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Initial results from a multiyear simulation of the NW European shelf seas

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Title: Initial results from a multiyear simulation of the NW European shelf seas


1
Initial results from a multi-year simulation of
the NW European shelf seas
  • Roger Proctor, Jason Holt, Graham Tattersall,
    Sarah WakelinProudman Oceanographic
    LaboratoryLiverpool, UK

2
Talk structure
  • Why do it?
  • Whats happened in last 50 years?
  • The model study
  • Initial results
  • Summary

3
Why do it?
  • Climate change is upon us
  • Need to understand its consequences
  • History best clue to the future
  • Need limits of predictability for future climate
    change
  • Need baseline values against which to deduce
    trend changes (for WFD as well as planning)
  • Modelling challenge
  • EC Water Framework Directive

4
Whats happened in the last 50 years
  • Evidence from
  • weather
  • sea level (PSMSL)
  • Temperature salinity (ICES database)
  • Continuous Plankton Recorder

5
ERA-40 period
After Hurrell www.cgd.ucar.edu/cas/jhurrell/indic
es.html
6
Effects of NAO
Lerwick, NW Scotland (winter)
1982-2000
94/95

95/96
Extracts from the IACMST report UK
Marine Waters 2004 Marine Processes and Climate
http//www.oceannet.org/medag/reports/IACMST_repo
rts/MCP_report/index.htm
-
7
Cypris station Irish Sea
8
Sea Level changes
  • Absolute rise 1mm/y
  • Relative rise (mostly increasing, except N
    coasts)
  • decrease in the rate of rise in the 20th Century
  • no long-term trends in tides

Wakelin et al. (2003) have shown that winter-mean
(December to March) sea levels and the NAO Index
are significantly correlated over much of the
northwest European shelf.
9
Marine Environmental Change Network (MECN)
  • Establish a network to measure
  • environmental change in marine
  • waters
  • Maintain and enhance existing
  • long-term research programmes
  • Restart important discontinued
  • long-term research programmes
  • Deliver and interpret long-term and
  • broad scale contextual information to
  • inform water quality monitoring
  • Demonstrate the benefits of
  • preserving and networking long-term
  • time series programmes
  • Provide information to policy makers
  • and other end-users to enable them to
  • produce more accurate accurate
  • assessments of ecosystem state

MECN partners
http//www.mba.ac.uk/MECN/about.htm
10
MECN Long time series measurements
Tiree Passage W Scotland
11
Temperature SST Atlantic
ICES
FRS
12
TemperatureSST - shelf
13
Temperature SST North Sea
Fair Isle N Scotland
NAO accounts for 40-50 of winter SST variability
in N Sea (Loewe, 1996)
FRS
ICES
14
Trends in Sea Surface Temperature
 
15
Temperature NBT winter (IBTS)
16
Temperature
  • No clear trend in summer SST in the eastern
    North Atlantic since the 1950s, but a warming in
    winter SST since the early 1990s.
  • SST at the Continental Shelf Edge warmed between
    0.12C and 0.29C over the past century.
  • Temperatures in the Rockall Trough were
    relatively low in the early 1990s but then
    increased. The highest temperatures reached in
    the 1990s were similar to those in the 1960s.
  • The Faroe Shetland Channel has become warmer over
    the last 40 years, with temperatures rising at a
    rate of approximately 0.3C per decade from the
    late 1960s minimum.
  • Waters around the UK have been warming since the
    1980s, with the trend more pronounced in the
    southern North Sea and the Irish Sea (between
    0.5C and 1.0C per decade) than elsewhere
    (between 0.0C and 0.5C per decade).
  • There is a warming trend in winter and summer
    SST averaged over the northern North Sea since
    the early 1980s, with a warming of about 1C and
    0.5C respectively.
  • North Sea winter bottom temperatures increased by
    about 0.3C and 0.6C per decade since a cool
    period in the late 1970s.
  • Irish Sea annual mean SST increased by about
    0.7C over the last 100 years. Winter SST from
    1950 to 2002 shows a clear warming since the
    1980s. An apparent cooling in summer SST since
    the 1980s may be due to sparse data.

17
Salinity SSS Atlantic
ICES
18
Salinity SSS North Sea
GSA
Fair Isle Almost cyclical variability since the
end of the GSA in the 1970s
ICES
19
Salinity SSS shelf
20
Salinity
  • Atlantic waters and adjacent shelf areas had low
    winter and summer sea surface salinity (SSS) in
    the mid-late 1970s (associated with the passage
    of the Great Salinity Anomaly (GSA)), followed by
    three decades of large inter-annual variability.
  • Salinity records from the Faroe Shetland Channel
    and the Ellett line indicate a recent trend to
    high salinity.
  • SSS averaged over the northern North Sea from
    1950 to 2002 shows decreasing salinity since the
    1970s and is reflected by observations at fixed
    locations in the Fair Isle Current and the North
    Sea fishing grounds.
  • There is no discernible trend in mean SSS in the
    English Channel from 1900 to the early 1980s.
  • SSS averaged over the Irish Sea from 1950 to
    2002 shows a decrease in both winter and summer.

21
The Continuous Plankton Recorder
Long-term changes at the base of the food web
  • Phytoplankton abundance in North Sea and NE
    Atlantic

Reid et al. (1998) Nature
22
The Continuous Plankton Recorder
Biogeographic Changes in the Northeast Atlantic
Warm temperate slope species
Beaugrand et al. Science 2002
23
The model study
  • Using POLCOMS POL Coastal Ocean Modelling
    System
  • Configured for ocean/shelf (AMM)
  • ERA-40 surface flux (SLP, 10m wind, bulk heat
    flux, E-P flux)
  • Daily river flux (mix of climatological and
    measured)
  • FOAM repeating annual cycle (2000/1)

24
POLCOMS
  • 3D Shallow Water equations
  • Horizontal finite difference discretization on an
    Arakawa B-grid
  • Spherical polar co-ordinates
  • Terrain following co-ordinates - horizontally
    varying S levels
  • Forward Time-Centred Space scheme in the
    horizontal
  • Equations split into depth-mean and
    depth-fluctuating components
  • Horizontal Advection
  • Piecewise Parabolic Method (PPM) for accurate,
    conservative representation of sharp gradients,
    fronts, thermoclines etc.
  • Horizontal pressure gradients
  • calculated by interpolation onto horizontal
    planes, improving numerical accuracy of S
    co-ordinates over steep topography
  • Vertical diffusion
  • Mellor-Yamada-Galperin level 2.5 turbulence
    closure scheme
  • GOTM (k-e), Canuto stability functions

25
AMM-12km
Atlantic Margin Model
N Atlantic FOAM 1/9o (T,S, ?, Q)
ECMWF ERA-40 1957-2002 1 degree 6-hourly SLP, 10m
wind, 2m AT, RH, CC, E-P
Tides (9C, ?, Q)
River discharge Daily 323 rivers
Physics (T,S, ?, U,V) No data assimilation or
relaxation to climatology Modules for spm,
(light, nutrients, biology) - ERSEM
26
Lack of ocean time varying bc means features
like GSA will not be simulated
27
Initial results
  • Point series comparisons (Cypris, )
  • ICES CTD database comparisons
  • Errors
  • Seasons
  • Trends

28
Cypris station Irish Sea
29
Cypris station Irish Sea
30
OB (Sevenstones) station Celtic Sea
31
OB (Sevenstones) station Celtic Sea
32
ICES CTD database analysis
Total 61,000 CTDs 20,000 this period (95-99)
33
Temperature errors Oct-Dec 1995-99
Surface
Near-bed
34
Salinity errors seasonal 1995-99
Surface
Near-bed
35
SST trends
36
Like-for-like trends 81-99 (min of 8 years 5
obs/season / 1o cell)
37
Summary
  • 40 year simulation of NW European shelf without
    data assimilation successfully reproduces many of
    the trends seen in the ICES and MECN observed
    data
  • Model errors highest in spring (T) and NCC (S)
  • Effect of climatic oceanic circulation not
    apparent
  • Model agrees better with obs when like-for-like
    measure used. Spatial variability allows error
    estimates to be made
  • Just the beginning, also started ecosystem runs

38
POLCOMS-ERSEM 15yr (1986-2001)
Mean chl errors mg/m3 (against ICES data)
39
NBT trends
40
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