PIES time series in the North Atlantic at the Mid-Atlantic Ridge (2006-2010)

In the western North Atlantic, warm and saline water is brought by the North Atlantic Current (NAC) from the subtropics into the subpolar gyre. Four inverted echo sounders with high precision pressure sensors (PIES) were moored between 47°40' N and 52°30' N to study the main pathways of the NAC from the western into the eastern basin. The array configuration that forms three segments (northern, central, and southern) allows partitioning of the NAC and some assessment of NAC flow paths through the different Mid-Atlantic Ridge fracture zones. We exploit the correlation between the NAC transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of NAC transports to the period from 1992 to 2013. The mean NAC transport over the entire 21 years is 27 ± 5 Sv, consisting of 60% warm water of subtropical origin and 40% subpolar water. We did not find a significant trend in the total transport time series, but individual segments had opposing trends, leading to a more focused NAC in the central subsection and decreasing transports in the southern and northern segments. The spectral analysis exhibits several significant peaks. The two most prominent are around 120 days, identified as the time scale of meanders and eddies, and at 4-9 years, most likely related to the NAO. Transport composites for the years of highest and lowest NAO indices showed a significantly higher transport (+2.9 Sv) during strong NAO years, mainly in the southern segment.

在西北大西洋海域，北大西洋流（North Atlantic Current, NAC）将亚热带海域的暖盐水团输送至亚极带环流区域。本研究于北纬47°40′至52°30′区间锚定部署了4台搭载高精度压力传感器的倒置回声测深仪（PIES），以探究北大西洋流从西大西洋盆地向东大西洋盆地的主要输运路径。该观测阵列分为北、中、南三个分段，可实现对北大西洋流的分段拆分，并评估其穿越大西洋中脊不同断裂带的流路特征。本研究借助2006—2010年实测的北大西洋流输运量与高度计数据反演的地转流流速之间的相关性，将北大西洋流输运量的时间序列拓展至1992—2013年时段。整个21年时段内，北大西洋流的平均输运量为27±5 Sv，其中60%为亚热带起源暖水团，40%为亚极带水团。整体输运量时间序列未呈现显著的长期趋势，但各分段输运量的变化趋势存在差异：中部分段的北大西洋流更为集中，而南部与北部分段的输运量则呈下降趋势。频谱分析结果显示存在多个显著峰值，其中最为突出的两个分别位于120天左右（对应海流弯曲与中尺度涡的时间尺度）以及4—9年时段，后者大概率与北大西洋涛动（North Atlantic Oscillation, NAO）相关。对北大西洋涛动指数极值年份的输运量合成分析结果表明，强北大西洋涛动年份的输运量显著偏高（+2.9 Sv），且该增量主要集中于南部分段。