Investigating how shallow water carbonate systems record the carbon cycle

地球上生命的历史和未来与生物圈、海洋、大气和岩石圈数十亿年来的共同进化错综复杂地联系在一起。古代沉积物是这些系统的碎片化记录，对我们星球发展过程中关键时刻的详细重建为我们提供了一个关于生命在我们宇宙中的稀有和作用的批判性视角。拟议研究方案的长期目标是从地球历史的碳酸盐沉积记录中记录过去的环境和地球系统变化，特别关注气候和生命的共同进化。地球的碳酸盐沉积记录为研究古代地球的浅海提供了一个窗口。这些沉积岩被层叠在一起，为重建过去提供了相对的年代学。半个多世纪以来，地球科学家一直在记录分散在地球历史上的古代碳酸盐的碳同位素组成。这些记录构成了我们对地球上大气中氧气和二氧化碳演化的最佳猜测的基础。然而，这些猜测通常假设浅海碳酸盐岩完美地记录了古代全球海洋的平均碳同位素组成。现代数据集表明，今天浅海碳酸盐岩的碳同位素组成可能与全球海洋显著不同，我们并不完全了解驱动这些变化的机制。为了约束沿海水域碳酸盐同位素组成的控制机制，我们将从碳酸盐沉积物活跃堆积的地点收集一套水质测量和沉积化学数据。选择这些地点是为了最大限度地发挥沿海碳循环过程的潜在信号。此外，选定的地点紧邻最近过去类似沉积矿床的岩石露头。当沉积物变成岩石(岩化)时，岩石的同位素化学可能与原始沉积物不同。为了评估这种岩化过程的影响，我们计划绘制岩化沉积物的碳同位素变异性图，并将这些变化与类似的现代沉积物和沿海海水的观测结果进行比较。为了了解浅海系统如何记录远洋碳化学的变化，我们还计划从远洋碳同位素变化独立于海洋岩心的时间间隔调查更古老的浅海碳酸盐岩。对开阔海域同位素组成的变化进行了充分的研究，为在同时代浅层碳酸盐系统中如何以及在哪里记录这些同位素变化提供了具体的目标。由于大多数地质记录缺乏关于海洋化学变化的深层海洋记录，从这项工作中获得的见解可以广泛应用于解释地球历史上巨大的浅层碳酸盐记录。

The history and future of life on Earth is intricately tied to the coevolution of the biosphere, oceans, atmosphere, and lithosphere over billions of years. Ancient sediments are the fragmented record of these systems, and detailed reconstructions of key moments in the development of our planet offer a critical perspective on the rarity and role of life in our universe. The long term goal of the proposed research program is to document past environmental and Earth systems change from the carbonate sedimentary record of Earth history, with particular focus on the coevolution of climate and life. The carbonate sedimentary record of Earth offers a window to investigate the shallow seas of the ancient Earth. These sedimentary rocks are stacked in layers that provide a relative chronology for reconstructing the past. For more than half a century, Earth scientists have been documenting the carbon isotopic composition of ancient carbonates from intervals of time scattered throughout Earth history. These records form the backbone of our best guesses about the evolution of atmospheric oxygen and carbon-dioxide on Earth. However, these guesses generally assume that shallow-marine carbonates perfectly record the average carbon isotopic composition of ancient global ocean. Modern datasets demonstrate that shallow-marine carbonates today can have carbon isotopic composition significantly different than the global ocean, and we do not fully understand the mechanisms driving these variations. To constrain the mechanisms controlling the isotopic composition of carbonates in coastal waters, we will collect a suite of water property measurements and sedimentary chemistry from sites where carbonate sediment is actively accumulating. The sites have been selected to maximize the potential signal of coastal carbon cycling processes. Moreover, the selected sites are immediately adjacent to rocky outcrops of analogous sedimentary deposits from the recent past. When sediments turn into rock (lithify), the isotopic chemistry of the rocks can differ from the original sediment. To assess the impact of this lithification process we plan to map the carbon isotopic variability of the lithified deposits and compare those variations to the observations of the analogous modern sediments and coastal sea-water. To understand how changes in open-marine carbon chemistry are recorded by shallow systems, we also plan to investigate much older shallow-carbonate rocks from a time interval where open-marine carbon isotopic changes are independently known from marine cores. Well studied shifts in open-marine isotopic composition offer opportunity to specifically target how and where these isotopic changes are recorded in the coeval shallow carbonate system. Because most of the geologic record lacks deep marine records of changes in ocean chemistry, insights gained from this work can be widely applied to interpreting the vast shallow carbonate record of Earth history.