Coastal sea level rise patterns in the North Atlantic and the Mediterranean Sea

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Coastal sea level rise patterns in the North
Atlantic and the Mediterranean Sea

• Marta Marcos and Mikis Tsimplis

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Motivation
Melting of ice-sheets and glaciers cause a
non-uniform sea level change. Thus the spatial
patterns of sea level variations can be used to
infer rates of ice melting
Mitrovica, J.X., M. E. Tamisiea, J. L. Davis, G.
A. Milne, 2001. Recentmass balance of polar ice
sheets inferred from patterns of global sea-level
change. Nature, Vol. 409, 1026-1029
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Coastal sea level measurement integrates
contribution from many forcing parameters
atmospheric forcing, thermal expansion, mass
addition, land movement
Estimates of sea level trends and the forcing
mechanisms by - Tide gauge records (40yrs) -
Numerical barotropic models - T,S climatologies -
GIA models
OBJECTIVE to remove all the contributions from
sea level data and test the spatial patterns of
the residual sea level changes
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Sea level data
PSMSL RLR tide gauges
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Sea level data
PSMSL RLR tide gauges
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Hindcast data
Resolution 1/3ºx1/2º Flather, R. A., J. A.
Smith, J. D. Richards, C. Bell, and D. L.
Blackman (1998), Direct estimates of extreme
storm surge elevations from a 40-year numerical
model simulation and from observations, Global
Atmos. Ocean Syst., 6, 165 176.
Resolution ¼ºx1/6º Forcing NCEP (dynamic
downscaling) García-Sotillo, M., A. W.
Ratsimandresy, J. C. Carretero, A. Bentamy, F.
Valero, and F. Gonzalez-Rouco (2005), A
high-resolution 44-year atmospheric hindcast for
the Mediterranean Basin Contribution to the
regional improvement of global reanalysis, Clim.
Dyn., 25, 219 236, doi10.1007/s00382-005-0030-7
.
Resolution 1/12º Forcing AES40 data set every 6
h Rms 8cm Bernier, N. B., and K. R. Thompson
(2006), Predicting the frequency of storm surges
and extreme sea levels in the Northwest
Atlantic, J. Geophys. Res., 111, C10009,
doi10.1029/2005JC003168.
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Hindcast data
Coherence of barotropic models HAMSOM (PdE)-CS3
(POL) Hourly outputs for the common period
1992-2001. For the CS3 model a tidal analysis has
been carried out because HAMSOM only accounts for
atmospheric pressure and wind effects. Each grid
point of CS3 model has been compared with the
closest point of HAMSOM model. Correlations of
0.8-0.9
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Sea level data
Observed and modelled sea level trends for
1960-2000 (in mm/yr)
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Sea level trends
Sea level trends for individual stations and for
the period 19602000
observations atm. corrected
Over the last 40 years there are significant sea
level trends caused by changing atmospheric
forcing
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Sea level trends
Seasonal sea level trends (1960-2000)
Observations
Atmospherically-corrected
yearly summer winter
Seasonal differences in trends are due to
atmospheric effects, except in the North Sea
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Sea level trends
Regional sea level trends (1960-2000) (in mm/yr)
Corrected trends are due to thermal expansion and
mass addition. The value is less than the 1.8
mm/yr stated by the IPCC
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Spatial gradients
Thermal expansion removed
-0.070.04mm/yr/ºlat
1.00.6 mm/yr 360216 Gt/yr
Reference Marcos, M., and M. N. Tsimplis (2007),
Forcing of coastal sea level rise patterns in the
North Atlantic and the Mediterranean Sea,
Geophys. Res. Lett., 34, L18604,
doi10.1029/2007GL030641.
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Ice melting rates
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Summarizing

• The atmospheric correction is important in
  obtaining consistent pattern of sea level trends.
  Over the last 4 decades of the 20th century it
  has been responsible of significant changes in
  sea level
• Sea level trends corrected for atmospheric
  forcing and GIA reflect the effect of the steric
  contribution and mass addition. Their values in
  the N. Atlantic and the Mediterranean Sea are
  lower than the IPCC values.
• Seasonal differences in trends are entirely due
  to atmospheric effects, except in the North Sea
• Sea level trends in the N. Atlantic corrected
  for atmospheric pressure, wind, PGR and steric
  effects provide with a value for Greenland ice
  melting rates of 1.00.6 mm/yr for the period
  1960-2000.

Many thanks to Roger Flather, Kevin Horsburgh,
Natacha Bernier, Mark Tamisiea and Puertos del
Estado (Spain)