Polar extremes affect tropics A Spanish-led team of scientists has proven that there is a link between ocean temperatures at Earth's polar extremes and the climate at the equator, thousands of miles away. The finding serves as further evidence that oceanic behaviour does indeed influence global climate. Re... A Spanish-led team of scientists has proven that there is a link between ocean temperatures at Earth's polar extremes and the climate at the equator, thousands of miles away. The finding serves as further evidence that oceanic behaviour does indeed influence global climate. Results from the study are published in the journal Science. Researchers from Universitat Autònoma de Barcelona (UAB) in Spain, Newcastle University in the UK and other European institutes focused their study on the sea-surface temperatures of the northern Pacific and southern Atlantic Oceans during the Pliocene era. This era, which began more than 3 million years ago, has been the subject of enormous research for several years now. It represents the most recent time in our planet's history during which the average temperatures on Earth were significantly higher than they are today. Scientists believe the Pliocene era might provide clues as to what to expect following global warming. The team analysed and measured the composition of alkenones in samples of marine sediment collected under the Integrated Ocean Drilling Program, a global marine research program exploring Earth's history and structure, and monitoring sub-seafloor environments. Alkenones are highly resistant organic compounds produced by surface-dwelling phytoplankton. Because these microscopic marine plants change their alkenone chemistry as temperatures fluctuate, the researchers were able to use them as biomarkers for reconstructing the temperatures of the ocean's surface millions of years ago. Newcastle University's Dr Erin McClymont explained that phytoplankton molecules are like fossils of shells or fish that fall to the ocean floor and are preserved. 'Molecules which remained from the phytoplankton were gradually buried beneath layers of sediment beneath the ocean floor, and by analysing these we were able to reconstruct the temperatures of the surface ocean in the past,' she pointed out. The scientists found that when the polar waters cooled and expanded between 1.8 and 1.2 million years ago, this increased the temperature difference between the equator and the poles. This contributed to the development of the 'cold tongue', a band of cold surface waters approximately 1,000 kilometres wide flowing along the equatorial Pacific. According to Dr McClymont, the team's findings show that the oceanic regions close to the poles play a fundamental role in determining the world's climate. She explained that one outcome of a rise in global temperature could be an increase in the depth of the thermocline, a layer of ocean water in which temperatures change rapidly, and a contraction of the cold tongue in the eastern Pacific, which currently brings cold, deep waters to the surface. Currently, the cold tongue in the Pacific almost disappears during El Niño conditions (El Niño is a phenomenon linked to dramatic weather disturbances such as floods and drought, and can have global repercussions). Studies conducted in the past have revealed that during warmer conditions of the Pliocene era the cold tongue was not present, and that this created somewhat of a permanent El Niño situation in the equatorial Pacific. 'The high latitudes are currently experiencing the largest climate changes, and our data show that this could impact on tropical climates as we saw in the Pliocene,' noted Dr McClymont. Based on their findings, the scientists suggest that we may eventually find ourselves in a situation where the cold tongue responds to the current global warming, which would see the planet spiral into a climatic scenario similar to that of the Pliocene era. Countries Spain, United Kingdom
