Depositional settings of an arctic coast:
a shallow seismic investigation
Radosavljevic, Boris 1 , H. Lantuit 1 , M. Fritz 1 , P. Overduin 1 , M. Krautblatter 2
1Alfred Wegener Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Telegrafenberg A43, 14473 Potsdam, Germany; 2Technische Universität München, Arcisstr. 21, 80333 Munich, Germany
Erosion of arctic coasts re- leases sediments and
carbon which are thought to be exported to the atmo-
sphere or deposited on the shelf. With the exception of breached thermokarst
basins, the arctic shore- face is considered ero- sional, thus no sediment deposition or carbon burial can occur (Ruz et al., 1992).
In this study, sub-bottom
profiles were obtained using a shallow seismic device in the area of Herschel Island, Yukon Territory, Canada
(Figure ). Different areas of the nearshore around the island were surveyed to in- vestigate if deposition can be ascertained based on stratigraphy shown on the seismograms.
Fig. 2. The study area in the shallow nearshore around Herschel Island, Yukon Terri- tory, Canada. Seismic profiles are indicated by green lines. Isobaths are also
shown (2 m interval). The basin SE off the island was excavated during the Wiscon- sin glaciation.
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Seismic Profiles
Results
Study Area Methods
Introduction
photo: M. Fritz
Herschel Island is located in the southern Beaufort Sea, about 70 km east of the Alaskan border. The
island is an ice push moraine deposit (Mackay, 1959;
Rampton, 1982), that formed during the Wiconsinian glaciation (Figure 2).
Coastal processes include wave and tide action, as well as storm surge, ice rideup, ice pileup, thermal abrasion, and thaw subsidence. Freeze-up typically begins by mid-October, and break-up in early June.
Sea-ice follows the Beaufort Gyre westward. The mean tidal range generally <0.5 m. Wind influence on both ice, tidal and wave processes can be in-
ferred from the wind roses shown in Figure 1.
0
45
90
135 180
225 270
315
0% 8% 12%
October-April 0
45
90
135 180
225 270
315
0% 8% 12%
March-September
<=10 >10 - 20 >20 - 30 >30
Wind Speed km h-1
Fig. 1. Wind chart showing fre-
quency and direction of seasonal winds at nearby Tuktoyuktuk for the period 2009-2012.
An Innomar SES-2000 compact Sub- Bottom Profiler was used in the course of the study. The instrument was
mounted on the AWI RV Christine (Fig.
3). Positional accuracy was <2 m with a WAAS corrected GPS antenna
(Trimble R4), shown in Figure 4.
Fig. 3. The AWI RV Christine was used to carry out the seismic surveys. The SES2000 can be seen on the port side of the
vessel.
Fig. 4. A WAAS cor- rected position was obtained with a
Trimble R4 antenna.
Fig. 5. Profiles E, I, and L from the SE quadrant of the Herschel Island nearshore. The presence of Herschel Basin and the glacial paleotopography amount to greater accom- modation space. In addition, Herschel Island shields this area from ice rafted onto the shelf after the spring breakup, and the grounding of ice floes drifting westward during winter. The presence of stratigraphy indicates deposition in this area. Only areas shallower than ~6 m are disturbed.
Fig. 7. Profiles T, V, and O from the NW and NE quadrant of the Herschel Island nearshore. All profiles show very little stratigraphy and a shallow contact to the paleotopography. Intense ice gouging of the sea floor is evident in the rough sur- face. Combined with the gentle slope of the shelf deposition in these areas is unlikely.
Have questions? Feel free to contact me!
boris.radosavljevic@awi.de
Discussion
The results of this study indicate:
• Disturbed stratigraphy to the NE and NW of Herschel Island due to gentle slope and intense cryogenic processes point to erosional nature of shoreface with little or no deposition
• The presence of Herschel Island shields the SE area from ice disturbance during conditions of complete ice cover
• The steeper shoreface profile of glaciogenic origin provides for accommodation space where sediments and possibly carbon are deposited
References
Bostock, H.S., 1970. Physiographic regions of Canada. Geol. Surv. of Can.
Mackay, J.R., 1959. Glacier ice-thrust features of the Yukon coast. Geogr. Bull. 13, 5–21.
Rampton, V.N., 1982. Quaternary geology of the Yukon coastal plain. Geol. Surv. of Can.Ruz, M.H., Héquette, A., Hill, P.R., 1992. A model of coastal evolution in a trans-
gressed thermokarst topography, Canadian Beaufort Sea. Mar. Geol. 106, 251–278.
SES2000
80 60 40 20 0
0 4 8
Depth (m)
L
Distance (km)
80 60 40 20 0
0 1 2 3 4
Depth (m)
I
Distance (km)
80 60 40 20 0
0 1 2 3
Depth (m)
E
Distance (km)
80 60 40 20 0
0 1 2 3
Depth (m)
O
Distance (km)
0 1 2 3 4
80 60 40 20 0
Depth (m)
T
Distance (km)
0 4 8 12
80 60 40 20 0
Depth (m)
V
Distance (km) paleosurface
paleosurface
ice gouging
paleosurface
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
´
ice gouging
Fig. 6. Hillshade of Pauline Cove bathymetry from 2012 data reveals benthic features of cryogenic origin. Ice gouging is intensive on the shallow sea bottom to the north and west of the island.
Interferometric Side scan sonar
