****************************************************************************************************************
$BBh(B 190 $B2s(B $BBg5$3$MNJ*M}3X!&5$8uNO3X%;%_%J!<(B $B$N$*$7$i$;(B
$BF|!!;~!'(B 1$B7n(B 29$BF|(B($BLZ(B) $B8aA0(B 09:30
$B>l!!=j!'(B $BDc292J3X8&5f=j(B 3$B3,(B $B9VF2(B
$BH/I=
$BBj!!L\!'(B$B%a%?%s%O%$%I%l!<%H$+$iJ|=P$5$l$?%a%?%s(B
$B%P%V%k$K4X$9$k%b%G%j%s%0(B
$BH/I=
$BBj!!L\!'(B$B2-FlCOJ}G_1+4|$N9_1+!'G_1+CfHW$K$*$1$k(B
$B0l;~E*$J>/1+$K$D$$$F(B
****************************************************************************************************************
$B%a%?%s%O%$%I%l!<%H$+$iJ|=P$5$l$?%a%?%s%P%V%k$K4X$9$k%b%G%j%s%0(B- ($B;3K\(B $BIKM'(B) $BH/I=MW;](B :
$B3$DlBO@QAXCf$KB8:_$9$k%a%?%s%O%$%I%l!<%H$NJ,2r$K$h$C$F5/$-$?Bg5$(B-$B3$MN$X(B $B$NBgNL$N%a%?%sJ|=P$O(B, $B2a5n$K5/$-$?5^7c$JCO5e29CH2=$r0z$-5/$3$7$?$H9M$($i(B $B$l$F$$$k(B(Dickens et al., 1995). $B$7$+$7Bg5$$KE~C#$7$?%a%?%s$N3d9g$,$h$/J,(B $B$+$C$F$$$J$$0Y(B, $B0z$-5/$3$5$l$?29CH2=$NDxEY$K$D$$$F$O?dDj$5$l$F$$$J$$(B. $B8=:_(B, $B3$Dl$+$iJ|=P$5$l$F$$$k%a%?%s%7!<%W$N4QB,$d%b%G%k$N8&5f$K$h$k$H(B, $B3$(B $BDl$+$iJ|=P$5$l$?%a%?%s$NK"$OBg5$$KE~C#$;$:3$MNCf$KMO2r$9$k$H<(:6$5$l$F$$(B $B$k(B(Greinart et al., 2006). $B$7$+$72a5n$K5/$-$?$H9M$($i$l$k$h$&$JBg5,LO$J(B $B%a%?%sJ|=P$N>l9g(B, $B3$?e$,%a%?%s$GK0OB$5$l$F(B, $B%a%?%s$,Bg5$$KE~C#$7$?$+$b$7(B $B$l$J$$(B. $B$^$?%a%?%s$,K"$H$7$FJ|=P$5$l$?>l9g(B, $BK"$K$h$kAGAa$$1tD>M"Aw$G3$?e(B $B$,L$K0OB$G$bBg5$$KE~C#$7$?2DG=@-$,$"$k(B. $BK\8&5f$G$O(B, $B3$Dl$+$i?eCl$XO"B3E*$K%a%?%s$NK"$rJ|=P$7$?>l9g$N(B, $BK"$N5sF0(B $B$H?eCl$N%a%?%sG;EY$rM=Js$9$k%b%G%k$rMQ$$$F(B, $B3$Dl$+$iJ|=P$5$l$?%a%?%s$N(B $BK"$,Bg5$$KE~C#$9$k0Y$KI,MW$J(B, $B3$?eCf$N%a%?%sG;EY$r7W;;$7$?(B. $B$=$N7k2L(B, $B%a%?%s$NK"$O?eCl$N%a%?%sG;EY$,(B100%$B$h$j$b==J,Dc$$>l9g$G$bBg5$$KE~C#$9$k(B $B$3$H$,<(:6$5$l$?(B. $Bl9g$GBO@QAXCf$N%a%?%sNL$O(B, $B%a(B $B%?%s$NK"$,Bg5$$KE~C#$9$k0Y$KI,MW$J%a%?%sNL$h$j>/$J$$$3$H$,J,$+$C$?(B. $B$D(B $B$^$j(B, $BBgNL$N%a%?%s$,3$Dl$+$iJ|=P$5$l$F$bBg5$$KD>@\J|=P$5$l$k$3$H$O$J$/(B, $B3$?eCf$KMO2r$9$k$H<(:6$5$l$k(B. Abstract: Massive methane release due to decomposition of methane hydrate insea-floor sediments might have caused rapid global warming in the past(Dickens et al., 1995). However, the degree of global warming has not beenestimated due to uncertainty over the proportion of methane flux from the sea-floor to reach the atmosphere. According to present observations and model study of methane-bubbling seep sites, a methane bubble released from the sea-floor does not reach the atmosphere (Greinart et al., 2006). However, massive methane release would result in methane-saturated seawater, thus some methane would reach the atmosphere. Methane in the form of bubbles passing through undersaturated seawater may potentially reach the atmosphere due to rapid vertical transport. In this study, we calculated the methane concentration in the water column required for methane bubble to reach the atmosphere, using a one-dimensional numerical model integrated over time predicting methane bubbles and methane concentration in the water column under the condition of continuous methane input from the sea-floor to the water column. We found that some methane bubbles reach the atmosphere even when the methane saturation fraction in the water column is much lower than 100%. We compared the minimum amount of methane input from the sea-floor necessary for methane to reach the atmosphere to the amount of methane in the sediment. In most cases, our results suggest that the typical amount of methane in the sediment is significantly lower than the required minimum amount of methane input. It is, therefore, suggested that the massive quantity of methane bubbles released from the sea-floor would not reach the atmosphere directly but would be dissolved in the seawater.
$B2-FlCOJ}G_1+4|$N9_1+!'G_1+CfHW$K$*$1$k0l;~E*$J>/1+$K$D$$$F(B-($B2,ED(B $BLw;R(B)
$B!!G_1+$OF|K\$r4^$`El%"%8%"$N@92F$K@hN)$D1+5($G$"$k!#$=$N9_?e$OG_1+A0@~$*(B $B$h$SA0@~>e$GH/@8$9$kAm4Q"7%a%=%9%1!<%k9_?e%7%9%F%`$K$h$C$F$b$?$i$5$l$k!#(B $B4|4V$OK\=#!&6e=#$G(B6$B7n>e=\"7(B7$B7n2<=\$G$"$j!"G_1+A0@~$N0LCV$OBPN.7w2!<%s$H$7$FG'$a$i$l!"El7P(B130$B"7(B140$BEY0J@>$G$O?e>x5$8{G[!"(B $B0JEl$G$O290L8{G[$K$h$C$FFCD'IU$1$i$l$k!J(BNinomiya et al. , 1992$B!K!#0lJ}2-(B $BFlCOJ}$NG_1+$OK\=#!&6e=#$h$j(B1$B%v7nAa$$(B5$B7n>e=\"767n2<=\!"$=$N1+$N9_$jJ}$OC(B $BGB3E*$G$"$j!"G_1+F~$(Bj$B8e$b@2E7$r<($9$3$H$,B?!9$"$k!#$3$l$^$GK\=#!&6e=#$K(B $B$*$1$kG_1+$K$D$$$F$N8&5f$OB?!99T$o$l$F$-$?!#$7$+$7!"2-FlCOJ}$K4X$7$F$O2-(B $BFlCOJ}$N0LCV$d4|4V$N$:$l!"9_1+$NFCD'$J$I$+$iG_1+4|4V$rDL$7$F$NFCD'$O$O$C(B $B$-$j$7$F$$$J$$!#(B $B6aG/!"F#It(B(2006)$B$K$h$jK\=#!&6e=#$NG_1+F~$j$K@h6n$1$F0l;~E*$J>/1+$,3NG'$5(B $B$l$?!#;~4|$O(B5$B7nKv$G!"2-FlCOJ}$NG_1+CfHW$K$"$?$k!#2-FlCOJ}$G$b3NG'$7$?$H(B $B$3$m!"K\=#!&6e=#$HF1MM$K(B5$B7nKv$K2-FlCOJ}$G$b0l;~E*$J>/1+$r<($9$3$H$,3NG'(B $B$G$-$?!#$=$3$GK\8&5f$NL\E*$O!"0l;~E*$J>/1+$KCmL\$7!"$=$NA08e$N4|4V$NBg5$(B $B>l$NFCD'!"0l;~E*$J>/1+$r$b$?$i$9860x$rL@$i$+$K$9$k$3$H$G$"$k!#$=$N7k2L!"(B $B0l;~E*$J>/1+$r<($9$H$-$=$N9_1+0h$O2-FlCOJ}$NFnElJ}8~$X0\F0$7$F$$$k$N$,J,(B $B$+$C$?!#$3$N$H$-Cf9q2ZCf!&2ZKL$G$OCO>e5$29$N>e>:$,8+$i$l!"2-FlCOJ}0J@>!"(B $BKL0^Ls(B25$B"7(B30$BEY$G$O5$29$NFnKL8{G[$O x5$$NFnKL8{G[$,$O$C$-(B $B$j$9$k!#$3$l$O(BKato(1985)$B$,<($7$?(B5$B7n8eH>$NCf9q2ZFn$K$*$1$k290L8{G[$N x5$$N8{G[$,Cx$7$$$H$$$($k!#$^$?!">/1+4|$K$J$k$HCf9q2ZKLIU6a$K4(Nd12$,8+(B $B$i$l$k$h$&$K$J$j!"$=$l$KH<$C$F2-FlCOJ}$X4%AgBg5$$NN.F~$,3NG'$G$-$k!#$3$l(B $B$K$h$j2-FlCOJ}$O>/1+$r<($7!"<>=a$JBg5$$N<}B+$OFnEl$X0\F0$7$?$H9M$($i$l$k!#(B
-----
$BO"Mm@h(B