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Santander 2011
Monitoring the Rockall TroughToby Sherwin1
Penny Holiday2, Jane Read2, Clare Johnson1
and many others, including Bill Turrell3
(with posthumous acknowledgement to David Ellett1)
1 Scottish Association for Marine Science, Oban
2 National Oceanography Centre, Southampton
3 Marine Scotland, Aberdeen
AABW & LSW
0.9 Sv (0.3)
NAW
0.6 Sv
~3 Sv
Anton Dohrn
The Rockall Trough
Temperature / oC
AABW
ENAW
LSW
WTOW
Salinity
Anton
Dohrn
Rockall
ENAW – Eastern North Atlantic WaterWTOW – Wyville Thomson Ridge Overflow WaterLSW – Labrador Sea WaterAABW – Antarctic Bottom Water
Santander 2011
Three parts to talk:
1. Historical observation record
2. Future advances
3. Nutrients
Santander 2011
Three parts to talk:
1. Historical observation record
2. Future advances
3. Nutrients
Santander 2011
The Ellett Line
• Shared by SAMS and NOCS• Regular sections since 1975• Initially 4 times a year• More recently annually• Nutrients since 1996
RRS Challenger
David Ellett
Santander 2011
θ and S across the Rockall Trough
Annual std dev indicated
Averaged three timesi) Across the RTii) Between 30 and 800 miii) By year (when >1 cruises)
θ increase reversal
S increase levelling out
Santander 2011
Observations by Ocean Weather Ships
• UK Met Office• 1948 to 1992• Various tracks S of Anton Dorhn• Surface T and S• Measurement technique changed
over time• Averaged across the trough by
Ellett and Jones, MAFF Rpt 36, 1994
• Look at winter months JFM
Santander 2011
OWS Surface θ and S across RT
Great salinity anomaly
JFM averages
Annual averages
Santander 2011
OWS Surface Temperature and Salinity across RT
Towed thermometer
Mercury in board
Autolab salinometer Guildline salinometer
Thermistors
In board sampling
Titration
Santander 2011
-16 -14 -12 -10 -8 -6 -455
56
57
58
59
60
61
Roc
kall
Ban
k
Roc
kall
Trou
gh
WTR
Synthesis of Sea Surface Temperatures
• HadiSST - UK Met Office• 1856 onward by vessels of opportunity• Synthesis of sea surface temperature (SST) only• Area average into 5o by 5o boxes
Santander 2011
HadiSST JFM averages
HadiSST SSTs in the north-eastern North Atlantic
Santander 2011
Surface versus deep observations
Ellett Line
+ top 4 m
● 30 to 800 m
?
Santander 2011
Part 1 conclusions:
1. OWS surface salinity seem good before 1986
2. HadiSST SSTs seem to be ‘reasonable’ proxy for RT
winter water column temperatures
The standard Ellett Line data are the ‘gold standard’
But will that always be the case?
Santander 2011
Three parts to talk:
1. Historical observation record
2. Future advances
3. Nutrients
Santander 2011
Glider observations
• Operated SAMS• Started winter 2009/2010• Continuous monitoring to 1000 m• Latest mission started May 2011
Santander 2011
Glider temperature and salinity winter 09/10
Santander 2011
Santander 2011
Three parts to talk:
1. Historical observation record
2. Future advances
3. Nutrients
-17 -16 -15 -14 -13 -12 -11 -10 -9
0
500
1000
1500
2000
P314 PO4
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
-17 -16 -15 -14 -13 -12 -11 -10 -9
0
500
1000
1500
2000
P314 NO23
0
2
4
6
8
10
12
14
16
18
2022
24
26
28
30
32
-17 -16 -15 -14 -13 -12 -11 -10 -9
0
500
1000
1500
2000
P314 Si
2
4
6
8
10
12
14
16
18
20
22
24
26
28P314
July 2004
NO23 (μM)
PO4 (μM)
Si (μM)
Rockall
A ‘typical’ year
July 2004
Temperature / oC
AABW
ENAW
LSW
WTOW
Nutrient profiles
East of Anton DorhnNO23 PO4 Si
West of Anton DorhnNO23 PO4 Si
0
2000
2500
0
Nutrient time series east of Anton Dohrn 1996 - 2009
Month of cruise indicated
Santander 2011
Nutrient observations since 1996
Santander 2011
Conclusions (wrt last decade)
• The rise in surface temperature since 1995 seems to be tailing off
• Salinities continue to rise and have returned to pre-GSA levels
• Neither θ nor S levels appear significantly higher than historical
values, but …
• LSW signature continues to freshen and cool
• There are real trends in nutrient levels need to be explained by a
nutrient chemist
Santander 2011
Chnbo Guo
Svein Osterhus
Detlef Quadfasel
Bogi Hansen
