为了早日实现碳中和，阻止全球进一步变暖，海洋绿化被认为是清除大气CO2的重要组成部分，然而最新研究发现，海洋中的“植树造林”在大时间尺度上并不一定助力碳中和！

Ocean afforestation is considered to an important component of atmospheric CO2 removal (CDR) in order to achieve early carbon neutrality and stop further global warming, yet new research has found that “afforestation” in the ocean does not necessarily contribute to carbon neutrality in the long term!

2021年5月7日，来自澳洲塔斯马尼亚大学和南新威尔士大学的研究人员在国际顶尖期刊《Nature Communications》上在线发表了一篇名为“Testing the climate intervention potential of oceanafforestation using the Great Atlantic Sargassum Belt”的研究论文，文章的中文译名是《利用大西洋马尾藻带测试海洋绿化的气候干预潜力》。

On May 7, 2021, researchers from the University of Tasmania and the University of New South Wales published a paper online entitled “Testing the climate intervention potential of ocean afforestation using the Great Atlantic Sargassum Belt” whose Chinese title was《利用大西洋马尾藻带测试海洋绿化的气候干预潜力》in the leading international journal Nature Communications.

 

 在对亚热带北大西洋马尾藻带引起的钙化和营养物质通量的重新分配进行分析之后，研究人员发现，由于复杂的物理和生物地球化学反馈，海洋绿化的CO2清除潜力和副作用都具有极大的不确定性。

After analyzing two biogeochemical feedbacks, nutrient reallocation and calcification by the Great Atlantic Sargassum Belt, the researchers found that the CDR potential and side effects of ocean afforestation are highly uncertain due to complex physical and biogeochemical feedbacks.

对此，文章的主要作者Lennart T. Bach认为，“利用海洋绿化来吸收大气CO2看似将开阔的沙漠化海洋转化为欣欣向荣的绿色海藻生态系统，其实这将可能以付出更多的CO2排放量为代价”。

In this regard, the lead author Lennart T. Bach argued that “Capturing atmospheric CO2 using ocean afforestation converts seemingly unproductive open ocean deserts into thriving seaweed ecosystems, but in fact it will likely come at the cost of higher CO2 emissions.”

据悉，Lennart T. Bach是澳洲塔斯马尼亚大学海洋与南极研究所的博士后研究员，研究领域主要集中在海洋碳循环相关方向。

Lennart T. Bach is a postdoctoral researcher at the Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia, and he focuses on ocean carbon cycle.

研究天然类似物是一种低风险、低成本的方法来评估大规模海洋绿化带来的影响，例如皮纳图博火山喷发向海洋输入的大量铁肥，为我们在地球系统对大规模短期扰动响应方面的研究取得了突破。因此，最近出现的（亚）热带北大西洋马尾藻带为研究大规模海洋造林提供了机会。研究人员随即对其进行了卫星勘测和现场调查，如下图所示。

Studying natural analogues presented a low-risk, cost-effective way to evaluate the potential of ocean afforestation on the scale needed to contribute significantly to CDR. Indeed, there were prominent examples where studying natural analogues of climate intervention, such as the Mount Pinatubo volcanic eruption or glacial–interglacial ocean iron fertilisation, has led to breakthroughs in our understanding of the response of the Earth System to perturbation. Thus, the recent emergence of this Great Atlantic Sargassum Belt (GASB) offered an opportunity to study large-scale ocean afforestation, and researchers had conducted satellite reconnaissance and in situ study.

 

在测算了生物量、表面附着生物钙化和营养物质通量等数据之后，研究人员对海洋绿化的效果进行了评估，发现马尾藻带的CO2吸收潜力比原本预期的会降低20～100%。

After measuring biomass, surface-attached biocalcification and nutrient fluxes, the researchers evaluated the effects of ocean afforestation and found that the CDR efficacy of Sargassum was reduced by 20-100% than originally expected.

通过海洋绿化进行气候干预与陆地造林类似，必须考虑其复杂的地球系统反馈，如下图所示。

The analysis pointed towards a similar conclusion as for terrestrial afforestation; i.e., climate intervention through ocean afforestation must consider complicated Earth-system feedbacks

作者提出了两种影响CO2清除效果的反馈机制：

The authors proposed five feedback mechanisms that influenced the effectiveness of CDR.

第一，海洋绿化虽然可以通过光合作用消耗CO2，但藻类为表生生物提供了生存环境，表面附着生物钙化形成的颗粒无机碳会降低海水碱度，促进CO2释放；

First, while ocean afforestation could consume CO2 through photosynthesis, algae provided a living environment for epifaunas, and particulate inorganic carbon formed by calcification of surface-attached organisms could reduce seawater alkalinity and promote CO2 emission.

第二，海洋绿化争夺了浮游植物的营养物质，使其POC产量减少，可能影响浮游植物主导的CO2吸收

Second, marine afforestation competed for nutrients from phytoplankton, reducing their POC production and possibly affecting phytoplankton-dominated CO2 absorption.

第三，绿化藻类死亡后，会沉积到深海沉积物中，其中90%的沉积碳会被重新矿化，最终在较大时间尺度上（如百年或千年），矿化产生的CO2会被重新输送回大气；

Third, when algae for afforestation died and deposited into deep-sea sediments, 90% of the deposited carbon was mineralized again and eventually the CO2 from mineralization was transported back to the atmosphere on larger time scales (e.g., 100 years or 1,000 years).

第四，陆地造林会降低反照率，相反的，海洋绿化反照率会增加，因为海藻比海水会反射更多的短波辐射，会将太阳辐射更多的反射到空间中，促进暖化；

Fourth, terrestrial afforestation would reduce albedo, and conversely, ocean afforestation albedo would increase because seaweed would reflect more short-wave radiation than seawater, which meant that the afforestation would reflect more solar radiation into space and promote warming.

第五，实施海洋绿化过程中，种植、培育、收割和运输等各环节产生的碳排放，都需要精准量化和评估。

Fifth, the carbon emissions generated in the various stages of planting, cultivation, harvesting and transportation during the implementation of ocean afforestation needed to be precisely quantified and assessed.

研究人员认为，到目前为止，我们对海洋绿化的副作用知之甚少，全面评估海洋绿化对CO2清除的效率与潜力，仍然具有很大挑战，不能忽略现实地球系统反馈的复杂性。

Even though little was known about the CDR potential and side-effects of ocean afforestation when upscaled. Model simulations were the first step to explore these unknowns, but they inevitably missed many complexities associated with real-world systems.

总之，人们的设想总是美好的，而自然往往超出我们的认知。

In short, our expectations are always good, but nature often exceeds our perceptions.

---

参考文献：https://www.nature.com/articles/s41467-021-22837-2.pdf

简述翻译者：海南大学研究生李凤莹