1. science
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OCE - MARINE GEOLOGY AND GEOPHYSICS
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Woods Hole Oceanographic Institution
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NSF RIDGE 2000 Postdoctoral Fellowship: Development of Raman
spectroscopy for in situ quantification and speciation of hydrothermal
Fe and Mn particulates and sediments
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266 Woods Hole Rd., MS 7
Applied Ocean Physics and Engineering
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Woods Hole, MA 02543
United States
508-457-2006
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High Degree
Yr of Degree
Telephone Number
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PhD
2000
508-289-3740
[email protected]
ScD
1988
508-289-2853
[email protected]
PI/PD NAME
Sheri N White
CO-PI/PD
Chris German
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Page 1 of 2
NSF RIDGE 2000 Postdoctoral Fellowship: Development of Raman spectroscopy for in situ
quantification and speciation of hydrothermal Fe and Mn particulates and sediments.
Project Summary
Co-PIs: Sheri N. White & Christopher R. German
Woods Hole Oceanographic Institution, Woods Hole, MA 02543
Postdoctoral Fellow: John A. Breier
Currently at: The University of Texas at Austin, Austin, TX 78712
The goal of this proposal is to develop methods, at WHOI, for in situ Raman spectroscopy to investigate
the fate of hydrothermal Fe and Mn discharged to the oceans. When Fe and Mn enriched hydrothermal fluid
mixes with seawater, polymetallic sulfides precipitate and seawater trace elements are scavenged onto Fe
and Mn oxyhydroxides. These processes are important because approximately 10,000 liters of deep-ocean
seawater is entrained with every liter of venting hydrothermal fluid. Thus, the equivalent of the entire ocean
volume is exposed to co-precipitation reactions with polymetallic sulfides and Fe-Mn oxyhydroxides on
timescales that are similar to global thermohaline circulation. In situ investigations of Fe and Mn precipitates
are now required to better understand the extent and effects of Fe and Mn scavenging on seawater chemistry.
Laser Raman spectroscopy is capable of chemical speciation as well as quantitative chemical analysis
of solids, liquids and gases. A sea-going Raman system has been built. A strength of Raman spectroscopy,
is that it allows for in situ, non-invasive, non-destructive measurements of Fe and Mn compounds. The
proposed work consists of laboratory experiments and a minor engineering development effort to determine
the requirements for interfacing a Raman spectrometer to a sediment trap. The major set of laboratory
experiments will focus on characterizing the temperature, pressure, and composition effects that will likely
be encountered when collecting in situ Raman spectra of Fe and Mn mineral particulate. The engineering
development effort will be related to this aspect of the research since this goal is the most readily achievable.
Two secondary sets of experiments will be run to determine the feasibility of making in situ measurements
of suspended and dissolved Fe and Mn phases at hydrothermally relevant concentrations.
On a RIDGE 2000 cruise, I became interested in German’s (co-PI) work in developing the use of in situ
chemical sensors on AUVs. I have since become very interested in using in situ sensors and sensor networks
to study large scale processes. The development and application of in situ sensors is a natural merging of
my marine science and engineering backgrounds. My five years as an engineer in the Navy’s Naval Reactors
engineering department gave me experience and exposure to a wide variety of engineering solutions for
mechanical, electrical, nuclear, and fluid problems. WHOI’s history of developing innovative engineering
solutions to oceanographic science appeals to my interests in both of these fields. This project would aid
me in effectively pursuing my future research goals concerning both short and long term biogeochemical
processes associated with the exchange of water between the ocean, seafloor, and continental margins.
Intellectual Merit– This project will develop the methods necessary to characterize hydrothermal Fe and Mn
phases in situ – where they are stable – and follow the long term temporal changes in Fe and Mn chemistry
as vent systems age. In situ laser Raman spectroscopy of Fe and Mn minerals, will provide oceanographers
a new method for investigating hydrothermal chemistry and its effects on the global oceans.
Broader Impacts– The main facets of this proposal are the training of a post-doctoral fellow and development of in situ sensors. Upon successful development, these in situ instruments would also represent an
obvious addition to any long-term mid-ocean ridge observatory and could be anticipated to broadcast novel
in situ chemical data to researchers and the public alike. To disseminate information to the public, students,
and the greater oceanographic community, we will develop a website on the Chemical Sensor work undertaken at WHOI, and develop modules on Raman spectroscopy instrumentation and sediment traps for the
Ocean Instruments website (http://www.whoi.edu/science/instruments/).
Project Summary–1
NSF RIDGE 2000 Postdoctoral Fellowship: Development of Raman spectroscopy for in situ
quantification and speciation of hydrothermal Fe and Mn particulates and sediments.
Project Description
Co-PIs: Sheri N. White & Christopher R. German
Woods Hole Oceanographic Institution, Woods Hole, MA 02543
Postdoctoral Fellow: John A. Breier
Currently at The University of Texas at Austin, Austin, TX 78712
1 Introduction
I propose to develop methods, at WHOI, using in situ Raman spectroscopy to investigate the
fate of dissolved Fe and Mn discharged from hydrothermal plumes to the oceans. Fe and Mn are the
most abundant heavy metals on earth but are typically present in only trace amounts in the oceans
due to their low solubility in such an oxidizing environment. In reducing hydrothermal systems,
by contrast, dissolved Fe(II) and Mn(II) are present in much higher concentrations, typically 10e6
fold greater than the open ocean. It is the reactions that take place when hydrothermal fluids enter
the ocean that determine the net effect of hydrothermal circulation at mid-ocean ridges upon global
ocean chemical budgets. Two key processes have been identified in hydrothermal plumes that modify the gross flux to the oceans: a) co-precipitation of Fe and other chalcophile elements to form
polymetallic sulfide phases immediately when the fluids enter the ocean (a “quenching” effect); b)
co-precipitation of trace elements with, and adsorption of dissolved metals onto, freshly-formed Fe
and Mn oxyhydroxide phases as the reduced vent-fluids progressively entrain, and become turbulently mixed with, more oxidizing ambient ocean waters.
The mixing process in (b) is important because for every liter of vent-fluid emitted from hightemperature hydrothermal vents, approximately 10,000 liters of deep-ocean seawater is entrained
into the resulting buoyant hydrothermal plume that is emplaced 100–300m above the seafloor on
a timescale of approximately 1 hour after vent-fluid expulsion from the seabed (Lupton, 1995;
German and Von Damm, 2003). Thus, while the entire volume of the global ocean may only be
circulated to depth within young oceanic crust and raised to temperatures close to 400◦ C on a timescale of ca.10Ma, this same volume of the global ocean is cycled through hydrothermal plumes
much faster, on a timescale of 1–10,000 years. Accordingly, the equivalent of the entire ocean volume is exposed to co-precipitation reactions with polymetallic sulfides and Fe-Mn oxyhydroxides
on timescales that are similar to global thermohaline circulation. The possibility exists, consequently, that processes active in hydrothermal plumes may have a direct effect in regulating the
global composition of seawater.
Previously, empirical studies have identified bulk elemental compositions of various metal
phases within hydrothermal plumes and their underlying sediments. But those achievements remain rather unsatisfactory because they lack information concerning the processes by which such
uptake proceeds and, hence, the predictive capabilities arising from those studies are of only limited potential. More detailed investigations of Fe and Mn precipitates are now required in order to
better our understanding of the extent and effects of these powerful scavengers on seawater trace
chemistry. Techniques are required that can observe not only the composition but also the nature of
Project Description–1
the phases present and the bonding within them, both for laboratory studies (e.g. down-core within
sedimentary records of hydrothermal discharge taken from active – and ancient – vent-sites) and in
situ, in the deep ocean, in rising buoyant plumes where particles first form and within and beneath
non-buoyant hydrothermal plumes, as the bulk of hydrothermal Fe and Mn flux is deposited to the
seafloor.
Of course, both Fe(II) and Mn(II) oxidation are also important energy sources for chemosynthetic microbial communities in the water column as well as at the seafloor (e.g. Edwards et al.,
2003; Zbinden et al., 2004). Once again, however, simple measurements of elemental concentration shed only limited light on how such symbioses proceed: the hydrothermal supply of dissolved
Fe and Mn varies with time and between vents; speciation and oxidation rates vary with seawater
redox conditions as well as vent fluid composition; and the potential for non-equilibrium phases
to be particularly important raises the possibility that all ex situ Fe and Mn measurements may be
particularly biased towards thermodynamically stable phases.
Laser Raman spectroscopy is a type of vibrational spectroscopy which provides a compositional
and structural “fingerprint” of a molecule. It is capable of chemical speciation as well as qualitative
and quantitative chemical analysis of solids, liquids and gases. A sea-going Raman system has
been built (Brewer et al., 2004; Pasteris et al., 2004) and deployed to analyze gases (White et al.,
in press); synthetic and natural clathrate hydrates (Hester et al., in press; Peltzer et al., 2004); and
minerals, fluids, and bacterial mats at hydrothermal vents (White et al., 2004, in prep.). Raman
spectroscopy has great potential to perform in situ, long-term monitoring of hydrothermal vent
systems as a part of a cabled or moored observatory, or an AUV.
A particular strength of Raman spectroscopy, is that it allows for in situ, non-invasive, nondestructive measurements of Fe and Mn compounds. This allows for reliable measurements of
thermodynamically unstable phases to be made, in situ, and for long term variations in hydrothermal Fe and Mn compounds/speciation as well as concentrations, to be monitored. A particular
advantage would be the ability to track chemical transformations of Fe/Mn-rich material within
evolving hydrothermal plumes — both rising above a vent-site as well as during dispersal through
the water column and settling to the water column. Such an approach would greatly improve our
understanding of: i) the impact of Fe and Mn cycling upon global ocean chemistry; ii) the extent
to which Fe- and Mn-oxidation energy can fuel (micro)biogeochemical cycling within the water
column above hydrothermal vent-sites; iii) the chemical evolution of hydrothermal systems themselves; iv) the mechanisms by which depositional records of the history of hydrothermal discharge
are laid down and preserved in deep-ocean sediments.
1.1
Relevancy to the Ridge 2000 Science Plan
The work proposed here will address perhaps the least investigated of the Ridge 2000 program’s
key questions (Ridge 2000 Program Science Plan, 2005):
Q7. How and to what extent does hydrothermal flux influence
the physical, chemical, and biological characteristics
of the overlying ocean?
Project Description–2
2 Background
2.1
Chemisty of Hydrothermal Fe and Mn
Fe and Mn, the two most abundant heavy metals in the earth’s crust, are only trace constituents
in seawater yet their enrichment in deep sea hydrothermal fluids has a significant effect on global
ocean chemistry. High temperature hydrothermal vents or black smokers are acidic and highly reducing. They contain high concentrations of sulfide, Fe(II), and Mn(II) and other metals that when
mixed with cold, oxic seawater initiate a series of redox reactions that results in the precipitation
of a variety of Fe sulfides and sulfates and Fe and Mn oxides as well as numerous other minerals
(German and Von Damm, 2003). Precipitation occurs in different stages and varies depending on
vent fluid composition and ambient seawater pH and redox state (Field and Sherrell, 2000; Statham
et al., 2005).
When H2 S concentrations are high relative to Fe(II), black Fe sulfides such as pyrite precipitate immediately upon discharge giving black smokers there characteristic color (German and
Von Damm, 2003). Larger precipitates settle immediately while smaller precipitates and a large
dissolved fraction of the initial Fe(II) continues to rise with the buoyant plume (Mottl and McConachy, 1990). The reduced, dissolved and particulate Fe is oxidized as it rises. The smaller Fe
sulfide particles remaining in the plume undergo oxidative dissolution which adds colloidal Fe(III)
back into solution (Field and Sherrell, 2000). Oxidation may be completed in the buoyant plume or
may continue into the nonbuoyant plume depending on the pH and redox conditions of the ambient
seawater and potentially the speciation of the Fe phases. In the young oxygen rich waters of the
north Atlantic Fe oxidation occurs within approximately 2 minutes of discharge, oxidation in the
Indian ocean takes 2.3 hours (Statham et al., 2005), and Fe oxidation can take from 3.3 to >40 hrs
in the eastern Pacific (Field and Sherrell, 2000; Statham et al., 2005). As Fe and Mn precipitate they
scavenge a variety of trace elements from seawater (German et al., 1991a; Cave et al., 2002, 2003;
Chavagnac et al., 2005). These compounds are removed from the oceans to the extent these Fe
and Mn precipitates settle and are buried. This scavenging of trace elements is significant because
ocean mixing through deep sea hydrothermal plumes is thought to be relatively rapid occurring
once every 4–8 thousand years on the same time scale as deep ocean water turnover (Statham et al.,
2005).
There are many questions that remain concerning the fate and effects of hydrothermal Fe and
Mn. Fe and Mn concentrations within hydrothermal plumes are temporally and spatially variable
due to plume turbulence and vent evolution (Lupton, 1995; Von Damm et al., 1995). Fe and Mn
speciation is diverse involving numerous phase transitions, changes in redox state, kinetically controlled reactions, meta-stable phases, colloidal aggregations, and interactions with organic matter
(Lilley et al., 1995). Existing ex situ methods of hydrothermal particle analysis including ex situ
mass spectroscopy, X-ray diffraction, scanning and transmission electron microscopy, and energy
dispersive X-ray spectroscopy (e.g. Ludford et al., 1996; Buatier et al., 2004) are ultimately limited
to a small set of samples.
Project Description–3
2.2
Raman Spectroscopy
The Raman effect is essentially a wavelength shift in radiation scattered from molecular bonds.
It was discovered by Raman and Krishnan (1928). Raman scattering theory is covered in detail
in Nakamoto (1997) and Ferraro et al. (2003). Many practical applications of this relatively weak
effect (1 in 108 photons are Raman scattered) developed rapidly after the advent of the laser (Adar,
2001) which provides a powerfull, stable, monochromatic excitation source. Raman spectra provide compound specific compositional and structural information. Raman spectroscopy is capable
of both qualitative and quantitative, nondestructive molecular identification of solids, liquids and
gases. It can measure multiple species simultaneously and requires no reagents or consumables,
making it ideal for in situ long term deployments. Raman spectroscopy analyzes targets remotely
by exciting the target with a laser and observing the backscattered radiation, making it ideal for use
in extreme environments such as high temperature hydrothermal vent fluids. Standoff optics allow
measurements to be made from behind pressure windows and at remote distances up to 66 meters in
air (Sharma et al., 2002). Modern Raman spectroscopy instruments use a laser for excitation; holographic transmissive gratings and notch filters for high signal to noise ratios in the backscattered
light, and charge coupled devices (CCDs) to image the entire Raman spectrum simultaneously
(Adar, 2001; Owen et al., 1998). Current systems are very amenable to miniaturization which
would reduce their power consumption as well as size and weight. A small Raman system is even
being developed for use on a Mars rover for in situ soil and rock analysis (Haskin et al., 1997; Wang
et al., 2003).
In addition to being ideal for long-term, in situ operation in extreme environments, Raman
spectroscopy is also well suited to making measurements in the ocean because water is a relatively
weak Raman scatter (Williams and Collette, 2001). Attenuation in water is minimized by using
excitation wavelengths in the visible spectrum (350–700 nm). A typical excitation wavelengths
used for ocean work is 532 nm. Since the intensity of Raman scattering is inversely proportional
to λ4 , the 532 nm wavelength produces the stronger scattering intensity than the industry-preferred
wavelength of 785 nm. One drawback to the 532 nm wavelength is that it can produce fluorescence in organic compounds which decreases the signal to noise ratio. However deep-sea Raman
measurements to date have not been significantly affected by this problem (White et al., 2005).
If fluorescence is an issue for specific analytes then longer excitation wavelengths can be used to
reduce this effect (Ferraro et al., 2003).
Several oceanographic applications of Raman spectroscopy are decades old. Since the Raman
spectrum of water is temperature dependent, the temperature of the surface ocean (<100 m) can
be measured remotely (via aircraft Raman) from the shape of the Raman water spectra (Leonard
et al., 1977, 1979; Becucci et al., 1999). The intensity of Raman water spectra has also been
used to determine the depth of laser penetration to correct airborne fluorescence measurements of
phytoplankton density (Bristow et al., 1981). Interestingly, these applications make direct use of
waters weak Raman spectra. One of the goals of White (co-PI) is to use the Raman spectra of water
as a reference for determining absolute concentrations in aqueous solutions.
More recently, interest has grown in using Raman spectroscopy to make chemical measurements in the coastal ocean and deep sea (Kronfeldt and Schmidt, 1999; Battaglia et al., 2004; Pasteris et al., 2004). The Deep Ocean Raman In Situ Spectrometer (DORISS) built by Brewer et al.
Project Description–4
(2004) has already been used to make a variety of in situ measurements of gases, solids, clathrate
hydrates, and biomolecules. In situ measurements of the composition of natural gas venting in
Guaymas Basin and along Hydrate Ridge have shown the gas to be 97% CH4 (White et al., 2003;
Peltzer et al., 2004). Raman spectroscopy has been used in ocean experiments to measure the rate
of CO2 dissolution (White et al., in press) and to determine the structure of synthetic and natural
clathrate hydrates and the gas molecules they contain (Peltzer et al., 2004; Hester et al., in press).
Barite and anhydrite minerals have been successfully identified at hydrothermal vents as have the
aragonite and calcite phases of CaCO3 in seafloor shells (White et al., in prep.). And lastly, elemental sulfur in an S8 configuration along with beta carotenes have been detected in seafloor bacterial
mats (White et al., in prep.). In addition to the DORISS system, a deep-sea system using 785
nm excitation has recently been deployed by Battaglia et al. (2004) but results have not yet been
published.
These deep sea deployments have proven the versatility and value of in situ Raman systems.
At the same time they have highlighted the need for a better understanding of the effects of temperature, salinity, pressure, and sample composition on Raman spectra. To date deep sea Raman
applications have mainly been qualitative with the exception of White et al. (in press) which measured CO2 dissolution rates.
Laser Raman spectroscopy is well suited to the qualitative chemical identification of solids,
gases, and liquids. Matching collected spectra with that of standards enables rapid and unambiguous identification including distinguishing polymorphs by structural variations and hydration state
(Pasteris, 1998). Covalently bonded gases and complex solutes dissolved in liquids can also be analyzed (e.g. Murata et al., 1997; White et al., in press) though simple ionic electrolytes (e.g. Na+ ,
Cl+ ) cannot as no molecular bond is present.
Raman spectroscopy can also be used to make quantitative measurements. Raman scattering
intensity is proportional to analyte concentration as in:
I r = IL · σ · η · P · C
(1)
where Ir is the Raman scattering intensity (peak area), Il is the laser intensity, σ is the Raman
scattering efficiency which is analyte specific and a function of temperature and pressure, η are the
collective instrument constants including collection efficiency and optical throughput, P is the path
length, and C is the analyte concentration (Pelletier, 1999). However Equation 1 is impractical to
apply directly because instrument constants, particularly those that affect irradiance to the sample
volume, are difficult to measure or maintain constant (Wopenka and Pastersis, 1986). Instead two
separate methods are used to quantify the relative chemical proportions within a sample: the ratio
of Raman intensities is used for gases and liquids and “point counting methods” are used for solids.
In the case of gases, liquids, and dissolved solutes in liquids, relative quantifications are made
by looking at Raman scattering intensity ratios of two or more analytes simultaneously as in:
I1 σ2
C1
=
C2
I2 σ1
(2)
where the terms η and P from Equation 1 are the same for all analytes and drop out. This is the
method used by White et al. (in press) to measure the CO2 dissolution rate in seawater in an at sea
Project Description–5
experiment. In this way only the Raman scattering efficiencies need to be characterized in order to
quantify relative concentrations.
In the case of solid samples, such as rocks, sediments, and particulates, “point counting methods” are used in which many measurements are made (100 for Wang et al. (2003)) and the number
of observations of analytes are used to determine their relative proportions (Haskin et al., 1997;
Wang et al., 2003). In this method Raman bands are used to identify species; Raman intensities are
not used to infer concentration. In the case of rocks and sediments at rest, a spatial point counting
method is used where the Raman probe is linearly transversed across the sample surface making
measurements incrementally; in the case of Wang et al. (2003) measurement spacing is 12.3µm.
The WHOI Laser Raman Lab setup (described in the Facilities statement) has an xyz stage for conducting point count sampling. Since suspended sediments are in motion a temporal point counting
method may instead be possible. This would be analogous to the spatial method but the Raman
probe would be stationary and the sample targets in motion.
2.3 In situ Chemical Sensors
There is a widely recognized need for chemical sensor development to support long-term, in situ
studies of coastal and deep sea processes (Gallagher and Whelan, 2003; Daly et al., 2004; Ocean
Observatories Initiative Science Plan, 2005). Our understanding of many oceanographic processes
is currently limited by our inability to sample data with sufficient frequency and over time periods
of appropriate length. Chemical sensors will enable us to do this and fulfill the potential of AUVs
and ocean observatories to provide spatially and temporally rich information.
A group of scientists and engineers in WHOI’s Deep Submergence Lab are focussing on the
development of in situ chemical sensors including mass spectroscopy, laser induced breakdown
spectroscopy, and Raman spectroscopy. White (co-PI) is working on Raman spectroscopy and has
a laser Raman laboratory setup and high pressure optical cells to simulate deep sea, hydrothermal
conditions.
3 Research Plan
This project consists of three sets of related laboratory experiments and a minor engineering
development effort to determine the requirements for interfacing a Raman spectrometer to a sediment trap. The primary set of laboratory experiments and major focus will be on characterizing
the temperature, pressure, and composition effects likely to be encountered while collecting in situ
Raman spectroscopy measurements of settled Fe and Mn mineral particulates. The engineering
development effort will be related to this aspect of the research since this goal is the most readily
achievable.
The secondary focus will be to run experiments to determine if it is possible to make in situ
measurements of suspended Fe and Mn phases at hydrothermally relevant concentrations using
normal Raman spectroscopy. The detection limits for suspended Fe and Mn minerals phases will
be determined along with the effects of temperature, pressure, composition, and particle velocity.
Project Description–6
If detection limits are too high to use existing Raman systems for in situ applications then the
experimental results will be used to determine the requirements for a Raman system with sufficient
sensitivity.
A third focus will be to run experiments to determine if it is possible to make in situ measurements of dissolved Fe and Mn phases at hydrothermally relevant concentrations using SERS.
Laboratory experimentation is needed in order to determine if a SERS response can be obtained
from important dissolved Fe and Mn phases such as FeOH+ and MnOH+ . Experimentation will
involve trying different combinations of electrode materials (e.g. Ag, Au, Pd), surface roughness,
and electric potential (Shelton et al., 1994; Bonin et al., 2000; Pergolese et al., 2005).
All experiments will use a laboratory model laser Raman spectrometer from Kaiser Optical Systems, Inc. with a remote probe head and microscope attachment that is equivalent to the DORISS
II instrument so that these experimental results will also apply to the DORISS II system. High and
low temperature/ high pressure optical cells capable of 300 ◦ and 400 bar will be used to simulate
deep sea hydrothermal conditions. Both the laser Raman system and the high pressure optical cells
are described in the Facilities statement.
3.1
Determining Representative Fe and Mn Phase Composition and Concentrations for Experimentation
It is important that the concentrations and component mixtures used in the laboratory experiments accurately reflect the range of mineral assemblages found in nature. While there is extensive
data on the elemental composition of hydrothermal particulate (e.g. German et al., 1991a; Ludford
et al., 1996; Cave et al., 2002), the mineralogy is less well characterized. Using a combination
of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray
spectroscopy (EDX), Mottl and McConachy (1990) characterized the mineralogy of hydrothermal
plumes and metalliferous sediments near 21◦ N EPR. The most abundant phases were the Fe sulfides: pyrrhotite, pyrite, sphalerite, and chalcopyrite. Using similar methods Buatier et al. (2004)
was able to characterize the Mn oxides from the flank of the Juan de Fuca Ridge as poorly crystallized phyllomanganates, todorokite, and birnessite. A variety of Fe oxides may be present in the
neutrally buoyant plume as well as colloidal Fe(III) aggregates. These Fe sulfides and Fe and Mn
oxides (Table 1) are likely to be the most abundant Fe and Mn minerals encountered in hydrothermal systems. For these phases the settling flux and suspended concentrations are greatest for the
Fe sulfides which precipitate nearest the vent. Fe and Mn oxide suspended concentrations in the
buoyant plume will be much lower and may range from 2 to 100 mg/L (Mottl and McConachy,
1990).
Since the available mineralogical data is sparse it would be prudent to accurately characterize
the mineralogy of hydrothermal sediments and plume particulates from as many vent sites as possible. Samples with which to start are available at WHOI and at the National Oceanographic Centre,
Southhampton, UK through German (co-PI/coadvisor). A set of sediment trap samples is available
from 9◦ N EPR and a replicate sediment sub-core is available from the Rainbow vent site (Cave
et al., 2002). It may be possible to obtain additional plume particulate samples using in situ pumps
Chris German is procuring. All of these samples will be mineralogically characterized using the
Project Description–7
XRD and XRF facilities at WHOI and then used as natural mineral assemblages for the laboratory
experiments.
Table 1: Relevant Fe and Mn minerals.
Fe sulfides
Fe oxides
pyrrhotite
ferrihydrite
pyrite
hematite
sphalerite
magnetite
chalcopyrite goethite
3.2
Mn oxides
todorokite
birnessite
Experiments to Characterize Fe and Mn Mineral Particulates
Laboratory Raman measurements of the Fe and Mn minerals listed in Table 1 will be obtained
from thin sections and prepared precipitates first in ambient rooms conditions then under a range
of temperature, pressures(e.g. Gillet et al., 1993), and salinities. Environmental parameters will be
varied individually to determine there individual effects. This will serve two purposes 1) it will
verify the Raman scattering cross sections for these minerals and 2) determine the effect of environmental factors on the Raman spectra. The Raman bands of sulfide, sulfate, and oxide minerals
generally occur in the ranges of 200-500, 950-1100, and 300-700 cm−1 (Wang et al., 1994). The
Raman bands for some of the specific minerals in Table 1 are 465 and 373 cm− 1 for pyrrhotite and
338, 521, 678, and 686 cm− 1 for pyrite (Pasteris, 1998; Wang et al., 2003; Battaglia et al., 2004).
Once the environmental effects on the Raman spectra have been confirmed, I will experimentally determine the detection limits for the different minerals in a settled sediment mixture. I will
grind up specimens of the solid minerals or precipitate them from solution and mix them with different percentages of CaCO3 until the detection limit is reached. I will repeat this last step using
pyrite vice CaCO3 and then again using organic matter collected from surface plankton tows vice
pyrite. Running the sediment mixtures using these three different major components will determine if sediment compostion has a significant effect on the Raman spectra of the different minerals
and also if the organic matter content of the suspended particulate is likely to induce fluorescence.
One of the goals of this set of experiments is to use the spatial “point counting method” to make
quantitative measurements of relative concentrations (e.g. Wang et al., 2003).
3.3
Measurements of Suspended Fe and Mn Particulates
In this set of experiments, I will determine the detection limits for the different minerals in an
aqueous suspension. Working with one mineral at a time in ambient air conditions, I will mix the
powdered minerals in small volumes (100 mL) of water until the detection limit is determined.
Once the detection limit is determined I will repeat the experiment in the pressure cells at varying
salinities, temperatures, pressures, and sediment stirring rates. I will then repeat the experiments at
ambient air conditions but with binary mixtures of sediments in seawater. During this set of experiments a temporal “point counting method” approach will be used to quantify relative compositions.
Project Description–8
Figure 1: An example of a SERS spectra for a 100
ppm CN− in a 0.1 M KCl solution (Shelton et al.,
1994). Using a 5x25x1 mm Ag plate polished with
1.0 and 0.3 µm aluminum oxide paper as the working
electrode, Shelton et al. (1994) was able to quantitatively measure aqueous cyanide down to a detection
limit of 10 ppb. The electrode potential was swept
from 0.0 to -1.2 V at 5 mV/s and the maximum Raman intensity was taken as the measurement. Response was linear from 100 ppm to 10 ppb. From
Shelton et al. (1994).
Based on whether or not the detection limits are low enough for in situ hydrothermal applications I will either continue with further experimentation on suspended particulates or evaluate what
potential improvements would most likely enable in situ Raman measurements of suspended particulate. If the system is able to make in situ measurements I would conduct additional experiments
to determine what the effects of different sampling optics would have on the results.
3.4
Measurement of Dissolved Fe and Mn Phases
The last set of laboratory experiments would involve developing a method for using Raman
spectroscopy to measure dissolved Fe and Mn compounds at hydrothermally relevant concentrations. Based on thermodynamic modelling using PHREEQC (Parkhurst and Appello, 1999) with
the chemistry of 21◦ N EPR (Von Damm et al., 1995) as an example the most abundant potential
target species are FeCl+ , MnCl+ , FeOH+ , and MnOH+ . The concentrations of these compounds
in vent fluids may be no more than 1-100 µM, therefore successful measurements using normal
Raman spectroscopy are unlikely. However the combination of Raman spectroscopy with surface
electrodes is capable of increasing the Raman signal up to 8 orders of magnitude. This technique is
referred to as surface enhanced Raman spectroscopy (SERS) and has been used to measure a variety
of compounds down to ppb concentrations (Williams and Collette, 2001; Smith et al., 2001).
Taking each species separately, I would start by finding solution concentrations for which a
normal Raman signal can be obtained. At these concentrations I would experiment with different
Ag and Au electrodes (e.g. Anderson, 2000; Pergolese et al., 2005) to determine what if any SERS
enhancement is possible. Surface roughness, electrode construction, and electric potential (Shelton et al., 1994) will all be varied to determine their influence on the SERS response. Once the
best combination of electrode material, construction, surface roughness, and electric potential are
determined I will lower the solution concentration to determine a new detection limit.
If environmentally relevant concentrations of dissolved Fe and Mn can be detected using SERS,
additional experiments would be necessary to determine signal stability, detection latency, electrode hysteresis, and matrix, temperature, and pressure effects. In addition electrode reproducibility, durability, and temperature and corrosion resistance would be evaluated to determine the best
electrode for extended deployment in hydrothermal environments.
Project Description–9
3.5 Engineering Development of a Raman Spectrometer/Sediment Trap Interface
Sediment traps (e.g. Khripounoff and Alberic, 1991) are robust, proven oceanographic tools.
Instrumenting a sediment trap with an in situ Raman spectrometer would significantly increase
the amount of data collected during sediment trap deployments. It is also feasible with existing
technology and if such a system were funded it could be built in short order. Deploying an in situ
Raman spectrometer in this fashion would also circumvent the potential problem of trying to detect
relatively low suspended sediment concentrations.
Alternatively but also potentially complimentary, it may be possible to develop an automated
Raman spectrometer/particulate filtering system to filter,collect, and analyze a series of suspended
hydrothermal particulate samples. A similar system was developed by Sholkovitz et al. (2001) for
an autonomous aerosol sampling/XRF elemental analyzer designed for ocean buoys. This aerosol
analyzer could autonomously collect 24 aerosol samples on filters and perform XRF analysis of
the samples. The filters were on a rotating carousel. Using a similar scheme an automated in situ
pump system could collect hydrothermal particulate on a filter which a Raman spectrometer could
then analyze. Such a Raman spectrometer/particulate filtering system could be used to analyze
samples in the neutrally bouyant plume and if deployed above a Raman spectrometer/sediment trap
the sinking particulate fraction and the compositional differences between suspended and sinking
particulate composition could be determined.
If deployed at a Ridge 2000 integrated study site such as the Lau Basin or Endeavor such a
system would enable long term temporal tracking of changes in the composition and dispersal
of hydrothermal particulates. In the case of the Raman spectrometer/sediment traps, an initial
short term proof of concept deployment during a cruise would also determine to what extent the
composition of sediment trap samples are altered by oxidation, oxidative dissolution, or microbial
activity.
In this part of the study I will use the results of the initial experiments to automate (with software: HoloGRAMS, GRAMS/AI and Matlab) the conversion of acquired Raman spectra to relative
mineral concentrations. I will work with White (co-PI) to automate spectra acquisition, spectra intensity correction, periodic calibration, instrument monitoring, data storage, and communication
interfaces with ocean observatories. I will also determine the most appropriate sampling rate,
power requirements, power source, and design a method for interfacing a laser Raman system to
a Khripounoff and Alberic (1991) style sediment trap and evaluate the feasibility of an automated
Raman spectrometer/particulate filtering system.
4 Postdoctoral Fellowship
4.1
Career Goals and Professional Development
I graduated from Texas A&M University in 1995 with a Bachelor of Science degree in mechanical engineering and was subsequently commissioned as an officer in the U.S. Navy. During five
years of active duty, I trained and worked as a reactor design engineer, managing and coordinating
Project Description–10
Figure 2: Sediment trap developed by Khripounoff and Alberic (1991) for collecting sinking particulate beneath hydrothermal plumes. Khripounoff and Alberic (1991) deployed an array of nine traps at 13 ◦ N EPR for 18 days during
the Hydronaut cruise. More recently German et al. (2002)
deployed a similar array for 1 year at the same location.
A Raman spectrometer and power supply could be housed
within the structure with an optical probe head pointed down
into the trap to continuously recorded the percent mineral
composition of the most recently settled particulate. The
long term deployment of such a system at a RIDGE 2000
ISS would enable us to determine long temporal changes in
hydrothermal particulate composition and dispersal. From
Khripounoff and Alberic (1991).
work related to the design, construction, disposal, and operation of naval nuclear reactors. In 2000,
I chose to leave the Navy to return to school and pursue a career in marine science. In 2001, I was
accepted into the marine science department at The University of Texas at Austin where I am currently working on a doctoral degree in chemical oceanography with Dr. Henrietta Edmonds as my
research advisor. The objective of my dissertation is to quantify submarine groundwater discharge
(SGD) to Texas bays and estuaries using naturally occurring radium isotopes as chemical tracers.
To this end, groundwater discharge is estimated using a mixing model based on water, radium, and
salt balances. Measurements of radium, thorium, and uranium isotopes are made using a combination of gamma, alpha, and mass spectrometry techniques. I am also using geophysical techniques
and CH4 measurements as additional indicators of groundwater circulation. My expected graduation date is December 2005.
In addition to my dissertation research I have also been involved in my advisor’s research on
submarine hydrothermal systems. In the fall of 2004, I took part in a RIDGE 2000 cruise where I
worked with Dr. Edmonds and Dr. Chris German on measuring dissolved methane concentrations
and methane isotopic composition in hydrothermal plumes overlying vent fields in the Lau Basin
west of the Tongan arc. During the cruise I also became interested in Dr. German’s work with
the WHOI Autonomous Benthic Explorer (ABE) team in developing the use of in situ chemical
sensors on AUVs as hydrothermal search aids.
I have since become very interested in the use of in situ sensors and sensor networks to study
large scale fluxes such as hydrothermal plume precipitates, diffuse hydrothermal discharge, as well
as SGD. In many ways research on SGD and seafloor venting systems are similar, for instance both
involve the study of water-rock interaction and the elucidation of difficult to measure processes. In
addition, the development and application of in situ sensors is a natural merging of my engineering
and marine science backgrounds. WHOI’s history of developing innovative engineering solutions
to oceanographic questions appeals to my interests in both of these fields.
I am seeking a postdoctoral research project which allows me to integrate my science and
engineering backgrounds. In my five years as a mechanical engineer in the Navy’s Naval Reactors
engineering department I worked with and was exposed to a wide variety of engineering efforts
Project Description–11
for mechanical, electrical, nuclear, and fluid systems. This broad exposure gives me an array of
engineering solutions to draw from and apply to my work. It also has helped developed my sense
for what can and cannot be made to work. It did not, however, give me the opportunity to see
engineering projects from start to finish. I now enjoy the relative freedom science offers to pose
questions, seek funding, initiate research, and follow projects through to conclusion.
After postdoctoral work I plan to pursue a position in research and teaching at either a university or research institution. Working on this project in collaboration with WHOI faculty and staff
would give me the chance to combine both my science and engineering experiences. This would
enable me to effectively pursue my future research goals concerning both short and long term biogeochemical processes associated with the exchange of water between the ocean, seafloor, and
continental margins. AUVs, ocean observatories, and other in situ instruments are the necessary
tools for conducting these long term, spatially distributed investigations.
4.2
Dissertation Abstract and Publications
My dissertation concerns quantifying and characterizing the processes controlling submarine
groundwater discharge to coastal bays and estuaries. The research uses a combination of naturally
occurring Ra isotopes, salinity, and water budgets to place constraints on the magnitude and origin of submarine groundwater discharge (SGD) to three adjacent south Texas bays. These bays
are located in a semi-arid coastal plain where 1) evaporation is high, 2) precipitation is seasonal,
and 3) terrestrial aquifer recharge is limited. To account for these features the analysis used in
this study significantly expands on that used in previous SGD investigations. The analysis goes
beyond typical steady state assumptions and instead makes explicit use of the dynamic changes in
bay dissolved radium activities and salinity. The result is both a more realistic and accurate representation of the system and allows the advecting groundwater (AGW) and recirculated seawater
(RSW) components of SGD to be clearly distinguished. This distinction, though widely made, is
seldom quantified but useful for determining the origin and biogeochemical implications of SGD.
The study consists of two components 1) a detailed evaluation of SGD to Nueces Bay and 2) a regional intercomparison of SGD to three adjacent bays of comparable size and free watershed area
but which differ in net precipitation, surface water input, aquifer water level, and salt marsh area.
The goal of the detailed assessment of Nueces Bay is to quantify the AGW and RSW components
of SGD using Ra isotopes and verify and elucidate these findings using a combination of geophysical and chemical techniques. The goal of the regional intercomparison is to evaluate regional
differences in SGD and link them with the differences in bay hydrology just mentioned.
The initial 2002–2003 field season focused on a single bay (Nueces Bay) in order to investigate
the relative contributions of AGW and RSW. The results provided evidence of a substantial submarine input of dissolved 226 Ra to Nueces Bay (Breier et al., 2002). The dissolved Ra activities of
Nueces Bay are among the highest observed in coastal estuaries; as great as 2600 dpm/m3 for 228 Ra
and 660 dpm/m3 for 226 Ra. Using a combination of salt and Ra mass balances we demonstrate that
river discharge and bay bottom sediments can not supply the Ra needed to balance tidal export
(Breier and Edmonds, 2004). In the case of 226 Ra there is an additional source of 398±102% 106
dpm/day which is 10 times the supply from bay bottom sediments and 100 times the Ra supplied
by the Nueces River (Breier and Edmonds, submitted). Only a portion of this large flux can be
Project Description–12
supplied by AGW and RSW based on the Ra activity of local groundwater. The remainder is most
likely supplied by leakage of oilfield brine from submerged petroleum wells and pipelines. Such
large fluxes of brackish groundwater and oilfield brine should be considered when determining the
freshwater inflow requirements for Nueces Bay and similar estuaries.
To further investigate the potential roles of AGW, RSW, and oilfield brine leakage a synoptic
geophysical and geochemical survey was conducted to detect the occurrence and spatial distribution
of submarine discharges of water to Nueces Bay, Texas (Breier et al., submitted). The survey
was conducted in the 12 km2 head of Nueces Bay where previous dissolved Ra measurements
suggested a significant submarine groundwater discharge. The 17 kilometer survey incorporated
continuous resistivity profiling; measurements of surface water salinity, temperature, and dissolved
oxygen; and point measurements of dissolved Ra isotopes. The survey found vertical fingers of high
conductivity extending up through 7 meters of bay bottom sediments into the surface water within
100 m of surface salinity and dissolved Ra maxima (226 Ra >600 dpm/m3 ). At these locations
there were also peaks in water temperature and lows in dissolved oxygen. These results indicate
either submarine brackish groundwater discharge or the leakage of oil field brine from submerged
petroleum pipelines. This study demonstrates how techniques like sediment resistivity profiling can
be used as part of a comprehensive characterization of submarine discharge using a sequence of 1)
large scale chemical tracer assessments, 2) detailed synoptic surveys including resistivity profiling,
and ultimately 3) targeted water chemistry samples and direct physical measurements.
During the current 2004–2005 field season, SGD to Nueces Bay is being assessed again as well
as SGD to Copano and Baffin Bays. During the second field season, I am assessing SGD to all three
bays, each at three periods during the seasonal transition from relatively freshwater to seawater to
determine the regional variability of SGD. Samples for Br/Cl determination and dissolved CH4
are being used as independent indicators of oilfield brine leakage and SGD in order to corroborate
our Ra based estimates. Additionaly measurements of 210 Pb, U, and Th isotopes in bay bottom
sediment cores are being used to better constrain the benthic bottom supply of Ra to the bays. If
even a fraction of the estimated RSW flux is circulating through the salt marsh this could remobilize
chemical species previously thought to be retained and buried in the sediments and deliver them
instead back to the surface. This would have important implications for bay nutrient supply, carbon
cycling, and the mobility of heavy metals in the salt marsh and bay bottom sediments.
The results of the 2002–2003 Nueces Bay field season have been submitted for review (Breier
and Edmonds, submitted), as have the results of the Nueces Bay synoptic Ra and sediment resistivity survey (Breier et al., submitted). The data for the 2004–2005 season for the three adjacent bays
is being completed now and publication is planned in the fall.
4.3
Statement of Support from Sponsoring Scientists
Sheri N. White, Department of Applied Ocean Physics & Engineering
Christopher R. German, Department of Geology & Geophysics
Woods Hole Oceanographic Institution, Woods Hole, MA 02543
We are fully in support of John Breier’s application for a RIDGE 2000 Postdoctoral Fellowship
to be held at WHOI. As recent arrivals at WHOI ourselves, we are both fully committed to the
Project Description–13
development of innovative in situ chemical capabilities for the future of hydrothermal research.
John’s proposal, and his own track record, encapsulate exactly that mix of scientific and engineering
interdisciplinarity required to push this field forward. Most importantly, the research proposed here
not only fits well to both our own individual future plans but would consolidate them into a much
more coherent, larger, program from which Breier would be particularly well placed to make a
significant impact of his own.
What has become indisputable in recent years is the need for improved in situ chemical and biological sensor development if the future of Ocean Science is to succeed both in terms of long-term
monitoring and (at least as relevant to this proposal) in terms of understanding processes active in
dynamic deep-ocean environments such as those found at hydrothermal vents. The development
of ocean observatories, whether as cabled seafloor networks or interactive moored buoys, offers a
fantastic potential that, without the appropriate sensors to utilize them, will never be satisfactorily
fulfilled. At National Oceanographic Centre (NOC), in the UK, this issue was first recognized
during German’s term as Head of Research Development there, and responded to through the first
recruitment of chemists and installation of chemical laboratories in their Ocean Engineering division. One of the major successes of that initiative has been the recent demonstration of a nextgeneration suite of in situ chemical (flow) sensors that can be used to study dissolved Fe(II) and
Mn(II) cycling in near-vent hydrothermal plume systems (example shown illustrates dissolved Mn
and Fe data collected by ABE in Spring 2005). While the capability exists to study the “removal”
of Fe from solution in hydrothermal plumes, however, what is still lacking is a system to study the
products of such removal processes — polymetallic sulfide precipitation and Fe-Mn oxyhydroxide
formation and uptake. Breier’s proposed work will aim to fill that analytical gap and, as such,
represents an obvious next-step building on from the current state-of-the-art.
Figure 3:
Examples of
dissolved Fe and Mn measured in situ in buoyant
hydrothermal plumes using
recently established sensors
from NOC (UK) (German
et al., 2005a). Hydrothermal/
oceanographic research now
requires a complementary
capability for analysis of solid
Fe-Mn phases.
At Woods Hole, we are pleased to report that the commitment to in situ chemical sensor development is at least as strong. An obvious example, is the recent arrival of one of us (White)
who, like Breier, boasts an interdisciplinary background (BS in Engineering, PhD in Ocean Sciences) and who, since joining AOP&E’s Deep Submergence Lab in January has already convened
WHOI’s first Chemical Senors Group which spans four research departments: AOP&E, Marine
Chemistry & Geochemistry, Geology & Geophysics, Biological Oceanography.
White’s own particular interest is in the development of in situ sensors using spectroscopic
techniques and most recently, her focus has been in the use of Raman laser systems to investigate
Project Description–14
molecular species in the deep ocean such as may be found around cold seeps and hydrothermal
vents. Again, therefore, Breier’s interests in using Raman laser spectroscopy will build upon and
expand White’s own research accelerating the rate of development in this field which holds much
potential for a wide diversity of applications.
We consider that John Breier’s background in science and engineering make him uniquely
qualified to work on the development of new sensors to answer outstanding problems in ocean
geochemistry. His specific plan of attack complements perfectly our own interest in developing
the application of Raman spectroscopy for deep-sea oceanography (White) while his direct goal —
in situ analysis of solid-phase Fe and Mn precipitates in hydrothermal plumes and sediments —
dove-tails perfectly with the recent development of robust methods for studying dissolved Fe(II)
and Mn(II) in hydrothermal plumes (German).
With our interests, breadth of expertise, experience and enthusiasm for the work, we also think
that we can provide a particularly stimulating environment in which John (Chip) would flourish.
Few organizations can boast the strength in depth of the multi-disciplinary sensors group we have
recently established, not to mention the even more extensive know-how available from the wider
Deep Submergence Group with whom he would be able to interact. Further, with German as a comentor, Breier would benefit from a Senior Scientist directly interested in the field and likely enjoy
access to numerous opportunities/synergies that can be expected to arise from German’s broader
responsibilities both nationally, as Chief Scientist for Deep Submergence, and internationally —
through InterRidge and as co-chair of the Census of Marine Life program dedicated to hydrothermal
vent and cold seep studies — ChEss.
5 Future directions and broader impacts
The purpose of this proposal is to support the interdisciplinary training of a post-doc. The work
performed on this project will lead to the development of techniques and instrumentation which
will be valuable to the greater oceanographic community. To disseminate knowledge about the
topic of chemical sensors to the public and scientific community, we will develop a website on
Chemical Sensors to highlight the work undertaken at WHOI. Additionally, we will develop modules on Raman spectroscopic instrumentation and sediment traps for the Ocean Instrument website
(http://www.whoi.edu/science/instruments/) developed by the WHOI Academic Programs Office.
This website provides information on a variety of oceanographic instruments for use by the general
public and undergraduate institutions. Of course, upon successful development, these in situ instruments would also represent an obvious addition to any long-term mid-ocean ridge observatory.
As such, they could be anticipated to broadcast novel in situ chemical data to researchers and the
public alike, in future, worldwide via the internet.
6 Results from Prior NSF Support
S. N. White and C. R. German are recently appointed scientists (Assistant Scientist and Senior
Scientist, respectively) at WHOI and have not yet received prior NSF support as PIs.
Project Description–15
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