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 sedimentsIllustration of high resolution coastal change data from cores
Particle size distribution ‘shape’ as a sea level proxyTesting the hypothesis of palaeo-marsh altitude
Dee (and other UK)Yangtze
Barrier estuary sedimentation: ICOLL dynamics Underlying principlesBarrier 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.
Altit
ude
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 20101.0
1.5
2.0
2.5
3.0 OBDMc OBDM3H&E 4b Annual mean sea-level (Liverpool) Monthly mean sea-level (Liverpool)
Alti
tude
(mO
D)
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 1000m
% b
ol
‘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
0.393
00000
00000
030.5
71
0.829
00000
00000
011.2
041.7
482.5
393.6
87
5.354
99999
99999
87.7
7611.
29 16.423.
8234.
5950.
2372.
94105
.9153
.8223
.4324
.4471
.1684
.2993
.6144
3
0-26-812-1418-2024-2630-3236-3842-4450-5256-5862-6468-7074-7680-8286-8892-94
Particle Size Contour Plot
0-22-44-66-88-1010-1212-1414-1616-1818-2020-2222-2424-2626-2828-3030-3232-34
Grain Size (um)
Dep
th (
cm)
Particle size (μm)
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 1 2 3 4 5 602468
1012141618202224262830323436384042
CX-2 Core Palaeomarsh Altitude
TS ratio and Palaeomarsh Altitude
Dep
th (
cm)
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
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 75 765
6
7
8Depth (cm)
Mea
n G
rain
Siz
e (φ
)
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
210Pb & 137Cs 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 [email protected]