海洋在全球碳循環(huán)中起著極為重要的作用,，能夠吸收大約一半由人類活動(dòng)產(chǎn)生的溫室氣體,，而其中大部分的反應(yīng)都發(fā)生在海洋表面以下100米的區(qū)域之內(nèi),。海洋中多種浮游植物能夠通過光合作用捕獲碳,，而當(dāng)它們死后,，會(huì)穿過海洋的“昏暗帶”（twilight zone）沉至永遠(yuǎn)漆黑的海底,。然而,，美國(guó)科學(xué)家進(jìn)行的一項(xiàng)最新研究表明,，海洋“昏暗帶”的生物活動(dòng)實(shí)際上是碳沉積的“把關(guān)人”，決定著浮游植物捕獲的碳被永遠(yuǎn)存儲(chǔ)于海底,，還是很快又再回到海洋表層,。4月27日的《科學(xué)》雜志以封面文章的形式發(fā)表了這一研究成果。
在2004年和2005年,，美國(guó)馬薩諸塞州Woods Hole海洋研究所的生物地球化學(xué)家Ken Buesseler領(lǐng)導(dǎo)的一支科學(xué)家小組對(duì)太平洋兩個(gè)區(qū)域的“昏暗帶”進(jìn)行了研究,，分別是美國(guó)的夏威夷和俄羅斯的堪察加半島（Kamchatka Peninsula）。利用隨著海流飄移的新型傳感器,，研究人員對(duì)浮游生物進(jìn)行了取樣,，并測(cè)定了沉降至深海以及循環(huán)回海洋表層的生物固碳總量，從而對(duì)海洋真正的碳沉積能力作出了估計(jì),。
這兩次研究所得到的碳沉積數(shù)據(jù)結(jié)論是一致的：在堪察加半島海域,，較冷的水溫和更多的營(yíng)養(yǎng)物質(zhì)促進(jìn)了包括浮游植物、珊瑚等在內(nèi)的海洋生態(tài)系統(tǒng)的繁榮,，因此,，有大約50%捕獲的碳穿過“昏暗帶”沉入海底。相比而言，夏威夷溫和的海水則有利于更小的浮游動(dòng)物的發(fā)展,，因此,，只有20%的碳真正得到沉積。Buesseler表示,，深度一旦超過1000米,，這些碳再回到淺海的可能性就不大了，那里的海水幾個(gè)世紀(jì)甚至數(shù)千年都不會(huì)‘再見天日’,。
Buesseler解釋說,，深海儲(chǔ)碳的變化往往不是由海洋表層控制，而是受“昏暗帶”變化的影響,。它的作用就好比是能夠使碳轉(zhuǎn)移到深海的“大門”,，海洋儲(chǔ)碳的能力與“昏暗帶”的微生物活動(dòng)緊密相關(guān)。
海洋的碳捕獲量通常由20世紀(jì)90年代提出的馬丁曲線（Martin curve）來確定,，它包含的一系列數(shù)據(jù)能夠說明海洋碳捕獲量隨著深度增加的變化,。不過，Buesseler表示,，根據(jù)最新研究結(jié)果,，馬丁曲線低估了堪察加半島海域50%的碳沉積能力，但將夏威夷海域高估了一倍,。他說,，“馬丁曲線很好地表達(dá)了平均水平，但不能描述海洋儲(chǔ)碳的系統(tǒng)動(dòng)力學(xué),。”
該研究小組已經(jīng)改進(jìn)了他們的傳感器,，并打算繼續(xù)對(duì)北大西洋的百慕大群島海域進(jìn)行研究，確定碳沉積隨著季節(jié)的變化情況,。（科學(xué)網(wǎng)任霄鵬/編譯）
原始出處:
Science 27 April 2007:
Vol. 316. no. 5824, pp. 567 - 570
DOI: 10.1126/science.1137959
Research Articles
Revisiting Carbon Flux Through the Ocean's Twilight Zone
Ken O. Buesseler,1* Carl H. Lamborg,1 Philip W. Boyd,2 Phoebe J. Lam,1 Thomas W. Trull,3 Robert R. Bidigare,4 James K. B. Bishop,5,6 Karen L. Casciotti,1 Frank Dehairs,7 Marc Elskens,7 Makio Honda,8 David M. Karl,4 David A. Siegel,9 Mary W. Silver,10 Deborah K. Steinberg,11 Jim Valdes,12 Benjamin Van Mooy,1 Stephanie Wilson11
The oceanic biological pump drives sequestration of carbon dioxide in the deep sea via sinking particles. Rapid biological consumption and remineralization of carbon in the "twilight zone" (depths between the euphotic zone and 1000 meters) reduce the efficiency of sequestration. By using neutrally buoyant sediment traps to sample this chronically understudied realm, we measured a transfer efficiency of sinking particulate organic carbon between 150 and 500 meters of 20 and 50% at two contrasting sites. This large variability in transfer efficiency is poorly represented in biogeochemical models. If applied globally, this is equivalent to a difference in carbon sequestration of more than 3 petagrams of carbon per year.
1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
2 National Institute of Water and Atmospheric Research Centre for Physical and Chemical Oceanography, Department of Chemistry, University of Otago, Dunedin, New Zealand.
3 Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania and Commonwealth Scientific and Industrial Research Organisation, Marine and Atmospheric Research, Hobart, 7001, Australia.
4 Department of Oceanography, University of Hawaii, Honolulu, HI 96822, USA.
5 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
6 Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA.
7 Analytical and Environmental Chemistry, Free University of Brussels, B-1050 Brussels, Belgium.
8 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Mutsu Institute for Oceanography, Yokosuka, Kanagawa 237-0061, Japan.
9 Institute for Computational Earth System Science, University of California, Santa Barbara, CA 93106, USA.
10 Ocean Sciences Department, University of California, Santa Cruz, CA 95064, USA.
11 Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA 23062, USA.
12 Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
* To whom correspondence should be addressed. E-mail: [email protected]
