C53A-01 INVITED
Future Projections of Climate Impacts From Rapid Arctic Sea Ice Decline
Few climate models can keep pace with observed sea ice decline in the Arctic. What is missing in modern climate models that suppresses sea ice sensitivity? How do other components of the climate system depend on the rate of sea ice decline? What other aspects of climate change are likely to be under-predicted as a consequence of sluggish sea ice retreat in climate model projections? I will discuss these and other issues involved in modeling impacts of Arctic sea ice decline. I will also describe new model features that are under swift development as climate models move towards Earth System Models, and their great potential to help us learn more about Arctic climate impacts and feedbacks.
C53A-02 INVITED
Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss
Coupled climate models and recent observational evidence suggest that Arctic sea ice may undergo abrupt periods of loss during the next fifty years. Here, we evaluate how rapid sea ice loss affects terrestrial Arctic climate and ground thermal state in the Community Climate System Model. We find that simulated western Arctic land warming trends during rapid sea ice loss are 3.5 times greater than secular 21st century climate- change trends. The accelerated warming signal penetrates up to 1500km inland and is apparent throughout most of the year, peaking in autumn. Idealized experiments using the Community Land Model, with improved permafrost dynamics, indicate that an accelerated warming period substantially increases ground heat accumulation. Enhanced heat accumulation leads to rapid degradation of warm permafrost and may increase the vulnerability of colder permafrost to degradation under continued warming. Taken together, these results imply a direct link between rapid sea ice loss and permafrost health.
C53A-03
Monitoring coastal erosion on the Beaufort Sea coast: Erosion process and the relative roles of thermal and wave energy
While coastal erosion rates along the Beaufort Sea coast in northern Alaska have been locally observed to exceed 30 meters/year over the past decade, few observational data exist to characterize how this erosion proceeds or why these rates are so high. We have begun a new monitoring project along a section of coastline in the northeastern National Petroleum Reserve-Alaska (NPR-A), approximately halfway between Barrow and Prudhoe Bay. In this setting, three-to five-meter high, ice-rich bluffs largely comprising silt and organic material are currently eroding at a rate of approximately 20 meters/year. Our study combines time- lapse photography and meteorological observations with historical observations of coastal erosion rates, measurements of substrate properties from intact bluffs, and size distributions of eroded blocks to support physically-based models of coastal erosion in this environment. Our observations indicate that this erosion is initiated by the topple-failure of large blocks, and is driven by a combination of thermal and mechanical processes. Episodic block failure during storm events is superimposed on a slow, steady notching at the base of the ice-rich bluffs which appears to be driven largely by melting from relatively warm seawater. Thermal degradation of bluffs through the summer months also appears to play a role in weakening the substrate, which increases the impact of late summer storm events. Once eroded blocks have toppled into the Beaufort Sea, rapid thermal disintegration of these blocks by warm nearshore waters, combined with the lack of coarse clastic material within the substrate, limits their ability to protect the coastline from wave attack. This observation suggests that there may be no strong negative feedback on these rapid erosion rates. Using time-lapse photography collected during the summer of 2008, we can begin to quantify the relative roles of thermal and mechanical degradation of Arctic coastlines. These new data will inform our understanding of how climate change, here largely manifested by increasing sea surface and permafrost temperatures and increased fetch across ice-free waters, may influence future Arctic landscape change.
C53A-04 INVITED
An Overview Of Physical And Biological Responses To Sustained Decreases Of Sea Ice In The Southern Beaufort Sea: Experiences From The IPY-CFL Project
The International Polar Year (IPY) Circumpolar Flaw Lead (CFL) System Study (www.ipy-cfl.ca) supported a
large multidisciplinary overwintering study of the Banks Island (NT) flaw lead system over the period
September 2007 to August 2008. A total of 11,000 person days were conducted by 295 investigators, from
28 different countries, making the IPY-CFL project the largest in the northern hemisphere. In the lead up to,
and during the CFL project, reductions in sea ice aerial extent and thickness in the southern Beaufort Sea
imparted a dramatic effect on physical, biogeochemical and ecological processes operating across the
ocean-sea ice-atmosphere (OSA) interface. In this paper we provide an overview of key findings of how
changes in sea ice areal extent, thickness, and associations with snow cover, affect both physical and
biological processes. We provide direct measurements of the physical system associated with the large
drawback of sea ice in the northern hemisphere in the fall of 2007 and follow the effects of this sea ice
minimum in terms of oceanic and atmospheric development. We describe key responses of chemical and
contaminant cycling within the system and describe how sea ice controls these biogeochemical processes.
We then provide preliminary results from a number of case studies to examine how changes in sea ice affect
various trophic levels and biogeochemical processes in the Arctic marine ecosystem.
http://www.ipy-cfl.ca
C53A-05
Solar Transmission Through Sea Ice in the Fram Strait: Implications for Biology and Climate
Snow and ice control the light penetration into ice-covered Arctic waters, determining the onset of biological production after the winter. Changes in the snow and ice cover and their characteristics influence both the amount of light and the spectral distribution of light transmitted to the underlying water, with effects on timing, distribution, production rate and even species composition of the Arctic marine production. Light transmitted through the sea ice also provides a source of heat to the upper part of the water column, and may promote melting of the ice from the bottom. Spectral measurements of the transmitted solar flux were made at several locations in the Fram Strait-East Greenland Shelf region in April---May 2008, as part of the iAOOS-Norway project of interdisciplinary observations in the Arctic Ocean, and in September 2007 and 2008. These transmission measurements were made both immediately below ice floes, and as profiles to a depth of 80~m both beneath floes and beneath open water in leads. During the spring cruise, the corresponding biological productivity and biomass in the water column below the ice were measured. Together such data will increase our understanding of how a changing Arctic climate will influence the ecosystem and productivity. This presentation will present results from these transmission measurements, the first of their kind from this important region of sea ice export and biological and oceanographic activity, and their relationship to biological productivity, along with their implications for climate processes, including the formation and melting of sea ice.
C53A-06 INVITED
Deciphering the Causality and Rate of Warming in the Arctic Ocean
Recent changes in the Arctic sea ice cover provide one of the most evident examples of warming climate. However, there is an ongoing scientific debate about the causes of the ice melt and its rate. Most climate models predict up to 50% reduction of summer sea ice cover in the Arctic Ocean by the end of this century, as a result of an amplified response to global warming. Though, satellite observations of ice extent and area imply much faster rate of melting ice which may result in ice-free summers in the Arctic Ocean by sometime between 2030 and 2040. Yet, when ice thickness and volume are taken into account the rate of decline of Arctic sea ice might be even faster. Hence one of the main questions to be addressed concerning the Arctic Ocean is: 'how fast is the Arctic sea ice melting and when it might be expected to disappear all together in summer'? Another equally important question is: 'can the recent negative trend in sea ice be stopped or reversed'? While the first question has to do with an improved knowledge of Arctic-wide changes in sea ice thickness and volume which is limited at present, the second question requires understanding of the causes of sea ice melt. In this talk we attempt to address the two questions posed above. First, we analyze trends of sea ice decline based on the output from a regional ice-ocean model of the pan-Arctic region forced with realistic atmospheric data in comparison with trends estimated from observations. Second, we investigate the effect, distribution, and timing of oceanic thermodynamic forcing of sea ice melt. The magnitude of oceanic forcing will be quantified, validated against available estimates from observations and compared with those derived from several global climate models participating in the Intergovernmental Panel for Climate Change Fourth Assessment Report (IPPC-AR4). Our findings imply that sea ice might be melting faster than predicted by both climate models and estimated from satellite observations. This implies that the Arctic not only might, but is likely to be ice-free during the summer in the near future. In addition, we argue that the oceanic forcing is critical especially in the western Arctic Ocean and its more realistic representation in climate models should improve their predictive skill.
C53A-07
Arctic atmospheric circulation and surface air temperature anomalies: are the rules changing?
Historically, there are clear relationships between regional temperature anomalies and those of atmospheric circulation. Regions of anomalous poleward heat transport tend to be associated with positive anomalies in surface air temperature and vice-verse. There is growing evidence that these relationships are starting to break down over the Arctic Ocean in autumn. Each of the past five years have seen record or near-record September minima in sea ice extent. Minima recorded in September 2007 and 2008 ranked as the lowest and second lowest since satellite records began in 1979. The past five years have also seen the emergence of strong positive temperature anomalies at the surface and in the lower troposphere over the Arctic Ocean in autumn. While there are strong tropospheric temperature signals related to circulation variability, surface and near-surface warming has grown with time and is clearly associated with strong upward heat fluxes to the atmosphere from anomalous areas of open water. In other words, relationships between atmospheric circulation and temperature in the Arctic appear to be changing. We address this issue through comparing patterns of surface air temperature anomalies for recent autumns with those of past autumns having similar atmospheric circulation patterns. For example, autumn 2007 saw a pattern featuring above average sea- level pressure in the Canadian Basin and below average pressure along the Siberian coast in autumn. While this pattern by itself is consistent with warm conditions north of Siberia, it is likely that the large magnitude of the temperature anomalies resulted from the effects of open water. By looking at temperature anomalies associated with similar patterns of atmospheric circulation in the past we quantify the impact of anomalous open water, thereby offering insight into the emerging Arctic Amplification.
C53A-08
Local sea-ice influence on Greenland surface melt
Continued reduction of Arctic sea ice may significantly alter the climate of the northern high latitudes and the mass balance of the Greenland ice-sheet. While sea ice loss and Greenland ice-surface melting both increased in the late-20th/early-21st century, the influence of sea ice on Greenland surface melt is unknown. In this presentation, we study the relationship between the variability of sea-ice/open-water and ice-sheet snow-melt extent by employing passive microwave satellite observations of both concurrently. We show that although melt and sea-ice/open-water extent vary independently in most of Greenland, anomalous covariability is observed in the general area of Kangerlussuaq, south-west Greenland. A prevalent time lag of approximately 0-2 days between the two variables suggests that sea-ice/open-water drive parts of the melt variability. In the Kangerlussuaq area, the anomalous sea-ice/open-water influence on melt variability may be a result of the proximity to the location of the average summertime sea ice edge in Davids Strait. We speculate that further northern retreat of sea ice could cause this covariability anomaly to also migrate north, to the vicinity of the Jakobshavn Isbrae.