a report of xcp and ctd data taken during june, 2001, rrs ... · pre-cruise support provided by the...

A Report of

XCP and CTD data taken during

June, 2001, RRS Discovery cruise 247B

A Process Study of the Faroe Bank Channel Overflow

April 30, 2001

DSO —EGC —

FBCO —NAC —

NADW —ISRO —

IC —

Denmark Strait OverflowEast Greenland CurrentFaroe Bank Channel OverflowNorth Atlantic CurrentNorth Atlantic Deep WaterIceland—Scotland Ridge OverflowIrminger Current

CoPIs: James F. Price, Woods Hole Oceanographic InstitutionThomas B. Sanford, Applied Physics Laboratory, Univ. of Washington

Cecilie Mauritzen, Woods Hole Oceanographic InstitutionMark Prater, Graduate School of Oceanography, Univ. of Rhode Island

2

1 Overview of the Field Program

Faroe Bank Channel (FBC) is the deepest passage between the Norwegian-Greenland Seaand the North Atlantic Ocean (Figure 1). There is observed to be a quasi-steady overflow ofdense water through FBC from the Norwegian-Greenland Sea into the abyssal North Atlanticat the rate of about 2 Sv. This dense overflow contributes significantly to the North EastAtlantic Deep Water, which in turn is a major component of North Atlantic Deep Water.The FBC and its overflow have thus been of great interest to physical oceanography sinceits prominent role in deep water formation was appreciated in the 1950s.

−15−10 −5

057

58

59

60

61

62

63

64

65

−3−2−1

01

East Longitude, deg.

km

SIR

WTR

FST FBC

Figure 1: A 3-D view of the ocean sea floor in the Faroe Bank Channel region. SIR is the Scotland-Iceland Ridge, FBC is the Faroe Bank Channel, WTR is the Wyville-Thomson Ridge and FST isthe Faroe Shetland Trough.

3

The goal of our field program was to acquire finely sampled measurements of currents andhydrography in the region several hundred kilometers up and downstream of the sill inFBC sufficient to address three specific questions: 1) What is the transport and momentumbalance of the overflow? 2) How does the overflow water approach the sill southwest of theFaroe Islands, and is the overflow hydraulically controlled? 3) Where and how does mixingoccur in the descending overflow?

Our starting point for addressing these questions was to acquire a data set sufficient to allowestimation of the volume, momentum, energy and vorticity budgets along the path of theoverflow. Bottom stress and vertical mixing with overlying North Atlantic water were ex-pected to be of significant importance for these budgets. The strategy of our field programwas to make measurements along a number of transverse sections that spanned the overflowfrom the Faroe-Shetland Trough (the approach) to the southern flank of the Faroe-IcelandRidge (the descending overflow). Currents were measured by expendable current profil-ers (XCP), ship-mounted acoustic Doppler current profiler (ADCP) and lowered acousticDoppler current profiler (LADCP). Hydrographic properties were measured by CTD, andby acquiring discrete water samples (oxygen and nutrients).

The instruments performed as expected, and there was only a very small data loss due tomechanical failure or operator error. In total, we made 217 CTD/LADCP profiles, and 114XCP profiles. Underway measurements were made by ADCP, and by a variety of navigationsensors (most importantly, differential GPS (DGPS)) and meteorological sensors. Bottom-following drifters were also deployed.

2 A Brief Chronology of the Cruise and the Sampling

Discovery departed Southampton on 5 June and steamed northward for the FBC region. Thefirst task was to deploy a sound source at approx. 62N, 11W. Once this was accomplished,Discovery proceeded to the sill region of the FBC southwest of the Faroe Islands and beganto sample along transverse sections labeled A, B, C, etc., in the order they were taken (Figure2). These sections were made up of closely spaced CTD/XCP stations. The usual courseof events was that an XCP was taken upon arrival at a CTD station. However, when wewere at the end of a section and no longer within the dense overflow, we sometimes chose towithhold the XCP.

Sampling proceeded as planned until near the end of section D when a major low pressureweather system began to deepen and approach our area. Gale force winds caused the ces-sation of our work for a period of about 36 hrs (details of this are in the Ship’s OperationsLog). Once the winds abated, we resumed sampling to finish section D and then occupiedsection E. We judged that most of the mixing that was expected in the overflow had occurredby section E, and we never proceeded westward of about 10 40W.

Upon completion of E we returned to the sill section A, with the intent of continuing eastwardto survey the approach of the overflow in the Faroe-Shetland Trough. We first reoccupiedsection A, calling the new section Ar, and discovered that a noticeable change - a considerably

4

−14 −12 −10 −8 −6 −4 −2 059

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West Longitude, deg.

Nor

th L

atitu

de, d

eg.

Faroe−Iceland Ridge

Faroe IslandsFaroe−ShetlandTrough

Wyville−ThomsonRidge

ShetlandIslands

Norwegian Sea

Faroe BankChannel

Faroe Islands and Faroe Bank Channel

A

B

C

DE

G HI

J

−0.5

−1.25

−1

−1.5

−0.25

−0.75

K

Figure 2: The approximate location of the CTD sections. There were about 30 CTD stationsmade as part of a time series or to close off the northern or southern end of sections that are notindicated here. The red dashed line labelled ’K’ is a synthetic longitudinal section made up fromstations selected from the transverse sections (the solid blue lines) and is intended to show the coreof the overflow.

thicker and slightly colder overflow layer than at the time of A. We then sampled sectionG, and for the first time noticed what appeared to be high frequency (tidal or inertialperiod) fluctuation of the currents and hydrographic fields. This impression of variabilitywas confirmed at section H, where we found quite large tidal or inertial variability thatrequired repeated sampling. In all, we spent three days sampling on section H, or about twodays more than anticipated. As part of section H we went to the Wyville-Thomson Ridge andobserved a small and evidently fluctuating overflow (southward) across the ridge. We thensampled the approach along section I, where there was much less tidal/inertial variability,and proceeded to section J, completing the approach survey.

Given the significant change in the overflow from A to Ar we decided to occupy section A twomore times, and then repeated sections C, D and E (C for the third time). On this secondoccupation of the descending overflow sections we found a somewhat larger volume of colderoverflow water, indicating that the overflow had a greater transport during the second halfthe field program.

5

Compared to our original plan, we completed a slightly greater number of stations thananticipated. Also compared to the original plan, we used a greater fraction of these stationsin a repeat sampling mode (e.g., we occupied section A four times vs. twice planned)on account of the evidence of temporal variability noted above. Similarly, we made sevensections on the approach; G twice, H three times, and I twice. Given the conditions wefound, this repeat sampling seemed essential, though it was necessarily done at the expenseof more extensive spatial coverage.

Sec A, 10 JuneSec B, 10 JuneSec C, 11 JuneSec D first half, 12 JuneStorm delay, 13 JuneSec D, resume, 14 JuneSec E, 15 JuneSec Ar, 16 JuneSec Cr, 17 JuneSec G, 18 JuneSec Arr, 18 JuneSec H, 20 JuneSec Hr, 21 JuneSec I, 22 JuneSec J, 23 JuneSec Arrr, 25 JuneSec Crr, 27 JuneSec Drr, 28 JuneSec Er, 29 JuneSec Gr, 29 JuneSec Ir 30 June

The analysis of this data set will require many months of concerted effort, and we will notattempt here to forecast scientific conclusions. We are confident, however, that the horizontalresolution along sections is generally sufficient to resolve the mesoscale, transverse structureof the overflow, including the relative vorticity (an exception to this may be section H, wheretidal/inertial variability was very large, though repeatedly sampled). As well, the changesobserved from one section to the next appear ’coherent’ (mapable) and hence we believe thatthe goal of estimating mixing-induced changes along the path of the descending overflow willalso be achievable.

6

3 About This Report

This report is a working draft. It’s main purpose is to disseminate results as quickly aspossible to those involved in the project. This report is also available on an anonymous ftpsite and so in that regard it is also in the public domain. However, we request that anyonewanting to use the report for anything other than their own information should contactone of the PIs for permission. The results shown here are fresh and untested; they may besignificantly incomplete (the sampling of transport on section E, for example), and may evencontain outright errors.

This report shows something less than half of the total data set. The full set of figures for allof the sections may be found on a web site, http://www.whoi.edu/science/PO/people/jprice/under a section entitled overflow models etc.; go directly to the ftp site. The graphics files arein eps format, and their content is coded into the file name as follows: the ctd section dataare in five figures, say for section Ar - ctdAr1.eps is the potential temperature, ctdAr2.eps issalinity, 3 is the oxygen, 4 is the density, 5 is the T/S diagram and ctdmapAr.eps is the mapof station locations. XCP data are in a similar form: xcpArr1.eps is the contour of velocity,xcpAr2.eps is the histogram of property transport and mapxcpAr.eps is the map of stationlocations (very similar to the CTD maps shown here).

4 Acknowledgements

This field project was made possible by the efforts of many skilled and dedicated people. XCPoperations were set up by John Dunlap and James Girton, and assisted ably by Dicky Allison.The shipboard technical staff led by Jeff Benson was responsible for a flawless CTD andADCP operation. The CTD data was logged by Deborah West-Mack assisted by the CTDwatchstanders, Liz Hawker, Laura Cornick, Heather Deese, Avon Russell, Patricia Kassisand Peter Huybers. George Tupper managed much of the pre- and post-cruise logisticaleffort, and while at sea analyzed the salinity and oxygen samples. Dan Torres set up andsupervised the LADCP operation. We are most grateful to Capt. Robin Plumley and theofficers and crew of RRS Discovery for their steadfast support of all aspects of the project.Pre-cruise support provided by the Research Vessel Services staff, Edward Cooper, AndyLouch and Conor Mowltz, is also greatly appreciated. Penny Foster organized travel andother pre-cruise administrative matters with efficiency and good humor. This project wasfunded by the U. S. National Science Foundation through grants OCE 99-06736 (to J. F.Price and C. Mauritzen) and OCE 99-11492 (to M. Prater).

List of Figures

1 A 3-d perspective on the Faroe Bank Channel. . . . . . . . . . . . . . . . . . 2

2 The approximate location of the CTD sections. . . . . . . . . . . . . . . . . 4

7

3 XCP profile from section Arr, in the narrow portion of Faroe Bank Channel. 10

4 XCP profile from section Cr. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5 XCP profile from section G, at the entrance to Faroe Bank Channel. . . . . . 12

6 Station map of CTD section A. . . . . . . . . . . . . . . . . . . . . . . . . . 13

7 CTD section A, T and S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

8 CTD section A, O and ρ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

9 CTD section Ar, T and S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

10 CTD section Ar, O and ρ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

11 CTD section Arr, T and S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

12 CTD section Arr, O and ρ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

13 CTD section Arrr, T and S. . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

14 CTD section Arrr, O and ρ. . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

15 T/S diagram from section A. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

16 T/S diagram from section Ar. . . . . . . . . . . . . . . . . . . . . . . . . . . 19

17 T/S diagram from section Arr. . . . . . . . . . . . . . . . . . . . . . . . . . . 20

18 T/S diagram from section Arrr. . . . . . . . . . . . . . . . . . . . . . . . . . 21

19 XCP section A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

20 XCP section Ar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

21 XCP section Arr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

22 XCP section Arrr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

23 3d view of XCP-measured currents from section Arr. . . . . . . . . . . . . . 26

24 Transport by parameter class, section A. . . . . . . . . . . . . . . . . . . . . 27

25 Transport by parameter class, section Ar. . . . . . . . . . . . . . . . . . . . . 28

26 Transport by parameter class, section Arr. . . . . . . . . . . . . . . . . . . . 29

27 Transport by parameter class, section Arrr. . . . . . . . . . . . . . . . . . . . 30

28 Station map of CTD section Cr. . . . . . . . . . . . . . . . . . . . . . . . . . 31

29 CTD section Cr, T and S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

30 CTD section Cr, O and ρ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

31 T/S diagram from section Cr. . . . . . . . . . . . . . . . . . . . . . . . . . . 33

8

32 XCP section Cr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

33 Transport by parameter class, section Cr. . . . . . . . . . . . . . . . . . . . . 35

34 Station map of CTD section G. . . . . . . . . . . . . . . . . . . . . . . . . . 36

35 CTD section Cr, T and S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

36 CTD section Cr, O and ρ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

37 T/S diagram from section G. . . . . . . . . . . . . . . . . . . . . . . . . . . 38

38 XCP section G. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

39 Transport by parameter class, section G. . . . . . . . . . . . . . . . . . . . . 40

40 CTD station map for section Er. . . . . . . . . . . . . . . . . . . . . . . . . . 41

41 Potential temperature from section Er. . . . . . . . . . . . . . . . . . . . . . 42

42 Salinity from section Er. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

43 Oxygen from section Er. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

44 Potential density from section Er. . . . . . . . . . . . . . . . . . . . . . . . . 45

45 T-S diagram from section Er. . . . . . . . . . . . . . . . . . . . . . . . . . . 46

46 XCP section Er. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

47 Transport by parameter class, section Er. . . . . . . . . . . . . . . . . . . . . 48

48 CTD station map for section K, along the path of the Faroe Bank Channeloverflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

49 Potential temperature made up from CTD stations taken along the path ofthe Faroe Bank Channel overflow. . . . . . . . . . . . . . . . . . . . . . . . . 50

50 Salinity made up from CTD stations taken along the path of the Faroe BankChannel overflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

51 Dissolved oxygen made up from CTD stations taken along the path of theFaroe Bank Channel overflow. . . . . . . . . . . . . . . . . . . . . . . . . . . 52

52 Potential density made up from CTD stations taken along the path of theFaroe Bank Channel overflow. . . . . . . . . . . . . . . . . . . . . . . . . . . 53

53 T-S diagram from section K. . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

54 3d view of XCP currents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

55 Velocity-weighted transport of temperature, salinity and oxygen. . . . . . . . 56

56 Transport and velocity-weighted density transport. . . . . . . . . . . . . . . 57

57 Bottom stress estimates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

9

58 The ensemble average of the near-bottom current. . . . . . . . . . . . . . . . 59

59 The ensemble average rms of the deviation of the current from a log fit toeach profile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

10

5 Selected XCP and CTD Profiles from the Faroe Bank

Channel.

−1 −0.5 0−0.5

00.5

0

100

200

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500

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700

800

900

U, m s−1

dept

h, m

27 27.5 28 28.5

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100

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500

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800

900

pot. density, kg m−3

section Arr

0 0.5 1

0

100

200

300

400

500

600

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800

900

Rich. no.

Figure 3: XCP and CTD profile data taken near the center of section Arr. (right most panel)Richardson number computed by vertical differencing over an interval of 10 m. The red dots onthe Ri diagram indicate that the estimated density gradient exceeded 0.001 kg m−1.

11

−1 −0.5 0−0.5

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800

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U, m s−1

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27 27.5 28 28.5

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700

800

900


section Cr

0 0.5 1

0

100

200

300

400

500

600

700

800

900

Rich. no.

Figure 4: XCP and CTD profile data taken near the center of section Cr. (right most panel)Richardson number computed by vertical differencing over an interval of 10 m. The red dots onthe Ri diagram indicate that the estimated density gradient exceeded 0.001 kg m−1.

12

−1 −0.5 0 −0.50

0.5

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U, m s−1

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section G

0 0.5 1

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Rich. no.

Figure 5: XCP and CTD profile data taken near the center of section G. (right most panel)Richardson number computed by vertical differencing over an interval of 10 m. The red dots onthe Ri diagram indicate that the estimated density gradient exceeded 0.001 kg m−1.

13

6 Section A Repeat Sampling.

Section A, located near the center of the Faroe Bank Channel (see figure 6) was occupied fourtimes during the cruise. These repeated sections are shown together in a common format sothat temporal variability may be assessed.

−11 −10 −9 −8 −7 −6 −5 −4 −359.5

60

60.5

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61.5

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62.5

Longitude, deg.

La

titu

de

, d

eg

.

ctd section Arr

8996

Figure 6: Station locations for section Arr; the other occupations of this section, A, Ar and Arr,were along the same line.

14

Theta

(°C)

−1

0

1

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3

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0 5 10 15

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CTD CTD4 38

CTD7

CTDCTD6

CTD5

Depth

(m)

ctd section A

Distance (km)

Salin

ity

34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 5 10 15

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500

1000

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CTD CTD4 38

CTD7

CTDCTD6

CTD5

Depth

(m)

ctd section A

Distance (km)

Figure 7: A section of potential temperature (left) and salinity (right) made up from CTD stationstaken across the narrow part of the Faroe Bank Channel overflow (see Figure 6 for details of stationlocations). This view is to the west and in the direction of the overflow current.

Dens

ity

27

27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

28

28.1

28.2

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500

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CTD CTD4 38

CTD7

CTDCTD6

CTD5

Depth

(m)

ctd section A

Distance (km)

Oxyg

en

5.5

5.7

5.9

6.1

6.3

6.5

6.7

6.9

0 5 10 15

0

500

1000

1500

CTD CTD4 38

CTD7

CTDCTD6

CTD5

Depth

(m)

ctd section A

Distance (km)

Figure 8: A section of potential density (left) and oxygen concentration (right) made up fromCTD stations taken across the narrow part of the Faroe Bank Channel overflow (see Figure 6 forthe station locations for this section A). This view is to the west, or in the direction of the overflowcurrent.

15

Thet

a (°C

)−1

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CTD CTD66 6759

CTD60

CTD61CTD

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63CTDCTD

64CTD

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Dept

h (m

)ctd section Ar

Distance (km)

Salin

ity

34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 5 10 15 20

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CTD CTD66 6759

CTD60CTD

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65

Dept

h (m

)

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Distance (km)


Dens

ity

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27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

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28.1

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CTD CTD66 6759

CTD60CTD

61CTD

62CTD

63CTDCTD

64CTD

65

Dept

h (m

)

ctd section Ar

Distance (km)

Oxyg

en

5.5

5.7

5.9

6.1

6.3

6.5

6.7

6.9

0 5 10 15 20

0

500

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CTD CTD66 6759

CTD60CTD

61CTD

62CTD

63CTDCTD

64CTD

65

Dept

h (m

)

ctd section Ar

Distance (km)

Figure 10: A section of potential density (left) and oxygen concentration (right) made up fromCTD stations taken across the narrow part of the Faroe Bank Channel overflow (see Figure 6 fordetails of station locations). This view is to the west, or in the direction of the overflow current.

16

Theta

(°C)

−1

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1

2

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4

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6

7

8

9

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0 5 10 15

0

500

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CTD CTD95 9689

CTD90CTD

91CTD

92CTD CTD

93CTD

94

Depth

(m)

ctd section Arr

Distance (km)

Salin

ity

34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 5 10 15

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500

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1500

CTD CTD95 9689

CTD90CTD

91CTD

92CTD CTD

93CTD

94

Dept

h (m

)

ctd section Arr

Distance (km)


Dens

ity

27

27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

28

28.1

28.2

0 5 10 15

0

500

1000

1500

CTD CTD95 9689

CTD90CTD

91CTD

92CTD CTD

93CTD

94

Depth

(m)

ctd section Arr

Distance (km)

Oxyg

en

5.5

5.7

5.9

6.1

6.3

6.5

6.7

6.9

0 5 10 15

0

500

1000

1500

CTD CTD95 9689

CTD90CTD

91CTD

92CTD CTD

93CTD

94

Depth

(m)

ctd section Arr

Distance (km)


17

Thet

a (°C

)−1

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2

3

4

5

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7

8

9

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CTD CTD157 158150

CTD151CTD

152CTD

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154CTDCTD

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156

Dept

h (m

)ctd section Arrr

Distance (km)

Salin

ity

34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 10 20

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1000

1500

CTD CTD157 158150

CTD151CTD

152CTD

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155CTD

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Dept

h (m

)

ctd section Arrr

Distance (km)


Dens

ity

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27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

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28.1

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1500

CTD CTD157 158150

CTD151CTD

152CTD

153CTD

154CTDCTD

155CTD

156

Dept

h (m

)

ctd section Arrr

Distance (km)

Oxyg

en

5.5

5.7

5.9

6.1

6.3

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6.7

6.9

0 10 20

0

500

1000

1500

CTD CTD157 158150

CTD151CTD

152CTD

153CTD

154CTDCTD

155CTD

156

Dept

h (m

)

ctd section Arrr

Distance (km)


18

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section A

27.75

27.8

27.85

27.9

27.95

28

28

28.0

5

28.1

28.15

28.2

28.2

5

Figure 15: T-S diagram from section A. The colors indicate profiles made from south (red) tonorth (to blue).

19

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section Ar

27.75

27.8

27.85

27.9

27.95

28

28

28.05

28.1

28.1

5

28.2

28.2

5

Figure 16: T-S diagram from section Ar. The colors indicate profiles made from south (red) tonorth (to blue).

20

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section Arr

27.75 27.827.85

27.927.95

28

28

28.05

28.1

28.1

5

28.2

28.2

5

Figure 17: T-S diagram from section Arr. The colors indicate profiles made from south (red) tonorth (to blue) and the contours are of potential density.

21

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section Arrr

27.75

27.8

27.85

27.9

27.95

28

28

28.05

28.1

28.1

5

28.2

28.2

5

Figure 18: T-S diagram from section Arrr. The colors indicate profiles made from south (red) tonorth (to blue).

22

Temp

eratur

e (°C)

−1.5−1−0.500.511.522.533.544.555.566.577.588.599.510

2 4 6 8 10

0

500

1000

1500

A2

Vel towards 134 ° in cm s −1

A3

Vel towards 134° in cm s−1

10

10−80

−70−60

−60

−50

−50

−40 −40

−40

−30

−30

−20

−20

−20−20

−10

−10 −100

0

0

0

A4A5

distance (km)

Section A

depth

(m)

Figure 19: XCP-measured temperature (color coded) and current conmponent normal to thesection (contoured, units are cm s−1) on section A.

23

Tem

pera

ture

(°C)

−1.5−1−0.500.511.522.533.544.555.566.577.588.599.510

0 5 10 15

0

500

1000

1500Vel towards 128° in cm s−1Vel towards 128 ° in cm s −1

Ar6 Ar7

10

10

20

20

30

30

30

30

303040 40

405050

50

60

−90−80

−80

−70

−70

−60

−60

−60 −60

−60

−50

−50

−50−50

−40

−40

−30

−30

−20

−10

0

0

0

Ar1 Ar2 Ar3 Ar4 Ar5 Ar8

Section Ar

dept

h (m

)

distance (km)

Figure 20: XCP-measured temperature (color coded) and current component normal to the section(contoured, units are cm s−1) on section Ar.

24

Temp

eratu

re (°C

)

−1.5−1−0.500.511.522.533.544.555.566.577.588.599.510

0 5 10 15

0

500

1000

1500

Arr8


Arr7


10

10

20

2020

20

30

30

3030

40

40

40

50

−70

−60

−60

−60

−50

−50

−50

−40

−40

−30

−30

−20

−20

−10

−10

00

0

0

Arr6Arr2 Arr3 Arr4 Arr5

distance (km)

Section Arr

depth

(m)

Figure 21: XCP-measured temperature (color coded) and current conmponent normal to thesection (contoured, units are cm s−1) on section Arr.

25

Temp

eratu

re (°C

)

−1.5−1−0.500.511.522.533.544.555.566.577.588.599.510

0 10

0

500

1000

1500

Arrr8


Arrr7


10

10

20

20

−70

−70

−60

−60−50

−50−50

−40

−40

−30

−30

−30

−20

−20

−20

−20−20

−10

−10

−100

0

0

0

0

Arrr2 Arrr6Arrr3 Arrr4 Arrr5

distance (km)

Section Arrr

depth

(m)

Figure 22: XCP-measured temperature (color coded) and current conmponent normal to thesection (contoured, units are cm s−1) on section Arrr.

26

−1.5

−1

−0.5

0

0.5

1

1.5

−1.5−1

−0.50

0.51

1.5

0

100

200

300

400

500

600

700

800

East, m s−1

Section Arr

North current, m s−1

Depth

, m

N

Figure 23: Currents measured by XCPs across a narrow section (section Arr) of the Faroe BankChannel. In the current diagram, the view is toward the east, and currents with temperature lessthan 7 C are shown in blue (the overflow water that flows west-northwestward at this section).The shallower currents are mainly eastward flowing and comparatively warm North Atlantic water(temperatures greater than 7 C are red vectors).

27

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0−2

0

2

4

6

8

transport per 0.5 C, Sv

tem

pera

ture

cla

ssSection A

<T> = 2.27 C

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 034.5

35

35.5

transport per 0.05, Sv

salin

ity c

lass

<S> = 35.01

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 06.2

6.4

6.6

6.8

7

7.2

transport per 0.05 ml l−1, Sv

oxyg

en c

lass

<O2> = 6.77 ml l−1

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 027.5

28

28.5

transport per 0.05 kg m−3, Sv

dens

ity c

lass

<ρ> = 27.92 kg m−3

Figure 24: Transport of temperature, salinity, density and oxygen shown in variable classes acrosssection A. Currents were measured by XCP and hydrographic variables by CTD.

28

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0−2

0

2

4

6

8


tem

pera

ture

cla

ssSection Ar

<T> = 1.09 C

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 034.5

35

35.5


salin

ity c

lass

<S> = 34.99

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 06.2

6.4

6.6

6.8

7

7.2


oxyg

en c

lass

<O2> = 6.83 ml l−1

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 027.5

28

28.5


dens

ity c

lass

<ρ> = 27.93 kg m−3

Figure 25: Transport of temperature, salinity, density and oxygen shown in variable classes acrosssection Ar. Currents were measured by XCP and hydrographic variables by CTD.

29

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0−2

0

2

4

6

8


tem

pera

ture

cla

ssSection Arr

<T> = 1.04 C

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 034.5

35

35.5


salin

ity c

lass

<S> = 34.97

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 06.2

6.4

6.6

6.8

7

7.2


oxyg

en c

lass

<O2> = 6.83 ml l−1

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 027.5

28

28.5


dens

ity c

lass

<ρ> = 27.98 kg m−3

Figure 26: Transport of temperature, salinity, density and oxygen shown in variable classes acrosssection Arr. Currents were measured by XCP and hydrographic variables by CTD.

30

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0−2

0

2

4

6

8


tem

pera

ture

cla

ssSection Arrr

<T> = 1.57 C

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 034.5

35

35.5


salin

ity c

lass

<S> = 34.96

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 06.2

6.4

6.6

6.8

7

7.2


oxyg

en c

lass

<O2> = 6.81 ml l−1

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 027.5

28

28.5


dens

ity c

lass

<ρ> = 27.94 kg m−3

Figure 27: Transport of temperature, salinity, density and oxygen shown in variable classes acrosssection Arr. Currents were measured by XCP and hydrographic variables by CTD.

31

7 Other, Selected CTD and XCP Sections

A few other sections are shown next. These comprise about one third of the remainingsection data. The other sections may be found on the web site.

−11 −10 −9 −8 −7 −6 −5 −4 −359.5

60

60.5

61

61.5

62

62.5

Longitude, deg.

La

titu

de

, d

eg

.

ctd section Cr

68

79

72

Figure 28: Station locations for section Cr.

32

Thet

a (°C

)

−1

0

1

2

3

4

5

6

7

8

9

10

11

12

0 20 40 60

0

500

1000

1500

CTD CTD78 7968

CTD69CTD

70CTD

71CTD

72CTD

73CTD

74CTD

75CTD CTD

76CTD

77

Dept

h (m

)ctd section Cr

Distance (km)

Salin

ity

34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 20 40 60

0

500

1000

1500

CTD CTD78 7968

CTD69CTD

70CTD

71CTD

72CTD

73CTD

74CTD

75CTD CTD

76CTD

77

Dept

h (m

)

ctd section Cr

Distance (km)

Figure 29: A section of potential temperature (left) and salinity (right) made up from CTD stationstaken across the Faroe Bank Channel overflow just to the west of the narrow channel. (see Figure28 for details of station locations). This view is to the west and in the direction of the overflowcurrent.

Dens

ity

27

27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

28

28.1

28.2

0 20 40 60

0

500

1000

1500

CTD CTD78 7968

CTD69

CTD70

CTD71CTD

72CTD

73CTD

74CTD

75CTD CTD

76CTD

77

Dept

h (m

)

ctd section Cr

Distance (km)

Oxyg

en

5.5

5.7

5.9

6.1

6.3

6.5

6.7

6.9

0 20 40 60

0

500

1000

1500

CTD CTD78 7968

CTD69

CTD70

CTD71CTD

72CTD

73CTD

74CTD

75CTD CTD

76CTD

77

Dept

h (m

)

ctd section Cr

Distance (km)

Figure 30: A section of potential temperature (left) and salinity (right) made up from CTD stationstaken across the Faroe Bank Channel overflow just to the west of the narrow channel. (see Figure28 for details of station locations). This view is to the west, or in the direction of the overflowcurrent.

33

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section Cr

27.75

27.8

27.85

27.9

27.95

28

28

28.05

28.1

28.15

28.2

28.2

5

Figure 31: T-S diagram from section Crr. The colors indicate profiles made from south (red) tonorth (to blue).

34

Tem

pera

ture

(°C

)

−1.5−1−0.500.511.522.533.544.555.566.577.588.599.510

0 5 10 15 20 25 30

0

500

1000


Cr9 Cr10

1010

10

10

10

20 20

20

2020

3030

3040

−80−70−60

−50

−40

−40−30−20−20

−20

−10

−10

−10

−10

−10

−10

−100 00

0

0

0

00

0

0

Cr5 Cr6 Cr7 Cr8 Cr11

Section Cr

dept

h (m

)

distance (km)

Figure 32: XCP-measured temperature (color coded) and current conmponent normal to thesection (contoured, units are cm s−1) on section Cr.

35

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0−2

0

2

4

6

8


tem

pera

ture

cla

ssSection Cr

<T> = 2.39 C

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 034.5

35

35.5


salin

ity c

lass

<S> = 35.03

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 06.2

6.4

6.6

6.8

7

7.2


oxyg

en c

lass

<O2> = 6.62 ml l−1

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 027.5

28

28.5


dens

ity c

lass

<ρ> = 27.92 kg m−3

Figure 33: Transport of temperature, salinity, density and oxygen shown in variable classes acrosssection Crr. Currents were measured by XCP and hydrographic variables by CTD.

36

−11 −10 −9 −8 −7 −6 −5 −4 −359.5

60

60.5

61

61.5

62

62.5

Longitude, deg.

La

titu

de

, d

eg

.

ctd section G

8088

Figure 34: Station locations for section G.

37

The

ta (

°C)

−1

0

1

2

3

4

5

6

7

8

9

10

11

12

0 10 20 30 40

0

500

1000

1500

CTD CTD87 8880

CTD81CTD

82CTD

83CTD

84CTDCTD

85CTD

86

Dep

th (

m)

ctd section G

Distance (km)

Sa

linity

34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 10 20 30 40

0

500

1000

1500

CTD CTD87 8880

CTD81

CTD82

CTD83

CTD84

CTDCTD85CTD

86

De

pth

(m

)

ctd section G

Distance (km)

Figure 35: A section of potential temperature (left) and salinity (right) made up from CTD stationstaken across the Faroe Bank Channel overflow just to the east of the narrow channel. (see Figure34 for details of station locations). This view is to the west and in the direction of the overflowcurrent.

De

nsi

ty

27

27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

28

28.1

28.2

0 10 20 30 40

0

500

1000

1500

CTD CTD87 8880

CTD81CTD

82CTD

83CTD

84CTDCTD

85CTD

86

De

pth

(m

)

ctd section G

Distance (km)

Oxy

ge

n

5.5

5.7

5.9

6.1

6.3

6.5

6.7

6.9

0 10 20 30 40

0

500

1000

1500

CTD CTD87 8880

CTD81

CTD82CTD

83CTD

84CTDCTD

85CTD

86

De

pth

(m

)

ctd section G

Distance (km)

Figure 36: A section of potential temperature (left) and salinity (right) made up from CTD stationstaken across the Faroe Bank Channel overflow just to the east of the narrow channel. (see Figure34 for details of station locations). This view is to the west, or in the direction of the overflowcurrent.

38

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section G

27.7527.8

27.8527.9

27.95

28

28

28.05

28.1

28.1

5

28.2

28.2

5

Figure 37: T-S diagram from section G. The colors indicate profiles made from south (red) tonorth (to blue).

39

Tem

pera

ture

(°C

)

−1.5−1−0.500.511.522.533.544.555.566.577.588.599.510

5 10 15 20 25

0

500

1000


G6 G7

10

10

10

10

10

10

10

10

10

1010

10

−40

−30 −30

−30

−30

−20

−20

−20

−20

−20

−10 −10

−10

−10

−10

−10−10

−10

−10

−10

−10−10

0 0 0 00

0

0

0

0

0

0

0

0

00

0

0

000

0

0 0

0

00

G2 G3 G4 G5 G8

Section G

dept

h (m

)

distance (km)

Figure 38: XCP-measured temperature (color coded) and current conmponent normal to thesection (contoured, units are cm s−1) on section G.

40

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0−2

0

2

4

6

8


tem

pera

ture

cla

ssSection G

<T> = 1.18 C

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 034.5

35

35.5


salin

ity c

lass

<S> = 34.96

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 06.2

6.4

6.6

6.8

7

7.2


oxyg

en c

lass

<O2> = 6.79 ml l−1

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 027.5

28

28.5


dens

ity c

lass

<ρ> = 27.97 kg m−3

Figure 39: Transport of temperature, salinity, density and oxygen shown in variable classes acrosssection G. Currents were measured by XCP and hydrographic variables by CTD.

41

−11 −10 −9 −8 −7 −6 −5 −4 −359.5

60

60.5

61

61.5

62

62.5

Longitude, deg.

La

titu

de

, d

eg

.

ctd section Er

203

195

Figure 40: CTD stations along section Er, the westernmost section.

42

Theta

(°C)

−1

0

1

2

3

4

5

6

7

8

9

10

11

12

0 20 40 60 80 100

0

500

1000

1500

CTD CTD196 195203

CTD202CTD

201CTD

200CTD

199CTDCTD

198CTD

197

Depth

(m)

ctd section Er

Distance (km)

Figure 41: A section of potential temperature from section Er. (see Figure 40 for details of stationlocations).

43

Salin

ity34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 20 40 60 80 100

0

500

1000

1500

CTD CTD196 195203

CTD202CTD

201CTD

200CTD

199CTDCTD

198CTD

197

Depth

(m)

ctd section Er

Distance (km)

Figure 42: A section of salinity from section Er. (see Figure 40 for details of station locations).

44

Oxyg

en

5.5

5.7

5.9

6.1

6.3

6.5

6.7

6.9

0 20 40 60 80 100

0

500

1000

1500

CTD CTD196 195203

CTD202CTD

201CTD

200CTD

199CTDCTD

198CTD

197

Depth

(m)

ctd section Er

Distance (km)

Figure 43: A section of dissolved oxygen from section Er. (see Figure 40 for details of stationlocations).

45

Dens

ity

27

27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

28

28.1

28.2

0 20 40 60 80 100

0

500

1000

1500

CTD CTD196 195203

CTD202CTD

201CTD

200CTD

199CTDCTD

198CTD

197

Depth

(m)

ctd section Er

Distance (km)

Figure 44: A section of potential density from section Er. (see Figure 40 for details of stationlocations).

46

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section Er

27.75

27.8

27.85

27.9

27.95

28

28

28.05

28.1

28.1

5

28.2

28.2

5

Figure 45: T-S diagram from section Er. The colors indicate west(red) to east(blue).

47

Tem

pera

ture

(°C)

−1.5−1−0.500.511.522.533.544.555.566.577.588.599.510

20 40 60

0

500

1000

1500

Er1


Er2


10

10

10

10

10

1010

20

−40−30−20

−20

−20

−20

−10

−10

−10

−10

−10

−10

−10

0

0

0

0 0

0

0

0

0

0

Er3Er6 Er5 Er4

distance (km)

Section Er

dept

h (m

)

Figure 46: XCP-measured temperature (color coded) and current conmponent normal to thesection (contoured, units are cm s−1) on section Er.

48

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0−2

0

2

4

6

8


tem

pera

ture

cla

ssSection Er

<T> = 3.87 C

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 034.5

35

35.5


salin

ity c

lass

<S> = 35.06

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 06.2

6.4

6.6

6.8

7

7.2


oxyg

en c

lass

<O2> = 6.48 ml l−1

−2 −1.8 −1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 027.5

28

28.5


dens

ity c

lass

<ρ> = 27.84 kg m−3

Figure 47: Transport of temperature, salinity, density and oxygen shown in variable classes acrosssection er. Currents were measured by XCP and hydrographic variables by CTD.

49

8 A Longitudinal Section

The sections we occupied were generally transverse to the overflow. In order to assess the lon-gitudinal structure of the overflow, we have made up a synthetic, longitudinal section, calledK, by selecting stations that were in the core (maximum density and maximum thickness)as seen in the transverse sections.

−11 −10 −9 −8 −7 −6 −5 −4 −359.5

60

60.5

61

61.5

62

62.5

Longitude, deg.

La

titu

de

, d

eg

.

ctd section K

201

209

300

Figure 48: CTD stations along the path of the Faroe Bank Channel overflow. Station 300 is a waypoint only (no CTD data at that point.)

50

Thet

a (°C

)

−1

0

1

2

3

4

5

6

7

8

9

10

11

12

0 50 100 150 200 250 300 350 400

0

500

1000

1500

209CTDCTD

300201CTD

189CTD

179CTD

154CTD

84CTD

105

ctd section K

Distance (km)

Dep

th (m

)

Figure 49: A section of potential temperature made up from CTD stations taken along the path ofthe Faroe Bank Channel overflow (see Figure 48 for details of station locations). The Norwegian-Greenland Sea is to the right, and the northern North Atlantic is to the left.

51

Salin

ity

34.8

34.85

34.9

34.95

35

35.05

35.1

35.15

35.2

35.25

35.3

35.35

35.4

0 50 100 150 200 250 300 350 400

0

500

1000

1500

209CTDCTD

300201CTD

189CTD

179CTD

154CTD

84CTD

105

ctd section K

Distance (km)

Dep

th (m

)

Figure 50: A section of salinity made up from CTD stations taken along the path of the FaroeBank Channel overflow (see Figure 48 for details of station locations). The Norwegian-GreenlandSea is to the right, and the northern North Atlantic is to the left.

52

Oxy

gen

5.5

5.7

5.9

6.1

6.3

6.5

6.7

6.9

0 50 100 150 200 250 300 350 400

0

500

1000

1500

209CTDCTD

300201CTD

189CTD

179CTD

154CTD

84CTD

105

ctd section K

Distance (km)

Dep

th (m

)

Figure 51: A section of dissolved oxygen made up from CTD stations taken along the path ofthe Faroe Bank Channel overflow (see Figure 48 for details of station locations). The Norwegian-Greenland Sea is to the right, and the northern North Atlantic is to the left.

53

Den

sity

27

27.1

27.2

27.3

27.4

27.5

27.6

27.7

27.8

27.9

28

28.1

28.2

0 50 100 150 200 250 300 350 400

0

500

1000

1500

209CTDCTD

300201CTD

189CTD

179CTD

154CTD

84CTD

105

ctd section K

Distance (km)

Dep

th (m

)

Figure 52: A section of potential density made up from CTD stations taken along the path ofthe Faroe Bank Channel overflow (see Figure 48 for details of station locations). The Norwegian-Greenland Sea is to the right, and the northern North Atlantic is to the left.

54

34.8 34.85 34.9 34.95 35 35.05 35.1−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

2.5

3

salinity

po

ten

tia

l te

mp

era

ture

, C

section K

27.75

27.8

27.85

27.9

27.95

28

28

28.05

28.1

28.1

5

28.2

28.2

5

Figure 53: T-S diagram from section K. The colors indicate west(red) to east(blue).

55

−3−2

−10

12

3

−3−2

−10

12

3

−1000

−800

−600

−400

−200

0

East, m s−1North, m s−1

De

pth

, m

E D

C A G H

−12

−10

−8

−6

59.5

60

60.5

61

61.5

62

62.5

63

−1.5−1

−0.50

H

GAC

DE

km

North lat.

East lon.

Figure 54: A 3-d perspective view of XCP currents along section K.

56

9 Velocity-weighted Property Transports.

The velocity-weighted transport of temperature, salinity, oxygen and density are shownbelow. These are the integral transports for the available CTD/XCP sections and showhow these integral properties vary along the overflow. The date (in June, 2000) of thecorresponding section is shown beside the data point.

−150 −100 −50 0 50 100 1500

1

2

3

4

5

6

10.2

16.218.9

26.3

10.711.517.327.3

12.3

28.2

15.2

29

18.2

20.3

T, C

Transport−weighted T, S and O

−150 −100 −50 0 50 100 15034.7

34.8

34.9

35

35.1

35.2

10.216.218.926.3

10.711.517.3

27.3

12.3

28.2

15.2

29

18.2

20.3

S

−150 −100 −50 0 50 100 1506.4

6.5

6.6

6.7

6.8

6.9

7

10.2

16.218.926.3

10.711.5

17.3

27.3

12.328.2

15.229

18.2

20.3

distance from A, km

Oxy

gen

conc

, ml l−1

Figure 55: Velocity-weighted transport of temperature, salinity and oxygen. Each estimate cor-responds to a section; the small number to the right of the data point is the date in June. Thesedata are preliminary (even more than the rest!). Section H (easternmost) is very poorly sampled,and section E (westernmost) is incompletely sampled.

57

−150 −100 −50 0 50 100 1500

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

10.2

16.2

18.9

26.310.7

11.5

17.3

27.312.3

28.2

15.229

18.2

20.3

Tran

psor

t, Sv

Transport and transport−weighted density

−150 −100 −50 0 50 100 15027.7

27.75

27.8

27.85

27.9

27.95

28

28.05

28.1

10.216.2

18.9

26.3

10.711.5

17.327.3

12.3

28.2

15.2

29

18.2

20.3

distance from A, km

dens

ity, k

g m−3

Figure 56: Transport (above) and velocity-weighted density transport (lower). Each estimatecorresponds to a section; the small number to the right of the data point is the date in June. Thesedata are preliminary (even more than the rest!). Section H (easternmost) is very poorly sampled,and section E (westernmost) is not completely sampled.

58

10 Bottom Stress Estimates

Bottom stress has been estimated from 2 db-sampled XCP data using a straightforwardlog-layer formulation. The data used were the deepest 10 m of the profile (assuming that theprofile terminated at the sea floor) and assuming that that the temperature difference overthis interval was less than 0.03 C. This latter condition was intended to minimize the effectsof stratification which in a few profiles was fairly large. Other values for this temperaturecutoff, 0.02 and 0.01 C gave very similar results.

0 0.2 0.4 0.6 0.8 10

1

2

3

4

speed2, m2 s−2

str

ess,

Pa

from du/dz

0 0.2 0.4 0.6 0.8 10

1

2

3

4

speed2, m2 s−2

str

ess,

Pa

from fitting to log(z)

Figure 57: Bottom stress estimates from a log layer analysis of XCP data. (upper) By estimatingand averaging du/d(log(z)), and (lower) by fitting the current to a log(z) profile. Data were fromthe depth range 1 to 11 m above the bottom. Profiles were excluded if the temperature differenceover this depth range exceeded 0.03 C (about 20 percent of the data set). The red line is a linearleast squares fit of stress(speed2), and the intercept at speed2 = 1 provides an estimate of the 10m drag coefficient times density, i.e., Cd10 ≈ 2.0 × 10−3.

59

−0.20

0.20.4

0.6 −0.4

−0.2

0

0.2

0.4

0

5

10

15

V, m s−1

U, m s−1

he

igh

t a

bo

ve

bo

tto

m,

m

Figure 58: The ensemble average of the rotated current vectors (blue vectors) and correspondinglog layer profile of current having the same average bottom stress and the Cd10 from Figure 57.

60

0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.043

4

5

6

7

8

9

10

11

rms U‘, rms V‘

he

igh

t a

bo

ve

bo

tto

m,

m U‘V‘

Figure 59: The ensemble average rms of the deviation of the current from a log fit to each profile.The blue line is the deviation in the along mean current direction, while the green line is thedeviation in the direction normal to the mean current. Note that the rms deviation is about 5 to10 percent of the mean current (compare this to Figure 58 where the ensemble mean current isabout 0.35 m s−1). This is a reasonable variance for a wall-bounded boundary layer.

a report of xcp and ctd data taken during june, 2001, rrs ... · pre-cruise support provided by the...

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