Tiree Passage (1981 – 2006)Tiree Passage (1981 – 2006)and and

Ellett Line Shelf Stations (1975 – 2005): Ellett Line Shelf Stations (1975 – 2005):

Tides, Seasonality and ClimatologyTides, Seasonality and Climatology

Mark Inall, Mark Inall, Phil GillibrandPhil Gillibrand, Colin Griffiths, Colin GriffithsNeil MacDougal, Kimberly Blackwell, Graham WalkdenNeil MacDougal, Kimberly Blackwell, Graham Walkden

OutlineOutline

• Oceanographic context: NW UK Shelf• The “Observatory”• Tiree Passage “continuous” time series

– Variability: tidal to inter-decadal– Forcing of residual flow

• Ellett Line shelf stations: shelf-wide context

• Where do we go from here?

CirculationCirculation

Ellett and Edwards schematic circulation of the NW UK Shelf

• Based on a variety of sources, including 137Cs distributions

Surface SalinitySurface Salinity

Semi-diurnal tides (Semi-diurnal tides (POLCOMSPOLCOMS))

Moorings

Met. Stations

Tide gauges

CTD Section

SST/SSS Station (Port Erin)

The “Observatory”The “Observatory”

plus satellite imagery, model products and ‘foul weather CTD opportunities’

AVHRR 11 May 2000. Peter Miller PML

POLCOMSPOLCOMS

Ellett LineEllett Line• 75 occupations since 1975• SAMS 1975 – 1992• NOC 1992-1995• SAMS/NOC Joint 1996 - present• No occupations in 1986 and 2002• SAMS Northern Seas Programme Occupations in 2001

(partial) 2003 (full), 2005 (partial), 2006 (happening now!)

Tiree Passage: Tiree Passage: Longest temperature and flow time series Longest temperature and flow time series

on the NW European continental shelfon the NW European continental shelf

• June 1981: Hourly current and temperature (11 m a.b.)• November 1987 2nd meter added at 22 m a.b.• Ended in September 1997 at both depths. • Restarted June 1999 to February 2000 and then May 2002

until the present with RCMs at 11m and 22 m a.b.• Seabird salinity added in August 2002 at 22 m above bed.• A total of 61 deployments.

Raw Tiree time seriesRaw Tiree time series

Inevitable gaps, but tidal to inter-annual (decadal?) variability captured

Temperature

Velocity

Tiree VariabilityTiree Variability

10-2

10-1

100

10-3

10-2

10-1

100

101

102

103

104

Frequency (cpd)

Pow

er

SA

K1

M2 S2

10-2

10-1

100

10-2

10-1

100

101

102

103

104

Frequency (cpd)

Pow

er

SA K1

M2 S2

10-2

10-1

100

10-2

10-1

100

101

102

103

104

Frequency (cpd)

Pow

er

SA

K1

M2 S2

Temperature: SA dominant, weak tidal

Along channel velocity: tides dominate, SA significant

X-channel velocity: tides and broad SA dominate

Northward residual flowNorthward residual flow

Residual flow for full time series = 10.8 cms-1 northwardsEquating to 6.7 104 m3s-1

SA clear in monthly means

Moorings

Met. Stations

Tide gauges

CTD Section

SST/SSS Station (Port Erin)

The “Observatory”The “Observatory”

plus satellite imagery, model products and ‘foul weather CTD opportunities’

Tiree Passage Tiree Passage Barotropic dynamicsBarotropic dynamics

Correlation Coefficients

<AD> = 0.11

<BD> = 0.46

<CD> = 0.53

<BC> = 0.83

<E,-A-B> = 0.08

<E,C> = 0.12

<E,C-A-B-D> = 0.03

EDCBA

Dt

Dv

h

rv

hy

p

yg SyA

1

(local only)

Atmospheric forcing of residual flow: Atmospheric forcing of residual flow: NAO IndexNAO Index

r = 0.59

Tiree temperature anomalies Tiree temperature anomalies Irish Sea vs. NE AtlanticIrish Sea vs. NE Atlantic

TIME SERIES r2 SIGNIFICANT

Tiree and Port Erin 0.5047 Yes

Tiree and Rockall 0.1674 Yes

Port Erin and Rockall 0.1117 Yes

Tiree and Qnet 0.0005 No

Port Erin and Qnet 0.0423 Yes

Rockall and Qnet 0.0071 No

Port Erin vs. Tiree PassagePort Erin vs. Tiree Passage

Coastal warming trendCoastal warming trend

0.57 C per decade.

Note broad cooling in late 1980s and early 1990s, and peaked warm episodes of late 1980s and 1990s.

Seasonal shiftsSeasonal shifts

Advance of date of maximum temperature by 9 days/decade: clearly not sustainable. No significant trend in date of minimum temperature

Reliable salinity - only recently:Reliable salinity - only recently:

seasonality? Probably not (Ellett Line) – too early to tellseasonality? Probably not (Ellett Line) – too early to tell

Shelf-wide ContextShelf-wide Context

Ellett Shelf StationsEllett Shelf Stations

Ellett Shelf StationsEllett Shelf Stations

Seasonally adjusted bottom and surface (10m) temperature.

Salinity ClimatologySalinity Climatology

• Salinity trend– Surface (10m) +0.044 psu/decade– Bottom +0.036 psu/decade

Where do we go from here?Where do we go from here?

• Modeling context for– Process studies of cross shelf

exchange– 30 year Hindcasts of inter-annual

variability

• X-shelf surface elevation data• Acoustics• Time to work on the data !

Predictive Capability ?Predictive Capability ?

Peak Karenia bloom versus distance from first instance (excluding Skye from correlation)

y = 0.0813x + 196.35R2 = 0.9729

150

170

190

210

230

250

270

0 100 200 300 400 500 600 700

distance (km) from point zero (Mull)

day

of

year

of

pea

k o

f b

loo

m

Mull, Lew is, Orkney, Shetland

skye

Linear (Mull, Lew is, Orkney,Shetland)

Karemia mikimotoi bloom during summer 2005

Progression of bloom from Mull – Lewis – Orkney - Shetland

MODIS Aqua image, 31 July 2005 (RSDAS)