The Arctic ice is melting into Nordic Seas but the Gulf Stream remains

Mosaic of images of the Arctic by MODIS on the Aqua satellite. 

Credit: NASA

The melting ice in the Arctic is not the source of reduced saline in Nordic Seas.

It is the Gulf Stream that has provided less salt.

A new study published Sunday in Nature Geoscience claims; the source of fresher Nordic Seas, since 1950, is rooted in the saline Atlantic, as opposed to an influx of Arctic freshwater, dispelling the common inference.

"This is an important finding as it shows that the Gulf Stream is not about to short circuit. A halting Gulf Stream has been a concern with ongoing climate change; its collapse was taken to the extreme in the Hollywood blockbuster The Day After Tomorrow," says Tor Eldevik, professor in oceanography at the University of Bergen and the Bjerknes Centre.

Reversing the chain of events
The Nordic Seas have freshened substantially since 1950. At the same time, there has been observed an increased river runoff and net ice melting in the Arctic.

The concurrence of a less saline ocean and Arctic freshwater input has given the climate research community reason for concern.

"It has been a concern that a layer of Arctic freshwater could impede the Gulf Stream's Arctic branch."

"Going back in time, into and through the ice ages, such a freshwater lid has been understood to reduce ocean circulation and thus the Gulf Stream's poleward heat transport," says Tor Eldevik.

Eldevik is co-author of the study where Mirjam Glessmer and colleagues at the Bjerknes Centre in Bergen, Norway, show that change in the Nordic Seas is at the receiving end of change in the more global climate system.

Southern freshwater
The researchers from the Bjerknes Centre have analysed the available observations back to 1950 and conclude that the changing salt content in the Nordic Seas is explained by the variable salinity of the Gulf Stream's Arctic branch entering the seas from the south.

The mode of operation is also realised in a numerical ocean model forced by the observed stated of the atmosphere during the period in question.

Although not part of the present study, it appears to be several reasons for the freshening of the Atlantic source waters.

A dominant explanation is a general increase in net precipitation over the North Atlantic Ocean (which may very well relate to global climate change).

The contribution is spread over the Gulf Stream system, and accordingly transported further northward.

The analysis of Glessmer and colleagues further shows, and in line with the above, that the salt deficit in the Nordic Seas is not related to a surface layer of freshwater.

The low-salinity anomaly since 1950 is distributed throughout the water column following the Gulf Stream's northern overturning from warm surface flow to cold deep water.

Potential for climate prediction
The study has important practical implications.

The Bjerknes Centre is presently developing the Norwegian Climate Prediction Model, with the aim of establishing a Norwegian operational system for climate prediction on seasonal to decadal time scale.

"Our study documents how large-scale changes in our marine climate propagate with the extension of the Gulf Stream into the Nordic Seas."

"This suggests that the marine climate could be predictable on the time scale that a climate signal is travelling north," concludes Tor Eldevik.

More information: Glessmer, M.S., T. Eldevik, K. Våge, J.E.Ø. Nilsen, and E. Behrens, 2014: "Atlantic origin of observed and modelled freshwater anomalies in the Nordic Seas." Advance online publication Nature Geoscience, dx.doi.org/10.1038/ngeo2259

Sun's energy influences 1,000 years of natural climate variability

This is a composite created from three images received from MODIS instruments carried on NASA's Terra and Aqua polar orbiting satellites. 

The images were received at the Dundee Satellite Receiving Station at 1151, 1205 and 1342 UTC on 7th Jan. 2010. 

Credit: NASA

Changes in the sun's energy output may have led to marked natural climate change in Europe over the last 1000 years, according to researchers at Cardiff University.

Scientists studied seafloor sediments to determine how the temperature of the North Atlantic and its localised atmospheric circulation had altered.

Warm surface waters flowing across the North Atlantic, an extension of the Gulf Stream, and warm westerly winds are responsible for the relatively mild climate of Europe, especially in winter.

Slight changes in the transport of heat associated with these systems can led to regional climate variability, and the study findings matched historic accounts of climate change, including the notoriously severe winters of the 16th and 18th centuries which pre-date global industrialisation.

The study found that changes in the Sun's activity can have a considerable impact on the ocean-atmospheric dynamics in the North Atlantic, with potential effects on regional climate.

Predictions suggest a prolonged period of low sun activity over the next few decades, but any associated natural temperature changes will be much smaller than those created by human carbon dioxide emissions, say researchers.

The study, led by Cardiff University scientists, in collaboration with colleagues at the University of Bern, is published today in the journal Nature Geoscience.

Paola Moffa-Sanchez

Dr Paola Moffa-Sanchez, lead author from Cardiff University School of Earth and Ocean Sciences, explained: "We used seafloor sediments taken from south of Iceland to study changes in the warm surface ocean current."

"This was done by analysing the chemical composition of fossilised microorganisms that had once lived in the surface of the ocean."

"These measurements were then used to reconstruct the seawater temperature and the salinity of this key ocean current over the past 1000 years."

The results of these analyses revealed large and abrupt temperature and salinity changes in the north-flowing warm current on time-scales of several decades to centuries.

Cold ocean conditions were found to match periods of low solar energy output, corresponding to intervals of low sunspot activity observed on the surface of the sun.

Using a physics-based climate model, the authors were able to test the response of the ocean to changes in the solar output and found similar results to the data.

Ian Hall

"By using the climate model it was also possible to explore how the changes in solar output affected the surface circulation of the Atlantic Ocean," said Prof Ian Hall, a co-author of the study.

"The circulation of the surface of the Atlantic Ocean is typically tightly linked to changes in the wind patterns."

"Analysis of the atmosphere component in the climate model revealed that during periods of solar minima there was a high-pressure system located west of the British Isles."

"This feature is often referred to as atmospheric blocking, and it is called this because it blocks the warm westerly winds diverting them and allowing cold Arctic air to flow south bringing harsh winters to Europe, such as those recently experienced in 2010 and 2013."

The study concludes that although the temperature changes expected from future solar activity are much smaller than the warming from human carbon dioxide emissions, regional climate variability associated with the effects of solar output on the ocean and atmosphere should be taken into account when making future climate projections.

More information: Solar forcing of North Atlantic surface temperature and salinity over the past millennium, Nature Geoscience, DOI: 10.1038/ngeo2094

Nasa: Gulf Stream around North America

This NASA image shows the Gulf Stream around North America.

It is taken from Perpetual Ocean, a visualisation of some of the world's surface ocean currents from June 2005 through December 2007.

Picture: NASA/Reuters

NASA Earth Observatory: Atlantic Heat Source for Hurricane Irene

As Hurricane Irene rumbles through the Atlantic Ocean, it needs fuel to sustain itself.

Warm water is the main fuel, and there is plenty of it right now, as there usually is this time of year.

The map above shows sea surface temperatures (SST) in the Atlantic Ocean, Gulf of Mexico, and the Caribbean Sea on August 23, 2011.

The measurements come from the Advanced Microwave Scanning Radiometer (AMSR-E) on NASA’s Aqua satellite and the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on both the Terra and Aqua satellites.

The satellites measure the temperature of the top millimeter of the ocean.

Waters typically need to be above 27.8 degrees Celsius (82 Fahrenheit) to properly fuel tropical storms with warm, moist air. Red, orange, and yellow colors depict waters above the 27.8 degree mark.

The warmer the water, the more intense the storm can grow, if upper level wind patterns cooperate. In the map above, such waters dominate the Gulf of Mexico and tropical Atlantic in late August 2011.

They also run up the southeastern coast of the United States, following the Gulf Stream to Cape Hatteras before giving way to slightly cooler waters (shades of blue) in the Middle and North Atlantic.

As of 5 p.m. Eastern Daylight Time on August 24, 2011, the NOAA National Hurricane Center reported Irene had maximum sustained winds of 195 kilometers (120 miles) per hour and was located at 23.1 degrees North and 74.7 degrees West, about 45 kilometers (30 miles) east-southeast of Long Island in the Bahamas.

The forecasted path had the hurricane sweeping over nearly all Bahaman islands, then turning toward the North Carolina coast and eventually New England. Forecasts are updated roughly every six hours.

Irene is the first hurricane of the Atlantic season, and potentially the first to make landfall in the United States in several years.


Further Reading

1. National Hurricane Center. (2011, August 24). Hurricane Irene. National Weather Service. Accessed August 24, 2011.
2. NASA Earth Observatory. (n.d.). Global Maps: Sea Surface Temperature. Accessed August 24, 2011.

Gulf of Mexico Oil Spill: Loop Current and the Gulf Stream

This Envisat image shows the Straits of Florida, the area where the Loop Current flows eastward out of the Gulf of Mexico (visible west of Florida) before joining the Gulf Stream and flowing along the eastern coastlines of the US and Newfoundland.

This image was acquired by Envisat’s Medium Resolution Imaging Spectrometer (MERIS) on 1 April 2010 at a resolution of 300 m.

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Credits: ESA