Hansel Colleen M.

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Hansel

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Colleen M.

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0000-0002-3506-7710

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Now showing 1 - 20 of 47

Plastic formulation is an emerging control of its photochemical fate in the ocean

(American Chemical Society, 2021-09-08) Walsh, Anna N. ; Reddy, Christopher M. ; Niles, Sydney F. ; McKenna, Amy M. ; Hansel, Colleen M. ; Ward, Collin P.

Sunlight exposure is a control of long-term plastic fate in the environment that converts plastic into oxygenated products spanning the polymer, dissolved, and gas phases. However, our understanding of how plastic formulation influences the amount and composition of these photoproducts remains incomplete. Here, we characterized the initial formulations and resulting dissolved photoproducts of four single-use consumer polyethylene (PE) bags from major retailers and one pure PE film. Consumer PE bags contained 15–36% inorganic additives, primarily calcium carbonate (13–34%) and titanium dioxide (TiO2; 1–2%). Sunlight exposure consistently increased production of dissolved organic carbon (DOC) relative to leaching in the dark (3- to 80-fold). All consumer PE bags produced more DOC during sunlight exposure than the pure PE (1.2- to 2.0-fold). The DOC leached after sunlight exposure increasingly reflected the 13C and 14C isotopic composition of the plastic. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that sunlight exposure substantially increased the number of DOC formulas detected (1.1- to 50-fold). TiO2-containing bags photochemically degraded into the most compositionally similar DOC, with 68–94% of photoproduced formulas in common with at least one other TiO2-containing bag. Conversely, only 28% of photoproduced formulas from the pure PE were detected in photoproduced DOC from the consumer PE. Overall, these findings suggest that plastic formulation, especially TiO2, plays a determining role in the amount and composition of DOC generated by sunlight. Consequently, studies on pure, unweathered polymers may not accurately represent the fates and impacts of the plastics entering the ocean.
The spatial and temporal variability of Mn speciation in the coastal Northwest Atlantic Ocean

(American Geophysical Union, 2019-12-20) Oldham, Véronique E. ; Lamborg, Carl H. ; Hansel, Colleen M.

Manganese (Mn) is distributed widely throughout the global ocean, where it cycles between three oxidation states that each play important biogeochemical roles. The speciation of Mn in seawater was previously operationally defined on filtration, with soluble Mn presumed to be Mn(II) and solid‐phase Mn as Mn(III/IV) oxides. Recent findings of abundant soluble Mn(III) complexes (Mn(III)‐L) highlights the need to reexamine the redox cycling of Mn, as these complexes can donate or accept electrons. To better understand the complex cycling of Mn in coastal waters, the distribution of Mn species at four Northwest Atlantic sites with different characteristics was examined. Diurnal influences on Mn speciation were investigated within a productive site. At all sites, Mn(III)‐L complexes dominated, particularly in surface waters, and Mn oxides were low in abundance in surface waters but high in bottom waters. Despite intrasite similarities, Mn speciation was highly variable between our stations, emphasizing the diverse processes that impact Mn redox. Diel Mn measurements revealed that the cycling of Mn is also highly variable over time, even on time scales as short as hours. We observed a change of over 100 nM total Mn over 17 hrs and find that speciation changed drastically. These changes could include contributions from biological, light‐mediated, and/or abiotic mechanisms but more likely point to the importance of lateral mixing at coastal sites. This exploration demonstrates the spatial and temporal variability of the Mn redox cycle and indicates that single timepoint vertical profiling is not sufficient when describing the geochemistry of dynamic coastal systems.
The molecular products and biogeochemical significance of lipid photooxidation in West Antarctic surface waters

( 2018-04) Collins, James R. ; Fredricks, Helen F. ; Bowman, Jeff S. ; Ward, Collin P. ; Moreno, Carly ; Longnecker, Krista ; Marchetti, Adrian ; Hansel, Colleen M. ; Ducklow, Hugh W. ; Van Mooy, Benjamin A. S.

The seasonal depletion of stratospheric ozone over the Southern Hemisphere allows abnormally high doses of ultraviolet radiation (UVR) to reach surface waters of the West Antarctic Peninsula (WAP) in the austral spring, creating a natural laboratory for the study of lipid photooxidation in the shallow mixed layer of the marginal ice zone. The photooxidation of lipids under such conditions has been identified as a significant source of stress to microorganisms, and short-chain fatty acids altered by photochemical processes have been found in both marine aerosols and sinking marine particle material. However, the biogeochemical impact of lipid photooxidation has not been quantitatively compared at ecosystem scale to the many other biological and abiotic processes that can transform particulate organic matter in the surface ocean. We combined results from field experiments with diverse environmental data, including high-resolution, accurate-mass HPLC-ESI-MS analysis of lipid extracts and in situ measurements of ultraviolet irradiance, to address several unresolved questions about lipid photooxidation in the marine environment. In our experiments, we used liposomes — nonliving, cell-like aggregations of lipids — to examine the photolability of various moieties of the intact polar diacylglycerol (IP-DAG) phosphatidylcholine (PC), a structural component of membranes in a broad range of microorganisms. We observed significant rates of photooxidation only when the molecule contained the polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA). As the DHA-containing lipid was oxidized, we observed the steady ingrowth of a diversity of oxylipins and oxidized IP-DAG; our results suggest both the intact IPDAG the degradation products were amenable to heterotrophic assimilation. To complement our experiments, we used an enhanced version of a new lipidomics discovery software package to identify the lipids in water column samples and in several diatom isolates. The galactolipid digalactosyldiacylglycerol (DGDG), the sulfolipid sulfoquinovosyldiacylglycerol (SQDG) and the phospholipids PC and phosphatidylglycerol (PG) accounted for the majority of IP-DAG in the water column particulate (≥ 0.2 μm) size fraction; between 3.4 and 5.3 % of the IP-DAG contained fatty acids that were both highly polyunsaturated (i.e., each containing ≥ 5 double bonds). Using a broadband apparent quantum yield (AQY) that accounted for direct and Type I (i.e., radical-mediated) photooxidation of PUFA-containing IP-DAG, we estimated that 0.7 ± 0.2 μmol IP-DAG m-2 d-1 (0.5 ± 0.1 mg C m-2 d-1) were oxidized by photochemical processes in the mixed layer. This rate represented 4.4 % (range, 3-21 %) of the mean bacterial production rate measured in the same waters immediately following the retreat of the sea ice. Because our liposome experiments were not designed to account for oxidation by Type II photosensitized processes that often dominate in marine phytodetritus, our rate estimates may represent a sizeable underestimate of the true rate of lipid photooxidation in the water column. While production of such diverse oxidized lipids and oxylipins has been previously observed in terrestrial plants and mammals in response to biological stressors such as disease, we show here that a similar suite of molecules can be produced via an abiotic process in the environment and that the effect can be commensurate in magnitude with other ecosystem-scale biogeochemical processes.
Constraints on superoxide mediated formation of manganese oxides

(Frontiers Media, 2013-09-03) Learman, Deric R. ; Voelker, Bettina M. ; Madden, Andrew S. ; Hansel, Colleen M.

Manganese (Mn) oxides are among the most reactive sorbents and oxidants within the environment, where they play a central role in the cycling of nutrients, metals, and carbon. Recent discoveries have identified superoxide (O−2) both of biogenic and abiogenic origin as an effective oxidant of Mn(II) leading to the formation of Mn oxides. Here we examined the conditions under which abiotically produced superoxide led to oxidative precipitation of Mn and the solid-phases produced. Oxidized Mn, as both aqueous Mn(III) and Mn(III/IV) oxides, was only observed in the presence of active catalase, indicating that hydrogen peroxide (H2O2), a product of the reaction of O−2 with Mn(II), inhibits the oxidation process presumably through the reduction of Mn(III). Citrate and pyrophosphate increased the yield of oxidized Mn but decreased the amount of Mn oxide produced via formation of Mn(III)-ligand complexes. While complexing ligands played a role in stabilizing Mn(III), they did not eliminate the inhibition of net Mn(III) formation by H2O2. The Mn oxides precipitated were highly disordered colloidal hexagonal birnessite, similar to those produced by biotically generated superoxide. Yet, in contrast to the large particulate Mn oxides formed by biogenic superoxide, abiotic Mn oxides did not ripen to larger, more crystalline phases. This suggests that the deposition of crystalline Mn oxides within the environment requires a biological, or at least organic, influence. This work provides the first direct evidence that, under conditions relevant to natural waters, oxidation of Mn(II) by superoxide can occur and lead to formation of Mn oxides. For organisms that oxidize Mn(II) by producing superoxide, these findings may also point to other microbially mediated processes, in particular enzymatic hydrogen peroxide degradation and/or production of organic ligand metabolites, that allow for Mn oxide formation.
Design optimization of a submersible chemiluminescent sensor (DISCO) for improved quantification of reactive oxygen species (ROS) in surface waters

(MDPI, 2022-09-03) Grabb, Kalina C. ; Pardis, William A. ; Kapit, Jason ; Wankel, Scott D. ; Hayden, Eric B. ; Hansel, Colleen M.

Reactive oxygen species (ROS) are key drivers of biogeochemical cycling while also exhibiting both positive and negative effects on marine ecosystem health. However, quantification of the ROS superoxide (O2−) within environmental systems is hindered by its short half-life. Recently, the development of the diver-operated submersible chemiluminescent sensor (DISCO), a submersible, handheld instrument, enabled in situ superoxide measurements in real time within shallow coral reef ecosystems. Here, we present a redesigned and improved instrument, DISCO II. Similar to the previous DISCO, DISCO II is a self-contained, submersible sensor, deployable to 30 m depth and capable of measuring reactive intermediate species in real time. DISCO II is smaller, lighter, lower cost, and more robust than its predecessor. Laboratory validation of DISCO II demonstrated an average limit of detection in natural seawater of 133.1 pM and a percent variance of 0.7%, with stable photo multiplier tube (PMT) counts, internal temperature, and flow rates. DISCO II can also be optimized for diverse environmental conditions by adjustment of the PMT supply voltage and integration time. Field tests showed no drift in the data with a percent variance of 3.0%. Wand tip adaptations allow for in situ calibrations and decay rates of superoxide using a chemical source of superoxide (SOTS-1). Overall, DISCO II is a versatile, user-friendly sensor that enables measurements in diverse environments, thereby improving our understanding of the cycling of reactive intermediates, such as ROS, across various marine ecosystems.
Mineralogy of deep-sea coral aragonites as a function of aragonite saturation state

(Frontiers Media, 2018-12-10) Farfan, Gabriela A. ; Cordes, Erik E. ; Waller, Rhian G. ; DeCarlo, Thomas M. ; Hansel, Colleen M.

In an ocean with rapidly changing chemistry, studies have assessed coral skeletal health under projected ocean acidification (OA) scenarios by characterizing morphological distortions in skeletal architecture and measuring bulk properties, such as net calcification and dissolution. Few studies offer more detailed information on skeletal mineralogy. Since aragonite crystallography will at least partially govern the material properties of coral skeletons, such as solubility and strength, it is important to understand how it is influenced by environmental stressors. Here, we take a mineralogical approach using micro X-ray diffraction (XRD) and whole pattern Rietveld refinement analysis to track crystallographic shifts in deep-sea coral Lophelia pertusa samples collected along a natural seawater aragonite saturation state gradient (Ωsw = 1.15–1.44) in the Gulf of Mexico. Our results reveal statistically significant linear relationships between rising Ωsw and increasing unit cell volume driven by an anisotropic lengthening along the b-axis. These structural changes are similarly observed in synthetic aragonites precipitated under various saturation states, indicating that these changes are inherent to the crystallography of aragonite. Increased crystallographic disorder via widening of the full width at half maximum of the main (111) XRD peaks trend with increased Ba substitutions for Ca, however, trace substitutions by Ba, Sr, and Mg do not trend with crystal lattice parameters in our samples. Instead, we observe a significant trend of increasing calcite content as a function of both decreasing unit cell parameters as well as decreasing Ωsw. This may make calcite incorporation an important factor to consider in coral crystallography, especially under varying aragonite saturation states (ΩAr). Finally, by defining crystallography-based linear relationships between ΩAr of synthetic aragonite analogs and lattice parameters, we predict internal calcifying fluid saturation state (Ωcf = 11.1–17.3 calculated from b-axis lengths; 15.2–25.2 calculated from unit cell volumes) for L. pertusa, which may allow this species to calcify despite the local seawater conditions. This study will ideally pave the way for future studies to utilize quantitative XRD in exploring the impact of physical and chemical stressors on biominerals.
Dynamic regulation of extracellular superoxide production by the coccolithophore Emiliania huxleyi (CCMP 374)

(Frontiers Media, 2019-07-12) Plummer, Sydney ; Taylor, Alexander E. ; Harvey, Elizabeth L. ; Hansel, Colleen M. ; Diaz, Julia M.

In marine waters, ubiquitous reactive oxygen species (ROS) drive biogeochemical cycling of metals and carbon. Marine phytoplankton produce the ROS superoxide (O2−) extracellularly and can be a dominant source of O2− in natural aquatic systems. However, the cellular regulation, biological functioning, and broader ecological impacts of extracellular O2− production by marine phytoplankton remain mysterious. Here, we explored the regulation and potential roles of extracellular O2− production by a noncalcifying strain of the cosmopolitan coccolithophorid Emiliania huxleyi, a key species of marine phytoplankton that has not been examined for extracellular O2− production previously. Cell-normalized extracellular O2− production was the highest under presumably low-stress conditions during active proliferation and inversely related to cell density during exponential growth phase. Removal of extracellular O2− through addition of the O2− scavenger superoxide dismutase (SOD), however, increased growth rates, growth yields, cell biovolume, and photosynthetic efficiency (Fv/Fm) indicating an overall physiological improvement. Thus, the presence of extracellular O2− does not directly stimulate E. huxleyi proliferation, as previously suggested for other phytoplankton, bacteria, fungi, and protists. Extracellular O2− production decreased in the dark, suggesting a connection with photosynthetic processes. Taken together, the tight regulation of this stress independent production of extracellular O2− by E. huxleyi suggests that it could be involved in fundamental photophysiological processes.
Carbon near edge X-ray absorption fine structure (NEXAFS) spectra from pelagic sediment from the North Atlantic gyre, South Pacific gyre, and Peru Basin from cruises KN223 (R/V Knorr), KNOX02RR (R/V Roger Revelle), and ODP leg 201 between 2002 and 2014

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-07-23) Estes, Emily ; Hansel, Colleen

Carbon near edge X-ray absorption fine structure (NEXAFS) spectra from pelagic sediment from the North Atlantic gyre, South Pacific gyre, and Peru Basin from cruises KN223 (R/V Knorr), KNOX02RR (R/V Roger Revelle), and ODP leg 201 between 2002 and 2014. 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/815380
Coastal water biogeochemistry collected aboard the R/V Endeavor along the North Atlantic coast from 2017-08-20 to 2017-08-28

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-09-13) Hansel, Colleen ; Lamborg, Carl

Samples were collected from four water column sites along the Northeast Coast of the United States in August 2017 aboard the R/V Endeavor. Samples were collected using a 12-bottle trace metal clean CTD (Conductivity, Temperature and Depth) rosette, and were kept clean by using acid washed tubing to collect water directly into acid-washed 1 L PTFE bottles. Sample depths were chosen based on the water column profile obtained from a separate 24-bottle CTD rosette system equipped with Seabird software, which also provided the temperature, dissolved oxygen, salinity, PAR, beam transmission and fluorescence profiles reported here. 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/765327
Organic carbon, d13C, and total nitrogen content of pelagic sediment from the North Atlantic gyre, South Pacific gyre, and Peru Basin from cruises KN223, KNOX02RR, and ODP leg 201 between 2002 and 2013

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-07-14) Estes, Emily ; Hansel, Colleen

Organic carbon, d13C, and total nitrogen content of pelagic sediment from the North Atlantic gyre, South Pacific gyre, and Peru Basin from cruises KN223 (R/V Knorr), KNOX02RR (R/V Roger Revelle), and ODP leg 201 between 2002 and 2013. Sediment samples were taken with gravity corers, multi corers, piston and advanced piston corers (APC). 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/782736
Carbon near edge X-ray absorption fine structure (NEXAFS) spectra of standard compounds

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-07-23) Estes, Emily ; Hansel, Colleen

Carbon near edge X-ray absorption fine structure (NEXAFS) spectra of standard compounds. These data contain incident energy and absorption values at that energy for a standard compounds. 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/815362
Species-level variability in extracellular production rates of reactive oxygen species by diatoms

(Frontiers Media, 2016-03-30) Schneider, Robin J. ; Roe, Kelly L. ; Hansel, Colleen M. ; Voelker, Bettina M.

Biological production and decay of the reactive oxygen species (ROS) hydrogen peroxide (H2O2) and superoxide (O−2) likely have significant effects on the cycling of trace metals and carbon in marine systems. In this study, extracellular production rates of H2O2 and O−2 were determined for five species of marine diatoms in the presence and absence of light. Production of both ROS was measured in parallel by suspending cells on filters and measuring the ROS downstream using chemiluminescence probes. In addition, the ability of these organisms to break down O−2 and H2O2 was examined by measuring recovery of O−2 and H2O2 added to the influent medium. O−2 production rates ranged from undetectable to 7.3 × 10−16 mol cell−1 h−1, while H2O2 production rates ranged from undetectable to 3.4 × 10−16 mol cell−1 h−1. Results suggest that extracellular ROS production occurs through a variety of pathways even amongst organisms of the same genus. Thalassiosira spp. produced more O−2 in light than dark, even when the organisms were killed, indicating that O−2 is produced via a passive photochemical process on the cell surface. The ratio of H2O2 to O−2 production rates was consistent with production of H2O2 solely through dismutation of O−2 for T. oceanica, while T. pseudonana made much more H2O2 than O−2. T. weissflogii only produced H2O2 when stressed or killed. P. tricornutum cells did not make cell-associated ROS, but did secrete H2O2-producing substances into the growth medium. In all organisms, recovery rates for killed cultures (94–100% H2O2; 10–80% O−2) were consistently higher than those for live cultures (65–95% H2O2; 10–50% O−2). While recovery rates for killed cultures in H2O2 indicate that nearly all H2O2 was degraded by active cell processes, O−2 decay appeared to occur via a combination of active and passive processes. Overall, this study shows that the rates and pathways for ROS production and decay vary greatly among diatom species, even between those that are closely related, and as a function of light conditions.
Soluble Mn speciation from CTD casts in the Ross Sea, Southern Ocean taken during RVIB Nathaniel B. Palmer cruise NBP1801 in Jan-Feb 2018

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2021-04-27) Oldham, Veronique ; Hansel, Colleen ; Saito, Mak A.

Soluble Mn speciation from CTD casts in the Ross Sea, taken in Jan-Feb 2018. Speciation was performed using a porphyrin ligand substitution method with a 100 cm pathlength cell in a UV-Vis spectrophotometer. 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/850300
Differential patterns of microbiota recovery in symbiotic and aposymbiotic corals following antibiotic disturbance

(American Society for Microbiology, 2021-04-13) Bent, Shavonna M. ; Miller, Carolyn A. ; Sharp, Koty H. ; Hansel, Colleen M. ; Apprill, Amy

Microbial relationships are critical to coral health, and changes in microbiomes are often exhibited following environmental disturbance. However, the dynamics of coral-microbial composition and external factors that govern coral microbiome assembly and response to disturbance remain largely uncharacterized. Here, we investigated how antibiotic-induced disturbance affects the coral mucus microbiota in the facultatively symbiotic temperate coral Astrangia poculata, which occurs naturally with high (symbiotic) or low (aposymbiotic) densities of the endosymbiotic dinoflagellate Breviolum psygmophilum. We also explored how differences in the mucus microbiome of natural and disturbed A. poculata colonies affected levels of extracellular superoxide, a reactive oxygen species thought to have both beneficial and detrimental effects on coral health. Using a bacterial and archaeal small-subunit (SSU) rRNA gene sequencing approach, we found that antibiotic exposure significantly altered the composition of the mucus microbiota but that it did not influence superoxide levels, suggesting that superoxide production in A. poculata is not influenced by the mucus microbiota. In antibiotic-treated A. poculata exposed to ambient seawater, mucus microbiota recovered to its initial state within 2 weeks following exposure, and six bacterial taxa played a prominent role in this reassembly. Microbial composition among symbiotic colonies was more similar throughout the 2-week recovery period than that among aposymbiotic colonies, whose microbiota exhibited significantly more interindividual variability after antibiotic treatment and during recovery. This work suggests that the A. poculata mucus microbiome can rapidly reestablish itself and that the presence of B. psygmophilum, perhaps by supplying nutrients, photosynthate, or other signaling molecules, exerts influence on this process. IMPORTANCE Corals are animals whose health is often maintained by symbiotic microalgae and other microorganisms, yet they are highly susceptible to environmental-related disturbances. Here, we used a known disruptor, antibiotics, to understand how the coral mucus microbial community reassembles itself following disturbance. We show that the Astrangia poculata microbiome can recover from this disturbance and that individuals with algal symbionts reestablish their microbiomes in a more consistent manner compared to corals lacking symbionts. This work is important because it suggests that this coral may be able to recover its mucus microbiome following disturbance, it identifies specific microbes that may be important to reassembly, and it demonstrates that algal symbionts may play a previously undocumented role in microbial recovery and resilience to environmental change.
Dark reduction drives evasion of mercury from the ocean

(Frontiers Media, 2021-04-27) Lamborg, Carl H. ; Hansel, Colleen M. ; Bowman, Katlin ; Voelker, Bettina M. ; Marsico, Ryan M. ; Oldham, Véronique E. ; Swarr, Gretchen J. ; Zhang, Tong ; Ganguli, Priya M.

Much of the surface water of the ocean is supersaturated in elemental mercury (Hg0) with respect to the atmosphere, leading to sea-to-air transfer or evasion. This flux is large, and nearly balances inputs from the atmosphere, rivers and hydrothermal vents. While the photochemical production of Hg0 from ionic and methylated mercury is reasonably well-studied and can produce Hg0 at fairly high rates, there is also abundant Hg0 in aphotic waters, indicating that other important formation pathways exist. Here, we present results of gross reduction rate measurements, depth profiles and diel cycling studies to argue that dark reduction of Hg2+ is also capable of sustaining Hg0 concentrations in the open ocean mixed layer. In locations where vertical mixing is deep enough relative to the vertical penetration of UV-B and photosynthetically active radiation (the principal forms of light involved in abiotic and biotic Hg photoreduction), dark reduction will contribute the majority of Hg0 produced in the surface ocean mixed layer. Our measurements and modeling suggest that these conditions are met nearly everywhere except at high latitudes during local summer. Furthermore, the residence time of Hg0 in the mixed layer with respect to evasion is longer than that of redox, a situation that allows dark reduction-oxidation to effectively set the steady-state ratio of Hg0 to Hg2+ in surface waters. The nature of these dark redox reactions in the ocean was not resolved by this study, but our experiments suggest a likely mechanism or mechanisms involving enzymes and/or important redox agents such as reactive oxygen species and manganese (III).
Inhibited manganese oxide formation hinders cobalt scavenging in the Ross Sea

(American Geophysical Union, 2021-04-30) Oldham, Véronique E. ; Chmiel, Rebecca ; Hansel, Colleen M. ; DiTullio, Giacomo R. ; Rao, Deepa ; Saito, Mak A.

The Southern Ocean plays a critical role in regulating global uptake of atmospheric CO2. Trace elements like iron (Fe), cobalt (Co), and manganese (Mn) have been shown to modulate this primary productivity. Despite limited data, the vertical profiles for Mn, Fe, and Co in the Ross Sea show no evidence of scavenging, as typically observed in oceanic sites. This was previously attributed to low-particle abundance and/or by mixing rates exceeding scavenging rates. Scavenging of some trace metals such as cobalt (Co) is thought to be largely governed by Mn (oxyhydr)oxides, assumed to be the main component of particulate Mn (pMn). However, our data show that pMn has an average oxidation state below 3 and with nondetectable Mn oxides. In addition, soluble Co profiles show no evidence of scavenging and Co uptake measurements show little Co uptake in the euphotic zone and low/no scavenging at depth. Instead, high concentrations of dissolved Mn (dMn, up to 90 nM), which is primarily complexed as Mn(III)-L (up to 100%), are observed. Average dMn concentrations (10 ± 14 nM) are highest in bottom and surface waters. Manganese sources may include sediments and sea-ice melt, as elevated dMn was measured in sea ice (12 nM) compared to its surrounding waters (3 nM), and sea ice dMn was 97% Mn(III)-L. We contend that the lack of Co scavenging in the Ross Sea is due to a unique Mn redox cycle that favors the stabilization of Mn(III)-complexes at the expense of Mn oxide particle formation.
Spectroscopic insights into ferromanganese crust formation and diagenesis

(American Geophysical Union, 2020-10-26) Sutherland, Kevin M. ; Wankel, Scott D. ; Hein, James R. ; Hansel, Colleen M.

Marine ferromanganese deposits, often called the scavengers of the sea, adsorb and coprecipitate with a wide range of metals of great interest for paleo‐environmental reconstructions and economic geology. The long (up to ∼75 Ma), near‐continuous record of seawater chemistry afforded by ferromanganese deposits offers much historical information about the global ocean and surface earth including crustal processes, mantle processes, ocean circulation, and biogeochemical cycles. The extent to which the ferromanganese deposits hosting these geochemical proxies undergo diagenesis on the seafloor, however, remains an important and challenging factor in assessing the fidelity of such records. In this study, we employ multiple X‐ray techniques including micro–X‐ray fluorescence, bulk and micro–X‐ray absorption spectroscopy, and X‐ray powder diffraction to probe the structural, compositional, redox, and mineral changes within a single ferromanganese crust. These techniques illuminate a complex two‐dimensional structure characterized by crust growth controlled by the availability of manganese (Mn), a dynamic range in Mn oxidation state from +3.4 to +4.0, changes in Mn mineralogy over time, and recrystallization in the lower phosphatized portions of the crust. Iron (Fe) similarly demonstrates spatial complexity with respect to concentration and mineralogy, but lacks the dynamic range of oxidation state seen for Mn. Micrometer‐scale measurements of metal abundances reveal complex element associations between trace elements and the two major oxide phases, which are not typically resolvable via bulk analytical methods. These findings provide evidence of post‐depositional processes altering chemistry and mineralogy, and provide important geochemical context for the interpretation of element and isotopic records in ferromanganese crusts.
Species-specific control of external superoxide levels by the coral holobiont during a natural bleaching event

(Nature Publishing Group, 2016-12-07) Diaz, Julia M. ; Hansel, Colleen M. ; Apprill, Amy ; Brighi, Caterina ; Zhang, Tong ; Weber, Laura ; McNally, Sean ; Xun, Liping

The reactive oxygen species superoxide (O2·−) is both beneficial and detrimental to life. Within corals, superoxide may contribute to pathogen resistance but also bleaching, the loss of essential algal symbionts. Yet, the role of superoxide in coral health and physiology is not completely understood owing to a lack of direct in situ observations. By conducting field measurements of superoxide produced by corals during a bleaching event, we show substantial species-specific variation in external superoxide levels, which reflect the balance of production and degradation processes. Extracellular superoxide concentrations are independent of light, algal symbiont abundance and bleaching status, but depend on coral species and bacterial community composition. Furthermore, coral-derived superoxide concentrations ranged from levels below bulk seawater up to ∼120 nM, some of the highest superoxide concentrations observed in marine systems. Overall, these results unveil the ability of corals and/or their microbiomes to regulate superoxide in their immediate surroundings, which suggests species-specific roles of superoxide in coral health and physiology.
Microbial- and thiosulfate-mediated dissolution of mercury sulfide minerals and transformation to gaseous mercury

(Frontiers Media, 2015-06-23) Vazquez-Rodriguez, Adiari I. ; Hansel, Colleen M. ; Zhang, Tong ; Lamborg, Carl H. ; Santelli, Cara M. ; Webb, Samuel M. ; Brooks, Scott C.

Mercury (Hg) is a toxic heavy metal that poses significant environmental and human health risks. Soils and sediments, where Hg can exist as the Hg sulfide mineral metacinnabar (β-HgS), represent major Hg reservoirs in aquatic environments. Metacinnabar has historically been considered a sink for Hg in all but severely acidic environments, and thus disregarded as a potential source of Hg back to aqueous or gaseous pools. Here, we conducted a combination of field and laboratory incubations to identify the potential for metacinnabar as a source of dissolved Hg within near neutral pH environments and the underpinning (a)biotic mechanisms at play. We show that the abundant and widespread sulfur-oxidizing bacteria of the genus Thiobacillus extensively colonized metacinnabar chips incubated within aerobic, near neutral pH creek sediments. Laboratory incubations of axenic Thiobacillus thioparus cultures led to the release of metacinnabar-hosted Hg(II) and subsequent volatilization to Hg(0). This dissolution and volatilization was greatly enhanced in the presence of thiosulfate, which served a dual role by enhancing HgS dissolution through Hg complexation and providing an additional metabolic substrate for Thiobacillus. These findings reveal a new coupled abiotic-biotic pathway for the transformation of metacinnabar-bound Hg(II) to Hg(0), while expanding the sulfide substrates available for neutrophilic chemosynthetic bacteria to Hg-laden sulfides. They also point to mineral-hosted Hg as an underappreciated source of gaseous elemental Hg to the environment.
Heterotrophic bacteria exhibit a wide range of rates of extracellular production and decay of hydrogen peroxide

(Frontiers Media, 2020-02-18) Bond, Robin J. ; Hansel, Colleen M. ; Voelker, Bettina M.

Bacteria have been implicated as both a source and sink of hydrogen peroxide (H2O2), a reactive oxygen species which can both impact microbial growth and participate in the geochemical cycling of trace metals and carbon in natural waters. In this study, simultaneous H2O2 production and decay by twelve species of heterotrophic bacteria were evaluated in both batch and flow-through incubations. While wide species-to-species variability of cell-normalized H2O2 decay rate coefficients [2 × 10–8 to 5 × 10–6 hr–1 (cell mL–1)–1] was observed, these rate coefficients were relatively consistent for a given bacterial species. By contrast, observed production rates (below detection limit to 3 × 102 amol cell–1 hr–1) were more variable even for the same species. Variations based on incubation conditions in some bacterial strains suggest that external conditions may impact extracellular H2O2 levels either through increased extracellular production or leakage of intracellular H2O2. Comparison of H2O2 production rates to previously determined superoxide (O2–) production rates suggests that O2– and H2O2 production are not necessarily linked. Rates measured in this study indicate that bacteria could account for a majority of H2O2 decay observed in aqueous systems but likely only make a modest contribution to dark H2O2 production.

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