Measurements of the ratio of calcium to magnesium in the shells of a single-celled organism called Hyalinea balthica, collected from sediment cores, enabled a team of researchers to create a 10,000-year record of ocean temperatures from the middle-depth waters where H. balthica lived – about 450–900 metres below the surface.
The results suggested that although the climate of the past 10,000 years has been relatively stable, the Pacific intermediate depths have generally been cooling, probably because of changes in the Earth’s orientation toward the sun, which affected how much sunlight fell on the poles. In 1600 or so, temperatures gradually started to rise, before increasing rapidly over the past 60 years. During that period, water column temperatures, averaged from the surface to 670 metres, increased by 0.18°C per year – 15 times faster than they have at any period in the past 10,000 years.
‘We may have underestimated the efficiency of the oceans as a storehouse for heat and energy,’ said the study’s lead author, Yair Rosenthal, a climate scientist at Rutgers University in New Jersey. ‘It may buy us some time – how much time, I don’t really know – but it’s not going to stop climate change.’
This story was published in the December 2013 edition of Geographical Magazine