西北太平洋台风对海气CO2通量的影响和机制研究

Influence of Typhoons in the Western North Pacific on Air-sea CO2 Flux Variations and Underlying Mechanisms

  • 摘要: 为探究西北太平洋频发的台风如何调控海气界面CO2通量,本研究利用基于神经网络反演的高分辨率海气CO2通量数据集,结合1982—2022年间的台风轨迹密度函数,系统提取了天气尺度下台风影响下的CO2通量响应特征,并分析了其驱动机制。研究结果表明,海气界面的气体传输系数与海水CO2溶解度分别在台风影响下升高了11.52%与3.11%,而CO2分压差下降了10.10%,最终导致台风期间海洋向大气输送的CO2通量密度增加了2.58 (mmol/m2)/d。在空间上,台风期间海气界面的CO2分压差异常呈现区域性差异,即南海表现为正异常,而太平洋表现为负异常。台风引起的海表面温度降低致使海水CO2溶解度升高,从而使海水CO2分压在南海和太平洋分别降低了2.08与1.97 µatm(1 atm=101325 Pa),但是台风引起的混合与上升流促使次表层富含CO2的冷水与表层海水混合,导致海水CO2分压在南海与太平洋分别上升了2.85与0.99 µatm。这种太平洋热力作用主导而南海非热力作用主导的空间差异最终导致CO2分压差的变化在海盆间的差异。总体而言,台风对海气CO2通量的调控以风场驱动为主,贡献了52.62%的通量变化。热力作用在源汇过渡区域主导,贡献12.15%的总通量变化,而非热力(动力混合)过程在南海近岸海域主导,贡献8.83%的总通量变化。本研究阐明了台风对区域碳循环的调节作用,为更准确地估算区域碳收支以及预测未来气候变暖背景下碳汇的演变提供重要的科学依据。

     

    Abstract: To investigate how frequent typhoons in the western North Pacific (WNP) regulate air-sea CO2 flux, this study uses a high-resolution air-sea CO2 flux dataset based on neural-network inversion, together with a typhoon track density function during 1982–2022, to systematically extract the characteristics of CO2 flux responses to typhoons at the synoptic scale and to analyze the associated driving mechanisms. The results indicate that under typhoon influence, the gas transfer coefficient and seawater CO2 solubility increase by 11.52% and 3.11%, respectively, while the air-sea CO2 partial pressure gradient ( \Delta f\mathrmC\mathrmO_2 ) decreases by 10.10%. Ultimately, these combined alterations lead to an average enhancement in the oceanic CO2 efflux density of 2.58 (mmol/m2)/d during typhoon events. Spatially, the anomalies in \Delta f\mathrmC\mathrmO_2 exhibit pronounced regional divergence, characterized by positive anomalies in the South China Sea (SCS) and negative anomalies in the WNP. This basin-scale contrast is controlled by the interplay between thermal and non-thermal (dynamic mixing) processes. Typhoon-induced sea surface cooling enhances CO2 solubility, effectively reducing seawater f\mathrmC\mathrmO_2 by 2.08 µatm in the SCS and 1.97 µatm in the WNP. In contrast, strong vertical mixing and upwelling entrain CO2-rich subsurface waters into the surface layer, raising seawater pCO2 by 2.85 µatm in the SCS and 0.99 µatm in the WNP. As a result, thermal processes dominate in the WNP, whereas non-thermal dynamic mixing processes prevails in the SCS, jointly shaping the observed basin-scale \Delta f\mathrmC\mathrmO_2 variations. Mechanism decomposition further reveals that the typhoon-driven CO2 flux variation is primarily contralled by extreme wind forcing, which account for 52.62% of the total flux change. Regionally, thermal processes dominate in source-sink transition zones, contributing 12.15% to the total variance, while non-thermal dynamic mixing processes dominate in the SCS, contributing 8.83%. These findings highlight the critical role of extreme weather events in regional carbon cycling, providing a robust scientific basis for refining regional carbon budget estimates and for projecting the evolution of oceanic carbon sinks under future climate warming scenarios.

     

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