Models of the Ocean Carbonate cycle and the Glacial-Interglacial CO2 Variations

冰川-间冰期CO2变化的机制是地球科学中尚未解决的主要问题之一。冰芯测量表明，在寒冷的冰川期，二氧化碳水平约为每分钟190分，但在温暖的间冰期达到280 p. p.m.虽然已经假设了许多机制，但仍然不清楚为什么会发生这些大的CO2变化，以及在冰川时期多余的CO2储存在哪里。虽然人们普遍认为海洋碳酸盐循环是（大约）在稳定状态下，在冰期和间冰期，我们建议探索碳酸盐循环自主动力学行为的可能性和潜在影响。马萨诸塞州理工学院的一组研究人员假设存在一个“地球化学振荡器”，作为冰期-间冰期二氧化碳变化的贡献者，在这个项目中，他们将检验这个假设。 他们初步的、高度理想化的模型揭示了海洋碳酸盐循环内部振荡的可能性，它有几个有趣的特征：（i）它造成全球海洋碱度的振荡（因此大气中的二氧化碳）与冰芯记录中观察到的特征性波浪形，（ii）振荡是由于钙化和非钙化初级生产者之间的生态相互作用，振荡的周期取决于所选择的参数，但在一个范围内与观察到的冰川间冰期的变化，和（iv）模型预测？刺钉？在冰川-间冰期过渡期钙化生产力增强，与沉积记录一致。因此，该团队将研究这些机制的潜在作用，采用复杂性截然不同的模型层次，从一组两个常微分方程开始，逐步发展到一个完整的大气环流模型，其中包含明确和详细的地球化学成分，包括明确的生态模型。使用这种分层方法的优点是，理想化的模型可以帮助深入了解背后的机制和更现实的复杂耦合模拟的结果的鲁棒性。他们将根据冰芯测量的二氧化碳、（碳酸盐）沉积物积累的冰川-间冰期变化观测以及海洋碳同位素分布观测来测试模型结果。更广泛的影响：这项工作显然与理解历史气候变化有关，但在考虑地球系统将如何应对温室气体排放的二氧化碳方面也应该具有重要意义。该项目具有高度的多学科性，将地球化学和海洋环流模型方面的专门知识与先进的数学分析和地质观测数据结合起来。

The mechanisms underlying the glacial-interglacial CO2 variations constitute one of the major unsolved problems in the Earth Sciences. Ice-core measurements have shown that during cold glacial periods, CO2 levels are around 190 p.p.m., but reach 280 p.p.m. during warm interglacials. Though many mechanisms have been hypothesized, it still remains unclear why these large CO2 variations occur, and where the excess CO2 is stored during glacial periods. While it has generally been assumed that the ocean carbonate cycle is (approximately) at steady state, both during glacial and interglacial periods we propose to explore the possibility, and potential impact, of autonomous dynamical behavior of the carbonate cycle.A team of researchers at the Massachusetts Institute of Technology hypothesize the existence of a "biogeochemical oscillator" as a contributor to the glacial-interglacial CO2 variations, and in this project they will test that hypothesis. Their preliminary, highly-idealized model reveals the possibility of an internal oscillation of the ocean carbonate cycle which has several interesting features: (i) it produces oscillations in global ocean alkalinity (and thus atmospheric carbon dioxide) with the characteristic sawtooth shape observed in the ice-core record, (ii) the oscillations are due to ecological interactions between calcifying and noncalcifying primary producers, (iii) the period of the oscillations depends upon the chosen parameters but is in a range consistent with the observed glacial-interglacial variations, and (iv) the model predicts ?spikes? of enhanced calcifier productivity at the glacial-interglacial transitions, consistent with sedimentary records. Thus, the team will investigate the potential role of these mechanisms, employing a hierarchy of models of vastly different complexities, starting from a set of two ordinary differential equations and working up to a full general circulation model with explicit and detailed biogeochemical components including an explicit ecological model. The advantage of using such a hierarchical approach is that the idealized models can help to gain insight into the mechanisms behind and the robustness of the results from more realistic complex coupled simulations. They will test the model results against ice-core measurements of CO2, observations of glacial-interglacial variations in (carbonate) sediment accumulation, and observations of carbon isotope distributions in the oceans. Broader Impact : This work is obviously relevant for understanding historical climatic change, but should also be of significance in considering how the Earth system will respond to anthropogenically emitted CO2. The project is highly multidisciplinary, bringing together expertise in biogeochemical and ocean circulation models with advanced mathematical analysis and data from geological observations.