Where did all the CO2 go? Insights from boron isotopes in deep-sea corals

所有的二氧化碳都去哪儿了？

• 批准号: NE/J021121/1
• 负责人: J Roberts
• 金额: $ 20.15万
• 依托单位: Heriot-Watt University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ021121%2F1
• 关键词: Where; did; CO2; go; Insights

Over the last 2.5 million years or so the Earth's climate has regularly oscillated between warm periods, like today called interglacials, and frigid cold periods called glacials when several kms of ice blanketed the Northern Hemisphere. Bubbles of ancient air trapped in ice cores tell us that, although the cycles are ultimately triggered by changes in the Earth's orbit around the Sun, they are largely driven by increases in the atmospheric concentration of the greenhouse gas carbon dioxide (CO2) - CO2 is low during glacial periods and high during interglacial periods. During each cycle, cooling into a glacial tends to be rather slow (taking between 90 to 30 thousand years) and the warming that terminates each glacial period tends to be very rapid (~10 thousand years in length). Since these warming events caused the dramatic and rapid retreat of the northern hemisphere ice sheets they are known as deglacials. The last deglacial began around 18 thousand years ago and was completed by around 10 thousand years ago. Despite these glacial-interglacial cycles being the most dramatic and significant recent examples of global climate change, their exact cause is not known. What we do know however is that during a deglacial CO2 is most likely being moved out of the deep oceans where it is stored during glacial periods, to the atmosphere, where it warms the Earth up and drives the retreat of the ice sheets, until the next cooling cycle begins. In order to tie down which mechanisms are responsible for moving the CO2 around like this we need to know exactly where in the ocean it is going. Some studies point to it being stored in the deep abyss in water that circulates around Antarctica, therefore suggesting it is mechanisms operating in this region that are responsible. Although this agrees with many of our observations, some other clues point to the North Pacific on the other side of the globe, as being important. And it has even been recently suggested that the deep ocean isn't involved at all. In this proposal we shed light on this debate by determining whether or not CO2 was stored around Antarctica.No actual measurements exist of the CO2 of seawater 18 thousand years ago, therefore we have to use indirect measurements known as proxies. The proxy we will use is based on boron in ancient deep-sea coral skeletons. Deep-sea corals, like their cousins found in warm tropical seas, make skeletons out of calcium carbonate. The isotopic composition of boron in their calcium carbonate skeleton is related to the pH in which the coral grew and the pH of seawater is proportional to the amount of CO2 it contains. Therefore, pH is a very useful and direct tracer ofthe CO2 stored in the glacial abyss. However, in order to get the best pH reconstructions we first need to calibrate the proxy better than it is currently. We will mainly do this by growing deep-sea corals at known pH in the laboratory and measuring their boron composition. Armed with this better understanding we will not only get an idea of how these animals will be affected by future ocean acidification, but, by making measurements of the boron isotopic composition of ancient deep-sea coral skeletons of different ages we can reconstruct how pH evolved in one location through the entire deglacial. We have a number of deep-sea coral samples from around 1500 m water depth in the SW Pacific that are from 30 to 8 thousand years old. We are interested in this region because it has been put forward as a key route for CO2 as it is mixed from the deep abyss into the upper levels of the ocean and then ultimately into the atmosphere. The pH record we will produce will be a thorough test of our current ideas of how CO2 moves between ocean and atmosphere during a deglacial; this study will therefore provide valuable insights into the mechanisms responsible for glacial-interglacial pCO2 change.

在过去 250 万年左右的时间里，地球气候经常在温暖时期（如今天的间冰期）和寒冷时期（称为冰期）之间波动，当时数公里的冰覆盖了北半球。冰芯中的古代空气气泡告诉我们，虽然这些循环最终是由地球绕太阳轨道的变化引发的，但它们很大程度上是由大气中温室气体二氧化碳（CO2）浓度的增加驱动的——二氧化碳在冰河期较低，在间冰期较高。在每个周期中，进入冰川的冷却往往相当缓慢（需要 90 至 3 万年），而结束每个冰川期的变暖往往非常迅速（长度约为 1 万年）。由于这些变暖事件导致北半球冰盖急剧而迅速地消退，因此被称为冰川消退。最后一次冰消期大约开始于 18000 年前，结束于大约 10000 年前。尽管这些冰期-间冰期循环是全球气候变化最近最引人注目和最重要的例子，但其确切原因尚不清楚。然而我们所知道的是，在冰消期期间，二氧化碳很可能从冰河期储存的深海转移到大气中，使地球变暖并推动冰盖后退，直到下一个冷却周期开始。为了确定哪些机制负责将二氧化碳像这样移动，我们需要确切地知道它在海洋中的哪个位置。一些研究指出，它被储存在南极洲周围循环的水中的深渊中，因此表明这是该地区运作的机制造成的。尽管这与我们的许多观察结果一致，但其他一些线索表明地球另一端的北太平洋也很重要。最近甚至有人提出深海根本不参与其中。在本提案中，我们通过确定南极洲周围是否储存有二氧化碳来阐明这一争论。18000年前海水中的二氧化碳没有实际测量结果，因此我们必须使用称为代理的间接测量。我们将使用的代理是基于古代深海珊瑚骨骼中的硼。深海珊瑚就像它们在温暖的热带海洋中发现的表亲一样，由碳酸钙制成骨骼。碳酸钙骨架中硼的同位素组成与珊瑚生长的 pH 值有关，而海水的 pH 值与其中含有的 CO2 量成正比。因此，pH 值是冰川深渊中储存的二氧化碳非常有用且直接的示踪剂。然而，为了获得最佳的 pH 重建，我们首先需要比当前更好地校准代理。我们将主要通过在实验室已知 pH 值的条件下培养深海珊瑚并测量其硼成分来实现这一目标。有了更好的了解，我们不仅可以了解这些动物将如何受到未来海洋酸化的影响，而且通过测量不同年龄的古代深海珊瑚骨骼的硼同位素组成，我们可以重建整个冰消期中一个地点的 pH 值如何演变。我们在西南太平洋水深约 1500 米处拥有许多深海珊瑚样本，年龄从 30 到 8000 年不等。我们对这个地区很感兴趣，因为它被认为是二氧化碳从深渊混合到海洋上层，然后最终进入大气的关键路线。我们将制作的 pH 记录将彻底测试我们目前关于冰消期间二氧化碳如何在海洋和大气之间移动的想法；因此，这项研究将为冰期-间冰期 pCO2 变化的机制提供有价值的见解。

项目成果

Chapter 42. Cold-water corals

第42章.冷水珊瑚

• 发表时间: 2016
• 作者: Cordes, E

Marine Animal Forests - The Ecology of Benthic Biodiversity Hotspots

海洋动物森林 - 底栖生物多样性热点地区的生态

• DOI: 10.1007/978-3-319-17001-5_6-1
• 发表时间: 2015
• 作者: Henry L

Chapter 51 . Biological Communities on Seamounts and Other Submarine Features Potentially Threatened by Disturbance

第51章。

• 发表时间: 2016
• 作者: Koslow, AJ

Physiological response of the cold-water coral Desmophyllum dianthus to thermal stress and ocean acidification.

• DOI: 10.7717/peerj.1606
• 发表时间: 2016
• 期刊: PeerJ
• 影响因子: 2.7
• 作者: Gori A;Ferrier-Pagès C;Hennige SJ;Murray F;Rottier C;Wicks LC;Roberts JM
• 通讯作者: Roberts JM

Sensitivity of marine protected area network connectivity to atmospheric variability.

• DOI: 10.1098/rsos.160494
• 发表时间: 2016-11
• 期刊: Royal Society open science
• 影响因子: 3.5
• 作者: Fox AD;Henry LA;Corne DW;Roberts JM
• 通讯作者: Roberts JM