Sub-Surface Water Trajectories from USF Ocean Circulation Model
400 m
Motivation for cruise:
- Pelican cruise
suggested subsurface
oil to the SW
-Ocean circulation
models suggested limb
of subsurface oil should
be entrained in the
currents to the NE
1000 m
-Trajectories to the NE
has the potential to
impact the continental
slope and shelf
Goals of cruise:
-Search for subsurface
oil to the NE of DWH
wellhead
Weatherbird II Cruise May 22 - 28, 2010
Surface and Subsurface Sampling Sites
Ship track
Oils of the Deep-Water Horizon: At the Wellhead & On the Surface
Intensity
Intensity
DWH -Riser Fluid/M252Oil
April 28, 2010
• Typical GC trace of hydrocarbons from light
crude oil (BP M252)
• Smooth abundance distribution, L & HMW
n-alkanes, >C7 to C-42,
• Thermally mature oil
C22
Surface Oil
May 28, 2010
• Altered GC trace from DWH BP M252 crude oil
• Loss of LMW hydrocarbons including alkanes
<C18
• Smooth abundance distribution, n-alkanes
C-18 to C-42, peak at C-22
13
• δ C individual n-alkanes range 5‰, -26 - -31‰
• Characteristics of mildy Biodegraded M252 Oil
C28
C18
n-alkanes
Time
Comparison of Surface Oil with Clean Sub-Surface (1000 m) Particles
C22
Intensity
Surface Oil
C28
C18
n-alkanes
Time
DSH01- 1000 m Particulates
Clean Water, No Hydrocarbons
Florida Waters
Comparison of Deep Water Column Particulates
and Florida’s “Clean” Deep Waters
C32
Site 07- 400 m Particulates
• Unusual distribution for modern POM
C28
C28
Site 08- 400 m Particulates
C37
C32
C37
C32
• Traces of algal inputs, C-17 to C-20
• HMW n-alkanes not from plant inputs
- No odd/even predominance
- Trace of C-23.C-25 and C-27
• Complete loss LMW n-alkanes
Site 09- 1000 m Particulates
• Smooth abundance distribution >C-30
C28
Site 01- 1000 m Particulates
Clean Water
• Peak at C-32, not biological
• Looks like physically fractionated
(processes at wellhead including
addition of dispersants) and/or
biodegraded oil
Comparison of n-alkanes in 400 m and 1000 m Particulates
C32
Site 07- 400 m Particulates
30
20
C37
10
C28
0
C28
30
C32
Site 08- 400 m Particulates
20
C37
10
•All particulate
samples have a HC
distribution
characteristic of
physically
fractionated and/or
biodegraded oil
• HCs range from
~200 to 750 ppb
C24
0
• 1000 m sample has
~2x amount of HCs
wrt 400 m
C32
70
Site 09- 1000 m Particulates
50
30
10
C37
C28
• HC gradient in
water column infers
a source from depth
Weatherbird II Cruise May 22 - 27, 2010
Surface and Subsurface Sampling Sites
Sampled Area of
Biodegraded Oils
Comparing Degree of Degradation:
DWH BP-M252 Oil, Surface Oil & Subsurface Oils
DWH - Riser Fluid/Oil
Degradation Sequence:
-Alkanes before aromatics
-LMW before HMW
-Short before long-chain
Signal
April 28, 2010
No biodegradation
C22
Signal
30
20
Degraded Surface Oil
May 28, 2010
Site
07-biodegradation
400 m Particulates
mild
C18
C32
C28
10
C37
C28
0
Signal
C28
C32
Site 08- 400 m Particulates
mild-moderate biodegradation
C37
C24
Signal
C32
Site 09- 1000 m Particulates
Moderate biodegradation
C28
Time and/or Temperature
C37
Comparison of Samples
- See progressive loss of
short-chain n-alkanes
- Biodegraded oils suggests
active microbial consumption
(see δ15N signals associated
with hydrocarbons)
-Dispersants could be cause
of selective loss of LMW
compounds
- Physical chemical reaction
of petroleum emitted
Initial Conclusions: Organic Geochemistry
• Biodegraded oil, as micron sized particles (invisible to naked eye) was found
at multiple depth below the surface and in deep water samples.
• The molecular organic geochemistry of the deep water sample at 1000 m was
identical to the 400 m samples.
• The deep sample at 1000 m had higher hydrocarbon concentrations (~2-fold)
than the shallower 400 m sub-surface.
• Origins of hydrocarbon are likely from a deep-sea source
• With additional research cruises and with information from BP on the oil
composition and its concentration coming out the wellhead we can:
-determine whether the sub-surface oil is from natural seeps or from
the leaking Deep Water Horizon.
-calculate length of time these potentially toxic molecules, such as
saturated and aromatic hydrocarbons, can persist in
the environment.