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HOW TO MEASURE OCEANIC FLUXES FROM THE NORTH

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Arctic-Subarctic Ocean Flux Array for European Climate: North
HOW TO MEASURE OCEANIC FLUXES FROM THE NORTH ATLANTIC THROUGH FRAM STRAIT ?
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E. Fahrbach , A.Beszczynska-Möller , E. Hansen , J. Meincke , S. �sterhus , G. Rohardt , U. Schauer ,A. Wisotzki
1)
Alfred Wegener Institute for Polar and Marine Research, PO Box 120161, D-27515 Bremerhaven, Germany, efahrbach@awi-bremerhaven.de
2)
3)
4)
ARRANGEMENT OF INSTRUMENTS AT MOORINGS
IN FRAM STRAIT IN 1997-2002
F14
F13
F12
F11
F10
F8
F9
F7
F6
Norwegian Polar Institute, Polar Environmental Centre ,9296 TromsГё, Norway
Institute of Marine Research, University of Hamburg, Troplowitzstr. 7, D-22529 Hamburg, Germany
Bjerknes Center, Geophysical Institute, University of Bergen, N-5014 Bergen, Norway
BAROTROPIC VELOCITY DERIVED AS AVERAGE OF VERTICAL
PROFILE (upper fig.) AND CALCULATED RELATIVE BOTTOM
PRESSURE (lower fig.) IN 1998-1999
LOCATION OF MOORINGS IN FRAM STRAIT IN 1997-2002
F5 F4
BOTTOM PRESSURE DIFFERENCE AND SEA LEVEL ELEVATION
BETWEEN MOORINGS F8 AND F6B IN 2001-2002
BAROTROPIC VELOCITY
F3 F2 F1
0
500
1000
F8
n
dia
na in
Ca Bas
500
1000
F7
F6
53 km
z
sia
ra
North
Eu
Greenland
1500
1500
Barents
Sea
Greenland
West
- 000
500
2000
5
F6
6
7
8
9
F8
3000
500
1000
1000
10
500
00
2000
78В°
76В°
1500
1500
2000
2000
ACM-CTD
-8
AVTS(P)
AVT(P)
DCM12
-7
0
-2
-2
-4
-4
-6
-6
-8
-8
-10
-10
74В°
SEACAT/
MICROCAT
2500
2
0
AUG-2001
Depth [m]
F2
F2
F6
0
0
20
0
Bottom Pressure Difference (10-2 dbar)
F6-F8
2500
233
F3 F2 F1
2
RELATIVE BOTTOM PRESSURE
Spitsbergen
F5 F4
2500
1998-99
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
15В°W
9
10В°
5В°
0В°
5В°
10В°
Sea Level Elevation (10-2 m)
at F7
4
F7
JUL-2002
3
F8
JUN-2002
2
APR-2002
1
MAY-2002
0
F9
JAN-2002
-1
FEB-2002
-2
F10
MAR-2002
-3
F11
Latitude (- West, + East)
F12
DEC-2001
-4
F13
NOV-2001
-5
F14
SEP-2001
-6
0
-7
2500
1997-98
100
-8
80В°
AVTS(P)
AVT(P)
DCM12
2500
SEACAT/
MICROCAT
1500
ACM-CTD
2500
OCT-2001
Depth [m]
n
Ba
82В°N
sin
0
15В°E
Latitude (- West, + East)
F6
F5
F4
F3 F2 F1
-700
0
-500
-500
0
20
40
2000
60
80
100
120
140
160
-1000
86
14
Depth [m]
88
14
148
8
-8
-500
-6
-1500
-4
-2
0
2
4
6
Longitude
-1000
-1500
-2000
SEACAT/
MICROCAT
-2500
-7
-4
-3
-2
-1
0
1
2
3
4
5
F7
F6
6
7
F5
F4
8
-187
-188
-174
-168
-167
-166
-148
-147
-160
-146
-145
-143
-144
-153
-142
-154
-141
-155
-223
-222
-221
-220
-219
-218
-217
-216
-215
-214
-213
-212
-211
-209
-208
-207
-203
-206
-205
-204
-201
-200
-199
-198
-195
-197
-196
-186
-186
1466
1468
62
14
8
1466
1470
1472
1472
1474
1476
1476
1476
1478
1480
1482
1480
1484
1486
2001
1480
1482
1484
1484
-2500
-5
6
1464
1468
2000
-2500
2000-01
-6
4
1470
1464
1500
2500
BOTTOM
PRESSUR
RECORDER
-8
1000
-2000
AVTS(P)
AVT(P)
DCM12
ADCP
2
1455
8
-2000
ACM-CTD
0
500
3000
0
-1500
1488
2003
F2 F1
-2
1450
1445
1468
F3
-4
1440
1462
F4
0
1486
1464
F5
88
F6
14
F7
-6
Longitude
1484
1484
1486
2500
-8
1482
1482
1482
2002
3000
1476
1478
1480
-900
Distance [km]
F8
-1000
-1000
1474
1476
-800
data from AREX’2001
r.v. OCEANIA, IO PAN Sopot
-41
F7
-39
-40
F8
-38
F9
1486
1488
8
-35
-36
-37
F10
8
14
88
F11
76
F12
14
F13
1474
1482
1484
1486
1488
1486
88
14
1472
1482
1484
1484
2500
1472
1478
1478
1480
1482
1470
1500
1476
1478
14
-500
1466
1474
1474
2000
1468
1470
1472
1466
-400
1466
1462
1468
1470
1500
-34
-300
1462
-31
-200
1000
-30
-100
-29
0
-600
F14
0
-797
-795
-794
-793
-787
-786
-785
-784
-783
-789
-778
-777
-776
EB2-1
-28
EB2-3
EB2-2
1484
1486
1486
1488
EB2-4
-27
9
EB2-5
-26
8
EB2-6
-61
7
EB2-7
-62
6
EB2-8
-63
5
EB2-9
1460
4
0
EB2-1
1
1464
-64
3
EB2-1
1460
1464
1462
1462
1468
-65
2
2
EB2-1
3
EB2-1
1450
1460
1000
-66
1
4
1440
1455
-67
0
Latitude (- West, + East)
EB2-1
1445
500
-68
-1
Baroclinic geostrophic velocity [cm/s] - upper 1000 m
0
1472
-69
-2
1462
-70
-3
1468
62
-71
-4
14
88
-5
1450
1472
500
Pressure (dbar)
-6
0
-300
160
Depth [m]
-7
140
64
-8
2500
1999-2000
120
14
-2500
100
74
SEACAT/
MICROCAT
80
14
ACM-CTD
AVTS(P)
AVT(P)
DCM12
60
1468
2000
40
1460
-2000
-200
20
Depth [m]
-100
0
68
Depth [m]
ADCP measured current velocity [cm/s]
45
40
35
30
25
20
15
10
5
2
1
0
-1
-2
-5
-10
-15
-20
-25
-30
-35
-40
-45
14
1500
-224
1000
-1500
-225
-1000
DISTRIBUTION OF SOUND VELOCITY AT SECTION ACROSS FRAM STRAIT IN 2000-2003
14
500
-226
0
-500
-227
0
EXAMPLE OF EDDY STRUCTURES MEASURED IN 2001
(upper fig.) AND SCHEME OF MESOSCALE EDDIES
IN FRAM STRAIT (lower fig.)
Pressure (dbar)
F3 F2F1
-73
-72
F5 F4
-75
-74
F6
Pressure (dbar)
F10
60
F11
1466
F12
14
F13
-740
-739
-738
-737
-736
-735
-734
-733
-775
-771
-770
-769
-768
-767
-763
-762
-761
-760
-759
-758
-727
-726
-743
-745
-747
-749
-
F14
3000
2
3
4
5
6
7
8
9
-8
-6
-4
-2
0
Longitude [deg]
9
2
4
6
8
Longitude
1440
-1000
-1500
-1500
14
1000
14
-260
-261
-280
1478
1482
1478
-8
14
1484
1482
1482
-6
80
-4
-2
0
2
4
6
8
Longitude
BOTTOM
PRESSUR
RECORDER
-7
1472
1478
1480
2000
-8
-150
1474
1476
1484
1486
3000
-2000
AVTS(P)
AVT(P)
DCM12
ADCP
-279
1470
1472
76
1478
SEACAT/
MICROCAT
-2500
1466
1468
1472
2000
1468
1462
1464
1468
1500
1472
1460
1462
60
1464
2500
ACM-CTD
1464
55
14
Pressure (dbar)
Depth [m]
-1000
-2000
1450
2
1460 146
500
-500
1466
0
0
-500
-174
0
-173
F3 F2 F1
-183
F8
-190
F9
-245
F10
-192
F11
-195
-193
F12
-194
F13
-205
-201
-200
-199
-198
-202
F14
-207
Latitude (- West, + East)
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
PIES (Pressure Inverted Echo Sounder)
-2500
2001-02
9
Latitude (- West, + East)
MEAN SOUND VELOCITY PROFILES
ACROSS FRAM STRAIT IN 1997-2003
16
14
12
10
8
6
- F3
- F2
- F1
- F5
- F4
- F6
- F7
- F8
- F9
- F10
- F11
- F12
0
- F13
- F14
May
Jan.02
Sep
Sep
May
May
Jan.00
Jan.01
Sep
Sep
May
May
Jan.98
Jan.99
Sep.97
4
10
direct
NET AND NORTHWARD VOLUME AND HEAT TRANSPORTS CALCULATED
DIRECTLY AND BASED ON LINEAR REGRESSION MODEL (upper tab.)
AND POINTS WITH SIGNIFICANT CORRELATION COEFFICIENTS
BETWEEN CURRENT VELOCITY AND TRANSPORTS (lower tab.)
8
ABOVE 0.51
0.40 - 0.51
0.34 - 0.40
0.30 - 0.34
0.00 - 0.30
-0.30 - 0.00
-0.34 - -0.30
-0.40 - -0.34
-0.51 - -0.40
BELOW -0.51
2000
2500
Distribution of correlation coefficient
between VC and net volume transport
-8
-10
- F3
- F2
- F1
- F5
- F4
- F6
- F7
- F8
- F9
- F10
- F11
- F12
- F13
- F14
0
May
Jan.02
Sep
450
May
400
Sep
350
May
-12
300
Distance (km)
Jan.00
250
-6
Jan.01
200
Period
direct
9.97-8.98 -5.5 В±3.2
9.98-8.99
-3.0 В±3.3
-4
Sep
150
F12
May
100
Net Volume Transport
(Sv)
0
Sep
50
2
-2
May
0
F8
Sep.97
3000
4
Jan.98
1500
6
Jan.99
1000
Depth
Net volume transport [Sv]
500
85
80
1500
Heat transport [TW]
1000
2000
65
60
55
50
45
40
35
30
25
20
15
2500
10
Distribution of correlation coefficient
between VC and heat transport
May
Jan.02
Sep
May
450
Sep
400
May
0
350
Jan.00
Distance (km)
5
300
Jan.01
250
Sep
200
May
150
Sep
100
May
50
Jan.98
0
Jan.99
3000
Sep.97
Depth
F5
70
ABOVE 0.51
0.40 - 0.51
0.34 - 0.40
0.30 - 0.34
0.00 - 0.30
-0.30 - 0.00
-0.34 - -0.30
-0.40 - -0.34
-0.51 - -0.40
BELOW -0.51
F8
-4.6
-4.2
-3.8
-4.9
-4.3
-4.5
-2.7
-0.7
-4.2
-3.7
-3.0
9.5 В±1.4
Heat Transport
(TW)
direct
21 В±10
F5
25
42 В±10
38
11.7
42
10.8
9.8
9.5
10.3
10.2
37
33
32
35
34
36 В±7
direct
75
500
10.997.00
8.00-6.01
8.01-7.02
9.97-8.99 -4.2 В±2.3
9.97-6.01
9.97-7.02
F12
-4.4
Northward
Volume
Transport
(Sv)
direct
F5
8.4
9.0 В±0.9
10.1
10.7
В±2.2
Period (approx. Sep.- Aug.)
Mooring Depth Significance 97-98 98-99 99-00 00-01 01-02
99%
F8
250m
Net
F9
1500m
99%
Volume
2500m
99%
Transport
95%
F12 250m
Northward
99%
Volume
F5
250m
Transport
99%
80m
F5
250m 99% (max)
Heat
1500m
99%
Transport
2000m
99%
F4
60m
99%
250m
99%
Highly barotrophic character of currents
in Fram Strait suggests that reasonable
estimations of volume transport variations can
be obtained from measurements with bottom
pressure recorders. The accuracy of bottom
pressure recorders must be good enough to
resolve the seasonal range of pressure
variations.To
estimate their orders, the
monthly mean barotropic currents from the
moored instruments at each mooring location
and the related bottom pressure gradients
were calculatedc under the assumption of
geostrophic conditions Obtained relative
bottom pressure profiles reveal strong
horizontal gradients related to West
Spitsbergen Current in the eastern and East
Greenland Current in the western part of the
strait. Seasonal variations of these gradients
correspond to the seasonal signal found in the
relative pressure gradient obtained from later
measurements by the bottom pressure
recorders (see figs in upper right corner).
Close relationship between the mean
temperature of the water column (mostly
determined by variations in the Atlantic layer)
and sound velocity (see figs to the left) makes
possible to use inverted echo sounders for
monitoring the heat content variations. Also
baroclinic transport can be obtained from a
measured specific volume anomaly. For the
first time three PIES (Pressure Inverted Echo
Sounders) were deployed in Fram Strait
in 2003.
1460
Lance'97 (1997)
ARK XIV/2a (1998)
ARK XV/3 (1999)
ARK XVI/2 (2000)
ARK XVII/1 (2001)
ARK XVIII/1B (2002)
ARK XIX/4B (2003)
1450
1440
-8
-6
-4
-2
0
2
4
6
8
MEAN TEMPERATURE AND
ACOUSTIC TWO PATH TRAVEL TIME
AT MOORINGS F1 AND F8 IN 1997-1999
4.5
0.44
4
0.439
3.5
0.438
3
Two Path Travel Time (sec)
F5, 250m
direct
18
1470
0.437
2.5
Mooring F1, 321m
2
0.436
Sep
Jan 98
May
Sep
Jan 99
May
0.5
3.356
0.4
3.355
0.3
3.354
0.2
3.353
0.1
3.352
0
Mooring F8, 2465 m
-0.1
3.351
Sep
Jan 98
May
Sep
Jan 99
May
Two Path Travel Time (sec)
Distribution of correlation coefficient
between VC and northward volume transport
20
mean sound velocity (Fram Strait 79В°N)
1480
Mean Temperature (В°C)
Northward volume transport [Sv]
22
Fluxes from the North Atlantic through Fram Strait affect the water mass properties and the oceanic components of
the heat budget in the Arctic Ocean. Variability of the northward fl ow of water of Atlantic origin in Fram Strait in
temperature and volume transport requires time series of the temperature and current fi elds to determine relevant changes
which can have an impact on the Arctic Ocean. For this purpose measurements with moored instruments were initiated under
the MAST III project VEINS. The evaluation of the obtained data revealed intensive variations on a wide range of scales.
Variations on a seasonal time scale are significant suggesting that measurements excluding the winter months are seriously
biased. Mesoscale fl uctuations determine the uncertainty of the estimated transports.To reduce the uncertainty either a
larger number of moorings and instruments is needed or integral methods have to be applied. With this purpose the potential
of bottom pressure recorders to estimate the barotropic current and of inverted echo-sounders to derive the heat content
of the water column are investigated in the frame of the EU funded ASOF-N project. Fram Strait is also an area of strong
recirculations, which have to be included in the measurements. The deployment of two additional moorings in the central part
of the strait since 2002 will help to understand the potential role of the unresolved recirculation in producing unrealistic
features.
Correlation of transport time series with monthly mean zonal current velocities at selected locations seems promising.
Volume and heat fluxes derived directly from measured current/temperature fields and estimated with use of linear
regression model for selected locations reveal satisfying agreement. The present status of the evaluation suggests that a
combination of bottom pressure recorders, inverted echo sounders and a few full size moorings equipped with current meters
and temperature/salinity recorders can deliver time series of northward heat transport after appropriate calibration.
Mean Temperature (В°C)
F3
F2
F1
F5
F4
F6
F7
F8
F9
F10
F11
F12
F13
F14
CORRELATION BETWEEN CROSS-SECTION CURRENT AND NORTHWARD, NET VOLUME AND HEAT
TRANSPORTS (left figs) AND TIME SERIES OF NORTHWARD, NET VOLUME AND HEAT TRANSPORTS
CALCULATED DIRECTLY AND WITH USE OF LINEAR REGRESSION MODEL (right figs)
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