Temporal evolution of the deep-sea carbonate system and implications for the role of the oceans in glacial-interglacial changes in atmospheric CO2

大面积的洋底覆盖着主要由生物碳酸钙组成的沉积物，即钙质生物（有孔虫、颗石藻、翼足类）的遗骸，其外壳由碳酸钙矿物方解石或文石组成。在许多海洋区域的海洋沉积物中的CaCO 3含量随着冰川-间冰期循环的气候变化而变化：较低的CaCO 3含量与大陆冰盖的形成相一致。深海中“CaCO 3沉积物”的存在对于缓和大气CO2变化的极限至关重要。这是因为深海中碳酸盐离子的浓度与大气中CO2的浓度呈反比关系。碳酸根离子浓度[CO 32-]是控制CaCO 3溶解度的主要因素。由于这种反向关系，古海洋学家多年来一直在努力寻找深海[CO 32-]的替代物。深海CaCO 3含量的记录提供了海洋化学如何随气候变化的重要证据，但证据是间接的，因为CaCO 3记录代表了对海洋沃茨或孔隙沃茨碳酸盐化学变化的响应。其他使用的方法也是间接的，依赖于钙质生物体外壳的溶解。利用底栖（深海）有孔虫方解石中硼（B）的掺入，我们开发了一种新的方法来估算过去海洋中的深海[CO 32-]。底栖生物B/Ca使我们能够确定海洋沃茨的[CO 32-]，从而确定水柱“饱和层”的深度，根据CaCO 3的溶解度，在该深度以上水是过饱和的，而在该深度以下是欠饱和的。我们的目标是在海洋的关键区域生成深海[CO 32-]的记录，这将大大有助于了解海洋在大气CO2循环中的作用。

Large areas of the floor of the oceans are draped with sediment chiefly composed of biogenic calcium carbonate, the remains of calcareous organisms (foraminifera, coccolithophores, pteropods) whose shells are composed of the CaCO3 minerals calcite or aragonite. The CaCO3 contents of marine sediments in many oceanic regions have varied with climate over glacial-interglacial cycles: lower contents of CaCO3 coinciding with the build-up of continental ice sheets. The existence of 'CaCO3 sediments' in the deep ocean has been crucial for moderating the limits of variation in atmospheric CO2. This is because there is an inverse relationship between the concentration of carbonate ion in the deep ocean and the concentration of atmospheric CO2. Carbonate ion concentration, [CO32-], is a major factor controlling the solubility of CaCO3. Because of this inverse relationship, palaeoceanographers have strove for many years to find a proxy for deep sea [CO32-]. The records of deep-ocean CaCO3 content provide important evidence of how ocean chemistry changed with climate but the evidence is indirect because the CaCO3 records represent a response to changes in the carbonate chemistry of ocean waters or of pore waters. Other methods in use are also indirect and rely on the dissolution of the shells of the calcareous organisms. We have developed a new method to estimate deep sea [CO32-] in past oceans using the incorporation of boron (B) in benthic (deep sea) foraminiferal calcite. Benthic B/Ca allows us to define [CO32-] of ocean waters and thus the depth of the water column 'saturation horizon' above which water is oversaturated, and below which is undersaturated, with respect to CaCO3 solubility. We aim to generate records of deep-ocean [CO32-] in critical regions of the oceans that should add significantly to understanding the role of the oceans in atmospheric CO2 cycles.