Sept. 19th - Oct. 10th 2000
Claudia Sprengel (University Bremen)
Markus Geisen (The Natural History Museum)
Coccolithophorids are a diverse group of marine phytoplankton belonging to the algal class Prymnesiophyceae. Their cell surfaces are covered by minute external calcite scales (coccoliths) which, when shed or post-mortem, form an important part of fine-grained deep-sea sediments and, therefore, are extensively used in palaeontological and palaeoceanographic studies. A basic understanding of the modern ecological affinities of coccolithophorids is essential for the interpretation of fossil coccolith assemblages in marine sediments. Their distribution in sediments is relatively well known, but information about their abundance, ecology and physiology in surface waters is rare. Samples have been collected from the ships surface water pump system, from bottle samples collected with the CTD and with a surface plankton net. These samples will be analysed in collaboration with co-workers in the EC funded TMR network CODENET (COccolithophoriD evolutionary biodiversity and Ecology NETwork).
Filter samples (CS, MG)
A total of 79 surface water samples have been taken from the ships
membrane pump system at a depth of 5m. Additionally 18 stations up to 10
depths between 10 and 200m have been sampled from bottles attached to a
CTD.
At each site 2-4 litres of water per depth were filtered for on cellulose
nitrate filters (47mm diameter, 0.8µm pore size) using a vacuum pump.
Duringfiltration thefilteres were rinsed carefully with water to prevent
the crystallisation of salt. Afterwards the filters were dried at45°C
for 12h.
First analysis of the filters with a Leitz light microscope revealed
a strong dominance of diatoms over coccolithophorids in the nearshore stations
with upwelling and highly diverse assemblages in the open ocean stations.
The samples will be used to determine coccolithophorid assemblage diversity
and absolute cell density as well as cell and coccolith morphology with
both light- and scanning electron microscopy (Natural History Museum, University
Bremen).
Alkenone samples (CS)
Certain species of Coccolithophorid are able to build up long-chain
(C37, C38, C39) carbon compounds called alkenones, which consist primarily
of di- and triunsaturated methyl and ethyl ketones. Laboratory experiments
show that the degree of unsaturation in the ketone series biosynthesized
depends on growth temperature, a physiological response observed for classical
membrane lipids (Uk37 index; Brassell et al., 1986). The calibration curve
of the long-chain ketone series versus growth temperature depends on the
investigated geographic area and accurately predicts unsaturation patterns
in natural particulate materials collected from oceanic waters of known
temperature. In addition, Uk37 has proven to be a useful proxy for past
sea surface temperature in low to mid latitudes:
T(°C) = (Uk37 - 0,039)/0.034 (Prahl and Wakeham, 1987)
3 samples of 36-56 litres have been taken from the ships sea water
pump system at a water depth of approximately 5 metres. Samples were filtered
through a 47 mm diameter glass fibre filter. Future work will include extraction,
separation and gas chromatography-mass spectrometry (GC-MS) analysis of
the alkenones (University Bremen).
Living plankton communities (MG)
13 samples of concentrated seawater have been collected using a plankton
net with 5µm mesh width. Samples were either taken from the CTD rosette
(at depths between 10-40m) or from the surface water (5-15m) with a 5µ
and a 10µm plankton net. Isolation of coccolithophorids for laboratory
culture will take place at the Natural History Museum and the Univerity
Caen (France). Future work will include molecular genetics on monoclonal
strains of the cultured species (Alfred Wegener Institut, Bremerhaven)
to establish phylogenetic relationships. Additionally physiological experiments
are planned to obtain data on growth rates and intraspecific morphological
variation of strains grown at various light, temperature and nutrient levels
experiments (Natural History Museum, University Caen).
Cell ultrastrucure observations in TEM thin sections will be performed
at the University Caen).
Fine fraction calcite (MG)
For fine fraction calacite analyses seawater from the ships sea water
membrane pump system was prefiltered with a 90µm mesh sieve and filtered
on a polycarbonate filter filters (140mm diameter, 0.45µm pore size).
On 18 stations 10 to 72 litres of sea water have been filtered. The samples
will be analysed at the Free University (Amsterdam).
Acknowledgements
Markus Geisen wishes to convey his appreciation and thanks to
the constituent bodies of the Meteor cruise M48 for inclusion in leg 4.
This work will contribute to the EC funded TMR network CODENET.
Please send comments, complaints, or contributions to Markus Geisen