Carbonate sediment production by marine fish: quantifying production across carbonate provinces and applications to global marine carbonate modelling

海洋-大气碳循环的一个主要组成部分是海水中碳酸钙的沉淀和溶解。碳酸钙是构成石灰石和白垩岩等岩石的矿物。对这一组成部分的详细了解对于我们理解全球碳循环以及整个地球系统都很重要。这一建议建立在最近的发现基础上，这些发现代表着我们对海洋碳循环的一个方面，即碳酸盐沉积物产生的理解发生了根本性的和以前意想不到的变化。具体地说，我们最近发现了一种来自海洋硬骨鱼(如梭鱼、比目鱼和石斑鱼，统称为硬骨鱼)的全新碳酸盐沉积物来源。所有硬骨鱼都会在肠道中沉淀碳酸盐，作为持续饮用富含钙和镁的海水的副产品，将摄入的海洋钙和镁以不溶性碳酸盐的形式排泄到海洋环境中。通过2008年NERC的一笔小额赠款(NE/G010617/1)，我们在这些鱼类碳酸盐在热带浅海环境中的重要性方面取得了一系列引人注目的发现，这些发现对碳酸盐沉积学领域具有重大影响。具体地说，我们发现，在该地区，鱼类大量生产和排泄各种细粒(大多为30微米)的沉淀碳酸钙。这种碳酸盐既有“低”镁方解石，也有“高”镁方解石和文石。此外，利用特定地点的鱼类生物量和测量的碳酸盐排泄率数据，我们估计整个巴哈马群岛鱼类每年产生约610万公斤碳酸钙沉积物，估计鱼类对总碳酸盐泥浆产量的贡献总体平均为~14%，在特定生境中超过70%。最后，我们进行了至关重要的观察，即鱼类产生的晶体通常出现在巴哈马所有沉积环境中表层沉积物的最细沉积物部分中，从而证明这种物质确实代表了一种新的、在数量上重要的海洋碳酸盐沉积物来源。因此，上述发现直接应用于概念上的想法，即浅海碳酸盐工厂在今天和过去是如何发挥作用的。然而，由此引发了一系列关于碳酸盐沉积物来源在不同海相碳酸盐沉积环境中更广泛的全球意义的基本问题：Q1。鱼类是否在不同的海洋环境中产生类似类型的细粒碳酸盐沉积物(在形态和成分上)，以及这些碳酸盐沉积物在热带到凉爽温带环境梯度上的可变性范围是多少？Q2.与其他热带、亚热带和温带地区相比，巴哈马群岛的鱼类碳酸盐沉淀物的产生率如何，根据温度和身体大小能否可靠地预测这一点？第三季度。在不同的海洋环境中，鱼类产生的碳酸盐沉积相范围的保存(和溶解)潜力有多大？问题4.在不同环境中产生的碳酸盐的总体速率和相如何随当地鱼类群落结构和丰度的变化而变化？为了解决这些问题，我们建议收集关于鱼类在横跨热带到凉爽温带海洋环境(~30至~12摄氏度)的纬度梯度(140度至43摄氏度)产生的碳酸盐沉积物的类型和速率的数据，并利用这些数据：(1)确定鱼类碳酸盐沉积物在这些环境中的溶解/保存潜力(取决于组成和形态)；(2)在区域和全球两级对最初产生并随后在不同海洋环境中保存或溶解的鱼源沉积物的体积和相进行模拟。

A major component of the marine-atmospheric carbon cycle is the precipitation and dissolution of calcium carbonate in seawater. Calcium carbonate is the mineral that makes up rocks such as limestone and chalk. Detailed knowledge of this component is important to our understanding of the global carbon cycle, and to the earth system as a whole. This proposal builds upon recent findings that represent a fundamental and previously unexpected change to our understanding of one aspect of marine carbon cycling, namely carbonate sediment production. Specifically, we have recently discovered an entirely new source of carbonate sediment derived from marine bony fish (like barracuda, flatfish and grouper, collectively known as 'teleosts'). All teleosts precipitate carbonates within their guts as a by-product of continuously drinking Ca- and Mg-rich seawater, excreting the ingested marine Ca and Mg as insoluble carbonate into the marine environment. Funded through a NERC small grant in 2008 (NE/G010617/1) we made a series of remarkable discoveries regarding the significance of these fish-derived carbonates within shallow tropical marine environments, and which have major implications for the field of carbonate sedimentology. Specifically, we showed that in that region fish produce and excrete, in very large amounts, a wide range of fine-grained (mostly <30 micron) precipitated calcium carbonates. This carbonate is in the form of both 'low' and 'high' Mg-calcite, and aragonite. Additionally, using site specific fish biomass and measured carbonate excretion rate data, we estimated that fish produce ~6.1 million kg of calcium carbonate sediment per year across the Bahamian archipelago, and that estimated contributions from fish to total carbonate mud production average ~14 % overall, and exceed 70 % in specific habitats. Finally, we made the crucial observation that the crystals produced by fish occur commonly in the finest sediment fractions of surface sediments from all sedimentary environments examined in the Bahamas, thus demonstrating that such material does indeed represent both a novel and quantitatively important source of marine carbonate sediment.The above discoveries thus have direct application to conceptual ideas of how shallow marine carbonate factories function both today and in the past. Arising from this however are a series of fundamental questions about the wider global significance of this carbonate sediment source in different marine carbonate depositional environments:Q1. Do fish produce similar types of fine-grained carbonate sediment (morphologically and compositionally) in different marine environments and what is the range in variability of these carbonate sediments across tropical to cool temperate environmental gradients? Q2. How do rates of fish-derived carbonate sediment production derived from sites in The Bahamas compare to those in other tropical, subtropical and temperate regions, and can this be reliably predicted from temperature and body size? Q3. How variable is the preservation (and dissolution) potential of the range of carbonate sedimentary phases produced by fish in different marine environments? Q4. How do overall rates and phases of carbonate produced in different environments vary as a function of local fish community structure and abundance? To address these questions we propose to collect data on the types and rates of carbonate sediment produced by fish across a latitudinal gradient (14o to 43oS) that spans tropical through to cool temperate marine environments (~30 to ~12oC), and to use this data: (i) to determine the dissolution/ preservation potential of fish-derived carbonate sediments (as a function of composition and morphology) across these environments; and (ii) to model, at regional and global scales, the volumes and phases of fish-derived sediment that are initially produced, and then either preserved or dissolved in different marine environments.