Direct Determination of the pH Distribution in the Glacial Oceans Based on the Boron Isotope Composition of Foraminifera

为解释冰芯中记录的80 ppm的冰期与间冰期大气CO2含量差异而设计的情景可分为两类，一类涉及海洋生物泵，另一类涉及海洋CaCO3循环。前一组最受关注；但对有孔虫的镉浓度和碳同位素测量似乎不利于他们。从某种程度上说，后一组观点被立即否定了，因为深海沉积物的溶解记录似乎表明，要实现观测到的大气二氧化碳变化，CO32含量的变化并不大。最近，Archer和Maier-Reimer找到了一种绕过解散记录限制的方法。他们表明，由于呼吸作用的影响，二氧化碳被释放到沉积物的上层厘米处，因此溶斜深度的稳定状态可能会发生相当大的变化。本研究将采用硼同位素方法来确定Archer和Maier-Reimer情景是否可行。对冰期和全新世配对有孔虫（底栖和浮游）的初步测量表明，正如Archer和Maier-Reimer情景所要求的那样，海洋的pH值在冰期高出0.2至0.3个单位。这项研究的主旨是以最高的精度进行更多的此类测量，并探索用于海洋CaCO3的硼同位素pH方法所基于的众多假设的有效性。

9402263 BROECKER Scenarios designed to explain the 80 ppm glacial to interglacial difference in atmospheric CO2 content recorded in ice cores can be placed into tow categories, those involving the ocean's biologic pump and those involving the ocean's CaCO3 cycle. The former group received most attention; but cadmium concentration and carbon isotope measurements on foraminifera appear to rule against them. The latter group have, to some extent, been rejected out of hand because the dissolution record for deep sea sediments appears to dictate against the rather large CO32 content changes required to accomplish the observed atmospheric CO2 change. Recently Archer and Maier-Reimer have found a way around the dissolution record constraint. They show that because of the influence of respiration CO2 released to the upper centimeter of sediment it is possible to have a rather large change in the steady state lysocline depth. This study will employ the boron isotope method to determine whether the Archer and Maier-Reimer scenario is feasible. Preliminary measurements on paired glacial and holocene foraminifera (both benthic and planktonic) suggest that the ocean's pH was, as required by the Archer and Maier-Reimer scenario, 0.2 to 0.3 units higher during glacial time. The thrust of this research is to make more such measurements with the highest attainable accuracy and also to explore the validity of the numerous assumptions on which the boron isotope pH method as applied to marine CaCO3 is based.