Acyclic Lipids in Amazon Shelf Waters
Estuarine, Coastal and Shelf Science,
Volume 50, Issue 2,
V. O. Elias, J. N. Cardoso and B. R. T. Simoneit
Summary of
Points:
·
Acyclic lipids
were analyzed for dissolved and particulate material from surface water of the
Amazon continental shelf to correlate the direct inputs with diagenetic processes of the organic matter and to assess
the differences in compound distribution patterns of the samples.
·
The
dissolved samples contained n -alkanes with an
unusual even-to-odd carbon number predominance <C30and CPIs
(carbon-preference index) varying from 0·35 to 1·22 (C17¯C22range)
and 0·52 to 1·33 (C23¯C28range). Carbon number maxima (Cmax) occurred
at C18and/or C22Pr/Ph ratios varied from 0·28 to 2·62.
The n -alkanes in particulate samples ranged
from C15to C35(CPI17¯22from
0·15 to 0·50 and CPI23¯28from 0·52 to 1·12) with Cmaxat
C18and C20, while pristane and phytane on the other hand were present in particulate
matter only at trace amounts and hence Pr/Ph ratios could not be calculated.
·
Both
dissolved and particulate phases showed saturated C14, C16and
C18alkanoic acids and an unsaturated C16:1acid as major
components. The chemical composition of these acyclic
lipids indicates an origin from micro-organisms, probably diatoms.
·
Although
minor, a contribution of components derived from plant waxes are more abundant
in the particulate phase with profiles indicating a remineralized
residue. Plant waxes are effectively biodegraded in the shelf waters during
downstream transport in the Amazon.
·
Furthermore,
the Pr/Ph ratios calculated for the dissolved samples indicate that the organic
matter in the surface of the highly turbid waters passed through an anaerobic
stage. The differences in the acyclic hydrocarbon profiles of the dissolved and
particulate phases show that organic inputs are preserved differently in
smaller and larger particles.
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