25th International Meeting on Organic Geochemistry IMOG 2011

P-431
Carbohydrate dynamics in Cariaco Basin pore water and
sediments
Melesio Quijada 1 , Armelle Riboulleau 1 , Yann Guerardel 2
1 FRE 3298 CNRS Géosystèmes, UFR des Sciences de la Terre, Université de Lille 1, Villeneuve d'Ascq,
France, 2 UMR 8576 CNRS Laboratoire de Glycobiologie Structurale et Fonctionnelle, Université de Lille 1,
Villeneuve d'Ascq, France (corresponding author:ma.quijada-hermoso@gmail.com)
Carbohydrates are one of the major constituents of
the biomass, and account for a substantial amount of
the total organic carbon (TOC) in water and
sediments in marine environments.
It is often accepted that structural carbohydrates are
rapidly re-mineralized during early diagenesis and do
not make substantial contribution to total organic
carbon in ancient sediments and kerogens.
However some studies has shown that structural
carbohydrates may escape decomposition and
remineralization depending on different factors, such
as paleoproductivity, presence of oxygen in water and
sediments and sedimentation rate (Moers et al. 1994).
Even more, some studies report that once particulate
carbohydrates escape water column in non
oxygenated environments, they may be preserved
within the organic matrix (Cowie and Hedges, 1984).
In our study we investigated the neutral
carbohydrates (NCHO) variation in sediments from
Cariaco Basin, covering a period of time of 135ky.
For that, 15 sediment samples were obtained from
sediment cores 1002 D & E collected on the central
saddle of the Cariaco Basin during the ODP Leg 165.
The NCHO where determined quantitatively after (i)
water extraction to explore pore water carbohydrates
(PNCHO) and (ii) acid hydrolysis to investigate
structural and sediment-attached monomers
(HNCHO).
Monosaccharides were analyzed by GC-FID and
GC/MS after derivatization of aldoses to their
corresponding alditol acetates as described in Eder et
al. (2010).
Sequential hydrolysis (2N, 4N and 6N trifluoroacetic
acid) was used to avoid amino-acids and
carbohydrates glycosidic reaction to form melanoidins
(Quijada et al. 2008). Variations in acid concentration
during hydrolysis yielded different amounts of
individual monosaccharides for the same sample.
These differences are related with differences in
glycosidic bonds behavior during hydrolysis (Mopper,
1977).
The total content of carbohydrates ranged from 0,66
to 2,25 wt% of the TOC in PNCHO and from 5,3 to
11,36 wt% of the TOC in HNCHO. Hydrolysates were
dominated by hexoses in both fractions, and no
correlation with TOC was found.
Nine monosaccharides were identified in the 15
samples. Deoxysugars (fucose and rhamnose) are
apparently more susceptible to 2N TFA hydrolysis.
The contribution of deoxysugars to the TOC (focusing
on rhamnose) is considered to be indicative for the
presence of bacteria.
Hexoses (galactose, manose, glucose) yielded mostly
in the 4N hydrolysis. The large contribution of glucose
is related with the presence of storage
polysaccharides (cyanobacteria accumulate polyglucoses
in certain conditions. Lehmann and Wöber,
1976). Manose and galactose present a large
contribution to the total NCHO budget, corresponding
to structural sugars of microorganisms.
Xylose was more susceptible to 6N hydrolysis in all
samples suggesting to be a building block
carbohydrate, like previously reported for microbial
resistant sheath material (Klok et al. 1984).
We used the hexose to pentose ratio (Oades, 1984)
to investigate the origin of sugars and its variation
with depth. The (galactose + manose) / (arabinose +
xylose) ratio>2 indicated an algae and zooplankton
origin for NCHO during the all period studied.
The NCHO profile present individual variations with
depth depending on their individual reactivity and
resistance to degradation. Some sedimentary facies
are characterized by a rather increase in NCHO
content reflecting environmental control. Globally, the
NCHO content decrease with depth reflecting
heterotrophic degradation and/or preservation via
natural sulfurization (van Dongen et al. 2006).
References:
- Cowie and Hedges (1984). Geochim. Cosmochim.
Acta 48, pp. 2075-2087.
- Eder et al. (2010). Org. Geochem. 41, pp. 580-585.
- Lehmann and Wöber (1976) Arch. Microbiol. 111,
93-97
- Klok et al. (1984). Org. Geochem. 7, pp. 73-84.
- Mopper (1977). Mar. Chem. 5, pp. 585-603.
- Oades et al. (1984). Plant Soil 76, pp. 319–337.
- Quijada et al. (2009) 24 th IMOG. Poster.
- van Dongen et al. (2006) Org. Geochem. 37, pp.
1052-1073.
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