It’s All About Fresh Water — Rapid Sea Level Rise Points To Massive Glacial Melt in Antarctica

It’s all about fresh water. In this case, massive freshwater outflows from the vast glaciers covering Antarctica.

This week, a new scientific report published in the Journal Nature found that from 1992 through 2012 freshwater outflow from Antarctica’s massive glaciers exceeded 400 gigatons each year. An immense flood of cold, fresh water. One that helped push sea levels rapidly higher around the Antarctic continent.

But with glacial melt on the rise and with mountains of ice now inexorably sliding seaward, these freshwater flows may just be the start of even more powerful outbursts to come. And such prospective future events have far-ranging implications for sea level rise, global weather, sea ice, human-caused climate change, and world ocean health.

Flood of Fresh Water Drives More Sea Level Rise Than Expected

The researchers discovered the tell-tale signature of this vast freshwater flood through chemical analysis of the seas surrounding Antarctica. The analysis pointed to a broad and expanding fresh water layer over-riding a warmer, saltier current issuing in from the Southern Ocean.

Since fresh water is less dense than salt water, the freshwater layer expands at the ocean surface causing sea levels to rise more rapidly. Meanwhile, the heating of the deep ocean surrounding Antarctica is thought to result in additional thermal expansion of the water column.

The researchers note:

On the basis of the model simulations, we conclude that this sea-level rise is almost entirely related to steric adjustment [changes that effect atomic spacing], rather than changes in local ocean mass, with a halosteric [salt based] rise in the upper ocean and thermosteric [heat based] contributions at depth. We estimate that an excess freshwater input of 430 ± 230 Gt yr−1 is required to explain the observed sea-level rise. We conclude that accelerating discharge from the Antarctic Ice Sheet has had a pronounced and widespread impact on the adjacent subpolar seas over the past two decades.

Antarctic Sea level Trend

(Rate of sea level rise in the seas surrounding Antarctica since 1992. Aggregate sea level rise is indicated in black. Individual seas data is broken out by color. Image source: Nature.)

Previously, increased rates of sea level rise surrounding Antarctica were thought to have been set off by increasing winds around the continent. The winds were thought to push more water up against the ice faces forming a kind of perpetual, low-grade storm surge. But the current finding provides strong evidence that the source of the sea level rise is due to less dense fresh water over-topping saltier waters flowing in from the Southern Ocean combined with increasing heat along the Antarctic sea bed. And, notably, this is not the first study to find increasing freshwater flows spilling into the Southern Ocean. Last year, a KNMI expedition uncovered similar results.

More Evidence of Large-Scale Melt

The study comes on the back of other recent findings showing that warm water invasion at Antarctic glacier bases had led to more rapid than expected melt and destabilization. In May, two NASA studies showed that a broad section of West Antarctica had destabilized and was sliding at an ever more rapid pace toward the ocean (see reports here and here). These findings held stark implications for global sea level rise as large ice regions of Greenland and West Antarctica, containing enough water to raise seas at least 15 feet, are likely already in a state of irreversible collapse.

 

Regional Anomaly Sea level Antarctic

(Sea level rise anomaly of the region surrounding Antarctica compared with the rest of the Southern Ocean. Red indicates faster than normal sea level rise. Blue indicates slower than normal sea level rise. Image source: Nature.)

This intensifying glacial melt and associated freshwater cap expanding out from the pole has implications — not just for sea level rise, but for sea ice, weather, and world ocean system health.

Impacts For Sea Ice

Large outflows of glacial fresh water may well be involved in the recent observed expansion of sea ice in the zone surrounding Antarctica (see recent related study). Fresh water serves as an insulative cap on the ocean surface preventing warm water from entering the top layer from below. The warm, salty water, in the Antarctic instead pools near the bottom or at the base of the great ice sheets.

Fresh water also freezes at a higher temperature than salt water. So sea ice in an expanding freshwater zone around Antarctica would have naturally higher resiliency even to the rising temperatures now occurring due to human-caused warming. Eventually, however, human heat forcing would overwhelm the ice, but not before a period of related, localized negative feedbacks.

The Iceberg Cooling Effect

The fresh water is a haven for sunlight-reflecting sea ice. It is interspersed with ice bergs from the glacial discharge and the large ice bergs cool the surrounding air. The fresh water layer prevents warm water upwelling from the warm, deep waters surrounding Antarctica. And the leading edge of the fresh water would drive salt-water down-welling along its advancing front. This would push warmer waters toward the ocean bottom, resulting in a kind of heat sink. And this is exactly the kind of dynamic that appears to be ongoing in the Southern Ocean now. These combined impacts are what is known as the ice berg cooling effect associated with large-scale glacial outbursts known as Heinrich Events. And we may well be in the process of setting off one of these geological scale nightmares.

20121230_iceberg_cooling_effect_Hansen_Sato

(Iceberg cooling effect under a mid-range warming scenario when global climate models were set to include the effects of large freshwater outflows from polar glaciers at a fast enough rate to raise seas by 60 cm through 2060 and 144 cm through 2080 [left frames]. Note the cooler zones in the Southern Ocean and North Atlantic adjacent to Greenland. Right frames include mid range emissions/warming scenarios and IPCC projected rates of sea level rise. It is worth noting that the amplifying effects of potential additional ghg release from the global climate system, particularly from Arctic and world ocean carbon stores, are not included in these simulations. Image source: Hansen and Sato.)

For global weather, such events have major implications. Regional cooling in the zone of freshwater outflow would juxtapose regional warming in the southern hemisphere meridional zones. This temperature differential would increase with the strength of the fresh water outflow and the rising intensity of the human-driven warming. The result would be a powerfully intensified storm track. Both the intensified storm track and increased atmospheric moisture loading due to human warming would result in much more powerful weather events than we are currently used to and the potential for catastrophic storms would drastically increase.

Amplifying Feedbacks and a Blow to World Ocean Health

Lastly, the expanding flood of fresh water would result in an increasing stratification of the world ocean system. This stratification would drive warm, salty water toward the ocean bottom and deplete already low oxygen reserves in that region. In addition, the extra heat is more likely to destabilize deep-sea clathrates — releasing methane which will speed in the oxygen depletion of the abyssal waters even as it tips the world ocean system to stop storing carbon and to begin releasing it. A combined feedback that is both an ocean killer and an amplifier to the already extraordinarily powerful human heat forcing mechanism.

Links:

Rapid Sea Level Rise Along Antarctic Margins Due to Increasing Glacial Discharge

Important Role For Ocean Warming and Enhanced Ice Shelf Melt in Sea Ice Expansion

Update on Greenland Ice Sheet Mass Loss: Exponential?

Grim News From NASA: West Antarctica’s Entire Flank is Collapsing

Nature: Human-Destabilized Antarctica Capable of Glacial Outbursts Contributing to Up to 14 Feet of Sea Level Rise Per Century

 

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Record Canadian Floodwaters Flow into Region of Arctic Ocean Radically Altered by Climate Change

Canadian Floodwaters Hit Mackenzie Delta

(Image source: NASA/Lance-Modis)

A record flood that inundated large regions of Canada last week is now sending a large pulse of silty water out through the Mackenzie Delta and into the Beaufort Sea. The pulse of floodwater is so large and bears so much silt that it has painted a wide section of the Arctic Ocean near the Mackenzie Delta brown.

You can see this major out-flow and brown coloration in the satellite image above, provided by NASA.

The fresh flood waters coming from the Mackenzie River are much warmer than the Arctic Ocean waters and the sea ice they contact as they push out from the continent. This flush of warmer water enhances sea ice melt even as it causes the local Arctic Ocean to heat up.

Large, warm flows of fresh water during spring and summer often initiate and enhance ice edge melt in the Arctic. They also rejuvenate the Arctic Ocean’s fresh water supply and, when combined with increasing glacial melt, serve to enhance the rate at which sea ice forms during fall and winter. The reason for this is that fresh water forms a protective layer keeping warmer, saltier water away from the ice even as it tends to freeze at a higher temperature than saltier ocean water. It is this combination of factors that is implicated in a temporary increase in sea ice coverage at the South Pole, even as atmospheric and ocean warming advance ice sheet melt there.

Since heat transfer to the Arctic Ocean from the continents via warm floods serves to increase ice melt rates in the summer season and since increasing flows of fresh water from both the continents (snow melt, increased summer storms) and glaciers (increasing rates of ice sheet melt brought on by human-caused warming) serve to enhance ice formation during the winter season, the Arctic is pushed to see-saw between record and rapid melt and rapid refreeze.

That said, an overall accumulation of heat in the Arctic Ocean has resulted in sea ice extent, area and volume decline during all seasons as the ice is unable to recover to past levels during winters. It’s just that the decline rate is fastest and most greatly amplified during summer.

The below graph, provided by Wipneus, displays this summer melt exaggeration:

Sea Ice Volume Losses Wipneus

(Arctic sea ice volume losses with trend lines. Image source: Wipneus)

Note the faster rate of loss during June, July, August, and September when compared to months during other seasons.

New Ocean Circulation Transfers Most Fresh Water to Beaufort

Increasing flows of fresh water via snow, glacial melt, and more rainfall has now met with strange changes to Arctic Ocean currents, wind patterns and circulation that, according to NASA, is both preserving some of the thermohaline circulation in the Arctic and pulling more fresh water into the Canada Basin and Beaufort Sea.

A visual presentation of these changes is provided by NASA below:

In its press release, NASA noted:

The transpolar drift (purple arrows) is a dominant circulation feature in the Arctic Ocean that carries freshwater runoff (red arrows) from rivers in Russia across the North Pole and south towards Greenland. Under changing atmospheric conditions, emergent circulation patterns (blue arrows) drive freshwater runoff east towards Canada, resulting in freshening of Arctic water in the Canada Basin (full press release here)…

Knowing the pathways of freshwater is important to understanding global climate because freshwater protects sea ice by helping create a strongly stratified cold layer between the ice and warmer, saltier water below that comes into the Arctic from the Atlantic Ocean. The reduction in freshwater entering the Eurasian Basin resulting from the Arctic Oscillation change could contribute to sea ice declines in that part of the Arctic.

NASA shows how changes in Arctic Ocean circulation have already re-distributed fresh water into the Beaufort Sea in the image below:

Fresh Water, Canada Basin

(Image source: NASA)

Higher concentrations of fresh water in the Beaufort would tend to preserve more sea ice there. Ironically, this ice is vulnerable to late-season melt due to its proximity to the North American Continent and away from the relative cool of Greenland. Higher salt water concentrations running from Greenland to the North Pole to the Laptev and then toward Wrangle Island would tend to enhance early season edge melt there.

Overall, this new distribution of fresh water combined with heat transfer into the Arctic Ocean via the continents makes it difficult to provide a case for long-term ice preservation under a regime of increasing human-caused warming. A fresh water cap near Greenland would have combined with cooler regional temperatures to preserve ice for longer periods there. Instead, we have the more resilient ice placed in close proximity to hot continental land rather than cold Greenland ice. Since these changes have yet to be fully understood, new reports will, hopefully, generate more clarity.

Emerging and amplifying flows of fresh water from both continents and glaciers along with changing Arctic Ocean circulation represent yet one more example of how human fossil fuel emissions are radically altering the Arctic. Though not quite as threatening as increasing releases from Arctic carbon stocks or as directly visible as an increasing number of heatwaves in the Arctic, these new pulses of fresh water, when combined with changing ocean circulation, are driving profound changes to the Arctic environment.

Links:

NASA/Lance-Modis

Wipneus

NASA

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