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/J021075/1
• 负责人: Gavin Foster
• 金额: $ 40.07万
• 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: 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%2FJ021075%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.

在过去的250万年中，地球的气候在温暖时期之间定期振荡，如今天所谓的冰川间，而冰冷的寒冷时期被称为冰川，当几公里的冰覆盖了北半球。被困在冰块中的古代空气的气泡告诉我们，尽管循环最终是由地球周围围绕太阳的变化触发的，但它们在很大程度上是由于在冰川期间，在冰川期间，在冰川期间，二氧化碳二氧化碳碳（CO2）的大气浓度的增加驱动。在每个周期中，冷却冰川的变化往往很慢（在90至30千年之间），而终止每个冰川时期的变暖往往非常迅速（长度约为10千年）。由于这些变暖事件导致北半球冰盖的戏剧性和快速撤退，因此被称为冰脱冰片。最后一次冰期始于大约18000年前，大约在1万年前完成。尽管这些冰川间间循环循环是全球气候变化的最引人注目，最重要的例子，但它们的确切原因却尚不清楚。但是，我们所知道的是，在冰冰过程中，很可能会从冰川期间存储的深海中移出，并将其温暖到地球并驱动冰片的撤退，直到下一个冷却周期开始。为了绑定哪些机制负责这样将二氧化碳移动到这样的机制，我们需要确切知道它在海洋中的位置。一些研究指出，它存储在围绕南极洲循环的水中的深渊中，因此表明它是该区域中运行的机制。尽管这与我们的许多观察结果一致，但其他一些线索指向全球另一端的北太平洋，这很重要。最近，最近有人提出，深海根本不涉及。在该提案中，我们通过确定二氧化碳是否存储在南极洲周围，从而阐明了这一辩论。18000年前，海水的CO2没有实际测量值，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，就像他们在温暖的热带海洋中发现的堂兄一样，将骨骼从碳酸钙中产生。硼中碳酸钙骨架中硼的同位素组成与珊瑚生长的pH值有关，海水的pH值与所含的二氧化碳量成正比。因此，pH是存储在冰川深渊中的二氧化碳的非常有用且直接的示踪剂。但是，为了获得最佳的pH重建，我们首先需要比目前更好地校准代理。我们将主要通过在实验室中的已知pH中种植深海珊瑚并测量其硼组成来做到这一点。有了更好的理解，我们不仅会了解这些动物将如何受到未来的海洋酸化的影响，而且还通过对不同年龄的古代深海珊瑚骨骼的硼同位素组成进行测量，我们可以通过整个脱胶质重建pH在一个位置中演变。我们有来自SW太平洋大约1500 m水深的许多深海珊瑚样品，这些年龄是30至8000年的历史。我们对该地区感兴趣，因为它已被提出为二氧化碳的关键途径，因为它从深渊混合到海洋上层，然后最终进入大气。我们将产生的pH记录将是我们当前关于二氧化碳在冰冰过程中如何在海洋和大气之间移动的想法的彻底检验。因此，这项研究将提供对负责冰川间冰2变化的机制的宝贵见解。

项目成果

Boron isotope sensitivity to seawater pH change in a species of Neogoniolithon coralline red alga

• DOI: 10.1016/j.gca.2017.08.021
• 发表时间: 2017-11-15
• 期刊: GEOCHIMICA ET COSMOCHIMICA ACTA
• 影响因子: 5
• 作者: Donald, Hannah K.;Ries, Justin B.;Foster, Gavin L.
• 通讯作者: Foster, Gavin L.

Deglacial upwelling, productivity and CO2 outgassing in the North Pacific Ocean

• DOI: 10.1038/s41561-018-0108-6
• 发表时间: 2018-04
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: W. Gray;J. Rae;Robert C.J. Wills;A. Shevenell;B. Taylor;A. Burke;G. Foster;C. Lear

Coral Sr-U thermometry

• DOI: 10.1002/2015pa002908
• 发表时间: 2016-06-01
• 期刊: PALEOCEANOGRAPHY
• 作者: DeCarlo, Thomas M.;Gaetani, Glenn A.;Stewart, Joseph A.
• 通讯作者: Stewart, Joseph A.

Structural limitations in deriving accurate U-series ages from calcitic cold-water corals contrast with robust coral radiocarbon and Mg/Ca systematics

从方解石冷水珊瑚推导准确 U 系列年龄的结构限制与强大的珊瑚放射性碳和 Mg/Ca 系统学对比

• DOI: 10.1016/j.chemgeo.2013.07.002
• 发表时间: 2013
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Gutjahr M

Intrareef variations in Li/Mg and Sr/Ca sea surface temperature proxies in the Caribbean reef-building coral Siderastrea siderea

• DOI: 10.1002/2016pa002968
• 发表时间: 2016-10-01
• 期刊: PALEOCEANOGRAPHY
• 作者: Fowell, Sara E.;Sandford, Kate;Foster, Gavin L.
• 通讯作者: Foster, Gavin L.