Lead Sources to the Amundsen Sea, West Antarctica

This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlThe global prevalence of industrial lead (Pb) contamination was exemplified decades ago by the predominance of anthropogenic Pb in samples of Antarctic surface ice and in Southern Ocean surface waters. Decreases in environmental Pb contamination corresponding with the near-global phase-out of leaded automobile gasoline beginning in the 1970s have since been observed. Measurements of Pb concentration in snow and ice core samples from Antarctica show that recent fluxes of industrial Pb to Antarctica have similarly declined. Here, we present measurements of Pb concentrations and isotopic compositions in seawater and surface sediments from the Amundsen Sea continental shelf including the Amundsen Sea Polynya. Both sets of measurements show that most (∼60–95%) of the Pb at our sites, at the time of sampling, is natural in source: that is, derived from the weathering of Antarctic continental rocks. These fluxes of natural Pb then become entrained into polynya waters either from sediment resuspension or from the transport of sediment-laden glacial melt waters to the polynya.publishedVersio

Asian anthropogenic lead contamination in the North Pacific Ocean as evidenced by stable lead isotopic compositions

This dissertation work determined the changing scope of lead (Pb) contamination in the North Pacific Ocean since the phase-out of leaded gasoline in most of the world. Chapters 1 and 2 consisted of validating our method for determining Pb concentrations and isotopic compositions in seawater. Chapter 3 established a baseline of Pb isotopic compositions (PbICs) in the western and central North Pacific in 2002. This was an ideal time to establish such a baseline because China had recently (mid-2000) ceased their use of leaded gasoline and simultaneously began consuming increasingly large amounts of coal, known to have relatively high Pb concentrations. We found subsurface waters were contaminated with Asian industrial Pb, predominantly Chinese coal emissions. In contrast, the abyssal waters were a mix of Asian industrial Pb and background (i.e., natural) Pb. Chapter 4 revisited the western and central North Pacific in 2009 - 2011 to determine what, if any, changes had occurred in this short time period. We found that Pb in subsurface and abyssal waters of the western North Pacific were similar to Chinese aerosols. Such a large change in the PbICs of abyssal water in 9 years was unanticipated and attributed to the relatively large flux of particle-bound Pb from the euphotic zone to the deep ocean, which was in isotopic equilibrium with the reservoir of dissolved Pb. In contrast, the central North Pacific abyssal water PbICs were similar to values previously reported because of the relatively lower particulate export. Based on comparisons to baseline PbIC data, we determined that abyssal waters in the western and central North Pacific would be isotopically indistinguishable from surface waters in the next three decades. Sources of Pb to coastal California waters were reevaluated in Chapter 5. Prior studies had found that surface waters of the California Current System (CCS) were isotopically consistent with both Asian industrial Pb and US leaded gasoline, still in use at that point in time. In 2010 and 2011, we found that surface and subsurface waters of the CCS were isotopically similar to Asian industrial emissions. However, remobilized US gasoline Pb from sediments in the San Francisco Bay, California, were accumulating in the "mud belt" on the continental shelf and changing the isotopic composition of overlying waters. During periods of intense upwelling, this historic Pb was brought to the surface of the water. However, the much larger quantity of Pb from Asian industrial emissions made the isotopic composition of Pb from historic US gasoline unidentifiable in off-shore waters. A secondary research focus of this dissertation was to improve my own teaching abilities. Chapter 6 explored the intersection of system thinking and aquatic toxicology in undergraduate education. Among a wealth of information, I found that group concept mapping was no more useful to student learning than the same activity done individually. This was due to poor implementation of team learning strategies by me and inadequate time for students to adjust to non-traditional instruction methodologies

Adventures n Dimerization: An Exploration of Intermolecular Forces

One of the oldest synthetic dyes, Rhodamine 6G was used in the first flashlamp-pumped dye laser as well as the first continuous-wave dye laser. Applications today utilize its fluorescing capabilities in biochemical research, and its photophysical properties in modern dye lasers. However, Rhodamine 6G in solution readily forms dimers, which affect laser efficiency. This investigation seeks to understand what kinds of intermolecular forces cause dimerization of this dye in aqueous solution. Utilizing visible spectroscopy, absorbance spectra of Rhodamine 6G in aqueous solution were studied as a function of temperature. As temperature increases, the monomer to dimer ratio increases, indicating that dimer formation is exothermic. Using DATAN software algorithms to analyze the change in monomer to dimer absorbance spectra ratios from 20 to 80 °C, the equilibrium constant for the process at 25°C is found to be about 5 x 103 which corresponds to an approximate G° of -20 kJ/mol. Utilizing this data, a constant H° from 20 to 80 °C is found to be about -40 kJ/mol, in agreement with the expectation that dimer formation is exothermic. The value of G° is similar in energy to weak bond formation, implying that a combination of electrostatic and van der Waals forces are what drive Rhodamine 6G to dimerize. Furthermore, literature on Rhodamine 6G structure suggests the existence of two different dimer conformations, whose forces are in agreement with our findings. Future studies of these structures are the key to minimizing their existence and thereby optimizing laser efficiency

Concentration of Dissolved Pb (Pb passing through a 0.2um Acropak capsule filter) from the US GEOTRACES Arctic Expedition (GN01, HLY1502) from August to October 2015

Dataset: GN01 Dissolved Pb - MITConcentration of Dissolved Pb (Pb passing through a 0.2um Acropak capsule filter) from the US GEOTRACES Arctic Expedition (GN01, HLY1502) 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/764309NSF Division of Ocean Sciences (NSF OCE) OCE-145928

Isotope ratios of Pb passing through a 0.2um Acropak capsule filter from the US GEOTRACES Arctic Expedition (GN01, HLY1502) from August to October 2015

Dataset: GN01 Dissolved Pb Isotope RatiosIsotope ratios of Pb passing through a 0.2um Acropak capsule filter from the US GEOTRACES Arctic Expedition (GN01, HLY1502) 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/764367NSF Division of Ocean Sciences (NSF OCE) OCE-145928

Lead isotope data collected from the R/V Pourquoi pas (GEOVIDE) in the North Atlantic, Labrador Sea (section GA01) during 2014

Dataset: Pb IsotopesLead isotope data collected from the R/V Pourquoi pas (GEOVIDE) in the North Atlantic, Labrador Sea (section GA01) during 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/652127NSF Division of Ocean Sciences (NSF OCE) OCE-135722

Dissolved lead data collected from the R/V Pourquoi pas (GEOVIDE) in the North Atlantic, Labrador Sea (section GA01) during 2014

Dataset: Dissolved PbDissolved lead data collected from the R/V Pourquoi pas (GEOVIDE) in the North Atlantic, Labrador Sea (section GA01) during 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/651880NSF Division of Ocean Sciences (NSF OCE) OCE-135722

Dissolved Pb passing through a 0.2 um Acropak capsule filter from R/V Thomas G. Thompson cruise TN303 in the Eastern Tropical Pacific in 2013 (U.S. GEOTRACES EPZT project)

Dataset: GP16 Pb DissolvedDissolved Pb passing through a 0.2 um Acropak capsule filter from R/V Thomas G. Thompson cruise TN303 in the Eastern Tropical Pacific in 2013. 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/644607NSF Division of Ocean Sciences (NSF OCE) OCE-123374

Historic and Industrial Lead within the Northwest Pacific Ocean Evidenced by Lead Isotopes in Seawater

We report the continued lead (Pb) contamination of the Northwest Pacific Ocean in 2002 and present the first comprehensive Pb isotope data set for that region. In the upper ocean, a Pb concentration maxima (64–113 pmol kg^–1) extended throughout the entire North Pacific Subtropical Gyre (NPSG). We determined most of the Pb in this feature was from industrial emissions by many nations in the 1980s and 1990s, with the largest contributions from leaded gasoline emissions. In contrast, the deep water (>1000 m) Pb concentrations were lower (6–37 pmol kg^–1), and constituted a mix of background (natural) Pb and anthropogenic Pb inputs from preceding decades. Deep water below the Western Subarctic Gyre (WSAG) contained more industrial Pb than below the NPSG, which was attributed to a calculated 60-fold greater flux of particulate Pb to abyssal waters near the Asian continent. Assuming Pb isotope compositions in the North Pacific Ocean were homogeneous prior to large-scale 20th century anthropogenic inputs, this evidence suggests a relatively faster change in Pb isotope ratios of North Pacific deep water below the WSAG versus the NPSG

Chronology of anthropogenic impacts reconstructed from sediment records of trace metals and Pb isotopes in Todos os Santos Bay (NE Brazil)

The evolution of the impacts of anthropogenic activities in Todos os Santos Bay was evaluated by profiles of trace metals and Pb isotopes determined in sediment cores. Fluxes of metals increased up to 12, 4 and 2 times for Cu, Pb, and Zn, respectively, compared to those recorded in the beginning of the 20th century. Stable Pb isotopes identified a decommissioned lead smelter and burning of fossil fuels as the main sources of Pb. Most metals showed minor to moderate enrichment factors (EF \u3c 4), but Cu and Pb were highly enriched (EF = 28 and 6, respectively) at the Aratu harbor. Temporal changes in sediments were associated to different activities, namely Pb smelting, burning of fossil fuels, maritime traffic, petroleum related activities, inputs of domestic effluents, and changes in land uses. The effects of the implementation of environmental policies to improve the waters of the bay could not be identified in the evaluated cores