scholarly journals Hydrothermal impacts on trace element and isotope ocean biogeochemistry

2016 ◽  
Vol 374 (2081) ◽  
pp. 20160035 ◽  
Author(s):  
C. R. German ◽  
K. A. Casciotti ◽  
J.-C. Dutay ◽  
L. E. Heimbürger ◽  
W. J. Jenkins ◽  
...  
Keyword(s):  
Trace Element ◽  
Thermohaline Circulation ◽  
Deep Ocean ◽  
Hydrothermal Activity ◽  
Global Scale ◽  
Ocean Ridges ◽  
Trace Element Chemistry ◽  
Climatic Impacts ◽  
Hydrothermal Plumes ◽  
High Concentrations

Hydrothermal activity occurs in all ocean basins, releasing high concentrations of key trace elements and isotopes (TEIs) into the oceans. Importantly, the calculated rate of entrainment of the entire ocean volume through turbulently mixing buoyant hydrothermal plumes is so vigorous as to be comparable to that of deep-ocean thermohaline circulation. Consequently, biogeochemical processes active within deep-ocean hydrothermal plumes have long been known to have the potential to impact global-scale biogeochemical cycles. More recently, new results from GEOTRACES have revealed that plumes rich in dissolved Fe, an important micronutrient that is limiting to productivity in some areas, are widespread above mid-ocean ridges and extend out into the deep-ocean interior. While Fe is only one element among the full suite of TEIs of interest to GEOTRACES, these preliminary results are important because they illustrate how inputs from seafloor venting might impact the global biogeochemical budgets of many other TEIs. To determine the global impact of seafloor venting, however, requires two key questions to be addressed: (i) What processes are active close to vent sites that regulate the initial high-temperature hydrothermal fluxes for the full suite of TEIs that are dispersed through non-buoyant hydrothermal plumes? (ii) How do those processes vary, globally, in response to changing geologic settings at the seafloor and/or the geochemistry of the overlying ocean water? In this paper, we review key findings from recent work in this realm, highlight a series of key hypotheses arising from that research and propose a series of new GEOTRACES modelling, section and process studies that could be implemented, nationally and internationally, to address these issues. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

New field, geochemical, and petrographic evidence from the Bon Accord nickel body: Contamination of a komatiite by deep mantle or meteorite source?

2021 ◽  
Author(s):  
Matthew S. Huber ◽  
Frederick Roelofse ◽  
Christian Koeberl ◽  
Marian Tredoux
Keyword(s):  
Trace Element ◽  
Lava Flow ◽  
Regional Distribution ◽  
Hydrothermal Activity ◽  
The Body ◽  
Geochemical Data ◽  
Trace Element Chemistry ◽  
Deep Mantle ◽  
Rich Material ◽  
Host Rocks

ABSTRACT The Bon Accord nickel body has been known since the 1920s to contain rocks with up to 50 wt% NiO. Numerous nickel-rich minerals have been described from this deposit. However, none of these minerals contains significant Cu or S, making the deposit chemically distinct from all other known Ni deposits. The origin of the Bon Accord nickel body is highly contentious, with previous studies suggesting three major possible origins: (1) a hydrothermal origin; (2) an Fe-Ni meteorite that fell into and was altered by an active ultramafic lava flow; or (3) a deep mantle plume that contained a fragment of nickel-rich material. Here, we present new field, petrograph ic, and geochemical data in an attempt to constrain the origin of this enigmatic body. Based on our fieldwork, there are at least two distinct Ni-rich bodies. Based on the trace-element chemistry, the protolith of the body was a komatiite, likely belonging to the Weltevreden Formation. Because the Ni end member of olivine (liebenbergite) is present in the form of euhedral crystals, this mineral most likely crystallized from a Ni-rich melt. The redistribution of the nickel appears to be due to hydrothermal activity that occurred during the intrusion of the Stentor pluton. Consistent with previous studies, we find that the komatiitic affinity of the host rocks, the stratigraphic controls on the deposit, and the regional distribution of Ni-rich material are inconsistent with a meteorite origin; instead, a komatiite plume sampling a Ni-rich portion of the mantle is currently the best explanation for the origin of the Ni-rich material.

scholarly journals Quantifying He fluxes from the mantle using multi-tracer data assimilation

2016 ◽  
Vol 374 (2081) ◽  
pp. 20150288 ◽  
Author(s):  
Reiner Schlitzer
Keyword(s):  
Large Scale ◽  
Ocean Model ◽  
Global Ocean ◽  
Depth Range ◽  
Ocean Ridges ◽  
Trace Element Chemistry ◽  
Mantle Helium ◽  
Climatic Impacts ◽  
Set Up ◽  
Spreading Rates

A global, coarse-resolution ocean model previously fitted to geostrophic shear estimates and to data of 10 hydrographic parameters and tracers has been used to simulate the 3 He and 4 He distributions resulting from the release of mantle helium from mid-ocean ridges. The model is in very good agreement with 14 C and chlorofluorocarbon data and has realistic global ocean overturning strength as well as water mass formation and transport rates. It is found that previously published global mantle 3 He fluxes are too high by a factor of about 2. In the model, optimal agreement of modelled δ 3 He with data is achieved for a global flux of 450 ± 50 mol 3 He yr −1 . The formulation of He source strengths proportional to ridge spreading rates appears compatible with data. A model/data misfit analysis shows significant and large-scale δ 3 He underestimation in the southwestern Pacific centred over the Lau Backarc Basin (approx. 179° W/20° S). These misfits disappear in a set-up with 30 of the 450 mol yr −1 global total 3 He flux released in the Lau Basin over a depth range between 1250 and 2500 m. Such He flux contributions are missing in present mantle He source compilations. Hydrothermal fluxes of other trace elements and isotopes (TEI) can be calculated from He fluxes on the basis of TEI : He ratios measured close to the sources. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

scholarly journals Diagnosing oceanic nutrient deficiency

2016 ◽  
Vol 374 (2081) ◽  
pp. 20150290 ◽  
Author(s):  
C. Mark Moore
Keyword(s):  
Large Scale ◽  
Nutrient Deficiency ◽  
Global Scale ◽  
Nutrient Ratios ◽  
Upper Ocean ◽  
Key Indicator ◽  
Trace Element Chemistry ◽  
Wide Range ◽  
Climatic Impacts ◽  
Microbial Systems

The supply of a range of nutrient elements to surface waters is an important driver of oceanic production and the subsequent linked cycling of the nutrients and carbon. Relative deficiencies of different nutrients with respect to biological requirements, within both surface and internal water masses, can be both a key indicator and driver of the potential for these nutrients to become limiting for the production of new organic material in the upper ocean. The availability of high-quality, full-depth and global-scale datasets on the concentrations of a wide range of both macro- and micro-nutrients produced through the international GEOTRACES programme provides the potential for estimation of multi-element deficiencies at unprecedented scales. Resultant coherent large-scale patterns in diagnosed deficiency can be linked to the interacting physical–chemical–biological processes which drive upper ocean nutrient biogeochemistry. Calculations of ranked deficiencies across multiple elements further highlight important remaining uncertainties in the stoichiometric plasticity of nutrient ratios within oceanic microbial systems and caveats with regards to linkages to upper ocean nutrient limitation. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

TRACE ELEMENT CHEMISTRY OF EMERALDS

2018 ◽  
Author(s):  
Casey Beaudoin ◽  
◽  
G. Nelson Eby
Keyword(s):  
Trace Element ◽  
Trace Element Chemistry ◽  
Element Chemistry

From wood to vent: first cocculinid limpet associated with hydrothermal activity discovered in the Weddell Sea

2020 ◽  
Vol 32 (5) ◽  
pp. 354-366
Author(s):  
Chong Chen ◽  
Katrin Linse
Keyword(s):  
Hydrothermal Vents ◽  
Deep Ocean ◽  
First Record ◽  
Hydrothermal Activity ◽  
Integrative Taxonomy ◽  
Weddell Sea ◽  
Anatomical Reconstruction ◽  
Cold Seeps ◽  
Evolutionary Trajectory ◽  
Genetic Sequencing

AbstractLush ‘oases’ of life seen in chemosynthetic ecosystems such as hot vents and cold seeps represent rare, localized exceptions to the generally oligotrophic deep ocean floor. Organic falls, best known from sunken wood and whale carcasses, are additional sources of such oases. Kemp Caldera (59°42'S, 28°20'W) in the Weddell Sea exhibits active hydrothermal vents and a natural whale fall in close proximity, where an undescribed cocculinid limpet was found living in both types of chemosynthetic habitats. This represents the first member of the gastropod order Cocculinida discovered from hot vents, and also the first record from the Southern Ocean. Here, we applied an integrative taxonomy framework incorporating traditional dissection, electron microscopy, genetic sequencing and 3D anatomical reconstruction through synchrotron computed tomography in order to characterize this species. Together, our data revealed an unusual member of the genus Cocculina with a highly modified radula for feeding on bacterial film, described herein as Cocculina enigmadonta n. sp. Its phylogenetically derived position within the largely wood-inhabiting Cocculina indicates that it probably evolved from an ancestor adapted to living on sunken wood, providing a compelling case of the ‘stepping stone’ evolutionary trajectory from organic falls to seeps and vents.

Chemical variation of clinopyroxene phenocrysts from the trachybasaltic lavas of Mount Etna, Sicily

1980 ◽  
Vol 43 (330) ◽  
pp. 765-770 ◽  
Author(s):  
A. M. Duncan ◽  
R. M. F. Preston
Keyword(s):  
Trace Element ◽  
Mount Etna ◽  
Chemical Variation ◽  
Etna Volcano ◽  
Trace Element Chemistry ◽  
Sector Zoning ◽  
Steady Decrease ◽  
Element Chemistry

SummaryThe chemical variation of clinopyroxene phenocrysts from the trachybasaltic lavas of Etna volcano is described. The phenocrysts show a limited, but distinct trend in chemical variation from calcic-augite in the hawaiites to augite in the benmoreites. The trend of this variation is unusual, being one of Mg-enrichment with differentiation of the magma. Ca shows a steady decrease in the clinopyroxenes from the hawaiites to the benmoreites. Na, however, shows little chemical variation in the pyroxenes. The trace element chemistry is briefly examined. The clinopyroxenes show well-developed oscillatory and sector zoning. The basal {11} sectors are enriched in Si and Mg and depleted in Ti, Al, and Fe relative to the {100}, {110}, and {010} prism sectors.

Paleoredox conditions, hydrothermal history, and target vectoring in the Macmillan Pass base-metal district, Yukon, Canada: 2 – Pyrite paragenesis and mineral chemistry

2021 ◽  
Vol 59 (5) ◽  
pp. 1233-1259
Author(s):  
Claire Leighton ◽  
Daniel Layton-Matthews ◽  
Jan M. Peter ◽  
Michael G. Gadd ◽  
Alexandre Voinot ◽  
...  
Keyword(s):  
Trace Element ◽  
Inductively Coupled Plasma ◽  
Mineral Chemistry ◽  
Hydrothermal Activity ◽  
Unconsolidated Sediments ◽  
Lateral Migration ◽  
Sulfide Mineralization ◽  
Ambient Seawater ◽  
Clastic Sediment ◽  
Icp Ms

ABSTRACT The MacMillan Pass district in Yukon, Canada, hosts the Tom and Jason clastic sediment-hosted Zn-Pb-Ag-(Ba) deposits. Pyrite-bearing drill core samples were collected from seven drill holes that intersected sulfide mineralization and time-stratigraphically equivalent rocks at varied spatial distances extending up to 3 km away from the deposits to assess the relative timing of pyrite mineralization and the chemistry of pyrite paragenesis. There are four pyrite morphologies: framboids and polyframboids (Py1), subhedral to euhedral inclusion-free crystals (Py2a), silicate inclusion-bearing nodules with serrated edges (Py2b), and euhedral idiomorphic overgrowths on preexisting pyrite morphologies (Py3). These morphological varieties correspond in time from syngenetic to earliest diagenetic growth (Py1), early to late diagenetic growth (Py2a, Py2b), and metamorphic crystallization and/or recrystallization of previous textural varieties (Py3). A representative subset of pyrite grains was analyzed for trace element contents and distributions by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Analyses by LA-ICP-MS reveal that each textural variety of pyrite has a distinct trace element composition that also varies depending on stratigraphic unit. A suite of clastic sediment-hosted sulfide mineralization-related elements was incorporated into Py2 within sulfide mineralized units at greater abundances than that in unmineralized units (e.g., Zn, As, Pb, Tl, Bi). Lead abundances and Pb/Se and As/Mo values in pyrite are the most robust vectoring tools documented. The timing for clastic sediment-hosted Zn-Pb mineralization was syn and/or post late diagenesis (Py2b). A Ba-enriched horizon was identified in rocks and this is interpreted to be the distal time-stratigraphic equivalent unit to Zn-Pb mineralization. The Ba-enriched horizon contains Py2 with anomalous metal (Tl, Co, Mn, Cd, Zn, Sb) contents and abundant macroscopic baryte, and it is interpreted to represent the distal expression of sulfide mineralization-forming hydrothermal activity. Four genetic models for mineralization are reviewed; however, the only model that is consistent with our whole rock and pyrite geochemistry involves venting of buoyant hydrothermal fluid, mixing with ambient seawater, and remaining or sinking into unconsolidated sediments, with lateral migration up to 2–3 km from the vent source.

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