Lecture 8 Tracers for Gas Exchange 华盛顿大学-海洋化学课件.ppt

The bomb spike: surface ocean and atmospheric Δ14C since 1950 Massive production in nuclear tests ca. 1960 (“bomb 14C”) Through air-sea gas exchange, the ocean took up ~half of the bomb 14C by the 1980s * Lecture 8 Tracers for Gas Exchange Examples for gas exchange using: 222Rn 14C Rates of Gas Exchange Stagnant Boundary Layer Model. Depth (Z) ATM OCN Cg = KH Pgas = equil. with atm CSW ZFilm Stagnant Boundary Layer – transport by molecular diffusion well mixed surface SW well mixed atmosphere 0 Z is positive downward ?C/ ?Z = - F = + (flux into ocean) see: Liss and Slater (1974) Nature, 247, p181 Broecker and Peng (1974) Tellus, 26, p21 Liss (1973) Deep-Sea Research, 20, p221 Expression of Air -Sea CO2 Flux k = piston velocity = D/Zfilm From wind speed From CMDL CCGG network S – Solubility From Temperature Salinity From measurements F = k s (pCO2w- pCO2a) = K ? pCO2 pCO2a pCO2w Need to calibrate! U-Th Series Tracers Analytical Method for 222Rn and 226Ra charcoal liquid N2 SW Example 226Ra Profile South Atlantic at 15°S ; 29.5°W 226Ra Distributions 226Ra in Atlantic and Pacific Q. What controls the ocean distributions of 226Ra? 226Ra – Si correlation Q. Why is there a hook at the end? 226Ra source from the sediments 222Rn Example Profile from North Atlantic 226Ra 222Rn Does Secular Equilibrium Apply? t1/2 222Rn t1/2 226Ra (3.8 d) (1600 yrs) YES! A226Ra = A222Rn Why is 222Rn activity less than 226Ra? Smethie et al. 1985 222Rn as a tracer for gas exchange Wind speed d222Rn/dt = sources – sinks = decay of 226Ra – decay of 222Rn - gas exchange to atmosphere ? 222Rn is a gas and the 222Rn concentration in the atmosphere is much less than in the ocean mixed layer (? mixed layer). Thus there is a net evasion of 222Rn out of the ocean. The 222Rn balance for the mixed layer, ignoring horizontal advection and vertical exchange with deeper water, is: ?ml l222Rn d[222Rn]/dt = ? ml l226Ra [226Ra] – ? l 222Rn [222RnML]