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The role of krill grazing in Southern Ocean nutrient cycles

磷虾放牧在南大洋营养循环中的作用

基本信息

批准号：
NE/F014635/1
负责人：
Eric Achterberg
金额：
$ 16.8万
依托单位：
University of Southampton
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF014635%2F1
关键词：
role krill grazing Southern Ocean

项目摘要

One of the major problems mankind is facing in this century is an increasing number and intensity of natural disasters (e.g. hurricanes, floods, melting ice sheets). Many of these disasters are indicators of global climatic changes related to the ever-increasing amount of CO2 humans release into the atmosphere. So far, a large proportion of these CO2 emissions has been absorbed by the oceans and tucked away for centuries, but to predict the future, we need to understand the mechanisms involved. This proposal tackles one possible mechanism within the Southern Ocean. We hypothesize that a small crustacean - Antarctic krill / helps the drawdown of carbon (C) from the atmosphere into the deep ocean. Three facts about krill lead to this suggestion: Firstly, krill are very abundant, with a total mass greater than that of the human population. Secondly, krill have very high feeding rates and feed mainly on phytoplankton, the algae, which build their own organic C from the CO2 dissolved in the water. Thirdly, krill faeces sink as compact pellets towards the seafloor. Thus, krill mediate the carbon transition from small floating algae to large sinking fecal pellets, a process known as the 'biological C pump'. Unfortunately, it is slightly more complicated than this. With the sinking pellets, krill might also export other elements from the surface layer, e.g. iron (Fe) and silicon (Si) that are essential for the algae to grow and often in limiting concentrations. Even though krill are a key species in the Southern Ocean food web and commercially fished for, little is known about their role in biogeochemical cycles. None of the essential processes has been measured before in detail, thus, we need more information to test our hypothesis: 1. How much C, Si and Fe are in the krill fecal pellets? 2. Do the elements dissolve out of the pellets before sinking to depth? 3. Do krill accumulate Fe into their bodies? 4. How much Fe and Si do krill release in dissolved form when feeding? The last question is especially important, because a fast regeneration of particulate Fe into the dissolved form via krill might stimulate algal growth and therefore a further uptake of CO2. Our plan is to tackle these questions during a cruise in the Southern Ocean. We will collect krill and incubate them on board to measure the rates of pellet production and release of dissolved nutrients. We will sample their pellets from different water depths, to compare the total numbers and the content of C, Fe and Si. These measurements will be related to water column profiles of Fe and Si, both in dissolved form as nutrients and in particulate form in algal cells. We will sample at a range of stations within different environments / some with lots of algae, others with few, some with sufficient Fe and Si, others with too little. This will enable us to make simple equations that relate the various rates in krill (see 4 questions above) to their available food and nutrient situation. With help of these equations, we can scale up the results from our sampling sites to answer our overall question: Do krill support the biological C pump by exporting C and recycling nutrients, or do they stop the pump by removing Fe and Si from surface water? Our ship-time bid is for 11 days in the Scotia Sea during 2009/2010. To increase our seasonal and regional coverage, we will supplement the data set with a range of frozen samples from previous cruises. Both measuring Fe and handling krill are non-trivial tasks; therefore the proposal combines expertise across two institutes, the British Antarctic Survey and the National Oceanography Centre Southampton. The scientists involved supply all the essential skills in locating, catching and experimenting with krill (Atkinson, Fielding, Schmidt), in trace metal clean work (Achterberg, Rijkenberg), in oceanography (Venables) and in marine chemistry (M. Whitehouse).

本世纪人类面临的主要问题之一是自然灾害(如飓风、洪水、冰盖融化)的数量和强度不断增加。其中许多灾害是全球气候变化的指标，这些变化与人类排放到大气中的二氧化碳数量不断增加有关。到目前为止，这些二氧化碳排放中的很大一部分已经被海洋吸收，并被藏了几个世纪，但要预测未来，我们需要了解其中的机制。这项提议解决了南大洋内的一种可能的机制。我们假设，一种小型甲壳类动物--南极磷虾/有助于将碳(C)从大气中吸收到深海中。关于磷虾的三个事实导致了这一观点：首先，磷虾非常丰富，其总质量超过了人类的总人口。其次，磷虾的摄食率非常高，主要以浮游植物为食，浮游藻类从溶解在水中的二氧化碳中生成自己的有机碳。第三，磷虾粪便以致密颗粒的形式下沉到海底。因此，磷虾介导了从小型漂浮藻类到大型下沉粪便颗粒的碳转移，这一过程被称为“生物C泵”。不幸的是，它比这稍微复杂一些。利用下沉的颗粒，磷虾还可能从表层输出其他元素，例如铁(Fe)和硅(Si)，这是藻类生长所必需的，而且通常是在有限的浓度下。尽管磷虾是南大洋食物网中的关键物种，也是商业捕捞的对象，但人们对它们在生物地球化学循环中的作用知之甚少。这些基本的过程以前都没有被详细测量过，因此，我们需要更多的信息来验证我们的假设：1.磷虾粪便颗粒中有多少C、Si和Fe？2.这些元素在下沉到深处之前会从颗粒中溶解出来吗？3.磷虾是否会将铁积累到它们的体内？4.当摄食时，磷虾以溶解的形式释放出多少铁和硅？最后一个问题尤其重要，因为通过磷虾将颗粒铁快速再生为溶解形式，可能会刺激藻类生长，从而进一步吸收二氧化碳。我们的计划是在南大洋的一次航行中解决这些问题。我们将收集磷虾并在船上孵化它们，以测量颗粒生产和溶解营养物质的释放速度。我们将从不同的水深对它们的球团进行采样，比较它们的总数和C、Fe、Si的含量。这些测量将与铁和硅的水柱剖面相关联，铁和硅作为营养物质以溶解形式存在，在藻类细胞中以颗粒形式存在。我们将在不同环境中的一系列站点进行采样/有些站点藻类丰富，有些站点藻类很少，有些站点的铁和硅充足，有些站点的藻类太少。这将使我们能够建立简单的方程式，将磷虾的不同比率(见上文4个问题)与其可获得的食物和营养状况联系起来。在这些公式的帮助下，我们可以放大我们采样点的结果来回答我们的总体问题：磷虾是通过输出碳和循环营养物质来支持生物C泵，还是通过从地表水中去除铁和硅来停止泵？我们的船期投标是2009/2010年间在斯科舍海停留11天。为了扩大我们的季节性和地区性覆盖范围，我们将用以前邮轮的一系列冷冻样本来补充数据集。测量铁和处理磷虾都不是微不足道的任务；因此，该提案结合了英国南极调查局和南安普敦国家海洋学中心这两个研究所的专业知识。参与的科学家提供了定位、捕捉和试验磷虾(Atkinson，Fiding，Schmidt)、痕量金属清洁工作(Achterberg，Rijkenberg)、海洋学(Venables)和海洋化学(M.Whitehouse)的所有基本技能。