 |
|
 |
|
||
|
||
|
||
 Home Atmosphere Sea Ice Ocean Land Greenland Biology |
|
|
|
|||||||||||||||||||
| |
Sea Ice Cover J. Richter-Menge1, J. Comiso2, W. Meier3, S. Nghiem4, and D. Perovich1 1ERDC-Cold Regions Research and Engineering Laboratory, Hanover, NH New! Monthly Sea Ice Outlook from SEARCH/Arcus Summary The continued significant reduction in the extent of the summer sea ice cover is a dramatic illustration of the pronounced impact increased global temperatures are having on the Arctic regions. There has also been a significant reduction in the relative amount of older, thicker ice.Extent and thickness Satellite-based passive microwave images of the sea ice cover have provided a reliable tool for continuously monitoring changes in the extent of the Arctic ice cover since 1979. During 2008 the summer minimum ice extent, observed in September, reached 4.7 million km2 (Fig. S1, right panel). While slightly above the record minimum of 4.3 million km2, set just a year earlier in September 2007 (Fig. S1, left panel), the 2008 summer minimum further reinforces the strong negative trend in summertime ice extent observed over the past thirty years. At the record minimum in 2007, extent of the sea ice cover was 39% below the long-term average from 1979 to 2000. A longer time series of sea ice extent, derived primarily from operational sea ice charts produced by national ice centers, suggests that the 2007 September ice extent was 50% lower than conditions in the 1950s to the 1970s (Stroeve et al. 2008). The spatial pattern of the 2008 minimum extent was different than in 2007. The 2007 summer retreat of the ice cover was particularly pronounced in the East Siberian and Laptev Seas, the Beaufort Sea, and the Canadian Archipelago. In 2008, there was less loss in the central Arctic, north of the Chukchi and East Siberian Seas and greater loss in the Beaufort, Laptev and Greenland Seas.
The annual maximum sea ice extent typically occurs in March. In March 2008, the maximum ice extent was 15.2 million km2 (Figure S1, center panel). This marked a second year of slight recovery in winter ice extent from the record minimum of 14.4 million km2 for the period 1979–2008, which was observed in 2006. For comparison, the mean monthly ice extent for March and September, for the period 1979–2008, is 15.6 and 6.7 million km2, respectively. The annual variation of the extent of the Arctic sea ice cover in 2007 and 2008, relative to past years, is shown in Fig. S2. As explained in Comiso et al. (2008), the 2007 Arctic ice cover was comparable to the 2005 ice cover through mid-June but then began a more precipitous decline. In 2008, the rapid decline did not begin until mid-August. Five-year averages from 1980 through 2004 show a general decrease in the Northern Hemisphere sea ice extent throughout the seasonal cycle, with this pattern being especially strong in the late summer and early fall. The 2007 ice extent rebounded with a rapid early autumn growth, albeit with an exceptionally slow recovery in the Chukchi and Barents Seas. By early November 2007, the ice extent conditions were comparable to those observed in recent years, while remaining well below the long-term (1979–2007) average.
Figure S3 shows the time series of the anomaly in ice extent in March and September for the period 1979–2008. Both winter and summer have a negative trend in extent: –2.8% decade–1 for March and –11.1% decade–1 for September. The seasonality of the observed ice retreat, with a great rate of reduction of the summer extent versus winter extent, is consistent with model projections (e.g. Stroeve et al, 2007).
Ice thickness is intrinsically more difficult to monitor. With satellite-based techniques (Laxon et al. 2003; Kwok et al. 2004, 2007) only recently introduced, observations have been spatially and temporally limited. This said available data from a variety of sources consistently indicate a net thinning of the Arctic sea ice cover. Data from submarine-based observations indicate that over the period of available records, 1975 to 2000, the annual mean thickness of the ice cover declined from a peak of 3.71 m in 1980 to a minimum of 2.46 m in 2000, a decrease of 1.25 m (Rothrock et al. 2008). Satellite-derived estimates of sea-ice age and thickness, combined to produce a proxy ice thickness record for 1982–2007, also indicate the ice has thinned significantly between 1982 and 2007 (Maslanik et al. 2007). Helicopter-borne and ice-based electromagnetic measurements indicate a reduction of modal and mean sea ice thicknesses in the region of the North Pole of up to 53 and 44%, respectively, between 2001 and 2007 (Haas et al., 2008). In contrast to the central Arctic, measurements of the seasonal and coastal ice cover do not indicate any statistically significant change in thickness in recent decades (Melling et al. 2005; Haas 2004; Polyakov et al. 2003). This observation indicates that the thinning of the ice cover is primarily the result of changes in the characteristics of the perennial ice. Seasonal versus perennial ice
The Arctic sea ice cover is composed of perennial ice (the ice that survives year-round) and seasonal ice (the ice that melts during the summer). Consistent with the diminishing trends in the extent and thickness of the cover is a significant loss of the older, thicker perennial ice in the Arctic (Fig. S4). Data from the NASA QuikSCAT launched in 1999 (Nghiem et al., 2007) and a buoy-based Drift-Age Model (Rigor and Wallace, 2004) indicate that the amount of perennial ice in the March ice cover has decreased from approximately 5.5 to 3.0 million km2 over the period 1958–2007. While there is considerable interannual variability, an overall downward trend in the amount of perennial ice began in the early 1970s. This trend appears to coincide with a general increase in the Arctic-wide, annually averaged surface air temperature, which also begins around 1970 (see Fig. A1). In recent years, the rate of reduction in the amount of older, thicker perennial ice has been increasing, and now very little ice older than 5 yr remains (Maslanik et al. 2007). Many authors have recently acknowledged that a relatively younger, thinner ice cover is more susceptible to the effects of atmospheric and oceanic forcing (e.g. Gascard et al., 2008; Stroeve et al., 2008; Kwok, 2007; Ogi and Wallace, 2007; Maslanik et al., 2007; Serreze et al., 2007; Shimada et al., 2006). In the face of the predictions for continued warming temperatures (Christensen et al., 2007), the persistence of recent atmospheric (Comiso et al., 2008; Kwok, 2008) and oceanic circulation patterns (Steele et al. 2008; Polyakov et al. 2007), and the amplification of these effects through the ice albedo feedback mechanism (Perovich et al., 2008), it is becoming increasingly likely that the Arctic will change from a perennially ice-covered to an ice-free ocean in the summer.References Christensen, J. H., and Coauthors, 2007: Regional climate projections. Climate Change 2007: The Physical Science Basis, S. Solomon, et al., Eds., Cambridge University Press, 847–939. Comiso, J. C., C. L. Parkinson, R. Gersten, and L. Stock, 2008: Accelerated decline in the Arctic sea ice cover. Geophys. Res. Lett., 35, L01703, doi:10.1029/2007GL031972. Gascard, J. C., and Coauthors, 2008: Exploring Arctic transpolar drift during dramatic sea ice retreat. Eos, Trans. Amer. Geophys. Union, 89, 21–28. Haas, C., 2004: Late-summer sea ice thickness variability in the Arctic Transpolar Drift 1991–2001 derived from ground-based electromagnetic sounding. Geophys. Res. Lett., 31, L09402, doi:10.1029/2003GL019394. Kwok, R., 2007: Near zero replenishment of the Arctic multiyear sea ice cover at the end of 2005 summer. Geophys. Res. Lett., 34, L05501, doi:10.1029/2006GL028737. Kwok, R., 2008: Summer sea ice motion from the 18 GHz channel of AMSR-E and the exchange of sea ice between the Pacific and Atlantic sectors, Geophys. Res. Lett ., 35, L03504, doi:10.1029/2007GL032692, 2008 Kwok, R., H.J. Zwally, and D. Yi, 2004: ICESat observations of Arctic sea ice: A first look. Geophys. Res. Lett., 31, L16401, doi: 10.1029/2004GL020309. Laxon, S., N. Peacock, and D. Smith, 2003: High interannual variability of sea ice thickness in the Arctic Region. Nature, 425, 947–950. Maslanik, J. A., C. Fowler, J. Stroeve, S. Drobot, J. Zwally, D. Yi, and W. Emery, 2007: A younger, thinner Arctic ice cover: Increased potential for rapid, extensive sea-ice loss. Geophys. Res. Lett., 34, L24501, doi:10.1029/2007GL032043. Melling, H., D. A. Riedel, and Z. Gedalof, 2005: Trends in the draft and extent of seasonal pack ice, Canadian Beaufort Sea. Geophys. Res. Lett., 32, L24501, doi:10.1029/2005GL024483. Nghiem, S. V., I. G. Rigor, D. K. Perovich, P. Clemente-Colon, J. W. Weatherly, and G. Neumann, 2007: Rapid reduction of Arctic perennial sea ice. Geophys. Res. Lett., 34, L19504, doi:10.1029/2007GL031138. Ogi, M., and J. M. Wallace, 2007: Summer minimum Arctic sea ice extent and the associated summer atmospheric circulation. Geophys. Res. Lett., 34, L12705, doi:10.1029/2007GL029897. Perovich, D.K., J.A. Richter-Menge, K.F. Jones, and B. Light, 2008: Sunlight, water, and ice: Extreme Arctic sea ice melt during the summer of 2007, Geophys. Res. Lett., 35, L11501, doi:10.1029/2008GL034007. Polyakov, I. V., and Coauthors, 2003: Long-term ice variability in arctic marginal seas. J. Climate, 16, 2078–2085. Polyakov, I., et al., 2007: Observational Program Tracks Arctic Ocean Transition to a Warmer State, Eos Trans. AGU, 88(40), doi:10.1029/2007EO400002. Rigor, I. G., and J. M. Wallace, 2004: Variations in the age of Arctic sea ice and summer sea-ice extent, Geophys. Res. Lett., 31, L09401, doi:10.1029/2004GL019492. Rothrock, D. A., D. B. Percival, and M. Wensnahan, 2008: The decline in arctic sea-ice thickness: Separating the spatial, annual, and interannual variability in a quarter century of submarine data, J. Geophys. Res., 113, C05003, doi:10.1029/2007JC004252. Serreze, M. C., M. M. Holland, and J. Stroeve, 2007: Perspectives on the Arctic's shrinking sea-ice cover. Science, 315, 1533–1536. Shimada, K., T. Kamoshida, M. Itoh, S. Nishino, E. Carmack, F. A. McLaughlin, S. Zimmermann, and A. Proshutinsky, 2006: Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean. Geophys. Res. Lett., 33, L08605, doi:10.1029/2005GL025624. Steele, M., W. Ermold, and J. Zhang, 2008: Arctic Ocean surface warming trends over the past 100 years, Geophys. Res. Lett., 35 , L02614, doi:10.1029/2007GL031651. Stroeve, J., M. M. Holland, W. Meier, T. Scambos and M. Serreze, 2007: Arctic sea ice decline: Faster than forecast, Geophysical Research Letters, Vol. 34, L09591, doi: 10.1029/2007GL029703. Stroeve, J., M. Serreze, S. Drobot, S. Gearhead, M. Holland, J. Maslanik, W. Meier, and T. S. Scambo, 2008: Arctic sea ice extent plummets in 2007. Eos, Trans. Amer. Geophys. Union, 89, 13.
Printable Handout :: Full Arctic Report Card (PDF) |
|
|||||||||||||||||
|
|||||||||||||||||||
|
|
DOC | NOAA | NOAA Arctic Research Program |
