Spreading velocities and dilution of North Atlantic Deep Water in the tropical Atlantic based on CFC time series
Spreading velocities and dilution of North Atlantic Deep Water in the tropical Atlantic based on CFC time series
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基于CFC时间序列的热带大西洋北大西洋深水扩散速度和稀释
DOI：
10.1029/2003jc002050
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发表时间：
2004
影响因子：
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通讯作者：
M. Rhein
中科院分区：
文献类型：
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作者：
R. Steinfeldt;M. Rhein
[1]重复观测CFC-11和CFC-12在热带大西洋西部在1990年至2002年期间被用来拟合参数的年龄谱的几个北大西洋深水组件：上部拉布拉多海水（ULSW），拉布拉多海水（LSW），和较低的北大西洋深水（LNADW）。最可靠的结果是拉布拉多海和丹麦海峡形成区的平均扩散速度u，两个LSW水团和LNADW分别为1.5 ± 0.3 cm/s和2.0 ± 0.2 cm/s。这些值相当于16°N所有三个分量的年龄约为15-22岁，而在35°W赤道的年龄约为21-31岁。结果与简单的示踪方法，CFC比率或“有效”年龄是兼容的。“年轻”组分的分数f（即，在过去50年中，水团的比例被证明是相当小的，范围从25%到不到5%。下游f的减少表明年轻的NADW与CFC贫乏的老NADW年份和/或与来自南半球的其他不含CFC的水团混合。在LNADW中发现的分数最低，从35°W到10°S的赤道下游急剧减少，可能是由于分支为沿着2°S的纬向流和沿沿着巴西海岸的南向流。不像小的不确定性估计的推断速度，等密度扩散系数，κ，范围从100到10000 m2/s。f在LSW的时间演化表现出极大值，在1996年从7°N向下游传播到5°S的深层西边界流，沿沿着2°S传播到23°W。我们将此信号解释为1972-1976年形成的强烈通风LSW的到来。在2000年和2002年之间，赤道以南的ULSW和LSW的比例减少，这可能是由当地的动力学造成的。
[1] Repeated observations of CFC-11 and CFC-12 in the western tropical Atlantic over the period from 1990 to 2002 are used to fit parameters of the age spectra for several North Atlantic Deep Water components: the upper Labrador Sea water (ULSW), the Labrador Sea water (LSW), and the lower North Atlantic Deep Water (LNADW). The most robust results are the mean spreading velocities, u, from the formation region in the Labrador Sea and the Denmark Strait, of 1.5 ± 0.3 cm/s for the two LSW water masses and 2.0 ± 0.2 cm/s for LNADW, respectively. These values are equivalent to an age of about 15–22 years for all three components at 16°N and 21–31 years at the equator at 35°W. The results are compatible with simpler tracer methods, as CFC ratios or “effective” ages. The fractions, f, of the “young” component (i.e., the fraction of the water mass ventilated in the last 50 years), turned out to be quite small, ranging from 25% to less than 5%. The downstream decrease of f indicates mixing of young NADW with CFC-poor older NADW vintages and/or mixing with other CFC-free water masses from the Southern Hemisphere. The lowest fractions were found in the LNADW, with a sharp downstream decrease from the equator at 35°W to 10°S, probably caused by the bifurcation into a zonal flow along 2°S and a southward flow along the Brazilian coast. Unlike the small uncertainties estimated for the inferred velocities, isopycnal diffusivities, κ, range from 100 to 10000 m2/s. The temporal evolution of f in the LSW shows a maximum, propagating from 7°N in 1996, downstream to 5°S in the Deep Western Boundary Current, and along 2°S to 23°W. We interpret this signal as the arrival of the intensely ventilated LSW formed in 1972–1976. Decreasing fractions of the ULSW and LSW south of the equator between 2000 and 2002 are presumably caused by local dynamics.