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Two messages in a bottle
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On 29 July Johan Pauw, Managing Director of SAEON received this intriguing e-message from Werner van Schalkwyk of BHP Billiton:
I found your contact details on the SAEON website after looking at the flow of the Agulhas current. Maybe you can explain the logic behind the following story:
A friend of mine picked up a bottle with two messages inside about 20 km north of Maputo a month ago. After opening this bottle he found two letters inside written by two girls from Cape Town. They placed the bottle in the ocean at Simon’s Town harbour on 16 June 2002.
It seems as if the bottle travelled either against the current from Simon’s Town to Maputo or from Simon’s Town in the direction of Australia and somehow ended back up at Maputo.
Can you shed any light on this mystery?
Johan Pauw subsequently sent the message to Dr Juliet Hermes, Manager of SAEON’s Egagasini Node for marine-offshore systems and a respected oceanographer.
Would Juliet be able to clarify the mystery?
Juliet responded as follows:
Dear Mr Van Schalkwyk, my director forwarded me this message as I am a physical oceanographer (and the author of the Agulhas article). It sounds like a very interesting story. I will discuss it further with colleagues to get their opinions but in the meantime, there are a number of possibilities.
Firstly, if the bottle was floating on the surface it is likely to have been influenced by local winds. I would imagine it got swept out to sea, caught in the inner side of the Agulhas retroflection and floated back to coast in a recirculation gyre. However, this shouldn't take seven years and so I doubt it was a direct route.
An experiment done in 1973 by what was then Sea Fisheries, deployed a number of 'drifter cards' from various locations, several of which were from South Africa. These were recovered a few years later in Mauritius, Rodriguez and St Raphael, with one card being found in Kenya and further cards found on the east coast of South Africa after three years.
A possibility for the girls' bottle is that it travelled with the Agulhas Return Current to Australia before heading back in the South Equatorial Current. However, a complete trip in the gyre should take approximately 38 months. There are a number of other drifter studies but most drifters have been shown to follow this route, or else get swept in to the South Atlantic by an Agulhas eddy or filament.
I guess there is a remote possibility that the bottle did a whole tour of the South Atlantic before getting caught up in the Antarctic Circumpolar current and being swept along to Australia and back into the South Indian Ocean gyre. If the bottle remained near the coast there is a chance that it got caught inside a trapped eddy, headed northward and then left the eddy perhaps moving further with the wind until it got trapped in another eddy. I believe there are turtles that do this.
The final option is that the girls were playing a trick! I wonder what sort of condition the bottle was in and whether any algae survived when it was washed up. An endless number of possibilities, but it certainly gave me pause for thought!
This might be an interesting case to include in SAEON’s education programme! If you would like to know about any of the oceanographic work we are doing here or have any further questions, please don't hesitate to contact me.
The plot thickens
Werner shared Juliet’s response with his friend André Wolhüter, who subsequently sent the following explanation to Juliet:
Dear Juliet, I am Werner's friend who were given the bottle by Tienie Ras, who initially found the bottle in Mozambique.
The two letters were put into an old Krest lemonade bottle. These bottles were green with a white plastic cap, and white lettering printed onto the glass in a paint that permanently adheres to the surface. If one holds the bottle up against the light one can very vaguely distinguish the markings. Plastic also degenerates very slowly but if one looks at the cap it is busy falling apart and needs to be handled very carefully. When one looks at the way the two letters have faded and worn away, it is quite evident that they’ve been in the bottle for a very long time.
I am not an expert, but by just looking at the evidence I would definitely rule out the possibility of a hoax.
We would obviously like to find the two girls and get their side of the story to close the last chapter of this intriguing and romantic story.
We will keep you posted.
Juliet’s response reads as follows:
I am also sure it was not a hoax, it was just a last option!
It is a lovely story and I certainly hope you find the girls. I live near Simon's Town so if I can be of any assistance let me know. Given that it was put in the water on Youth Day I wonder if it was a school initiative. What a shame they didn't give contact details.
Will they find the girls?
A day later Juliet received exciting news from André:
I found the girls. We are meeting them and Lynette Kempston, their mom at our house in Fish Hoek on Saturday morning. I would like to know if it would be possible for you join us at 11h00 to give us your part of the story and tell us about the sea currents around the continent.
All’s well that ends well
Came Saturday, Juliet drove to Fish Hoek and met André, the two girls and their mom. Tienie Ras, who initially found the bottle in Mozambique, joined them for tea.
The pictures tell their own story ...
