Icebergs and Growlers in the South Atlantic - SA Agulhas Gough Relief Voyage
Ian T. Hunter, Manager, Maritime Services, South African Weather ServiceVoluntary Observing Ships and Ice
The research ship SA Agulhas belongs to the Department of Environmental Affairs and Tourism in South Africa. She is managed by Smit Marine (SA) and makes regular voyages to the outlying weather stations run by the South African Weather Service. The vessel is the leading supplier of voluntary observing ship (VOS) reports in the South African VOF (voluntary observing fleet). These observations are frequently from data-sparse areas of the South Atlantic and South-West Indian Ocean.
During September and October the Agulhas undertook its annual relief cruise to Gough and Tristan Islands. She also did a week-long buoy deployment cruise which looped south-west of Gough Island down to latitude 50S.
The table below, provided by the vessel's Master, Captain Frikkie Viljoen, lists all icebergs sighted (longer than 50 m) - either visually or on the ship's radar:
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Icebergs encountered during the 'SAWS' buoy run, September 2004 | ||
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22/09 1800 46° 49.4'S 017° 58.8'W |
1(50-200m) | |
| 23/09 0000 47° 34.6'S 018° 50.96'W | 4(50-200m) | 1(200-500m) |
| 23/09 0600 48° 22.1'S 020° 00.2'W | 1(50-200m) | |
| 23/09 1200 49° 01.2'S 020° 43.3'W | 3(50-200m) | 1(200-500m) |
| 23/09 1800 48° 52.5'S 020° 36.0'W | 2(50-200m) | |
| 24/09 0600 48° 35.0'S 021° 15.0'W | 1(200-500m) | |
| 24/09 1200 48° 32.4'S 021° 26.3'W | 3(200-500m) | |
| 24/09 2000 49° 07.0'S 019° 26.9'W | 3(50-200m) | |
| 25/09 0000 49° 30.1'S 018° 32.6'W | 2(50-200m) | |
| 25/09 0600 49° 58.9'S 017° 02.8'W | 5(50-200m) | |
| 25/09 1200 49° 02.1'S 016° 29.0'W | 2(50-200m) | 6(200-500m) |
| 25/09 1800 48° 14.7'S 017° 20.3'W | 4(50-200m) | 1(200-500m) |
| 26/09 0600 46° 24.3'S 014° 12.0'W | 1(>1000m) | |
Icebergs encountered during the 'SAWS' buoy run, September 2004.
The actual dimensions of the last iceberg were : 4.6 nmi x 2 nmi x 50 m freeboard
These observations were done at 6 hourly intervals.
In October 1998 a huge portion of the Ronne Ice Shelf broke away from the Antarctic mainland. It was over 80 nmi long and more than 26 nmi wide- 'A38' i.e. the 38th sighting to meet NIC (National Ice Centre) criteria, between Greenwich and 90W (area A). Within 9 days A38 had split into A38-A, A38-B and A38-C.
After almost 6 years A38-A was tracked to a position approximately 600 nmi SSW of Gough Island (NIC archives, last entry 10 August). It had been a captive of the western Weddell Sea for 4 years, and finally escaped to sail past the South Orkneys and South Georgia into the above position. Similarly A38-D, E & F (or fragments thereof) - had also drifted into the area where the Agulhas was sent to deploy her load of drifting weather buoys. A38-B and C were further west.
Thus it seems highly likely that at least some of the icebergs spotted by the ship have their origins in the Ronne ice shelf breakaway of October 1998. Apart from the icebergs recorded by the deck officers of the SA Agulhas, a great many growlers were spotted in amongst the wind-swept waters of the South Atlantic. Perhaps the greatest danger posed by these lurking iceberg fragments is to ocean-going yachts competing at high latitudes. A 'bergy bit' with insufficient freeboard to trigger the radar alarm could well pierce a hull if struck at a high speed.
In February 2002 a voluntary observing ship reported seeing a growler/'bergy bit' at latitude 29° 45.6' south, off the coast of the Northern Cape. Needless to say the 'ICE' group in the VOS observation can contain some valuable information for navigational safety.
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