Deep ocean oxygen concentrations and efficiency of the biological pump

氧气是我们大气的主要成分(20%)，由植物光合作用产生。光合作用利用二氧化碳、水和来自阳光的能量来制造有机碳。呼吸作用和有机碳的衰变消耗氧气。海水中的溶氧量远小于大气中的氧量，并与有机碳的温控溶解度和呼吸作用有关。海洋中的溶解氧分布并不均匀。在深水(深度超过1.5公里)，通过呼吸作用使有机碳重新矿化，导致北大西洋(形成深水的地方)前往太平洋途中的溶解氧浓度下降。海水温度升高、表层水中产生的有机碳的沉降量增加以及这种有机碳的呼吸作用以及深海形成的减少都是导致深海溶解氧浓度降低的机制。最近的几项研究表明，由于全球变暖，到公元3000年，全球海水溶解氧浓度将下降30%。因此，了解溶解氧浓度的自然变化对于推进未来的预测至关重要，也是一个重要的研究问题。在冰河时期(冰川时期)，越来越多的证据表明，海洋吸收了我们大气中温暖气候(间冰期)时(自然)存在的大约30%的二氧化碳。这种碳固存是由多种生物(呼吸作用)、物理(温度、海洋环流)和化学(通过保存和溶解碳酸钙微体化石进行碳酸盐缓冲)机制造成的。每一种机制的贡献都没有得到很好的量化，我们也不完全知道大气中的碳储存在海洋的什么地方。通过光合作用和水柱深处的呼吸作用产生的有机物质将在一段时间内将二氧化碳从大气中分离出来。有机材料生产和出口的增加以及深层再矿化(例如更强大的生物泵)是被提议作为二氧化碳封存机制的一种机制。由于氧的溶解度主要受温度控制，我们可以通过从测量的溶解氧浓度中减去初始饱和溶解氧浓度来计算水团的总耗氧量(通过有机物的再矿化)。由此，我们可以计算出该水团中被隔离的碳的数量。我开发了一种新技术，利用从深海沉积物样品中获得的底栖生物(微化石)来测量深海和中层海洋的氧浓度。对于这项研究，我建议生成深海和中层海洋氧浓度的历史(冰期-间冰期)记录，并测试大气二氧化碳的变化是否与生物固碳直接相关。然后，我将使用地球系统模型来检验几个假设，即为什么冰川海洋中有更多生物隔离的碳。

Oxygen forms a major component of our atmosphere (20%) and is produced by plant photosynthesis. Photosynthesis uses carbon dioxide, water and energy from sunlight to make organic carbon. Respiration and the decay of organic carbon consumes oxygen. The amount of dissolved oxygen in seawater is much smaller than the amount of oxygen in the atmosphere, and is related to temperature-controlled solubility and respiration of organic carbon. The distribution of dissolved oxygen in the oceans is not uniform. In deep waters (deeper than 1.5 km) the remineralization of organic carbon through respiration causes a decrease in dissolved oxygen concentrations from the North Atlantic Ocean (where deep waters are formed) en route to the Pacific Ocean. Warmer seawater temperatures, increased sinking of organic carbon produced in surface waters and respiration of this organic carbon, as well as a reduction in deep water formation, are all mechanisms that lead to a reduction in deep ocean dissolved oxygen concentrations. Several recent studies have suggested that global seawater dissolved oxygen concentrations will decline by 30% by the year 3000 as a result of global warming. Knowledge of natural variations of dissolved oxygen concentrations is therefore crucial to advance future predictions and an important research question. During ice ages (glacial times) there is mounting evidence that the oceans sequestered about 30% of the carbon dioxide that is (naturally) present during warm climates (interglacials) in our atmosphere. This carbon sequestration was caused by a variety of biological (respiration), physical (temperature, ocean circulation) and chemical (carbonate buffering through preservation and dissolution of calcium carbonate microfossils) mechanisms. The contribution of each of these mechanisms is poorly quantified, and we do not fully know where in the oceans the atmospheric carbon was stored. Production of organic material by photosynthesis, and respiration deeper down the water column will isolate carbon dioxide from the atmosphere for some time. An increase in organic material production and export and remineralization at depth (e.g. stronger biological pump) is one mechanism that is proposed to have acted as a carbon dioxide sequestration mechanism. As oxygen solubility is mainly temperature controlled, we can calculate the amount of total consumed oxygen (through remineralization of organic material) of a water mass by subtracting the initial saturated dissolved oxygen concentration from the measured dissolved oxygen concentration. From this we can then calculate the amount of sequestered carbon in that water mass. I have developed a novel technique to measure deep and intermediate ocean oxygen concentrations using benthic organisms (microfossils) obtained from deep sea sediment samples. For this fellowship I propose to generate historical (glacial-interglacial) records of deep and intermediate ocean oxygen concentration and test whether changes in atmospheric carbon dioxide are directly related to biological carbon sequestration. I am then going to use earth system models to test several hypothesis of why there was more biologically sequestered carbon in the glacial ocean.