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DATA
DISTRIBUTION MAPS
ALL
DSDP/ODP SITES
SULFATE
DATA
MANGANESE
DATA
IRON
DATA
NITRATE
DATA
METHANE
DATA
CHEMICAL
PROFILE MAPS
SULFATE
PROFILE MAP
METHANE
PROFILE MAP
BACK
TO URI ASTROBIOLOGY SUBSEAFLOOR DATABASE
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The map section is broken
into two categories. The first
category contains maps showing the geographic and depth distribution
of available porewater chemical data for sulfate, iron, mangnese and
nitrate. For details follow the links under "Data Distribution Maps"
on the navigation bar to the left.
The maps in this section are intended to give the user an idea of the
data that are available via the Ocean
Drilling Program (ODP) and Deep
Sea Drilling Program(DSDP) /
ODP archives at the National
Geophysical Data Center (NGDC ) and this web site. The first map
simply shows the locations of all DSDP/ODP sites from Leg 1 through
Leg 185 (we are in the process of updating all maps through Leg 191).
The chemical maps illustrate the geographic distribution of available
data. These maps only indicate the maximum depth at which a measurement
was made, they do not contain any information regarding the value of
that measurement or its quality. For more information on the data used
to create all maps on this web site, visit the Data Information page.
Sulfate (SO4-2) is the most abundant terminal electron acceptor in sediments
deep beneath the seafloor. Because porewater SO4-2 was consistently
measured throughout the DSDP and ODP there is a wealth of data available.
We have used a subset of the available data to create a global map illustrating
the character of subsurface SO4-2 profiles.
Nitrate, manganese oxide (MnO2) and iron oxides (e.g. Fe2O3 and Fe3O4)
are electron acceptors that typically yield much higher free energies
of reaction than SO4-2. Consequently, they're generally assumed to be
exhausted at much shallower burial depths than SO4-2 (e.g., Froelich
et al, 1979). Although porewater Mn+2 concentrations have not been consistently
measured on DSDP or ODP legs , enough data is available to show that
MnO2 reduction and, by inference, active MnO2- reducing bacteria, can
occur at burial depths as great as 60 meters in open-ocean sediments
where dissolved SO4-2 concentrations are relatively stable throughout
the sediment column (see Site 321). Porewater concentrations of NO3
and Fe+2 have been too rarely measured on DSDP and ODP cruises to characterize
subseafloor patterns of nitrate and iron reduction.
The second category contains maps showing
some details for the sulfate and methane data. These maps are under
the "Chemical Profile Maps" links on the navigation bar to the left.
These maps were created from our edited database. We removed several
hundred sites because we deemed the data of poor quality or poor resolution.
We also removed data points that we considered to be "bad". This exercise
consisted of plotting and examining nearly 1,000 profiles and sorting
the good from the bad. Once that was accomplished, a program was
used to classify the profiles. A sulfate profile could be placed
into one of the following categories:
- sulfate stabilizes at
some point downhole
- sulfate decreases continuously
to the bottom of the hole
- sulfate decreases to background
(2 mM) and stays there
- sulfate decreases to background
then increases farther down the hole
- the sulfate profile is
complicated
Stabilization is defined
as +-2mM. So, going down the hole, if two adjacent sulfate measurements
differ by less than +-2mM, the upper depth is chosen as the depth of
stability. Then, if every deeper sulfate measurement differs by less
than +-2mM relative to that first point, the profile is declared stable.
Decreasing to zero means that the sulfate concentration decreases to
background (<2 mM). The concentration may then increase again if
flow or diffusion from brine at a greater depth brings in sulfate (See
site 680 biogeochemical profile, for example). If the concentration
reaches 2.5 mM above background, then the site is classified as number
4 above.
Category 5 is a catch all for profiles that don't fit 1 through 4.
Categories 1, 3, and 4 are plotted on the sulfate map.
Methane data are only available
for ODP sites.
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