Huge 20-Year Build up of Arctic Fresh Water May Flood North Atlantic & Stall Gulf Stream

by FishOutOfWater, DailyKos, December 13, 2016



"Figure 3 Time series of freshwater content in different layers of the Beaufort Gyre region. Blue bars depict total liquid freshwater content. Black bars show freshwater content in sea ice. Yellow bars – freshwater content in the mixed layer, red bars – in the Pacific and green bars – in the Atlantic water layer. Freshwater content is shown in thousand cubic kilometers. Upper left bars shows total annual freshwater flux into the Arctic Ocean from all rivers; green and black small bars show errors in liquid and sea ice freshwater content estimates. All freshwater contents are calculated relative to 34.8 reference water salinity." The build up in volume from 2002 to 2015 is about the volume of Lake Michigan which stores 4,918 cubic km of water.

Huge volumes of fresh water have been building up over the past 20 years in the Arctic waters north of Alaska. A volume the size of Lake Michigan built up from 2003 through the end of 2015. Before the 1990s, there were regular cycles of fresh water build up and release within decades as periods of high pressure north of Alaska were followed by periods of stormy weather. Scientists suspect that over the past 20 years large amounts of melt water from Greenland’s glaciers have changed the dynamics of the North Atlantic ocean and the Arctic atmosphere. Since the 1990s, a dome of high pressure has persisted in the Beaufort sea and the anticyclonic winds have pumped fresh water towards the high’s center building up a mound of relatively fresh water over a huge area north of Alaska. The primary source of the fresh water is rivers that flow into the Arctic. Over the past several decades, sea ice melting has added about 20%  to the increase of fresh water in the Beaufort sea.

The freshwater content of the Beaufort gyre  increased by a volume the size of lake Michigan from the 1970s to 2008.

A major 2008 report by a team of scientists led by Wood’s Hole oceanographer Andrey Proshutinsky found an increase of 5000 km3 of fresh water from the 1970s to 2008. www.whoi.edu/…

From 2008 to 2015 an additional 2000 km3 was added so the total increase in fresh water is 7,000km3. The total volume of the world’s second largest lake by volume, Lake Michigan, is just under 5,000km3.

Preliminary data from the BGOS 2008 cruise indicate that the FWCL in the BG continued to rise in 2008 and reached 21,000 km3– a historical maximum from all available years of observations. Compared to 1970s climatology (the pre-90s decade with the most extensive data coverage, (Figure 1) there has been a FWCL increase in the BG of approximately 5,000 km3. This is comparable with the volume of fresh water annually delivered to the Arctic Ocean by rivers and through Bering Strait (5700 km3 per year, Serreze et al., [2006]).

The freshwater layer in the Beaufort sea deepened by 3 meters - about 10 feet from 2003 to 2007. Because the Beaufort gyre covers a large area, this is a huge volume of fresh water. Anticyclonic winds associated with persistent high pressure in 2007 caused Siberian and North American river water and water from a record melt of sea ice in 2007 to flow into this Arctic sea north of Alaska.

The persistent anticyclonic Beaufort high pressure builds up a mound of water under it because the direction of a mass of water moves to the right of the wind  direction in the northern hemisphere because  the rotation of the earth gives the water spin. See this post at Neven’s sea ice blog by an Arctic oceanographer for details. neven1.typepad.com/...

On the other hand, cyclonic rotation associated with low pressure areas causes water to well up from below the center of the low. Thus  years of high pressure followed by  years of storminess cause moderate periodic surges of fresh water from the Arctic to the north Atlantic ocean. It was like the Arctic breathed in fresh water then breathed it out in a period of a decade or less. The largest observed freshwater surge called the “Great Salinity Anomaly” happened in the early 1970’s.

The Great Salinity anomaly was one of the likely causes of the brutal American winters of the 1970s. Fresh water tends to float over denser warm salty Gulf Stream water in sub-Arctic seas of the north Atlantic. This keeps the warm salty water from releasing its heat to the atmosphere and sinking thousands of feet into the deep Atlantic. This disruption of the thermohaline circulation is popularly called slowing down the Gulf Stream. The deep overturning circulation brings Gulf Stream water to the subarctic seas, warming Europe and north America. When deep water formation slows brutal winters tend to follow.  This effect, combined with the reflective effects of growing levels of sulfuric acid pollution over the north Atlantic in the 1960s and 1970s caused cold north American and European winters  in those decades. This cool period that broke up the trend of greenhouse gas caused global warming that has been ongoing since the turn of the twentieth century has been intentionally misinterpreted by climate change deniers to confuse politicians and the public about climate change.

Winters were miserably cold in Minnesota and the central and eastern U.S. in the 1970s.

Last spring, following the extremely abrupt collapse of the winter polar vortex in a sudden stratospheric warming a very intense Beaufort high developed driving more fresh water into the gyre. The strong high pressure in the sunny spring months melted out the ice early. Midwinter high pressure under dark skies is favorable for ice growth but under the bright long sunny days of May the ice melted and the water took up enormous amounts of heat. That warm water then opened up the ice plugged channels between the islands of northernmost Canada. If high pressure breaks down now the thick plugs of multi-year ice that used to block the channels won’t be there to impede the fresh water from draining out to the north Atlantic. The largest channels have a thin ice cover.

Arctic scientists fear that a large volume of the stored fresh water could be rapidly released, drastically impacting the northern hemisphere’s weather. earthobservatory.nasa.gov/...

As I said back in my first blog entry, one of the key objectives of the expedition was to produce an up-to-date assessment of the freshwater content of the Beaufort Gyre. Based on a preliminary analysis of the data collected on this cruise, my colleagues reckon the total freshwater content of the Gyre could be at a record high. A chemical analysis of the ocean surface suggests that sea ice melt contributed around 20 percent of the fresh water mixed up within the surface waters, compared to around 80 percent from Canadian and Russian rivers flowing into the Arctic. The sea ice contribution was thought to be neutral a few decades ago, but the ice is now melting more than it’s growing, as we clearly witnessed, causing an imbalance. The wind circulation is also important in driving the ocean circulation that sucks in fresher surface waters into the Gyre (see an earlier blog of mine for more details).

Why does this all matter? Well, some scientists posited that the Beaufort Gyre oscillates between periods of spinning up and sucking in freshwater, and spinning down and releasing fresh water. A kind of breathing, if you like. The Gyre has been spinning up and sucking in fresh water for a few decades now (2008 saw a big increase) and we keep waiting, with similarly bated breath, for this trend to reverse. If the Gyre does reverse (breathe out), the Arctic Ocean will likely dump a load of fresh water into the Atlantic Ocean (as we think it did in the 1970s), which could cause some big impacts on weather patterns across the Northern Hemisphere. We’re not expecting a scene out of The Day After Tomorrow, but we’re not entirely sure what could happen either.

This dark half of the Arctic year has been by far the warmest to date on record and storms have repeatedly slammed the sea ice to record lows while pulling in heat from both the Atlantic and Pacific oceans. If this stormy weather continues, the fresh water dome will break down and the fresh water rapidly drain towards the north Atlantic through the channels of the Canadian archipelago and through the Fram strait east of northern Greenland.

The weather forecast for the next 10 days by the European model is insane. Deep lows will pull massive amounts of heat into the Arctic, which will keep sea ice extent and volume at record low levels for the date and will work to spin down the currents that keep the dome fresh water in the Beaufort sea.

5 day ECMWF weather forecast shows storms entering the Arctic from both the Atlantic and Pacific. The winds will bring enormous amounts of atmospheric heat, taken from the Atlantic and Pacific oceans, into the Arctic.

The weather pattern developing in the Arctic is the pattern that has drained the fresh water form the Beaufort gyre in the past. Extremely deep lows are moving from the Atlantic into the Arctic. Low pressure is dominating the region from the Atlantic’s subarctic seas to the Arctic ocean. If this pattern continues through this winter, a volume of fresh water greater than lake Michigan could be set in motion towards the north Atlantic and the overturning circulation could stall when the light fresh water caps the Labrador sea. This could cause the Gulf Stream itself to slow while heat would build up in tropical oceans.

Extreme low pressure is forecast by the ECMWF model to cover the Arctic and north Atlantic in 7 days.

Scientists and Arctic observers are shocked by this year’s extraordinarily warm Arctic weather but the sudden release of fresh water to the Atlantic could cause a sudden shift to much colder winter weather towards the end of the decade. This is a very unpredictable situation, but Greenland ice cores show that rapid, extreme climate oscillations may be triggered by north Atlantic salinity cycles. www.atmosp.physics.utoronto.ca/…

We may be entering a period of extreme climate chaos.

http://www.dailykos.com/story/2016/12/13/1610344/-Huge-20-Year-Build-up-of-Arctic-Fresh-Water-May-Flood-North-Atlantic-Stall-Gulf-Stream

Readers, a must-read: The Antarctic Half of the Global Thermohaline Circulation Is Faltering

byFishOutofWaterFollowforOcean Advocates,  Daily Kos, April 10, 2013

The sudden cooling of Europe, triggered by collapse of the global thermohaline circulation in the north Atlantic and the slowing of the Gulf Stream has been popularized by the movies and the media. The southern half of the global thermohaline circulation is as important to global climate but has not been popularized. The global oceans' coldest water, Antarctic bottom water forms in several key spots around Antarctica. The water is so cold and dense that it spreads out along the bottom all of the major ocean basins except the north Atlantic and Arctic. Multiple recent reports provide strong evidence that the formation of Antarctic bottom water has slowed dramatically in response to massive subsurface melting of ice shelves and glaciers. The meltwater is freshening a layer of water found between depths of 50 and 150 meters. This lightened layer is impeding the formation of Antarctic bottom water, causing the Antarctic half of the global thermohaline circulation to falter.

Update from the comments

I have been asked what's going to happen in response to the faltering of the thermohaline circulation around Antarctica. This post is based on a synthesis of very recent research reports. The key report, that found the layer of fresh water between 50 and 150 meters deep, was just published. Deward Hastings explained, in a comment, how disruptive this lens of freshened water could be to the earth's climate system and our models of it:

it IS complicated, and confusing

That lens of (relatively) fresh water that is forming around Antarctica is challenging, and changing, almost everything in global circulation patterns.  It freezes sooner (and at a higher temperature).  That shields the water from the wind, and reduces wind-driven mixing.  It reduces, perhaps to the point of stopping altogether, the present global ocean circulation patterns.  That in turn will change global atmospheric weather.

Nobody knows exactly what comes next.  We've never seen it happen, and our models, not terribly accurate in describing the world we know, are completely untested in the coming world that we don't know.

Without a constant flow of cold water from the poles the Abyss will warm . . . and without cold slowly rising from the Abyss the mid-ocean and ocean surface will warm (already happening).  That will lead to more evaporation (driving a different haline circulation in the tropics) and stronger tropical winds driving different surface currents and greater mixing.

Pretty much everything changes as a result . . . pretty much everywhere.  After it's all over some places will have it better and some worse.  While it's changing everywhere will be worse, because there is no way to know what to expect (except that it won't be what you've prepared for).

The best guesses we can make now about the effects of this melt layer are based on paleoclimatology research. Possible effects, based on paleoclimatology studies, are presented in the last few paragraphs. The results of these new studies will be challenging climate modelers for many years.

Sea ice extent has been increasing around Antarctica. In September 2012, while Arctic sea ice was at record low levels, Antarctic sea ice extent hit a record high. Climate skeptics jumped on the Antarctic record as evidence of cooling, while sea ice researchers blamed it on the wind.

Since the start of the satellite record, total Antarctic sea ice has increased by about 1% per decade. Whether the small overall increase in sea ice extent is a sign of meaningful change in the Antarctic is uncertain because ice extents in the Southern Hemisphere vary considerably from year to year and from place to place around the continent. Considered individually, only the Ross Sea sector had a significant positive trend, while sea ice extent has actually decreased in the Bellingshausen and Amundsen Seas. In short, Antarctic sea ice shows a small positive trend, but large scale variations make the trend very noisy.

NSIDC scientist Ted Scambos said, "Antarctica's changes—in winter, in the sea ice—are due more to wind than to warmth, because the warming does not take much of the sea ice area above the freezing point during winter. Instead, the winds that blow around the continent, the "westerlies," have gotten stronger in response to a stubbornly cold continent, and the warming ocean and land to the north."

Several recent reports, however, paint a more complex and disturbing picture where the intensifying winds are speeding up below surface currents bringing more above freezing water in contact with deep ice around Antarctica. Twenty of the ice shelves and many of the glaciers that feed them are melting from below.

Researchers used 4.5 million measurements made by a laser instrument mounted on NASA’s ICESat satellite to map the changing thickness of almost all the floating ice shelves around Antarctica, revealing the pattern of ice-shelf melt across the continent. Of the 54 ice shelves mapped, 20 are being melted by warm ocean currents, most of which are in West Antarctica.

Figure 2 | Antarctic ice-shelf ice-thickness change rate DT/Dt, 2003–2008.

Seaward of the ice shelves, estimated average sea-floor potential temperatures (in uC) from the World Ocean Circulation Experiment Southern Ocean Atlas (pink to blue) are overlaid on continental-shelf bathymetry (in metres)30 (greyscale, landward of the continental-shelf break, CSB) Grey circles show relative ice losses for ice-sheet drainage basins (outlined in grey) that lost mass between 1992 and 2006 (after ref. 2).

The melting from below is creating a layer of relatively fresh water 50-150 meters below the surface around Antarctica. This layer of light fresh water is floating above a  salty layer below. When ice forms at the surface in the Antarctic winter, it creates cold dense salty water that tends to sink to the bottom, forming bottom water. However, this layer of light melt water is tending to block the water in the top 50 meters from sinking. The area of Antarctic sea ice has expanded because the layer of cold water has stayed on top and expanded outwards instead of sinking. Melting from below has created 2 stratified cold layers in the top 150 meters.

Note the bright pink area in the top 25 meters between 65° and 70° S. This top layer is becoming more saline. Brine is rejected from ice when sea ice forms. It isn't sinking because it is ponding above a freshening layer located at depths between 50 and 150 meters.

The freshened water column around Antarctica has become more stable between depths of 100 and 150 meters. This increasing stability is impeding the formation of Antarctic bottom water. Water that does sink is freshened through incorporation of glacial melt water.

Figure 3.  Austral winter half-year (April–September) zonal mean trends (1985–2010) of observed salinity, vertical density gradient and potential temperature, in the Southern Ocean. a, Salinity. b, Vertical density gradient. c, Potential temperature. Contours indicate the 1985–2010 mean state (psu; kg m^-4, °C). Colouring (bright or faint) indicates whether the trend is significant (yes or no) at p<0:1 65="" 70="" a="" according="" analysis="" and="" based="" between="" brine="" due="" en3="" font="" forms.="" from="" ice="" in="" increase="" is="" likely="" met="" most="" near-surface="" observations.="" observations="" ocean="" office="" on="" rejection="" salinity="" sea="" situ="" sub-surface="" t-test.="" taken="" the="" to="" two-sided="" were="" when="" which="">

Analysis of potential temperatures, which are temperatures adjusted for the effects of increasing pressure with depth, shows the surface water in the top hundred meters is cooling over a vast area from 40°-80° S, while the water in that vast area below 150 meters is warming.

These results show a trend towards reversal of vertical motions around Antarctica. Intermediate water is welling up around Antarctic melting ice from below, creating a freshened layer. Strengthening winds are blowing the cold surface water away from Antarctica. Bottom water formation, caused by the sinking of cold salty water formed by brine rejection, is declining.

The results of this study are confirmed by a detailed study of anthropogenic tracers in the Weddell sea.   Chlorofluorocarbon (CFC) observations showed increasing average ages of the deep water in the sea from 1984–2010. The average age increased because because bottom water formation, and outflow from the Weddell sea, declined.

...we find that all deep water masses in the Weddell Sea have been continually growing older and getting less ventilated during the last 27 years. The decline of the ventilation rate of Weddell Sea Bottom Water (WSBW) and Weddell Sea Deep Water (WSDW) along the Prime Meridian is in the order of 15–21%; the Warm Deep Water (WDW) ventilation rate declined much faster by 33%. About 88–94% of the age increase in WSBW near its source regions (1.8–2.4 years per year) is explained by the age increase of WDW (4.5 years per year). As a consequence of the aging, the anthropogenic Carbon increase in the deep and bottom water formed in the Weddell Sea slowed down by 14–21% over the period of observations.

The decline in Antarctic bottom water formation, combined with the southward expansion of warm subtropical water in the south Pacific and south Indian oceans has led to the rapid heating of intermediate and deep ocean water in the southern hemisphere.

Figure: Ocean Heat Content from 0 to 300 meters (grey), 700 m (blue), and total depth (violet) from ORAS4, as represented by its 5 ensemble members. The time series show monthly anomalies smoothed with a 12-month running mean, with respect to the 1958–1965 base period. Hatching extends over the range of the ensemble members and hence the spread gives a measure of the uncertainty as represented by ORAS4 (which does not cover all sources of uncertainty). The vertical colored bars indicate a two year interval following the volcanic eruptions with a 6 month lead (owing to the 12-month running mean), and the 1997–98 El Niño event again with 6 months on either side. On lower right, the linear slope for a set of global heating rates (W/m2) is given.

A new study of ocean warming has just been published in Geophysical Research Letters by Balmaseda, Trenberth, and Källén (2013).  There are several important conclusions which can be drawn from this paper.

• Completely contrary to the popular contrarian myth, global warming has accelerated, with more overall global warming in the past 15 years than the prior 15 years.  This is because about 90% of overall global warming goes into heating the oceans, and the oceans have been warming dramatically.

• As suspected, much of the 'missing heat' Kevin Trenberth previously talked about has been found in the deep oceans.  Consistent with the results of Nuccitelli et al. (2012), this study finds that 30% of the ocean warming over the past decade has occurred in the deeper oceans below 700 meters, which they note is unprecedented over at least the past half century.

As the earth has warmed in response to the effects of increasing levels of greenhouse gases the southern subtropical belt in the oceans and atmosphere has expanded, tightening the rings of winds and ocean currents around Antarctica. Enormous volumes of warm subtropical water have been added to the southern ocean at depths greater than 300 meters (greater than approximately 1000 feet).

Observed temperature trends in the Indian Ocean present complex patterns that cannot be explained by surface heating alone. The heat storage has apparently increased more in the southern part than in the northern part of the Indian Ocean (Levitus et al. 2005), although this result may be biased by the sparse data coverage, particularly in the south (Harrison & Carson 2007). The strongest warming is found near the subtropical front and extends as deep as 800 m; it is not directly linked to surface heating but rather due to a southward shift of the oceanic gyre circulation and associated thermal structure (Alory et al. 2007).

Another recent detailed study of the water properties of the southern ocean has independently determined that the southern branch of the global thermohaline circulation has slowed dramatically, contributing to a large uptake of heat by the deep southern ocean.

A statistically significant reduction in Antarctic Bottom Water (AABW) volume is quantified between the 1980s and 2000s within the Southern Ocean and along the bottom-most, southern branches of the Meridional Overturning Circulation (MOC). AABW has warmed globally during that time, contributing roughly 10% of the recent total ocean heat uptake. This warming implies a global-scale contraction of AABW.

Rates of change in AABW-related circulation are estimated in most of the world’s deep
ocean basins by finding average rates of volume loss or gain below cold, deep potential temperature (θ) surfaces using all available repeated hydrographic sections. The
Southern Ocean is losing water below θ = 0 °C at a rate of -8.2 (±2.6) × 106 m3 s-1.

The budget calculations and global contraction pattern are consistent with a global scale slowdown of the bottom, southern limb of the MOC.

The slowdown of the southern branch of the thermohaline circulation and the cooling of the surface waters close to Antarctica are enhancing the thermal gradient from the tropics to the pole, speeding up the winds in the Southern Hemisphere. These increases in wind speeds are likely increasing the flow of water from the Pacific to the Atlantic ocean, enhancing the northward flow of water, salt and heat from the south to the north Atlantic. Moreover, the southward movement of the subtropical front allows more flow of the Agulhas current around the south African capes from the Indian ocean to the south Atlantic.

Thus, increased melting of Arctic sea ice may be related to declines in Antarctic bottom water formation. Likewise, the cool Pacific, warm Atlantic pattern causing increased U.S. droughts and storminess in the north Atlantic may be tied to these changes in ocean circulation patterns. Paleoclimate studies have consistently shown oscillations between Antarctic and north Atlantic bottom water formation and between relative coolness around Antarctica and north Atlantic warmth.

The Arctic melt down that is far exceeding model predictions is connected to the slow down in Antarctic bottom water formation. Climate modelers will be challenged to model the connections and the details. The cooling waters around Antarctica, while apparently good news, are not. The rapid melting of the Arctic will be enhanced.

http://www.dailykos.com/story/2013/04/10/1200602/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-Is-Faltering