Wind and fetch dependence of gas transfer velocity in an Arctic sea-ice lead determined from eddy covariance CO2 flux measurements
Wind and fetch dependence of gas transfer velocity in an Arctic sea-ice lead determined from eddy covariance CO2 flux measurements
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通过涡流协方差 CO2 通量测量确定北极海冰中气体传输速度的风和取值依赖性
DOI：
10.1002/essoar.10502449.1
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
J. Prytherch
中科院分区：
文献类型：
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作者：
J. Prytherch
痕量气体（例如二氧化碳）的空气-水交换通常以气体传输速度来参数化，该速度可以通过直接测量空气-海洋气体通量得出。难溶性气体的传输速度是由近地表海洋湍流驱动的，海冰的存在可能会增强或抑制这种湍流。缺乏测量意味着极地地区的海气通量（二氧化碳的海洋汇尚不清楚）通常是使用按冰分数缩放的公海传输速度来估计的。在这里，我们描述了北冰洋中部夏秋过渡期间海冰引导处涡流协方差通量测量直接确定二氧化碳气体传输速度的方法。铅水吸收的 CO2 是通过在条件（低湿度和高 CO2 信号）下进行的水-大气和冰-大气通量测量的通量足迹分析来确定的，从而最大限度地减少湿度串扰造成的误差。研究发现，导线上的平均气体传输速度与风速呈二次相关：k660 = 0.189 U10^2，比常用的公海参数化低 25% 至 30%。因此，目前对极地海洋碳吸收的估计可能会高估典型夏季弱对流湍流条件下的气体交换率。气体传输速度还表现出对引线尺寸的依赖性，因为它对提取长度以及海况有影响。因此，区域气体交换估计的缩放传输速度参数化将需要结合引线宽度数据。
The air-water exchange of trace gases such as CO2 is usually parameterized in terms of a gas transfer velocity, which can be derived from direct measurements of the air-sea gas flux. The transfer velocity of poorly soluble gases is driven by near-surface ocean turbulence, which may be enhanced or suppressed by the presence of sea ice. A lack of measurements means that air-sea fluxes in polar regions, where the oceanic sink of CO2 is not well known, are generally estimated using open-ocean transfer velocities scaled by ice fraction. Here, we describe direct determinations of the CO2 gas transfer velocity from eddy covariance flux measurements at a sea-ice lead during the summer-autumn transition in the central Arctic Ocean. CO2 uptake by the lead water is determined using flux footprint analysis of water-atmosphere and ice-atmosphere flux measurements made under conditions (low humidity and high CO2 signal) that minimise errors due to humidity cross-talk. The mean gas transfer velocity over the lead is found to have a quadratic dependence on wind speed: k660 = 0.189 U10^2 which is 25 to 30% lower than commonly used open-ocean parameterizations. As such, current estimates of polar ocean carbon uptake are likely to overestimate gas exchange rates in typical summertime conditions of weak convective turbulence. The gas transfer velocities also exhibit a dependence on the dimension of the lead, via its impact on fetch length and hence sea state. Scaling transfer velocity parameterizations for regional gas exchange estimates will therefore require incorporating lead width data.