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Bermuda Coral Temperature Record Linksthe the North Atlantic Oscillation to Climate Warming

11 Feb 2009

 

Global warming is one of the most serious challenges faced by scientists and the world today. Dr Nathalie Goodkin, Assistant Professor of Environmental Science, The University of Hong Kong, and her co-workers from the Woods Hole Oceanographic Institution (WHOI) - Konrad Hughen, Scott Doney and William Curry generated the first continuous, ocean based record of the North Atlantic Oscillation (NAO) and found that climate change might be altering the long-term behavior of the NAO. The publication of the project was featured in the December issue of the journal Nature Geoscience in 2008, unveiling the correlation between the variability of North Atlantic Oscillation (NAO) and climate change.

NAO refers to the fluctuations in atmospheric pressure at sea-level between the polar low and the subtropical high over the North Atlantic Ocean during winter, influencing weather patterns over North America, Europe and North Africa. The research team found that the variability of the NAO decade-to-decade has experienced larger changes from high to low values, during the late twentieth century than in the early 1800s, implying that variability is linked to the mean temperature of the Northern Hemisphere which has generally increased over this time. The study suggests that the Industrial Revolution and human-related warming have augmented the potential for more violent swings and stronger long-term patterns of the NAO. "The increase in multi-decadal behavior was suspected from the instrumental and atmospheric records, but this is the first time the pattern has been documented in records from both the ocean and the atmosphere," said Goodkin. "While additional modeling and palaeoclimatic studies are needed, a broad distribution of marine records could advance our knowledge of NAO variability and serve to improve future projections."

With the use of a 218-year-long temperature record from a Bermuda brain coral, Goodkin and the WHOI scientists created the first non-terrestrial reconstruction showing the long-term behavior of NAO. Past reconstructions of the NAO have relied mainly on land-based records, such as tree ring chronologies combined with ice cores and historical climate data. However, those records cannot fully capture oceanic processes linked to NAO variability and instrumental records from relatively few locations limit the understanding of ocean-atmosphere dynamics with regard to the behavior of NAO.

Corals provide high resolution records that are well dated and centuries long. Similar to tree rings, corals accrete seasonal and annual growth layers as they extend.  "The proportions of some chemical elements found in coral skeleton layers largely depend on the temperature of seawater in which it was formed. By analyzing the strontium to calcium ratio in the coral, we were able to reconstruct monthly changes of ocean temperatures and evaluate variability of the NAO during both cold and warm periods from the Little Ice Age (1800-1850) to modern day," said Goodkin.

Challenges to the environment including global warming are of great concern in modern society. The Environmental Science Major, a new major of the Faculty of Science from 2009, offers an interdisciplinary education to undergraduate students on the interaction between human and Earth. It aims to provide students with solid scientific background in addressing environmental issues faced by mankind, and prepare them to work in industries and government agencies where they will have to wisely manage resources for which they are responsible. The Major of Earth Sciences is designed to enhance students' knowledge in the nature of Earth systems and Earth processes.

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About North Atlantic Oscillation (NAO)

The North Atlantic Oscillation is described by the NAO index, calculated as a weighted difference between the polar low and the subtropical high during the winter season. In a positive index, both the low-pressure zone over Iceland and high pressure over the Acores are intensified, resulting in changes in the strength, incidence, and pathway of winter storms crossing the Atlantic. In a negative phase, a weak subtropical high and a weak Icelandic low result in fewer and weaker winter storms crossing on a more west-east pathway.

Beginning in the early 1950s, the NAO experienced extended periods of intense negative and positive phases. An unusual period of positive phase between1970-2000 led to the suggestion that global warming was affecting the behavior of the NAO. The climatic influence of the NAO extends from the eastern United States to Western Europe, impacting human activities such as shipping, oil drilling, fisheries, hydroelectric power generation and coastal management. Improving the ability to predict shifts in the phase and intensity of the NAO is a prerequisite to mitigating the economic impacts of future climate change. (from Goodkin et al. 2008)

About Nature GeoScience

Nature Geoscience is a scientific journal published by Nature Publishing Group, publisher of the flagship journal Nature. It is a monthly multi-disciplinary journal aimed at bringing together top-quality research across the entire spectrum of the Earth Sciences along with relevant work in related areas. The journal's content reflects all the disciplines within the geosciences, encompassing field work, modelling and theoretical studies.