GOODHOPE V

HYDROGRAPHIC, BIOLOGICAL AND METEOROLOGICAL DATA REPORT

UCT OCEANOGRAPHIC REPORT 06-1 1ST DECEMBER 2005 – 19TH FEBRUARY 2006

Compiled by: Sebastiaan Swart*, Natalie Burls, Michael Funke, Neil Swart,
Isabelle Ansorge
Affiliation: Department of Oceanography, University of Cape Town,
Rondebosch, South Africa
* sswart@ocean.uct.ac.za

SANAE IV, ANTARCTICA RELIEF VOYAGE & SOUTH SANDWICH ISLANDS

 

CONTENTS

List of Figures……………………………………………………………………………..….3 List of Tables………………………………………………………………………………....5 List of Acronyms………………………………………………………………………...…...6 Synopsis of Events……………………………………………………………………….……...7

Abstract…..........................................................................................................................8

1.                  1. Introduction……………………………………………………………………….......................9

.2. Standard Procedures: Oceanographic…………………………………………...…….13

1.                  2.1. XBT…………………………………………………………………………..…….13

2.                  2.2. AOML Argo Profiling Floats…………………………………………………..…15

3.                  2.3. BMO Apex Profiling Floats………………………………………………………16

4.                  2.4. SVP……………………………………………………………………………..….17

5.                  2.5. DDS…………………………………………………………………………..……18

6.                  2.6. Meteorology……………………………………………………………………….19

.3. Results……………………………………………………………………………………..24 

.3.1. Frontal Positions……………………………………………………………….……….24

1.                  3.1.1. Subtropical Convergence……………………………………………….…….26

2.                  3.1.2. Subantarctic Front……………………………………………………….…….26

3.                  3.1.3. Antarctic Polar Front…………………………………………………….…….27

4.                  3.1.4. Southern Antarctic Circumpolar Front………………………………...…….27

5.                   3.1.5. Southern Boundary…………………………………………………..….……28

6.                  3.2. Baroclinic Transport Estimates for the ACC………………………………..…29

7.                   3.3. Nitrogen Uptake Experiments………………………………………………….34

2.                  4. Conclusions…………………………………………………………………………………….38

3.                  5. List of Participants and Affiliations………………………………………………..……………………………………..40

4.                  6. Acknowledgements…………………………………………………………………………….41

5.                  7. References…………………………………………………………………………….………..42

6.                  8. Appendix…………………………………………………………………………….………….45

 

LIST OF FIGURES Figure 1: Schematic diagram showing the average position of the subsurface temperature expressions of the STC (10ºC), SAF (6ºC) and APF (2ºC) south of South Africa. The SACCF is represented by the 1ºC isotherm, which lies below the Tmin.

Figure 2: A diagram showing the three major “chokepoints” of the ACC. The GoodHope transect (solid yellow line) aims to provide detailed information on the physical, biological and chemical structure of waters, south of Africa.

Figure 3: Position of all XBT stations (red dots) and SVP Drifter deployments (blue dots) during GoodHope V.

Figure 4: Position of all Argo Float deployments (green diamonds) during GoodHope

V.

Figure 5: Position of all XBT stations (red dots), SVP Drifter (blue squares) and Argo Float deployments (green triangles) during the return leg between Antarctica and Cape Town.

Figure 6: Position of all APEX floats deployed on the SAWS Buoy Run.

Figure 7: Sea surface temperature data plotted with latitude for the return transect between Antarctica and Cape Town (9 – 19 February 2006).

Figure 8: Position of all deployments made by the South African Weather Service during the voyage, including those deployed during the GoodHope V and return leg transects.

Figure 9: Sea-level pressure in hPa measured in one minute intervals during the GoodHope V transect completed between 1 – 14 December 2005.

Figure 10: Surface air temperature in °C measured in one minute intervals during the GoodHope V transect completed between 1 – 14 December 2005.

Figure 11: Relative humidity (%) measured in one minute intervals during the GoodHope V transect completed between 1 – 14 December 2005.

Figure 12: Temperature section from XBT data along GoodHope V. The dashed isotherms represent the subsurface axis of the STC (blue - 10ºC), SAF (orange – 6ºC), APF (green – 2ºC) and SACCF (red – 0ºC).

Figure 13: Temperature section from XBT data along the return transect between Antarctica and Cape Town (via Bouvetoya Island). 

Figure 14: Dynamic height (relative to 2500 m) plotted against vertically-averaged temperature (0 – 600 m) for three CTD transects (red star – AJAX, magenta star – A12, green star – A21). The solid curve depicts a smoothing spline fit to the data.

Figure 15: A comparison can be made between the dynamic height obtained from CTD data (stars) and those derived using the relationship found in Fig. 7 from XBT data during the GoodHope V transect (magenta dots). Note that the latitude limits represent the approximate boundaries of the ACC for the GoodHope transect.

Figure 16: Cumulative volume transport (above and relative to 2500 m) versus dynamic height at the sea surface relative to 2500 m, from three CTD sections in the Atlantic sector, south of Africa. The solid curve depicts a smoothing spline fit to the data.

Figure 17: (a) Northward cumulative baroclinic transport (referenced to 2500 dbar) for the ACC for the GoodHope V transect.  (b) Northward cumulative geostrophic transports (referenced to 2500 dbar) for three Atlantic CTD sections.

Figure 18: Position of all 22 stations occupied for nitrogen uptake experiments during the voyage. Note that the frontal positions have been determined using the GoodHope V hydrographic section.

Figure 19: Nutrient concentrations at underway stations.

Figure 20: Nutrient concentrations at stations near the ice shelf.

LIST OF TABLES

Table 1: Positions of each ARGO Float deployed during GoodHope V and the return leg to Cape Town. Note that floats 1 – 7 were deployed along the GoodHope V transect.

Table 2: Design specifics for ARGO profiling floats.

Table 3: Positions of each APEX float deployed during the SAWS buoy run to the South Sandwich Islands.

Table 4: Design specifics for APEX profiling floats.

Table 5: Positions of each SVP Drifter deployed during the voyage. Note that drifters 1 – 6 were deployed along the GoodHope V transect and drifters 7 – 9 were deployed on the return leg.

Table 6: Definition of the fronts bordering the Antarctic Circumpolar Current.

Table 7: The latitudinal positions of the ACC fronts are compared between the mean, GoodHope V and the return leg XBT transect. The mean has been derived from 4 previous GoodHope crossings of the ACC between February 2004 and October 2005. Note that all values are given in °S.  

Table 8: List of ship-based participants outlining their responsibilities and their affiliations. 

ACRONYMS 

AAD: Antarctic Divergence AAZ: Antarctic Zone ACC: Antarctic Circumpolar Current AOML: Atlantic Oceanographic & Meteorological Laboratory APF: Antarctic Polar Front CO2: Carbon Dioxide CTD: Conductivity Temperature Depth GADC: Global Argo Data Centre GH: GoodHope GMT: Greenwich Meridian Time ISOS: International Southern Ocean Study LPO: Laboratoire de Physique des Océans MOC: Meridional Overturning Circulation NOAA: National Ocean and Atmospheric Administration PIES: P Inverted Echo Sounders PFZ: Polar Frontal Zone SACCF: South Antarctic Circumpolar Current Front SAF: Subantarctic Front SAWS: South African Weather Service SAZ: Subantarctic Zone STC: Subtropical Convergence Sv: Sverdrup (106 m3/s) SVP: Surface Velocity Profilers T-S: Temperature-Salinity UCT: University of Cape Town WMO: World Meteorological Organisation WOCE: World Ocean Circulation Experiment XBT: eXpendable Bathythermographs

SYNOPSIS OF EVENTS

¾ 1 December 2005 – 14 December 2005: GoodHope V Hydrographic Transect; Nitrate Experiments

¾ 23 December 2005 - 25 December 2005: Nitrate Experiments (Antarctic Shelf)

¾ 8 January 2006 - 22 January 2006: SAWS Buoy Run (South Sandwich Islands)

¾ 23 January 2006 - 7 February 2006: Nitrate Incubations (Antarctic Shelf)

¾ 9 February 2006 – 19 February 2006: Hydrographic Transect (Antarctica to Cape Town)

ABSTRACT

As a component of the Meridional Overturning Circulation (MOC), the Southern Ocean plays a major role in the global ocean circulation and it is hypothesised that it has an important impact on present day climate. However, our understanding of its complex three-dimensional dynamics and the impact of its variability on the climate system remain to this day rudimentary. The newly constituted, international GoodHope research venture aims to address this knowledge gap by establishing a programme of regular observations across the Southern Ocean between the African and Antarctic continents.

The objectives of this programme are five-fold: 

.(1) To gain a better understanding of Indo-Atlantic inter-ocean exchanges and their impact on the global thermohaline circulation and thus on global climate change;

.(2) To understand in more detail the impact these exchanges have on the climate variability of the southern African subcontinent; 

.(3) To monitor the variability of the  main Southern Ocean frontal systems associated with the Antarctic Circumpolar Current; 

.(4) To study air-sea exchanges and their role on the global heat budget, with particular emphasis on the intense exchanges occurring within the Agulhas Retroflection region south of South Africa, and 

.(5) To examine the role of major frontal systems as areas of elevated biological activity and as biogeographic barriers to the distribution of plankton.

 

We present here the fifth preliminary data report on the physical structure of the frontal system from data collected during the fifth GoodHope transect undertaken between 1st December 2005 – 19th February 2006.

1. INTRODUCTION

The global oceanic thermohaline circulation, often referred to as the Meridional Overturning Circulation, is a vital link in the global transport of heat from the tropics to higher latitudes. The physical structure of this circulation belt and its efficiency in regulating climate is substantially influenced by the nature of water mass exchange between ocean basins (Gordon, 1986; Rintoul, 1991; Speich et al., 2001).  The Antarctic Circumpolar Current (ACC) is by far the largest conduit for such exchange. Extending unbroken around Antarctica it is the primary means by which water, heat and salt are transferred between different ocean basins.  

The Southern Ocean plays a unique role in coupling the ocean to the atmosphere and cryosphere. Variations in these aspects of the global climate system may be expected to be linked to and perhaps drive global climate variability. The most relevant processes occurring in the Southern Ocean that may have a large influence in the global ocean circulation and possibly on the evolution of our climate include:

.(1) The Antarctic Circumpolar Current (ACC) is the only current that connects all three major ocean basins, thereby providing an essential heat and fresh water conduit.

.(2) The Southern Ocean provides a strong coupling of     the ocean and atmosphere within the Subantarctic belt and its polar-extrapolar communication of heat, freshwater and CO2 through the production of Antarctic Intermediate Water and Subantarctic Mode Water. These water masses spread northwards injecting cool low salinity water into and along the base of the main thermocline.

.(3) The upwelling of Circumpolar Deep Water south of the Antarctic Circumpolar Current provides a pathway in the transport heat from of >2000 m into the atmosphere and cryosphere.

.(4) The production of very cold dense Antarctic Bottom Water. 

.(5) The Antarctic sea ice fields represent a highly mobile and mutable surface property whose distribution and characteristics may play a major role in the global radiative budget and thus global climate.

.(6) The large-scale coherent variability of the atmospheric circulation over the Southern Ocean and the mechanisms of these variations and their geographic communication, are directly involved in the propagation of anomalies across the various climate zones.

 

Figure 1: Schematic diagram showing the average position of the subsurface temperature expressions of the STC (10ºC), SAF (6ºC) and APF (2ºC) south of South Africa. The SACCF is represented by the 1ºC isotherm, which lies below the Tmin.

Interpreting the causes of temperature and salinity variability observed in the ocean interior requires an understanding of the formation of Southern Ocean water masses and the circulation paths they follow. Changes in heat supplied by the deep ocean may influence the atmosphere directly or through changes in sea ice. As these exchanges play an important role in regulating mean global climate, sustained hydrographic observations are essential in order to describe and better understand the physical and dynamic processes, which are responsible for the variability of the ACC (Budillon and Rintoul, 2003).  The major part of the flow associated with the ACC is concentrated at a number of circumpolar fronts, which act as boundaries separating zones of uniform water masses (Whitworth, 1980) (Figure 1). From north to south the fronts and associated zones of the Southern Ocean are: Subtropical Convergence (STC), Subantarctic Zone (SAZ), Subantarctic Front (SAF), Polar Frontal Zone (PFZ), Antarctic Polar Front (APF), Antarctic Zone (AAZ) and Antarctic Divergence (AAD).

South of Africa, the Southern Ocean plays a unique role in providing a source for the equatorward flux of heat into the South Atlantic. However, it has been suggested (Speich et al., 2001; 2002) that water mass differences between the South Indian and Atlantic Ocean basins would be far more prominent were it not for various smaller inter-ocean links. South of Africa, water masses originating in the Indian Ocean are injected into the South Atlantic both by anticyclonic ring shedding processes at the Agulhas Retroflection region (Lutjeharms and van Ballegooyen, 1988) and by filaments of Agulhas Current water (Lutjeharms and Cooper, 1996). Recent modelling studies on the global ocean circulation suggest that Indo-Atlantic interocean exchanges through the Agulhas Current system are far more important for the thermohaline circulation than the direct input of water from the Drake Passage (Speich et al., 2001; 2002). Estimates of the percentage of mode and intermediate waters entering the Atlantic via the Agulhas region is highly variable ranging from 0% (Rintoul, 1991) to 50% (Gordon et al., 1992). Therefore, in order to understand the role of this key component of the MOC on the global ocean circulation and its possible role in climate it is critical that the inflow of Indian waters into the Atlantic Ocean be properly quantified, and monitored.

The aim of the GoodHope programme is to establish an intensive monitoring platform that will provide detailed information on the physical structure and volume flux of waters south of South Africa, where the interbasin exchanges occur. A key component of this programme is the implementation of the high-density XBT line AX25 that runs from Cape Town to Antarctica.  The advantages of the GoodHope programme are four-fold:

.(1) It runs approximately along with the TOPEX/POSEIDON – JASON 1 altimeter ground-tracks and will serve for ground-truthing of altimetry-derived sea height anomaly data;

.(2) The southern fraction of this line (south of 50ºS) is currently monitored by a mooring array aimed at investigating the formation of deep and bottom water in the Weddell Sea deployed during the WECCON project by the Alfred Wegener Institute for Polar and Marine Research. 

                        (3) The northern section of the GoodHope line also overlaps the region being studied by the USA - ASTTEX programme, enabling observations in the Southern Ocean to be linked with data collected within the Benguela region and the west coast of Southern Africa.  ASTTEX examines the fluxes of heat, salt and volume entering the South Atlantic Ocean via the Agulhas Retroflection, thereby providing a quantitative, Eulerian measurement of the strength and characteristic scales of the volume and mass transport of the Agulhas Current into the South Atlantic.  It has been estimated that up to half of the Agulhas-South Atlantic exchange is contained in mesoscale rings and eddies (Byrne, 2000) and that the strength of the mesoscale fluxes could potentially have a very large temporal variability. Results from altimetry

                        observations have shown that Agulhas rings are shed intermittently with periods of several months when there is no ring formation. However, this remains to be confirmed by a single, consistent set of in-situ and hydrographic observations (Byrne, 2000). GoodHope will provide additional support in determining the nature and scale of the injection of Indian Ocean water into the southeastern South Atlantic via the Agulhas Retroflection, and,

.(4) GoodHope will support and contribute to the data collected by two Pressure Inverted Echo Sounder (PIES) mooring already deployed along this line. 

 

Sustained observations such as repeat transects along AX25 will provide the only means to monitor the vertical structure and to investigate the variability of the fronts in this region. The GoodHope programme will investigate year-to-year and longer period variability in the fluxes, such as those related to the Antarctic Circumpolar Wave. Such intense and periodic monitoring has been underway in the Drake Passage (Sprintall et al., 1997) and south of Tasmania (Budillon and Rintoul, 2003) since the 1970s. A repeat transect between South Africa and Antarctica, the third Southern Ocean “choke point”, was only implemented during the first GoodHope cruise in 2004.

Figure 2: A diagram showing the three major “chokepoints” of the ACC. The GoodHope transect (solid yellow line) aims to provide detailed information on the physical, biological and chemical structure of waters, south of Africa.

2. STANDARD PROCEDURES: OCEANOGRAPHIC

2.1. XBT

To effectively measure oceanic changes of heat fluxes, in particular across regions of interbasin exchange, high-density observations need to be undertaken. Repeat XBT sections across “chokepoint” sections provide measurements of changes in upper ocean heat content and SST on both seasonal and inter-annual time scales. In addition, by exploiting the relationship between upper ocean temperature and dynamic height, XBTs can be used to infer velocities even in the Southern Ocean where salinity changes are important (Rintoul and Sokolov, 2001; Legeais et al., in press). In this way, XBT sections serve as a useful tool in measuring changes in the interocean exchange of heat. 

In the framework of GoodHope V and return leg between Antarctica and Cape Town, XBTs were funded by the NOAA's Office of Global Programs as part of their High Density XBT project at NOAA/AOML. A total of 198 Sippican Deep Blue XBTs were deployed between 33.85° S, 17.61° E and 69.94° S, 3.76° W (Figure 3) for GoodHope V. XBTs were deployed at ~15 nautical mile intervals increasing to every ~10 nm over the main frontal regions. Positions for each XBT deployment are given in Appendix 1. In total, 42 XBTs (17%) failed mainly as a result of strong winds and sea swell blowing the running signal wire against the ship’s hull, which resulted in the XBT wire stretching and thus insulation leakages. On the return leg, 152 XBT’s were deployed of which 6 (~4%) malfunctioned. The positions of these XBT deployments are given in Appendix 2.

Data pertaining to the GoodHope V and return leg (Antarctica to Cape Town) XBT transects can be obtained at:

http://www.aoml.noaa.gov/phod/hdenxbt/high_density_home.html

Figure 3: Position of all XBT stations (red dots) and SVP Drifter deployments (blue dots) during GoodHope V.

Figure 4: Position of all Argo Float deployments (green diamonds) during GoodHope

V.

Figure 5: Position of all XBT stations (red dots), SVP Drifter (blue squares) and Argo Float deployments (green triangles) during the return leg between Antarctica and Cape Town. Note that the deviation in the return leg (between 48-50°S) was due to rough seas experienced.

2.2. AOML ARGO PROFILING FLOATS

In the remote regions of the Southern Ocean, the monitoring of changes in upper ocean temperature and salinity structure is only possible using drifting platforms due to the lack of routes of merchant ships. For example, profiling floats containing temperature and salinity sensors provide a cost-effective means of monitoring such regions. Along the first transect, 7 ARGO profiling floats were deployed at selected intervals (Figure 4). Along the return leg, the remaining 7 Argo profiling floats were deployed at predetermined intervals as shown in Fig. 5. Each float descended to a “parking depth” of 1000 m before profiling the upper 1800 m, a cycle that is repeated every 10 days. Data can be obtained from USGODAE at:

http://www.usgodae.org/argo/argo.html

Float No.

Float ID

Date

GMT

Latitude

Longitude

1

509/57437

02/12/2005

19:48

35° 27.42 S

013° 47.01 E

2

514/57442

03/12/2005

12:27

37° 52.48 S

012° 14.80 E

3

514/57445

06/12/2005

21:51

47° 29.83 S

004° 24.43 E

4

516/57444

07/12/2005

21:22

50° 02.23 S

001° 41.88 E

5

519/57447

08/12/2005

10:37

51° 58.85 S

000° 00.03 E

6

503/57431

08/12/2005

22:41

54° 00.99 S

000° 01.02 E

7

526/57454

09/12/2005

11:03

55° 59.56 S

000° 01.19 W

8

510/57438

12/02/2006

08:44

58° 49.71 S

001° 20.09 E

9

523/57451

13/02/2006

05:13

54° 58.75 S

003° 05.53 E

10

527/57455

14/02/2006

03:52

52° 00.98 S 

005° 20.92 E

11

524/57452

14/02/2006

23:36

48° 59.96 S

007° 03.15 E

12

513/57441

15/02/2006

20:21

46° 01.84 S

008° 30.88 E

13

518/57446

16/02/2006

17:12

43° 00.24 S 

011° 25.98 E

14

512/57440

17/02/2006

14:53

40° 00.39 S

014° 07.52 E

 

Table 1: Positions of each ARGO Float deployed during GoodHope V and the return leg to Cape Town. Note that floats 1 – 7 were deployed along the GoodHope V transect.

Number of Cycles

200

Cycle Period (days)

10

Drift Sample Period (hours) 

48

Ascent Sampling Period (Hz)

2

Ascent Rate (m/s)

0.1

Descent Rate (m/s)

0.1

Drift Depth (m)

1000

Profile Depth (m)

1800

 

Table 2: Design specifics for ARGO profiling floats.

2.3. BMO APEX PROFILING FLOATS

During the SAWS buoy run to the South Sandwich Islands, six APEX profiling floats were deployed (Fig. 6). These deployments hope to improve this hydrographically data sparse region of the South Atlantic. Data can be obtained from the UK Argo Data Centre at http://www.bodc.ac.za/projects/international/argo/uk_floats/ or from the two Global Argo Data Centres (GADC): Coriolis: http://www.coriolis.eu.org/ USGODAE: http://www.usgodae.org/argo/argo.html Profiles are available within 24-48 hours of the float surfacing and data can be accessed either using the Argos numbers or WMO numbers.

Float No.

Float ID

Argo No.

WMO

Date

GMT

Latitude

Longitude

1

2464

61885

7900104

14/01/2006

13:03

55° 56.47 S

027° 02.33 W

2

2463

61884

7900103

15/01/2006

15:04

52° 00.19 S

029° 59.95 W

3

2461

61882

7900101

16/01/2006

09:06

52° 59.85 S

025° 00.66 W

4

2462

61883

7900102

17/01/2006

02:36

55° 00.35 S

020° 59.28 W

5

2465

61886

7900105

17/01/2006

22:28

57° 00.15 S

016° 01.59 W

6

2466

61887

7900106

18/01/2006

14:08

59° 01.19 S

012° 58.21 W

 

Table 3: Positions of each APEX float deployed during the SAWS buoy run to the South Sandwich Islands.

Figure 6: Position of all APEX floats deployed on the SAWS Buoy Run.

Cycle Period (days)

10

Drift Sample Period (hours) 

11

Ascent Rate (m/s)

0.08

Ascent Time (hours)

9.5

Drift Depth (m)

1000

Profile Depth (m)

2000

 

Table 4: Design specifics for APEX profiling floats.

2.4. SVP DRIFTERS

In addition to these floats, 6 SVP surface drifters were deployed along the GoodHope V transect and three were deployed on the return leg (Table 5, Fig. 3 , Fig. 5). These surface drifters are drogued at a depth of 18 m and are able to measure surface temperature, velocity and geographic position, which are relayed to ARGOS ground stations. SVP drifters are designed to have a drag area ratio of ~40 (i.e. the ratio of the drag area of the drogue to that of the tether and surface float), which yields a wind slippage of <1 cms-1 (Niiler et al., 1995). Satellite tracked drifters have become invaluable tools for studying ocean circulation and provide mixed layer velocity and temperature observations over 5 year periods in all major ocean basins. Data pertaining to the SVP drifters can be obtained from the Drifting Buoy Data Assembly Centre at http://www.aoml.noaa.gov/phod/dac/

Drifter No.

Drifter ID

Date

GMT

Latitude

Longitude

1

60288

04/12/2005

20:16

42° 00.06 S

009° 16.15 E

2

60309

05/12/2005

13:40

44° 00.22 S

007° 38.98 E

3

60310

06/12/2005

06:55

45° 58.35 S 

005° 54.08 E

4

60307

07/12/2005

21:28

50° 03.10 S  

001° 40.80 E

5

60301

08/12/2005

19:30

53° 30.00 S  

000° 00.05 E

6

60306

09/12/2005

19:29

57° 15.23 S

000° 03.25 W

7

60253

12/02/2006

03:38

59 49.07 S

000 51.75 E

8

60286

14/02/2006

03:46

52 01.90 S

005 20.15 E

9

60287

18/02/2006

16:19

36 59.54 S

016 13.99 E

 

Table 5: Positions of each SVP Drifter deployed during the voyage. Note that drifters 1 – 6 were deployed along the GoodHope V transect and drifters 7 – 9 were deployed on the return leg.

2.5. DDS

Surface temperature and salinity data were recorded continuously by the shipboard thermosalinograph. However, due to technicalities, the thermosal (temperature and salinity) data was lost for the GoodHope V transect and only the surface temperature was captured on the return transect between Antarctica and Cape Town (Figure ?). 

Figure 8: Position of all deployments made by the South African Weather Service during the voyage, including those deployed during the GoodHope V and return leg transects.

Ship-based synoptic observations were carried out at 3-hourly intervals, according to Universal Time (UTC), coded according to the WMO ‘ship synop’ BBXX coding convention and transmitted via Thrane+Thrane Capsat equipment to UKMO (UK Met Office). UKMO, in turn, ensured that the coded information was made available on the GTS (Global Telecommunication System) for other Meteorological agencies. As such, ‘ship synop’ messages, although extremely concise (1-2 lines of 5 digit numeric code groups) contain a wealth of information regarding standard meteorological parameters, such as temperature, dewpoint, barometric pressure, pressure tendency, wind direction (true) and wind speed. The ship’s position (latitude / longitude), heading and speed (knots). Detailed information regarding current weather and past weather (previous 3 to 6 hours) as well as cloud amount and cloud types are also encoded in this message. Valuable information regarding SST, wind waves, swell (direction, height and period (seconds)) are also routinely observed. Whenever sea ice and/or icebergs are observed, then an ancillary section is appended to the BBXX message, prefixed by the ICE identifier. Information regarding sea ice type, concentration and thickness (as well as evolution thereof) can also be inferred from the synoptic coded message. From the time of first leaving the port of Cape Town, to the date of the final return of the SA Agulhas to Cape Town, a VAISALA MILOS Automatic Weather Station (AWS) automatically logged time, latitude, longitude, pressure, temperature and relative humidity at 1-minute intervals for the entire voyage (the only exception being the period between the 27th December 2005 to 8th January 2006, when the AWS unit shut down due to the burn­out of an AC power smoothing circuit).

Figure 9: Sea-level pressure in hPa measured in one minute intervals during the GoodHope V transect completed between 1 – 14 December 2005. 

The very latest model VAISALA RS-92 GPS radiosondes (containing a GPS tracking unit to accurately calculate upper air winds) were launched twice daily (10h30UTC and 22h30UTC) for the duration of the voyage (except whilst the ship was at the Antarctic ice shelf and relatively close to the Neumayer Antarctic base (Germany)). This was partly to avoid duplication of data (as the instruments are costly) and partly to avoid instrument interference, as both ourselves and the Neumayer meteorologists were using identical tracking equipment and radiosondes. The radiosonde instrument measures air temperature, relative humidity and pressure and ascends at about 360 metres/minute, climbing to an altitude of 20-25km (0ver 70 000’) during a flight lasting 70-80 minutes. True wind direction and speed are also monitored and calculated throughout, whilst the radiosonde is tracked by as many as 10 to 12 GPS satellite platforms. Helium-filled latex balloons (350g envelope mass) were used, to maximise safety on board the vessel (hydrogen gas was used on previous voyages). The resultant data, coded automatically by VAISALA software into WMO standard format, was then immediately transmitted via satellite to Goonhilly Earth Station and thence to UKMO, whereupon the data was uploaded onto the GTS. The upper-air data was also ingested into NWP models at UKMO, hopefully enhancing output of same.    

The Southern Hemisphere is a very data-sparse environment, from a meteorological perspective. Unlike the Northern Hemisphere, where there is extensive land-mass coverage at high northerly latitudes (and hence more opportunity for land-based synoptic observation of prevailing weather conditions at the surface, as well as in the upper-air); landmass in the Southern Hemisphere occupies a significantly smaller portion of the surface of the Earth than do the southern oceans. Naturally ship-based observations are relatively valuable against this context. The value is twofold – firstly, to quantify the state of the atmosphere at that point, at that specific time. In the case of a ship-based upper-air sounding; this is especially true, with information on pressure, relative humidity, temperature and wind being gained up to an altitude of about 25 km above sea level. Secondly, modern NWP (Numeric Weather Prediction) models rely heavily on the input of as much real-time data as possible, to arrive at a prognosis that is as closely linked to reality as possible, at the analysis time (T+00) of the model. At high southerly latitudes, beyond the normal mid-latitude shipping lanes (and commercial aircraft flight routes), meteorological data in the Southern Hemisphere becomes even more sparse, apart from isolated island bases (such as Gough, Marion, Crozet, Kerguelen) and Antarctic research stations. Hence, it is clear that any real-time data from moving ship platforms (either surface weather data or otherwise) is extremely valuable towards furthering meteorological science and forecasting endeavour in the short-term. Perhaps more importantly, any effort to broaden or expand the net of incoming meteorological data in the Southern Hemisphere can only be beneficial, both on the short- and longer-term. 

In the context of expanding the network of data collection, it is notable that no less than 21 drifting weather buoys were deployed during the voyage in question (16 of which being SVP-B ‘barometric drifter buoys’, whilst the remainder were non-barometric SVP drifters); vastly improving data coverage of the southern oceans between Cape Town and Queen Maud Land (Norwegian sector), Antarctica and between Antarctica and South Sandwich Islands. At time of writing, all the abovementioned data platforms are transmitting to ARGOS and only one buoy has partially failed (in terms of losing its drogue, but continuing to transmit nevertheless). An ICEX AWS (property of SA Weather Service) was also installed on South Thule island (the southernmost island in the South Sandwich group), with kind permission of the British Government and the Falklands Island Administration. This was done on 13th January 2006, during a brief shore operation, utilising 2 zodiac ‘rubber-duck’ craft from the SA Agulhas. On the return voyage to Cape Town, a similar ICEX buoy (property of Christian Michelsen Research (CMR), Bergen University, Norway) was installed on Bouvet (Bouvetoya) island, during a brief hour-long helicopter operation on the island. During this operation, the old Norwegian ICEX instrument was retrieved, cleaned and crated, ready for shipping back to CMR Norway. Both the Thule ICEX as well as the Bouvet ICEX are functioning and regularly transmitting to the ARGOS satellite system.   

3. RESULTS

3.1. FRONTAL LOCATIONS

The Southern Ocean is characterised by the strong zonal nature of its main frontal bands, and its spatial structure is strongly determined by the position and flow regime of a number of frontal system separating different ACC zones (Belkin and Gordon, 1996). Extensive measurements have been made in the South Atlantic and South Indian sectors of the Southern Ocean over the past 3 decades (Lutjeharms and Valentine, 1984; Lutjeharms, 1985; Lutjeharms and McQuaid, 1986; Lutjeharms, 1990). Full depth CTD measurements have been made during AJAX (Whitworth and Nowlin, 1987) SR2 WOCE (Roman, 2003) and on an opportunistic basis enroute to the ice edge. Unlike other regions of the Southern Ocean where frontal systems display high bands of variability with enhanced eddy activity such as at the Drake Passage and South Georgia (White and Peterson, 1996), at the South-West Indian Ridge (Park et al., 2001; Pollard and Read, 2001; Ansorge and Lutjeharms, 2003) and south of Australia (Sokolov and Rintoul, 2002; Budillon and Rintoul, 2003) the frontal characteristics in the region of the Greenwich Meridian line are less intense and variable, as can be inferred from altimetry and from historic hydrographic data (Lutjeharms et al., 1993).

Identification of the main ACC fronts is essential in order to trace the upper level circulation associated with the baroclinic shear. However, accurate identification of the fronts is not always simple especially in regions where they remain merged  (Park et al., 2001). One major difficulty is the various definitions that have been given for the characterisation of the fronts bordering the ACC (Belkin and Gordon, 1996). Depending on authors, these definitions are based on either surface or subsurface property values, whereas others have used phenomenological definition. Definitions used by Belkin and Gordon (1996) for both surface and subsurface ranges are given in Table 6. However, in order to unambiguously place the fronts before describing the frontal features observed along the GoodHope V transect, each front will be defined using their representative subsurface axial values at 200 m where generally each front is marked best. Note that the positions of the ACC fronts for the return transect between Antarctica and Cape Town is given in Table 7.

FRONT

SURFACE

SUBSURFACE (200 m)

STC

10.6 – 17.9ºC: 34.3 – 35.5

8.0 – 11.3ºC: 34.42 – 35.18 Axial value: 10ºC, 34.8

SAF

6.8 – 10.3ºC: 33.88 – 34.36

4.8 – 8.4ºC: 34.11 – 34.47 Axial value: 6ºC, 34.3

APF

2.5 – 4.1ºC

Axial value: 2ºC

 

Table 6: Definition of the fronts bordering the Antarctic Circumpolar Current.

In order to define the subsurface expression of the APF, the definition given by Orsi et al. (1995), in which the axial value marks the intersection of the 2°C isotherm at 200 m, will be used. Extensive analysis by Belkin and Gordon (1996) have found the subsurface SAF and APF axial values to remain fairly stable between 0° and 150°E.

3.1.1. SUBTROPICAL CONVERGENCE

The Subtropical Convergence (STC) marks the boundary between warm, salty subtropical surface water and cooler, fresher Subantarctic Surface Water to the south. It is the most northerly front associated with the ACC (Figure 1) and the most prominent surface thermal front. XBT data collected from over 70 crossings of the STC have shown that in the South Atlantic the STCs mean position lies at 41º40’S (Lutjeharms, 1985).

The subsurface expression of the STC, identified by the 10ºC isotherm at 200 m, was found at 40.4°S during GoodHope V. The average position of the STC for the previous four GoodHope cruises was 40.46°S, which shows that the STC was found further to the north during the GoodHope V transect. Previous studies in the South­east Atlantic sector of the Southern Ocean (Smythe-Wright et al., 1998) have identified two separate fronts associated with the Northern (NSTC) and Southern boundaries (SSTC) of the STC. These observations have been made from over 10 datasets extending across the South Atlantic from the Brazil Current at 42ºW to the Agulhas - Benguela region at 11ºE.

3.1.2. SUBANTARCTIC FRONT

The Subantarctic Front (SAF) marks the northern boundary of the Polar Frontal Zone (PFZ), which is a transitional zone between SASW and AASW. In comparison to the STC, which is clearly characterised by a sharp and consistent gradient in both surface and subsurface expressions, making identification extremely easy (Lutjeharms and Valentine, 1984; Lutjeharms, 1985), the SAF is less clear in its surface expression. The exact boundaries of the PFZ can therefore be difficult to identify due to the weak nature of this front. The SAF is predominantly a subsurface front and can be defined by the most vertically orientated isotherm within a temperature gradient lying between 3ºC and 5ºC, while it’s surface expression extends between 8ºC and 4ºC (Lutjeharms, 1985). Lutjeharms and Valentine (1984) have identified the SAF as having a mean position of 46º23’S south of Africa. Using the criteria described by Belkin and Gordon (1996) in which the subsurface temperature range between 4.8 - 8.4°C and 34.11 - 34.47 at 200m, with axial values of 6°C and 34.3. We observed the subsurface axis of the SAF at 45.08ºS during GoodHope V (Figure 4), while the surface expression ranged between 43º16.14 – 47º15.00S and lay further to the north than during the GoodHope I cruise (44º05’S – 49º16’S). The mean position of the SAF for the previous four GoodHope cruises was 44.3° S. Therefore the SAF’s position during GoodHope V is found considerably further south (86.7 km) compared to the mean. The SAF appears to be considerably wider than in other regions of the Southern Ocean (Belkin and Gordon, 1996). However, recent investigations (Smythe-Wright, 1998) have shown that in the South Atlantic, the SAF is often found as a broad frontal band extending over 250km. 

3.1.3. ANTARCTIC POLAR FRONT

The APF marks the northern limit of the Antarctic zone and the subsurface expression of the APF is historically identified by the northern limit of the 2ºC temperature minimum at a depth of 200m (Whitworth, 1980; Belkin and Gordon, 1996). In some instances this is not coincident with the surface expression of the APF (Lutjeharms and Valentine, 1984) and instead the surface expression can be identified by the maximum temperature gradient between 6ºC and 2ºC.  The APF is characterised by a shallow temperature minimum associated with the remnants of Winter Water, which lies at depths between 50 – 150m. Temperatures for this water mass range from -1.8 – 6°C at the APF and salinity from 33.4 - 34.2. During GoodHope V the subsurface expression of the APF was found to lie further south at 50.39ºS when compared to the mean of 50.11°S for the previous four GoodHope transects.

3.1.4. SOUTHERN ANTARCTIC CIRCUMPOLAR FRONT

Orsi et al. (1995) have identified an additional ACC front, which they have termed the Southern ACC Front (SACCF) and described as a circumpolar, deep reaching front lying south of the APF. The position of this front corresponds to the position of the atmospheric low-pressure belt Antarctic trough, which separates the easterly and westerly wind belts at ~65ºS. In contrast to the other fronts associated with the ACC, the SACCF does not separate distinct surface water masses, instead it is defined by the temperature and salinity characteristics of the Upper Circumpolar Deep Water (UCDW). Two branches of the SACCF, marked by a high salinity gradient 33.80 –

33.63 at 63.4ºS and 33.78 - 33.09 at 64.7ºS between 0.9 –0.7ºC, were observed by Holliday and Read (1998) in the SE Atlantic from their RRS Discovery dataset. South of Australia (Budillon and Rintoul, 2003) the SACCF has been identified by the location of the 0ºC isotherm along the Tmin, which places the front at a mean position of 63º48’S. Increase in air temperatures between December – February results in the warming of the surface mixed layer and the northern extent of the TML cooler than 0ºC forming a reliable indicator of the position of the SACCF (Orsi et al., 1995). Using this definition, places the SACCF during GoodHope V at 51.96ºS (Figure 4). The previous four GoodHope transects produce a mean position of 52.93°S for the APF. The SACCF, therefore, deviated 107.2 km north of the mean during GoodHope V. In this region the Tmin formed by the presence of the remnants of Winter Water averages 80m in thickness and is centred at 150m.

3.1.5. SOUTHERN BOUNDARY OF THE ACC

Upper Circumpolar Deep Water (UCDW) is the only water mass found exclusively in the ACC. Orsi et al. (1995) have defined the southern terminus of UCDW characteristics as the southern boundary of the ACC, separating the ACC from the subpolar regime. Over the Greenwich Meridian a sharp termination to the poleward extent of the UCDW signal has been revealed by closely spaced stations. This boundary also coincides with the separation between the ACC and the Weddell Gyre. Using temperature criteria, the southern boundary is identified where the southern limit of temperatures greater than 1.5°C occur. During GoodHope V, this limit was found at 55.67°S. The GoodHope I transect identified the southern boundary at 55.55°S which compares similarly with that of GoodHope V.

ACC Fronts

Mean

GoodHope V

Return Leg

STC

40.46

40.4

40.69

SAF

44.45

45.08

45.27

APF

50.16

50.39

51.81

SACCF

52.73

51.96

52.9

Southern Bdy

55.61

53.33

55.67

 

Table 7: The latitudinal positions of the ACC fronts are compared between the mean, GoodHope V and the return leg XBT transect. The mean has been derived from 4 previous GoodHope crossings of the ACC between February 2004 and October 2005. Note that all values are given in °S.  

3.2. BAROCLINIC TRANSPORT ESTIMATES FOR THE ACC

Within the last five years, studies by Rintoul et al. (2002) and Sokolov et al. (2004) have uncovered how the use of hydrographic sections (mostly obtained from XBT lines) can be used to calculate baroclinic transports of the ACC.    

One of the conclusions of the International Southern Ocean Study (ISOS), in the 1970’s, was that the variability of the ACC was primarily barotropic. More recent World Ocean Circulation Experiment (WOCE) sections completed in the Drake Passage suggested that the baroclinic and barotropic variability were comparable (Cunningham et al., 2003). This observation suggests that monitoring the ACC transport variability requires measurements of the density field as well as the pressure field associated with the barotropic flow (Sokolov et al., 2004). To observe the density field, full depth hydrographic sections are needed. 

Density, dynamic height and velocities can be calculated from temperature and salinity measurements as shown by Stommel (1947). In many regions of the world’s oceans, well-defined temperature-salinity (T-S) relationships exist. From these relations, the T-S curve can be exploited to identify the salinity corresponding to each temperature observation and from this one is able to determine the geostrophic velocities. In the Southern Ocean, however, such a “tight” T-S curve does not exist (Sokolov et al., 2004). Due to the Southern Ocean’s connections with ice formation and melt and the fact that warmer, saltier subtropical waters border it to the north, temperature and salinity profiles generally cool and freshen to the south, and at some locations the relationship is multi-valued (one temperature corresponds with several salinity values). If enough studies and hydrographic sections, relating to both temperature and salinity, have taken place in a region, the mean T-S curve can be determined for that particular region. This was done in a study by Rintoul et al. (2002) between Tasmania and Antarctica.

The regional T-S curve in the Southern Ocean is, however, “stable” in the sense that each front and the zones between these fronts have a characteristic family of T-S curves which do not change with time. Rintoul et al. (2002) explain that this stability of the T-S curve can be exploited by generalising the technique of inferring S from observed T as commonly used in lower latitudes. 

A tight correlation exists between temperature (averaged between 0 and 600 m) and dynamic height (at the sea surface relative to 2500 m) using CTD data from three transects. A smoothing spline has been fit to the data from the AJAX, A12 and A21 CTD transects completed in the south Atlantic region, south of Africa during February 1984, May 1992 and February 1990, respectively. We exploit this correlation (shown in Fig. 7) to determine dynamic height (relative to 2500 dbar) from average temperature data (0-600 m) from XBT measurements obtained from the GoodHope V hydrographic section (Fig. 8). 

Rintoul et al. (2002) found that a very tight empirical relationship exists between surface dynamic height relative to 2500 dbar and cumulative transport for the SR3 line, south of Australia. We show that this relationship exists along the GoodHope transect (Fig. 9). This allows us to estimate the baroclinic transport using surface dynamic height.

Dynamic height values inferred from XBT data are applied to the spline function shown in Fig. 9 to produce a northward cumulative baroclinic transport estimate of

88.55 Sv, relative to 2500 dbar (Fig. 10a). This estimate is closely comparable to the mean geostrophic transport of 88.92±5 Sv (0.37 Sv  higher) from the three available Atlantic CTD sections, relative to 2500 dbar (Fig. 10b). These transport estimates are defined between the northern (STC) and southern (Southern Boundary) boundaries of the ACC as indicated by the front locations, which has been described earlier in the text.

3.3. NITROGEN UPTAKE EXPERIMENTS

The rapid increase in atmospheric greenhouse gas concentrations over the past century, and the associated implications for the world’s climate system, has led to a substantial development of interest in the global carbon cycle. Indeed, understanding the possible sources and sinks of atmospheric carbon is vital for the successful modelling of future climates. The global ocean has the ability to sequestrate carbon, through photosynthetic carbon fixation and subsequent draw-down. It follows that the sequestration is likely to be higher in regions of elevated primary productivity, such as at oceanic fronts, or regions where nutrient concentrations are high. The Southern Ocean contains several convergent fronts, such as the STC, SAF and APF, which tend to concentrate nutrients and biological productivity. Furthermore, in the Antarctic Zone south of the APF, nutrient concentrations are generally substantially elevated, due to the upwelling of water from below the thermocline. Therefore, the Southern Ocean is potentially highly productive, and capable of exporting carbon to the ocean floor. The experiments undertaken on the voyage seek to quantify the potential carbon fixation of the shelf waters adjacent to the Antarctic ice shelf near the Greenwich Meridian, using the nitrogen uptake of phytoplankton.   

during the voyage. Note that the frontal positions have been determined using the GoodHope V hydrographic section.

On the voyage of the SA Agulhas from Cape Town to Antarctica, along the GoodHope hydrographic transect, sampling was undertaken so as to coincide with the major oceanic fronts of the Southern Ocean, namely the Sub-Tropical Convergence, the Sub-Antarctic Front and the Antarctic Polar Front. Subsequent to arriving at the ice shelf at Penguin Bukta (~70.282° S; 2.7543° W) a further 15 stations were occupied in the vicinity. One further station was occupied at Atka Bukta to the west (70.5285°S; 8.1142°W). Figure 18 depicts the positions of the 22 stations occupied, together with the location of the oceanic fronts, as determined from the Goodhope V hydrographic transect.

At each station a bulk surface water sample of approximately 10 litres was collected via bucket. The bulk sample was then immediately sub-divided into three 2 litre sub samples, each of which were decanted into a labelled glass Schott bottle. Water samples for nutrient determinations and freezing were also obtained from the bulk sample. 15N salts containing known concentrations of urea, ammonium (NH4) and Nitrate (NO3) were then used to spike the three sub samples in the Schott bottles. The volume of the spikes was determined so as to add approximately 10% of the ambient nutrient concentrations to each sample. For the entire experiment a 1µM spike was added to the NO3 sample, while a 0.1µM spike was used for both urea and NH4 samples (In all cases this corresponded to 0.2ml of the salt). Once the spikes had been added, the Schott bottles were closed and gently mixed. 

The three Schott bottles containing the spiked samples were then placed in the incubator and a start time for the incubation was recorded. The incubator itself was positioned on the heli-deck of the SA Agulhas, where it was secured to the top of the safety nets, ensuring that shading of the samples was minimised at all times. To maintain the samples at their ambient temperature, the incubator was supplied with running sea surface water, obtained from the scientific sea water pump. 

Determination of the concentrations of urea, NO2, NO3 and NH4 were conducted on the water obtained from the bulk sample, within a half an hour of collection. The nutrient determinations were conducted according to the methods described in Grasshoff et al (1983) scaled down to 5 ml samples. An additional sample was frozen for back up nutrient determinations, to be conducted post-cruise. Approximately 24 hours after the start time of the incubation, the three Schott bottles were collected from the incubator, and placed in a dark bag so as to stop photosynthesis, and stop time was recorded for the incubation. Actual incubation times at individual stations varied between 20 and 24 hours, with an average incubation time of 22 hours.

The spiked and incubated samples were subsequently each removed from the dark bag and filtered onto individual 25 mm Whatman glass fibre filters (GFFs). The volume filtered varied between 1 and 2 litres depending on the phytoplankton density in water sample at each station. In all cases the volume filtered was sufficient enough to obtain a visible green build up on the GFF. Station dates, positions, volumes of Urea (Ur), NO3 and NH4 filtered, spikes added and incubation durations are presented in Appendix 3. Once filtering of the relevant sample was complete, the GFF was placed in a plastic Petri dish, labelled and frozen. Therefore the product of the experiment at each station was three frozen GFF filters, containing the contents of the samples spiked with NO3, urea and NH4 respectively.

The frozen GFF filters will be analysed by means of a mass spectrometer at the University of Cape Town. This analysis will yield the concentrations of N and 15N contained within the phytoplankton on the GFFs. The original concentrations of urea, NO3, NH4 and the 15N spikes added to each sample are known. Therefore, the ratio of N: 15N contained within the phytoplankton can be used to infer the rate at which the algae took up nitrogen. The rate of nitrogen uptake is then directly related to the amount of carbon fixation through the Redfield ratio.  Since the period of incubation, and the volume filtered is known for each sample, the amount of carbon fixation can be adjusted to a figure in g.C.l-1.hr-1. These results are forthcoming.       

Since the analysis of the frozen GFFs is still to be undertaken, the only results available at this stage are the nutrient concentrations at each station. While urea and NO2/NO3 concentrations were determined at all 22 stations, NH4 determinations were abandoned after station 5, due to technical problems with chemical reagents. The nutrient concentrations at the underway stations (1 – 6) are shown in figure 19. Nitrate concentrations increase strongly towards the south, reaching 20µM by station 6 at the ice shelf. Nitrite concentration underwent a certain increase between stations 1 and 3, south of which they remained at approximately 0.4 µM. Urea concentrations can also be seen to have increased southward from station 1 to 5, after which they declined to 0.52 µM at station 6.  The ammonium concentrations did not exhibit any clear trend, and are thought to be questionable.

The concentrations of NO2, NO3 and urea for stations 8-22, occupied at the ice shelf, are given in figure 20. While the concentrations exhibited a fair degree of variability, they fall within the limits of the values which can be expected for this region (Waldron, pers. comm.). Tentatively, NO2 and urea concentrations seem to be inversely correlated, which could possibly be explained by regeneration following a phytoplankton ‘bloom’. Following a peak of 27 µM at stations 10 and 12, NO3 concentrations were surprisingly stable at approximately 15 µM. More substantial results will be available following the analysis of the GFFs in Cape Town. 

4. CONCLUSIONS

The Antarctic Circumpolar Current forms an important link in the global thermohaline overturning circulation. Modifications in the saline characteristic of water masses associated with the ACC play a vital role in maintaining both global heat and salt budgets. Determining the transport flux of the ACC south of South Africa has been an observational goal for many years. Such observations have been conducted during the World Ocean Circulation Experiment (WOCE) during the 1990s in which repeat transects across the ACC were restricted to 3 chokepoints. Intense and periodic monitoring of both the Drake Passage and south of Tasmania have continued since WOCE, however a regular monitoring line between South Africa and Antarctica has only commenced earlier this year.

Our understanding of how and why this transport varies with time and season remains incomplete due to the severe lack of observations. The sources, pathways and characteristics of these exchanges are not well-enough established to allow their influence on the climate system south of South Africa, to be quantified. The aim of GoodHope is therefore to establish an intensive monitoring line that will provide new information on the volume flux of the region south of South Africa, in particular the Indo-Atlantic exchange. An investigation studying the empirical relationship between upper ocean temperature and the baroclinic transport stream from repeat hydrographic sections across the ACC, south of South Africa is now currently underway. Application of this empirical relationship to all the past and future observations will be necessary to monitor the variations and variability of the ACC south of South Africa. By further defining a second empirical relationship between surface dynamic height and cumulative transport (following Rintoul and Sokolov, 2001) it will be possible in future to extrapolate the ACC behaviour, in particular its seasonality and inter-annual variability, through satellite altimetry.

In addition, comparison between the 5 GoodHope cruises show the effect seasonality has on the position and strength of the main frontal cores. It is hoped that one outcome of the GoodHope project is to establish a long term monitoring line in which a clearer understanding of the seasonal behaviour of the frontal regions is established.

This is the start of a new and exciting multi-national and inter-disciplinary endeavour aimed at integrating high-resolution physical, biological and atmospheric observations with along-track satellite and model data. It is hoped that the outcome of the GoodHope project will result in a clearer understanding of the Indo-Atlantic inter-ocean exchange in this region of the Southern Ocean and its impact on both regional and global present day climate changes.

5. LIST OF PARTICIPANTS AND AFFILIATIONS

PARTICIPANTS

ROLE

AFFILIATION

Sebastiaan Swart

Team Leader; XBT; TSG; ARGO, APEX & SVP Deployments; Nitrate Incubations

UCT

Neil Swart

Nitrate Incubations; XBT; TSG; ARGO, APEX & SVP Deployments

UCT

Natalie Burls

XBT; TSG; ARGO, APEX & SVP Deployments; Nitrate Incubations

UCT

Michael Funke

XBT; TSG; ARGO, APEX & SVP Deployments; Nitrate Incubations

UCT

Kevin Rae

SVP-B Deployments; Met Observations & Forecasting

SAWS

 

Table 8: List of ship-based participants outlining their responsibilities and their affiliations. 

INSTITUTE ADRESSES

UCT                                                                Ocean Climatology Research Group   Department of Oceanography University of Cape Town   Rondebosch 7701   South Africa   sswart@ocean.uct.ac.za

SAWS                                                              South African Weather Service   PO Box X097 Pretoria kevin@weathersa.co.za

6. ACKNOWLEDGEMENTS

The successful completion of the survey would not have been possible without the invaluable assistance of Captain David Hall, the officers and the crew of the S.A. Agulhas. We are grateful to Dr Silvia Garzoli, Robert Roddy, Steven Cook, Craig Engler and Jim Farrington of NOAA/AOML and OGP/NOAA for their support and immense generosity towards this cruise. We would also like to thank Henry Valentine, Angelo van Niekerk and Sam Oosthuizen of the South African National Antarctic Programme for the help they gave us in dealing with the administration and planning procedures for GoodHope V. Special thanks is extended to Dr Isabelle Ansorge for her guidance and support in completing a successful GoodHope V cruise. Last, but by no means least, the determination that was kept over such a long voyage, by my three accompanying GoodHopers from UCT, will always be appreciated.

Sebastiaan Swart    March 2006

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