Spatial and seasonal variability of the air-sea equilibration timescale of carbon dioxide
Spatial and seasonal variability of the air-sea equilibration timescale of carbon dioxide
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DOI：
10.1002/2014gb004813
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发表时间：
2014-11-01
影响因子：
5.2
通讯作者：
Hsu, Wei-Ching
中科院分区：
文献类型：
--
作者：
Jones, Daniel C.;Ito, Takamitsu;Hsu, Wei-Ching
海洋和大气之间的二氧化碳交换通过降低气-水界面的分压梯度，使混合层内的沃茨趋于平衡。然而，平衡过程不是瞬时的;一般来说，在强迫和响应之间有一个滞后。海气平衡的时间尺度取决于几个因素，包括混合层的深度、风速和碳酸盐化学。我们使用一套观测数据集生成的气-海平衡时间尺度的气候和季节合成图。松弛时间尺度表现出相当大的空间和季节变化，主要是由混合层深度和风速的变化。净效应主要由混合层深度决定，气体交换速度和碳酸盐化学参数仅提供部分补偿。一般来说，调整时间尺度往往随着纬度的增加而增加。我们比较了观测得出的海气交换时间尺度与模型得出的表面停留时间和数据得出的水平运输时间尺度，这使我们能够定义两个无量纲指标的平衡效率。这些参数突出了热带、亚热带和北大西洋北方地区，这些地区的海气平衡效率低下，碳异常相对可能持续存在。这里提出的效率参数可以作为一个简单的工具，了解大尺度持续的海气不平衡的CO2观测和模式。
The exchange of carbon dioxide between the ocean and the atmosphere tends to bring waters within the mixed layer toward equilibrium by reducing the partial pressure gradient across the air-water interface. However, the equilibration process is not instantaneous; in general, there is a lag between forcing and response. The timescale of air-sea equilibration depends on several factors involving the depth of the mixed layer, wind speed, and carbonate chemistry. We use a suite of observational data sets to generate climatological and seasonal composite maps of the air-sea equilibration timescale. The relaxation timescale exhibits considerable spatial and seasonal variations that are largely set by changes in mixed layer depth and wind speed. The net effect is dominated by the mixed layer depth; the gas exchange velocity and carbonate chemistry parameters only provide partial compensation. Broadly speaking, the adjustment timescale tends to increase with latitude. We compare the observationally derived air-sea gas exchange timescale with a model-derived surface residence time and a data-derived horizontal transport timescale, which allows us to define two nondimensional metrics of equilibration efficiency. These parameters highlight the tropics, subtropics, and northern North Atlantic as regions of inefficient air-sea equilibration where carbon anomalies are relatively likely to persist. The efficiency parameters presented here can serve as simple tools for understanding the large-scale persistence of air-sea disequilibrium of CO2 in both observations and models.