New study on climate history: Arctic sea ice influenced force of the Gulf Stream

from the Alfred-Wegener-Institut

Bremerhaven, 15 August 2014. The force of the Gulf Stream was significantly influenced by the sea ice situation in the Fram Strait in the past 30,000 years. Scientists at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) come to this conclusion in a new study that appears today in the journal Earth and Planetary Science Letters. On the basis of biomarkers in deposits on the seafloor, the geologists involved managed for the first time to reconstruct when and how the marine region between Greenland and Svalbard was covered with ice in the past and in what way the Gulf Stream reacted when the sea ice cover suddenly broke up. They concluded that when large amounts of Arctic ice drifted through the Fram Strait to the North Atlantic, the heat transport of the Gulf Stream declined noticeably.

For AWI geologist Juliane Müller the Fram Strait is a key region in the global oceanic circulation. “On the east side of this passage between Greenland and Svalbard warm Atlantic water flows to the north into the Arctic Ocean while on the west side cold Arctic water masses and sea ice push their way out of the Arctic into the North Atlantic. A considerable portion of the Atlantic water cools here on its way to the north and sinks to deeper layers. The circulation of the water caused in this manner drives the global band of oceanic currents like a giant pump and influences, among other things, how much heat the Gulf Stream transports towards Europe,” says the scientist.

If the pulse frequency of this circulation pump changes, this gives rise to direct changes in the climate – for instance, at the end of the past glacial period and during the transition to our present-day interglacial. “In the past 30,000 years the Gulf Stream has lost an extraordinary amount of force at least twice – once 17,600 years ago and about 12,800 years ago. Both times the climate in Europe consequently cooled down significantly – and now we also know why,” says Juliane Müller.

She and her AWI colleague Ruediger Stein were the first scientists to succeed in reconstructing the sea ice conditions in the Fram Strait for this critical period at the end of the last glacial and thus in finding a direct connection between changes in sea ice cover and fluctuations in the Gulf Stream.

A nine metre long sediment core served as a window into the past for the geologists. It was drilled on a Fram Strait expedition conducted on the research vessel Maria. S. Merian and has such clearly defined layers that the scientists can read it like a book. “This core stems from the western continental slope of Svalbard, a region with an unusually high sedimentation rate. That means a very large number of sediment particles – the stores of climate information – trickle to the seafloor. This is the only explanation for the fact that we find the climate data from five to ten years over a length of one centimetre in this core while it could easily be as many as 1,000 years per centimetre of sediment sample in cores from low-particle regions. And, of course, 1,000 years are much too long a period to be able to clearly identify short-term climate fluctuations at all,” explains Juliane Müller.

Two kinds of fossil molecules, also designated as biomarkers, served as indications of the existence and the duration of an ice cover for Juliane Müller. One kind is produced by diatoms living in the sea ice, the other by algae that prefer the open water. “The markers provide us with astonishing insights into the climate history of the Fram Strait. For instance, we now know that a thick ice cover did not form until after the actual high point of the last glacial period. However, it held for around 1,000 years and influenced the oceanic currents in the North Atlantic on a long-term basis,” says Juliane Müller.

The reason for this is that the ice cover delayed the breakup of the large ice sheets that covered large sections of Europe and North America at that time. “The sea ice stabilised the glacier fronts of these ice sheets like a dam wall and prevented icebergs from calving. Export of freshwater from the Arctic to the North Atlantic, which otherwise would have been enormous, was thus checked for a certain time,” explains the geologist.

When the ice cover then broke up within an extremely short time 17,600 years ago, tremendous ice masses poured into the North Atlantic. There they melted and released large volumes of freshwater. “This sudden freshening of the North Atlantic altered the density structure of the water and led to significant weakening of the Atlantic overturning circulation, or to put it more simply, to weakening of the Gulf Stream,” says Juliane Müller.

According to the study, a similar chain reaction occurred yet another time during the Younger Dryas around 12,800 years ago when enormous amounts of sea ice again left the Arctic moving towards the North Atlantic and heat transport via the Gulf Stream declined. “The results of our study show how important Arctic sea ice is for the global oceanic circulation and that sudden changes in the sea ice cover of the Arctic Ocean is directly connected with abrupt climate fluctuations,” says the AWI scientist.

She will now provide the newly obtained data to AWI’s climate modellers. “With the help of these specific data we can check how reliably our models depict the sea ice situation of the past 30,000 years. In this way the data from the past help us to improve our models and consequently enable us to make more precise statements on the future of the Gulf Stream,” states Juliane Müller.

Notes for Editors:

Original study: Juliane Müller / Ruediger Stein: High-resolution record of late glacial and deglacial sea ice changes in Fram Strait corroborates ice-ocean interaction during abrupt climate shifts. Earth and Planetary Science Letters, Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2014.07.016

Your scientific contact person at the Alfred Wegener Institute is: Dr Juliane Müller (e-mail: Juliane.Mueller@awi.de ; phone +49 471 288-2224); Sina Löschke, Dept. of Communications and Media Relations, is available for further questions (phone +49 471 4831-2008; e-mail: medien(at)awi.de).

http://www.awi.de/en/news/press_releases/detail/item/fram_strait_sea_ice_conditions_triggered_the_power_of_the_gulf_stream/

Robert Spielhagen: 2,000 year water temperature high underlines Arctic threat

2,000 year water temperature high underlines Arctic threat

by andyextance, Simple Climate, January 29, 2011

The water flowing from the Atlantic Ocean into the Arctic through the Fram Strait is warmer today than any time in the past 2,000 years. That's what microscopic seabed deposits have told Robert Spielhagen of the Academy of Sciences, Humanities, and Literature in Mainz, Germany, and his colleagues. The scientists have shown that the average temperature of water flowing into the Arctic since 1890 is 2 ºC higher than it has been on average in the previous two millennia. This sends a stark message about the prospects for the Northern polar region. “I am afraid that my children – now 14 and 17 years old – will be able to see a summer ice-free Arctic Ocean,” Spielhagen told Simple Climate.

On August 4, 2007, Spielhagen and his co-workers extracted the key deposits when they drilled a 46-cm-long cylinder of rock from the sea bed. Such “sediment cores” had previously been used to look at temperature changes as far as 12,000 years into the past, but could only provide measurements for periods of a few hundred years at a time. That's down to how much sediment settles to the sea bed, with too little deposition for high-resolution temperature measurements occurring where cores have been taken before. By contrast, Spielhagen's team was able to give temperatures on a scale of 2–3 decades at a time. “We took our core in a place where a lot of fine-grained particles settle, due to diminished bottom currents,” he explained. “We were the first to find such a spot.”

Microscopic photo of the coarse fraction -- particles greater than 0.1 mm -- of a sample from the team's sediment core. White grains are the foraminifers used for the study published in Science. Image courtesy of Kirstin Werner (IFM-GEOMAR, Kiel).

The key element needed to determine temperature within the deposits are the shells of single-celled animals called foraminiferas. Together with researchers from the US, Norway and Germany, Spielhagen investigated the shells in two different ways. “Method one uses the various species of foraminifers in the sediment,” the scientist explained. “There is only one species which prefers very cold water, from –2 ºC to +2 ºC, and several species which live in warmer waters.” Comparing the percentages of different species in the sample can give historical temperature values. The second method uses the ratio of the elements magnesium and calcium in foraminifera shells, which is directly linked to temperature.

Method	Pre-1850 minimum temperature (°C)	Pre-1850 average temperature (°C)	Pre-1850 maximum temperature (°C)	Post 1890 minimum temperature (°C)	Post 1890 average temperature (°C)	Post 1890 maximum temperature (°C)
1	2.8	3.4	4.4	4.1	5.2	6
2	N/A	3.6	N/A	4.4	5.8	7.1

The team found that the proportion of foraminifer species typically found in warmer water in the sample has seen an “unprecedented increase” at the location they sampled in the past 120 years. Spielhagen admitted that the corresponding rate of temperature increase that they reported in top journal Science on Friday was unexpected. “Publications about the dramatic atmospheric temperature increase in the Arctic made me expect that we should find something similar for the ocean waters,” he said. “I was somewhat surprised, however, how strong the temperature increase in the last 100–120 years was, according to our data.”

Bathymetric map of the Norwegian-Greenland Sea and Arctic Ocean (base map: www.ibcao.org). White shading marks average summer sea ice cover. White arrows mark ice drift directions. Red arrows mark the transport path of warm Atlantic water entering the Arctic where it submerges under the cold, ice-covered surface layer. The yellow spot marks the site the sediment core used in the study was taken from. Image courtesy of Robert Spielhagen (IFM-GEOMAR, Kiel)

Historical ocean temperatures at the sample site measured by Spielhagen's team. The upper graph is produced using the SIMMAX method, based on comparing the numbers of different species of foraminifera. The lower graph is produced by comparing the amounts of the elements magnesium (Mg) and calcium (Ca) in the foraminifera shells, which is proportional to temperature. Courtesy of Robert Spielhagen (IFM-GEOMAR, Kiel).

While such efforts to reconstruct historical temperatures can attract a lot of scepticism, Spielhagen asserted that his findings are robust. “The results from both methods are very similar,” Spielhagen underlined. “The very good correspondence make us very confident about the data. The methods we have applied for our records are well established and have been found to give very reliable results in many different ocean basins.”

These findings were published just a week after measurements showing that the proportion of the year in which the Greenland ice sheet was melting rather than freezing in 2010 was a record 50 days longer than average. Spielhagen emphasized that warmer water flowing into the Arctic could be contributing to this. “Warm water releases heat to the atmosphere,” he explained. “The warmer and stronger the transport of Atlantic Water to the Arctic is, the more heat may be released to the Arctic atmosphere and distributed there – potentially also reaching Greenland.”

http://simpleclimate.wordpress.com/2011/01/29/2000-year-water-temperature-high-underlines-arctic-threat/

Shell Oil seems to be losing its own unscientific push-poll on Scientific American

The world's demand for energy continues to grow due to population growth and improving standards of living. At the same time, the days of "easy oil and gas" are over. Until now, the focus has been to discover new resources from increasingly challenging reservoirs and locations. Yet existing reservoirs typically yield only 30-35% of their potential.

What do you see as the main benefit of using enhanced oil recovery (EOR) techniques?

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Please share your thoughts in the comment section below.

Click on a region to discover what other people around the world are thinking.

Link: http://www.scientificamerican.com/sponsored/energyforthefuture/index.cfm?id=poll-4&WT.mc_id=SA_shell_p4_300x100ros_n

Temperatures of North Atlantic “are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming”

Temperatures of North Atlantic “are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming” — Science

The 3.5 °F warming of Fram Strait water over the past century is "not just the latest in a series of natural multidecadal oscillations."

by Joseph Romm, Climate Progress, January 27, 2011

Study after study finds recent warming is unprecedented in magnitude and speed and cause.  The anti-science crowd keeps trying to debunk one or two old Hockey Sticks, but new ones crop up faster than a speeding puck.

Science just published a new one, “Enhanced Modern Heat Transfer to the Arctic by Warm Atlantic Water” (subs. req’d), news release here, “Warming North Atlantic water tied to heating Arctic, according to new study.”

I have pulled out the key graph — and it is one heck of a Hockey Stick.  It is derived from “planktic foraminifers in a sediment core”:

Temperature reconstructions of upper Atlantic Water in the eastern Fram Strait over the past ~2100 years

Thin lines are raw data, bold lines are three-point running means….  (C) Summer temperatures at 50-m water depth (red)….  Gray bars mark averages until 1835 CE and 1890 to 2007 CE. Blue line is the normalized Atlantic Water core temperature (AWCT) record … from the Arctic Ocean (1895 to 2002; 6-year averages)….  (D) Summer temperatures (purple) [calculated with a different method]

This astonishing warming in the past century is clearly not, as the anti-science crowd likes to say, some sort of recovery from the so-called Little Ice Age (see “A detailed look at the Little Ice Age“), which, in any case, is barely noticeable in this data.   The lead author, Robert Spielhagen of the Leibniz Institute of Marine Sciences, said, “Such a warming of the Atlantic water in the Fram Strait is significantly different from all climate variations in the last 2,000 years.”  The fact is, over 90% of human-caused warming is going into the oceans — and it is melting ice wherever it goes (see “Deep ocean heat is rapidly melting Antarctic ice“).

Air temperatures in Greenland have risen roughly 7 °F in the past several decades, thought to be due primarily to an increase in Earth’s greenhouse gases, according to CU-Boulder scientists. 

“We must assume that the accelerated decrease of the Arctic sea ice cover and the warming of the ocean and atmosphere of the Arctic measured in recent decades are in part related to an increased heat transfer from the Atlantic,” said Spielhagen.

Here are the abstract and conclusion:

The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water [AW] is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79 °N). We find that early–21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming... 

Although we cannot quantify from our data the variability of previous AW inflow to the Arctic by volume, our temperature data series and the above observational link suggest that the modern warm AW inflow (averaged over two to three decades) is anomalous and unique in the past 2000 years and not just the latest in a series of natural multidecadal oscillations. Both effects — a temperature rise as well as a volume transport increase — introduce a larger heat input into the Arctic Ocean. Although there is no direct contact of the AAWL [Arctic Atlantic Water Layer] with the ocean surface in the Arctic, such an increased heat input has far-reaching consequences. The strong AW warming event in the Arctic Ocean in the 1990s caused a shoaling of the AW core and an enhanced heat flux to the surface , concurrent with decreasing sea ice. Recent oceanographic data from the Laptev Sea continental margin indicate the impact of warm AW-related water masses on the shallow (<50 m) shelf, a feature not observed before in a >80-year time series. The data also provide evidence for a significant heat flux to the overlying shelf waters. Even without any modification of the vertical heat transfer processes, the enhanced temperature contrast between the AW and the surface sea water freezing point (increased from ~5 to 7 K as identified here) leads to an increase in the vertical heat flux of ~40%. Any positive-feedback mechanism will magnify the effect of this flux increase on the ice cover. Complementing the strong feedback between ice and atmospheric temperatures, warming of the AW layer, unprecedented in the past 2000 years, is most likely another key element in the transition toward a future ice-free Arctic Ocean.

In September 2010, a first-of-its-kind analysis by an international team of 18 top scientists found “less ice covers the Arctic today than at any time in recent geologic history” and this ice loss is “unexplainable by any of the known natural variabilities.”

In November 2010, Rear Admiral David Titley, the Oceanographer of the Navy and the Director of Navy’s Task Force Climate Change, told Congress, “the volume of ice as of last September has never been lower…in the last several thousand years.”

Arctic sea ice is in the last legs of its death spiral.

Using different data proxies for Arctic temperature itself (rather than the water entering the Arctic), the National Center for Atmospheric Research (NCAR), came to a roughly similar conclusion two years ago (see Human-caused Arctic warming overtakes 2,000 years of natural cooling, “seminal” study finds):

Arctic temperatures in the 1990s reached their warmest level of any decade in at least 2,000 years, new research indicates. The study, which incorporates geologic records and computer simulations, provides new evidence that the Arctic would be cooling if not for greenhouse gas emissions that are overpowering natural climate patterns.

As with a pride of lions, and a delusion of disinformers, perhaps the grouping should get its own name, like “a team of hockey sticks” (see “The Curious Case of the Hockey Stick that Didn’t Disappear“).

1. GRL:  “We conclude that the 20th century warming of the incoming intermediate North Atlantic water has had no equivalent during the last thousand years.“
2. JGR:  “The last decades of the past millennium are characterized again by warm temperatures that seem to be unprecedented in the context of the last 1600 years.”
3. The Geophysical Research Letters paper, “Twentieth century warming in deep waters of the Gulf of St. Lawrence: A unique feature of the last millennium” concludes: “irrespective of the precise mechanisms responsible for the temperature variations reconstructed from core MD99‐2220, it is unquestionable that the last century has been marked there by a warming trend having no equivalent over the last millennium.”

The bottom line is that:

The rate of human-driven warming in the last century has exceeded the rate of the underlying natural trend by more than a factor of 10, possibly much more.  And warming this century on our current path of unrestricted greenhouse gas emissions is projected to cause a rate of warming that is another factor of 5 or more greater than that of the last century.  We are punching the climate beast — and she ain’t happy about it!

Link:  http://climateprogress.org/2011/01/27/science-temperatures-atlantic-water-arctic-unprecedented-2000-years-linked-to-arctic-amplification-of-global-warming/

Arcti Sea ice arches at the northern end of the Fram Strait permit thickest multi-year ice to flow out, creating a positive feedback loop

Ice arches and positive feedback

by Graham Cogley, environmentalresearchweb.org, March 8, 2010

The shrinking extent of sea ice in the Arctic has been a cause of concern for some decades, and the record low extent measured with passive-microwave radiometers in September 2007 gathered a good deal of publicity. The September minimum was 7.11 million km2 on average during 1979-1998. In 2007 it was 4.30 million km2. The two minima since then have each been greater. 2008 saw the second lowest and 2009 the third lowest extent.

You can check out the state of Arctic sea ice at the National Snow and Ice Data Center in Boulder, Colorado. Thus far during the present winter, 2009-2010, the extent has been tracking pretty closely the course followed in 2007, so two successive years of increased minimum annual extent do not justify us in concluding that the ice pack might be recovering. Equally, there is no sign of an impending catastrophe at the top of the world, but we would still like to understand why 2007 was a record-breaker. There have been several interesting attempts to explain it.

A particularly interesting attempt by Ron Kwok and colleagues appeared last month. They focus on a detail of the bigger picture, the outflow of sea ice through Nares Strait, the narrow gap between northwest Greenland and Ellesmere Island. To put this study in context, we need to step up from thinking about sea-ice extent to thinking about sea-ice mass.

Very roughly, the ice is 3 m thick on average, for a total mass each average September of about 19 million gigatonnes (but only 12 million Gt in 2007). The mass of the ice pack is the result of a balance between freezing, melting and export. The exported bergs and floes eventually melt, but not within the Arctic Ocean.

Most of the export, about 2000 Gt/yr, is through Fram Strait, between Greenland and Svalbard. Of the other possible outlets, the channels between the islands of the Canadian arctic archipelago contribute little. Apart from being narrow, they are most often blocked at their northward ends by plugs or “arches” of immobile ice. The arches form during the winter and persist until the end of summer, so that for much of the year there is effectively no southward ice export.

Kwok and colleagues found that no arch formed in 2007 at Nares Strait, which was therefore an open passageway for the full 365 days. Between 1998 and 2006, the open-channel state prevailed for only 140 to 230 days per year. From 2004 to 2006, when ice thickness measurements are available from the ICESat laser altimeter, the mass export was about 80-85 Gt/yr, but in 2007 it was 230 Gt/yr.

Why worry about such tiny amounts? The export through Nares Strait in 2007 was only 10% of that through Fram Strait, and insignificant in comparison with the total mass of the pack. The answer is that the ice in the Lincoln Sea, just north of Nares Strait, is some of the thickest, at about 5 m on average, in the whole Arctic Ocean.

The decline of Arctic sea ice is usually discussed in terms of its extent, but that is mainly because we have lots of information about extent. Measurements of thickness are harder to come by, and therefore so are estimates of total mass (area times thickness, multiplied by 900 kg m-3, the density of ice). But one of our main concerns about Arctic sea ice is that apart from shrinking in extent it is also getting thinner.

The impact on ice extent of the free evacuation of thick Lincoln Sea ice in 2007 was small, but it depleted the thick end of the frequency distribution of ice thickness. An ice pack with relatively more thin ice is less likely to survive the summer melt season, so the non-formation of ice arches in Nares Strait constitutes a positive feedback, magnifying the vulnerability of the ice pack as a whole. And it may be a positive feedback in another sense. Presumably arching, that is, blockage, is more likely when the supply of thick chunks of ice is greater. If an episode of free outflow decreases that supply, future episodes of free outflow become more probable.

Link: http://environmentalresearchweb.org/blog/2010/03/ice-arches-and-positive-feedba.html