Monday, 27 October 2008
If its Monday .. we must be heading east ...again!!
So what are we doing and where are we?
We are slowly moving northwards towards the gap between the Nazareth and the Saya de Malha Bank (see a previous blog). The last 2 weeks have seen us sailing back and forward and forward and back along acoustic lines, which have been set up to study the fish stocks over the plateau as well as improve our knowledge of the seafloor in this region. It’s pretty amazing to see the seafloor rise from 3000 m to 50 m in about 8 miles! Think of climbing Table Mountain from Cape Town centre and then triple the distance up!!.
As we move northwards we have been measuring sea surface temperatures and you can see from the map on the right that there is a gradual increase from 24 to 26° C with distance north. Dotted along the plateau are sampling stations where we collect bottles of water for oxygen, salinity, nutrient, chlorophyll and zooplankton concentrations from top to bottom...in some places this takes minutes because the seafloor is only 30 m deep!.
..and last week we started receiving data from the drifters thrown in at the start of the cruise. The 2 southern drifters certainly seem to be in pole position! travelling over 50 cm per second westwards we suspect that they have been caught up in a strong current channelled by the gap to the north of Mauritius.
The other 2 drifters on the east side of the plateau were only deployed at the end of last week and we think that they will move south rather than over the plateau.. and that’s an interesting fact because it suggests that the Mascarene Plateau acts as a huge barrier to all surrounding flow. This certainly raises questions on whether the ecosystem varies between the deep ocean and the plateau and how water masses may differ from one region to another. ..hopefully by next week we will have some more data to prove or disprove various theories.. .. so keep posted and we’ll soon update the blog on our progress north!
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