The impact of submarine diagenesis of tephra on seawater chemistry

我们长期以来一直在考虑为什么海洋是咸的这个问题，多年来我们在研究海洋化学的方法上变得越来越复杂，但什么控制海水化学的问题仍然是科学的核心。解决这个问题不仅仅是简单地描述为什么海水有我们今天测量的成分。我们还知道，海水的组成在控制定义我们周围世界的许多过程中起着重要作用。例如，海水在控制大气中二氧化碳和氧气浓度方面起着关键作用。因此，如果我们能更多地了解赋予海水独特化学成分的过程，我们就会更好地了解它在温室效应中扮演的角色，以及它们如何促进地球上生命的进化。许多为我们提供现代工业经济所需材料的矿藏是由加热的海水流过岩石而形成的。矿床的性质和规模在一定程度上取决于海水的组成。我们知道，不同类型的矿藏形成于地球历史上不同的时期。地质学家将这种变化的一部分解释为海水化学成分的变化，但为什么海水会改变其组成呢？除非我们知道今天控制海水化学的是什么过程，否则我们无法真正回答这个问题。当然，影响海洋组成的一些因素是显而易见的。我们可以测量河水的化学成分，我们知道有多少河水流入海洋，所以我们可以很好地估计这种溶解元素来源的作用。海洋中溶解元素的另一个主要来源被认为来自大洋中脊发现的温泉。同样，我们已经测量了这些温泉的化学成分，但要测量环绕地球的6万公里大洋中脊上有多少温泉，就有点困难了。事实上，当我们试图平衡从温泉和河流进入海洋的溶解物质的量与从海洋中移入沉积物的物质的量时，我们发现许多元素存在不平衡。换句话说，我们发现，对于许多元素，我们无法平衡进入海洋的溶解物质的数量与从海洋中清除的数量。海洋的化学成分可能正在发生变化，但对海水中最重要的元素来说，这似乎不太可能。因此，似乎还有其他一些过程正在影响海水化学，但我们还没有确定。我们的想法是，这一不明过程是位于海洋附近的许多活火山倾倒在海水中的火山灰的变化。火山灰是一种高活性物质。当它进入海水时，一些元素会很快从火山灰中释放出来，一些元素会被火山灰从海水中吸收。尽管一些教科书仍然引用了50年前的研究，表明火山灰在海洋地球化学循环中并不是一个重要的参与者，但更现代的研究表明，这个过程可能比人们迄今认为的更重要。(一句警告：聪明勤奋的科学家不依赖教科书中报告的第三手数据-他们去原始来源并适当地检查他们的事实！)在这项研究中，我们将进行实验，以测量火山灰变化的速度以及火山灰和海水之间元素交换的程度。通过这样做，我们希望检验这样一种假设，即火山灰确实在控制海水成分方面发挥了重要作用，甚至可能参与决定海洋某些地区的生物活动水平。

Explanation of proposal 'The impact of submarine diagenesis of tephra on seawater chemistry' We have long considered the question as to why the sea is salty and over the years we have become increasingly sophisticated in our approach to studying the chemistry of the oceans, but the question as to what controls the chemistry of seawater remains central to science. Resolving this problem extends beyond simply describing why seawater has the composition we measure today. We also know that the composition of seawater is important in controlling many of the processes that define the world around us. For example, seawater plays a key role in controlling the concentration of carbon dioxide and oxygen in the atmosphere. Hence, if we can find out more about the processes that give seawater its distinct chemical composition, we will better understand what role it plays in the greenhouse effect and how they contributed to the evolution of life on Earth. Many ore deposits that supply us with the materials necessary for a modern industrial economy were created by the flow of heated seawater through rock. The nature and size of the ore deposits depends, in part, on the composition of seawater. We know that different types of ore deposits formed at different times in the Earth's history. Geologists have interpreted some of this variation as due to changes in the chemistry of seawater, but why did seawater change its composition? We cannot really answer this question unless we know what processes control seawater chemistry today. Of course, some of the factors that influence the composition of the oceans are obvious. We can measure the chemistry of river waters and we know how much river water flows into the oceans, so we can make a pretty good estimate of the role of this source of dissolved elements. The other major source of dissolved elements to the oceans is thought to come from the hot springs found on the mid-ocean ridges. Again, we have measured the chemistry of these hot springs, but it is a bit more difficult to measure how many hot springs there along the 60,000 km of mid-oceans ridges that circle the planet. Indeed, when we try and balance the amount of dissolved material entering the oceans from hot springs and rivers versus the amount of material removed from the oceans into sediments, we discover an imbalance in many elements. In other words, we find that for a lot of elements we cannot balance the amount of dissolved material entering the oceans versus the amount that is removed from the oceans. It is possible that the chemistry of the oceans is changing, but this does not seem likely for the most important elements in seawater. Hence, it appears that there is some other process that is affecting seawater chemistry, but we have yet to identify. Our idea is that this unidentified process is the alteration of volcanic ash dumped into seawater by the many active volcanoes that are located close to the oceans. Volcanic ash is a highly reactive material. When it enters seawater, some elements are quickly released from the ash and some elements are absorbed from seawater by the ash. Although some textbooks still quote studies from 50 years ago that suggest ash is not an important player in marine geochemical cycles, more modern research indicates that this process may be more important than has been hitherto regarded. (A word of warning: intelligent hard-working scientists do not rely on 3rd hand data reported in textbooks - they go to the original sources and check their facts properly!) This study we will carry out experiments to measure how quickly ash alters and the magnitude of the exchange of elements between ash and seawater. In doing so, we hope to test the hypothesis that volcanic ash does play a major role in controlling the composition of seawater, and that it may even be involved in determining the level of biological activity in some parts of the oceans.