Tag Archives: Atlantic

Weakening Gulf Stream may disrupt world weather

The Gulf Stream is growing feebler, the Arctic seas are gaining fresh water. Together they could affect the world’s weather.

LONDON, 2 March, 2021 − The Atlantic Conveyer, otherwise the Gulf Stream − that great flow of surface water pouring northwards that overturns in the Arctic and heads south again at great depth − is now weaker than at any point in the last 1,000 years, European scientists report.

And in a second, separate but related study, researchers have found that the Beaufort Sea, in the Arctic, has gained two-fifths more fresh water in the last 20 years: water that could flow into the Atlantic to affect the Conveyor, and with it, climatic conditions.

Scientists call it the Atlantic Meridional Overturning Circulation or just AMOC. Europeans know it as the Gulf Stream: the current that conveys tropic warmth to their coasts and keeps Britain and Western Europe at a temperature several degrees higher than latitude alone might dictate.

And for years, oceanographers and climate scientists have been observing a slowing of the flow, by as much as 15%. But direct measurement of the great current began only relatively recently in 2004: researchers needed to know whether the slowdown was part of a natural cycle, or a consequence of climate change driven by global heating.

Now they know a little more. European researchers report in Nature Geoscience that they looked for evidence of ocean circulation shifts in what they call “proxy evidence”: the story of climate change told by tree growth rings, ice cores, ocean sediments, corals and historical records, including naval logbooks.

The combined evidence of temperature patterns, the sizes of particles of ocean floor sediment and the salinity and density of sub-surface water helps build up a picture of the Atlantic current for the last 1,600 years.

“The Gulf Stream System moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow”

The verdict? Up to the 19th century, ocean currents were stable. The flow is now more sluggish than at any time in the last millennium.

This is roughly what climate models have predicted: the warm salty water moves north, cools, becomes more dense, sinks to the deep and flows back south. But the Arctic has begun to warm, Greenland to melt, and the flow of fresh water into the northern seas to intensify.

Since the flow is driven by the difference in temperatures, any change in the regional thermometer will play back into the rate of flow. And any extra arrival of fresh water could further slow the overturning circulation.

“The Gulf Stream system works like a giant conveyor belt, carrying warm surface water from the equator up north, and sending cold, low-salinity deep water back down south. It moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow,” said Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research, in Germany, one of the authors.

“For the first time, we have combined a range of previous studies and found they provide a consistent picture of the AMOC evolution over the past 1600 years. The study results suggest that it has been relatively stable until the late 19th century.

“With the end of the Little Ice Age in about 1850, the ocean currents began to decline, with a second, more drastic decline following since the mid-20th century.”

Outcome awaited

The change could have ominous consequences for European weather systems: it could also deliver more intense coastal flooding to the US eastern seaboard. If the current continues to weaken, the consequences could be catastrophic.

Which is why a new study in Nature Communications matters so much. US researchers tracked the flow of fresh water from the Beaufort Sea − melt water from glaciers, rivers and disappearing Arctic sea ice − through the Canadian Archipelago and into the Labrador Sea.

Arctic water is fresher than Atlantic water, and richer in nutrients. But this extra volume, measured at a total of 23,300 cubic kilometres, could also affect the rate of flow of the overturning circulation. That is because relatively fresh water is less dense than saline water, and tends to float on top.

Quite what role it could play is uncertain: the message is that, sooner or later, it will escape into the North Atlantic. Then the world will find out.

“People have already spent a lot of time studying why the Beaufort Sea fresh water has gotten so high in the past few decades,” said Jiaxu Zhang,  of the Los Alamos National Laboratory, first author. “But they rarely care where the freshwater goes, and we think that’s a much more important problem.” − Climate News Network

The Gulf Stream is growing feebler, the Arctic seas are gaining fresh water. Together they could affect the world’s weather.

LONDON, 2 March, 2021 − The Atlantic Conveyer, otherwise the Gulf Stream − that great flow of surface water pouring northwards that overturns in the Arctic and heads south again at great depth − is now weaker than at any point in the last 1,000 years, European scientists report.

And in a second, separate but related study, researchers have found that the Beaufort Sea, in the Arctic, has gained two-fifths more fresh water in the last 20 years: water that could flow into the Atlantic to affect the Conveyor, and with it, climatic conditions.

Scientists call it the Atlantic Meridional Overturning Circulation or just AMOC. Europeans know it as the Gulf Stream: the current that conveys tropic warmth to their coasts and keeps Britain and Western Europe at a temperature several degrees higher than latitude alone might dictate.

And for years, oceanographers and climate scientists have been observing a slowing of the flow, by as much as 15%. But direct measurement of the great current began only relatively recently in 2004: researchers needed to know whether the slowdown was part of a natural cycle, or a consequence of climate change driven by global heating.

Now they know a little more. European researchers report in Nature Geoscience that they looked for evidence of ocean circulation shifts in what they call “proxy evidence”: the story of climate change told by tree growth rings, ice cores, ocean sediments, corals and historical records, including naval logbooks.

The combined evidence of temperature patterns, the sizes of particles of ocean floor sediment and the salinity and density of sub-surface water helps build up a picture of the Atlantic current for the last 1,600 years.

“The Gulf Stream System moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow”

The verdict? Up to the 19th century, ocean currents were stable. The flow is now more sluggish than at any time in the last millennium.

This is roughly what climate models have predicted: the warm salty water moves north, cools, becomes more dense, sinks to the deep and flows back south. But the Arctic has begun to warm, Greenland to melt, and the flow of fresh water into the northern seas to intensify.

Since the flow is driven by the difference in temperatures, any change in the regional thermometer will play back into the rate of flow. And any extra arrival of fresh water could further slow the overturning circulation.

“The Gulf Stream system works like a giant conveyor belt, carrying warm surface water from the equator up north, and sending cold, low-salinity deep water back down south. It moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow,” said Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research, in Germany, one of the authors.

“For the first time, we have combined a range of previous studies and found they provide a consistent picture of the AMOC evolution over the past 1600 years. The study results suggest that it has been relatively stable until the late 19th century.

“With the end of the Little Ice Age in about 1850, the ocean currents began to decline, with a second, more drastic decline following since the mid-20th century.”

Outcome awaited

The change could have ominous consequences for European weather systems: it could also deliver more intense coastal flooding to the US eastern seaboard. If the current continues to weaken, the consequences could be catastrophic.

Which is why a new study in Nature Communications matters so much. US researchers tracked the flow of fresh water from the Beaufort Sea − melt water from glaciers, rivers and disappearing Arctic sea ice − through the Canadian Archipelago and into the Labrador Sea.

Arctic water is fresher than Atlantic water, and richer in nutrients. But this extra volume, measured at a total of 23,300 cubic kilometres, could also affect the rate of flow of the overturning circulation. That is because relatively fresh water is less dense than saline water, and tends to float on top.

Quite what role it could play is uncertain: the message is that, sooner or later, it will escape into the North Atlantic. Then the world will find out.

“People have already spent a lot of time studying why the Beaufort Sea fresh water has gotten so high in the past few decades,” said Jiaxu Zhang,  of the Los Alamos National Laboratory, first author. “But they rarely care where the freshwater goes, and we think that’s a much more important problem.” − Climate News Network

Warmer Atlantic widens invader’s hunting ground

The exotic lionfish, already a long way from the reefs of its Indo-Pacific home, is heading further north up the US coast as global warming causes big changes to ocean habitats. LONDON, 28 September, 2014 − The venomous lionfish is on the move. This invasive species has been observed in deeper waters off the North Carolina coast since the turn of the century, but new research suggests it may now be expanding its range into the shallower levels. Since the lionfish (Pterois volitans) is actually native to the Indo-Pacific region, it is already a long way from home. But what now gives it licence to hunt further north is warmer sea temperature. Global warming has already begun to make huge differences to ocean habitat. The bluefin tuna is a temperate zone fish that has already been observed in Arctic waters off the coast of Greenland, and commercial species such as red mullet, a creature of the Mediterranean, has been seen in the North Sea and even in Norwegian waters. Now researchers in the US have reported that the lionfish – an invader first observed off the Florida coast in the 1980s − is spreading through the north-west Atlantic. Temperature is the key determinant for a fish on the move. Fisheries biologist Paula Whitfield, of the National Oceanic and Atmospheric Administration’s National Centres for Coastal Ocean Science, and colleagues report in the journal Marine Ecology Progress Series that they surveyed 40 species of fish off the reefs of North Carolina.

Tropical species

These reefs have always been home both to temperate and tropical species, at the limits of their ranges. But now the reefs are becoming more tropical − and so is the local population. “Along the North Carolina coast, warming water temperatures may allow the expansion of tropical fish species, such as lionfish, into areas that were previously uninhabitable due to cold winter temperatures,” Whitfield says. “The temperature thresholds collected in this study will allow us to detect and estimate fish community changes related to water temperature.” The lionfish tends to prefer water warmer than 15.2°C, and so normally inhabits the warm currents of the deeper waters in the temperate Atlantic. It is a carnivore that seems to enjoy a wide range of prey. It makes itself at home in a wide variety of habitat, and is considered a serious threat to other species of reef fish. – Climate News Network

The exotic lionfish, already a long way from the reefs of its Indo-Pacific home, is heading further north up the US coast as global warming causes big changes to ocean habitats. LONDON, 28 September, 2014 − The venomous lionfish is on the move. This invasive species has been observed in deeper waters off the North Carolina coast since the turn of the century, but new research suggests it may now be expanding its range into the shallower levels. Since the lionfish (Pterois volitans) is actually native to the Indo-Pacific region, it is already a long way from home. But what now gives it licence to hunt further north is warmer sea temperature. Global warming has already begun to make huge differences to ocean habitat. The bluefin tuna is a temperate zone fish that has already been observed in Arctic waters off the coast of Greenland, and commercial species such as red mullet, a creature of the Mediterranean, has been seen in the North Sea and even in Norwegian waters. Now researchers in the US have reported that the lionfish – an invader first observed off the Florida coast in the 1980s − is spreading through the north-west Atlantic. Temperature is the key determinant for a fish on the move. Fisheries biologist Paula Whitfield, of the National Oceanic and Atmospheric Administration’s National Centres for Coastal Ocean Science, and colleagues report in the journal Marine Ecology Progress Series that they surveyed 40 species of fish off the reefs of North Carolina.

Tropical species

These reefs have always been home both to temperate and tropical species, at the limits of their ranges. But now the reefs are becoming more tropical − and so is the local population. “Along the North Carolina coast, warming water temperatures may allow the expansion of tropical fish species, such as lionfish, into areas that were previously uninhabitable due to cold winter temperatures,” Whitfield says. “The temperature thresholds collected in this study will allow us to detect and estimate fish community changes related to water temperature.” The lionfish tends to prefer water warmer than 15.2°C, and so normally inhabits the warm currents of the deeper waters in the temperate Atlantic. It is a carnivore that seems to enjoy a wide range of prey. It makes itself at home in a wide variety of habitat, and is considered a serious threat to other species of reef fish. – Climate News Network