研究人员在北极发现碳传送带

　　每年，从巴伦支海和卡拉海跨大陆架运输的富含碳的颗粒可以在北极深海中结合多达360万吨的二氧化碳数千年。
　　北极碳传送带的插图。图片来源:Andreas Rogge。
　　阿尔弗雷德·韦格纳研究所及其合作机构的科学家在本期《自然地球科学》杂志上报告称，就这一地区而言，一种较早的不熟悉的运输路线利用生物碳泵和洋流吸收大气中的二氧化碳，其规模相当于冰岛每年的总排放量。
　　与其他海洋相比，北冰洋中部的生物生产力一直受到限制，因为阳光往往只能短暂地被接收（要么是极地之夜的结果，要么是海冰覆盖的结果）而且可获得的营养来源不足。
　　因此，与其他水域的同类相比，上层水域的微藻(浮游植物)吸收的能量更少。从根本上说，当俄罗斯科考船Akademik Tryoshnikov在2018年8月和9月的ARCTIC2018之旅中，在北极中部的南森盆地发现了大量的颗粒碳时也就是储存在植物残骸中的颗粒（要么是由于极夜，要么是由于海冰覆盖），震惊是巨大的。
　　下面的分析揭示了一个由巴伦支海的底水构成的水体，在水深达2公里的地方含有大量的碳微粒。后者是在冬季海冰形成时产生的，然后寒冷和重水下沉，水从浅海陆架流下大陆斜坡，流入北极盆地深处。
　　＂根据我们的测量，我们计算出，通过这种水质量运输，每天有超过2000公吨的碳流入北极深海，相当于大气中8500公吨的二氧化碳。推算出每年的总排放量甚至有1360万吨二氧化碳，这与冰岛全年的总排放量相同。＂
　　——安德烈亚斯·罗格博士，研究第一作者和海洋学家，阿尔弗雷德·韦格纳研究所，亥姆霍兹极地和海洋研究中心
　　这些富含碳的水覆盖了巴伦支海架和卡拉海架，进入北极盆地大约1000公里。根据这一新发现的机制，巴伦支海（早前被认为是北极地区高产的边缘海）似乎能以一种比先前认为的更有效的方式从空气中多消除约30%的碳。
　　此外，基于模型的模拟发现，这种外流表现为季节性的脉冲，如在北极沿海海域，浮游植物在夏季吸收二氧化碳。
　　理解碳循环中的运输和转化过程对于制定全球二氧化碳预算和全球变暖预测是必要的。在海洋表面，单细胞藻类倾向于从空气中吸收二氧化碳，并在破碎时沉入深海。
　　一旦以这种方式结合的碳获得了深水，它就会在那里聚集，直到倾覆的洋流把水带回海洋表面。这在北极要花上几千年。此外，假设碳已经沉积在深海沉积物中。在这种情况下，它甚至可能被困在那里数百万年，因为只有火山活动才有可能释放它。
　　这一过程也被称为生物碳泵，它可能在很长一段时间内消除空气中的碳，并构成地球碳循环中的一个重要汇。
　　此外，这一过程也是当地深海动物的食物来源，如海星、海绵和蠕虫。只有进行额外的研究，才能确定碳是否被生态系统吸收。
　　极地陆架海还蕴藏着其他巨大的未被发现的区域，在这些区域，底水已经发育并流入深海。就其本身而言，我们可以假设，这一机制作为碳汇的全球影响在相对而言确实要大得多。
　　＂然而，由于持续的全球变暖，冰越来越少，因此形成的底部水也越来越少。与此同时，浮游植物可以获得更多的光线和营养，从而可以结合更多的二氧化碳。因此，目前不可能预测这个碳汇将如何发展，而确定潜在的临界点迫切需要更多的研究。＂
　　——安德烈亚斯·罗格博士，研究第一作者和海洋学家，阿尔弗雷德·韦格纳研究所，亥姆霍兹极地和海洋研究中心
　　原文：Researchers Identify Carbon ‘Conveyor Belt’ in Arctic
　　Annually, the cross-shelf transport of carbon-rich particles from the Barents and Kara Seas can bind up to 3.6 million metric tons of CO2 in the Arctic deep sea for millennia.
　　As far as this region is concerned, an earlier unfamiliar transport route makes use of the biological carbon pump and ocean currents to engross atmospheric CO2 on the scale of Iceland’s total annual emissions, as per scientists from the Alfred Wegener Institute and partner institutes report in the present issue of the journal Nature Geoscience.
　　Compared to the other oceans, the biological productivity of the central Arctic Ocean has been restricted, as sunlight is often received in brief supply—either as a result of the Polar Night or sea-ice cover—and the accessible nutrient sources are insufficient.
　　As a result, microalgae (phytoplankton) in the upper water layers have entry to less energy compared to their counterparts in other waters. Fundamentally, the shock was huge when, on the journey ARCTIC2018 in August and September 2018 on board the Russian research vessel Akademik Tryoshnikov, huge quantities of particulate—that is, stored in plant remains—carbon was found in the Nansen Basin of the central Arctic.
　　The following analyses disclosed a body of water with large amounts of particulate carbon to depths of up to 2 km, made of bottom water from the Barents Sea. The latter is generated when sea ice develops in winter, then cold and heavy water sinks, and water flows from the shallow coastal shelf down the continental slope and into the deep Arctic Basin.
　　＂Based on our measurements, we calculated that through this water-mass transport, more than 2,000 metric tons of carbon flow into the Arctic deep sea per day, the equivalent of 8,500 metric tons of atmospheric CO2. Extrapolated to the total annual amount revealed even 13.6 million metric tons of CO2, which is on the same scale as Iceland’s total annual emissions.＂
　　Dr. Andreas Rogge, Study First Author and Oceanographer, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
　　This plume of carbon-rich water covers the Barents- and Kara Sea shelves to roughly 1,000 km into the Arctic Basin. In light of this newly found mechanism, the Barents Sea—earlier known to be the highly productive marginal sea present in the Arctic—would seem to be in an efficient manner to eliminate approximately 30% more carbon from the air compared to earlier thought.
　　Furthermore, model-based simulations identified that the outflow manifests in seasonal pulses, as in the Arctic’s coastal seas, the absorption of CO2 by phytoplankton takes place in summer.
　　Comprehending transport and transformation processes inside the carbon cycle is necessary to make global carbon dioxide budgets and projections for global warming. On the ocean’s surface, single-celled algae tend to absorb CO2 from the air and sink toward the deep sea when broken.
　　As soon as the carbon bound in this manner obtains the deep water, it girdles there until overturning currents get the water back to the surface of the ocean. This takes various thousand years in the Arctic. Also, suppose the carbon has been deposited in deep-sea sediments. In that case, it could even be trapped there for millions of years, as only volcanic activity has the potential to liberate it.
　　This process, also called the biological carbon pump, can potentially eliminate carbon from the air for long periods of time and constitutes a vital sink in the planet＂s carbon cycle.
　　Furthermore, the process constitutes a food source for the local deep-sea fauna like sea stars, sponges, and worms. Only by performing additional research can whether the carbon is absorbed by the ecosystem be determined.
　　The polar shelf seas harbor other hugely undiscovered regions in which bottom water has been developed and flows into the deep sea. By itself, it could be presumed that the global impact of this mechanism as a carbon sink is really much greater in a comparative manner.
　　＂However, due to the ongoing global warming, less ice and therefore less bottom water is formed. At the same time more light and nutrients are available for the phytoplankton, allowing more CO2 to be bound. Accordingly, it’s currently impossible to predict how this carbon sink will develop, and the identification of potential tipping points urgently calls for additional research.＂
　　Dr. Andreas Rogge, Study First Author and Oceanographer, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research