Derek R. Mueller

Evolution of cryoconite holes and their contribution to meltwater runoff from glaciers in the McMurdo Dry Valleys, Antarctica

Abstract Cryoconite holes are water-filled holes in the surface of a glacier caused by enhanced ice melt around trapped sediment. Measurements on the ablation zones of four glaciers in Taylor Valley, Antarctica, show that cryoconite holes cover about 4–6% of the ice surface. They typically vary in diameter from 5 to 145 cm, with depths ranging from 4 to 56 cm. In some cases, huge holes form with 5 m depths and 30 m diameters. Unlike cryoconite holes elsewhere, these have ice lids up to 36 cm thick and melt from within each spring. About one-half of the holes are connected to the near-surface hydrologic system and the remainder are isolated. The duration of isolation, estimated from the chloride accumulation in hole waters, commonly shows ages of several years, with one hole of 10 years. The cryoconite holes in the McMurdo Dry Valleys create a near-surface hydrologic system tens of cm below the ice surface. The glacier surface itself is generally frozen and dry. Comparison of water levels between holes a few meters apart shows independent cycles of water storage and release. Most likely, local freeze–thaw effects control water passage and therefore temporary storage. Rough calculations indicate that the holes generate at least 13% of the observed runoff on the one glacier measured. This hydrologic system represents the transition between a melting ice cover with supraglacial streams and one entirely frozen and absent of water.

Gradient analysis of cryoconite ecosystems from two polar glaciers

The cylindrical meltholes present in the ablation zones of many glaciers (termed cryoconite holes) contain complex microbial communities. A canonical correspondence analysis (CCA) of community structure and environmental gradients for cryoconite holes on two glaciers was undertaken. The Canada Glacier (77°37′S, 162°55′E) is located in the McMurdo Dry Valleys of Antarctica. The White Glacier (79°27′N, 90°40′W) is located on Axel Heiberg Island, Nunavut Territory, Canada. These glaciers are at similar, yet antipodal latitudes, are roughly the same size and endure approximately the same mean annual temperature. The Canada Glacier cryoconite communities were found to be significantly (P=0.001) associated with six environmental variables, which together explained 55% of the biological variation. The White Glacier cryoconite communities were not significantly associated with environmental variables. The differences in CCA results were attributed to the relative amount of disturbance and isolation between each glacier’s cryoconite holes. Canada Glacier cryoconite holes were mostly ice-covered and undisturbed by meltwater flow, whereas high meltwater production and open cryoconite holes on the White Glacier may continually reset the community structure and habitat variability due to inter-hole mixing.

Rapid loss of the Ayles Ice Shelf, Ellesmere Island, Canada

[1] On August 13, 2005, almost the entire Ayles Ice Shelf (87.1 km 2 ) calved off within an hour and created a new 66.4 km 2 ice island in the Arctic Ocean. This loss of one of the six remaining Ellesmere Island ice shelves reduced their overall area by ∼7.5%. The ice shelf was likely weakened prior to calving by a long-term negative mass balance related to an increase in mean annual temperatures over the past 50+ years. The weakened ice shelf then calved during the warmest summer on record in a period of high winds, record low sea ice conditions and the loss of a semi-permanent landfast sea ice fringe. Climate reanalysis suggests that a threshold of >200 positive degree days year -1 is important in determining when ice shelf calving events occur on N. Ellesmere Island.

Examining Arctic Ice Shelves Prior to the 2008 Breakup

The last time researchers stood on the surface of the Serson Ice Shelf, at the northern end of Ellesmere Island, Canada, it was a chilly 26°C April day in 2008. On a relatively warm 8°C day 3 months later, the ice shelf began to break apart and within 3 weeks lost 122 square kilometers (60%) of its area. This past summer, Ellesmeres 50-square-kilometer Markham Ice Shelf also broke away, and there was major fracturing throughout the eastern half and well into the western half of the Ward Hunt Ice Shelf, which is the largest remaining ice shelf in the Northern Hemisphere.

Environmental Gradients, Fragmented Habitats, and Microbiota of a Northern Ice Shelf Cryoecosystem, Ellesmere Island, Canada

ABSTRACT Over the course of the last century, the 9000-km2 Ellesmere Ice Shelf (82–83°N, 64–90°W) fragmented into six main ice shelves now totaling 1043 km2. This ensemble of thick ice environments lies along the northern coast of Ellesmere Island in the Canadian High Arctic and provides a cryohabitat for microbial communities that occur in association with eolian and glacially entrained sediments on the ice surface. We undertook a comparative analysis of physical, chemical, and biological characteristics of five of the remnant ice shelves including geographic information system (GIS) mapping of ice types. Each of these remnants is a thick (>20 m) mass of ice with substantial sediment overburden that promotes the formation of oligotrophic meltwaters in the summer. Microbiota occurred in all sampled sediment, forming a continuum of abundance from sparse to loosely cohesive and pigmented microbial mats. Using digital images from over-flight transects we determined that 8% of the combined ice-shelf area was suitable microbial mat habitat, and contained an estimated 34 Gg of organic matter stocks for the entire system. A gradient of increasing chlorophyll a, organic content, and conductivity was found from west to east. This is likely related to the surface ice type (meteoric versus marine) and to the relative availability of sediment. Our results indicate that differences in phototrophic community structure (microalgae and cyanobacterial morphotypes) were associated with different ice and microbial mat types. In addition, the relative abundance of dominant taxa was significantly associated with environmental gradients of conductivity, soluble reactive phosphorus, and nitrate and ammonium concentrations. There were distinct differences between each ice shelf with regards to ice type and sediment availability but no differences in taxonomic richness or diversity, indicating little effect of habitat fragmentation on these community attributes. However, the ensemble of ice shelves that compose this unique cryoecosystem remains vulnerable to habitat attrition and complete loss with ongoing climate warming.

Extreme Ecosystems and Geosystems in the Canadian High Arctic: Ward Hunt Island and Vicinity

Abstract: Global circulation models predict that the strongest and most rapid effects of global warming will take place at the highest latitudes of the Northern Hemisphere. Consistent with this prediction, the Ward Hunt Island region at the northern terrestrial limit of Arctic Canada is experiencing the onset of major environmental changes. This article provides a synthesis of research including new observations on the diverse geosystems/ecosystems of this coastal region of northern Ellesmere Island that extends to latitude 83.11° N (Cape Aldrich). The climate is extreme, with an average annual air temperature of -17.2 °C, similar to Antarctic regions such as the McMurdo Dry Valleys. The region is geologically distinct (the Pearya Terrane) and contains steep mountainous terrain intersected by deep fiords and fluvial valleys. Numerous glaciers flow into the valleys, fiords, and bays, and thick multi-year sea ice and ice shelves occur along the coast. These extreme ice features are currently undergoing rapid attrition. The polar desert landscape contains sparse, discontinuous patches of vegetation, including dense stands of the prostrate shrub Salix arctica (Artic willow) at some sites, and 37 species of vascular plants on Ward Hunt Island. Diverse aquatic ecosystems occur throughout the area, including meromictic, epishelf, and perennially ice-covered lakes. Many of these have responded strongly to climate shifts in the past and like other geosystems/ecosystems of the region are now sentinels of ongoing global climate change.

Glacial Periods on Early Earth and Implications for the Evolution of Life

Aquatic Ecosystem Studies at Laval University, Québec City, Canada. He obtained his Ph.D. in Ecology from the University of California, Davis, in 1977. He is a Fellow of the Royal Society of Canada and an Honorary Fellow of the Royal Society of New Zealand. His current research concerns underwater light, the ecology of Cyanobacteria and the effects of climate on high latitude lakes, wetlands, rivers and coastal seas.

Rapid disappearance of perennial ice on Canada's most northern lake

Field records, aerial photographs, and satellite imagery show that the perennial ice cover on Ward Hunt Lake at Canadas northern coast experienced rapid contraction and thinning after at least 50 years of relative stability. On all dates of sampling from 1953 to 2007, 3.5 to 4.3 m of perennial ice covered 65–85% of the lake surface in summer. The ice cover thinned from 2008 onward, and the lake became ice free in 2011, an event followed by 26 days of open water conditions in 2012. This rapid ice loss corresponded to a significant increase in melting degree days (MDD), from a mean (±SD) of 80.4 (±36.5) MDD (1996–2007) to 136.2 (±16.4) MDD (2008–2012). The shallow bathymetry combined with heat advection by warm inflows caused feedback effects that accelerated the ice decay. These observations show how changes across a critical threshold can result in the rapid disappearance of thick perennial ice.

Changes in Canadian Arctic Ice Shelf Extent Since 1906

The ice shelves along the northern coast of Ellesmere Island have been in a state of decline since at least the early twentieth century. Available data derived from explorers’ journals, aerial photographs and satellite imagery have been compiled into a single geospatial database of ice shelf and glacier ice tongue extent over 13 observation periods between 1906 and 2015. During this time there was a loss of 8,061 km2 (94%) in ice shelf area. The vast majority of this loss occurred via episodic calving, in particular during the first six decades of the twentieth century. More recently, between 1998 and 2015, 515 km2 of shelf ice calved. Some ice shelves also thinned in situ, transitioning to thinner and weaker ice types that can no longer be considered ice shelf, although the timing of this shift is difficult to constrain with the methods used here. Some ice shelves composed partly of ice tongues (glacier or composite ice shelves) also disintegrated to the point where the ice tongues were isolated, representing a loss of ice shelf extent. Our digitization methods are typically repeatable to within 3%, and generally agree with past determinations of extent. The break-up of these massive features is an ongoing phenomenon, and it is hoped that the comprehensive dataset presented here will provide a basis for comparison of future changes in this region.

Loss of Multiyear Landfast Sea Ice from Yelverton Bay, Ellesmere Island, Nunavut, Canada

Abstract For much of the 20th century, multiyear landfast sea ice (MLSI) formed a permanent ice cover in Yelverton Bay, Ellesmere Island. This MLSI formed following the removal of ice shelf ice from Yelverton Bay in the early 1900s, including the well-documented Ice Island T-3. The MLSI cover survived intact for 55–60 years until 2005, when >690 km2 (90%) of MLSI was lost from Yelverton Bay. Further losses occurred in 2008, and the last of the Yelverton Bay MLSI was lost in August 2010. Ground penetrating radar (GPR) transects and ice cores taken in June 2009 provide the first detailed assessment of MLSI in Yelverton Inlet, and indeed the last assessment now that it has all been replaced with first-year ice. A detailed history of ice shelf, glacier, and MLSI changes in Yelverton Bay since the early 1900s is presented using remotely sensed imagery (air photos, space-borne optical, and radar scenes) and ancillary evidence from in situ surveys. Recent changes in the floating ice cover here align with the broad-scale trend of long-term reductions in age and thickness of sea ice in the Arctic Ocean and Canadian Arctic Archipelago.