The North Atlantic Basin is a major sink for atmospheric carbon dioxide (CO₂) due in part to the extensive plankton blooms which form there supported by nutrients supplied by the three-dimensional ocean circulation. Hence, changes in ocean circulation and/or stratification may influence primary production and biological carbon export. In this study, we assess this possibility by evaluating inorganic nutrient budgets for 2004 and 2010 in the North Atlantic based on observations from the transatlantic A05-24.5°N and the Greenland-Portugal OVIDE hydrographic sections, to which we applied a box inverse model to solve the circulation and estimate the across-section nutrient transports. Full water column nutrient budgets were split into upper and lower meridional overturning circulation (MOC) limbs. According to our results, anomalous circulation in early 2010, linked to extreme negative NAO conditions, led to an enhanced northward advection of more nutrient-rich waters by the upper overturning limb, which resulted in a significant nitrate and phosphate convergence north of 24.5°N. Combined with heaving of the isopycnals, this anomalous circulation event in 2010 favored an enhancement of the nutrient consumption (5.7 ± 4.1 kmol-P s⁻¹) and associated biological CO₂ uptake (0.25 ± 0.18 Pg-C yr⁻¹, upper-bound estimate), which represents a 50% of the mean annual sea–air CO₂ flux in the region. Our results also suggest a transient state of deep silicate divergence in both years. Both results are indicative of a MOC-driven modulation of the biological carbon uptake (by the upper MOC limb) and nutrient inventories (by the lower MOC limb) in the North Atlantic.

中文翻译：

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抵消上下经向翻转肢体对北大西洋营养预算的贡献：2010 年失衡加剧

北大西洋盆地是大气二氧化碳 (CO ₂) 部分原因是在那里形成了广泛的浮游生物，由三维海洋环流提供的养分支持。因此，海洋环流和/或分层的变化可能会影响初级生产和生物碳输出。在这项研究中，我们根据跨大西洋 A05-24.5°N 和格陵兰-葡萄牙 OVIDE 水文剖面的观察结果，通过评估北大西洋 2004 年和 2010 年无机营养预算来评估这种可能性，我们对其应用了箱逆模型求解循环并估计横截面养分输送。全水柱养分预算分为上下经向翻转循环 (MOC) 分支。根据我们的结果，2010 年初的异常环流与极端负 NAO 条件有关，导致营养丰富的水通过上倾覆翼增强向北平流，从而导致 24.5°N 以北的硝酸盐和磷酸盐显着收敛。结合等密度升高，2010 年的这一异常环流事件有利于养分消耗的增加 (5.7 ± 4.1 kmol-P s^-1 ) 和相关的生物 CO ₂吸收（0.25 ± 0.18 Pg-C yr ^-1，上限估计），代表该地区年平均海气 CO ₂通量的 50% 。我们的结果还表明，这两年都存在深硅酸盐分歧的瞬态。这两个结果都表明北大西洋生物碳吸收（通过上 MOC 肢）和养分库存（通过下 MOC 肢）的 MOC 驱动调节。