The lower limb of the Atlantic meridional overturning circulation (AMOC) is the equatorward flow of dense waters formed through the cooling and freshening of the poleward-flowing upper limb. In the subpolar North Atlantic (SPNA), upper limb variability is primarily set by the North Atlantic Current, whereas lower limb variability is less well understood. Using observations from a SPNA mooring array, we show that variability of the AMOC's lower limb is connected to poleward flow in the interior Irminger Sea. We identify this poleward flow as the northward branch of the Irminger Gyre (IG), accounting for 55% of the AMOC's lower limb variability. Over 2014–2018, wind stress curl fluctuations over the Labrador and Irminger Seas drive this IG and AMOC variability. On longer (>annual) timescales, however, an increasing trend in the thickness of intermediate water, from 2014 to 2020, within the Irminger Sea coincides with a decreasing trend in IG strength.

中文翻译：

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伊明格环流是北大西洋副极地翻转的关键驱动因素

大西洋经向翻转环流（AMOC）的下肢是向极地流动的上肢冷却和清新后形成的向赤道流动的稠密水流。在北大西洋副极地（SPNA），上肢变异主要由北大西洋洋流决定，而下肢变异则不太了解。利用 SPNA 系泊阵列的观测结果，我们表明 AMOC 下肢的变化与内陆伊尔明格海的极地流有关。我们将这种向极地流动确定为伊明格环流 (IG) 的北支，占 AMOC 下肢变异的 55%。 2014-2018 年，拉布拉多海和伊尔明格海的风应力旋度波动推动了 IG 和 AMOC 的变化。然而，在较长（>年度）时间尺度上，从 2014 年到 2020 年，伊尔明格海内中间水厚度的增加趋势与 IG 强度的下降趋势一致。