Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective
Assessing the role of North Atlantic freshwater forcing in millennial scale climate variability: a tropical Atlantic perspective
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DOI：
10.1007/s00382-004-0499-5
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发表时间：
2005-02
期刊：
影响因子：
4.6
通讯作者：
K. Dahl;A. Broccoli;R. Stouffer
中科院分区：
文献类型：
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作者：
K. Dahl;A. Broccoli;R. Stouffer
这项研究分析了一组由三人组成的实验，其中向北大西洋施加了 100 年的 0.1 Sv 淡水，以解决北大西洋大量淡水输入导致气候突变的可能性。使用的模型是 GFDL R30 耦合海洋大气环流模型。我们特别关注这种强迫对热带大西洋地区的影响，古气候学家对此进行了广泛的研究。为了应对淡水强迫，到 100 年淡水脉冲结束时，北大西洋经向翻转环流减少到大约 40%。因此，北大西洋地区气温下降高达 8°C。北大西洋的极度变冷增加了极地到赤道的温度梯度，需要从热带大西洋向高纬度大西洋提供更多的热量。为了适应增加的热量需求，ITCZ 向南移动，以允许更多的热量穿过赤道输送。伴随着 ITCZ 向南移动，东北信风增强，整个热带大西洋的降水模式发生变化。其中，巴西东北部降水增加，非洲降水略有减少。此外，我们发现热带大西洋和非洲的地表气温升高，但南美洲北部的气温较低。热带大西洋的海面温度略有升高，温跃层出现较大的温暖异常。这些响应对于该集合中的每个成员来说都是稳健的，并且现在已经被使用耦合 OAGCM 的许多淡水强迫研究所确定。正如新仙女木期的古气候数据所表明的那样，模型对淡水强迫的响应通常幅度较小，但具有相同的方向。然而，在某些情况下，模型响应和古气候数据直接相互矛盾。模型模拟与古气候数据之间的差异可能是由于多种因素造成的，包括淡水强迫的不准确、边界条件不适当以及古气候数据解释的不确定性。尽管存在这些差异，但从我们的结果中可以清楚地看出，北大西洋高纬度地区的气候突变有可能对热带气候产生重大影响。这需要对淡水强迫在驱动气候变化中的作用进行进一步的模型实验。
This study analyzes a three-member ensemble of experiments, in which 0.1 Sv of freshwater was applied to the North Atlantic for 100 years in order to address the potential for large freshwater inputs in the North Atlantic to drive abrupt climate change. The model used is the GFDL R30 coupled ocean–atmosphere general circulation model. We focus in particular on the effects of this forcing on the tropical Atlantic region, which has been studied extensively by paleoclimatologists. In response to the freshwater forcing, North Atlantic meridional overturning circulation is reduced to roughly 40% by the end of the 100 year freshwater pulse. Consequently, the North Atlantic region cools by up to 8°C. The extreme cooling of the North Atlantic increases the pole-to-equator temperature gradient and requires more heat be provided to the high latitude Atlantic from the tropical Atlantic. To accommodate the increased heat requirement, the ITCZ shifts southward to allow for greater heat transport across the equator. Accompanying this southward ITCZ shift, the Northeast trade winds strengthen and precipitation patterns throughout the tropical Atlantic are altered. Specifically, precipitation in Northeast Brazil increases, and precipitation in Africa decreases slightly. In addition, we find that surface air temperatures warm over the tropical Atlantic and over Africa, but cool over northern South America. Sea-surface temperatures in the tropical Atlantic warm slightly with larger warm anomalies developing in the thermocline. These responses are robust for each member of the ensemble, and have now been identified by a number of freshwater forcing studies using coupled OAGCMs. The model responses to freshwater forcing are generally smaller in magnitude, but have the same direction, as paleoclimate data from the Younger Dryas suggest. In certain cases, however, the model responses and the paleoclimate data directly contradict one another. Discrepancies between the model simulations and the paleoclimate data could be due to a number of factors, including inaccuracies in the freshwater forcing, inappropriate boundary conditions, and uncertainties in the interpretation of the paleoclimate data. Despite these discrepancies, it is clear from our results that abrupt climate changes in the high latitude North Atlantic have the potential to significantly impact tropical climate. This warrants further model experimentation into the role of freshwater forcing in driving climate change.