Suspended particle dynamics and related fjord sedimentation in Kangerlussuaq and Sermilik fjord, SW and SE Greenland (CRIK and POEM Projects)

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21 Φεβ 2014 (πριν από 3 χρόνια και 5 μήνες)

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OS51B
-
1852.

Suspended particle dynamics and related fjord sedimentation in

Kangerlussuaq and Sermilik fjord, SW and SE Greenland (CRIK and POEM Projects)


Scientific objective:

Fjord sediments as climate, calving
and melting archives


The CRIK project (Kangerlussuaq fjord) and POEM project
(Sermilik fjord) both aim at examining the climate history in
the areas by use of analysis of Holocene fjord sediments. The
examined parameters are accumulation rates of fine
-
grained
sediment (
210
Pb and
137
Cs dating) as well as biological proxies
(e.g. dinoflaggelate cysts and diatoms).


In both fjords the field
-
work consists of core sampling as well
as water column measurements using CTDs and a LISST
100C particle sizer. The water column measurements are
carried out in order to aid the interpretation of the sediment
cores and for Sermilik fjord also to examine the properties of
the ocean water which is responsible for a significant part of
the melting which takes place at the front of tidewater
-
glaciers entering the head of the fjord (Straneo et al., 2010).





















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Sediment archive in Kangerlussuaq
fjord


Kangerlussuaq fjord receives melt
-
water from Watson river
which drains approximately 10.000 km
2

of the Greenland Ice
Sheet (GIS).The long

term sedimentation rate which can be
calculated simply by diving the thickness of Holocene
sedimentation (at least 60m) by the time since de
-
glaciation
of the fjord (around 6000 years) gives a sedimentation rate in
the order of 10 mm y
-
1
. However , a calculation based on the
average SPMC (2 mg l
-
1
) and settling velocity (0.02 mm s
-
1
)
and assuming deposition 6 months each year only gives a
sedimentation of 1.2 mm y
-
1
. The discrepancy is most likely
due to substantial sedimentation from gravity flows
originating from the rapid sedimentation in front of the delta
at the head of the fjord.


Flocculation of suspended sediment


Substantial flocculation of the suspended material takes
place in both fjords. One consequence is that changes in
primary particle size in fjord sediments most likely does not
reflect changes in sediment supply or distance to sediment
source as the sediment is deposited as flocs.





Thorbjoern Joest Andersen
1
, Thor Nygaard Markussen
1
, Marianne
Ellegaard
2
, Morten Holtegaard Nielsen
4
, Lars Chresten Lund
-
Hansen
3
,
Morten Pejrup
1


1. Department of Geography and Natural Resource Management + CENPERM, University of Copenhagen, Denmark.

2. Department of Biology, University of Copenhagen, Denmark

3. Department of Biology, University of Aarhus, Aarhus, Denmark.

4. DTU Byg, Danish Technical University, Lyngby, Denmark.


Sediment cores in Sermilik fjord


210
Pb/
137
Cs analysis and biological proxies
Calving/melting archive


Sediment cores were retreived from all the stations in August
2012. Chronologies will be established by
210
Pb and
137
Cs dating
at the Gamma Dating Centre in Copenhagen (run by T.J.
Andersen) and the temporal variation of accumulation rates will
be used to determine the temporal variation of calving and
melting during the last 120 years.


The cores will also be analysed for their content of dino
-
flagellate cysts and diatoms which are ancitipated to reflect
changes in salinity and/or temperature of the water reaching the
fjord. This should enable us to examine the drivers of possible
changes in sedimentation rate through time.


References

-

Straneo, F., Hamilton, G.S., Sutherland, D.A:, Stearns, L.A., Davidson, F.,
Hammill, M.O., Stenson, G.B., Rosing
-
Asvid, A., 2010. Rapid circulation
of warn subtropical waters in a major glacial fjord in East Greenland.
Nature Geoscience, NGEO764.

-
Schjøth, F., Andresen, C.S., Straneo, F., Murray, T., Scharrer, K., Korablev,
A., 2012. Campaign to map the bathymetry of a major Greenland fjord.
EOS 93 (14), 141
-
142.








Department of Geosciences and Natural Resource Management

U N I V E R S I T Y O F C O P E N H A G E N

Sermilik fjord with sampling locations. Both sediment
coring and water column measurements were carried out at
each stations. Bathymetry from Schjøth et al., 2012.

Lab experiment on fjord sediments. Red: Kangerlussuaq, Blue: Sermilik. Open
circles = grain size, filled symbols = SPMC.

Kangerlussuaq sediment shows stronger flocculation than Sermilik sediment.

0.001
0.01
0.1
1
G
r
a
i
n

s
i
z
e

(
m
m
)
0
10
20
30
40
%

i
n

i
n
t
e
r
v
a
l
Typical primary and
in situ
grain size distributions from the two fjords.

Red: Kangerlussuaq, Blue: Sermilik.

Open symbols: Primary grain size, filled symbols: In situ grain size
.

Kangerlussuaq fjord.
Distribtution of salinity, temperature and
suspended particulate matter (SPMC) in kangerlussuaq, August 2007.

Sermilik fjord.
Distribtution of salinity, temperature and suspended
particulate matter (SPMC) and in situ grain size in
Sermilik, August 2012.

Note the layering of the watercolumn.

0:00
4:00
8:00
12:00
16:00
T
i
m
e

(
h
o
u
r
s
)
0
0.02
0.04
0.06
M
e
a
n

G
r
a
i
n

s
i
z
e

(
m
m
)
10
100
S
P
M
C

(
m
g

l
-
1
)
0.001
0.01
0.1
1
G
r
a
i
n

s
i
z
e

(
m
m
)
0
10
20
30
40
%

i
n

i
n
t
e
r
v
a
l
S
t
a
r
t
8

h
o
u
r
s
3

h
o
u
r
s
2

h
o
u
r
s
0.001
0.01
0.1
1
G
r
a
i
n

s
i
z
e

(
m
m
)
0
10
20
30
40
%

i
n

i
n
t
e
r
v
a
l
S
t
a
r
t
8

h
o
u
r
s
3

h
o
u
r
s
2

h
o
u
r
s
Lab
-
experiment on dispersed sediment


The degree and time
-
scale of flocculation was examined in
laboratory experiments on dispersed bed sediment suspended
in water with S = 11 PSU and T = 20
0
C. The suspensions
were left overnight to flocculate and settle. Substantial
flocculation was observed even within 6 hours.




Grain size distributions from
Lab
-

experiment,

Sermilik fjord sediment













Grain size distributions from
Lab
-

experiment,
Kangerlussuaq fjord sediment

Kangerlussuaq fjord with its conspicuous sediment plume
originating at Watson River.