dank Global Warming hat Südafrika wieder mal ein neues touristisches Highlight: einen waschechten Eisberg, leider sind noch keine Fotos da, hoffe da kommt mal bald eins. Da das Verhältnis der Masse 1:8 (über Wasser zu unter Wasser) ist, heisst dass da noch ein wenig Eis unter dem Wasser ist.
Könnte man das noch mit Knut aus Berlin verbinden,
hätte die Bild Zeitung wochenlang zu tun...
Hier noch der komplette Bericht:
Iceberg sighted off Cape St Francis - 8 October 2007
The skipper of the trawler F/V 'Ntini' has reconfirmed his report of an iceberg roughly 74 km southwest of Cape St Francis on Monday evening. No other sightings have been made since then but the 'berg would have moved further and further away from the coast in the ~ 3 km/ hr southwest-setting current that was observed at the time.
Fig 1 is a photo of a typical 'bergy bit' which has survived into relatively low latitudes (47°S). This was taken from the 'SA Agulhas' during her annual buoy deployment voyage in 2004, to the southwest of Gough Island. Sea temperatures would have been around 5°C. This chunk of ice would have capsized many times. Note that the ratio of (roughly) 1:8 so frequently quoted refers to mass below water level versus that above. Thus the actual freeboard to draft ratio in a non-tabular iceberg can be a lot lower - the keel will not be as deep as implied by this commonly used ratio.
Thus it is now out of the main shipping lanes. A preliminary fly over was unsuccessful and the one satellite which can detect something of this size (even through cloud cover) will not pass over the region again until Monday. This is not to say that it would definitely spot the iceberg (assuming the radar was switched on) - in its highest resolution mode it has a very narrow swath width.
By extrapolation and allowing for some meandering in the current, the iceberg should be (very) roughly 160 km southwest of Cape Seal (Plettenberg Bay) by this afternoon, 12 October. From its reported position and the observed current speeds the 'berg must be close to the core of the Agulhas Current - i.e. in sea temperatures in excess of 20°C (see Fig 2). However it is not just this large temperature differential which will be eating away at the iceberg - sea state has an important role to play in deterioration, and wave action is always enhanced in the Current.
Fig 2 and 3 give some idea of how extremely unusual this event is. Large icebergs usually pass well to the south of the subcontinent heading in an easterly direction. Most of these originate in huge parent 'bergs which have initially tracked westwards along the Antarctic coastline after calving off from the ice shelf. They may run-aground, they will split eventually - in most cases those encountered in the South Atlantic have drifted clockwise around the Weddell Sea gyre and then moved to the north before turning east and starting to disintegrate (melting rates depending on latitude i.e. sea temperature). They can be well over 5 yrs old by the time they reach a position southwest of Gough Is.
A likely track has been added to the SST analysis. Even in a large meander in the Agulhas return flow an iceberg would have to survive a long transit in relatively warm water. Thus it would have to have started off as a large berg, probably big enough to be included in the National Ice Center's database (i.e. > 10 nm long) - at a relatively low latitude (~ N of 50S).
At present the closest 'big' (>10nm long) iceberg - in longitude - to South Africa is over 2000 km SSW of Port Elizabeth - B15G. Admittedly the 'St Francis' iceberg is miniscule compared with this giant (26 X 12 nm). But this is how all low latitude icebergs originate.
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Fig 2 shows the sea temperature analysis on 10 November 2006 south of New Zealand. On this day icebergs were spotted from Dunedin - for the first time in 75 years. The largest were described as being 'house size' (cf St Francis 'berg : 25m long by 20m high). However Dunedin is over 1000 km further south than Cape St Francis and is not affected by a warm western boundary current (i.e. the Agulhas). Note the very significant difference in sea water temperatures which an incoming berg would have to transit in the New Zealand case.
All of the above facts would imply that a large iceberg - not quite big enough to be reported by NIC - reached an unusually low latitude (40-45°S) in order to be advected rapidly northwards by a big meander in the Agulhas return flow.
