Page 1 - Basso_Neururer_et_al

2nd Swiss Geoscience Meeting, Lausanne, 2004

Biogeochemistry of coralline red algae

Basso, D.(1), Neururer, C.(2), Spezzaferri, S.(2) & Grobéty, B.(2)

(1)University of Milano Bicocca, Piazza della Scienza, 4, 20126 Milano, Italia. daniela.basso@unimib.it; (2)University
of Fribourg, Department of Geosciences, Geology and Paleontology, Ch. Du Musée 6, 1700 Fribourg, Switzerland.
christoph.neururer@unifr.ch, silvia.spezzaferri@unifr.ch, bernard.grobety@unifr.ch

Compositional variations ob- within the talli, with the ultimate trated at the cell wall. Occasional
served in biogenic carbonates have goal to relate these variations to the large cells within the Mg-poor bands
been investigated since the middle different environments the samples show the same Mg-rich rim.
of the last century as potential indi- come from.
cators of paleoenvironmental change References
(Chave, 1954). The periodically The analyses were done on a Adey W.H., MacIntyre I.G., 1973.
changing composition of long-lived scanning electron microscope type
hermatypic corals and mollusks, iden- XL30 Sirion FEG (FEI). Optimum Crustose coralline Algae: a re-
tified as tissue banding, allows recon- imaging conditions for high-Mg cal- evaluation in the geological
struction of temperature and salinity cite were obtained by the following sciences: Geol. Soc. Of Am.
variations of surface water masses preparation and measuring methods: Bull., 84: 883-904.
and climate-ocean events (Cole & The coralline alga was incorporated Basso D., 1992. Le rodoficee calcaree
al., 1993; Jones, 1983). However, the in an electrically conductive phenol dei fondi mobili circalitorali del
restricted geographical distribution of resin for polishing. A slight edging Mar Tirreno: le “rodoliti” attuali
reef-building corals and of the mol- with basic solution accentuated the in una prospettiva paleoecologica.
luscan species considered so far limits visibility of the algae cells. The car- PhD Thesis, 139 pp., Dip.to Sc.
the application of the method. bon coating thickness for an optimum Terra, Univ. Studi, Milano.
ratio between electrical charging and Chave K.E., 1954. Aspects of the
Coralline algae are very com- loss of phase contrast is at 10nm. A biogeochemistry of Magnesium.
mon on temperate shelfs, from the scintillation type centaurus back- 1. Calcareous marine organisms.
intertidal down to the lower limit of scattered detector is used for phase Journal of Geology, 62: 266-599.
the photic zone (Adey & MacIntyre, contrast imaging. Chemical analyses Cole J.E., Fairbanks R.G., Shen G.T.,
1973). They are long-lived and have were made with an EDAX x-ray 1993. Recent variability in the
a very wide geographical distribution. micro analytical system specially de- Southern Oscillation: isotopic
Their cell walls are made of high-Mg signed to measure light, non conduc- results from a Tarawa Atoll coral.
calcite. Early observations on the tive and beam sensitive materials. Science, 260: 1790-1793.
periodicity of growth bands and on Halfar J., Zack T., Kronz A., Zachos
the relationship between Mg content The measured material volume, J.C., 2000. Growth and high-
and temperature date back to Lem- using an accelerating voltage of 12 resolution paleoenvironmental
oine’s monography (1911) However, KV and a beam current of 100nA, is signals of rhodoliths (coralline
only recently could electron micro- about 1.2 um3. This is small enough to red algae): a new biogenic
probe analyses provide evidence of obtain accurate full standard quantita- archive. Journal of Geophysical
periodical cycles in the Mg/Ca ratio tive EDS results from a single algae research, 105: 22,107-22,116.
(Moberly, 1968; Basso, 1992; Halfar cells. The element maps, however, Jones D.S., 1983. Sclerochronology:
& al., 2000). have an even better resolution. reading the record of the
molluscan shell. American
We have investigated the biogeo- As preliminary results we have Scientist, 71: 384-391.
chemistry of Lithothamnion coral- obtained high-resolution chemical Lemoine, M.me P., 1911. Structure
lioides Crouan & Crouan from 4 dif- maps for the elements Ca and Mg. anatomique des Melobesiées.
ferent locations e.g. Baie de Morlaix These elements vary within each Ann. Inst. Océanogr. De Monaco,
(Atlantic Ocean, water depth 12 m), thallus according to growth bands. II (1), 215 pp. the Frontal Pennine
Marettimo (Sicily, southern Tyrrhe- As observed by Basso (1992), the Thrust near Briançon, Western
nian Sea), Elba and Pontine Islands bands with larger cells display higher Alps. Eclogae Geol. Helv. 92,
(northern and central Tyrrhenian Sea) magnesium content than those with 171-181.
with water depths between 40 and 45 smaller cells. The high resolution
m to trace eventual changes in the maps, however, show that the high
distribution of chemical elements Mg-bands are chemically not homo-
geneous, but that the Mg is concen-

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