Simulation of distribution of carbon and nutrient in the ocean based on the global oceanic carbon cycle model MOM4_L40

Since the late twentieth century, global warming has become one of the increasingly serious ecological and environmental problems. While one of the important reasons for global warming is the greenhouse effects caused by the increases of atmospheric carbon dioxide (CO2) concentration. The ocean absorbing carbon dioxide plays a crucial role in the global carbon cycle. A global oceanic carbon cycle circulation model developed by National Climate Center of China Meteorological Administration is introduced and its performances are analyzed and evaluated. The oceanic carbon cycle model is developed on the basis of the global oceanic general circulation model Modular Ocean Model version 4 (MOM4) of Geophysical Fluid Dynamics Laboratory (GFDL) of the United States. It has 40 z-levels in the vertical direction and 3-dimension oceanic biogeochemistry processes, so it is named as MOM4_L40 for short. This model is integrated for 1000 years under climate force fields to simulate the natural distribution of temperature, salinity, carbon, and nutrient in the ocean. The simulations are analyzed and compared with observations so as to evaluate the basic capability of the model. From the modeling experiments and analyses, some major outcomes are obtained as followings: ( 1) Simulations of the vertical profiles of the global and regional mean temperature, salinity, carbon, and nutrients agree wellwith observations. (2) The model reproduces well the observational features of sea surface temperature, salinity, carbon, and nutrients. (3) The high values of observed and simulated CO2 partial pressure differences are mainly located in the vicinity of the equatorial Pacific, the tropical Atlantic Ocean, and Bering Strait. The low valuesare mainly located in the middle latitudes of Pacific, Atlantic, and Indian Ocean, especially in the North Pacific, North Atlantic, and South Atlantic. The surface CO2 partial pressure is the highest in the eastern equatorial Pacific Ocean, where is the strongest CO2 source in the global oceans; while it is relatively low in the South Indian, Atlantic, and Pacific Ocean at middle latitudes, where are major CO2 sinks in the global oceans. (4) The major absorption areas of dissolved inorganic carbon are located in the equatorial Indian Ocean, the Southwest Indian Ocean, the eastern and centralequatorial Pacific, the equatorial Atlantic, and the North Atlantic. Significant alkalinity sinks are located in the Southeast Atlantic and Southwest Indian Ocean (0 degrees E-60 degrees E, 40 degrees S-60 degrees S) and Southeast Pacific (170 degrees E-90 degrees W, 60 degrees S-70 degrees S). Significant phosphate sinks are located in the South IndianOcean (50 degrees E-100 degrees E, 40 S-60 degrees S). (5) The simulated vertical structures of oceanic temperature, salinity, carbon, and nutrient are similar to observations although there are differences. The distribution of simulated oceanic total carbon dioxide is in agreement with that of observation, such as low values on the sea surface and high values underlying in the vicinity of 10 degrees S-60 degrees N. However, comparing with observations, the values of simulated carbon dioxide are smaller in the ocean above 2000 m and larger below 2000 m. The concentrations of total CO2 and phosphate are low in the equator and high in the middle and high latitudes, which is contrary to the distribution of temperature. The distributions of alkalinity and salinity are similar, that is, the high concentrationsare located in the tropical areas of the Atlantic, South Indian, and South Pacific Ocean, as well as the Arabian Sea. The simulations of total alkalinity are generally consistent with observations in the Indian Ocean. The simulations of total alkalinity in the North Pacific and North Atlantic are better than the South Pacific and South Atlantic Ocean, respectively. Simulations of total carbon dioxide and phosphate are better in the North Atlantic than in the South Atlantic Ocean. The results show that MOM4_L40 model is a reliable tool for the simulation and research of oceanic carbon cycle. Because it has relatively highhorizontal and vertical resolutions as well as the sea ice model, this model can reasonably simulate the surface and vertical distribution of oceanic temperature, salinity, dissolved inorganic carbon, phosphate, and alkalinity. Due to the constraints of calculation condition, integration time, and model itself, there are some deviations between simulations and observations, which will be worked on continually in future.