Questions from a Science teacher
Questions from a Science teacher
Mike Williams has answered the first six questions:
1. Why do the scientists and technicians work shifts? Why don't you just work daylight hours and then go to bed like normal?
RV Tangaroa costs thousands of dollars a day to charter which means that every minute we can work we do - be it day or night. Hence the splitting of shifts. This means that there can be some tired people on board (especially those who have to rise at 3am) and in between samples people may often be seen sneaking a cat nap on the many bean bags.
That said, some work does have to happen during the day e.g. the moorings that we are recovering have to be collected when it is light,at night time we would not see them bobbing at the surface - it can require some keen eyes to spot them as it is.
However, the CTD, core work and biological sampling can happen day or night, and does. Obviously working on deck at night can have more challenges but the deck is well lit and the laboratories and biological sorting stations have electricity so we can see what is happening.
2. The Antarctica Circumpolar Current (ACC) has a strong flow and the Macquarie ridge must act as a barrier to this in many places.
The flow in the ACC is separated into several branches, or fronts. Macquarie Ridge impedes the two northernmost branches, namely the Subantarctic Front and the Polar Front. Ocean ridges divide the flow, so the Macquarie Ridge pushes the Polar Front south around its southern end, and the Subantarctic Front north until it finds a gap in the ridge.
3. Are the moorings placed upstream or downstream of the ridge?
It’s in these gaps that we put the moorings to measure how much water is flowing in the northernmost branch of ACC, so they aren’t really either upstream or downstream of the ridge.
4. Do you expect to find signs of current change at certain depths? If so do how will you know this?
On each mooring there are several current meters at different depths. Each current meter measures the speed of the ocean, which gets slower as it nears the bottom. Typically in the ACC the bottom of the ocean is moving at about 2 cm s-1 while near the surface it can be over 20 cm s-1.
5. Will eddies or similar be formed?
Ocean ridges are a rich area for ocean eddies to form, and the Macquarie Ridge generates lots of eddies. However, it’s hard to see the eddies that come from the Macquarie Ridge, as upstream of the ridge there is another strong generation area. This means that by the time the ACC gets to the Macquarie Ridge, it is already carrying so many eddies that it’s difficult to see the new ones.
6. Do you expect the current flow to be significantly less downstream of the ridge?
In general we expect the flow, in terms of amount of water, downstream of the ridge to be the similar to the speed through the gaps in the ridge, but the speeds are expected to be lower, because the current broadens out as it moves away from the ridge. This is why oceanographers often talk in terms of transport, as this allows us to combine both area and speed of the current into one number.
Islands in the stream
Ahh, we were just getting used to the more fun questions when along comes some more serious science-related questions. Time then to push through the brain torpor that descends on some of us once the waves have shaken the inside of the skull to a dense mush. The affected organ can now just about organise the body to carry out the functions necessary for taking samples, turning up for mealtimes, and setting the alarm clock to be up in time to...take the next samples, consume the next batch of carbohydrates, proteins and fats...
So to the questions:
7. Because of the ACC do the biologists sample in the lee of the seamounts specifically?
The short answer is No. The seamount sampling programme is not designed to address questions related directly to the influence of the ACC on the distribution/composition of the faunal assemblages on a seamount. Therefore we do not direct our principal sampling to one ‘side’ of the seamount or the other. Instead we randomly sample each seamount (non bias sampling of the entire seamount) with the epibenthic sled in order that we can make valid statistical comparisons of the fauna between seamounts. Our sampling strategy is designed to reveal how the composition of the faunal assemblage may change between seamounts along the Macquarie Ridge, and also between the Macquarie Ridge seamounts and those elsewhere in the region.
It is possible, indeed probable, that the ACC will influence the distribution of organisms between seamounts along the ridge. For example, the current may act as a north-south impediment to the dispersal of larvae of seamount fauna. This potential ‘barrier’ could contribute to any differences we may observe in the assemblages along the ridge. We certainly hope that an analysis of data recovered on this voyage will contribute to our understanding of the relationship between the structure of the Macquarie Ridge, and associated features such as the ACC, and the types of animals found and their distribution.
8. Do you see increased signs of the deep water equivalent of erosion on the upstream side of seamounts?
Whilst the sampling we conduct with the epibenthic sleds is random, when we collect seabed images using the DTIS we try to do so by running a transect from the peak to the base of the seamount down the steepest slope. Unfortunately it is not always possible to obtain transects from both the ‘upstream’ and ‘downstream’ sides of the seamount. Current and wind direction affect the ship’s officers ability to determine the direction in which the ship moves whilst towing the DTIS at the optimum speed of 1 knot. So far we have only managed to obtain images of the ‘two sides’ of a seamount on one occasion. As to whether we can observe a difference in the seabed substrates, from one side of the seamount to the other, which would be indicative of a difference in current regime – well unfortunately a firm yes or no on that will have to wait until we analyse the images in detail. At sea we conduct only a coarse level analysis and natural scientific caution prevents me from committing to a firm answer. Sorry.
9. Would there be more “erosion” than on any other seamount chain because of the ACC?
Not necessarily. There are likely to be seamounts elsewhere in the world that experience the affects of relatively high current flow. Off the top of my head I don’t know where such seamounts may be located, but it’s not hard to imagine that the gross morphology of the seabed and ocean currents interact elsewhere to produce circumstances similar to those experienced by seamounts on the Macquarie Ridge. Perhaps I can ask a question in return – can you identify any likely candidate seamounts areas?
Answer from the Science teacher: I dont know my ocean currents that well but anywhere there is no deep cold current. Maybe in the Carribean? Or the Emperor seamounts? You would have to compare seamounts without active volcanism as that would have a major influence on the topography
10. Is there a change in adaptations or distribution of certain species because of the ACC?
As I’ve already noted earlier – it is quite possible that the ACC will influence the distribution of species between seamounts. But here’s a distribution-related question for you that we could illustrate an answer for (using photographs that we obtained from a seamount yesterday) but only after you’ve attempted to supply a written answer: What changes in the distribution (and associated adaptations) of animals on seamounts would you expect to observe along a depth gradient from the base of the seamount to its peak?
Answer from the Science teacher: Logic suggests that there would be less species and smaller populations as you go deeper but life is always full of surprises so I won't pressume. Also distribution may depend on the presence of any volcanic activity which would warm the water and possibly provide some light in that area.
As for adaptations - where to start? Here are some suggestions:
- because the light goes from being very dim to dark and very dark animals will have special adaptations for detecting prey, such as very large eyes, a possible increase in the size of any olfactory organs, an increase in size or amount of organs or cells detecting vibrations or water movement that could be from prey.
- adaptations for the increased pressure such as organic compounds that allow cellular processes to still work despite the pressure, thick polysaccarides maybe?
- ditto for increased cold, "antifreeze" types of molecules, also unique enzymes or unique amino acid sequences within common enzymes
- reproduction from a distance seeing that it maybe hard to find a sexual partner, maybe some unusual reproductive methods such increased asexual reproduction?
- increasing size or sensitivity of light receiving cells of eyes to cope with decreasing light intensity - from black to pitch black for example
- decreasing need to hide in crevices - there is no reason when your predators can't see you
- more boring colours - no need for visual displays
- adaptations for detecting prey - special organs using fluorescence of some sort
- long arms or tentacles, which may be quite delicate because the current flow is slower deep down.
11. Just so things don't get too serious - do you ever play practical jokes on each other?
Jokes on board - well that would be telling! But one member did regale us with some tales of pinning a colleague's undies on a self made washing line across the deck. Not to mention filling gum boots with icy water...
I have to admit in the past, when I was younger and more, well less mature shall we say, I did play practical jokes on folk. I remember one trip in particular when a watch mate and I used to spend the last hour of our midnight-to-four watch organizing a joke for one of the guys who would soon replace us bleary-eyed. I won’t go into these antics in detail – some of them were funny but as time progressed we moved unnoticed into the realms of cruelty. Being at sea, particularly living strange hours on little sleep, can do weird things to your perception about what’s acceptable and what is not. Suffice it to say we eventually crossed a line and only a great deal of pacifying action saved our skins. Whilst having fun is an essential part of a happy and enjoyable voyage, it should never be achieved at the expense of any one else. It’s a potentially delicate balance – the social dynamic on a ship – it’s best not to do anything that could upset it. We are here on 70m of metal, hundreds of miles from land, no one can walk off.
There is always a lot of banter and teasing on board, a good sense of humour is essential in this line of work. In terms of jokes we had April Fools day and sent one back to shore -- did you get it?