物理學(xué)家查爾斯·達(dá)爾文爵士是進(jìn)化論創(chuàng)始人查爾斯·達(dá)爾文的孫子,，他的一項(xiàng)被人遺忘的貢獻(xiàn)解決了關(guān)于海洋混合的一個(gè)長(zhǎng)期爭(zhēng)論。他在1953年提出,，游泳的動(dòng)物也許對(duì)海洋中水的混合有相當(dāng)大貢獻(xiàn),。今天，關(guān)于海洋中由生物造成的海水混合的爭(zhēng)論集中在對(duì)動(dòng)物尾流擾動(dòng)與海洋擾動(dòng)的對(duì)比上,。“達(dá)爾文式”混合是不同的,，它是當(dāng)在一種流體中運(yùn)動(dòng)的一個(gè)固態(tài)物體使其周圍的一部分流體運(yùn)動(dòng)起來(lái)、并沿該物體傳播時(shí)發(fā)生的,。
加州理工學(xué)院的Kakani Katija 和John Dabiri利用對(duì)在一個(gè)偏僻海島湖泊中游動(dòng)的水母所做的現(xiàn)場(chǎng)測(cè)定,、并結(jié)合一個(gè)新的理論模型發(fā)現(xiàn)，活生物通過(guò)這一機(jī)制對(duì)海洋混合的貢獻(xiàn)是相當(dāng)大,。
研究人員利用小型水母進(jìn)行實(shí)驗(yàn),。他們?cè)谒蟹胖脠F(tuán)狀染料，然后觀測(cè)水母從中游過(guò)時(shí)染料的分布情況,。結(jié)果發(fā)現(xiàn),，水母游過(guò)的路徑上出現(xiàn)一長(zhǎng)條染料“尾巴”,，其中90％都是由于“達(dá)爾文機(jī)制”的作用。
研究人員說(shuō),，一個(gè)小型海洋生物只要游出幾個(gè)身長(zhǎng)的距離,，就會(huì)帶動(dòng)相當(dāng)于自身4倍體積的液體。由于海洋中存在大量的小型生物,，它們通過(guò)“達(dá)爾文機(jī)制”而產(chǎn)生的能量非?？捎^，與風(fēng)和潮汐的作用在同一個(gè)數(shù)量級(jí)上,。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 460, 624-626 (30 July 2009) | doi:10.1038/nature08207
A viscosity-enhanced mechanism for biogenic ocean mixing
Kakani Katija1 & John O. Dabiri1,2
1 Bioengineering,
2 Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, California 91125, USA
Recent observations of biologically generated turbulence in the ocean have led to conflicting conclusions regarding the significance of the contribution of animal swimming to ocean mixing. Measurements indicate elevated turbulent dissipation—comparable with levels caused by winds and tides—in the vicinity of large populations of planktonic animals swimming together1. However, it has also been noted that elevated turbulent dissipation is by itself insufficient proof of substantial biogenic mixing, because much of the turbulent kinetic energy of small animals is injected below the Ozmidov buoyancy length scale, where it is primarily dissipated as heat by the fluid viscosity before it can affect ocean mixing2. Ongoing debate regarding biogenic mixing has focused on comparisons between animal wake turbulence and ocean turbulence3, 4. Here, we show that a second, previously neglected mechanism of fluid mixing—first described over 50 years ago by Charles Darwin5— is the dominant mechanism of mixing by swimming animals. The efficiency of mixing by Darwin's mechanism is dependent on animal shape rather than fluid length scale and, unlike turbulent wake mixing, is enhanced by fluid viscosity. Therefore, it provides a means of biogenic mixing that can be equally effective in small zooplankton and large mammals. A theoretical model for the relative contributions of Darwinian mixing and turbulent wake mixing is created and validated by in situ field measurements of swimming jellyfish using a newly developed scuba-based laser velocimetry device6. Extrapolation of these results to other animals is straightforward given knowledge of the animal shape and orientation during vertical migration. On the basis of calculations of a broad range of aquatic animal species, we conclude that biogenic mixing via Darwin's mechanism can be a significant contributor to ocean mixing and nutrient transport.
