Geology topics

Alyssa J. Findlay

Publications and source records attributed to Alyssa J. Findlay.

3 recordsLinked to original sources

USGS2020

Impacts of hydrothermal plume processes on oceanic metal cycles and transport

Chemical, physical and biological processes in hydrothermal plumes control the flux of elements from hydrothermal vents to the global oceans. The timescales of these processes range from less than a second, as the hydrothermal fluid mixes with seawater at the seafloor, to decades, as the plume disperses over thousands of kilometers. Integrating hydrothermal geochemistry throughout the lifetime of the plume reveals some well constrained processes, along with many surprises. For instance, contrary to the idea that metals are removed from the hydrothermal plume via oxidation, a survey of recent datasets reveals that oxidation of iron and manganese does not consistently result in their removal from the plume, and that manganese may be lost from the water column more rapidly than iron. These observations suggest that the understanding of element transport in hydrothermal plumes is incomplete, partly due to the change in removal processes as the plume disperses from less than 1 km from the vent to more than 4,000 km. We suggest that characterizing the plume based on regions that retain some reduced components versus those that are fully oxidized, in addition to buoyancy, will illuminate the nature of the dominant processes and allow a more complete understanding of the ultimate fate of hydrothermally derived metals.

Nature Geoscience↗

USGS2019

Iron and sulfide nanoparticle formation and transport in nascent hydrothermal vent plumes

Deep-sea hydrothermal vents are a significant source of dissolved metals to the global oceans, producing midwater plumes enriched in metals that are transported thousands of kilometers from the vent source. Extensive particle precipitation upon emission of hydrothermal fluids, due to temperature and pH changes during mixing with ambient seawater, controls metal speciation and the magnitude of metal export. Here, we document the formation and spatial distribution of metal sulfide particles, including pyrite (nano)particles, within the first meter of buoyant plumes from three high-temperature hydrothermal vents at the East Pacific Rise (9°50’ N). We observe a zone of particle settling 10 – 20 cm from the orifice, indicated by the stable sulfur isotope distribution of sulphide in the plume; however, we also demonstrate that nanoparticulate pyrite (FeS2) is not removed from the plume and can account for over half of the filtered Fe (≤ 0.2 µm) up to one meter from the vent orifice. The persistence of nanoparticulate pyritic Fe beyond the first meter demonstrates that it is an important mechanism for near-vent Fe stabilisation that may further allow transport of Fe to midwater plumes, and highlights the potential role of nanoparticles in element transport.

Nature Communications↗

USGS2019

The role of nanoparticles in mediating element deposition and transport at hydrothermal vents

Precipitation processes in hydrothermal fluids exert a primary control on the eventual distribution of elements, whether that sink is in the subseafloor, hydrothermal chimneys, near-field metalliferous sediments, or more distal in the ocean basin. Recent studies demonstrating abundant nanoparticles in hydrothermal fluids raise questions as to the importance of these nanoparticles relative to macro minerals, as well as the fate of such particles in hydrothermal systems. Here we evaluate the particle geochemistry of black smoker fluids from Niua South vent field, including nanoparticles and macro minerals, in order to consider how the processes of mineral precipitation affect mineral size and morphology, and how this mineral precipitation may dictate element sinks as hydrothermal fluids begin to mix with seawater. We find that the Niua vent fluids are dominated by sulfide and sulfate minerals, with the mineralogy of major and minor minerals changing with temperature, degree of mixing with seawater and rate of precipitation. The majority of particles are submicron in size, and sulfide minerals become larger and exhibit more crystalline morphology with increasing seawater content in the fluids. Minor minerals include gold and bismuth tellurides, and nanoparticulate chalcopyrite and nano-zinc sulfide occur. These findings are consistent with major mineral classes and precipitation processes observed in other systems, while providing further insight into the details of mineral precipitation at Niua including the separate and combined influences of boiling, mixing and cooling during hydrothermal fluid transport and initial interactions with seawater. This work demonstrates that boiling and rapid mixing encourages the formation of nanoparticles, whereas conductive cooling encourages particle growth. Further, these data demonstrate that the possible influence of nanoparticles in hydrothermal systems are not restricted to enhancing element transport, but may also include restricting mineral growth and affecting physicochemical properties of hydrothermal chimneys

Geochimica et Cosmochimica Acta↗