Warm-water discharge into Beaufort Sea from Mackenzie River corresponds to melting Arctic sea ice

Warm rivers play role in Arctic sea ice melt

These images show sea surface temperatures of the Beaufort Sea where Canada's Mackenzie River discharges into the Arctic Ocean, as measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra spacecraft.  Photo: NASA. Click on image to enlarge.

ScienceDaily, March 5, 2014

The heat from warm river waters draining into the Arctic Ocean is contributing to the melting of Arctic sea ice each summer, a new NASA study finds.

A research team led by Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, Calif., used satellite data to measure the surface temperature of the waters discharging from a Canadian river into the icy Beaufort Sea during the summer of 2012. They observed a sudden influx of warm river waters into the sea that rapidly warmed the surface layers of the ocean, enhancing the melting of sea ice. A paper describing the study is now published online in the journal Geophysical Research Letters.

This Arctic process contrasts starkly with those that occur in Antarctica, a frozen continent without any large rivers. The sea ice cover in the Southern Ocean surrounding Antarctica has been relatively stable, while Arctic sea ice has been declining rapidly over the past decade.

"River discharge is a key factor contributing to the high sensitivity of Arctic sea ice to climate change," said Nghiem. "We found that rivers are effective conveyers of heat across immense watersheds in the Northern Hemisphere. These watersheds undergo continental warming in summertime, unleashing an enormous amount of energy into the Arctic Ocean, and enhancing sea ice melt. You don't have this in Antarctica."

The team said the impacts of these warm river waters are increasing due to three factors. First, the overall volume of water discharged from rivers into the Arctic Ocean has increased. Second, rivers are getting warmer as their watersheds (drainage basins) heat up. And third, Arctic sea ice cover is becoming thinner and more fragmented, making it more vulnerable to rapid melt. In addition, as river heating contributes to earlier and greater loss of the Arctic's reflective sea ice cover in summer, the amount of solar heat absorbed into the ocean increases, causing even more sea ice to melt.

To demonstrate the extensive intrusion of warm Arctic river waters onto the Arctic sea surface, the team selected the Mackenzie River in western Canada. They chose the summer of 2012 because that year holds the record for the smallest total extent of sea ice measured across the Arctic in the more than 30 years that satellites have been making observations.

The researchers used data from satellite microwave sensors to examine the extent of sea ice in the study area from 1979 to 2012 and compared it to reports of Mackenzie River discharge. "Within this period, we found the record largest extent of open water in the Beaufort Sea occurred in 1998, which corresponds to the year of record high discharge from the river," noted co-author Ignatius Rigor of the University of Washington in Seattle.

The team analyzed data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite to examine sea ice patterns and sea surface temperatures in the Beaufort Sea. They observed that on June 14, 2012, a stretch of landfast sea ice (sea ice that is stuck to the coastline) formed a barrier that held the river discharge close to its delta. After the river water broke through the ice barrier, sometime between June 14 and July 5, the team saw that the average surface temperature of the area of open water increased by 11.7 degrees Fahrenheit (6.5 degrees Celsius).

"When the Mackenzie River's water is held back behind the sea ice barrier, it accumulates and gets warmer later in the summer," said Nghiem. "So when it breaks through the barrier, it's like a strong surge, unleashing warmer waters into the Arctic Ocean that are very effective at melting sea ice. Without this ice barrier, the warm river waters would trickle out little by little, and there would be more time for the heat to dissipate to the atmosphere and to the cooler, deeper ocean."

"If you have an ice cube and drop a few water droplets on it, you're not going to see rapid melt," said co-author Dorothy Hall of NASA's Goddard Space Flight Center in Greenbelt, Md. "But if you pour a pitcher of warm water on the ice cube, it will appear to get smaller before your eyes. When warm river water surges onto sea ice, the ice melts rapidly."

Nghiem's team has linked this sea ice barrier, which forms recurrently and persistently in this area, to the physical characteristics of the shallow ocean continental shelf, and concludes the seafloor plays a role in delaying river discharge by holding the barrier in place along the shore of the Mackenzie delta.

The team estimated the heating power carried by the discharge of the 72 rivers in North America, Europe and Asia that flow into the Arctic Ocean. Based on published research of their average annual river discharge, and assuming an average summer river water temperature of around 41 degrees Fahrenheit (5 degrees Celsius), they calculated that the rivers are carrying as much heat into the Arctic Ocean each year as all of the electric energy used by the state of California in 50 years at today's consumption rate.

While MODIS can accurately measure sea surface temperature where rivers discharge warm waters into the Arctic Ocean, researchers currently lack reliable field measurements of subsurface temperatures across the mouths of river channels. Nghiem said more studies are needed to establish water temperature readings in Arctic-draining rivers to further understand their contribution to sea ice melt.

NASA monitors Earth's vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better understand how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

For more information about NASA's Earth science activities in 2014, visit: http://www.nasa.gov/earthrightnow . For information on the latest NASA Earth science findings, visit: http://www.nasa.gov/earth .

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Story Source:

The above story is based on materials provided by NASA/Jet Propulsion Laboratory. The original article was written by Maria-Jose Vinas. Note: Materials may be edited for content and length.

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Journal Reference:

1. S. V. Nghiem, D. K. Hall, I. G. Rigor, P. Li, G. Neumann. Effects of Mackenzie River discharge and bathymetry on sea ice in the Beaufort Sea. Geophysical Research Letters, 2014; DOI: 10.1002/2013GL058956

http://www.sciencedaily.com/releases/2014/03/140305134019.htm

Benjamin Rabe et al., Deep Sea Research Part I: Ocean. Res. Papers, 58 (2), An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006–2008 period

Deep Sea Research Part I: Oceanographic Research Papers, Vol. 58, No. 2, pp. 173-185 (February 2011) 


An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006–2008 period
Benjamin Rabe, Michael Karcher, Ursula Schauer, John M. Toole, Richard A. Krishfield, Sergey Pisarev, Frank Kauker, Rüdiger Gerdes and Takashi Kikuchi


Abstract


Unprecedented summer-season sampling of the Arctic Ocean during the period 2006–2008 makes possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins. In comparison to observations from 1992 to 1999, LFW content relative to a salinity of 35 in the layer from the surface to the 34 isohaline increased by 8,400±2,000 km³ in the Arctic Ocean (water depth greater than 500 m). This is close to the annual export of freshwater (liquid and solid) from the Arctic Ocean reported in the literature.

Observations and a model simulation show regional variations in LFW were both due to changes in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a mean freshening of the water column above this depth, associated with an increased net sea ice melt and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a quarter of the salinity contribution, and non-linear effects due to both factors were negligible.

Link to abstract:  http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGB-51PRY50-1&_user=10&_coverDate=02%2F28%2F2011&_rdoc=6&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%236034%232011%23999419997%232888746%23FLA%23display%23Volume)&_cdi=6034&_sort=d&_docanchor=&_ct=8&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b66a96c384b5ac1306e5c4033d0f79e3&searchtype=a

NOAA issues Arctic report, cites ‘drastic changes’: Loss of sea ice 'messing with that thermostat for the whole globe'

U.S. issues Arctic report, cites ‘drastic changes’

Loss of sea ice 'messing with that thermostat for the whole globe'


msnbc.com staff and news service reports, October 22, 2009

WASHINGTON (AP) -- Federal scientists on Thursday issued their annual "Arctic Report Card," citing "consistent evidence" of warming in three key indicators: the atmosphere, sea ice and Greenland's ice sheet.

"The Arctic we see today is very different from the Arctic we saw even five years ago," Jackie Richter-Menge, the report’s chief technical editor, said in a statement. "It’s a warmer place with less thick and more mobile sea ice, warmer and fresher ocean water, and increased stress on caribou, reindeer, polar bears and walrus in some regions."

The Obama administration was quick to echo the findings. "Scientists are seeing drastic changes in the region from just five years ago and at rates faster than anticipated," the National Oceanic and Atmospheric Administration said in a statement accompanying the report card.

Richard Spinrad, head of research at NOAA, said the report shows that warming temperatures are changing wind patterns in the Arctic, melting sea ice and glaciers, and affecting ocean and land life.

The Arctic is a sort of natural regulator in terms of the amount of heat stored in the ocean and ice, Spinrad told reporters, and "especially the loss of sea ice is messing with that thermostat for the whole globe."

A particular problem is the disappearance of old, thick sea ice that has been present for thousands of years, added James Overland of NOAA's Pacific Marine Environmental Research Laboratory. "It's very difficult to get that (ice) back," he said.

Among the findings of the update:

• Air temperatures over the Arctic Ocean reached an unprecedented 7 °F above normal in October-December of 2008.
• There is evidence that the higher air temperatures are causing changes in the air circulation in both the Arctic and northern mid-latitudes.
• The area covered by sea ice this summer was 25% below the average from 1979 to 2000 and was the third lowest since satellite records were begun in 1979.
• The melting ice resulted in an unprecedented amount of fresh water in the surface layer of the Arctic Ocean.
• "Record-setting summer temperatures around Greenland" led to further melt of the ice sheet.
• The amount of land covered by snow in the winters of 2007-2008 and 2008-2009 continued the trend toward shorter snow seasons due to earlier spring melt, although there is considerable annual and regional variability.

The Arctic Report Card has been issued annually since 2006.

The 2009 report card cited "many indications of warming" for the three other tracked indicators: wildlife biology, the ocean and land.

Link to AP article:   http://www.msnbc.msn.com/id/33437613/ns/us_news-environment/

Robert Dickson: New techniques for observing the Arctic Ocean circulation and its freshwater budget

Nuuk Climate Days 2009: Changes of the Greenland Cryosphere Workshop & The Arctic Freshwater Budget International Symposium, Nuuk, Greenland, 25-27 August 2009

Primary author: DICKSON, Robert (CEFAS, Lowestoft), r.r.dickson@cefas.co.uk

Abstract ID: O8

New techniques for observing the Arctic Ocean circulation and its freshwater budget

In one way or another, the two-way influences of global climate on the Arctic, and of the Arctic on global climate, center on its ice and freshwater budget. As the Arctic sea-ice declines, climate models anticipate regional effects on the atmospheric circulation (e.g. through changes in albedo and ocean-atmosphere heat exchange); and since the pioneering work of Bryan and Manabe in the 1980s, we have come to expect remote effects also, as a changing freshwater efflux from the Arctic reaches south to affect the Atlantic thermohaline circulation. That said, however, it remains true that climate models are inherently weak in quite a long list of the processes that are important to our understanding of how change takes place in northern seas and how it might affect climate. And the fact that the Arctic-subarctic system is both under-sampled and rapidly-changing is also problematic when establishing freshwater budgets; put simply, the large variability in the supply, storage and transfer of freshwater throughout this system may prevent us from discriminating inconsistency from change in our estimates.

After a brief recap of a representative freshwater budget for the Arctic and of how climate models expect the freshwater delivery to the Arctic to change, this talk concentrates on five areas where our understanding of the freshwater budget and the processes important to it appear to have been materially advanced during recent years, including but not necessarily restricted to the IPY. These include: (1) new ideas on the behaviour of the greatest oceanic freshwater reservoir on Earth (Proshutinsky, Toole); (2) new intricate ideas on ocean-climate feedback processes along the Arctic margin of the Beaufort and Chukchi seas as the land-fast ice thins and breaks free (Shimada); (3) new ice-thickness techniques in support of sea ice prediction (Laxon/Giles,  Wadhams, Gascard); (4) a new and practical approach to monitoring the freshwater flux through the Canadian Arctic Archipelago by combining observations with models (Prinsenberg, Peterson); and (5) new direct observations of the freshwater flux passing south through the Fram Strait (de Steur et al., Rabe et al.). Such a diverse set of examples serves to illustrate the broad front over which progress is needed -- and is being made -- in developing our understanding of these processes, their changes, their feedbacks and their likely climatic impacts to the point where they can be of practical use to the development of climate models. Meanwhile, in many cases, we are still in the process of exploration.

Contact for symposium information: Sune Nordentoft Lauritsen, e-mail: snl@space.dtu.dk