Transcript High Resolution Coupled Physics-Ecosystem Modelling on the

Initial results from a multi-year simulation of
the NW European shelf seas
Roger Proctor, Jason Holt, Graham Tattersall, Sarah Wakelin
Proudman Oceanographic Laboratory
Liverpool, UK
www.pol.ac.uk
Talk structure
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Why do it?
What’s happened in last 50 years?
The model study
Initial results
Summary
Why do it?
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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
What’s happened in the last 50 years
• Evidence from
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weather
sea level (PSMSL)
Temperature & salinity (ICES database)
Continuous Plankton Recorder
ERA-40 period
After Hurrell: www.cgd.ucar.edu/cas/jhurrell/indices.html
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_reports/MCP_report/index.htm
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Cypris station Irish Sea
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.
Marine Environmental Change Network (MECN)
MECN partners
• 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
http://www.mba.ac.uk/MECN/about.htm
• Have a clearer understanding of factors
influencing change in marine ecosystems.
MECN Long time series measurements
Tiree
Passage
W Scotland
Temperature – SST Atlantic
ICES
FRS
Temperature
SST - shelf
Temperature – SST North Sea
Fair Isle
N Scotland
FRS
ICES
NAO accounts for
40-50% of winter SST
variability in N Sea
(Loewe, 1996)
Trends in Sea Surface Temperature
Nominal
position
Data
Span
Trend
(°C/decade)
Spurn Point
53.5N 00.0E
1966-2002
+ 0.17
Humber LV
53.5N 00.0E
1880-1989
+ 0.01
Newarp LV
53.0N 02.0E
1880-1986
+ 0.02
Lowestoft
52.5N 02.0E
1966-1991
+ 0.16
Sizewell
52.0N 01.5E
1967-2002
+ 0.77
Bradwell
52.0N 01.0E
1964-2001
+ 0.15
Dover
51.0N 01.5E
1926-2001
+ 0.09
Eastbourne
51.0N 00.0E
1892-2002
+ 0.06
Shoreham
51.0N 00.0E
1966-1997
+ 0.31
E1
50.0N 04.5W
1921-1987
- 0.13
Sevenstones LV
50.0N 06.0W
1881-1986
+ 0.04
St Gowan LV
51.5N 05.0W
1953-1987
- 0.17
Swansea
51.5N 04.0W
1976-1997
+ 0.58
54.0N 04.5W
1904-2003
+ 0.07
North Sea SST
English Channel, Celtic Sea
and Bristol Channel SST
Irish Sea SST
Port Erin, Isle of Man
Temperature – NBT winter (IBTS)
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 0.12°C and 0.29°C 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 0.3°C 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 0.5°C and 1.0°C per decade) than elsewhere
(between 0.0°C and 0.5°C 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 1°C and 0.5°C respectively.
North Sea winter bottom temperatures increased by about 0.3°C and 0.6°C per decade since a
cool period in the late 1970s.
• Irish Sea annual mean SST increased by about 0.7°C 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.
Salinity – SSS Atlantic
ICES
Salinity – SSS North Sea
GSA
Fair Isle
Almost cyclical variability since
the end of the GSA in the 1970s
ICES
Salinity – SSS shelf
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.
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
The Continuous Plankton Recorder
Biogeographic Changes in the Northeast Atlantic
Warm temperate slope species
Beaugrand et al. Science 2002
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)
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-ε), Canuto stability functions
AMM-12km
Atlantic Margin Model
N Atlantic
FOAM 1/9o
(T,S, ζ, Q)
Tides
(9C, ζ, Q)
ECMWF
ERA-40
1957-2002
1 degree
6-hourly
SLP, 10m wind,
2m AT, RH, CC,
E-P
River discharge
Daily
323 rivers
Physics (T,S, ζ, U,V)
No data assimilation or relaxation to climatology
Modules for spm, (light, nutrients, biology) - ERSEM
Lack of ocean time varying bc means features like
GSA will not be simulated
Initial results
• Point series comparisons (Cypris, …)
• ICES CTD database comparisons
– Errors
– Seasons
– Trends
Cypris station – Irish Sea
Cypris station – Irish Sea
Irish Sea only (Holt&Young06)
OB (Sevenstones) station – Celtic Sea
OB (Sevenstones) station – Celtic Sea
ICES CTD
database analysis
Total
61,000 CTDs
20,000 this period (95-99)
Temperature errors – Oct-Dec 1995-99
Surface
Near-bed
Salinity errors seasonal 1995-99
Surface
Near-bed
Winter
Summer
SST trends
Like-for-like trends ‘81-99
(min of 8 years & 5 obs/season / 1o cell)
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
POLCOMS-ERSEM 15yr (1986-2001)
Mean chl errors mg/m3 (against ICES data)
NBT trends