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One of the
most important problems in marine geochemistry is the transformation
and fate of organic matter produced by phytoplankton
and other organisms in the water column. We have been studying
the carbon cycle in the Cariaco Basin, a large permanently anoxic
basin on the continental shelf of Venezuela, because the sediments
in the Cariaco preserve a high resolution record of deposition
of material, including organic carbon, over more than 100,000 years.
The value of the sediment record is enhanced if we understand the
origin and transformations that sinking material experiences in
the system.
In the CARIACO
(Carbon Retention in a Colored Ocean) program, I am collaborating
with Gordon Taylor of SoMAS, Frank
Muller-Karger
of the University of South Florida and Robert Thunell of the
University of South Carolina, along with scientists from the
Fundación
la Salle and the Universidad de Oriente in Venezuela. The SoMAS
component of the study is using a variety of techniques (including
measurements of potential oxidants such as sulfur species (elemental
sulfur, thiosulfate, sulfite) and forms of manganese and iron,
as well as fatty acid concentrations and turnover rates (Scranton),
and measurements of bacterial abundance and production and chemosynthesis
(Taylor)) to determine how bacterial activity is influenced by
carbon supply (primary production, particle flux, chemoautotrophic
production under suboxic conditions), and oxygen content. We
have recently been funded to extend the microbiological aspects
of the
project (see Gordon Taylor’s webpage). At present, the
CARIACO program has been underway for over 8 years.
Our results
show that respiration and fermentation are elevated
both in surface waters and near the oxic/anoxic interface,
and that these processes respond to changes in carbon supply
caused
by changing fluxes of carbon from the surface waters. However
although chemoautotrophic production results in large inputs
of organic
matter at mid-depth (dark fixation of CO2), it does not seem
to respond directly to changes in productivity. Rather, intrusions
of oxygenated water from outside the basin seem to strongly
influence carbon cycling at the interface. The time series program
has
been
funded until 2008. Our next goal is to try to assess the extent
of spatial variability in chemistry and microbiology within
the basin, as we would expect the effect of intrusions to vary
a
lot as we move away from the sill area.
I also continue
a long-standing interest in methane geochemistry. We have studied
methane within
the Hudson River, in seasonally
and permanently anoxic basins, and most recently in the waters
of the North Atlantic on and near the US North-East continental
shelf. In this latter study, we are investigating the role
of seeps and vents, and possibly of destabilizing gas hydrates,
in controlling
water-column methane concentrations. The methane concentrations
in a number of areas over the shelf and slope are elevated,
suggesting
flux of fluids containing methane (and probably other important
chemical species) from the sediments. Most recently, this
project resulted in a cruise on the Atlantis and a dive in the
ALVIN.
Selected Publications
Ho, T.-Y.,
G.T. Taylor, Y. Astor, R. Varela, F. Muller-Karger and M.I.
Scranton.
2003. Vertical and temporal variability of redox
zonation in the water column of the Cariaco Basin: implications
for organic carbon oxidation pathways. Marine Chemistry, 86, 89-104.
Astor,
Y, F. Muller-Karger and M.I. Scranton. 2003. Seasonal and interannual
variation in the hydrography of the Cariaco Basin,
Venezuela: Implications for basin ventilation. Continental Shelf
Research., 23, 125-144. Taylor, G.T.,
J. Way and M.I. Scranton. 2003. Planktonic carbon cycling and
transport in surface waters
of the highly urbanized
Hudson River Estuary. Limnology and Oceanography, 48, 1779-1795.
Taylor,
G.T., J. Way, Ying Yu and M.I. Scranton. 2003. Ectohydrolase
activity in surface waters of the Hudson River and western Long
Island Sound estuaries. Marine Ecology Progress Series. 263,
1-15.
Madrid,
V.M., G.T. Taylor, M.I. Scranton, and A.Y. Chistoserdov. 2002.
Phylogenetic diversity of prokaryotic communities in the
anoxic zone of the Cariaco Basin. Appl. Environ. Microbiol.,
67, 1663-1674.
Ho, T.-Y.,
M.I. Scranton, G.T. Taylor, R.C. Thunell, R. Varela and F. Muller-Karger.
2002. Acetate cycling in the water
column
of the Cariaco Basin: Seasonal and vertical variability and implication
for carbon cycling. Limnology and Oceanography, 47, 1119-1128. Muller-Karger,
F., R. Varela, R. Thunell, M. Scranton, R. Bohrer, G.Taylor,
J. Capelo, Y. Astor, E. Tappa, T.-Y. Ho, M. Iabichella,
J.J. Walsh and J.R. Diaz. 2000. The CARIACO Project: Understanding
the Link between the Ocean Surface and the Sinking Flux of Particulate
Carbon in the Cariaco Basin, EOS (Transactions of the American
Geophysical Union), 81, 529 & 534-535. Taylor, G.T.,
M.I. Scranton, M. Iabichella, T.-Y. Ho, R.C. Thunell and R. Varela.
2001. Chemoautotrophy
in the redox transition zone
of the Cariaco Basin: A significant source of midwater organic
carbon production. Limnology and Oceanography, 46 148-163. Muller-Karger,
F., R. Varela, R. Thunell, M. Scranton, R. Bohrer, G. Taylor,
J. Capelo, Y. Astor, E. Tappa, T.-Y. Ho and J.J. Walsh.
2001. The annual cycle of primary production in the Cariaco Basin:
Implications for vertical export of carbon along a continental
margin. Journal Geophysical Research, 106, 4527-4542. Scranton,
M.I., Y. Astor, R. Bohrer, T.-H. Ho and F. Muller-Karger. 2001.
The effect of subsurface water mass intrusions on the geochemistry
of the Cariaco Basin. Deep-Sea Research, 48, 1605-1625. DeAngelis,
M.A. and M.I. Scranton. 1993. Fate of methane in the Hudson River
and Estuary. Global Biogeochemical Cycles, 7, 509-523. Scranton,
M.I., P. Crill, M.A. deAngelis, P. L. Donaghay and J.McN. Sieburth.
1993.The importance of episodic events in controlling
the flux of methane from an anoxic basin. Global Biogeochemical
Cycles, 7, 491-507.
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last modified on Friday, March 19, 2004 by George
E. Carroll |
