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Sea‐ice ice shelves, at the apex of North America (>80° N), constitute the oldest sea ice in the Northern Hemisphere. We document the establishment and subsequent stability of the Ward Hunt Ice Shelf, and multiyear landfast sea ice in adjacent fiords, using 69 radiocarbon dates obtained on Holocene driftwood deposited prior to coastal blockage. These dates (47 of which are new) record a hiatus in driftwood deposition beginning ∼5500 cal yr BP, marking the inception of widespread multiyear landfast sea ice across northern Ellesmere Island. This chronology, together with historical observations of ice shelf breakup (∼1950 to present), provides the only millennial‐scale record of Arctic Ocean sea ice variability to which the past three decades of satellite surveillance can be compared. Removal of the remaining ice shelves would be unprecedented in the last 5500 years. This highlights the impact of ongoing 20th and 21st century climate warming that continues to break up the remaining ice shelves and soon may cause historically ice‐filled fiords nearby to open seasonally.

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Water resources is one of the highest-priority issues with respect to climate change impacts and adaptation in Canada. A clean and reliable water supply is critical for domestic use, food and energy production, transportation, recreation and maintenance of natural ecosystems. Although Canada possesses a relative abundance of water on a per capita basis, the uneven distribution of water resources and year-to-year variability mean that most regions of the country have experienced water-related problems, such as droughts, floods and associated water quality issues.Such problems are expected to become more common as a result of climate change. The hydrological cycle is greatly influenced by temperature Photo courtesy of Natural Resources Canadax Climate Change Impacts and Adaptation and precipitation, and even small changes in these parameters can affect water supply through shifts in runoff, evaporation and water storage (e.g., in glaciers, lakes and soil). There are still uncertainties, however, regarding the magnitude, and in some cases the direction, of future changes, in part due to the limitations of climate models. Although impacts would vary on a regional basis, it is apparent that certain aspects, including extreme events, reduced ice cover and shifts in flow regimes, are concerns in many areas of the country. Overall, the most vulnerable regions would be those already under water stress, such as parts of the Prairies and the Okanagan Valley, where demand is already approaching or exceeding supply.In many regions, decreases in flow volumes and water levels are expected to create or increase water supply problems during the summer months. In Prairie rivers, for example, summer flows are expected to decrease due to reduced water supply from snowmelt and glacier runoff. In fact, data indicate that a long-term trend of declining flows has already begun. Accompanying decreases in shallow groundwater resources could further compound water shortages. Water supply issues are also expected to become a greater concern in the Great Lakes basin, where a range of sectors would be affected by declining water levels (Figure 2). In the winter, however, less ice cover, more rain-on-snow precipitation events and more frequent winter thaws would increase the risk of flooding in many regions of the country.Changes in flow patterns and water levels could also result in decreased water quality. Lower water levels and higher temperatures could increase levels of bacterial, nutrient and metal contamination, while an increase in flooding could increase the flushing of urban and agricultural waste into source water systems. This would cause taste and odour problems and increase the risk of water-borne FIGURE 2: Water resources is a crosscutting issue Decreased depth of navigation channels, stranded docks and harbours More beaches, aesthetic issues, less access to marinas and lake front Loss of species, loss of habitat (e.g., spawning areas), contamination Less potential for hydropower, less water for industrial operations Increased w...

Terrestrial and marine records provide the first reconstruction of past glacial events on west-central Axel Heiberg Island. Lateral moraines along Expedition Fiord define an early Holocene ice margin when a trunk glacier occupied the inner half of the fiord. Limited sediment accumulation in the outer fiord (< 10–40 m) questions whether this ice margin records the limit of the last glaciation. Ice retreat began > 8.4 ka BP, principally by calving of an unstable ice front to a position well upvalley of the present ice limit. Rapid deglaciation is evidenced by (i) an absence of ice marginal landforms and related marine biofacies; (ii) a scarcity of raised marine sediments; and (iii) exceptionally thin sediments (< 5–20 m) in the inner fiord. A transition from a Hiatella arctica – Mya truncata macrofossil assemblage to an Astarte borealis – Mya truncata assemblage reflects a change from moderate to low energy depositional environments at the fiord head by 7.9 ka BP.The extensive ice advance into Expedition Fiord is contrasted by a more restricted advance in adjacent Strand Fiord, which contains both glacial and marine features that appear to predate the last glaciation. The difference in ice extent between the two fiords is explained by drainage basin morphometry and fiord bathymetry, and reflects modern analogues. Initial retreat of trunk glaciers may have occurred in response to rising sea level, with regionally synchronous ice retreat occurring at 8.4 ka BP when climatic factors were dominant. Glacier dynamics controlled the rate of ice retreat, with tidewater glaciers retreating much more rapidly than those with terrestrial margins.