Chmiel
Rebecca
Chmiel
Rebecca
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ArticleDoes sea spray aerosol contribute significantly to aerosol trace element loading? a case study from the US GEOTRACES Pacific Meridional Transect (GP15)(American Geophysical Union, 2022-07-21) Marsay, Christopher M. ; Landing, William M. ; Umstead, Devon ; Till, Claire P. ; Freiberger, Robert ; Fitzsimmons, Jessica N. ; Lanning, Nathan ; Shiller, Alan M. ; Hatta, Mariko ; Chmiel, Rebecca ; Saito, Mak A. ; Buck, Clifton S.Atmospheric deposition represents a major input for micronutrient trace elements (TEs) to the surface ocean and is often quantified indirectly through measurements of aerosol TE concentrations. Sea spray aerosol (SSA) dominates aerosol mass concentration over much of the global ocean, but few studies have assessed its contribution to aerosol TE loading, which could result in overestimates of “new” TE inputs. Low-mineral aerosol concentrations measured during the U.S. GEOTRACES Pacific Meridional Transect (GP15; 152°W, 56°N to 20°S), along with concurrent towfish sampling of surface seawater, provided an opportunity to investigate this aspect of TE biogeochemical cycling. Central Pacific Ocean surface seawater Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb concentrations were combined with aerosol Na data to calculate a “recycled” SSA contribution to aerosol TE loading. Only vanadium was calculated to have a SSA contribution averaging >1% along the transect (mean of 1.5%). We derive scaling factors from previous studies on TE enrichments in the sea surface microlayer and in freshly produced SSA to assess the broader potential for SSA contributions to aerosol TE loading. Maximum applied scaling factors suggest that SSA could contribute significantly to the aerosol loading of some elements (notably V, Cu, and Pb), while for others (e.g., Fe and Al), SSA contributions largely remained <1%. Our study highlights that a lack of focused measurements of TEs in SSA limits our ability to quantify this component of marine aerosol loading and the associated potential for overestimating new TE inputs from atmospheric deposition.
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ArticleInhibited 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.
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ArticleMajor processes of the dissolved cobalt cycle in the north and equatorial Pacific Ocean(European Geosciences Union, 2022-05-05) Chmiel, Rebecca ; Lanning, Nathan ; Laubach, Allison ; Lee, Jong-Mi ; Fitzsimmons, Jessica N. ; Hatta, Mariko ; Jenkins, William J. ; Lam, Phoebe J. ; McIlvin, Matthew R. ; Tagliabue, Alessandro ; Saito, Mak A.Over the past decade, the GEOTRACES and wider trace metal geochemical community has made substantial contributions towards constraining the marine cobalt (Co) cycle and its major biogeochemical processes. However, few Co speciation studies have been conducted in the North and equatorial Pacific Ocean, a vast portion of the world's oceans by volume and an important end-member of deep thermohaline circulation. Dissolved Co (dCo) samples, including total dissolved and labile Co, were measured at-sea during the GEOTRACES Pacific Meridional Transect (GP15) expedition along the 152∘ W longitudinal from 56∘ N to 20∘ S. Along this transect, upper-ocean dCo (σ0<26) was linearly correlated with dissolved phosphate (slope = 82±3, µmol : mol) due to phytoplankton uptake and remineralization. As depth increased, dCo concentrations became increasingly decoupled from phosphate concentrations due to co-scavenging with manganese oxide particles in the mesopelagic. The transect revealed an organically bound coastal source of dCo to the Alaskan Stream associated with low-salinity waters. An intermediate-depth hydrothermal flux of dCo was observed off the Hawaiian coast at the Loihi Seamount, and the elevated dCo was correlated with potential xs3He at and above the vent site; however, the Loihi Seamount likely did not represent a major source of Co to the Pacific basin. Elevated concentrations of dCo within oxygen minimum zones (OMZs) in the equatorial North and South Pacific were consistent with the suppression of oxidative scavenging, and we estimate that future deoxygenation could increase the OMZ dCo inventory by 18 % to 36 % over the next century. In Pacific Deep Water (PDW), a fraction of elevated ligand-bound dCo appeared protected from scavenging by the high biogenic particle flux in the North Pacific basin. This finding is counter to previous expectations of low dCo concentrations in the deep Pacific due to scavenging over thermohaline circulation. Compared to a Co global biogeochemical model, the observed transect displayed more extreme inventories and fluxes of dCo than predicted by the model, suggesting a highly dynamic Pacific Co cycle.
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ThesisDistributions and perturbations of the marine dissolved cobalt cycle in a changing ocean(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2023-02) Chmiel, Rebecca ; Saito, Mak A.Cobalt is a necessary nutrient for many marine phytoplankton, but its hybrid-type nature results in small marine inventories that make it one of the scarcest bioactive trace metals in the oceans. This study examines the marine dissolved cobalt cycle in two regions: the Pacific Ocean and Antarctic coastal seas. In the North Pacific, elevated cobalt stoichiometries among phytoplankton were linked to nitrogen, iron and phosphate stress protein biomarkers at the boundaries of oceanographic provinces and upwelling zones, providing insight into the flexibility of cobalt stoichiometry. In both regions, perturbations to the marine cobalt cycle were either predicted or observed; in the equatorial Pacific, the dissolved cobalt inventory was predicted to increase by up to 28% due to the expansion of oxygen minimum zones in a warmer ocean, while in the Antarctic, melting ice shelves have the potential to shift the nutrient regime from iron limitation towards zinc and vitamin B12 limitation, resulting in higher cobalt demand and a lower dissolved cobalt inventory. When the global cobalt cycle was estimated throughout four of Earth’s systems (the lithosphere, biosphere, hydrosphere and the anthroposphere – the human environment), it was determined that the scale of the cobalt flux through the anthroposphere is only one order of magnitude lower than the inventory of the entire hydrosphere (10(9) mol Co yr-1 and 10(10) mol Co, respectively), revealing a vulnerability to anthropogenic perturbation of the marine cobalt inventory through human mining, use and disposal of cobalt if appropriate pollution abatement, disposal and recycling infrastructure is not established. In light of observed and predicted changes to cobalt biogeochemistry, this research suggests that the marine cobalt cycle is particularly vulnerable to anthropogenic perturbation from both global climate change and pollution due to its low ocean inventory and interconnection to other nutrient biogeochemical cycles.
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ArticleStrategies for and barriers to collaboratively developing anti‐racist policies and resources as described by geoscientists of color participating in the unlearning racism in Geoscience (URGE) program(American Geophysical Union, 2023-02-17) Burton, Carlene ; Duran, Gabriel ; Wright, Vashan ; Chmiel, RebeccaThe Unlearning Racism in Geosciences (URGE) program guides groups of geoscientists as they draft, implement, and assess anti‐racist policies and resources for their workplace. Some participating Geoscientists of Color (GoC) shared concerns about microaggression, tokenism, and power struggles within their groups. These reports led us to collect and analyze data that describe the experiences of GoC in URGE. The data are from five discussion groups and two surveys. Our analyses revealed that participating GoC want to continue working with White colleagues on anti‐racist work. GoC want White colleagues not to shy away from doing anti‐racist work. Instead, GoC want White colleagues (a) to create and adhere to robust behavioral codes of conduct, (b) to focus discussions on anti‐racism, (c) to act on anti‐racism initiatives, (d) not to prompt GoC to educate them or reveal trauma, and (e) to refrain from microaggressions and tokenism. These desired outcomes were achieved in some groups with varying degrees of success. Correcting a history of mistrust relating to racism and anti‐racism action is key to implementing and assessing effective anti‐racist policies and resources. This requires leadership support, following through on anti‐racism action, and deepening relationships between GoC and White colleagues. Future anti‐racist programs should spend a substantial amount of time on and demonstrate the importance of training participants how to discuss racism effectively and how to create and adhere to robust behavioral codes of conduct. Future programs should also explore developing a robust program‐wide code of conduct that includes a policy for reporting offenses.
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ArticleLow cobalt inventories in the Amundsen and Ross seas driven by high demand for labile cobalt uptake among native phytoplankton communities(European Geosciences Union, 2023-10-04) Chmiel, Rebecca J. ; Kell, Riss M. ; Rao, Deepa ; Moran, Dawn M. ; DiTullio, Giacomo R. ; Saito, Mak A.Cobalt (Co) is a scarce but essential micronutrient for marine plankton in the Southern Ocean and coastal Antarctic seas, where dissolved cobalt (dCo) concentrations can be extremely low. This study presents total dCo and labile dCo distributions measured via shipboard voltammetry in the Amundsen Sea, the Ross Sea and Terra Nova Bay during the CICLOPS (Cobalamin and Iron Co-Limitation of Phytoplankton Species) expedition. A significantly smaller dCo inventory was observed during the 2017/2018 CICLOPS expedition compared to two 2005/2006 expeditions to the Ross Sea conducted over a decade earlier. The dCo inventory loss (∼ 10–20 pM) was present in both the surface and deep ocean and was attributed to the loss of labile dCo, resulting in the near-complete complexation of dCo by strong ligands in the photic zone. A changing dCo inventory in Antarctic coastal seas could be driven by the alleviation of iron (Fe) limitation in coastal areas, where the flux of Fe-rich sediments from melting ice shelves and deep sediment resuspension may have shifted the region towards vitamin B12 and/or zinc (Zn) limitation, both of which are likely to increase the demand for Co among marine plankton. High demand for Zn by phytoplankton can result in increased Co and cadmium (Cd) uptake because these metals often share the same metal uptake transporters. This study compared the magnitudes and ratios of Zn, Cd and Co uptake (ρ) across upper-ocean profiles and the observed order-of-magnitude uptake trends (ρZn > ρCd > ρCo) that paralleled the trace metal concentrations in seawater. High rates of Co and Zn uptake were observed throughout the region, and the speciation of available Co and Zn appeared to influence trends in dissolved metal : phosphate stoichiometry and uptake rates over depth. Multi-year loss of the dCo inventory throughout the water column may be explained by an increase in Co uptake into particulate organic matter and subsequently an increased flux of Co into sediments via sinking and burial. This perturbation of the Southern Ocean Co biogeochemical cycle could signal changes in the nutrient limitation regimes, phytoplankton bloom composition and carbon sequestration sink of the Southern Ocean.