Preproposal for NGI Oil-Related Funding, OBSERVE & UNDERSTAND Clusters
Continuation of “Chemical effects associated with leaking Macondo well oil in the
Northern Gulf of Mexico”
PI’s: Alan M. Shiller and Laodong Guo
Proposed Budget: $120,000
Introduction
Our ongoing work (funded during the first phase of NGI/BP funding) has focused on analysis of
organic matter, trace elements, oxygen and nutrients in the oil spill region. Our working
hypotheses included:
-Selective evaporation and photodegradation of oil components in the water column should be
reflected in variations in the optical properties based on light absorbance and EEM fluorescence.
-The presence of spilled oil in the water column should alter the partitioning of organic carbon,
shifting the size distribution into more colloidal and particulate phases after selective
evaporation, photodegradation and oxidation of oil components.
-Distributions of Ni and Cu will be affected by input from crude oil, though V will not be
because of its higher natural levels. Distributions of Mn and Fe will be affected if the presence of
oil affected dissolved oxygen levels. Dispersants may also affect metal distributions if the
presence of complexing sulfonic acids is significant.
-The presence of oil will exacerbate hypoxia problems by limited air-sea exchange of oxygen
and contributing to respiration. Alternatively, the oil may limit phytoplankton growth which then
diminishes the supply of natural organic matter fueling hypoxia.
Work to date
We obtained samples from the R/V Pelican and R/V Walton Smith cruises to the spill area in
May, from a Mississippi Sound/Bight sampling campaign in August, and from the R/V Cape
Hatteras cruise in October. The types of analyses we are engaged in includes:
Pelican cruise: Water column DOC, optical characterization of DOC, dissolved and colloidal
trace elements, PAH’s, nutrients.
Walton Smith cruise: Same suite as for the Pelican cruise.
Mississippi Sound/Bight: Water column DOC, DIC, optical characterization of DOC, dissolved
and colloidal trace elements, oxygen, nutrients.
Cape Hatteras cruise: Water column DOC, DIC, methane, optical characterization of DOC,
stable C isotopic composition of DOC and DIC, dissolved and colloidal trace elements, oxygen,
nutrients. Sediment samples are also available for Fe, Mn, and Ba analysis. We also collected
samples for collaborators looking at Ra isotopes and Hg.
We have also obtained samples of oil from the wellhead and dispersant (both via BP) and field
samples of weathered oil.
To date we have made the following observations:
a) PAH’s are enriched in samples closest to the wellhead and show characteristics compatible
with a Louisiana light sweet crude origin as well as some evidence of fractionation of
components from wellhead to deep plumes to surface waters.
b) Trace element analyses to date show no evident anomalies in Ba, Cr, Fe, Mn, or V. However,
we are awaiting further work to determine Cu, Ni, and Pb.
c) Methane was essentially gone from the water column within 100 km of the wellhead during
the October cruise. It was also not enriched in core top waters. Nor were there substantial oxygen
anomalies observed in the water column.
d) Both wellhead oil and dispersant were characterized in terms of optical properties, such as
spectral slope, and fluorescence EEM spectrum. Both oil and dispersant show unique Ex/Em
characteristics and could be identified in natural seawater samples.
e) DOC data show no elevated values even in those seawater samples with obvious oil
fluorescence signatures.
f) Samples collected from Mississippi Sound/Bight are being processed for the measurements of
stable C isotopic composition.
So far, we have contributed to one publication (Diercks et al., 2010) and have a number of
presentations scheduled for the Fall AGU meeting and other venues such as the NSF oil spill
conference in New Orleans in Nov. 2010 and the Bays and Bayous Symposium in Dec. 2010.
Objectives of Proposed Continuation Work
Initial funding has allowed us to collect a large suite of samples and to analyze them for some
parameters (as outlined above). However, the limited funding has not allowed us to complete all
analyses. Furthermore, additional opportunities have arisen which will require further support. In
particular we propose the following work plan:
1. Analysis of PAH from water and sediment samples collected in October 2010. Sediment
samples were collected that have an oil smell or showed an oil sheen on overlying waters.
Similarly, some water samples showed a slight elevation of hydrocarbon fluorescence.
Identification and quantification of this material is needed. We will collaborate with Patrick
Louchouarn of Texas A&M Galveston on this work.
2. Analysis of Fe, Mn, and Ba in sediment cores collected in October 2010. Sediment cores
showed a dark layer on top which is likely a normal oxidized sediment layer. Analysis of Fe and
Mn can confirm this. Analysis of Ba will test for the presence of drilling muds.
3. Continued analysis of trace element samples from the water column as well as experiments
with oil addition to water. We have analyzed our water samples for some key indicator elements
(e.g., V from oil and Ba from drilling mud). However, we have yet to analyze them for Cu and
Ni, which have been suggested to be enriched in the water column following a past oil spill.
Also, we still need to do experiments in which we add oil to clean seawater and examine the
effects on metal concentrations.
4. 13C in dissolved inorganic carbon (DIC). Methane has a very negative 13C value. During the
spill, extremely high levels of methane were observed in the water column, but were not present
during our October 2010 cruise. If the methane were oxidized, it should therefore affect the 13C
of seawater DIC. We do have a few preserved samples from the October cruise that could be
analyzed for this.
5. Analysis of DOC, DIC, CDOM and fluorescence EEM. A large number of samples of DOC
and DIC have not yet been measured. In addition, measurements of both CDOM and fluo-EEM
and data processing, such as spectral slope calculation and PARAFAC analysis, are time
consuming. While we have analyzed selected samples for presentations, funding for further
sample analysis and data processing are needed. Furthermore, we would like to use the flow
field flow fractionation technique to characterize the colloidal size distribution in selected
samples to test our hypotheses.
6. 13C in particulate organic phase. We have also collected POM samples during Mississippi
Bight/Sound sampling trips and during the R/V Cape Hatteras cruise. We expected that if there
is oil present in the water column, it is likely to adsorb onto particle phases and become part of
POM pool, resulting in a shifting in stable C isotopic composition of the POM samples. This
will be highly complementary to the stable isotopic composition measurements in the DIC pool,
which will also be done during this project.
7. Sample collection during summer 2011. Dr. Kevin Briggs (Naval Research Laboratory) has a
week of ship time next summer. He has offered to return us to the oil spill area for continued
follow-up sampling. This would be valuable for two reasons. First, we could examine the
recovery of the sediments that were contaminated with oil. Second, we can examine the water
column under what are likely to be more normal conditions for comparison with our recent data.
8. We will also participate in field work early next year in the Mississippi Sound and Bight
which will repeat transects we participated in this year. We will also work with the
Yeager/Brunner/Briggs group who are proposing a cruise to the spill area.
Approach
We will continue to utilize the same methods as in the first phase of this funding.