15 research outputs found
Arctic deep water ferromanganese-oxide deposits reflect the unique characteristics of the Arctic Ocean
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 3771–3800, doi:10.1002/2017GC007186.Little is known about marine mineral deposits in the Arctic Ocean, an ocean dominated by continental shelf and basins semi-closed to deep-water circulation. Here, we present data for ferromanganese crusts and nodules collected from the Amerasia Arctic Ocean in 2008, 2009, and 2012 (HLY0805, HLY0905, and HLY1202). We determined mineral and chemical compositions of the crusts and nodules and the onset of their formation. Water column samples from the GEOTRACES program were analyzed for dissolved and particulate scandium concentrations, an element uniquely enriched in these deposits. The Arctic crusts and nodules are characterized by unique mineral and chemical compositions with atypically high growth rates, detrital contents, Fe/Mn ratios, and low Si/Al ratios, compared to deposits found elsewhere. High detritus reflects erosion of submarine outcrops and North America and Siberia cratons, transport by rivers and glaciers to the sea, and distribution by sea ice, brines, and currents. Uniquely high Fe/Mn ratios are attributed to expansive continental shelves, where diagenetic cycling releases Fe to bottom waters, and density flows transport shelf bottom water to the open Arctic Ocean. Low Mn contents reflect the lack of a mid-water oxygen minimum zone that would act as a reservoir for dissolved Mn. The potential host phases and sources for elements with uniquely high contents are discussed with an emphasis on scandium. Scandium sorption onto Fe oxyhydroxides and Sc-rich detritus account for atypically high scandium contents. The opening of Fram Strait in the Miocene and ventilation of the deep basins initiated Fe-Mn crust growth ∼15 Myr ago.National Science Foundation Grant Numbers: 1434493, 1713677;
NSF-OCE Grant Number: 15358542018-05-0
THE BIOGEOCHEMICAL CYCLING OF DISSOLVED AND COLLOIDAL TRACE METALS IN THE WESTERN ARCTIC OCEAN
The Arctic Ocean is characterized by broad continental shelves, large river inputs, sea ice coverage, and limited exchange with other major ocean basins. This provides a unique environment in which to examine the distribution of trace metal micronutrients such as Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb. Many trace metals are essential micronutrients for phytoplankton in the surface ocean, serving as metal centers for important metabolic reactions such as photosynthesis, nitrogen fixation, and carbon uptake. The distribution and behavior of these metals are relatively unexplored in the Arctic Ocean. However, this dataset collected within the international GEOTRACES program presents an opportunity to explore elemental cycling and size speciation on an unprecedented spatial scale in the Western Arctic Ocean. It also bridges together the overall dissolved, colloidal, and soluble size distribution of these trace metals. The colloidal size fraction (here defined between 0.003 μm or 0.02 μm and 0.20 μm) is an operationally defined component of the dissolved phase (<0.20μm) that may be more bioavailable to phytoplankton and represents an intermediary between the soluble and the more refractory particulate phase. Our methodology allows us to combine and exploit the characteristics of multiple trace metals at once to expand our understanding of the biogeochemical processes governing the Arctic Ocean.
Overall, this work defined the unique behavior of trace metals in the Arctic Ocean. First, we outline our methodology, including the under-explored effects of storage on filtration and sorption to bottle walls, important tenets of the trace metal field. We then spend the next three chapter outlining the unique cycling of different metals within the Western Arctic Ocean. First, we first examined the dissolved biogeochemical cycling of Zn, an essential micronutrient that often cycles with major macronutrients such as silicate. This study illuminated the role of the Chukchi Shelf as a major factor controlling the distribution of Zn. The Chukchi Shelf was also critical for Fe and Mn, where elevated concentrations on the shelf persisted offshore within a water mass known as the halocline and allowed us to explore scavenging rates for these important “scavengers of the sea.” Finally, metals such as Cu and Ni that typically share no relationship in the global ocean were surprisingly correlated in the Arctic Ocean, leading to a comparison between sources and sinks of these elements in the Arctic, such as major rivers, sea ice melt, and water mass advection. Finally, we describe the results of a comparison of metal size partitioning across cryospheric waters: snow, meltponds atop the sea ice, sea ice, and the underlying seawater. This study was an unprecedented opportunity to assess the effects of incubation and mixing of these pools on the size distribution of trace metals and how, if at all, the melting of sea ice and snow in the Arctic will affect the availability of trace metals to the surface Arctic Ocean. Overall, this dissertation attempts to determine what major processes affect dissolved and colloidal trace metals in the Arctic Ocean and how this connects to our global understanding of biogeochemical cycling
Concentrations of dissolved micronutrient trace metals (Fe, Zn, Ni, Cu, Cd, Pb, Mn) in seawater, sea ice, and melt ponds collected during the US GEOTRACES Arctic cruise (HLY1502; GN01) on USCGC Healy from August to October 2015
Dataset: GN01 Dissolved Micronutrient Trace MetalsConcentrations of dissolved micronutrient trace metals (Fe, Zn, Ni, Cu, Cd, Pb, Mn) in seawater, sea ice, and melt ponds collected on the US GEOTRACES Arctic cruise (HLY1502, GN01) from August to October 2015.
For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/817259NSF Division of Ocean Sciences (NSF OCE) OCE-1713677, NSF Division of Ocean Sciences (NSF OCE) OCE-143449
Concentrations of dissolved micronutrient trace metals (Fe, Zn, Ni, Cu, Cd, Pb, Mn) in seawater, sea ice, and melt ponds collected during the US GEOTRACES Arctic cruise (HLY1502; GN01) on USCGC Healy from August to October 2015
Dataset: GN01 Dissolved Micronutrient Trace MetalsConcentrations of dissolved micronutrient trace metals (Fe, Zn, Ni, Cu, Cd, Pb, Mn) in seawater, sea ice, and melt ponds collected on the US GEOTRACES Arctic cruise (HLY1502, GN01) from August to October 2015.
For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/817259NSF Division of Ocean Sciences (NSF OCE) OCE-1713677, NSF Division of Ocean Sciences (NSF OCE) OCE-143449
A Lagrangian View of Trace Elements and Isotopes in the North Pacific
Ocean time‐series sites are influenced by both temporal variability, as in situ conditions change, as well as spatial variability, as water masses move across the fixed observation point. To remove the effect of spatial variability, this study made sub‐daily Lagrangian observations of trace elements and isotopes (Al, Sc, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, 232Th, and 230Th) in surface water over a 12‐day period (July–August 2015) in the North Pacific near the Hawaii Ocean Time‐series Station ALOHA. Additionally, a vertical profile in the upper 250 m was analyzed. This dataset is intercalibrated with GEOTRACES standards and provides a consistent baseline for trace element studies in the oligotrophic North Pacific. No diel changes in trace elements could be resolved, although day‐to‐day variations were resolved for some elements (Fe, Cu, and Zn), which may be related to organic matter cycling or ligand availability. Pb concentrations remained relatively constant during 1997–2015, presenting a change from previous decreases. Nutrient to trace element stoichiometric ratios were compared to those observed in phytoplankton as an indication of the extent of biological trace element utilization in this ecosystem, providing a basis for future ecological trace element studies
Crystal structures of trans-acetyldicarbonyl(η5-cyclopentadienyl)(dimethylphenylphosphane)molybdenum(II) and trans-acetyldicarbonyl(η5-cyclopentadienyl)(ethyldiphenylphosphane)molybdenum(II)
The title compounds, [Mo(C5H5)(COCH3)P(CH3)2(C6H5)(CO)2], (1), and [Mo(C5H5)(COCH3)P(C2H5)(C6H5)2)(CO)2], (2), have been prepared by phosphine-induced migratory insertion from [Mo(C5H5)(CO)3(CH3)]. Both complex molecules exhibit a four-legged piano-stool geometry with trans-disposed carbonyl ligands along with Mo—P bond lengths and C—Mo—P angles that reflect the relative steric pressure of the respective phosphine ligand. The structure of compound (1) exhibits a layered arrangement parallel to (100). Within the layers molecules are linked into chains along [001] by non-classical C—H...O interactions between the acetyl ligand of one molecule and the phenyl and methyl phosphine substituents of another. In the structure of complex (2), a chain motif of centrosymmetrical dimers is found along [010] through C—H...O interactions
A Refinement of the Processes Controlling Dissolved Copper and Nickel Biogeochemistry: Insights From the Pan‐Arctic
Recent studies, including many from the GEOTRACES program, have expanded our knowledge of trace metals in the Arctic Ocean, an isolated ocean dominated by continental shelf and riverine inputs. Here, we report a unique, pan-Arctic linear relationship between dissolved copper (Cu) and nickel (Ni) present north of 60°N that is absent in other oceans. The correlation is driven primarily by high Cu and Ni concentrations in the low salinity, river-influenced surface Arctic and low, homogeneous concentrations in Arctic deep waters, opposing their typical global distributions. Rivers are a major source of both metals, which is most evident within the central Arctic's Transpolar Drift. Local decoupling of the linear Cu-Ni relationship along the Chukchi Shelf and within the Canada Basin upper halocline reveals that Ni is additionally modified by biological cycling and shelf sediment processes, while Cu is mostly sourced from riverine inputs and influenced by mixing. This observation highlights differences in their chemistries: Cu is more prone to complexation with organic ligands, stabilizing its riverine source fluxes into the Arctic, while Ni is more labile and is dominated by biological processes. Within the Canadian Arctic Archipelago, an important source of Arctic water to the Atlantic Ocean, contributions of Cu and Ni from meteoric waters and the halocline are attenuated during transit to the Atlantic. Additionally, Cu and Ni in deep waters diminish with age due to isolation from surface sources, with higher concentrations in the younger Eastern Arctic basins and lower concentrations in the older Western Arctic basins
The Residence Times of Trace Elements Determined in the Surface Arctic Ocean During the 2015 US Arctic GEOTRACES Expedition
Data collected during the US Arctic GEOTRACES expedition in 2015 are used to estimate the mean residence time of dissolved trace elements (Fe, Mn, Ni, Cd, Zn, Cu, Pb, V) in surface water with respect to atmospheric deposition. The calculations utilize mixed layer trace element (TE) inventories, aerosol solubility determinations, and estimates of the atmospheric trace element flux into the upper ocean. The trace element flux is estimated by the product of the 7Be flux (determined by the ocean 7Be inventory) and the TE/7Be ratio of aerosols. This method has been established elsewhere and is tested here by comparing 7Be-derived TE flux to the measured TE accumulation in recently deposited snow. Given the variability in snow and aerosol TE concentration observed over the expedition, and the limited timescale of the observations, agreement between the two methods is reasonable. While there are assumptions in these calculations, the distribution of residence times with respect to atmospheric input across the expedition track informs us of additional sources or sinks for each element. The residence time of dissolved Fe was ~ 20–40 y for most stations. However, several stations that display a longer, oceanographically inconsistent apparent Fe residence time of ~300–500 years are likely influenced by additional input from the Transpolar Drift (TPD), which has been shown to convey shelf water properties to the central Arctic. This was seen for Cu, Ni and Zn as well. The flux of Fe delivered by the TPD was ~ 10 nmol/m2/d for these stations, an order of magnitude greater than the soluble atmospheric input. On the other hand, V and Pb show a decrease in the apparent residence times within TPD water, suggesting removal of these elements from the source region of the TPD. For Mn, there is no obvious trend in residence time among the stations; however the apparent residence time (400–1400 y) is significantly greater than the ~20 y calculated for atmospheric input elsewhere, signifying appreciable input from other sources. It has been suggested that about 90% of Mn input to the Arctic Ocean originates from Arctic rivers, shelf sediments, and coastal erosion. Results here suggest a flux from these sources of ~30 nmol/m2/d which is significantly greater than the atmospheric input of Mn in the Arctic