Estimation of gas exchange rate and carbon dioxide gas flux at the sea-air interface
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摘要: 海−气界面CO2通量的估算采用块体公式，其等于气体交换速率、CO2溶解度以及海水与大气的CO2分压差的乘积，其中的气体交换速率通常与风速相联系，不同作者提出了气体交换速率为风速不同幂次多项式的参数化方案。本文对比了气体交换速率为风速函数的主要研究结果，发现与风速多项式的依赖关系相比，观测数据所基于的观测方法对于气体交换速率的影响更大。在此基础上，本文用多种不同的气体交换速率参数化公式计算了1982−2018年全球的CO2通量，海洋整体上是大气CO2的汇，赤道海区是源，南北半球40°附近的海域构成沿纬向的强吸收带。37 a间，海洋CO2通量的年平均值(以碳计)为(−1.53±0.15) Pg/a, 1999年前，海洋吸收量逐年减小，1999年达到最小值，之后海洋吸收量开始增大，海洋吸收量的增大主要发生在南大洋。Abstract: The CO2 flux at the sea-air interface, which is equal to the product of the gas transfer velocity, solubility, and the CO2 partial pressure difference between sea and the atmosphere, is estimated using the bulk equation, where the gas transfer velocity is usually associated with the wind speed. Different authors have proposed different parameterization schemes, in which the gas transfer velocity is a polynomial of different powers of the wind speed. In this paper, we summarize the main findings on the gas transfer velocity as a function of wind speed. We discover that the observation method has a greater influence on the gas transfer velocity than the power of the wind speed polynomial. On this basis, this paper calculates the global CO2 flux from 1982−2018 using several different parametric formulas for the gas exchange rate. The ocean is a sink for atmospheric CO2, the equatorial sea area is a source, and the ocean near 40° in the northern and southern hemispheres forms a strong absorption zone along the latitudinal direction. The annual average value of oceanic CO2 absorption (in terms of carbon) over 1982−2018 is (−1.53±0.15)Pg/a. The oceanic absorption decreases year by year until 1999, reaching a minimum in 1999, after which the oceanic absorption begins to increase, with the increase in oceanic absorption occurring mainly in the Southern Ocean.
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Key words:
- gas transfer velocity /
- wind speed /
- carbon dioxide flux
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图 1 气体交换速率与风速二次方（a）、三次方（b）以及两种依赖关系（c）的参数化结果
五角星为14C 数据结果；倒三角为双示踪数据结果；圆圈为涡相关结果；虚线表示风速二次方依赖关系；实线表示风速三次方依赖关系
Fig. 1 Parameterization results for quadratic (a) , cubic dependence (b) and both of them (c) between gas transfer velocity and wind speed
The pentagram represents 14C data; the inverted triangle represents dual tracer date; the circle represents the results of eddy covarance; dotted line represents the quadratic relationship; solid line represents the cubic relationship
图 2 全球ΔpCO2标准气候平均值（1 atm=101 325 Pa）
正值代表海洋CO2分压大于大气CO2分压；负值代表海洋CO2分压小于大气CO2分压
Fig. 2 Global ΔpCO2 standard climatological normals (1 atm=101 325 Pa)
Positive value indicates that ocean CO2 partial pressure is greater than atmospheric CO2 partial pressure; negative value indicates that the ocean CO2 partial pressure is less than the atmospheric CO2 partial pressure
图 3 利用不同气体交换速率得到的1982−2018年海−气界面CO2通量平均值分布
正值代表海洋释放CO2；负值代表海洋吸收CO2
Fig. 3 The average of the results of the air-sea CO2 flux from 1982 to 2018 based on various gas transfer velocities
Positive value indicates the release of CO2 from the ocean; negative value indicates the absorption of CO2 by the ocean
图 4 CO2净通量的纬向分布
南大洋和全球CO2净通量分布在南纬高纬度海区重合
Fig. 4 The net CO2 flux obtained by zonal integration
The distribution of net CO2 flux in the South Ocean and the global coincide in the high latitude sea area of the south latitude
图 5 不同参数化方案算得的CO2通量随着时间的变化
黑色实线为不同参数化方案平均的结果；其余颜色代表1982−2018 年不同参数化结果估算的年净通量随时间的变化；圆圈代表涡相关结果；五角星代表14C 结果；倒三角代表双示踪结果；二次依赖关系用点线表示；三次依赖关系用虚线表示
Fig. 5 Variation of CO2 fluxes calculated by different parameterization schemes with time
The solid black line in the figure shows the results averaged for different parameterization schemes; the rest of the colors represent the annual estimated results of different parameterizations from 1982−2018 net fluxes over time; the circles represent the eddy covariance results; the pentagons represent the 14C results;the inverted triangles represent the dual tracer results; the quadratic dependence is shown by dotted lines; the cubic dependence is shown by dashed lines
图 6 2012年的CO2通量与1999年的CO2通量的差值
Fig. 6 Subtract the CO2 flux in 1999 from the CO2 flux in 2012
图 7 基于不同观测数据得到的CO2通量随着时间的变化
Fig. 7 Variation of the CO2 fluxes with time for different measurement schemes
图 8 全球大洋CO2通量的气候态平均结果随月份的变化
红色对应海洋释放CO2；蓝色对应吸收CO2；白色则表示海洋处于既不释放也不吸收的状态
Fig. 8 The monthly climatological average CO2 flux in global ocean
Red color represents the ocean releases CO2; blue color represents the ocean absorbs CO2; while white color means neither of the above
图 9 大西洋(a)、太平洋(b)、印度洋(c)和南大洋(d) CO2净通量分布
Fig. 9 The net CO2 flux of Atlantic Ocean (a), Pacific Ocean (b), Indian Ocean (c), and Southern Ocean (d)
图 10 大西洋(a)、太平洋(b)、印度洋(c)和南大洋(d)的气体交换系数（1 atm=101 325 Pa）
Fig. 10 The gas transfer coefficient of Atlantic Ocean (a), Pacific Ocean (b), Indian Ocean (c), and Southern Ocean (d) (1 atm=101 325 Pa)
图 11 1983–2018年赤道上135°E～105°W的海温变化(a)、pCO2变化(b)以及此期间对应的Niño3.4指数（c）
Fig. 11 SST variation (a), pCO2 variation (b) and the corresponding Niño3.4 index (c) over the equator from 135°E to 105°W from 1983 to 2018
图 12 1983−2018年的Niño3.4区域的月平均CO2释放量（蓝线）与Niño3.4指数（红线）
阴影区域是几次比较显著的ENSO事件期间
Fig. 12 Monthly mean CO2 flux (blue line) and Niño3.4 index (red line) for the Niño3.4 region from 1983 to 2018
The shaded areas in the figure are during several of the significant ENSO events
表 1 不同参数化结果估计的CO2通量的在不同海区的平均分布
Tab. 1 Mean distribution of CO2 fluxes estimated by different parameterization results in different areas
区域 面积/（106 km2） 海−气CO2通量/（Pg·a−1） 大西洋 太平洋 印度洋 南大洋 总和 50°N以北 16.2 −0.379 8 −0.055 3 − − −0.435 1 50°～14°N 69.1 −0.163 0 −0.346 0 −0.008 0 − −0.517 0 14°N～14°S 86.7 0.147 3 0.375 7 0.071 0 − 0.594 0 14°～50°S 109.6 −0.302 5 −0.433 9 −0.407 6 − −1.144 0 50°～62°S 29.7 − − − −0.017 9 −0.017 9 62°S以南 15.3 − − − −0.013 8 −0.013 8 海区通量(所占百分比) −0.698 0(46%) −0.459 5(30%) −0.344 6(22%) −0.031 7(2%) −1.533 8 海区总面积以及各海区比例 326.5 23% 47% 16% 14% 100% 
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