摘要:
How the Central American Seaway alters large-scale ocean circulation, climate and marine biogeochemistry The study of past climates using climate models and paleoclimate proxy records is helpful for understanding how the Earth system responds to external natural forcing on time scales longer than the current instrumental records. The Central American Seaway (CAS) was an important ocean gateway connecting the Pacific and Atlantic Oceans until its gradual shoaling and final closure near the end of the Pliocene (5.3-2.6 Ma), when paleoclimate proxy records indicate a major reorganization in large-scale ocean circulation and shifting spatial patterns in global climate and marine biogeochemistry. Climate models are not consistent in reconciling the impact of the seaway on global deep-water circulation, tropical Pacific and Southern Hemisphere physical mean state, and interannual tropical Pacific climate variability, and have not been able to explore the coupled impacts on ocean biogeochemistry or sediment calcium carbonate (CaCO3) long-term burial. For the first time, as far as this author knows, a suite of four idealized experiments, including a very narrow (109 km-wide) single meridional grid point channel, are performed for multi-millennial scale simulations using the Geophysical Fluid Dynamics Laboratory Earth System Model, GFDL-ESM2G, with high ocean spatial resolution to explore the mechanistic role of changing topography – varying only seaway widths and sill depths – associated with the various stages of seaway constriction and shoaling on global ocean circulation, climate and marine biogeochemistry compared to "preindustrial" 1860 climate. Model output is combined with an uncoupled box model to obtain the first sediment CaCO3 (as calcite) long-term burial estimates and atmosphere pCO2 concentrations associated with a very narrow seaway for comparison with proxy records. Independent of the CAS configuration in GFDL-ESM2G, the open CAS alters ocean physical mean st