Natural Organic Matter in Freshwater and Marine Environments
As human activity has initiated a global warming of the planet since the
beginning of industrialization, the ability of the ocean to act as a sink
for anthropogenic CO2 needs to be estimated. Land biota and oceans surface
represent the main CO2 sink from the atmosphere. However, half of the terrestrial
organic matter formed is mineralized and transferred back to the atmosphere,
and the limits of the oceanic net uptake of CO2 and its reversibility are
uncertain, even if it has restricted CO2 increase in the atmosphere.
The main source of organic carbon in the oceans is primary productivity,
which reduces carbon dioxide to dissolved and particulate organic matter
in surface waters.
In turn, riverine dissolved and particulate organic matter is a significant
source of organic carbon to continental margins. Particulate organic matter
(POM) in the surface oceans is transferred to the deep waters where it
is partially remineralized and partially buried in the sediment. It is
believed that dissolved organic matter is a by-product of the remineralization
of organic matter in sediments and may flux out of sediments and affect
the composition and concentration of oceanic DOM significantly. The processes
regulating the distribution and transformation of natural organic matter
in aquatic environments are not well known. In the geochemistry group,
several researchers currently study the formation and transformation of
natural organic matter in freshwater and marine environments. Their main
objective is to determine the physico-chemical properties of terrestrially-
and marine-derived natural organic matter and study their reactivity. Some
of the current research projects are presented below.
Physico-Chemical Properties of Humic Substances (J. Ritchie,
E. M. Perdue)
Coming Soon...
Bioavailability of Riverine Natural Organic Matter (J.-F.
Koprivnjak, E. M. Perdue)
Coming Soon...
Characterization of Marine Natural Organic Matter (P. Sannigrahi,
E. Ingall)
On a global basis, more organic carbon is dissolved in the ocean than is
contained in all land plants and marine organisms combined. Furthermore,
the amount of dissolved organic carbon (DOC) in the ocean is comparable
in size to the amount of carbon found in the atmosphere as carbon dioxide.
Thus, changes in the sources and sinks of marine dissolved organic matter
(DOM) may significantly influence levels of the important greenhouse gas
CO2 in the atmosphere. The objective of our research is to characterize
marine natural organic matter in order to gain a better understanding of
this dynamically and quantitatively important reservoir in the global C
cycle. For this purpose, we are studying dissolved and particulate
marine organic matter isolated using tangential-flow ultrafiltration from
the USJGOFS stations ALOHA (Pacific ocean) and BATS (Atlantic ocean).
The primary analytical technique being used is solid state 13C NMR spectroscopy,
which is an excellent non-destructive tool for obtaining molecular level
information. 13C NMR analyses are being carried out using a Bruker DSX400
spectrometer at the NMR
center located in the School
of Chemistry and Biochemistry at Georgia Tech.
We are focussing on studying the compositional variations in dissolved
and particulate organic matter with location and depth in the ocean and
also comparing the two size fractions. Preliminary results reveal
that dissolved and particulate organic matter are compositionally different
in terms of NMR analyses which leads us to conclude that the two size fractions
are
not simply formed by physical transformations (such as coagulation and
decomposition). Bulk plankton and sediment samples have also been
collected from these sites. NMR analyses coupled with elemental and
other compositional analyses of this material are being used to address
questions regarding composition, sources and cycling of marine organic
carbon.
Marine Dissolved Organic Phosphorus (P. Sannigrahi, E. Ingall)
Phosphorus is a limiting nutrient for marine primary productivity. Understanding
the cycling and the composition of P is of major significance
for the global ocean. Phospholipids, a significant fraction of dissolved
organic phosphorus, has yet to be fully understood and characterized.
One
our research goals is to measure and identify these compounds.