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

 

 

 

 

 

Justin Bergquist

 

University of Washington

School of Oceanography

Seattle, Washington 98105

 

docj@u.washington.edu

206-883-6569

 

 

 

20 February 2008

 

 

Project Summary

            In the last century, rapid retreat of temperate glaciers in Alaska has deposited a diverse suite of glacial sediments in Glacier Bay fjords.  The goal of this project is to characterize and sample different lithofacies in Glacier Bay to reveal a 100 year geochronology, that can be correlated with climate change in the last century.  Prior 210Pb analysis of sediment traps and cores in the fjords of Glacier Bay revealed some of the fastest accumulating sediments in the world (Cai et al 1997). To verify and compliment existing sediment accumulation rate data of Glacier Bay, four stations in the West Arm and Tarr Inlet and one station in Muir Inlet will be sampled from 19-22 March 2008 aboard the R/V Thompson, using a Van Veen grab sampler and a Kasten Corer. Sediment accumulation rates will be calculated using 210Pb analysis.   To determine 210Pb activities in the sediment 210Pb analysis based on alpha and gamma spectroscopy and the 210Po method will be conducted (Nittrouer et al. 1979).  X-ray stratigraphy and x-rayography will also be used to determine types and layering of sediment for geochronology.  This research will enhance previous data sets by characterizng sediment that has accumulated recently (~ 15 years).  These data wills also compliment previous sediment accumulation rate studies with the goal of using the rapid sediment accumulation rates that have been correlated directly with climate change by glacial retreat, tectonic uplift, glacial rebound, increased orogenic and glacial erosion (Hallet 1996).  The results of these studies are important because these changes are taking place on decadal time scales and rapid sedimentation has a strong impact on benthic communities and on the transfer of carbon and nutrients from the continents to the ocean.    Other carbon and nutrient studies from fellow classmates: Andrew Clos and Marcus Peterson could help constrain the magnitude of these fluxes.

 

 

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 . 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 in this proposal presents the first quantitative analyses of 210Pb, coupled with x-rayography 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.  Determination of sediment accumulation rates is critical to calculatng glacial erosion/sediment yields.  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 accordingly 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, ranged from 6 cm/yr to 3.2 cm/yr (Cai et al. 1997). 

This study will take Kasten cores from areas near previous sediment studies to augment previous sediment accumulation rates and also to determine 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 will also conduct sampling of Kasten cores near other inlet mouths in the West Arm that is fed by John Hopkins, Lamplugh , Geikie, Carroll and Rendu glaciers could reveal similarities and differences of sedimentation dynamics in Tarr and Muir Inlets.  210Pb analysis, x-rayography and x-ray stratigraphy of the sediments will be conducted to characterize different lithofacies.  These data will allow examination of rapid retreat and advance of glacier termini as indicated by thickness and type of sediment layering.    These results will be compared with previous results from Cai et al., 1997 to authenticate any similarities or differences.  “Although the scale may vary between depositional systems, the tidewater glaciers of Tarr Inlet have produced depositional environments with clearly defined seismic facies associations.  These same associations should be represented in other temperate fjord systems with tidewater glaciers, and possibly some continental shelf settings as well” (Cai et al., 1997).

Proposed Research

            To examine sediment accumulation rates in different places within the bay, five Kasten cores (3 m in length) will be obtained near Glacier National Park CTD station #’s 8, 10, 12, 16 and 23 (Fig 5).  Table 1 summarizes information on specific sites.

Table 1.

Station #

Location

Latitude

Longitude

Depth

Comments

8

Mouth or Rendu Inlet

58.86° N

136.59° W

426 m

 Near stream outlets

10

E. of Russell Island

58.89° N

136.83° W

361 m

 Near tidewater glaciers

12

N. Tarr Inlet

59.03° N

137.01° W

288 m

 

Near tidewater glaciers

16

E. of Hunter Cove

58.89° N

136.09° W

313 m

 Near Alpine Glaciers

23

W. Geikie Inlet

58.59° N

136.50° W

66 m

 Near stream oulets

 

The research sites were based on areas inTarr Inlet near Cai et al. 1997 sample sites and also in collaboration with Brandon Knox, who is studying ancient forest lignans buried in sediments near streams and receding glaciers.  To broadly characterize layering in the sub-sea floorand sediment thicknesses, 3.5 kHz surveys will be conducted in collaboration with Carmella Llaneta.  These data will be important in determining optimal sampling sites.  IN addition EM300 multibeam surveys will be co-located to provide additional information on bottom topography.  The EM300 will be lead by Josh Hill.

Following preliminary survey work, a Van Veen grab (Fig 3) sample of the proposed site will be conducted to determine the presence boulders or coarse-grain covered areas that would prevent taking a Kasten Core (Fig 4).  If the sampling site is adequate, a Kasten Core will be taken and recovered onto the boat deck.  Once on deck, splitting, sectioning, labeling and digital imagingof the core will be carried out, followed by immediate storage in the cold room.

Shore based analysis will be conducted in the Marine Science sediment lab.  X-ray trays will be digitally x-rayed, catalogued and compared to on deck descriptions of the sediments.  X-rayography and x-ray stratigraphy will allow identification of dark, fine-grained, low porosity sediments that are optimal for quantitative 210Pb analysis (Jaeger & Nittrouer, 1999).  In contrast, lighter-colored, higher porosity coarser-grained sediments will be sampled because they have been shown to reflect faster accumulation (Jaeger & Nittrouer, 1999).  Detailed descriptions of the core, and digital images will be used to examine the degree to which bioturbation has impacted the sediment.  Bioturbation has been shown to reflect periods of lower sedimentation deposition rates, while higher deposition rates inhibit bioturbation, allowing the preservation of depositional laminations (Jaeger & Nittrouer, 1999).  Higher deposition rates also reduce the dewatering of sediment, maintaining higher porosity sediments” (Jaeger & Nittrouer, 1999).  Burial of organisms should be important to marine-biologists, because it eliminates colonies of organisms and therefore makes room for new colonization of new organisms.  During this burial process carbon is sequestered into the sediments.

 Lab based procedure include first weighing ~ 20g of wet sediment at each depth interval of core needed.  Samples will be dried and weighed for porosity calculations.  Subsequently, stain the silver planchettes on one side twice (T. Drexler, 2007). Lab procedure includes:  First, weigh ~ 5g of dry sediment in 150ml beaker for each depth.   Second, spike sample with 1ml 209Po.  Then add 10ml 15.8 M HNO3 to the sample.  Put the beaker back on the hotplate, bringing the sample to near dryness.  Next, add 10ml of 6 N HCL to the beaker.  Put the beaker back on hot plate, bringing the sample to near dryness again.  Subsequently, rinse sample into centrifuge tubes and centrifuge the tubes for 10 minutes.  Afterward, pour supernatant into plating jars and repeat the last 3 steps (3 times).  Later, place plating jars with the magnetic stir bars onto the magnetic stir plates on the low setting.  Next, add absorbic acid to the plating jars until the yellow color is gone.  Soon after, suspend the labeled silver planchettes into the plating jars with fishing line.  Finally, the plating jars will be removed  from the magnetic stir plates 24 hours later. After that, rinse the planchettes with DI and allow them to dry for the alpha counting process.  Alpha counts are measured using Ortec PC and Ortec Plus machines for 24 hours to get sufficient activity counts (T. Drexler, 2007).

 

Time required on ship: Total sampling time for each Kasten core from start to finish should require a conservative four hours.  This estimate includes one hour of setup, sonar and Van Veen Grab sampling of the site.  Another hour is required for Kasten core deployment to the bottom and recovery of the device shipboard (Nittrouer, verbal communication, 2008).  Once on deck, two hours will be needed for photography, splitting, sectioning, labeling and cold storage of the cores.  This research should not require any on-board lab time.

 

Collaboative Research:  Station #s 10, 12 and 23 are located near glacier termini and stream outlets.  Sedimentation should be higher in stations near glacier termini.  Station #s 8 and 16 are near Alpine glaciers that were once close to the water.  Brandon will be searching for ancient forest lignans in these core samples near glacier termini and stream outlets, which could show history of glacier advance and retreat.  Christina Biladeau will be using sediment traps in transect of Tarr Inlet to determine hourly/daily sediment accumulation rates.   In concert, these sediment accumulation project results should compliment each other by comparing these accumulation rates with each other.  Coring operations are not time restricted, such that they can be conducted at any time.  Cores will be stored upright and padded in the R/V Thompson cold room at 0°- 4° until they can be analyzed shore based in the UW MSB sediment labs.

            Examining sediment accumulation rates in Glacier Bay is important because of the possible impacts of climate change on glacier behavior, sediment output and carbon flux to the sea.  Sediment yields might be able to be directly correlated with climate change since the Anthropocene.  A fundamental contribution of this study will be to determine if sedimentation rates have changed significantly from the 1990s.

 

Project Budget

            The cost of R/V Thompson is $22,000 a day, which will be subsidized by the UW.  Other supplies are specified below (Table 2). Chuck Nittrouer has decided to rent/loan me his Kasten Corer, x-ray trays, and ORTEC-PC and Plus alpha counter usage.  This project should well exceed this $600, but Chuck Nittrouer gave an aspiring oceanographer a deal for $600.

 

Table 2

Item

Unit cost

Quantity

Supplier

Cost

Kastenlot Corer

n/a

1

C. Nittrouer

free/loan

Van Veen grabber

$6 a day

1

UW

$72

X-ray trays

n/a

~30

C. Nittrouer

free/loan

metric tape measure

n/a

1

J. Bergquist

free/loan

whirl sediment baggies

$0.10 a bag

650

Sigma Aldrich

$65

sharpies

$7.99/ 12 pack

24

Office Max

$16

clips

n/a

25

C. Nittrouer

free/loan

spatulas

n/a

3

C. Nittrouer

free/loan

increment plates

n/a

20

C. Nittrouer

free/loan

foam pads

n/a

20

C. Nittrouer

free/loan

boxes

n/a

4

J. Bergquist

free/loan

extra screws

n/a

100

C. Nittrouer

free/loan

phillups screw driver

n/a

2

J. Bergquist

free/loan

Zip lock baggies

n/a

100

J. Bergquist

free/loan

storage bins

n/a

2

J. Bergquist

free/loan

R/V Thompson

$22,000 a day

1

UW

subsidized

Sed lab supplies

n/a

n/a

C. Nittrouer

free/loan

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure Legends

 

            Figure 1. Map of Glacier Bay National Park (Cai et al. 1997)

Figure 2. Map of Tarr Inlet identifying the Ice-proximal, Ice-berg and Ice-distal zones (Cai et al. 1997)

 

            Figure 3.  Picture of Van Veen Grab sampler (photo by B rittany Kimball)

 

            Figure 4.  Diagram of  a Kastenlot Corer (Kuehl et al. 1985)

           

            Figure 5.  Station #s 8, 10, 12, 16, 23 in Glacier Bay (Google Earth)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1                                                                                                Justin Bergquist

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2                                                                                                Justin Bergquist

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3                                                            Justin Bergquist

 

 

 

 

 

 

 

 

Figure 4                        Justin Bergquist

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5                                                                                                         Justin Bergquist