Does Sea Spray Aerosol Contribute Significantly To Aerosol Trace Element Loading? A Case Study From the U.S. GEOTRACES Pacific Meridional Transect (GP15)

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 \u3e1% 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 remaine

Distributions and perturbations of the marine dissolved cobalt cycle in a changing ocean

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 (10⁹ mol Co yr⁻¹ and 10¹⁰ 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.Ph.D

Inhibited manganese oxide formation hinders cobalt scavenging in the Ross Sea

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(5), (2021): e2020GB006706, https://doi.org/10.1029/2020GB006706.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.The authors acknowledge support from the NSF 1643684 (MS), NSF 1644073 (GRD), NSF OCE-1355720 (CMH), and the Woods Hole Oceanographic Institution Post-Doctoral Scholarship (VEO). The Stanford Synchrotron Radiation Lightsource was utilized in this study. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.2021-10-3

Inhibited Manganese Oxide Formation Hinders Cobalt Scavenging in the Ross Sea

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(5), (2021): e2020GB006706, https://doi.org/10.1029/2020GB006706.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.The authors acknowledge support from the NSF 1643684 (MS), NSF 1644073 (GRD), NSF OCE-1355720 (CMH), and the Woods Hole Oceanographic Institution Post-Doctoral Scholarship (VEO). The Stanford Synchrotron Radiation Lightsource was utilized in this study. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.2021-10-3

Major processes of the dissolved cobalt cycle in the North and equatorial Pacific Ocean

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chmiel, R., Lanning, N., Laubach, A., Lee, J.-M., Fitzsimmons, J., Hatta, M., Jenkins, W., Lam, P., McIlvin, M., Tagliabue, A., & Saito, M. Major processes of the dissolved cobalt cycle in the north and equatorial Pacific Ocean. Biogeosciences, 19(9), (2022): 2365–2395, https://doi.org/10.5194/bg-19-2365-2022.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.This research has been supported by the National Science Foundation (grant nos. OCE-1736599, OCE-1756138, OCE-1657781 and OCE-1736601) and the Horizon 2020 research and innovation program (BYONIC; grant no. 724289)

Development and validation of risk stratification trees for incident slow gait speed in persons at high risk for knee osteoarthritis

OBJECTIVES:Disability prevention strategies are more achievable before osteoarthritis disease drives impairment. It is critical to identify high-risk groups, for strategy implementation and trial eligibility. An established measure, gait speed is associated with disability and mortality. We sought to develop and validate risk stratification trees for incident slow gait in persons at high risk for knee osteoarthritis, feasible in community and clinical settings. METHODS:Osteoarthritis Initiative (derivation cohort) and Multicenter Osteoarthritis Study (validation cohort) participants at high risk for knee osteoarthritis were included. Outcome was incident slow gait over up to 10-year follow-up. Derivation cohort classification and regression tree analysis identified predictors from easily assessed variables and developed risk stratification models, then applied to the validation cohort. Logistic regression compared risk group predictive values; area under the receiver operating characteristic curves (AUCs) summarised discrimination ability. RESULTS:1870 (derivation) and 1279 (validation) persons were included. The most parsimonious tree identified three risk groups, from stratification based on age and WOMAC Function. A 7-risk-group tree also included education, strenuous sport/recreational activity, obesity and depressive symptoms; outcome occurred in 11%, varying 0%-29 % (derivation) and 2%-23 % (validation) depending on risk group. AUCs were comparable in the two cohorts (7-risk-group tree, 0.75, 95% CI 0.72 to 0.78 (derivation); 0.72, 95% CI 0.68 to 0.76 (validation)). CONCLUSIONS:In persons at high risk for knee osteoarthritis, easily acquired data can be used to identify those at high risk of incident functional impairment. Outcome risk varied greatly depending on tree-based risk group membership. These trees can inform individual awareness of risk for impaired function and define eligibility for prevention trials

Clinical significance of worsening versus stable preradiographic MRI lesions in a cohort study of persons at higher risk for knee osteoarthritis

Background Whether preradiographic lesions in knees at risk for osteoarthritis are incidental versus disease is unclear. We hypothesised, in persons without but at higher risk for knee osteoarthritis, that: 12–48 month MRI lesion status worsening is associated with 12–48 month incident radiographic osteoarthritis (objective component of clinical definition of knee osteoarthritis) and 48–84 month persistent symptoms. Methods In 849 Osteoarthritis Initiative participants Kellgren/Lawrence (KL) 0 in both knees, we assessed cartilage damage, bone marrow lesions (BMLs), and menisci on 12 month (baseline) and 48 month MRIs. Multivariable logistic regression was used to evaluate associations between 12–48 month worsening versus stable status and outcome (12–48 month incident KL ≥1 and KL ≥2, and 48–84 month persistent symptoms defined as frequent symptoms or medication use most days of ≥1 month in past 12 month, at consecutive visits 48–84 months), adjusting for age, gender, body mass index (BMI), injury and surgery. Results Mean age was 59.6 (8.8), BMI 26.7 (4.2) and 55.9% were women. 12–48 month status worsening of cartilage damage, meniscal tear, meniscal extrusion, and BMLs was associated with 12–48 month incident radiographic outcomes, and worsening of cartilage damage and BMLs with 48–84 month persistent symptoms. There was a dose-response association for magnitude of worsening of cartilage damage, meniscal tear, meniscal extrusion, and BMLs and radiographic outcomes, and cartilage damage and BMLs and persistent symptoms. Conclusions In persons at higher risk, worsening MRI lesion status was associated with concurrent incident radiographic osteoarthritis and subsequent persistent symptoms. These findings suggest that such lesions represent early osteoarthritis, and add support for a paradigm shift towards investigation of intervention effectiveness at this stage