Seasonal changes are one thing, but the conditions have been less than great for a while. Good diving days have been rare over the last six weeks. This weekend – again – is not too rosy from more than one angle.
Firstly, this week my tow vehicle decided to have a career change, so the boat has nothing to attach to. Secondly, even if I am able to wrest the panel van back from my wife, shore dives don’t look like a good option as there is a 2.5 metre, 16 second swell tomorrow. This grows to 4 metres on Sunday, and the swell goes somewhat southerly. This lingers on Monday, by which time the wind starts humping again.
Please bear in mind, if you do head out to Simon’s Town this weekend, that the navy is running a simulated disaster/attack scenario from early on Saturday morning, and you should expect detours and delays. Plan accordingly!
The Environmental Resource Management Department at the City of Cape Town needs your help:
We would like to try and get to whale carcasses well before they wash ashore on our coastline to deal with them more effectively and efficiently. As ocean users, if you come across a whale carcass floating anywhere in False Bay or from Cape Point north to Silwerstroom Strand we would be most grateful if you could call, whatsapp or sms 083 940 8143 (available 24/7) with an approximate location and time of sighting.
Please could I ask that you also forward/share this email to as many friends, colleagues or groups that you are aware of that use the ocean as we would like as large a network of people as possible that could report sightings.
Save that number in your cellphone contacts, and do your bit for beach safety and, hopefully, for the environment, by reporting sightings of deceased whales before they reach the beach.
Ideally (environmentally speaking) dead whales should be left out at sea to be scavenged upon by marine life and then sink to the bottom and return their nutrients to the ecosystem. Unfortunately the prevailing summer wind direction in Cape Town (south easterly) generally brings any such carcasses onto the beach in False Bay. This is a hazard to human safety because of the co-incident inshore presence of great white sharks during the summer months. A dead whale is a great feeding opportunity for sharks, and its accompanying oil slick will be evident from miles away, potentially bringing in more sharks to investigate. This is why the City wants the opportunity to deal with whale carcasses before they reach your local swimming beach.
It’s timely to remember that while some cetaceans die and end up on the beach because of reasons such as ship strikes, ingesting plastic or other pollutants, or acoustic disturbances related to human activity, some of these animals also die of natural causes or illness unrelated to man’s impact on earth. Many times, scientists will examine the dead animal and be able to state what most likely led to its demise. While it is distressing to see any dead animal, and particularly strange and discomfiting to see a whale on shore, this is not necessarily confirmation that “the ocean is dying” or that we are “killing False Bay.” Sometimes it’s just the circle of life. Dead whales were an important source of nutrients and building materials to Strandloper communities long before industrial shipping plied the world’s seas.
For more on what happens to whales that die at sea (hint: it’s magnificent), check out this video. For more on the collision of dead whales and the urban environment, there’s this post about a whale on the beach in Fish Hoek, this one about a whale on the road in Cape Town, and this one about a stranded whale in the United States.
But I digress. Save this phone number: 083 940 8143, and tell your ocean-loving paddler, surfer, sailor, boater and diver friends to do the same!
Summer weather patterns and wind direction are sure taking their time heading off. This far into March and we have not yet had any spectacular diving. Well it has to change sometime, but I don’t think the time is this weekend.
Saturday looks good from a wind point of view, however the swell is supposed to peak at 4 metres on Friday afternoon with a 14 second period. That will make for very surgy diving, and even deep dives will feel the 14 seconds. The swells don’t always arrive as predicted but this evening just before sunset it was already at 3 metres and starting to ruffle a few feathers.
Sadly, once again, I think we are set for a dry weekend. Sunday has more wind and less swell, and visibility will most likely be good out of Hout Bay but 15 knots of wind, 2-3 metre swells will not make for great diving. I have a sand dune at home so if you are at a loose end you are welcome to pop in and build a castle.
The water is really doing its best to limit diving right now. It is either murky green or way too windy for decent diving on a regular basis. At some point it will change, but I doubt it will change in time for the weekend. There are areas in False Bay that are clean and free of red tide, but you need to go and look for them.
Saturday has pretty strong south easterly wind and a fair amount of swell, Sunday is not looking much better. I have students who require shore and boat dives so I will launch at 6.00am onSaturday for a quick look and double tank dive, and plan the weekend around what we find.
If you’d like to be notified of diving plans that may materialise if we find suitable conditions, let me know!
It would seem from the forecast that it is a open and shut case of where to go and what to do this weekend. To be honest I am not too sure of the right thing to do! Both the Atlantic and False Bay are a colour that does not exactly inspire one to throw on a wetsuit.
The wind has blown more easterly and north easterly today than was expected, so it will not have done much for the visibility on either side. Sunday is out of the question as the forecast is for humping south easter, so that leaves Saturday.
I am launching from Hout Bay tomorrow afternoon and will have a better idea of whether it is clean enough for Saturday. The other option is shore diving at Long Beach. I reckon that there is about a strong chance that the water won’t be clean enough for any diving at all, though.
Today we took a load of surfers out to Dungeons. Amongst them were a few first timers at Dungeons and the happy cheers and bear hugs when they caught their first serious Dungeons roller was a sight worth seeing. Dungeons is a spectacular sight so if you haven’t been there do so at least once in your life.
Back to diving… We dived the Atlantic last weekend. Maori Bay was cold and clean-ish. Visibility was around 10 metres but then the temperature was also in the single digits. Die Josie was a lot cleaner and just as cold.
On Sunday we dived in False Bay – doing Search and Recovery for an Advanced course in 2 m visibility makes it a little more realistic!
Well… There is swell and wind in the forecast. The swell was not all that noticeable in False Bay today but was very surf-worthy at Dungeons and Muizenberg today. The wind is forecast at around 30 km/h for both days and for students doing their first boat dives I think it’s not that good an idea. So I have no launches planned for this weekend.
This will be a quick newsletter as we are downwind of a raging vegetation fire and the smoke is unbelievably thick. Even our tortoises are going to spend the night indoors. Firefighters, many of whom are volunteers, have been have a rough time of late and I admire their endurance, skills and management of these situations.
We had really good conditions in Hout Bay last weekend with clean and cold being the main factor. 8 degrees celcius is chilly but the viz was easy 15 metres.
The south easter has humped all week long and False Bay is a little messy. The visibility in the yacht basin today was actually very good but I think the rest of False Bay would have been messy. The yacht basin is protected from the south easter by the naval harbour.
The forecast leads me to believe that Hout Bay will be good on Saturday and False Bay on Sunday. I would also like to slip in a night dive on Saturday if the conditions permit.
Perhaps you have wondered what causes the patterns of strange coloured water in False Bay during the summer months. Perhaps you have dived in it, and wondered why sometimes you can’t see your hand in front of your face! Wonder no more – I am here to help.
Frequent visitors to and residents of the shores of False Bay will observe that at certain times of the year, the ocean is marked by bands and arcs of sharply contrasting coloured water. This phenomenon is known as a colour front. In oceanography, a front is the interface or boundary between two separate masses of water. In this case, the water masses are easy to discern, because they are of different colours. There are usually other characteristics of the water on each side of the front that differ, too. Fronts are either convergent (the water masses are moving towards each other) or divergent. The presence of marine debris (like pieces of kelp) at the front boundary suggests that it is convergent.
Causes of colour fronts in False Bay
Prior to 2005, there was much conjecture about the causes of these fronts (including the usual pollution bugbear), but little evidence to support any of the theories. By sampling, the fronts were found not to be caused by pollution, or by plankton blooms in the surf zone. It was known that a colour front was most likely to occur in False Bay after a period of southerly or south easterly wind lasting a few days. October and November seem to be prime months for the phenomenon.
When a large, obvious colour front arose near Simon’s Town in November 2005 with milky green water on one side, and darker blue-green water on the other, researchers from UCT and IMT sprang into action, sampling the water on each side of the boundary so that they could measure its characteristics. Speed is of the essence in these situations; colour fronts can disappear quickly. The one in the picture below is busy decaying – notice the smudged boundary.
Measurements revealed that the milky green water overlaid the clearer, bluer water, down to a depth of 11-12 metres (this will vary from front to front). The milky water did not extend to the ocean floor. Scuba divers around the Cape Peninsula will be familiar with the experience of diving through two or more layers of water, with varying turbidity (clarity) and temperature! (Here is picture of Tony and Christo diving near Oudekraal in the Atlantic that shows what the boundary between two layers of water can look like.)
The researchers found that the milky coloured greenish water was full of fine, almost neutrally buoyant particles of calcium-rich sediment. The green-blue water contained much less calcium, but relatively more silicon, which would suggest the presence of diatoms (a kind of phytoplankton – you can think of them as teeny tiny plant-like organisms) or sand in the water. The origins of the calcium-enriched sediment in the milky water are interesting: one source is from the shallows (less than 30 metres deep) of north western corner of False Bay, where the ocean floor is made up of rocks that are rich in calcium carbonate (such calcrete and limestone), some areas covered by a thin layer of sand.
The second probable origin for the particles of calcium-rich material is the interface between the sea and the land at the northern end of False Bay. The cliffs at Wolfgat/Swartklip at the head of the bay are made of calcrete, and at Swartklip the beach narrows to the extent that the cliffs erode directly into the water when the sea is high. Strong southerly winds create a wide (of the order of one kilometre) surf zone at Muizenberg and Strandfontein; a spring tide also adds to ideal conditions for the generation of a colour front.
The temperature of the milky water was found to be slightly (0.4 degrees Celcius) higher than the green-blue water. This measurement will also vary from front to front. The researchers speculate that the temperature difference could be because the milky water originated in the surf zone, which is shallower and therefore warmer, or because the high concentration of suspended particles in the milky water caused greater absorption of heat from the sun.
Here’s the tl;dr: strong southerly and/or south easterly winds, perhaps coupled with spring tide conditions, set up a very wide surf zone along the northern end of False Bay, which disturbs the sediment on the ocean bottom and drives the waves further up the beach than usual. Particles of buoyant calcium carbonate from the sea floor and eroded from the cliffs at Swartklip are lifted up into the water column, changing its colour to a milky-green shade. Wind-driven circulation patterns in the bay push the front from its original location in a southerly direction, towards Simon’s Town.
What to do?
Contrary to what your friends on social media may claim, not all colour changes in the ocean around Cape Town can be attributed to a giant sewerage plume. Hardly any of them can, in fact. In summer, the reason for the ocean looking green, red or even brown is likely to do with a plankton bloom of some description, or related to suspended sediments (as in this case) or other naturally arising material in the water. Instead of using this as an opportunity to become hysterical on the internet, how about celebrating the incredibly dynamic system that we can observe, living near the ocean? Drive up a mountain next to the ocean and take in the spectacle from on high. Dip your face in the water and see what it does to the viz. Take some pictures for posterity. And – if you don’t know what’s causing it – try to find and question someone who does know, like a scientist, or consult a good non-fiction book, to find out some facts.
The south easter has been blowing for a while now… Almost non stop. Windy, our wind generator at home who generates about a third of our monthly electricity requirements, has been having such a great time that she almost fell off the roof this week. She brakes herself when the wind reaches 78 km/h, and on several occasions the wind gusts exceeded that.
The Atlantic went from clean and cold, to cleaner and colder. The water colour in False Bay is not that bad but the surface conditions are pretty hectic. Fortunately I have had a lot of students requiring pool time so we have at least been getting wet.
There is wind and some swell for the weekend but I do believe that there is a possibility that Hout Bay will be good on Sunday. I have a bunch of students so will plan for both morning and afternoon dives, wind and swell dependent.
If the wind is driving you crazy too, check out the suggestions for land-based marine-related entertainment in last week’s newsletter.
We are back from a trip up north… Really far north – so far north that the temperatures, so I was told, were 0 – 2 degrees Celcius but to me felt like minus 50 degrees. It was great diving in False Bay this week in 22 degree water.
The weekend is a little on the questionable side as the wind and swell forecasts are not promising. I think the best option is going to be Table Bay, and If we go it will be to North and South Paw. I will take a look there tomorrow at the conditions and confirm late afternoon to those on the list if we are diving. Let me know if you’re keen to dive by email, text, or message in a bottle.