Sediment accumulation rates in the West Arm of Glacier Bay, Alaska based on 210 Pb analysis, geochronology and X-radiography

 

 

 

 

 

Justin Bergquist

 

University of Washington

School of Oceanography

Seattle, Washington 98105

 

docj@u.washington.edu

206-883-6569

 

 

 

29 May 2008

 

 

 

                                   

 

Non -Technical Summary

 

            In the last century, fast retreat of glaciers in Alaska has deposited a diverse collection of glacial sediments in Glacier Bay inlets.  The goal of this project was to describe sediment layers in Glacier Bay to reveal a 100-year timeline that can be correlated with climate change in the last century.  Previous studies of sediment traps and cores in Glacier Bay revealed some of the fastest accumulating sediments in the world (Cai et al 1997).  To compliment these previous sediment accumulation rate studies three new stations in the West Arm and one new station in Muir Inlet, all located in Glacier Bay, were sampled from March 18-21, 2008 aboard the Research Vessel Thomas G. Thompson using a coring device.  Sediment accumulation rates were calculated using various chemical analyses.  Photographs and x-rays were also taken to examine different layers of sediment to establish a timeline.  This research enhances previous data sets by examining sediment that has accumulated in the last 15 years.

 

Results in non-technical terminology to be completed soon

 

 

 

 

 

                       

 

 

 

 

 

 

 

 

 

 

 

 

 

Acknowledgements   

 

            I appreciate the assistance provided by the fellow scientists and students from the University of Washington Oceanography department.  Special thanks to Professor Chuck Nittrouer for the knowledge, encouragement and providing me all the gear and equipment for my research.  Thanks to Professor Deb Kelley for all the adventure, guidance, knowledge, editing and for believing in me.  Thanks to Professor Rick Keil for advice, knowledge, humoring me, visualizing my potential and a once in a life-time opportunity to visit Glacier Bay Alaska. Thanks to my colleague Brandon Knox for being my partner in this whole project, getting extremely dirty, cold, tired, fatigued and humoring me when I was starting to act a little goofy from sleep deprivation.  I could have not done it without you Brandon.  Thanks to Christina Biladeau for her help, advice and bag labeling.  Thanks also to Joshua Hill for making the night shift run smooth as silk, for helping me lift that heavy Soutar Corer repeatedly and for all the hands on help with Kasten core deployment.  Thanks to Eric Collins for the feedback, photographs, and making me laugh.  Thanks also to all of the other professors and students on the trip for making this trip to Glacier Bay a success.  The successful completion of this study was greatly facilitated by the crew of the R/V Thompson.

 

 

 

 

 

 

 

 

Abstract                     

            To be completed later

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Introduction

            Glacier Bay National Park and Preserve (Fig 1) is located ~ 100 km west of Juneau, Alaska.  In the late 19th century Glacier Bay was predominantly covered with glaciers from the Little Ice-Age period (Cai et al., 1997). In the following years, these glaciers have rapidly retreated, exposing numerous glacial-carved fjords.  Variations in sediment input into the bay are likely directly linked to these retreats.   “Koppes and Hallet (2002) note that fjords are efficient sediment traps for sediment produced by tidewater glaciers”.  “ These fjords contain complete sequences of glacial debris, from which we can assess the relationship of sediment production by glaciers to the extent of glacier cover, glacier mass balance and history of retreat” (Koppes & Hallet 2002).  “Erosion rates of tidewater glaciers in Alaska are on the order of cm/year for the last century, an order of magnitude higher than the highest erosion rates in the world” (Hallet 1996, Koppes & Hallet 2002).   “Studies in Glacier Bay National Park and Preserve elucidate interactions and linkages among terrestrial, lake, stream and marine intertidal ecosystems as the landscape evolves following ice recession”(Milner et al. 2007).  These ecosystems are shifting from a physical to a biotic control, enhancing the complexity of the communities (Milner et al. 2007).

 The study outlined presents the first quantitative analyses of 210Pb, coupled with x-radiography and stratigraphy to examine sediment accumulation rates in various environments with in Glacier Bay. These environments include Tarr and Muir Inlets and other inlet mouths in the West Arm (Fig 1).  Determination of sediment accumulation rates is critical to calculating sediment yields from glacial erosion.  Previous sediment trap and sediment core data show that sediment accumulation rates decrease away from the glacier termini of Tarr Inlet in three distinctive zones: Ice-proximal, Ice-berg and Ice-distal zones (Fig 2) (Cai et al., 1997).  In Tarr Inlet, the Ice-proximal zone is characterized by high and variable sediment accumulation rates ranging from tens of cm/yr to tens of m/yr, with an average of 3-4 m/yr.  Sediment accumulation rates in the Ice-berg zone: upper (closer to glacier terminus), middle and lower (furthest away from glacier terminus), range from 100 cm/yr, 40 cm/yr, and 19cm/yr, respectively.   In contrast, rates in the upper and lower areas of the Ice-distal zone, range from 6 cm/yr to 3.2 cm/yr (Cai et al. 1997). 

This study conducts Kasten core sampling from areas near previous sediment studies to augment information on accumulation rates and also determined if sedimentation rates have changed since the mid 1990s.  To examine possible similarities and differences of sedimentation dynamics in Tarr and Muir Inlets this study also conducted sampling of Kasten cores near other inlet mouths in the West Arm that are fed by John Hopkins, Lamplugh and Geikie glaciers.  210Pb analysis, x-radiography and x-ray stratigraphy of the sediments was conducted to characterize different lithofacies.  These data allow examination of rapid retreat and advance of glacier termini as indicated by thickness, type of sediment layering and determination of sediment accumulation rates. 

 

 

 

 

 

 

Methods

Seabed sampling in Glacier Bay was performed from the R/V Thomas G. Thompson during a cruise in March 2008.  To broadly characterize layering in the sub-sea floor and sediment thicknesses, 3.5 kHz surveys were conducted. These data were important in determining optimal sampling sites.  In addition, EM300 multi-beam surveys were co-located to provide additional information on bottom topography. Following preliminary survey studies, a Van Veen grab (Fig 3) or Soutar core (Fig 4) sample of the proposed site was conducted to determine the presence of boulders or areas of coarse-grained sediment accumulation that would prevent taking a Kasten Core (Fig 5).  If the sampling site was adequate, a Kasten Core was taken and recovered on deck.

  To provide information on sediment accumulation rates within Glacier Bay, four Kasten cores of various lengths were obtained near Glacier Bay National Park CTD stations, Station #s KC-10, 16, 21 and 23 (Fig 1).  Kastenlot corer was assembled and deployed (See Appendix A) on board.   Kasten cores were measured, described and digitally imaged upon recovery.  Kasten cores were subsampled on board for x-radiography, geochemistry and sedimentological properties. Plexiglas trays (5 X 2 X 30 cm) were inserted into the Kasten cores to provide samples for x-radiography performed back at Marine Science sediment lab.  Sediment was collected from 2 cm intervals and homogenized for geochemistry and sedimentological properties.  Two sediment samples from every 2 cm interval were bagged and labeled for archive and laboratory analyses back at Marine Science sediment lab.   X-ray trays and sediment baggies were stored in a cold room on board. On shore laboratory procedures include pre lab procedures (T. Drexler. 2007)(See Appendix B) and 210Pb analysis procedures based on alpha and gamma spectroscopy and the 210Po method (Nittrouer et al. 1979)(See Appendix C).

 

           

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Results

            Four Kasten cores were taken in Glacier Bay (Table 1, Fig1) in March 2008.   KC-23 was conducted in Geikie Inlet at 16:58 on March 18, 2008. A Van Veen grab sampler was conducted prior to ensure a quality Kasten core sample.   The Van Veen revealed muddy sediment with a polychaete.  The Kasten core was conducted at a 99 m depth and retrieved a 93 cm long core for sampling (Fig 6).  Three X-ray trays were taken from the core (Fig 7).  The core was characterized by lighter brown colored mud at the top with a progressively darker grey mud towards the bottom.  Total 210 Pb activities varied from       to       dpm g-1.  The resulting excess 210 Pb activities were           dpm g-1.  The sediment accumulation rate was       cm yr-1 (Fig 8). 

KC-21 was conducted in northern Tarr Inlet at 17:15 on March 20, 2008.  A Soutar core was conducted prior to ensure a quality Kasten core sample.  Two X-ray trays were taken from the top 30 cm of the Soutar core (Fig 9).   The Kasten core was conducted at a 217 m depth and retrieved a 57 cm long core for sampling (Fig 10).  Two X-ray trays were attempted, but only the top tray was recovered (Fig 11).  The bottom tray broke on a 8cm diameter cobble (Fig 12), found between 33- 43 cm depth of the core.  This core was characterized with a muddy top 30 cm, sandier mud at 30- 40 cm depth and sandy with smaller cobbles at 40- 57 cm depth.  Total 210 Pb activities varied from       to       dpm g-1.  The resulting excess 210 Pb activities were           dpm g-1.  The sediment accumulation rate was       cm yr-1 (Fig 13).

KC-10 was conducted between Reid Inlet and Russel Island at 22:15 on March 20, 2008.  A Soutar core was conducted prior to ensure a quality Kasten core sample.  The Kasten core was conducted at a 369 m depth and retrieved a 207 cm long core for sampling (Fig 14). No X-ray trays were taken from the core.  This core was characterized by very soupy mud all the way through. Total 210 Pb activities varied from       to       dpm g-1.  The resulting excess 210 Pb activities were           dpm g-1.  The sediment accumulation rate was       cm yr-1 (Fig 15).

KC-16 was conducted East of Hunter Cove in Muir Inlet at 21:02 on March 21, 2008.  A soutar core was conducted prior to ensure a quality Kasten core sample.  The Kasten core was conducted at a 294 m depth and retrieved a 68 cm long core for sampling (Fig 16).  No X-ray trays were taken from the core.  This core was characterized by lighter brown mud in the top 10 cm, getting progressively turning to darker grey mud with black bands intertwined into the sediment.  A 2.5 cm diameter rock was found at 38 cm depth in the core (Fig 17).  A chunk of wood was also found when the sediment dividers were being rinsed off.  Total 210 Pb activities varied from       to       dpm g-1.  The resulting excess 210 Pb activities were           dpm g-1.  The sediment accumulation rate was       cm yr-1 (Fig 18).

Data tables and porosity calculations are displayed in Appendix D.

 

 

 

 

 

 

 

 

Discussion

            To be completed later

Conclusions

            To be completed later

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References

Cai, J., R.D.Powell, E.A. Cowan ,and P.R. Carlson. 1997. Lithofacies and     seismic reflection interpretation of temperate glacimarine sedimentation in Tarr Inlet, Glacier Bay Alaska.  Mar. Geo.143: 5-37.

 

Drexler, T. 2007. 210Pb Analysis Instructions: Pre-Lab and Lab procedures. Handout.

 

Hallet, B., L.Hunter, and J.Bogen. 1996. Rates of erosion and sedimentation evacuation by glaciers: A review of field data and their implications. Global and Planetary Change 12: 213-235.

 

Jaeger, J.M. and C.A. Nittrouer. 1999. Marine record of surge-induced outburst

                 floods from the Bering Glacier, Alaska. Geology. 27: 847-850.

 

Jaeger, J.M. and C.A. Nittrouer. 1999. Sediment deposition in an Alaskan fjord:     Controls on the formation and preservation of sedimentary structures in Icy Bay. Journ. Sed. Res. 69: 1011-1026.

 

Koppes, M.N. and B. Hallet. 2002. Influence of rapid glacial retreat on the rate of erosion by tidewater glaciers. Geology. 30: 47-50.

 

Kuehl, S.A., C.A. Nirrtouer, D.J. DeMaster and T.B. Curtin. 1985. A long square-barrel gravity corer for sedimentological and geochemical investigation of fine-grained sediments.  Mar. Geo. 62: 365-370.

 

Milner, A.M., C.L. Fasie, F.S. Chapin III, D.R. Engstrom and L.C. Sharman. 2007.  Interactions and Linkages among Ecosystems during Landscape evolution. Bioscience. 57: 237-248.

 

Nittrouer, C.A., R.W. Sternberg, R. Carpenter, and J.T. Bennet. 1979. The use of Pb-210 geochronology as a sedimentary tool: application to the Washington Continental Shelf: Mar. Geo. 31: 297-316.

 

Appendices

            To be completed later

 

 

 

 

Table 1.

Station #

Location

Latitude

Longitude

Depth

Comments

KC-10

E. of Russell Island

58.89° N

136.83° W

369 m

 Near tidewater glaciers

KC-16

E. of Hunter Cove

58.89° N

136.09° W

294 m

 

Near Alpine Glaciers

KC-21

North Tarr Inlet

59.04° N

137.05° W

217 m

Near two tidewater glaciers

KC-23

W. Geikie Inlet

58.60° N

136.47° W

99 m

 Near tidewater glaciers and streams

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure Legend

Figure 1. Map of Glacier Bay Alaska (Cai et al. 1997) The colored dots indicate Kastenlot Core sampling sites. Green: KC-16, Yellow: KC-10, Blue: KC-23 and Red: KC-21.  Lattitude and Longitudes of the KC sites are located in Table 1.

 

Figure 2. Map of Tarr Inlet identifying the Ice-proximal (Bc & Bf), Ice-berg (IB)and Ice-distal (ID) zones (Cai et al 1997). The left side of this figure indicates Northeast and the right indicates the Southwest.  This figure if turned 90 degrees right corresponds to the black box in Figure 1 of Tarr Inlet.  The red dot indicates Kastenlot core sight KC-21.

 

Figure 3.  A picture of the Van Veen Grab sampler. (photo by Brittany Kimball).

 

Figure 4.  A picture of  the Soutar Core sampler.

 

Figures 5-18 coming soon

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1                                                                                    (Cai et al.1997)

 

 

 

 

 

 

 

 

 

Figure 2                                                                                              (Cai et al. 1997)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3                        (photo taken by Brittany Kimball)

 

 

 

 

 

 

 

Figure 4                                                            (photo taken by Brandon Knox March 2008)