Ion partitioning and the geochemistry of coral skeletons: solving the mystery of the vital effect
Ion partitioning and the geochemistry of coral skeletons: solving the mystery of the vital effect
复制标题
离子分配和珊瑚骨骼的地球化学：解开生命效应之谜
DOI：
10.1180/emu-notes.10.11
复制
发表时间：
2010
期刊：
影响因子：
3.7
通讯作者：
G. Gaetani
中科院分区：
文献类型：
--
作者：
L. Anne;G. Gaetani
我们对地球气候历史的大部分理解是基于对CaCO3测试和海洋生物骨架中地球化学变化的解释。地球化学气候指标通常是根据平衡热力学来预测的，但生物吸积的碳酸盐组成与与海水平衡的碳酸盐矿物预测之间存在重要差异。这些差异通常归因于“生命效应”，被认为是由钙化环境和晶体生长动力学的生物修饰引起的。如果这是真的，那么生物修饰的晶体化学可能是不可预测的或具有挑战性的数学模型，使得很难以任何程度的信心从生物碳酸盐中提取准确的气候信息。我们这篇论文的目标是以珊瑚骨骼为例，展示一种系统的方法来识别、表征和理解“重要效应”。通过在受控条件下从海水中实验沉淀的非生物文石，我们表明，珊瑚骨骼地球化学中许多所谓的“重要效应”实际上是非生物文石的特征，可以用可预测的物理化学过程进行数学描述。通过比较非生物文石与珊瑚文石的元素比（Mg/Ca、Sr/Ca、Ba/Ca），发现瑞利分选和晶体生长速率对珊瑚的元素化学性质起主导作用，温度的影响相对较小。在这些见解的基础上，我们开发了一种从珊瑚骨骼中提取温度信息的新方法，这种方法与传统的古测温法有着根本的不同，通过同时使用多种元素比例来绕过“重要影响”，以可靠地提取仅由温度驱动的骨骼变化的小组成部分。
Much of our understanding of Earth’s climate history is based on interpretation of geochemical variability within the CaCO3 tests and skeletons of marine organisms. Geochemical climate proxies are typically cast in terms of equilibrium thermodynamics, but there are important differences between the compositions of carbonates accreted by living organisms and predictions for carbonate minerals in equilibrium with seawater. These differences are commonly attributed to ‘vital effects’ thought to be caused by biological modification of the calcifying environment and of crystalgrowth kinetics. If this were true, then biologically modified crystal chemistry may be unpredictable or challenging to model mathematically, making it difficult to extract accurate climate information from biogenic carbonates with any degree of confidence. Our goal with this paper is to demonstrate a systematic approach to the identification, characterization and understanding of ‘vital effects’ using coral skeletons as an example. We show, through insights gained from abiogenic aragonites precipitated experimentally from seawater under controlled conditions, that many of the so-called ‘vital effects’ in coral skeletal geochemistry are actually characteristic of abiogenic aragonites and can be described mathematically in terms of predictable physicochemical processes. By comparing elemental ratios (Mg/Ca, Sr/Ca, Ba/Ca) of abiogenic aragonite with that of coral aragonite, we show that Rayleigh fractionation and crystal-growth rate exert the dominant controls on the elemental chemistry of corals, and that the contribution of temperature is relatively small. Building on these insights, we have developed a new approach to extracting temperature information from coral skeletons that is fundamentally different from conventional palaeo-thermometry, by-passing ‘vital effects’ through the simultaneous use of multiple element ratios to reliably extract that small component of skeletal variability that is driven solely by temperature.