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12.06.2016 11:17Bottom current measurements: done (Sources & Sinks: A Tale of Coastal Biogeochemistry - BONUS COCOA)

Being the 3rd year of COCOA most of us PhD students have finished or at least reduced their field work and spend their days analyzing and writing up their results. Also me, except that once each month I continue also in the second year to measure denitrification rates in the Tvärminne archipelago. 

This month, it was also time to finish the bottom current measurements I was doing since December at my sandy sediment sampling spot by means of a deployed Aanderaa Seaguard current meter. Sand sediments are usually located in areas of high water energy (bottom currents, wave influence), which transports away the finer sediments leaving only the coarser ones. Strong bottom currents affect both the bottom water layer (benthic boundary layer) and the sediment surface, and can ultimately influence the physical mass transport of matter into the sediment system. A characterization of the bottom current environment at my monthly sampling spot seemed therefore reasonable. :-)

Expecting winter and spring storms to bring peak events of water movement, we deployed the Seaguard (right picture) on a cold and dark December morning....

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...with a 40 kg ground weight (left picture), which doesn´t seem that heavy just looking at its dimensions. However, along the times of deployment, lifting up and re-deployment it took the help of Gösse, Veijo, Jukka, Heikki, Juhanni, Hanna, Matias and Joni to carry it up, down and around. I admit, 40 kg is nothing I can deal with myself, so I was grateful for their help!

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Winter bottom water temperatures around 1°C ate up the battery unfortunately much faster than expected, but with a renewed battery in April we continued measurements until June, where bottom water temperatures had eventually reached nearly comfortable 6°C.  

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Data extracted and biofouling removed it seems time to go back to the desk and a calmer environment without splashing waves..... and Army troops moving around:
This month´s sampling was not only exciting because I got the Seaguard back and heavy waves washed under my rubber suit (seriously?!), but the Tvärminne archipelago was also partly location of the NATO BALTOPS 2016 exercise, which added Navy ships, submarines, helicopters and a hover craft (picture: Tom Jilbert) to the usual sight of  the archipelago islands.  

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Thanks again to everyone helping with the Seaguard deployment and to Juha for the help with building the battery packages!

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