Saturday, 30 August 2008

Neat new toys!

Final post for the evening [if the internet ever comes up again!] - I need to get up early tomorrow to fix the bongo net that got a tear in it and lost a cod-end.

The ship is currently speeding along at just over 11 knots; the wind is blowing a "moderate breeze" on the Beaufort scale, and there's 71m of water under us.

Our current position is here.

My friend Guy Halse has created a very nifty PHP google maps mashup application (click here for working example for this blog - do check it out!) which strips the ship coordinates out of this blog and updates a "cruise track" map of where we've been. It's not totally accurate, as I don't update positions frequently enough (it would be cool to automate this process - the ship is continuously recording several parameters (including location) at once, and it should be easy enough to copy over bits of the log files somewhere...).

Finally, Raymond Roman, chief scientist on this leg of the ASCLME cruise (as he's known in South Africa) or co-cruise leader (as he's known aboard the Nansen) has given me some results from the first CTD line we did on the way towards Madagascar. Apparently, there is nothing particularly suprising about this data - it fits what you'd expect in the region (if you were a physical oceanographer!).

To the left, you'll find an image Raymond gave me that plots some preliminary results. Take a moment to open the full size version by clicking on it (perhaps open in a new window/tab if you know how, you may like to refer back to this page as you look at it). The axes and measurements illustrated are fairly self-expanatory, I think, but I'd like to draw your attention to the "hump" in the data around the 230km mark (look along the bottom axis for distance). This hump is a kind of upwelling, an oceanographic term that describes when deeper water is "lifted" into a shallower position than you would expect it to be (i.e. deep water coming up towards the surface). This can be driven by several processes, but this one is probably driven by eddies - something I hope to make the subject of a future post. An experienced oceanographer can detect within this picture a number of distinct water bodies formed in different parts of the ocean - some from as far away as the poles and the Red Sea.

Upwellings are not only interesting oceanographic phenomena, but they're also biologically important. Deep waters are generally rich in nutrients that phytoplankton (microscopic marine plants) need to grow - think of it as natural fertiliser! The Indian Ocean is fairly poor in nutrients, so this upwelling could be a major source of nutrients and therefore biological productivity. Understanding these processes and their linkages to the ecosystems we're studying is of fundamental importance to management of marine resources - the very reason we're out here doing this work!

In areas with frequent significant upwelling, very rich fisheries can develop, such as off Peru, the coast of California and, closer to us here, the Benguela Current system off the west coast of South Africa, Namibia and Angola. Such rich upwellings are not a feature of this area (and are driven by wind against continental margins, rather than by eddies). However, in a nutrient-poor (oligotrophic) area like the western Indian Ocean, even this more modest upwelling is likely to be important to the whole ecosystem. A later leg of the cruise will focus extensively on "hunting" eddies in the Mozambique channel and doing detailed analysis of the oceanographic conditions on the edges and through the middle of them. How you hunt an eddy is a story for another time...!

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