Muir Inlet Research Articles

Tree Ring—Dated Glacial History for the First Millennium c.e., Casement Glacier and Adams Inlet, Glacier Bay, Alaska, U.S.A.

ABSTRACTCalendar dating of tree-ring series from 16 logs sampled near the margin of Casement Glacier combined with tree-ring dates on 36 detrital logs from Adams Inlet, Glacier Bay National Park and Preserve, Alaska, show killing of trees by ice and lake sediments from the mid-sixth through mid-seventh centuries c.e. The dates from the land-terminating Casement Glacier show ice advance into a forest between 560 and 570 c.e. within a few kilometers of the 2011 retreating margin. Advance of the tidewater glacier in Muir Inlet blocked off Adams Inlet forming Lake Adams between 540 and 640 c.e. This glacier and lake history for Glacier Bay is consistent with other land-terminating ice expansions across the Gulf of Alaska that similarly show advance centered on 600 c.e., as well as other proxy records from lakes all suggesting cooling during this interval. The cooling closely follows a series of eruptions in the mid to late sixth century, which may have contributed to the cooling. Radiocarbon ages in Adams Inlet suggest that Lake Adams persisted through 880 cal. yr c.e. and drained by 1170 cal. yr c.e. Ice retreat and this lake drainage are broadly coincident with Medieval warming recognized along the Gulf of Alaska in dendroclimatic reconstructions. Shortly after this retreat, Little Ice Age readvance occurred with Casement Glacier coalescing with glaciers in Adams Inlet and the West Arm, subsequently filling all of Glacier Bay to its Holocene maximum by 1750 c.e.

Fjords as temporary sediment traps: History of glacial erosion and deposition in Muir Inlet, Glacier Bay National Park, southeastern Alaska

Glacimarine sedimentary deposits within the basins of Muir Inlet, a 48-km-long silled fjord, are interpreted from complimentary sets of high-resolution, seismic-reflection profiles using known glacial-advance and retreat history. Two prominent glacial erosion surfaces are identified: the lowest attributed to the Last Glacial Maximum (LGM) advance and the upper coincident with the Little Ice Age (LIA) advance. The LGM ice sheet, which advanced onto the continental shelf, was 1700 m thick in Muir Inlet and eroded bedrock, whereas the thinner LIA ice did not. LGM deposits >300 m thick occur beneath the LIA erosion surface in the deepest basins. Evidence for earlier Neoglacial advances is present in subaerial deposits; however, Neoglacial sediments preserved within the marine record are restricted to one depositional package on the entrance sill. Volumes of LIA retreat sediments were calculated within basins. An average annual sediment flux was calculated by modeling the duration of sediment contributed from Muir Glacier and from tributary glaciers and side-entry sources. The annual sediment flux ranged from 1.3 × 10 6 m 3 /yr to 4.6 × 10 7 m 3 /yr and increases logarithmically with increasing drainage basin area, similar to fluvial systems. This sediment flux does not only represent bedrock erosion. Additional sediment is contributed from persistent tributary glaciers and from LGM sediment stored within deeper basins. Basin-wide reflections characterize the most common seismic facies and indicate that strata are horizontal and continuous across each basin, confirming the importance of sediment gravity flows originating from sills and sloping fjord walls.

Spatial patterns and movements of red king and Tanner crabs: implications for the design of marine protected areas

Most examples of positive population responses to marine protected areas (MPAs) have been documented for tropical reef species with very small home ranges; the utility of MPAs for com- mercially harvested temperate species that have large movement patterns remains poorly tested. We measured the distribution and abundance of red king Paralithodes camtschaticus and Tanner Chio- noecetes bairdi crabs inside and outside of MPAs in Glacier Bay National Park, Alaska, USA. By tag- ging a sub-sample of crabs with sonic tags, we estimated the movement of adult crabs from one of the MPAs (Muir Inlet) into the central portion of Glacier Bay where fishing still occurs. Tanner crabs and red king crabs moved similar average distances per day, although Tanner crabs had a higher trans- fer out of the Muir Inlet MPA into the central bay. Tanner crab movements were characterized by large variation among individual crabs, both in distance and direction traveled, while red king crabs migrated seasonally between 2 specific areas. Although Tanner crabs exhibited relatively large movements, distribution and abundance data suggest that they may be restricted at large spatial scales by habitat barriers. MPAs that are effective at protecting king and especially Tanner crab brood stock from fishing mortality will likely need to be larger than is typical of MPAs worldwide. However, by incorporating information on the seasonal movements of red king crabs and the location of habitat barriers for Tanner crabs, MPAs could likely be designed that would effectively protect adults from fishing mortality.

Terrestrial gypsum from Alaska and Greenland in glacially influenced marine sediments

Abstract Gypsum grains were identified in Miocene–Pleistocene sediment cores from two deep-water ODP sites, Site 918 off the SE Greenland margin and Site 887 in the Gulf of Alaska, and in Holocene sediment cores from shallow-water localities in Disenchantment Bay and Muir Inlet in southern Alaska. Although initial morphologic and textural observations suggested a complex system in which the gypsum may have had more than one origin, quantitative sulfur isotope analyses of the gypsum provide evidence of its detrital nature. δ34S values in gypsum from southern Alaska range between +0.0 and +7.1‰. Gypsum has δ34S values between −27.1 and −27.5‰ in the Gulf of Alaska and values between −28.5 and +0.2‰ off the SE Greenland margin. All of these isotopic signatures are too highly depleted in δ34S to have precipitated from seawater, present or past. In addition there is no significant change in δ34S values for gypsum crystals with differing physical characteristics (abraded vs. unabraded) from the same stratigraphic horizon, suggesting all the gypsum is detrital regardless of the degree of abrasion. The isotopic and physical evidence, in combination with the onshore geology the environmental setting, and site characteristics of the gypsum-bearing marine localities, lead us to propose that the ultimate source of the gypsum is precipitation from freeze-induced terrestrial sediment or soil brines. Furthermore the combined evidence suggests that the subsequent occurrence of gypsum in glacimarine sediments results from ice-rafting (by icebergs or sea ice) of the frozen regolith and/or, in the proximal glacimarine setting of southern Alaska, very rapid burial via turbidity currents.

Modern tidal rhythmites deposited in a deep-water estuary

The sedimentary record in Muir Inlet, a macrotidal fjord in Alaska, is dominated by cyclic silt–mud rhythmites. Couplet thicknesses vary systematically in a vertical sequence and reflect a semidiurnal tidal regime. Semimonthly, monthly, bimonthly, and annual cycles can be identified both visually in cores and by spectral frequency analysis. An average annual sedimentation of 22.5 cmyr-1 occurs over a four-month meltwater season and is confirmed by 210Pb dating. These modern deep-water tidal rhythmites can be used to verify interpretations made on ancient rhythmites in the stratigraphic record, and they also provide a dating tool to interpret high latitude successions for high-resolution climate change.

Evaluation of conditions along the grounding line of temperate marine glaciers: an example from Muir Inlet, Glacier Bay, Alaska

In the marine environment, stability of the glacier terminus and the location of subglacial streams are the dominant controls on the distribution of grounding-line deposits within morainal banks. A morainal bank complex in Muir Inlet, Glacier Bay, SE Alaska, is used to develop a model of terminus stability and location of subglacial streams along the grounding line of temperate marine glaciers. This model can be used to interpret former grounding-line conditions in other glacimarine settings from the facies architecture within morainal bank deposits. The Muir Inlet morainal bank complex was deposited between 1860 A.D. and 1899 A.D., and historical observations provide a record of terminus positions, glacial retreat rates and sedimentary sources. These data are used to reconstruct the depositional environment and to develop a correlation between sedimentary facies and conditions along the grounding line. Four seismic facies identified on the high-resolution seismic-reflection profiles are used to interpret sedimentary facies within the morainal bank complex. Terminus stability is interpreted from the distribution of sedimentary facies within three distinct submarine geomorphic features, a grounding-line fan, stratified ridges, and a field of push ridges. The grounding-line fan was deposited along a stable terminus and is represented on seismic-reflection profiles by two distinct seismic facies, a proximal and a distal fan facies. The proximal fan facies was deposited at the efflux of subglacial streams and indicates the location of former glacifluvial discharges into the sea. Stratified ridges formed as a result of the influence of a quasi-stable terminus on the distribution of sedimentary facies along the grounding line. A field of push ridges formed along the grounding line of an unstable terminus that completely reworked the grounding-line deposits through glacitectonic deformation. Between 1860 A.D. and 1899 A.D. (39 years), 8.96×10 8 m 3 of sediment were deposited within the Muir Inlet morainal bank complex at an average annual sediment accumulation rate of 2.3×10 7 m 3/a. This rate represents the annual sediment production capacity of the glacier when the Muir Inlet drainage basin is filled with glacial ice.

CHANGES OF GLACIERS IN GLACIER BAY, ALASKA, USING GROUND AND SATELLITE MEASUREMENTS

The deglaciation of Glacier Bay, Alaska is studied using historical maps, field measurements, and satellite imagery. In general, both tidewater and non-tidewater glaciers in the area have receded during the last century, but the rates of recession are quite variable, especially in the case of the tidewater glaciers. Available average air temperature data from nearby meteorological stations show a general warming trend, especially over the last 20 years. Such a warming trend may help to explain recession of the non-tidewater glaciers of the area. Comparison of September Landsat multispectral scanner imagery from 1973 and 1986 shows that the amount of vegetation increased significantly and rapidly as glaciers receded. The vegetation within a Landsat subscene covering Muir Inlet increased about 86% during the 13-year period. The once-impressive Muir Glacier, a tidewater glacier, has receded dramatically since the late 1800s. Satellite measurements show that the terminus retreated >7.3 km between 1973 and 199...

Holocene Glaciolacustrine Sedimentation in Muir Inlet and Ice Advance in Glacier Bay, Alaska, U.S.A.

Holocene ice advance in the West Arm of Glacier Bay, southeast Alaska, resulted in damming of a tributary, Muir Inlet. Glaciolacustrine sediments record two separate damming events, and radiocarbon dates place these at 2500 to 2000 and 1700 to 900 BP. A third advance is known to have culminated in deposition of an end moraine at the mouth of the Bay ca. 300 BP. Very sketchy evidence from the West Arm suggests initial advance may have begun there ca. 4500 BP. At the resolution afforded by geologic data, the three well-documented advances of the Glacier Bay Glacier are broadly synchronous with advances of the Brady Glacier and glaciers in the Wrangell-St. Elias mountains and Icy Bay Fiord. All of these advances appear to have resulted from climatic fluctuations in the coastal sector of southern Alaska. At least one fiord glacier in the region, Lituya Glacier, has advanced and retreated in a manner apparently independent of climate.

Holocene Glaciolacustrine Sedimentation in Muir Inlet and Ice Advance in Glacier Bay, Alaska, U.S.A.

Holocene Glaciolacustrine Sedimentation in Muir Inlet and Ice Advance in Glacier Bay, Alaska, U.S.A.

Areal Distribution of Sedimentary Facies Determined from Seismic Facies Analysis and Models of Modern Depositional Systems: ABSTRACT

Seismic facies analysis was applied to 3.5-kHz single-channel analog reflection profiles of the sediment fill within Muir Inlet, Glacier Bay, southeast Alaska. Nine sedimentary facies have been interpreted from seven seismic facies identified on the profiles. The interpretations are based on reflection characteristics and structural features of the seismic facies. The following reflection characteristics and structural features are used: reflector spacing, amplitude and continuity of reflections, internal reflection configurations, attitude of reflection terminations at a facies boundary, body geometry of a facies, and the architectural associations of seismic facies within each basin. The depositional systems are reconstructed by determining the paleotopography, bedding patterns, sedimentary facies, and modes of deposition within the basin. Muir Inlet is a recently deglaciated fjord for which successive glacier terminus positions and consequent rates of glacial retreat are known. In this environment the depositional processes and sediment characteristics vary with distance from a glacier terminus, such that during a retreat a record of these variations is preserved in the aggrading sediment fill. Sedimentary facies within the basins of lower Muir Inlet are correlated with observed depositional processes near the present glacier terminus in the upper inlet.

Distribution and haul-out behavior of harbor seals in Glacier Bay, Alaska

Over 5000 harbor seals haul out on icebergs calved from tidewater glaciers in Muir and Johns Hopkins inlets in Glacier Bay, Alaska. During June, these sites are used primarily by parous females and pups, and in August, by molting seals. The number of mothers and pups was higher than expected for the total number of seals in Glacier Bay, indicating an immigration of some parturient females from outside Glacier Bay. The number of seals counted varied throughout the day with greatest numbers around midday. In Muir Inlet the number of seals hauled out was positively correlated with percent ice cover. Ice that is suitable for hauling out may presently limit the abundance of seals in this area. The retreat of Muir Glacier has dramatically reduced the ice available to seals and, if it continues, will likely result in the elimination of drift-ice habitat in the near future. Seals from both inside and outside Glacier Bay apparently use ice habitat in Muir and Johns Hopkins inlets when giving birth, when nursing pups, and when moulting for protection from terrestrial and marine predators, and because it is relatively abundant and easily accessible at all tides and times.

Interlaminated ice-proximal glacimarine sediments in Muir Inlet, Alaska

Muir Inlet in Glacier Bay, Alaska, is a glacial fjord receiving a tremendous volume of sediment annually. The rate of sediment accumulation is greatest proximal to Muir Glacier (about 9 m yr −1) and decreases away from the glacier. The primary sediment sources are meltwater streams discharging at subglacial and ice-marginal positions to form overflows, interflows, and underflows (continuous turbidity currents). Overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge. These effects produce cyclic deposits of a thin fine-grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina. This lamina couplet is termed a cyclopel. Underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems. Underflow deposits occur only in proximal positions (<0.5 km from glacier face), and are coarse-grained, reverse to normal graded, and exhibit an increase in sorting and sand content up-layer. Ice-rafted debris (identified as particles >177 μm) is ubiquitous, though low (<5% by weight), and occurs as isolated particles, frozen pellets, or as lenses that in cores may have a lamina appearance. Proximally, ice-rafted debris is difficult to identify because proximal sediment is often as coarse-grained. Deposited sediment may be reworked by tidal currents, and sediment gravity flows. Depositional processes operating in Muir Inlet produce interlaminated sand/silt/clay that characterizes sediment proximal to a glacier and fines seaward to mud. Sediment is classified into one of three sediment types: 1. (1) Type I sediment is very fine grained (mean 8.65–7.17 ø), low in sand (0.1–11.2%), and very poorly to poorly sorted. It is the dominant sediment type in Muir Inlet, and is transported by plumes and deposited by suspension settling. 2. (2) Type II sediment is fine- to coarse-grained (mean 6.70–3.12 ø), low to high in sand (5.1–86.6%), and very poorly to moderately sorted. It represents reworked sediment, proximal plume deposits, or coarse-grained laminae of cyclopels. 3. (3) Type III sediment is coarse-grained (mean 3.89–2.38 ø), high in sand (58.0–100.0%), and poorly to well sorted. It is deposited by sediment gravity flows or underflows.

On upwelling driven by the melt of ice shelves and tidewater glaciers

Enhanced biological activity at the faces of ice shelves and tidewater glaciers has long been noted. One of several possible mechanisms for driving upwelling in these areas, the melting of glacial ice and the resulting buoyant plume, has been investigated. Comparison of the upwelling effects in Muir Inlet, Alaska and d'Iberville Fiord, Northwest Territories, indicates that the temperature of the seawater far from the ice face (several glacier depths) has a strong influence on the convective process. Employing a simple equation of state, basic thermodynamics, and laboratory results from boundary layer measurements on heated plates in air, the melt rate of a vertical ice wall in a stratified ocean is shown to be ▪ where m is the melt rate, ΔT is the temperature difference between the ice-seawater boundary and the far field and ▪ is the far field density stratification in the ocean. The upwelling effect due to melting is strongly dependent upon the temperature elevation of the sea above the freezing point.

Seasonal Characteristics of Water Masses in Muir Inlet, a Fjord with Tidewater Glaciers

The presence of two distinct seasonal water masses with transitions between them has been revealed in Muir Inlet, a fjord with tidewater glaciers in southeast Alaska. In spring a homogeneous water mass was found in which over 70% of the water fell into the ranges 31.0–31.2‰ salinity and 3.0–3.5 C. Heterogeneous water masses were found in summer and fall. The transition from the homogeneous to the heterogeneous water mass is explained on the basis of an entrainment mechanism during the summer high runoff period. It is suggested that the homogeneous spring condition derives from the intrusion of water from outside the fjord over the entrance sill which continues into early summer. This water exchange is driven primarily by tidal energy and depends upon denser water being available outside the sill during fall and spring. The differences between inlets with and without tidewater glaciers result from the melting of glacial ice in contact with warm, saline water masses. The melting of glacial ice appeared to continue at all seasons in Muir Inlet. The dissolved oxygen content confirms tha almost continuous renewal, showing only relatively small seasonal variations.

The Role of Dryas Drummondii in Vegetation Development Following Ice Recession at Glacier Bay, Alaska, with Special Reference to Its Nitrogen Fixation by Root Nodules

Students of late-glacial and post-glacial paleoecology are continually trying to visualize the various stages through which the developing ecosystems passed following recession of continental ice sheets. Their interest in this subject has been so great that many biogeographers (see Love & Lbve 1963) have been stimulated to develop hypotheses to explain where, how and when the various species were dispersed, became established, and developed into mature communities. Specialized methods have been developed to investigate the problem including microand macro-fossil analyses from peat bog and lake sediments, use of plant distribution data, genecological studies and comparative ecological investigations. The last-named method makes use of analogues, i.e., present-day situations are studied and inferences are made to conditions as they may have existed in the past. In application to the post-glacial plant migration problem, the nearest present-day analogue is newly deglaciated terrain exposed to colonization by plants. Many areas of the world have undergone deglaciation in the past two or three centuries (Flint 1957), but none are known to be as extensive as those at Glacier Bay, Alaska (Fig. 1) where ice fronts today are as much as 61 miles (98 km) behind the positions occupied in 1760 (Lawrence 1958). The importance of the Glacier Bay area for its interpretative value in gaining an understanding of post-glacial plant migration problems was recognized by Cooper (1923), who credited Lawrence Martin of the United States Library of Congress for calling the area to his attention. Because of the rapid recession of ice in Glacier Bay, a large gap has been opened up between the source of seeds and spores and the newly-exposed surfaces at low altitude. At high altitude, however, there remain isolated colonies of alpine (and in some areas subalpine) vegetation that survived on high ridges and nunataks above the maximum 18th century ice limit. The establishment of forest trees on the shores of Glacier Bay has been a slow process, requiring 50-100 years in some places (Cooper 1923). Within the past 30 years perhaps 35-50 km2 of newly-bared terrestrial surfaces have been exposed near the head of Glacier Bay, especially in the vicinity of Muir Inlet, where insufficient time has elapsed for trees and shrubs to become established. The surfaces nearest the melting ice faces are devoid of any vascular plants. Others, somewhat older (Phot. 1) have scattered pioneers, at first depauperate individuals of dwarf fireweed (Epilobium latifoliumn L.), sedges (species of Carex, Juncus, Eriophorum, and others), cottonwoods (Populus trichocarpa Torr. & Gray) and willows (Salix spp.). Many woody plants which normally

The Changing Proglacial Environment of the Casement Glacier, Glacier Bay, Alaska

The glacier has an area of fifty to sixty square miles with extensive neve basins between 3000 and 5000 feet. The Casement Glacier has retreated north-eastward from Muir Inlet where it joined the Muir Glacier at the beginning of the present century, and northward from the shores of Adams Inlet where it once joined the Adams Inlet Glacier. Apart from the Klotz Hills (Fig. 2) in the south, and the area to the north of Forest Creek in the north, the area between Muir Inlet and the present ice margin consists entirely of glacial and fluvioglacial deposits. It is this area of approximately fifteen square miles that will be considered in this paper. A thick gravel deposit that has been shown to be Hypsithermal in age1 forms a steep scarp (Fig. 3) behind a series of gravel fans along the east shore of Muir Inlet. This steep scarp, which is generally thirty to sixty feet high, is backed by a more gentle slope rising to a northsouth trending ridge generally between 200 and 300 feet in altitude. To the east of this ridge the topography is irregular but has a general slope down to about 130 feet at the present ice margin. Several large meltwater channels have been cut through the main north-south ridge. Except for the most northerly of the channels, which is now occupied by a relatively small stream named Forest Creek, the channels are not occupied by streams. All the meltwaters flowing off the south-eastern part of the Casement Glacier now enter an arm of Adams Inlet which will be referred to in this paper as Seal Inlet. The glacial chronology since the retreat of the Wisconsin Age glaciers in Glacier Bay is well known. R. P. Goldthwait,2 using thirty-six radiocarbon dates, was able to date the deposits accumulated during the Hypsithermal period and the events of the Little Ice Age glaciation. He established that by 7500 years B.P., the Wisconsin Age glaciers had withdrawn farther than those existing at present. He also stated that gravel and lacustrine deposits filled the upper bays to present sea-level about 7000 years ago and reached Ioo metres above present sea-level between 1700 and 2500 years ago. The southward expansion of glaciers now referred to as the Little Ice Age began as early as 2735 B.P. These advancing glaciers eroded the outwash that accumulated during the Hypsithermal period, removing most of it from the middle of the valleys and streamlining those deposits that occurred in protected localities. During this period of glacier expansion, a silty grey till was laid down on top of the Hypsithermal deposits to a

Glacier Recession in Muir Inlet, Glacier Bay, Alaska

Glacier Recession in Muir Inlet, Glacier Bay, Alaska

The Muir Glacier

Based on the author9s observations in 1886, a description of the dimensions and characteristics of the glacier, its moraines, movement, subglacial streams, retreat, buried forest, kames and kettle-holes about its mouth, and transportation and waste by water; with mention of other glaciers reaching Glacier Bay, and a list of twenty-seven plants found during August in Muir Inlet.