Particle size evidence of recent coastal change.

sixcageyMécanique

22 févr. 2014 (il y a 3 années et 4 mois)

71 vue(s)

Particle size evidence of

recent coastal change.



Andy
Plater


…featuring
Dave Clarke,
Hayley Mills, Joe Brennan,
Weiguo

Zhang,
Rubina

Rahman
, James Walker and Samantha Godfrey


School
of Environmental Sciences,
University of Liverpool

Bridging Operational Scales...

Seminar structure:


Foundations: emergent themes…


Sea
-
level reconstruction from
saltmarsh

sediments


Illustration of high resolution coastal change data from cores


Particle size distribution ‘shape’ as a sea level proxy


Testing the hypothesis of
palaeo
-
marsh altitude



Dee (and other UK)



Yangtze


Barrier estuary sedimentation: ICOLL dynamics


Underlying principles


Barrier regimes



Pescadero


Summary

Saltmarsh

Data:
Foraminiferal

Transfer Function


As the surface of a
saltmarsh

slopes towards the sea, areas of a
saltmarsh

differ in the amount of tidal submergence and sub
-
aerial exposure
-

related to
elevation.


Different species assemblages occupy different altitudes or height above sea
-
level.


Intertidal foraminifera can be used to reconstruct
palaeo
-
sea level as their
distribution may be related to height above sea
-
level.


Altitude

Distance

Kemp, A.C. et al.
(2011) Climate
related sea
-
level
variations over the
past two millennia.
PNAS
doi
/10/1073

Saltmarsh

TF reconstructions widely accepted...

BUT:




Dating




Preservation
(Decalcification)




Compaction




Reworking (sediment
and foraminifera)




Tidal dynamics and
change


1975
1980
1985
1990
1995
2000
2005
2010
1.0
1.5
2.0
2.5
3.0
OBDMc
OBDM3H&E 4b
Annual mean sea-level (Liverpool)
Monthly mean sea-level (Liverpool)
Altitude (mOD)
Year
Reconstructed MTL for Mersey Estuary using ‘local’ and
‘hybrid regional’
foram

transfer functions compared with
Liverpool tide gauge data (Mills, 2011)

Can we obtain high resolution ‘process’ information
from sediment record of
palaeoenvironments
?

Rhythmites
: imperfect
preservation of tidal inundation
magnitude/frequency in
laminae

Re
-
examining particle size distributions



Sediments are present!



More robust than
palaeoecological

proxies (generally!)



Relationship with tidal flow vector


a function of tidal height



Rapid, high
-
resolution analysis


All curves Boulderwall Farm 0.44 to 1.44 m OD
0
1
2
3
4
5
6
7
0.1
1
10
100
1000

m
% bol
‘fast tide’, well
-
sorted,
fine
-
skewed, leptokurtic
fine sands

‘slow tide’, poorly
-
sorted,
near
-
symmetrical platy
-

to
mesokurtic

silts

(
Stupples

and
Plater
, 2007)

Infilling

Sea
-
level Rise

Dee estuary, NW England and N. Wales

0-2
6-8
12-14
18-20
24-26
30-32
36-38
42-44
50-52
56-58
62-64
68-70
74-76
80-82
86-88
92-94
0.393
0.52
0.688
0.91
1.204
1.593
2.107
2.787
3.687
4.878
6.453
8.537
11.29
14.94
19.76
26.15
34.59
45.76
60.53
80.07
105.9
140.1
185.4
245.2
324.4
429.2
567.8
751.1
993.6
1314
1739
Depth (cm)

Grain Size (um)

Particle Size Contour
Plot

10-12
8-10
6-8
4-6
2-4
0-2
Particle size (
μ
m)

Plotted after
Beierle

et al
. (2002)

Influence of proximity to creeks
and
microrelief
?

Elevation control?

Yangtze Estuary


Chong Xi Tidal Flat Study

Limited micro
-
topography


Negligible creek
network


Consistent
gradient


Sediment
surplus

6 km

Surface transects across tidal flats: MHWS
-
MLWS


Distance/
elevational

control on particle size data
and magnetic proxies

0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
0
1
2
3
4
5
6
Depth (cm)

TS ratio and Palaeomarsh Altitude

CX
-
2 Core Palaeomarsh Altitude

Sea
-
level rise

Palaeomarsh

altitude

(No modern analogue)

Pescadero Marsh, California

Mean particle size base level
sections:




Barrier regimes




Variability between end
-
member states




Aggregate state of barrier
estuary / lagoon




Disturbance and recovery




High energy events

5
6
7
8
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
Mean Grain Size (
φ)

Depth (cm)

56.2
-
56.4 cm

41.8
-
42 cm

48.6
-
48.8
cm

60.4
-
60.6 cm

64.8
-
65 cm

68.8
-
70 cm

210
Pb &
137
Cs chronology: approx 5mm/yr

Summary


Particle
size (shape) data show considerable potential for
saltmarsh
/mudflat elevation reconstruction... as well as providing data on
changing coastal environments and hydro/
morphodynamics

(long
-
,
medium
-

and short
-
term), e.g. estuary infilling, barrier regime shifts,
disturbance/recovery etc.


Data do not suffer from occurrence or preservation issues, but may suffer
from methodological issues re. analytical method/ particle shape


Technique is rapid and capable of very high resolution analysis


At the very minimum, particle size data are valuable for assessing viability
of a sediment record for sea
-
level reconstruction (infilling vs. sea level,
also disturbance)


Issues remain in relation to
microtopography

and creek proximity


as well
as sub
-
annual variability and extreme events BUT at least the data reveal
such phenomena.

Additional thanks to:


Weiguo

Zhang and colleagues, Stake Key Laboratory for Estuarine
and Coastal Research


Ken
Pye
, KPAL


Jimmy
Zheng
, Joe Brennan and many postgraduates from East
China Normal University


Jason Kirby, Liverpool John
Moores

University


Sandra Mather, Hayley Mills, Dave Clarke,
Rubina

Rahman
, Tim
Shaw, James Walker, Paul
Stupples
, Dan
Schillerreff

and Samantha
Godfrey, University of Liverpool


Simon Holgate, Svetlana
Jevrejeva

and Phil Woodworth, National
Oceanography Centre
-
Liverpool


Thanks for your attention


Andy
Plater

gg07@liverpool.ac.uk