Freshwater Integration study (FWI) Featured Project:

Assessing the Long-term Contribution of Landfast Ice to the Arctic Freshwater Budget

NSF OPP-0229473 Jan. 2003-Dec. 2005
PIs: Yanling Yu and Harry L. Stern
Polar Science Center, Applied Physics Laboratory, University of Washington

Project Overview | Principal Investigators | Support | Recent Findings | Conclusions

Project Overview

Landfast ice plays a unique role in the land-upper ocean freshwater cycle. Formed in the shallow water along the Arctic coasts, landfast ice can lock up a significant amount of freshwater from river discharge and ice melt, but most of this freshwater will be returned back to the shelves during summer melting. The freshwater stored in landfast ice is comparable to the total annual runoff of the four largest Arctic rivers. As a freshwater "reservoir", landfast ice acts like a rechargeable battery, storing freshwater in winter and releasing it later in summer. It is thus impossible to examine the land-upper ocean freshwater cycle without considering the freeze and thaw of landfast ice and its role and contribution.

The growth and melt of fast ice displays a large interannual variability. Of climatic significance are the year-to-year changes in the storage and the timing of the released fresh water. Recent observations indicate some substantial changes in the Arctic climate. These changes may affect the freshwater exchange between the land and the upper ocean, partly through altering the growth and melting patterns of landfast ice.

Under the Arctic Freshwater Integration study (FWI), funded by NSF, this project will examine the long-term changes in landfast ice and its contribution to the arctic freshwater budget. By modeling fast ice thickness and integrating these results with a 26-year record of landfast ice extent observation, this study will examine the basin-wide changes in landfast ice cover, including ice coverage, growth/melt, brine flux, and freshwater storage. To relate the results to the Arctic climate variability, the study will also compare the changes in fast ice with different Arctic climate variables.

Project Goals:

Examine the interannual fluctuation of landfast ice extent for the whole Arctic Basin;
Investigate the spatial and temporal changes in fast ice growth and melt as well as brine flux due to ice formation;
Analyze the long-term changes in fast ice volume in terms of freshwater storage by landfast ice in response to the Arctic climate variations, such as changes in snowfall, surface air temperature, wind, and major river discharge.
Integrate our research activities with university summer undergraduate program and get involved with student's learning process.

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Principal Investigators
		Yanling Yu Polar Science Center, Applied Physics Laboratory, University of Washington Dr. Yu investigates arctic sea ice and its role in the Arctic climate and ocean circulation. Analyzing submarine observations, she and her colleagues examine the long-term changes in mean ice thickness and its distribution. She also uses dynamic and thermodynamic models and statistic methods to search for clues as to why some changes have occurred and how these changes can be characterized in both space and time. She has developed an algorithm to derive arctic thin ice thickness by combining a thermodynamic sea ice model with the satellite observations from Advanced Very High Resolution Radiometer (AVHRR) imagery. This algorithm can be used to study the aggregated sea ice properties dependent on thin ice thickness distribution, such as brine flux from growing young ice and large-scale ice strength. Under the NSF funded Arctic Freshwater Integration study (FWI), Dr. Yu and her colleagues will investigate the interannual variability of arctic landfast ice and its contribution to the freshwater budget on the arctic shelves. She has published several research papers in geophysical journals. She joined PSC after receiving her Ph.D. in Physical Oceanography from the School of Oceanography, University of Washington. Phone: (206) 543-1254; Email: yanling@apl.washington.edu Website: http://psc.apl.washington.edu/pscweb2002/Staff/yu/yu.html
		Harry L. Stern Polar Science Center, Applied Physics Laboratory, University of Washington Harry Stern analyzes satellite data of the Arctic Ocean to study the motion and properties of sea ice. He helped to formulate the Radarsat Geophysical Processor System, and served as chairperson of the Alaska SAR Facility User Working Group for five years. He has been with the Polar Science Center since 1987. Phone: (206) 543-7253; Email: harry@apl.washington.edu Website: http://psc.apl.washington.edu/pscweb2002/Staff/stern/stern.html
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Support

This project is funded by the U.S. National Science Foundation, Office of Polar Programs, Arctic System Science Program (Grant OPP# 0229473, for years 2003-2005).

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Recent Findings

Analysis of weekly ice charts from 1975 to 2003 indicates significant decreases in winter landfast ice extent in the Laptev, Chukchi and Beaufort seas, as well as the Canadian Archipelago. Large declines are also found in the Kara and East Siberian seas, and along the east coast of Greenland. While the Barents Sea and the Sea of Okhotsk show increases in landfast ice extent, the trend for the Northern Hemisphere is significantly negative. The duration of the landfast ice season is significantly shorter in the East Siberian, Chukchi, and Bering seas, but longer in the Barents Sea; season duration for the Northern Hemisphere is slightly negative though insignificant. Several factors may be responsible for the decline of landfast ice, including changes in surface air temperature and atmospheric circulation.

Figure 1 - Map of Landfast Ice Regions

See Table 1 (below) for region labels.
The diamonds indicate 12 coastal weather stations.

Table 1 - Winter Landfast Ice Area and Length of Ice Season, 1975-2003

Annual change is the slope of the least squares line. Total change is the annual change multiplied by 28 years. Standard deviation is computed after removing the trend of the least squares line. Values in bold are significantly different from zero with 95% probability, and values underlined are significant with 99% probability.

Figure 2 - Decline of Landfast Ice in the N. Hemisphere

The figure on the upper left shows the trends in winter landfast ice extent over our 17 regions defined in Table 1. The trend is expressed as percent per decade as the color bar shown below. The regions with a significant change are indicated with flags. This figure shows that the significant decrease occurred in the Laptev, Chukchi and Beaufort seas, as well as the Canadian Archipelago. Large declines are also found in the Kara and East Siberian seas and along the east coast of Greenland.

The figure on the upper right shows the trends in the length of landfast ice season. The rest are the same as in the figure on the upper left. The duration of the landfast ice is significantly shorter in the East Siberian, Chukchi and Bering seas but longer in the Barents Sea.

Figure 3 - Decline of Landfast Ice in the N. Hemisphere

Winter landfast ice extent (top) and duration of landfast ice season (bottom) for the Northern Hemisphere. The red lines are the least-square fit. The figure shows that the area of landfast ice in the N. Hemisphere has declined significantly at a rate of -12,000 km²yr^-1. The season duration is slightly negative though insignificant.

Figure 4 - Decline of Landfast Ice and Changes in Arctic Surface Air Temperature (SAT)

The top figure shows the weekly fast ice extent for the N. Hemisphere. Heavy coastal ice occurred from the late 1970s to the mid-1980s but was light after the 1990. This pattern corresponds well with the warming along the arctic coasts indicated by the averaged Freezing-degree-days (FDD) and Thawing-degree-days (TDD). Over years, the FDD gradually decreased after the 1990, reaching the lowest during the winter of 2002-2003, whereas the TDD remained high after 1989, suggesting prolonged summer and fall seasons in recent years.

Figure 5 - SAT Trends in Spring and Fall

These two figures are from Rigor et al. (J. Climate, 2000). The significant warming trends were observed in spring over most of Arctic (left), but in fall, the changes is more variable in space, with cooling trends observed along the coasts of the Kara and the Barents seas. The coastal warming shown in Fig. 4, therefore, is a part of a broad, long-term warming in the Arctic, driven by the Arctic Oscillation (AO).

Conclusions

The winter landfast ice extent declined significantly in Laptev, Chukchi and Beaufort Seas, as well as the Canadian Archipelago. The trend is significantly negative for the N. Hemisphere;
The largest decrease in the length of fast ice season is observed in the East Siberian, Chukchi and Bering Seas. The changes indicate complicated impacts by regional climate during spring and fall;
The arctic warming likely contributes to the fast ice decline;
The decline of landfast ice is a part of the Arctic climate change that has widely spread around the basin since the 1990s, driven by the Arctic Oscillation;
The decline in landfast ice will profoundly impact coastal ecosystems, commerce and human activities.

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Graphics and text are courtesy of Yanling Yu and Harry Stern of the University of Washington. Material on this page is subject to copyright agreements; please contact Yanling Yu for more information.
You are also encouraged to visit her website: http://psc.apl.washington.edu/pscweb2002/Staff/yu/yu.html

Note to FWI Investigators:
To volunteer to be the next FWI Featured Project, email Jonathan Pundsack at the Arctic-CHAMP Science Management Office. We will Feature a different project every ~3 months. Also, if your project has its own website, please forward the address so we can include that in our links.

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