Stratospheric ozone depletion and emission of greenhouse gases lead to a trend of the southern annular mode (SAM) toward its high-index polarity. The positive phase of the SAM is characterized by stronger than usual westerly winds that induce changes in the physical carbon transport. Changes in the natural carbon budget of the upper 100 m of the Southern Ocean in response to a positive SAM phase are explored with a coupled ecosystem-general circulation model and regression analysis. Previously overlooked processes that are important for the upper ocean carbon budget during a positive SAM period are identified, namely, export production and downward transport of carbon north of the polar front (PF) as large as the upwelling in the south. The limiting micronutrient iron is brought into the surface layer by upwelling and stimulates phytoplankton growth and export production but only in summer. This leads to a drawdown of carbon and less summertime outgassing (or more uptake) of natural CO2. In winter, biological mechanisms are inactive, and the surface ocean equilibrates with the atmosphere by releasing CO2. In the annual mean, the upper ocean region south of the PF loses more carbon by additional export production than by the release of CO2 into the atmosphere, highlighting the role of the biological carbon pump in response to a positive SAM event.

中文翻译：

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响应南部环状模态的南大洋季节性不同碳通量变化

平流层臭氧消耗和温室气体排放导致南部环形模式（SAM）向高指数极性方向发展。SAM 的正相位的特点是比通常的西风更强，导致物理碳传输发生变化。通过耦合生态系统-大气环流模型和回归分析，探索了响应于正 SAM 阶段的南大洋上层 100 m 自然碳收支的变化。确定了以前被忽视的过程，这些过程在正 SAM 期间对上层海洋碳收支很重要，即极地锋 (PF) 以北与南部上升流一样大的碳的出口生产和向下传输。限制性微量营养素铁通过上升流带入表层并刺激浮游植物生长和出口生产，但仅限于夏季。这会导致碳的减少和自然二氧化碳的夏季释气（或更多的吸收）减少。在冬季，生物机制不活跃，表层海洋通过释放二氧化碳与大气平衡。在年平均值中，PF 以南的上层海洋区域通过额外的出口生产损失的碳比通过向大气释放 CO2 损失更多的碳，突出了生物碳泵在响应积极的 SAM 事件中的作用。海洋表层通过释放二氧化碳与大气平衡。在年平均值中，PF 以南的上层海洋区域通过额外的出口生产损失的碳比通过向大气释放 CO2 损失更多的碳，突出了生物碳泵在响应积极的 SAM 事件中的作用。海洋表层通过释放二氧化碳与大气平衡。在年平均值中，PF 以南的上层海洋区域通过额外的出口生产损失的碳比通过向大气释放 CO2 损失更多的碳，突出了生物碳泵在响应积极的 SAM 事件中的作用。