDU\SURGXFWLYLW\LVHYLGHQW 152
CHAPTER 3
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153
B1 2035
a) 120°E
140°E
160°E
180°
A2 2035
b) 160°W 140°W 120°E 140°E
160°E
180°
160°W 140°W
20°N 10°N 0° 10°S 20°S
c)
B1 2100
A2 2100
d)
20°N 10°N 0° 10°S 20°S
0.2
0.4
0.6
0.8
1.0
1.2
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154
CHAPTER 3
B1 2035
a) 120°E 140°E
160°E
180°
A2 2035
b) 160°W
140°W
120°E 140°E
160°E
180°
160°W
140°W
20°N 10°N
0° 10°S 20°S
c)
B1 2100
A2 2100
d)
20°N 10°N 0° 10°S 20°S
-30
-20
-10
0
10
20
30
Depth (m) )LJXUH3URMHFWHGFKDQJHVWRWKHDQQXDOPD[LPXPPL[HGOD\HUGHSWKLQZLQWHUIRU D WKH % VFHQDULR LQ E $ LQ F % LQ DQG G $ LQ UHODWLYH WR ² 7KHPD[LPXPPL[HGOD\HUGHSWKLVEDVHGRQWKHDYHUDJHVHDVRQDOF\FOHIURP \HDUWLPHVHULHVRI$5PRGHOV6KDGHGDUHDVLQGLFDWHZKHUHPRGHOVGRQRWSURMHFWD FRQVLVWHQWWUHQGDWWKH FRQÀGHQFHOHYHO
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155
a)
b)
Change in vertical velocity (x 10 -6 m per second)
Mean vertical velocity (x 10 -6 m per second)
30°S
20°S
10°S
0°
10°N
20°N
30°N
15 10 5 0 -5 1.5 1 0.5 0 -0.5 -1 -1.5 -2
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a) 120°E 140°E
160°E
180°
A2 2035
b) 160°W 140°W
120°E 140°E
160°E
180°
160°W 140°W
20°N 10°N 0° 10°S 20°S
B1 2100
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A2 2100
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20°N 10°N 0° 10°S 20°S
-40
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5
20
40
30
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3.3.5 Dissolved oxygen 3.3.5.1 Observed changes 8QWLO UHFHQWO\ OHYHOV RI GLVVROYHG R[\JHQ LQ WKH WURSLFDO 3DFLÀF 2FHDQ VKRZHG QR FOHDU WUHQG RU GHFUHDVHG ZLWK WLPH LQ UHJLRQV DZD\ IURP WKH VXEWURSLFV DW WKH WKHUPRFOLQH OHYHO GXH WR GHFUHDVHG ZDWHU UHQHZDO +RZHYHU UHFHQW GDWD IURP DXWRQRPRXV SURÀOLQJ ÁRDWVLY KDYH DOORZHG UHFRQVWUXFWLRQ RI XVDEOH WLPHVHULHV DW LY $UJRZZZDUJRXFVGHGX
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Depth (m)
250
500
100
750
1000 1960
Oxygen concentration (ȝmol per kg)
200
0 1970
1980
1990
2000
Year )LJXUH7LPHVHULHV VLQFH RIGLVVROYHGR[\JHQFRQFHQWUDWLRQVQHDU:DWWKH HTXDWRU 1²6 0HDVXUHPHQWVZHUHWDNHQEHWZHHQDQGPDQGVKRZDVWHDG\ LQFUHDVHLQWKHGHSWKUDQJHRIORZR[\JHQZDWHUV PROSHUNJZKLWHOLQH %ODFN OLQHV GHQRWH WKH 2[\JHQ 0LPLQXP =RQH 20= VXSHULPSRVHG RYHU LQWHUDQQXDO DQG GHFDGDOYDULDELOLW\ JUH\DUHDVFRUUHVSRQGWRJDSVLQWKHWLPHVHULHV VRXUFH 6WUDPPDHW DO
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CHAPTER 3
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120°E
180°
120°W
60°W
60°N
30°N
0°
30°S
60°S
0
10
20
30
40
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160
CHAPTER 3
3UHLQGXVWULDO 120°E 140°E
160°E
180°
160°W
20°S
140°W
10°S
0°
10°N
20°N
0 20°N
0° 10°S
Depth (m)
200 10°N
400 600 800
20°S 1000
Observed (1994) 0
20°N
0° 10°S
200
Depth (m)
10°N
400 600 800
20°S 1000
3URMHFWHG $ 0 20°N
0° 10°S
Depth (m)
200 10°N
400 600 800
20°S 1000
3URMHFWHG $ 0 10°N 0° 10°S
Depth (m)
20°N
200 400 600 800
20°S 1000
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140°E
160°E
180°
160°W
140°W
20°S
10°S
0°
10°N
20°N
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Depth (m)
20°N 200 400 600 800 20°S 1000
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162
CHAPTER 3
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163
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140°E
160°E
180°
160°W
140°W
30°N 20°N 10°N 0° 10°S 20°S 30°S -8
-4
4
8
12
16
20
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CHAPTER 3
a)
Sea level (cm)
2
1
0
-1 1960
1970
1980
1990
2000
1960
1970
1980
1990
2000
b)
Sea level (cm)
6
4
2
0
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166
CHAPTER 3
a) 180
Sea level (cm)
140
100
60
20 0 -20 1950
b)
2000
140°E 160°E
180°
2050
Year
160°W 140°W 120°W 100°W
2100
80°W
20°N 10°N 0° 10°S 20°S
-10 -8 -6 -4 -2 0
2 4
6
8 10
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168
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Observed changes South Pacific gyre has strengthened
2035 B1 A2 B1 SEC decreases at the equator; EUC becomes shallower; SECC decreases and retracts westward in the upper 50 m
+0.6 to +0.8°C
Ocean +0.6 to 1°C temperature since 1950 at 80 m
Equatorial upwelling Eddy activity
A2
Projected to increase significantly over the entire region
Sea surface temperature
Warm Pool
2100
+0.7 to +0.8°C
+0.4 to +0.6°C
+1.2 to +1.6°C
+2.2 to +2.7°C
+1.0 to +1.3°C
+1.6 to +2.8°C
Warmer and fresher
Extends eastward; water warms and becomes fresher, and area of warmest waters increases
Decreased
Integral transport 9°S–9°N remains unchanged
No measurable changes
Probable variations in regions where major oceanic currents change
Nutrient supply
Decreased slightly Decrease due to increased stratification and shallower mixed layer, with a possible in two locations decrease of up to 20% under A2 by 2100
Dissolved oxygen
Expansion of lowoxygen waters
Possible decrease due to lower oxygen intake at high latitudes Possible increase near the equator due to decreased remineralisation Aragonite saturation (Ω) projected to continue to decrease significantly
¾ Ω decreased from 4.3 to 3.9
n/a
Ω ~ 3.3
Ω ~ 3.0
Ω ~ 2.4
Ocean ¾ Ω horizon rises acidification from 600 to 560 m
n/a
~ 456 m
n/a
~ 262 m
n/a
~ 7.98
n/a
~ 7.81
¾ pH decreased from 8.14 to 8.08 Waves
Decreased in far west Pacific; no data elsewhere
Sea level
+6 cm since 1960
Slight increase (up to 10 cm) in swell wave height; patterns depend on ENSO and tropical cyclones Projected to rise significantly
Island effects
Not observed
*
+8 cm
+18 to +38 cm
+23 to +51 cm
**
+20 to +30 cm
+70 to +110 cm
+90 to +140 cm
Probable; undocumented
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Medium 33%
High 66%
Very high 95% 100%
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174
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References
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