In the XX century the World’s oceans experienced the strongest over the last 10 thousand years of warming, which led to a change in his circulation. The scientists were able to establish that, after analyzing the fossilized remains of plankton from the bottom of the Iceland basin. In an article published in the journal Geophysical Research Letters, said about the extinction of cold-water plankton in the Northern latitudes of the Atlantic and its replacement by thermophilic species for which started in the middle of the last century, the active inflow of subtropical waters.
The North Atlantic current connects the tropics and the Arctic zone, bringing heat from low to high latitudes. In this sub-polar front separates water of different temperatures: to the North, the Icelandic pool, circulates cold water near-polar latitudes, and to the South the warmer, saltier water of the subtropics. In the twentieth century has observed a warming of the waters and the disruption of ocean circulation in the North Atlantic, but climatologists were not convinced that these changes are associated with anthropogenic activities, and running out of range of natural variability.
Scientists led by Peter Spooner (Peter Spooner) from University College London studied 150 thousand samples of fossil planktonic foraminifera sampled in the North-Eastern part of the Atlantic ocean at the bottom of the Iceland basin. They were able to gather samples that were deposited on the seabed within 10 thousand years — that is almost the entire Holocene.
Oceanographers have identified species of foraminifera, and analyzed the isotopic ratios of nitrogen, oxygen and carbon in the samples to get ideas about the water temperature and the amount of dissolved oxygen in it at different periods of time (in the cool sub-polar water dissolves oxygen, so it is more productive in a warm, subtropical waters).
Scientists have discovered that in the time period from 6000 BC to around 1880 (the date of the end of the little ice age) in the Icelandic basin was dominated by Turborotalita quinqueloba view of plankton preferring cool Subpolar waters. It accounted for at least 40 percent of all types of floating foraminifera. Then its abundance decreased slightly, but he continued to hold a dominant position in the region. However, in the XX century since 1948, the number of Turborotalita quinqueloba began to decline sharply, and its share among all types of plankton has dropped to 15 percent — were replaced with heat-loving Neogloboquadrina incomptaincompta and Globigerinita glutinata. By 2010, only four percent of the plankton in Icelandic pool had on the native inhabitants of the Subpolar latitudes.