Donald B. Nuzzio

Chemical speciation drives hydrothermal vent ecology.

The physiology and biochemistry of many taxa inhabiting deep-sea hydrothermal vents have been elucidated; however, the physicochemical factors controlling the distribution of these organisms at a given vent site remain an enigma after 20u2009years of research. The chemical speciation of particular elements has been suggested as key to controlling biological community structure in these extreme aquatic environments. Implementation of electrochemical technology has allowed us to make in situ measurements of chemical speciation at vents located at the East Pacific Rise (9°u200950′ N) and on a scale relevant to the biology. Here we report that significant differences in oxygen, iron and sulphur speciation strongly correlate with the distribution of specific taxa in different microhabitats. In higher temperature (>u200930u2009°C) microhabitats, the appreciable formation of soluble iron-sulphide molecular clusters markedly reduces the availability of free H2S/HS- to vent (micro)organisms, thus controlling the available habitat.

Sulfur speciation monitored in situ with solid state gold amalgam voltammetric microelectrodes: polysulfides as a special case in sediments, microbial mats and hydrothermal vent waters{{

Sulfur speciation was determined in real time in salt marsh microbial mats, subtidal sediments and hydrothermal vent diffuse flow waters using solid state gold-amalgam voltammetric microelectrodes. Chemical species were measured in situ without any sample manipulation or processing. The partially oxidized sulfur species detected were polysulfides, thiosulfate, elemental sulfur and tetrathionate. Fe(III) oxidation of hydrogen sulfide does not occur within the mats where microbially mediated processes are responsible for oxidation of H2S. In sediments and diffuse flow vent waters, Fe(III) phases are the direct oxidant of H2S. Sulfur speciation determined in this work is due to in situ biogeochemical processes and is not due to artefacts of sample manipulation. The voltammetric data show that polysulfides are the first detectable intermediate during sulfide oxidation which is consistent with previous laboratory studies.

The Application of Electrochemical Tools for In Situ Measurements in Aquatic Systems

Analytical Instrument Systems, Inc., P.O. Box 458, Flemington, NJ 08822–0458, USAReceived: September 30, 1999Final version: November 22, 1999AbstractSince the 1970’s, when the first in situ measurements of oxygen in the oceans were reported, the development of electrochemical sensors forin situ measurements in aquatic systems has significantly intensified. A synthesis of the progress made in limnology and oceanography tomeasure chemical species in situ is presented. From amperometric and potentiometric sensors that can measure a single analyte to volt-ammetric sensors that can measure several species during the same scan, a variety of electrodes have been used in situ to better understandthe nature of the biogeochemical processes occurring in aquatic systems. The advantages and disadvantages of each technique, the technicalimprovements over the years, and some recommendations are presented together with representative data reported in the literature over thelast two decades.

Speciation of manganese in Chesapeake Bay waters by voltammetric methods

Abstract The Mn(II) to Mn(O) reduction wave (peak) at a mercury electrode was investigated for its analytical usefulness in anoxic Chesapeake Bay waters which contain significant quantities of dissolved and particulate organic matter. The Mn(II) to Mn(O) reduction is characteristic for all Mn(II), MN(III) and MN(IV) complexes and thus represents total dissolved Mn. It does not provide information on only the Mn(II) oxidation state as suggested previously. Inorganic Mn(II) and organic Mn(III) complexes were studied by sampled d.c. polarography, differential pulse polarography, cyclic voltammetry and square wave voltammetry. All methods show that the Mn(II) to Mn(O) reduction is quasi-reversible in sea water. Square wave voltammetry was used for analytical work on field samples. Both Mn(II) and Mn(III) give similar current versus concentration slopes for the Mn(II) to Mn(O) peak when added to Chesapeake Bay samples. The minimum detection limit is near 200 to 300 nM. Comparison of organic free and organic rich laboratory and field samples shows that Ep shifts to more negative potentials for the organic rich samples. Thus, a major finding of this voltammetric study is that manganese can be complexed by organic ligands in marine systems with zones characterized by high organic matter decomposition and low O2 concentrations. Organic complexation of dissolved Mn may have important consequences for Mn chemistry in marine systems characterized by an oxic / anoxic interface.

Interrelationships Between Vent Fluid Chemistry, Temperature, Seismic Activity, and Biological Community Structure at a Mussel-Dominated, Deep-Sea Hydrothermal Vent Along the East Pacific Rise

Abstract In April 1991, submarine volcanic eruptions initiated the formation of numerous hydrothermal vents between 9°45′ and 9°52′N along the crest of the East Pacific Rise (EPR). Dramatic changes in biological community structure and vent fluid chemistry have been documented throughout this region since the eruptive event. By April 2004, mussels (Bathymodiolus thermophilus) dominated the faunal assemblages at several of the vent sites formed during of after the 1991 eruptions, whereas other habitats within the region were dominated by the vestimentiferan Riftia pachyptila. In the present paper, we build upon the extensive data sets obtained at these sites over the past decade and describe a manipulative experiment (conducted at 9°49.94′N; 104°14.43′W on the EPR) designed to assess interrelationships between vent fluid chemistry, temperature, biological community structure, and seismic activity. To this end, in situ voltammetric systems and thermal probes were used to measure H2S/HS− and temperature over time in a denuded region of an extensive mussel bed in which an exclusion cage was placed to inhibit the subsequent migration of mussels into the denuded area. Fluid samples were taken from the same locations to characterize the associated microbial constituents. Basalt blocks, which were placed in the cage in April 2004 and subsequently recovered in April 2005, were colonized by more than 25 different species of invertebrates, including numerous vestimentiferans and remarkably few mussels. Recorded temporal changes in vent fluid chemistry and temperature regimes, when coupled with microbiological characterization of the vent fluids and seismic activity data obtained from ocean bottom seismometers, shed considerable light on factors controlling biological community structure in these hydrothermal ecosystems.

Hydrothermal Vent Mussel Habitat Chemistry, Pre- and Post-Eruption at 9°50′North on the East Pacific Rise

Abstract Between October 2005 and March 2006, a seafloor volcanic eruption occurred at 9°50′N East Pacific Rise (EPR), establishing a “time zero” for characterizing newly-formed hydrothermal vent habitats and comparing them to pre-eruption habitats. Before the eruption, mussels (Bathymodiolus thermophilus) formed large aggregates between 9°49.6′ and 9°50.3′N. After the eruption, the few mussels remaining were in sparsely-distributed individuals and clumps, seemingly transported via lava flows or from mass wasting of the walls of the axial trough. In situ voltammetry with solid state gold-amalgam microelectrodes was used to characterize the chemistry of vent fluids in mussel habitats from 2004 to 2007, providing data sets for comparison of oxygen, sulfide, and temperature. Posteruption fluids contained higher sulfide-to-temperature ratios (i.e., slopes of linear regressions) (10.86 μM °C−1) compared with pre-eruption values in 2004 and 2005 (2.79 μM °C−1 and −0.063 μM °C−1, respectively). These chemical differences can be attributed to the difference in geographic location in which mussels were living and physical factors arising from posteruptive fluid emissions.

Variation in Sulfur Speciation with Shellfish Presence at a Lau Basin Diffuse Flow Vent Site

Abstract Carbon fixation by sulfur-oxidizing chemosynthetic bacteria forms the base of the food chain in deep-sea (diffuse-flow) hydrothermal vent ecosystems. Temperature and the availability of oxygen and reduced sulfur are believed to be factors that contribute to the structure of hydrothermal vent communities. Sulfur concentration and speciation can change rapidly as highly reducing vent fluids mix with cold oxygenated seawater, thus the path followed by source water before passing over organisms hosting sulfur-oxidizing endosymbionts may have important implications for these animals. Here we show an apparent correlation between the zonation of symbiont-containing species and the sulfur chemical speciation (sulfide, polysulfides, thiosulfate) in the water bathing them. We also report in-situ measurements of thiosulfate (S2O3 2−) in hydrothermal fluids, predominantly in the area inhabited by the mussel, Bathymodiolus brevior. These results provide field evidence of environmental levels of thiosulfate that may be capable of supporting thiosulfate-utilizing symbionts at hydrothermal vents. The three dominant shellfish species were arranged concentrically in a distinct bulls eye pattern at our study site. Alviniconcha sp. 1 snails inhabited the central, most reducing sulfide-rich zone, Ifremeria nautilei snails formed a thin band surrounding the Alviniconcha, and B. brevior mussels were farthest away from the source fluid in the most oxidized region. After removal of many of the Alviniconcha, some I. nautilei moved into the vacated space, whereas the B. brevior remained around the extreme periphery of the area impacted by the diffuse flow. These results suggest that diffuse flow chemistry is one of the key parameters affecting organism distribution.

In situ study of short-term variations of redox species chemistry in intertidal permeable sediments of the Arcachon lagoon

We investigated the composition of porewaters in intertidal sediments in response to the diurnal rise and fall of tides. For this reason, we deployed an in situ voltammetric system to measure vertical distribution and time-series at defined depths of O2, Mn(II), Fe(II), and S(−II) in the porewater of permeable sediments from a protected beach in the Arcachon Bay. We also report microprofiles of O2 and pH together with sediment properties (organic carbon, particulate reactive manganese and iron, porosity and permeability). Results shows that the oxygen dynamics in the upper sediment at low tide appeared to be mainly controlled by microphytobenthos activity, which may migrate downward just before immersion. The tidal forcing seemed to influence the oxygen dynamic in a minor way through flushing of the uppermost sediment porewater layer at the beginning and end of immersion. Vertical profiles and time-series measurements showed that the distributions of reduced species varied with tides. Although this work reveals that the upper sediment layer was subject to redox changes, the response of vertical distributions of redox species to tidal and night–day cycles did not have a cyclic pattern.