Research papersA continental shelf sedimentary record of Little Ice Age to modern glacial dynamics: Bering Glacier, Alaska
Introduction
The dynamic behavior of continental ice and its relationship to global climate change have become a major concern because of the pronounced influence it has on regional climate, glacifluvial runoff, and eustacy. Strong evidence indicates that glaciers are experiencing increased ice discharge and accelerating rates of retreat that are likely climate driven (Arendt et al., 2002, Dyurgerov and Meier, 2000, Larsen et al., 2007, Oerlemans, 2005, Solomina et al., 2008). Interpreting the relationship between dynamic glacial behavior and climate forcing can provide a necessary perspective on larger spatial-scale changes observed over the past century (Davis et al., 2009, Oerlemans, 2005, Solomina et al., 2008). Surging glaciers experience quasi-periodic abrupt increases in ice-flow velocity and are found throughout the northern hemisphere under a range of thermal regimes (Barrand and Murray, 2006, Copland et al., 2003, Dowdeswell et al., 1995, Dowdeswell and Williams, 1997, Grant et al., 2009, Harrison and Post, 2003, Kamb et al., 1985, Moon et al., 2012, Striberger et al., 2011). Although not areally predominant, surging glaciers can dominate temporal fluctuations in ice flow velocity for certain regions (Alley et al., 2006, Moon et al., 2012). Surges rapidly transfer ice from accumulation to ablation zones (Knudsen et al., 2007, Muskett et al., 2003, Muskett et al., 2008, Roush et al., 2003, Sauber et al., 2000), releasing the stored water back into the fluvial and marine environment, which have both regional and global implications (Alley et al., 2006, Arendt et al., 2002, Fellman et al., 2010, Schroth et al., 2011). Although the exact mechanisms that lead to surge behavior are known at a rudimentary level (Alley et al., 2006, Eisen et al., 2001, Harrison and Post, 2003, Lingle and Fatland, 2003, Murray et al., 2003, Raymond, 1987), the role of climate change on surge dynamics is less well constrained, but must be related to changes in geometry that control internal shear stresses (Eisen et al., 2001, Harrison and Post, 2003). Glacier geometry variations (ice thickness, areal extent) are governed by climatically controlled changes in glacial mass balances (Dowdeswell et al., 1995, Eisen et al., 2001, Harrison and Post, 2003, Tangborn, 2002). The temporal variability in surge frequency influenced by changes in mass balances has been noted for both temperate and polythermal systems, where negative mass balances lead to longer quiescent periods between surges and positive mass balances result in the opposite (Dowdeswell et al., 1995, Eisen et al., 2001). The Little Ice Age (LIA; ca. cal yr AD 1200–1900) is generally considered a time of global glacier expansion (Grove, 2004, Grove, 2008). For surging glaciers, the general correlation between positive mass balances and surge frequency would imply that surging should have been more frequent during the LIA. However, given the remoteness of most surging glaciers, historical accounts of their behavior during the LIA are lacking.
The temperate glacial dynamics of southern Alaska are noteworthy. This area includes the piedmont Bering and Malaspina Glacier systems and is the most extensive glacierized area in continental North America (Molnia and Post, 2010a) (Fig. 1). Within this region, the majority of ice is stored within the Bering Glacier system, the world's largest temperate surging glacier. The most recent major surge event occurred from AD 1993 to 1995 and caused the Bering Glacier to advance ∼9 km within several months into its adjacent proglacial lakes (Fleisher et al., 2010, Molnia and Post, 2010b, Molnia et al., 1994). Holocene changes of the Bering Glacier system have been constrained by glacial termini positions and secondary depositional features, which reveal that the LIA advance of the glacier was the most extensive since the Last Glacial Maximum (Barclay et al., 2009, Calkin et al., 2001, Crossen and Lowell, 2010, Wiles et al., 1999, Wiles et al., 2008). Missing from these terrestrial studies is documentation of Bering Glacier dynamics during the LIA, including evidence of surge dynamics resulting from the presumptive positive mass balances during this period.
For this study, the sediment record on the continental shelf adjacent to the Bering Glacier in the Gulf of Alaska is examined to document late Holocene glacial dynamics. Large outburst floods associated with glacial surging transport sediment and water in the form of buoyant surface plumes to the Gulf (Molnia and Post, 2010a,b), and Jaeger and Nittrouer (1999) were able to identify outburst flood facies and correlate each deposit to known surges for the last century. It has been suggested that the timing between Bering Glacier surges is climatically driven, with surges occurring after a period of enhanced ice accumulation, similar to other surging glaciers (Eisen et al., 2001, Harrison and Post, 2003, Lingle and Fatland, 2003, Striberger et al., 2011, Tangborn, 2002). Perhaps coincidentally, the 20–30 yr periodicity of historic Bering surges is similar to the multi-decadal periodicity in regional climate known as the Pacific Decadal Oscillation (PDO). Mantua and Hare (2002) and Bitz and Battisti (1999) documented how decadal-scale PDO forcing has a notable impact on the mass balances of maritime glaciers in Alaska. If surge periodicity is related to the rate at which a critical cumulative mass balance is attained (Eisen et al., 2001, Tangborn, 2002), we hypothesize that enhanced periods of positive mass balance at the Bering, such as during the LIA, should lead to more frequent surges.
In this study, we describe changes in shelf sedimentation that provide an extended record of sediment discharge from the Bering Glacier that can be used as a proxy for glacial surges and other processes responding to changes in ice dynamics. To assess this, a multicore, trigger core, and jumbo core were collected at a location that preserves a record of 20th century surge events (Jaeger and Nittrouer, 1999). An age model is developed using 210Pb geochronology and five radiocarbon dates. X-radiographs, physical properties of the core, and grain size distributions are used to identify and interpret lithofacies. The reconstructed climatic conditions for the Gulf of Alaska from Wilson et al. (2007) are used in conjunction with the age model to compare the timing of climatic events to lithologic properties that reflect changes in glacial sediment discharge.
Section snippets
Gulf of Alaska climate
The climate in the Gulf is primarily controlled by the position of the Aleutian Low (AL) pressure system, which dominates in spring and winter months, whereas during the summer months, climate is influenced by the North Pacific High pressure cell (Bond et al., 2003, Stabeno et al., 2004). The AL experiences decadal-scale variability in position and intensity as seen in the North Pacific Index (NPI) (Trenberth and Hurrell, 1994) and the Pacific Decadal Oscillation (PDO) (Mantua and Hare, 2002)
Methodology
During the 2004 R/V Maurice Ewing cruise EW0408, a 0.5 m-long multicore EW0408‐81MC1 (59° 56.5729′N, 143° 43.6805′W, 166 m water depth), a 13.6 m-long jumbo piston core EW0408‐82JC (59° 56.6094′N, 143° 43.3545′W, 154 m water depth) and its 2 m-long trigger core EW0408‐82TC were collected ∼16 km southwest from the mouth of the Seal River on the continental shelf (Fig. 1). This site is the same location where core AH-181-111KC was collected as described in Jaeger and Nittrouer (1999), a generally flat
Chronology
The 210Pb activity profile reveals a general decrease in activity with depth while 226Ra activity remains close to 1 dpm g−1 (Fig. 3). The 210Pb profile can be characterized as a non-steady state profile (Jaeger et al., 1998), which is evident as relative lows in activity near supported levels at 28 cm and 98 cm depth. Both of these depths are associated with low-density beds. 210Pb activities decay close to supported levels (4–5 half-lives, or ∼100 yr) at 1.48 m depth. Based on the first appearance
Chronology
An age model was developed from 210Pb radioisotopes, five radiocarbon dates, and interpretations of the lithology from X-radiographs. Episodic, non-steady sediment deposition is evident as low excess 210Pb activity values at 28 cm and 98 cm (Fig. 3), suggesting rapid deposition and minimal scavenging activity in the water column (Dukat and Kuehl, 1995, Jaeger et al., 1998, Kniskern et al., 2010, Sommerfield and Nittrouer, 1999). Both of these decreases in 210Pb activity correlate with the base of
Conclusions
The results of this study reveal that over the past 400 yr, changes in sedimentation on the continental shelf seaward of the Bering Glacier correlate with historical records of surging events, outburst floods, and with Gulf of Alaska paleoclimate tree-ring proxy records. The Bering Glacier terminus position influences the delivery of sediment to the adjacent continental shelf. Sediment accumulation over the past century consists of interbedding of thick mottled to laminated mud beds in the upper
Acknowledgments
The authors appreciatively acknowledge the crew and science party of cruise EW0408 for assistance in sample collection, and J.E.T. Channell and Kainian Huang at the research center for Paleomagnetism and Environmental Magnetism at the University of Florida, for assistance in magnetic susceptibility measurements. We thank two anonymous reviewers for constructive improvements. We gratefully acknowledge the USGS for the Landsat image of the Bering Glacier, and Larry Mayer and the staff at the
References (93)
- et al.
Outburst flooding and the initiation of ice-stream surges in response to climatic cooling: a hypothesis
Geomorphology
(2006) - et al.
Regional atmospheric circulation change in the North Pacific during the Holocene inferred from lacustrine carbonate oxygen isotopes, Yukon Territory, Canada
Quaternary Research
(2005) - et al.
Holocene glacier fluctuations in Alaska
Quaternary Science Reviews
(2009) - et al.
Enhanced late Holocene ENSO/PDO expression along the margins of the eastern North Pacific
Quaternary International
(2011) - et al.
Emplacement, modification, and preservation of event strata on a flood-dominated continental shelf: Eel shelf, Northern California
Continental Shelf Research
(2003) - et al.
Event sedimentation, bioturbation, and preserved sedimentary fabric: field and model comparisons in three contrasting marine settings
Continental Shelf Research
(2006) - et al.
Holocene coastal glaciation of Alaska
Quaternary Science Reviews
(2001) - et al.
Holocene and latest Pleistocene alpine glacier fluctuations: a global perspective
Quaternary Science Reviews
(2009) Temporal and spatial variability of the sediment grain-size distribution on the Eel shelf: the flood layer of 1995
Marine Geology
(1999)- et al.
Stratigraphic signatures due to flood deposition near the Rhone River: Gulf of Lions, northwest Mediterranean Sea
Continental Shelf Research
(2008)
Non steady state 210Pb flux and the use of 228Ra/226Ra as a geochronometer on the Amazon continental shelf
Marine Geology
Wave-supported sediment gravity flows currents: effects of fluid-induced pressure gradients and flow width spreading
Continental Shelf Research
River flooding, storm resuspension, and event stratigraphy on the northern California shelf: observations compared with simulations
Marine Geology
The impact of glacier runoff on the biodegradability and biochemical composition of terrigenous dissolved organic matter in near-shore marine ecosystems
Marine Chemistry
A decade of sedimentation in ice-contact, proglacial lakes, Bering Glacier, AK
Sedimentary Geology
Glacimarine sedimentation in Kangerdluk (Disko Fjord), West Greenland, in response to a surging glacier
Marine Geology
Floodplain processes in the Bengal Basin and the storage of Ganges–Brahmaputra river sediment: an accretion study using Cs-137 and Pb-210 geochronology
Sedimentary Geology
A brief consideration of climate forcing factors in view of the Holocene glacier record
Global and Planetary Change
A quantitative examination of modern sedimentary lithofacies formation on the glacially influenced Gulf of Alaska continental shelf
Continental Shelf Research
Sediment accumulation patterns and fine-scale strata formation on the Waiapu River shelf, New Zealand
Marine Geology
Flocculation and the loss of sediment from the Po River plume
Continental Shelf Research
Glacimarine sedimentary processes, facies and morphology of the South Southeast Alaska shelf and fjords
Marine Geology
Application of an analytical model of critically stratified gravity-driven sediment transport and deposition to observations from the Eel River continental shelf, Northern California
Continental Shelf Research
Modern accumulation rates and a sediment budget for the Eel shelf: a flood-dominated depositional environment
Marine Geology
Meteorology and oceanography of the Northern Gulf of Alaska
Continental Shelf Research
Observations of sediment transport on the Amazon subaqueous delta
Continental Shelf Research
The role of wave-induced density-driven fluid mud flows for cross-shelf transport on the Eel River continental shelf
Continental Shelf Research
Observations and modeling of wave-supported sediment gravity flows on the Po prodelta and comparison to prior observations from the Eel shelf
Continental Shelf Research
Post-depositional alteration and preservation of sedimentary event layers on continental margins, I. The role of episodic sedimentation
Marine Geology
The large-scale distribution and internal geometry of the fall 2000 Po River flood deposit: evidence from digital X-radiography
Continental Shelf Research
Century to millennial-scale temperature variations for the last two thousand years indicated from glacial geologic records of Southern Alaska
Global and Planetary Change
Dendrochronology and late Holocene history of Bering Piedmont Glacier, Alaska
Quaternary Research
Pulsational gravity-driven sediment transport on two energetic shelves
Continental Shelf Research
Rapid wastage of Alaska glaciers and their contribution to rising sea level
Science
Multivariate controls on the incidence of glacier surging in the Karakoram Himalaya
Arctic Antarctic and Alpine Research
Interannual to decadal variability in climate and the glacier mass balance in Washington, western Canada, and Alaska
Journal of Climate
Recent shifts in the state of the North Pacific
Geophysical Research Letters
Distribution of bottom sediments on the continental shelf, northern Gulf of Alaska, Scale 1:500,000. U.S
Geological Survey
Sedigraph technique
The distribution and flow characteristics of surge-type glaciers in the Canadian High Arctic
Annals of Glaciology
Holocene history revealed by post-surge retreat; Bering Glacier forelands, Alaska
Special Paper—Geological Society of America
North Pacific sea surface temperatures: past variations inferred from tree rings
Geophysical Research Letters
Mass-balance change as a control on the frequency and occurrence of glacier surges in Svalbard, Norwegian high Arctic
Geophysical Research Letters
Surge-type glaciers in the Russian high arctic identified from digital satellite imagery
Journal of Glaciology
Physical properties of the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica
Terra Antartica
Twentieth century climate change: evidence from small glaciers
Proceedings of the National Academy of Sciences of the United States of America
Cited by (4)
Evidence of recent flood deposits within a distal shelf depocenter and implications for terrestrial carbon preservation in non-deltaic shelf settings
2021, Marine GeologyCitation Excerpt :This is most notable with the low activities at the base of this layer between 8 and 10 cm. Low 210Pbex activities have been shown to be diagnostic of event sedimentation (e.g. Jaeger and Kramer, 2014; Palinkas and Nittrouer, 2007; Sommerfield and Nittrouer, 1999). These low 210Pbex activities in event deposits have been explained through a dilution effect where suspended sediment concentrations are elevated to a point where all the 210Pb particles are scavenged from the water column (Sommerfield et al., 1999), and/or low-activity sediment is supplied via fluid mud transport (Dukat and Kuehl, 1995).
The role of the cryosphere in source-to-sink systems
2016, Earth-Science ReviewsCitation Excerpt :Alpine glacial termini advanced within a few centuries associated with LIA cooling, and their subsequent retreat occurred within ~ 50–100 years (Oerlemans, 2005; Barclay et al., 2009). The end of the LIA in Alaska is reflected in increased proglacial sediment accumulation and glacigenic sediment discharge (Fig. 2B; Molnia and Post, 1995; Wiles et al., 1999; Barclay et al., 2009; Crossen and Lowell, 2010; Jaeger and Kramer, 2014). Proxy records of ice retreat associated with the abrupt warming transition at the Bølling interstadial at ~ 14.8 ka BP indicate a response time within the precision of the chronometer (several hundred years; Praetorius and Mix, 2014).
Formation and preservation of sedimentary strata from coastal events: Insights from measurements and modeling
2014, Continental Shelf Research