The timing and nature of inorganic calcium carbonate precipitation within exposed basalt from the South Pacific Gyre, IODP Expedition 329.

南太平洋环流暴露的玄武岩中无机碳酸钙沉淀的时间和性质，IODP 第 329 次探险。

• 批准号: NE/L000024/1
• 负责人: Damon Teagle
• 金额: $ 4.51万
• 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: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FL000024%2F1
• 关键词: timing; nature; inorganic; calcium; carbonate

IODP Expedition 329 sailed a transect of over 11,000 km of ocean over a period of 66 days from Papeete, Tahiti to Auckland, New Zealand to recover sediment and basalt drillcores from within the South Pacific Gyre (SPG), the world's largest ocean current system. and one of the most poorly explored regions of Earth. Indeed the last scientific expedition which recovered samples from the seafloor within the SPG was over 130 years ago during the HMS Challenger Expedition (1872-1876). During IODP Expedition 329 we made great strides in addressing what, if any, microbial life occurs beneath the sea floor within the gyre and in what conditions (habitats) life occurs. We also explored the role the oceans, seafloor sediment, and underlying ocean crust plays in controlling habitats beneath the seafloor across a transect of the SPG.At three sites we took samples of the volcanic basement rocks beneath the sediment. The volcanic rocks, initially formed from eruptions of sub-sea volcanoes along mid ocean ridges (mid ocean ridge basalt) have since cooled and spread from the mid ocean ridge over millions of years to their present location.Chemical interaction with seawater that enters the ocean crust through fractures and joints (caused by post eruption cooling and tectonic movement) results in the formation of secondary minerals that fill fracture space and sometimes replaces the original volcanic rock. This 'seafloor weathering' process results in chemical transfer between seawater and volcanic rocks, altering the composition of ingressing seawater and the volcanic crust. Our research, based on the low temperature (<100 deg C) secondary mineral calcium carbonate will address some of the uncertainties associated with this process and in turn will answer some important questions regarding basement habitability and global geochemical cycles.The element Strontium (Sr), which is present in calcium carbonate, is extremely useful since its isotopic composition in seawater varies through time and this record is well known. We will use the Sr-isotopic composition in calcium carbonate to estimate how much seawater has mixed with mid ocean ridge basalt, which has a very different but well defined isotopic ratio. In addition, we will use Sr isotopes to partially constrain the timing of calcium carbonate formation. Since isotopes of Uranium (U) decay radioactively into stable isotopic 'daughters' of Lead (Pb) at a known rate, it is possible, given the right geological conditions and appropriate methods, to date the formation of mineral phases. U and Pb incorporated into calcium carbonate will provide insights into the timing of seafloor weathering processes in oceanic crust. We will utilize measurements of U and Pb isotopes to date calcium carbonate formation within the South Pacific Gyre.Temperature is known to control the preference of Oxygen (O) isotopes uptake during calcium carbonate formation. We will therefore use O-isotopes in carbonates to determine the temperature of formation to determine the thermal environment of formation. Knowledge of temperature will allows us to place limits on the extent of the sub seafloor biosphere. Impurities of Magnesium (Mg) and Sr that variably replace (substitute) for calcium (Ca) in the crystal structure of calcite can be measured to infer past Mg/Ca and Sr/Ca ratios of ancient seawater for upto 120 Myrs of geological time. These ratios act as proxies for ancient seawater chemistry, which in turn provide insights into geochemical processes that take place between the Earth's crust, the oceans, and the atmosphere. Our research will offer tantalizing clues into the potential habitat for microbial life within oceanic crust, offer insights into the timing of seafloor weathering processes within the SPG.

IODP 329 号探险队在 66 天的时间里从塔希提岛帕皮提到新西兰奥克兰，航行了超过 11,000 公里的海洋横断面，从世界上最大的洋流系统南太平洋环流 (SPG) 内回收沉积物和玄武岩钻芯。以及地球上探索最差的地区之一。事实上，最后一次从 SPG 海底回收样本的科学考察是在 130 多年前的英国皇家海军挑战者号远征期间（1872-1876 年）。在 IODP 第 329 次探险期间，我们在解决海底环流内的微生物生命（如果有的话）以及生命发生的条件（栖息地）方面取得了重大进展。我们还探索了海洋、海底沉积物和底层洋壳在控制 SPG 横断面海底栖息地方面所起的作用。在三个地点，我们采集了沉积物下方的火山基底岩石样本。这些火山岩最初是由沿着大洋中脊（大洋中脊玄武岩）的海底火山喷发形成的，经过数百万年的冷却并从大洋中脊扩散到目前的位置。与进入海洋的海水发生化学相互作用地壳通过裂缝和节理（由喷发后冷却和构造运动引起）导致形成次生矿物，填充裂缝空间，有时甚至取代原始火山岩。这种“海底风化”过程导致海水和火山岩之间的化学转移，改变了侵入海水和火山地壳的成分。我们基于低温（<100 摄氏度）次生矿物碳酸钙的研究将解决与该过程相关的一些不确定性，进而回答有关基底宜居性和全球地球化学循环的一些重要问题。元素锶 (Sr)碳酸钙中存在的同位素非常有用，因为它在海水中的同位素组成随时间而变化，并且这一记录是众所周知的。我们将使用碳酸钙中的锶同位素组成来估计有多少海水与大洋中脊玄武岩混合，其中玄武岩具有非常不同但明确的同位素比率。此外，我们将使用锶同位素来部分限制碳酸钙形成的时间。由于铀 (U) 同位素以已知速率放射性衰变成铅 (Pb) 的稳定同位素“子体”，因此，只要有正确的地质条件和适当的方法，就有可能确定矿物相的形成日期。碳酸钙中的 U 和 Pb 将为了解洋壳海底风化过程的时间提供见解。我们将利用 U 和 Pb 同位素的测量来确定南太平洋环流内碳酸钙形成的日期。众所周知，温度可以控制碳酸钙形成过程中氧 (O) 同位素吸收的偏好。因此，我们将使用碳酸盐中的O-同位素来确定地层温度，从而确定地层的热环境。了解温度将使我们能够限制海底生物圈的范围。通过测量方解石晶体结构中不同地取代（替代）钙 (Ca) 的镁 (Mg) 和 Sr 杂质，可以推断出长达 120 Myr 地质时期古代海水的 Mg/Ca 和 Sr/Ca 比率。这些比率充当古代海水化学的代表，反过来又提供了对地壳、海洋和大气之间发生的地球化学过程的见解。我们的研究将为海洋地壳内微生物生命的潜在栖息地提供诱人的线索，并为 SPG 内海底风化过程的时间提供见解。

项目成果

Presence of oxygen and aerobic communities from sea floor to basement in deep-sea sediments

• DOI: 10.1038/ngeo2387
• 发表时间: 2015-04-01
• 期刊: NATURE GEOSCIENCE
• 影响因子: 18.3
• 作者: D'Hondt, Steven;Inagaki, Fumio;Ziebis, Wiebke
• 通讯作者: Ziebis, Wiebke

Seafloor basalt alteration and chemical change in the ultra thinly sedimented South Pacific

南太平洋超薄沉积海底玄武岩蚀变和化学变化

• DOI: 10.1002/2013gc005141
• 发表时间: 2014-07
• 期刊: Geochemistry Geophysics Geosystems
• 影响因子: 3.5
• 作者: Guo-Liang Zhang;Christopher, Smith_Duque
• 通讯作者: Christopher, Smith_Duque