Distribution and Modeling of Chlorofluorocarbons in the Northwestern Pacific Ocean
Because CFC-11 and CFC-12 are extremely stable and purely anthropogenic and the CFCs enter the ocean through air-sea exchange at the sea surface, they serve as good tracers for studying the oceans. Since CFCs and tritium share similar characteristics such as their anthropogenic production, inertness to biological activities, a tritium box model applied to the North Atlantic Ocean by J. L. Sarmiento in 1983 is used to study the distribution of CFCs in the Northwest Pacific. This thesis attempts to use this model to calculate the past concentrations of CFCs in the atmosphere assuming equilibrium distribution between the surface ocean waters and the atmosphere in the source region of the oceans. The results may allow us to check the history of CFCs in the atmosphere.
The data used in this thesis are those reported by NOAA from three cruises: CO2-87 and CGC92 along 165oE and CO2-88 along 170oW, all from 40o to 10oN. This latitude range avoids the complex gyres and the sea-ice which may limit the air-sea exchange in the North, and also avoids the upwelling in the equatorial region. The outcrop of the 26.0 sq water is located at longitude about 52o-53oN along 165oE, but is located at about 40oN along 170oW. The outcrop will move southward in winter. The vertical distribution pattern of CFCs is similar to that of oxygen. Concentrations of CFCs in ocean water increase as potential temperature and salinity decrease. High latitudes of low temperature and salinity have high CFC solubility and high air-sea exchange rates, and are presumably the major areas for input of CFCs into the seawater. As the CFCs in the air increase over the years the concentrations of CFCs in the surface ocean water also increase but decrease with water depth. The solubility, F, of CFCs is a function of both temperature and salinity, but temperature prevails. The F values for CFC-11 and CFC-12 from 10o to 50oN along 165oE are 5.86-16.0 and 1.70-4.15 mmole/kg/ atm, respectively. The values along 170oW are, respectively, 6.60-22.2 and 1.89-5.55 mmole/kg/atm. The solubility of CFC-11 is about four times as large as that of CFC-12. The solubility of CFCs along 170oW is about 1.4 times along 165oE because of temperature and salinity differences. The exchange rate in the time scale for =1 year ranges 0.85-1.3 yr-1, CFC-11 has a mean of 0.99 yr-1, CFC-12 has a mean of about 1.04 yr-1. Along the isopycnal surface of sq=26.0, the highest exchange rate between two boxes is 2.34 yr-1, the lowest 0.06 yr-1. Based on the calculated concentrations of CFCs in the surface seawater from the atmospheric value in the past, apparent ages of the Mode Waters are similar for both CFC-11 and CFC-12. The apparent age along 165oE at 10oN is about 17 years on the defined isocypnal surface, and it is about 15 years along 170oW at 10oN. The spreading rate of CFCs in the Northwest Pacific is thus about 172-221 km/yr. During the 17 years, the annual increase in influx to the seawater is about 0.12 pM/kg/yr for CFC-11, and about 0.059 pM/kg/yr for CFC-12. The error in calculating atmosphere CFCs in the past is about 11 % for CFC-11, and 6 % for CFC-12.
Advisor:Ja-Son Yu; Jia-Lin Wang; Yu-Cheng Chung; Jiunn-Guang Lo
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:cfc exchange rate apparent age northcoast pacific
Date of Publication:01/17/2002