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CYCLOPS-7 Real-Time
Data Aids Study of Basin Scale Dynamics of Open Ocean Ecosystems
The Atlantic Meridional Transect (AMT) programme (1995 - present)
takes advantage of the biannual passage of the BAS research vessel
James Clark Ross from the UK (50°N) to the Falkland Islands (50°S)
to study basin scale patterns and dynamics of open-ocean planktonic
ecosystems (more information can be found at http://www.amt-uk.org).
An interest in open-ocean plankton has led to our understanding
of the importance of various groups of cyanobacteria along the AMT
transect: the dominance of small (< 0.002 mm) prochlorophytes
in the subtropical gyres, the importance of small Synechococcus
in equatorial and temperate waters and the vital nitrogen-fixing
role of large (> 2 mm) colony-forming Trichodesmium in equatorial
waters. Small cyanobacteria are usually detected through the collection
of discrete water samples and flow cytometric analysis, where cell
size and phycoerythrin fluorescence are used to identify the different
groups. Trichodesmium is collected with nets (or buckets!) and microscopic
examination of large water-volumes gives their abundance. A technique
that detects both is highly advantageous, allowing targeted sampling
and a better understanding of the ecology of marine cyanophytes.
During the 14th AMT cruise (April - June, 2004) we took advantage
of the opportunity to use one of the new CYCLOPS-7 fluorometers
set to detect phycoerythrin (a pigment mostly found in cyanobacteria).
Due to their insolubility in water, the cyanophyte pigments phycoerythrin
and phycocyanin cannot be extracted or eluded with standard pigment
analysis and thus our knowledge of the full pigment suite of open-ocean
communities has been limited. The use of the CYCLOPS-7 will provide
us with a better understanding of the pigments, community structure
and optical properties of the water-column.
Having sailed through the rough waters off the Falkland Islands
("roaring 40s") and into the South Atlantic Gyre we were able to
attach the CYCLOPS-7 fluorometer to our standard CTD package and
gain real-time profiles of phycoerythrin and cyanophyte distribution.
The appeal of using new technology on the AMT cruises is that the
interdisciplinary nature of the cruise allows novel measurements
to be related to other more traditional oceanographic measurements
(e.g. chlorophyll a concentration, rates of carbon fixation, nutrient
concentrations) as well as more specialised ones (e.g. Dimethylsulphide
concentration).
Although the results are preliminary and still being validated (frozen
and preserved samples to be analysed) several interesting results
have come about from the use of the Cyclops-7. Phycoerythrin was
highest in waters with high chlorophyll-a concentration, shallow
nitraclines (defined as the 1 mM nitrate contour), and high rates
of carbon fixation. Preliminary cell counts show that the source
of the phycoerythrin changes with latitude: from Synechococcus and
Trichodesmium in equatorial waters to Synechococcus and eukaryotic
flagellates (Cryptomonads) in northern temperate waters.
Over the next few months, pigment analysis will allow us to compare
phycoerythrin fluorescence to other phytoplankton pigments: previous
knowledge of the distribution of such pigments indicates that phycoerythrin
fluorescence shows a very similar distribution to the photoprotectant
cyanophyte-related pigment, zeaxanthin. Analysis of preserved water
samples may allow the phycoerythrin signal to be related to Trichodesmium
abundance, as it was noticed during the cruise that when Trichodesmium
was present in the water-column the Cyclops-7 signal was highly
spiky. Analysis of particle absorption samples and attempts to calibrate
the fluorometer will allow us to estimate the concentration of phycoerythrin
and its ratio to other phytoplankton pigments.
Many thanks to Turner Designs and RS Aqua (especially Charlotte
Deeley) for the opportunity to use the CYCLOPS-7, which will become
a regular feature on our CTD package during future cruises (AMT-15
sails September 2004!). I would also like to thank fellow AMT scientists
for access to their preliminary data from the cruise which has aided
in the interpretation of the CYCLOPS-7 signal so far (Dr Mike Zubkov,
Ms Jane Heywood and Ms Katie Chamberlain) and Jon Short and Dougal
Mountifield (UKORS) for technical support.
Dr Alex Poulton (aljp@soc.soton.ac.uk)
Research Fellow: Atlantic Meridional Transect (AMT) programme
Southampton Oceanography Centre, UK.
http://www.amt-uk.org
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