Nearshore Carbon and Sediment

(1)

Nearshore Carbon and Sediment

Dynamics of an Eroding Permafrost Coast: Herschel Island, YT, Canada

Radosavljevic, Boris , Lantuit, H., and M. Fritz

Results (Preliminary)

The 2012 field season yielded sidescan bathymetry and surface sediment samples (Figs. 4, 8, 9). Addi- tional sidescan-, seismic-, as well as the collection of surface grab samples and shallow cores is

planned for the summer of 2013 (Fig. 9).

Fig. 8. Hillshade of Pauline Cove bathymetry from 2012 data reveals benthic features of cryogenic origin. Simpson Pt, where the historic whaling settlement is located, grew considerably as the background image taken in 2001 indicates.

6 m

6 m 5 m

5 m 4 m

4 m 3 m

3 m 2 m

2 m

6 m

4 m 3 m

2 m

5 m Historic whaling settlement 9 m

9 m 8 m

7 m 7 m

8 m 7 m

shoreline change 2009

2012

Background Image:

IKONOS2, 2001-08-12

50 m

´

Study Area

Methods

Fig. 4. Map of Herschel Island showing sidescan coverage, and sound velocity profiles (SVPs) and their locations.

An array of complementary geophysical and conventional geologic methods are applied in this study.

• interferometric sidescan sonar (coupled with a real-time kinematic GPS system)

• seismic sub-bottom profiler

• surface sediment samples

• sediment cores

Fig. 6. Instruments and samples (purple) deliver data (grey) that answer relevant questions (blue) for the completion of study objectives.

Validation/

Stratigraphy Dating

grain size, CNS, δ

¹³

C Bathymetry/

Imagery

Seismic Short

Cores

Evolution of shoreface

Sedimentation/sequestration rates

Surface

Sediment Samples Multibeam/

Sidescan

Characterize sediments/carbon

&

Identify sediment sources, sinks, and pathways

SVP

measurement mounting

for seismic

320 315

321 310

165 168

167 166

USA

Canada

1 km

$

0 2 4 6 8 10

Depth (m) 1460

1465 1470 1475 1480 1485

Velocity (m s-1)

163 - 8/14 4:58 165 - 8/14 5:05 166 - 8/14 5:08 167 - 8/14 5:14 168 - 8/14 6:00 310 - 8/17 7:56 313 - 8/18 3:14 316 - 8/18 9:25

Canada USA

Herschel Island

Sound Velocity Profiles

Herschel Island

(Qikiqtaryuk)

Beauf

ort S ea

Pauline Cove

Simpson Pt Tethis

Bay

Osborn Pt Avadlek Spit

Lopez Pt

Bell Bluff

Orca Cove

Workboa

t Passage

Thrasher Bay

RTK GPS

Fig 7. The AWI RV Christine is

equipped to per- form sidescan and seismic surveys.

RTK GPS

Interferometric Sidescan mounting

for seismic

-25 -15 -10 -5

-20 0

Depth (m)

Thermal and Wave Erosion Zone

Wave and Current Reworking Zone

Ice-Push Zone Temporary Depocentre?

Ice Blocks

Ice Gouging Zone

Ice

Sediment

Resuspension

Erosion Accretion

Erosion

Coast Parallel Sed. Transport

Coast Perpendicular Sed. Transport after Hequette and Barnes, 1990

Introduction

Sediment/Organic Carbon Coastal

Erosion

Nearshore

Atmosphere Shelf Rock

Record

Burial Export

Physical, chemical and biological

processes

Rock Record

Through the combination of

thermal abrasion and coastal ero- sion, arctic coasts are highly

threatened by climate change that result in extremely high rates of shoreline retreat. The eroded materials contain large fractions of organic carbon

tems, and possibly act as a posi- tive feedback to ongoing climate change (Fig.1).

Sediments and carbon enter into the nearshore through “normal”

shoreline retreat, but also

through discharge of retrogres- sive thaw-slumps (RTS) that act as point sources. Previous work- ers hint at the possibility of de- position within the nearshore.

Submarine permafrost degrada- tion and sea-level rise are possi- bly creating accommodation space (Figs 2, 3).

Questions

This study focuses on the following questions:

• How is the cross-shore and longshore coastal morphology related to shoreface evolution?

• How does shoreface evolution relate to sequestration of carbon and coastal erosion?

• What percentage of eroded sediment is buried within the near shore?

• How might the shoreface evolve given present trends of climate change and sea-level rise?

• What changes can be anticipated for sedimentary features such as Simpson Point, the site of a historic whaling settlement?

Fig. 1. The fate of sediments and organic carbon released by coastal erosion.

Fig. 2. Conceptual model of shoreface processes in the Canadian Beaufort Sea.

Fig. 3. Shoreline retreat resulting from sea-level rise, the Bruun rule. Note deposition on lower shoreface.

Eroded Volume

Deposited Volume

Sea-level Shoreline Retreat

t

₁

after Bruun, 1954

t

₀

cliff erosion retrogressive thaw slump

mud delta

boris.radosavljevic@awi.de Have questions? Feel free to contact me!

Outlook

Fig. 9. Sidescan coverage, locations of surface grab samples, and soil organic carbon samples by a previous study. Areas shaded in green indicate future focus locations.

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1 km

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! Grab samples Couture, 2010 Sidescan Coverage Planned Sidescan

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planned transect