The summer extent of the Arctic sea ice cover, widely recognized as an indicator of climate change, has been declining for the past few decades reaching a record minimum in September 2007. The causes ...of the dramatic loss have implications for the future trajectory of the Arctic sea ice cover. Ice mass balance observations demonstrate that there was an extraordinarily large amount of melting on the bottom of the ice in the Beaufort Sea in the summer of 2007. Calculations indicate that solar heating of the upper ocean was the primary source of heat for this observed enhanced Beaufort Sea bottom melting. An increase in the open water fraction resulted in a 500% positive anomaly in solar heat input to the upper ocean, triggering an ice–albedo feedback and contributing to the accelerating ice retreat.
The Arctic sea ice cover evolves dramatically through the summer melt season. Floe size distribution (FSD) is a critical parameter used to examine this change as the ice cover transitions from large ...rectilinear plates in spring to an ensemble of discrete rounded floes by midsummer. The FSD at a given time impacts the dynamic and thermodynamic behavior of the ice cover. Focusing on the seasonal marginal ice zone in the Beaufort and Chukchi Seas from May to September 2014, we present qualitative and quantitative results derived from National Technical Means high‐resolution imagery and supported by ice mass balance buoy data. Results indicate that as melt accelerates, floe breaking pattern, and therefore FSD, is heavily influenced by the distribution of melt ponds. Discrete element model results using morphological conditions derived from analyzed satellite imagery confirmed that breaking occurs along ponds and perpendicular to applied stress.
Key Points
Floe size distribution in the marginal ice zone is heavily impacted by summer thermodynamics
A network of mature melt ponds acts as linked perforations facilitating floe breakup in summer
In the MIZ, FSD changes by the removal of thin floes due to surface and bottom melting
As part of a large interdisciplinary study of the Surface Heat Budget of the Arctic Ocean (SHEBA), we installed more than 135 ice thickness gauges to determine the sea ice mass balance. While ...installing these gauges during the fall of 1997, we found that much of the multiyear ice cover was only 1 m thick, considerably thinner than expected. Over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types, including first‐year ice, ponded ice, unponded ice, multiyear ice, hummocks, new ridges, and old ridges. Initial ice thicknesses for these sites ranged from 0.3 to 8 m, and snow depths varied from a few centimeters to more than a meter. However, for all of their differences and variety, these thickness gauges sites shared a common trait: at every site, there was a net thinning of the ice during the SHEBA year. The thin ice found in October 1997 was even thinner in October 1998. The annual cycle of ice thickness was also similar at all sites. There was a steady increase in thickness through the winter that gradually tapered off in the spring. This was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze‐up began. Maximum surface melting was in July, while bottom ablation peaked in August. Combining results from the sites, we found an average winter growth of 0.51 m and a summer melt of 1.26 m, which consisted of 0.64 m of surface melt and 0.62 m of bottom melt. There was a weak trend for thicker ice to have less winter growth and greater net loss for the year; however, ice growth was also impacted by the snow depth. Considerable variability was observed between sites in both accretion and ablation. The total accretion during the 9‐month growth season ranged from zero for thick ridged ice to more than a meter for young ice. Ponds tended to have a large amount of surface melting, while ridges had considerable bottom ablation.
The National Aeronautics and Space Administration (NASA)’s Operation IceBridge (OIB) was a 13-year (2009–2021) airborne mission to survey land and sea ice across the Arctic, Antarctic, and Alaska. ...Here, we review OIB’s goals, instruments, campaigns, key scientific results, and implications for future investigations of the cryosphere. OIB’s primary goal was to use airborne laser altimetry to bridge the gap in fine-resolution elevation measurements of ice from space between the conclusion of NASA’s Ice, Cloud, and land Elevation Satellite (ICESat; 2003–2009) and its follow-on, ICESat-2 (launched 2018). Additional scientific requirements were intended to contextualize observed elevation changes using a multisensor suite of radar sounders, gravimeters, magnetometers, and cameras. Using 15 different aircraft, OIB conducted 968 science flights, of which 42% were repeat surveys of land ice, 42% were surveys of previously unmapped terrain across the Greenland and Antarctic ice sheets, Arctic ice caps, and Alaskan glaciers, and 16% were surveys of sea ice. The combination of an expansive instrument suite and breadth of surveys enabled numerous fundamental advances in our understanding of the Earth’s cryosphere. For land ice, OIB dramatically improved knowledge of interannual outlet-glacier variability, ice-sheet, and outlet-glacier thicknesses, snowfall rates on ice sheets, fjord and sub-ice-shelf bathymetry, and ice-sheet hydrology. Unanticipated discoveries included a reliable method for constraining the thickness within difficult-to-sound incised troughs beneath ice sheets, the extent of the firn aquifer within the Greenland Ice Sheet, the vulnerability of many Greenland and Antarctic outlet glaciers to ocean-driven melting at their grounding zones, and the dominance of surface-melt-driven mass loss of Alaskan glaciers. For sea ice, OIB significantly advanced our understanding of spatiotemporal variability in sea ice freeboard and its snow cover, especially through combined analysis of fine-resolution altimetry, visible imagery, and snow radar measurements of the overlying snow thickness. Such analyses led to the unanticipated discovery of an interdecadal decrease in snow thickness on Arctic sea ice and numerous opportunities to validate sea ice freeboards from satellite radar altimetry. While many of its data sets have yet to be fully explored, OIB’s scientific legacy has already demonstrated the value of sustained investment in reliable airborne platforms, airborne instrument development, interagency and international collaboration, and open and rapid data access to advance our understanding of Earth’s remote polar regions and their role in the Earth system.
Regional variability in sea ice melt in a changing Arctic Perovich, Donald K.; Richter-Menge, Jacqueline A.
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
07/2015, Volume:
373, Issue:
2045
Journal Article
Peer reviewed
Open access
In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The ...amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover.
Sea ice drift estimates from feature tracking of satellite passive microwave data are used to investigate seasonal trends and variability in the ice circulation around the Beaufort Gyre, over the ...multidecadal period 1980–2013. Our results suggest an amplified response of the Beaufort Gyre ice circulation to wind forcing, especially during the late 2000s. We find increasing anticyclonic ice drift across all seasons, with the strongest trend in autumn, associated with increased ice export out of the southern Beaufort Sea (into the Chukchi Sea). A flux gate analysis highlights consistency across a suite of drift products. Despite these seasonal anticyclonic ice drift trends, a significant anticyclonic wind trend occurs in summer only, driven, in‐part, by anomalously anticyclonic winds in 2007. Across all seasons, the ice drift curl is more anticyclonic than predicted from a linear relationship to the wind curl in the 2000s, compared to the 1980s/1990s. The strength of this anticyclonic ice drift curl amplification is strongest in autumn and appears to have increased since the 1980s (up to 2010). In spring and summer, the ice drift curl amplification occurs mainly between 2007 and 2010. These results suggest nonlinear ice interaction feedbacks (e.g., a weaker, more mobile sea ice pack), enhanced atmospheric drag, and/or an increased role of the ocean. The results also show a weakening of the anticyclonic wind and ice circulation since 2010.
Key Points:
Amplified anticyclonic ice drift in the 2000s compared to the 1980s/1990s
Strongest drift curl trend in autumn, associated with increased ice export out of the southern Beaufort Sea
Limited wind trends suggest other processes driving the enhanced Beaufort Gyre ice circulation
Measurements from NASA IceBridge airborne surveys in March/April 2009–2013 over the western Arctic Ocean are presented in the context of previous observations to assess changes in the characteristics ...of the sea ice cover during the last decade, taking into account spatial and temporal limitations in the available data. Following a precipitous drop in the amount and thickness of multiyear (MY) ice in 2007–2008, the characteristics of the ice cover have remained largely consistent through March 2013. The central Arctic continues to be dominated by MY ice with mean and modal thicknesses of 3.2 m and 2.4 m, respectively. The southern Beaufort and Chukchi Sea region is a complex mixture of ~75% first‐year ice and 25% MY ice. IceBridge observations indicate that the mean thickness in the Beaufort and Chukchi Seas may have decreased from ~2.5 m to as low as 1.6 m over the 5 year period.
Key Points
We assess the conditions of sea ice in the western Arctic in March 2009‐2013
We use new sea ice thickness estimates from NASA IceBridge airborne surveys
Mean ice thicknesses in Central Arctic and Beaufort‐Chukchi Seas are compared
Loss of sea ice in the Arctic Perovich, Donald K; Richter-Menge, Jacqueline A
Annual review of marine science,
01/2009, Volume:
1
Journal Article
Peer reviewed
The Arctic sea ice cover is in decline. The areal extent of the ice cover has been decreasing for the past few decades at an accelerating rate. Evidence also points to a decrease in sea ice thickness ...and a reduction in the amount of thicker perennial sea ice. A general global warming trend has made the ice cover more vulnerable to natural fluctuations in atmospheric and oceanic forcing. The observed reduction in Arctic sea ice is a consequence of both thermodynamic and dynamic processes, including such factors as preconditioning of the ice cover, overall warming trends, changes in cloud coverage, shifts in atmospheric circulation patterns, increased export of older ice out of the Arctic, advection of ocean heat from the Pacific and North Atlantic, enhanced solar heating of the ocean, and the ice-albedo feedback. The diminishing Arctic sea ice is creating social, political, economic, and ecological challenges.
Seasonal evolution of melt ponds on Arctic sea ice Webster, Melinda A.; Rigor, Ignatius G.; Perovich, Donald K. ...
Journal of geophysical research. Oceans,
09/2015, Volume:
120, Issue:
9
Journal Article
Peer reviewed
Open access
The seasonal evolution of melt ponds has been well documented on multiyear and landfast first‐year sea ice, but is critically lacking on drifting, first‐year sea ice, which is becoming increasingly ...prevalent in the Arctic. Using 1 m resolution panchromatic satellite imagery paired with airborne and in situ data, we evaluated melt pond evolution for an entire melt season on drifting first‐year and multiyear sea ice near the 2011 Applied Physics Laboratory Ice Station (APLIS) site in the Beaufort and Chukchi seas. A new algorithm was developed to classify the imagery into sea ice, thin ice, melt pond, and open water classes on two contrasting ice types: first‐year and multiyear sea ice. Surprisingly, melt ponds formed ∼3 weeks earlier on multiyear ice. Both ice types had comparable mean snow depths, but multiyear ice had 0–5 cm deep snow covering ∼37% of its surveyed area, which may have facilitated earlier melt due to its low surface albedo compared to thicker snow. Maximum pond fractions were 53 ± 3% and 38 ± 3% on first‐year and multiyear ice, respectively. APLIS pond fractions were compared with those from the Surface Heat Budget of the Arctic Ocean (SHEBA) field campaign. APLIS exhibited earlier melt and double the maximum pond fraction, which was in part due to the greater presence of thin snow and first‐year ice at APLIS. These results reveal considerable differences in pond formation between ice types, and underscore the importance of snow depth distributions in the timing and progression of melt pond formation.
Key Points:
An algorithm was created to study melt pond evolution on drifting Arctic sea ice
Snow distribution and ice topography affect the onset and pace of melt pond formation
Variations in the Arctic central Canada Basin mixed layer properties are documented based on a subset of nearly 6500 temperature and salinity profiles acquired by Ice‐Tethered Profilers during the ...period summer 2004 to summer 2009 and analyzed in conjunction with sea ice observations from ice mass balance buoys and atmosphere‐ocean heat flux estimates. The July–August mean mixed layer depth based on the Ice‐Tethered Profiler data averaged 16 m (an overestimate due to the Ice‐Tethered Profiler sampling characteristics and present analysis procedures), while the average winter mixed layer depth was only 24 m, with individual observations rarely exceeding 40 m. Guidance interpreting the observations is provided by a 1‐D ocean mixed layer model. The analysis focuses attention on the very strong density stratification at the base of the mixed layer in the Canada Basin that greatly impedes surface layer deepening and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth/decay. The observations additionally suggest that efficient lateral mixed layer restratification processes are active in the Arctic, also impeding mixed layer deepening.
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