Research press release


Nature Climate Change

Climate change weakens deep ocean circulation


今回、Casimir de Lavergneたちは観察結果とモデルシミュレーションを分析し、南大洋での深い対流の変化を調べた。南大洋では、ウェッデル海とロス海の海流系が主な外洋対流域となっている。その結果、1950年代以降は海洋表層の淡水化によって塩分成層が拡大し、これが深部での混合を阻害していることが判明した。Lavergneたちは、産業革命以前の条件下で大規模な対流が起きていたことを示す25の気候モデルでは、高排出シナリオでは1900~2100年に対流の強さが低下することが明らかになったと指摘している。そのうち7つのモデルでは、深層循環が2030年までに完全に停止した。


Deep open-ocean convection in the Southern Ocean is projected to weaken and possibly stop due to climate change, suggests a study published online in Nature Climate Change this week. If this is the case, it has implications for bottom water formation, which contributes to global overturning circulation, as well as the storage of heat and carbon in the ocean.

Casimir de Lavergne and colleagues analysed observations and model simulations to investigate deep convection changes in the Southern Ocean, where the Weddell and Ross Sea ocean current systems are the main open-ocean sites. They found that freshening of the surface ocean has increased salinity stratification since the 1950s, which inhibits deep mixing. The authors note that 25 climate models, which show that significant convection occurred under pre-industrial conditions, found a decrease in its strength over the period 1900 to 2100 under a high-emissions scenario. In seven of these models, deep circulation was completely stopped by 2030.

This finding suggests that deep convection was more active historically and that climate change has caused it to weaken and will continue to do so.

doi: 10.1038/nclimate2132


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