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North Atlantic Warming: Patterns of Long-term Trend and Multidecadal Variability

North Atlantic Warming: Patterns of Long-term Trend and Multidecadal Variability
Type: 
Poster
Igor V. Polyakov1, Vladimir Alexeev2, Uma S. Bhatt3, Eugenia I. Polyakova4, Xiangdong Zhang5
1International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK, USA, igor [at] iarc [dot] uaf [dot] edu
2International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK, USA, valexeev [at] iarc [dot] uaf [dot] edu
3Atmospheric Sciences & Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA, usbhatt [at] alaska [dot] edu
4Stanford University, Stanford, CA, USA, jenya56 [at] yahoo [dot] com
5International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK, USA, xdz [at] iarc [dot] uaf [dot] edu

Climate fluctuations in the North Atlantic Ocean have wide-spread implications for Europe, Africa, and the Americas. This study assesses the relative contribution of the long-term trend and variability of North Atlantic warming using EOF analysis of deep-ocean and near-surface observations. Our analysis demonstrates that the recent warming over the North Atlantic is linked to both long-term (including anthropogenic and natural) climate change and multidecadal variability (MDV, *50 - 80 years). Our results suggest a general warming trend of 0.031 ± 0.006°C/decade in the upper 2,000 m North Atlantic over the last 80 years of the twentieth century, although during this time there are periods in which short-term trends were strongly amplified by MDV. For example, MDV accounts for ~60% of North Atlantic warming since 1970. The single-sign basin-scale pattern of MDV with prolonged periods of warming (cooling) in the upper ocean layer and opposite tendency in the lower layer is evident from observations. This pattern is associated with a slow- down (enhancement) of the North Atlantic thermohaline overturning circulation during negative (positive) MDV phases. In contrast, the long-term trend exhibits warming in tropical and mid-latitude North Atlantic and a pattern of cooling in regions associated with major northward heat transports, consistent with a slowdown of the North Atlantic circulation as evident from observations and confirmed by selected modeling results. This localized cooling has been masked in recent decades by warming during the positive phase of MDV. Finally, since the North Atlantic Ocean plays a crucial role in establishing and regulating the global thermohaline circulation, the multi- decadal fluctuations discussed here should be considered when assessing long-term climate change and variability, both in the North Atlantic as well as in the Arctic.

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National Science Foundation | Division of Arctic Sciences
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Association of Polar Early Career Scientists
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Bureau of Land Management
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International Study of Arctic Change
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Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies

This work is supported by the National Science Foundation (NSF) under the ARCUS Cooperative Agreement ARC-0618885. Any opinions, findings, and conclusions or recommendations expressed do not necessarily reflect the views of the NSF.