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The purpose of this chapter is to introduce the reader to the Bering Glacier and the Bering Glacier System. This will be done by (1) providing a summary of the early observations and geographic descriptions of Bering Glacier, (2) identifying scientific studies that have provided insights to the unique character of the Bering Glacier System and its unique surroundings, and (3) presenting descriptions of key geographic features that are part of the system and its surroundings. The Bering Glacier System is the largest glacier in continental North America and the largest temperate surging glacier on Earth.

Satellite remote sensing is an invaluable tool for monitoring and characterizing the Bering Glacier System. Applications of glacier remote sensing include, but are not limited to, mapping extent and features, ice velocities through sequential observations, glacier terminus locations, snow line location, glacier albedo, changes in glacier volume, iceberg surveys and calving rates, hydrographic and water quality parameters in ice marginal lakes, and land-cover classification maps. Historical remote sensing images provide a much needed geospatial time record of the dynamic changes that Bering Glacier has undergone, including changes from its surge behavior and response to climate change. Remote sensing images dating back to the early 1990s have been used to map the glacier terminus retreat of ~5 to 7 km, which has resulted in Vitus Lake increasing in volume 9.4 km 3 (~260%) from 1995 to 2006. Using elevation data obtained from remote sensing and GPS surface points, we have determined that the glacier elevation has decreased by ~150 m at the terminus and 30 m at the equilibrium line (~1300 m) since 1972. Satellite observations have recorded the upward migration in altitude of the equilibrium line to its present (2006) position (slightly >1200 m). The decrease in glacier volume, obtained using remote sensing–derived elevation data, from 1957 to 2004 is estimated at ~104 km 3 . Remote sensing data also have mapped the sediment-rich (rock flour) water flowing into Vitus Lake, providing insight into the hydrologic circulation of the Bering Glacier System, showing major glacier discharge from the Abandoned River, Arrowhead Point, and Lamire Bay in the area of Vitus Lake west of Taggland.

An extensive suite of physical oceanographic, remotely sensed, and water quality measurements, collected from 2001 through 2004 in two ice-marginal lakes at Bering Glacier, Alaska—Berg Lake and Vitus Lake—shows that each lake has a unique circulation controlled by specific physical forcing within the glacial system. Conductivity profiles from Berg Lake, perched 135 m above sea level (a.s.l.), show no salt in the lake, but the temperature profiles indicate an apparently unstable situation: the 4 °C density maximum lies at 10 m depth, not at the bottom of the lake (90 m depth). Subglacial discharge from the Steller Glacier into the bottom of the lake must inject a suspended sediment load sufficient to marginally stabilize the water column throughout the lake. In Vitus Lake, terminus positions derived from satellite imagery show that the glacier terminus rapidly retreated from 1995 to the present, resulting in a substantial expansion of the volume of Vitus Lake. Conductivity and temperature profiles from the tidally influenced Vitus Lake show a complex four-layer system with diluted (~50%) seawater in the bottom of the lake. This lake has a complex vertical structure that is the result of convection generated by ice melting in salt water, stratification within the lake, and fresh water entering the lake from beneath the glacier and surface runoff. Four consecutive years, 2001 through 2004, of these observations in Vitus Lake show little change in the deep temperature and salinity conditions, indicating limited deep water renewal. The combination of the lake level measurements with discharge measurements, through a tidal cycle, by an Acoustic Doppler Current Profiler (ADCP) deployed in the Seal River, which drains the entire Bering system, showed a strong tidal influence but no seawater entry into Vitus Lake. The ADCP measurements, combined with lake level measurements, established a relationship between lake level and discharge, which when integrated over a tidal cycle gave a tidally averaged discharge ranging from 1310 to 1510 m 3 s −1 .

Bering Glacier is rapidly retreating and thinning since it surged in 1993–1995. From 2002 to 2007 we have mapped the terminus position and measured the surface ablation from the terminus region up-glacier to the snowline in the Bagley Ice Field. Since the last surge the terminus has retreated, primarily by calving, ~0.4–0.5 km/a, and the terminus position is at the 1992 pre-surge position. The glacier surface in the terminus region is presently downwasting by melting at ~8–10 m/a and 3.5–6.0 m/a at the approximate altitude of the equilibrium line, 1200 m. The average daily melt for Bering Glacier is ~4–5 cm/d at mid-glacier, and this melt rate appears to be steady, regardless of insulation and/or precipitation. The melt from the Bering Lobe of the glacier system generates between 8 and 15 km 3 of fresh water yearly, which flows directly into the Gulf of Alaska via the Seal River, potentially affecting its circulation and ecosystem. Elevation measurements from 1957 compared with our measurements made in 2004, combined with bed topography from ice penetrating radar, show that the Bering Lobe has lost ~13% of its total mass.

Runoff from the mountains and large glaciers on the rim of the Gulf of Alaska is a critical driver for ocean circulation in the gulf and a major contributor to global sea level rise. Bering Glacier is the foremost glacier of this system, with one of the largest proglacial lake-river systems in the world, Vitus Lake, which is linked to the Gulf of Alaska by the Seal River. Vitus Lake, at sea level and >250 m deep in some locations, receives all of the runoff, rainfall, and glacial melt from the Bering Lobe, which then flows into the Gulf of Alaska in the 8-km-long Seal River. Six years of conductivity-temperature-depth (CTD) surveys in Vitus Lake show a highly stratified system with 50% diluted seawater at the bottom. The annual surveys show changes in the deep water temperature and salinity that are the result of seawater intrusions. To understand the complex interaction between lake level and area, glacier discharge, river morphology and flow, sea level fluctuations, and their associated impacts on the lacustrine ecology of Vitus Lake, we developed a hydrodynamic flow model that was calibrated using field measurements of lake level and the flow in Seal River. The model is used to analyze present conditions in Vitus Lake and shows that even with no runoff entering the lake, the distance from the Gulf of Alaska through Seal River to Vitus Lake is too great for typical tidal inflow to reach the lake. Furthermore, the model is used to understand the response of the glacier-lake system to possible future scenarios of glacier retreat or advance and changes in runoff. Finally, properly calibrated, such a model would be able to gauge the discharge from the Bering Glacier System by measuring only the lake level.

An inventory of the vascular flora of the Bering Glacier Region, south of the Bagley Ice Field, was conducted from 2000 to 2007. The area includes nunataks, mountains, and glacial forelands. The objectives of the inventory were to (1) assess the botanical biodiversity of the region, (2) identify rare taxa and areas of phytogeographic interest, and (3) provide data that would assist land managers with planning. The inventory has particular significance, as prior to this study the only specimens noted from this region were from the coastline. To date, 466 taxa have been identified, representing one quarter of the plant species of Alaska. Ninety-three of the species represent range extensions, 58 are gap fillers (species that fill distribution gaps), and 19 are rare species with a state rank of 3 or less on the Alaska Natural Heritage Program Vascular Plant Tracking List. Carbon Mountain, Robinson Mountains, and the Tashalich River sites contain 60% of the Heritage Tracking Plants. Three exotic weed species were found adjacent to Vitus Lake.

An inventory of fish species was conducted in the Bering Glacier Region, Alaska, in 2002–2006. Ten species were collected: surf smelt, coho salmon, sockeye salmon, rainbow trout, Dolly Varden, threespine stickleback, prickly sculpin, slimy sculpin, Pacific staghorn sculpin, and starry flounder. All are either marine in origin or tolerant of salt water; consistent with this, fishes in the watershed tolerate a wide range of water qualities in fresh water. Stickleback, prickly sculpin, slimy sculpin, coho salmon, and Dolly Varden are found most commonly either because they are early colonizing species or they are able to out-compete early colonizers. Species that readily assume residence in fresh water were found equally often in isolated and connected lakes and streams, whereas diadromous and marine species were found primarily in lakes and streams with outlets. Except for Dolly Varden, species were more likely to be found in nonglacial than in glacial lakes and streams. Greater species richness was associated with the presence of aquatic vegetation and algae, both of which provide structural complexity and indicate more abundant nutrient levels in otherwise oligotrophic waters. With the exception of Vitus Lake, which is tidally influenced, fish species richness was low. Older lakes and streams support more species than younger aquatic habitats, presumably owing to greater time for colonization and the formation of habitat complexity. This ever-changing aquatic landscape has been colonized by typical fish species in the region, but these colonists have evolved in atypical ways, including populations of dwarf Dolly Varden and stickleback species pairs.

Harbor seal (Phoca vitulina richardii) use of a haulout in Vitus Lake at the terminus of the Bering Glacier (60° 5′ N, 143° 30′ W) was characterized by conducting 69 aerial surveys over the 2001–2003 period. Harbor seals were observed hauling out only on low, flat icebergs in Vitus Lake, predominantly (80% ± 3%) at the head of Seal River. There was a marked increase in seal abundance in the fall (from <200 to >900 seals), and as seal abundance increased, the average number of seals per iceberg remained relatively constant (10 ± 1 seals/iceberg), while the average number of icebergs occupied increased (from 12 to 48 icebergs in 2002). In 2003 the number of icebergs used was lower, and therefore seal density per berg was higher, than in 2002, suggesting that the availability of suitable ice influences grouping behavior in harbor seals. Diet and genetic studies suggest that harbor seals move into Vitus Lake from stocks in both Southeast Alaska and Prince William Sound in order to forage on local salmon runs. These findings have implications for ongoing efforts to determine appropriate stock structure for management decisions and suggest that the frequency and extent of seasonal movements must be considered when conducting regional population monitoring surveys. As human activity in the Bering Glacier area increases, monitoring and educational efforts should be initiated in order to ensure that harbor seals remain a functioning element of the ecosystem.

A 25–30 yr surge cycle anticipated by Post (1972) was confirmed by the 1993–1995 surge, although the advance culminated more than a kilometer short of the 1965–1967 surge limit. During the initial 6 mo. of the 1993–1995 surge the eastern terminus of the Bering Glacier Piedmont Lobe advanced 1.0–1.5 km at a rate that varied between 1.0–7.4 m/d, and thickened by an estimated 125–150 m. One year after the surge began an outburst of pressured subglacial water temporarily interrupted basal sliding and slowed ice front advance. Within days gravel and blocks of ice transported and deposited by that flood partially filled an ice-contact lake, forming a 1.5 km 2 sandur. During the next few months a second outburst nearly dissected a foreland island with the resulting construction of two additional sandar, each nearly 1 km 2 . Both outburst sites coincided with a subglacial conduit system that has persisted for decades and survived two surges. When the surge resumed, advance was intermittent and slower. A prominent push moraine marks the limit of ice advance on the eastern sector. Although basal sliding across a saturated substrate was a major contributor to surge-related changes along the eastern sector, the most profound foreland alteration was the result of outburst-related erosion, deposition, and drainage modification associated with outburst floods. The dominant modification of overridden terrain was subglacial hydraulic scouring of sub-kilometer scale basins, 15–20 m deep, and outburst-related proglacial sandur development. Only after a decade of retreat was it possible to assess the limited direct effects of overriding ice, which were confined to deposition of a sub-meter-thick deformation till, decameter-scale flutes, and drumlinized topography accompanied by truncation of subglacial strata.

The Bering and Steller Glaciers of southern Alaska provide the opportunity to investigate relationships between climate and tectonics in a glaciated mountain belt. The glaciers profoundly impact the climate, ecology, and landscape of the northeastern Gulf of Alaska margin. The glaciers flow among and over deformed and eroded rocks of the Yakutat microplate, where geological structures impart topographic variations in the landscape that strongly affect glacier dynamics. The Bering Glacier flows along a tectonic boundary within the microplate that separates two regions of different structural style and history. East of the glacier, erosion of folded and thrust-faulted sedimentary strata creates E-W ridges and valleys oriented at high angle to ice flow. Farther west, second-phase folds and faults are superimposed on these structures, creating mountain blocks with complex structural geometry. Where the second-phase limbs have an E-W structural grain the glaciers flow around broad headlands, and meltwater streams discharge southward through narrow canyons. N to NE trending fold limbs are streamlined by glacial scouring parallel to folded bedding, and the elongated mountains are separated by narrow ice- and water-filled troughs, or flat-floored sediment-filled valleys. Measurements of ice motion and glacier surface topography are used in conjunction with geological mapping to constrain the location of the tectonic boundary beneath the Bering Glacier. The boundary is inferred to lie beneath the west-central terminus and extend up-glacier, passing west of the Grindle Hills and extending into the Khitrov Hills. The large volume of debris trapped in the Medial Moraine Band along the western edge of the Bering Glacier overlies a NNE-trending bedrock high formed by second-phase folding. The Bering and Steller Glaciers coalesce beneath the Medial Moraine Band, which then divides into several flows of faster and slower moving ice and debris. Thermokarst dominates the glacial structure on the lower part of the moraine band, where ice flow is 20 m/a or less. To the west, the Steller Glacier diverges into several lobes where it flows among remnants of second-phase folds. The tectonic boundary beneath the Bering Glacier is inferred to be a concealed thrust or oblique-slip thrust fault that rises from the Aleutian megathrust or subduction zone, juxtaposing the second-phase folded terrain against and over the E-trending fold belt beneath the glacier. There is no surface expression of the tectonic boundary because of intense erosion and transport of rock debris by the glacier and meltwater rivers. Trunk river channels beneath the Bering Glacier are presumably affected by remnant structures at its base, where NNE-trending ridges and sediment filled troughs are juxtaposed against E-trending topography oriented at high angle to ice flow. This change in basal topography and structure presumably constricts the basal drainage network opposite a sharp bend in the Khitrov Hills, where surging initiated in 1993. Episodic freezing or deformation by ice flow in this part of the drainage network may create elevated fluid pressure that triggers episodic surging.

Since 1890, Bering Glacier has been retreating from its Little Ice Age position near the Gulf of Alaska. Although this retreat has been punctuated by spectacular surge events, areas previously under the ice have regularly become exposed following surges. Sedimentary deposits above the current level of Vitus Lake are well dated to the past 2200 a. Older deposits eroded from the floor of the previous fjord are deposited above lake level by ice advance, and these sediments and fossils allow us to reconstruct the past history of Bering Glacier. Bering Glacier extended past the modern Pacific coastline during the Late Glacial Maximum (LGM), but retreated up its fjord by 13,000 a ago, leaving an embayed coastline inhabited by marine invertebrates until 5000 a ago. The shoreline was then uplifted, and terrestrial sandy outwash with intermittent peat bogs covered the landscape. Forests covered the area by 4000 a ago, with evidence of 800 a of continuous forest occupation (from 200 B.C. to A.D. 600) found at the Ancient Forest site. This forest was buried by rising lake levels, and between A.D. 600 and 1000, active gravel outwash deposition alternated with thin peats growing on more stable surfaces. Subsequently, active outwash deposits aggraded to 21 m above the current level of Vitus Lake as glacier outwash covered the forelands. A thin till capping the advance out-wash is the only indicator of the Little Ice Age advance that occurred sometime after A.D. 1100. The sediment record does not hold evidence for multiple advances of Bering Glacier during the past 2200 a.

A collection of marine invertebrates from Holocene glacial deposits of the Bering Glacier indicates that the Gulf of Alaska shoreline was several or more kilometers north of its present position during the late Pleistocene–early Holocene. Conventional radiocarbon dates of 29 bivalves from five localities range in age from 7590 ± 140 to 13,230 ± 25 14 C yr B.P. These marine invertebrates provide a new tool not previously used to refine glacial chronology. Because the invertebrates were deposited by meltwater at the face of the receding ice, they must have been incorporated into the ice stream at points inland (north) of the existing glacier front and transported in portions of the Bering Glacier flowing southward. The logical position for an ancient shoreline would be the topographic break between the base of the coastal mountains and the present forelands. If that is correct, then the forelands were deposited within the past 7000 a. Known habits of the collected invertebrates were used to reconstruct the nature and biological composition of the ancient nearshore environment. Our results are consistent with other work, demonstrating that mollusks inhabiting nearshore environments in the Arctic are particularly useful in the reconstruction of paleocommunities and paleoenvironments. The unusual preservation of delicate invertebrate skeletons during transport in glacial ice is difficult to explain. We have been unable to find a description of this type of entrainment, transport, and preservation elsewhere. Sediment preserved in the interior of some mollusk shells is a cohesive silt. If the invertebrates were encased in seafloor sediments and entrained into glacier ice, skeletons could have been protected by this sediment during transport and released intact when the silt blocks thawed during deposition of melt-out till. Melt-out till is sediment released by melting of stagnant or slowly moving debris-rich glacier ice. Fragments of shells are ubiquitous in all drift deposits (any type of sediment originating from glacial deposition) south of the glacier front, but fragile intact skeletal remains were commonly found only at four localities, suggesting unique depositional conditions. Intertidal and shallow subtidal species dominate the collection, indicating an origin close to a shoreline. A total of 110 species representing 6 invertebrate phyla were identified. Most species are mollusks (79%), but bryozoans (9%), arthropods (8%), polychaetes (2%), echinoderms (<1%), and a single protozoan (<1%) were also present. This biota includes species similar to those found in the modern Gulf of Alaska fauna. The identified species show a strong correlation with invertebrates described in studies of the contemporary Gulf of Alaska that include infaunal and epifaunal organisms from various depths and ecological habitats. Some invertebrate species indicate geographical shifts in distribution to the northwest and east.

The Bering Glacier Region reveals evidence of relative sea-level change or land uplift and subsidence resulting from predominantly glacio-isostatic and tectonic causes. From its glacial maximum extent on the continental shelf, Bering Glacier had retreated inland of the present coast and north of its present terminus by ca. 14,000 yr B.P. Relative sea level was above present ca. 9200 yr B.P. to at least 5000 yr B.P. before falling to below present. Analyses of sediment cores from the marsh east of Cape Suckling show a great earthquake ca. 900 cal (calendar) yr B.P. that caused coseismic land uplift and a tsunami. Relative sea level rose to above present by the early twentieth century, before coseismic land uplift, relative sea-level fall, in A.D. 1964. Correlation with sites from Cook Inlet to Icy Bay shows some critical differences between previous earthquake deformation cycles and A.D. 1964, related to the regional-scale tectonic setting.