Atlantic Ocean Capable of Dramatic Changes by Joshua S Hill

Scientists have long assumed that the long-lasting and severe cold spells in Europe that have taken place since the Last Glacial Maximum some 10,000 to 20,000 years ago have been the result of changes in the circulation of the Atlantic Ocean currents.

New research led by Cardiff University has now shown that ocean circulation changes may have been even more dramatic than previously assumed.

The new findings, which have been published in the latest edition of the journal Science, show that since the end of the Last Glacial Maximum the formation of deep water in the North-East Atlantic Ocean has repeatedly switched on and off, causing the climate to warm and cool for centuries at a time.

“We retrieved ocean sediment cores from the seafloor of the Northeast Atlantic which contained the shells of small organisms,” said lead author Dr David Thornalley, Cardiff School of Earth and Ocean Sciences, in explaining how the scientists studied changes in ocean circulation. “We used these shells to examine the past distribution of radiocarbon in the ocean. Radiocarbon is a radioactive form of carbon that acts like a natural stopwatch, timing how long it has been since water was last at the sea surface. This allows us to determine how quickly deep water was forming in the Northeast Atlantic at different times in the past.”

Deep water is the result of water cooling, increasing the density of the water and causing it to drop to deeper levels of the ocean. As part of the Great Conveyor Belt of the oceans, this sends cooler water down south and allows the warmer tropical waters to move north, affecting the atmospheric temperatures over Europe.

The team of scientists led by Thornalley found that each time deep water formation turned off, the North-East Atlantic did not fill with water that sank locally, but rather filled with water that had originally formed near Antarctica in the Southern Ocean which then spread rapidly northward.

These results show that the Atlantic Ocean is capable of radical changes in a very short amount of time, as small as a few decades.

“These insights highlight just how dynamic and sensitive ocean circulation can be,” said Dr Thornalley. “Whilst the circulation of the modern ocean is probably much more stable than it was at the end of the last Ice Age, and therefore much less likely to undergo such dramatic changes, it is important that we keep developing our understanding of the climate system and how it responds when given a push.”

From Cardiff.ac.uk 

Gulf Stream: Charting the Chaotic Current That Warms Norway

 

Chaotic: A spaghetti plot shows the trajectories of the drifting buoys. (Credit: Illustration: POLEWARD)

The North Atlantic Current -- popularly known as the Gulf Stream -- warms Norway and Northern Europe. It is the chaos of the seas that warms the country, researchers have discovered. If its waters flowed smoothly north along the Norwegian coastline, the current would deliver far less warmth.

Norway is situated at the same high northern latitude as Greenland, Northern Canada and Northern Siberia, but thanks to the Gulf Stream, its climate is significantly more temperate.

If the Norwegian branch of the North Atlantic Current flowed evenly, it would surge past Norway at a speed approaching one metre per second, roughly as fast as many rivers run. At that rate, the waters would need only 60 days or so to travel the length of Norway's mainland and reach Svalbard. This would mean that less of the current's heat would be transferred to the atmosphere, resulting in a substantially colder climate for Norway.

In the research project POLEWARD: A drifter experiment to quantify the poleward transport, transformation and spreading of oceanic properties, scientists have discovered that the current takes more than 500 days to flow past Norway, giving the waters more time to release their heat and warm up the country. The project received funding from the research programme on Climate Change and Impacts in Norway (NORKLIMA) at the Research Council of Norway.

Using buoys to chart the current

By deploying 150 marine buoys tracked by satellite, the POLEWARD project researchers were able to chart in detail how the current flows northward along the Norwegian coast.

The buoys revealed that the current often travels quickly, but because it is so irregular and thus highly variable -- indeed, chaotic may be the best description -- the Gulf Stream's journey takes perhaps as much as ten times longer than it would if it flowed smoothly. In this way there is time for the warm ocean current to convey a vastly greater proportion of its heat into the atmosphere, from which the warm air is carried on the predominantly westerly winds towards mainland Norway.

Read more @ ScienceDaily.com 

Ocean Currents and Climate Change

Ocean and atmosphere are inextricably linked. As global climate change alters wind, precipitation and temperature patterns worldwide, ocean currents will reflect these changes in often unpredictable ways. For example, increasing wind speeds arising from larger land-ocean temperature differences may drive stronger upwelling which will change near shore ecosystems and may cause hypoxic dead zones  

in some areas. Another key factor that influences ocean currents is the density of seawater. Both temperature and salinity contribute to seawater density, thus local changes in temperature and the magnitude of freshwater inputs from rivers and streams can alter near shore ocean currents.

Read more @ PISCO