Like tree rings and ice cores, the annual growth rings in deep sea gorgonian corals can tell us about the past environment, and are a new and dependable source of data about the deep ocean.
Dr Owen Sherwood, a biogeochemist and lead author of a new study spoke to The Earth Times today, 'Traditionally sediment cores have been used to infer climatological changes in the open ocean, but the records can be smeared by the actions of burrowing creatures and other marine organisms so you don't know if a layer was deposited in 1890 or 1990.'
Published in the journal PNAS, Sherwood, a Canadian, and a multinational team are the first to use nitrogen isotopes of amino acids present in the annual growth rings of corals to reveal details of the climate at the surface and of the prevailing ocean currents at the time.
The team collected samples of fossil and living corals using an underwater robot vehicle, and also from fishermen
Every living creature, animal and plant absorbs natural chemical isotopes with their food and incorporates them into body tissues such as leaves, bone or coral skeleton. The balance between the different isotopes can tell us what the corals have been eating, and where those nutrients came from and because different water masses in the ocean carry unique isotope signatures we can use the records from the corals to map changes in ocean currents over time, something that was very difficult to do before now.
These currents have a profound effect on climate dictating whether our winters are warm and wet, or cold and dry. The team detected a marked change in the ocean currents off Nova Scotia that began in the 1970's, the first in over 2,000 years of coral records studied. The seventies was when the early effects of climate change began. These changes seem to be linked with a shift in the North Atlantic Oscillation which began in the seventies.
The challenge now is to understand exactly how increased greenhouse gases in the atmosphere could affect deep ocean currents across the whole north Atlantic and what this means for the future climate.
Because the corals capture plant matter falling from above and turn it into their skeletons, through studying the growth rings, the corals can give us a window into the past and because the rings are deposited annually are far more accurate than sediment cores. As Sherwood says, 'Examining both living and fossilised deep sea corals gives us a link between what is happening climactically in the human time scale and what happened in the geological past.'