Testing the amplitude and rapidity of carbonate saturation change and global climate during the high pCO2 Oligocene 'cold house'

拟议研究的总体目标是确定渐新世期间海洋酸化变化的速度和幅度，利用海洋钻探计划最近在赤道太平洋建立的两个高分辨率单点记录，以检验最近提出的关于这些波动起源的模型假设。目前正在进行大量的努力来调查大气pCO $_2$的现代变化，并破译它们对全球和局部温度、海平面和水文循环的影响。然而，pCO $_2$的变化也通过海洋ph值的变化深刻地影响地球系统。事实上，正如英国皇家学会的一个工作组最近（2005年）所确定的那样，海洋酸化的影响是气候变化效应的附加影响，并可能加剧气候变化的影响。地质记录提供了回答与酸化过程的量化有关的一些关键问题的手段，以及可能需要采取哪些缓解措施，特别是：化石燃料（或添加的碳酸）中和的速度有多快？CaCO $_3$缓冲作用对海洋碳酸盐离子饱和度（以及大气pCO $_2$）的影响是什么？连接全球碳循环、大气pCO $_2$、温度、溶解海洋[CO $_3^{2-}$]和pH值的大量反馈成分需要受到当前测量数据以及地质档案数据的限制，以便推进对未来变化的时间和幅度的预测。以前对CCD和溶斜体变化的重建主要遵循两个攻角：利用硼同位素及其对海水pH值的敏感性的地球化学方法，或沉积学代理方法，绘制沉积物中碳酸钙的出现和缺失。后一种方法通常提供低分辨率但较大的区域视角。事实上，pi最近的研究已经对溶斜层和渐新世“冷库”之间的耦合产生了第一个限制，在此期间，CCD迅速而广泛地同时加深了$>$ 1公里，并且底栖动物氧同位素值向更大的值移动了超过1 permille。在这里，我们建议以一种新颖的方式，利用一个理想的“自然实验室”环境来重建渐新世期间海洋溶斜的变化，以及这些变化对古气候代用物（氧同位素）的影响，这些变化是由赤道太平洋1218和1219钻探点提供的。这两个地点都记录了渐新世的高分辨率气候代用记录，但在古深度上有大约300到500米的垂直偏移。目前的假设预测，这种垂直偏移应该导致碳酸盐溶解的差异，影响CaCO $_3$通量，以及散装和底栖有孔虫方解石中d13C和d18O的稳定同位素测量。来自这些地点的数据将提供第一次机会，在更高的pCO $_2$“冷库”条件下，在冰期-间冰期（kyr）时间尺度\citep{Palike2006}上测试最近模拟的短期海洋[CO $_3^{2-}$]（以及溶解石）变化，从而为未来海洋酸化状态的变化可能带来的影响提供更现实的方法。在什么时间尺度上，尽管海底碳酸盐溶解有缓冲作用，自然变化还是发生了。

The overarching objective of the proposed research is to establish the rapidity and amplitude of variations in ocean acidification during the Oligocene, exploiting the two high-resolution, single site records that have recently been established in the equatorial Pacific by the Ocean Drilling Program, with a view to test recently proposed model hypotheses as to the origin of these fluctuations . Numerous efforts are currently underway to investigate modern changes in atmospheric pCO$_2$, and to decipher their impact on global and local temperature, sea-level, and the hydrological cycle. Yet, pCO$_2$ changes also profoundly affect the Earth System through changes of ocean pH. Indeed, the impacts of ocean acidification are additional to, and may exacerbate, the effects of climate change, as recently established by a working group of the Royal Society (2005). Geological records provide the means to answer some of the key questions that relate to the quantification of the acidification process, and what measures of mitigation might be necessary, in particular: How fast is fossil fuel (or added carbonic acid) neutralised? What is the effect of CaCO$_3$ buffering on oceanic carbonate ion saturation (and in turn atmospheric pCO$_2$)? The large number of feedback components that connect the global carbon cycle, atmospheric pCO$_2$, temperature, dissolved oceanic [CO$_3^{2-}$] and pH need to be constrained by present-day measurements as well as data from the geological archive in order to advance the prediction of timing and amplitude of future changes. Previous reconstructions of CCD and lysocline variations have principally been following two angles of attack: a geochemical approach using boron isotopes and their sensitivity with respect to ocean water pH, or a sedimentological proxy approach, mapping the occurrence and absence of calcium carbonate in sediments. The latter approach generally provides a low-resolution but large regional perspective. Indeed, recent research by the PIs has resulted in the first constraints on a coupling between the lysocline and the onset of the Oligocene ``cold-house'' during a rapid and extensive simultaneous deepening of the CCD of $>$1 km, and a shift in benthic oxygen isotope values towards greater values by more than 1 permille. Here we propose to exploit, in a novel way, an ideal ``natural laboratory'' setting to reconstruct variations in the oceanic lysocline and the effect of these variations on a palaeoclimate proxy (oxygen isotopes) during the Oligocene, as provided by drill sites 1218 and 1219 in the Equatorial Pacific. Both sites record high-resolution climate proxy records for the Oligocene, but with a vertical offset in palaeodepth of about 300 to 500 metres. Current hypotheses predict that this vertical offset should result in a difference in carbonate dissolution affecting both CaCO$_3$ flux, and stable isotope measurements of d13C and d18O in bulk and benthic foraminiferal calcite. Data from these sites will provide the first opportunity to test recently modeled short-term oceanic [CO$_3^{2-}$] (and thus lysocline) variations on glacial-interglacial (kyr) time scales \citep{Palike2006}, within a setting of higher pCO$_2$ ``cold-house'' conditions, and thus provide a more realistic approach as to what future changes in ocean acidification state might entail, and on what time scales natural variability occurs despite the buffering effect of carbonate dissolution at the sea-floor.