GRGC: Modeling and Validating Cretaceous Climate and Ocean Circulation Based on New Boundary Conditions

GRGC：基于新边界条件的白垩纪气候和海洋环流建模与验证

• 批准号: 9405737
• 负责人: William Hay
• 金额: $ 21万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-09-15 至 1998-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9405737&HistoricalAwards=false
• 关键词: GRGC; Modeling; Validating; Cretaceous; Climate

19405737 Hay It has been common practice to run an atmospheric (AGCM) or oceanic (OGCM) general circulation model and search for results that might be confirmed or rejected by geologic data. AGCM output describes average conditions over large areas, but the non-marine geologic deposits providing the best record of climate were rarely laid down under average conditions. This mismatch between the model results and the geologic data that might be used for their validation has been a major problem in paleoclimate studies. A new AGCM, GENESIS, designed specifically for paleoclimate research, and a new method for validating the results of a paleoclimate model, the Proxy Formation Model (PFM), can be used together to make more realistic simulations that can be validated by comparison with real data. A validated AGCM can then be used to drive an OGCM to investigate circulation of the ocean. GENESIS began as a heavily modified version of CCM1 and differs from it in treatment of water vapor transport, atmospheric convection from the earth's surface, solar radiation related to aerosols, cloud parameterization, vegetation, soil, snow and sea ice. Its ocean is a slab, with heat capacity and ocean heat transport included. GENESIS has independent AGCM and surface grids, allowing for much better representation of surface paleogeographic, vegetation, and soil conditions. The PFM is a quantitative link between climate model data and geologic observations. PFM's are being developed for sedimentary deposits that form under known climatic conditions. 1) evaporites; 2) bauxites and laterites; 3) coal (peat). The PFM prescribes boundary conditions that must have existed at the location where the deposits occur. This additional "grid point" is inserted into the climate model, and the calculated environmental parameters (temperature, humidity, etc.) are compared with conditions required for formation of the deposit. Under this proposal, we will develop 4 additional PFM's : 1) sand deserts; 2) coastal sea ice; 3) mountain glaciers; 4) ice sheets. The climates of the Early and Late Cretaceous were different from each other and both were different from Late Cenozoic climates. In the Early Cretaceous there was high-latitude sea ice, strong mid- latitude seasonality, and a tendency for the "Atlantic" to become anoxic. In the Late Cretaceous there was no high-latitude ice, less seasonality, and a more oxic ocean (with two brief notable exceptions). The differences were a response to changing boundary conditions: 1) from isolation of the western Tethys-Atlantic-Indian seaway from the eastern Tethys-Panthalassic Ocean during the Early Cretaceous to more open connections in the Late Cretaceous: 2) rise in the atmospheric content of CO2 from a lower level in the Early Cretaceous to a high level in the Late Cretaceous: 3) increase in poleward ocean heat transport form a low level during the Early Cretaceous to a high level in the Late Cretaceous: and 4) rise of sea level to a mximum in the Late Cretaceous. The paleogeography, paleoclimatology energy balance of the Earth in the Cretaceous are well enough known to run AGCM's and subsequently OGCM's that can be rigorously validated using PFM's based on geologic data.

19405737 Hay通常的做法是运行大气（AGCM）或海洋（OGCM）环流模式，并寻找可能被地质数据证实或拒绝的结果。AGCM输出描述了大面积的平均条件，但提供最佳气候记录的非海洋地质矿床很少是在平均条件下建立的。模型结果与可能用于模型验证的地质数据之间的不匹配一直是古气候研究中的一个主要问题。专门为古气候研究设计的AGCM GENESIS和验证古气候模型结果的新方法代理地层模型（Proxy Formation model， PFM）可以一起使用，以进行更真实的模拟，并通过与实际数据的比较来验证。然后，一个经过验证的AGCM可以用来驱动OGCM来调查海洋环流。GENESIS最初是对CCM1进行了大量修改的版本，在处理水蒸气输送、地球表面的大气对流、与气溶胶有关的太阳辐射、云参数化、植被、土壤、雪和海冰方面与CCM1不同。它的海洋是一个平板，包括热容量和海洋热输送。GENESIS具有独立的AGCM和地表网格，可以更好地表示地表古地理、植被和土壤条件。PFM是气候模式数据和地质观测之间的定量联系。PFM正在开发用于在已知气候条件下形成的沉积物。1)蒸发岩;2)铝土矿和红土；3)煤（泥炭）。PFM规定的边界条件必须存在于沉积物发生的位置。这个额外的“网格点”被插入到气候模型中，计算出的环境参数（温度、湿度等）与沉积物形成所需的条件进行比较。根据这一建议，我们将开发4个额外的PFM: 1)沙漠；2)沿海海冰；3)山地冰川；4)冰盖。早白垩世和晚白垩世的气候不同，也不同于晚新生代的气候。早白垩纪有高纬度的海冰，中纬度的季节性很强，“大西洋”有缺氧的趋势。在晚白垩纪，没有高纬度的冰，季节性更少，海洋含氧量更高（有两个短暂的例外）。这些差异是对边界条件变化的响应：1)从早白垩世西部特提斯-大西洋-印度海道与东部特提斯-泛地中海海洋的隔离到晚白垩世更开放的连接；2)大气中CO2含量从早白垩世较低水平上升到晚白垩世较高水平；3)向极地海洋热输运由早白垩世的低水平增加到晚白垩世的高水平；4)海平面上升到晚白垩世的最大值。白垩纪地球的古地理、古气候学能量平衡已经足够了解，可以运行AGCM和随后的OGCM，并可以使用基于地质数据的PFM进行严格验证。