The temporal dynamics of terrestrial organic matter transfer to the oceans : initial assessment and application

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2007This thesis employs compound-specific stable carbon and radiocarbon isotopic analysis of organic biomarkers to (a) resolve petrogenic from pre-aged vascular plant organic carbon (OC) in continental margin sediments, (b) investigate the underlying mechanisms controlling the anomalously old ages that are often observed for the terrestrial component of sedimentary OC, and (c) address the associated consequences for biomarker-based climate reconstructions. In Chapters 2 and 3, coupled molecular isotope mass balances demonstrate that the amount of petrogenic OC residing on the Beaufort Shelf (Arctic Ocean) and the Eel River Margin (coastal California) has been previously overestimated due to the presence of significantly ‘pre-aged’ terrestrial OC. However, even though the contribution of organic matter emanating from sedimentary rocks may be smaller, these results reinforce the emerging notion that it is not completely oxidized during weathering and subsequent seaward transport. In Chapter 4, comparison of the down-core radiocarbon profiles for certain vascular plant biomarkers extracted from Cariaco Basin (Caribbean Sea) and Saanich Inlet (coastal British Columbia) sediments with the radiocarbon evolution of atmospheric carbon dioxide reveals that the vast majority of the terrestrial OC experiences multi-millennial residence times on land prior to entering the sea. Most of the remaining inventory is deposited in sediments within one or two decades, providing direct evidence that very little terrestrial organic matter is rapidly transferred to the marine environment. With this in mind, the striking modulation in the signal amplitude of a biomarker-based tropical paleoaridity record presented in Chapter 5 was instead used to evaluate the role of low versus high latitude forcing in abrupt paleoclimate oscillations during the last full glacial cycle. Seasonal variations in the position of the Intertropical Convergence Zone were interpreted to be a response to both high latitude adjustments in meridional overturning circulation and precessionally-driven modifications in local insolation. Finally, Chapter 6 addresses the broader implications of multi-millennial terrestrial residence times for paleoclimate records based on vascular plant biomarkers.The scientific analyses described herein were funded by the National Science Foundation through grants OCE-9907129 (T.I.E.), OCE-052626800 (T.I.E.), OCE- 0137005 (T.I.E. and K.A.H.), DEB-0447281 (K.A.H.), and the Stanley Watson Chair for Excellence in Oceanography (T.I.E.). N.J.D.’s tuition and stipend were supported by the graduate fellowships from the Stanley Watson Foundation, Schlanger Ocean Drilling Program, and Environmental Protection Agency’s Science to Achieve Results (STAR) Program, as well as by the WHOI Academic Programs Office

The Care Continuum for People Living With HIV in Georgia: How Can We Raise the Bar?

Background: Viral suppression (VS) improves quality of life and longevity for people living with HIV (PLWH) and reduces viral transmission, but is achieved by only a minority of PLWH in Georgia. Methods: By use of the Georgia HIV/AIDS surveillance database, the HIV Care Continuum was stratified by age. Results: Retention in care and VS generally increased with increasing age, with the exception of adolescents (aged 13-18 years), who had the highest retention and VS. Differences by sex, race and transmission category persisted across age groups. Among persons retained in care, the proportion achieving VS also generally increased with age. Linkage to care within 3 months of HIV diagnosis was lower among young adults (aged 19-24 years) (54%); young Black, non-Hispanic (NH) males (49%); and young Black NH men who have sex with men (MSM) (49%) as compared to those among adolescents (66%, 58%, and 57%). Conclusions: Retention in care and VS decreases with the transition from adolescence to young adulthood, possibly reflecting loss of support systems and competing priorities. At the other end of the age spectrum, health care and social support systems will be confronted with increasing numbers of older PLWH in Georgia. Challenges in HIV treatment and prevention include (a) the need for integrated medical care for aging PLWH with co-morbid conditions, and (b) the changing social environment of young PLWH

Effect of Medicaid Status on up-to-date Vaccination Rates Among two-year-old Children in Georgia, 2015

Background: The annual Georgia Immunization Study (GIS) employs a retrospective cohort design to determine the up-to-date (UTD) immunization rate of 24-month-old children in Georgia. Previous results have shown lower vaccination rates in the second year of life, particularly for DTaP. We sought to determine if a discontinuation of Medicaid coverage after the infant year contributed to lower immunization rates in the second year. Methods: A stratified random sample of 2,002 Georgia children born in January 2013 was drawn from electronic birth records. Immunization history and Medicaid status were obtained from the Georgia Registry of Immunization Transactions and Services (GRITS). Parents and providers of children inadequately immunized according to the Advisory Committee on Immunization Practices’ (ACIP) immunization schedule were contacted for additional information. UTD immunization rates were compared among participants based on Medicaid status (Medicaid both years, first year only, second year only, never on Medicaid). The relationship between Medicaid status and specific immunizations was also explored. Reasons for loss of Medicaid among children who were not UTD were sought via parent interview. Significance testing was performed using Chi-Square tests in SAS version 9.4. Results: Children covered by Medicaid both years or never covered by Medicaid were more likely to be UTD by 24 months (90.4% and 84.5%, respectively) than children no longer covered by Medicaid in their second year of life (49.2%). These children also demonstrated a significantly lower immunization rate for the 4th DTaP dose (p\u3c0.0001). Conclusions: A discontinuation of Medicaid coverage after the first year of life was associated with a lower UTD immunization rate among 24 month old children, particularly the 4th DTaP dose. Although reasons for discontinuation of Medicaid were beyond the scope of this study, lower vaccination levels among this group may reflect a lack of understanding of vaccine support services, and deserves further examination. Key words: immunization, Georgia, two year old, Georgia Immunization Study, GIS, 201

Surviving HIV and Dying for a Smoke: Implications for Tobacco Use Among People Living With HIV

Background: Since the advent of highly active antiretroviral therapy in the mid-nineties, deaths among persons living with HIV (PLWH) have declined nationally. Now a controllable condition, HIV has become a chronic disease, highlighting the importance of tobacco cessation in lowering morbidity and premature mortality. Current smoking is approximately twice as high among PLWH compared with the general population. PLWH who smoke experience higher rates of cardiovascular disease, AIDS-defining illnesses, and cancer than PLWH who do not smoke. Loss of life-years associated with smoking among PLWH is greater than life-years lost from HIV. Methods: Data on current smoking, derived from the 2009-12 Georgia Medical Monitoring Project (MMP) were analyzed. Smoking rates were calculated by demographic characteristics, and results were compared to those from the 2011 Georgia Behavioral Risk Factor Surveillance System (BRFSS), a population-based telephone survey. Results: The prevalence of current smoking among PLWH was 36.1%, compared with 21.2% among the general population in Georgia. Smoking prevalence for PLWH generally varied by demographic characteristics according to the same pattern as for the general population, but prevalence was consistently higher among PLWH. Conclusions: The prevalence of current smoking among PLWH in Georgia is high. Clinical and public health interventions must address smoking cessation as part of HIV care to prevent disease, improve quality of life, and reduce mortality. HIV infected smokers have more barriers to quitting (alcohol, depression, drug dependence, and inaccurate risk perception) and a lower quit rate than non-HIV-infected smokers. Efficacy studies of behavioral and pharmacological interventions for smoking cessation specific to PLWH are needed

Blank assessment for ultra-small radiocarbon samples : chemical extraction and separation versus AMS

Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 1322-1335.The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed protocols for analyzing radiocarbon in samples as small as ~0.001 mg of carbon (C). Mass-balance background corrections for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination of ~0.6 ± 0.3 μg C, while DC is ~0.3 ± 0.15 μg C. Today, the laboratory routinely analyzes graphite samples as small as 0.015 mg C for external submissions and ≅0.001 mg C for internal research activities with a precision of ~1% for ~0.010 mg C. However, when analyzing ultra-small samples isolated by a series of complex chemical and chromatographic methods (such as individual compounds), integrated procedural blanks may be far larger and more variable than those associated with combustion/graphitization alone. In some instances, the mass ratio of these blanks to the compounds of interest may be so high that the reported 14C results are meaningless. Thus, the abundance and variability of both MC and DC contamination encountered during ultra-small sample analysis must be carefully and thoroughly evaluated. Four case studies are presented to illustrate how extraction chemistry blanks are determined

Late Holocene sea-surface temperature and precipitation variability in northern Patagonia, Chile (Jacaf Fjord, 44°S)

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Research 72 (2009): 400-409, doi:10.1016/j.yqres.2009.06.010.A high-resolution multi-proxy study including the elemental and isotopic composition of bulk organic matter, land plant-derived biomarkers, and alkenone-based sea surface temperature (SST) from a marine sedimentary record obtained from the Jacaf Fjord in northern Chilean Patagonia (~ 44°20'S) provided a detailed reconstruction of continental runoff, precipitation, and summer SST spanning the last 1750 years. We observed two different regimes of climate variability in our record: a relatively dry/warm period before 900 cal yr BP (lower runoff and average SST 1°C warmer than present-day) and a wet/cold period after 750 cal yr BP (higher runoff and average SST 1°C colder than present-day). Relatively colder SSTs were found during 750-600 and 450-250 cal yr BP, where the latter period roughly corresponds to the interval defined for the Little Ice Age (LIA). Similar climatic swings have been observed previously in continental and marine archives of the last two millennia from central and southern Chile, suggesting a strong latitudinal sensitivity to changes in the Southern Westerly Winds, the main source of precipitation in southern Chile, and validating the regional nature of the LIA. Our results reveal the importance of the Chilean fjord system for recording climate changes of regional and global significance.The preparation of this article was made possible by the support of the Comité Oceanográfico Nacional Chile through the Special Fund to Promote Interdisciplinary Publications of the CIMAR Program. Sampling was funded by the CIMAR FIORDO-7 Program (Grant CPF 01-10)

Diverse soil carbon dynamics expressed at the molecular level

The stability and potential vulnerability of soil organic matter (SOM) to global change remains incompletely understood due to the complex processes involved in its formation and turnover. Here we combine compound-specific radiocarbon analysis with fraction-specific and bulk-level radiocarbon measurements in order to further elucidate controls on SOM dynamics in a temperate and sub-alpine forested ecosystem. Radiocarbon contents of individual organic compounds isolated from the same soil interval generally exhibit greater variation than those among corresponding operationally-defined fractions. Notably, markedly older ages of long-chain plant leaf wax lipids (n-alkanoic acids) imply that they reflect a highly stable carbon pool. Furthermore, marked 14C variations among shorter- and longer-chain n-alkanoic acid homologues suggest that they track different SOM pools. Extremes in SOM dynamics thus manifest themselves within a single compound class. This exploratory study highlights the potential of compound-specific radiocarbon analysis for understanding SOM dynamics in ecosystems potentially vulnerable to global change

Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds

Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core 14C profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called “bomb-spike”, and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times (“residence times”). Using a modeling framework, we find that, in addition to a "young" (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (±9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (±5.0) and 2.4 (±0.50) to 3.2 (±0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir. Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences

Influence of hydrodynamic processes on the fate of sedimentary organic matter on continental margins

Understanding the effects of hydrodynamic forcing on organic matter (OM) composition is important for assessment of organic carbon (OC) burial in marginal seas on regional and global scales. Here we examine the relationships between regional oceanographic conditions (bottom shear stress), and the physical characteristics (mineral surface area and grain size) and geochemical properties (OC content [OC%] and carbon isotope compositions [13C, 14C]) of a large suite of surface sediments from the Chinese marginal seas to assess the influence of hydrodynamic processes on the fate of OM on shallow continental shelves. Our results suggest that 14C content is primarily controlled by organo‐mineral interactions and hydrodynamically driven resuspension processes, highlighted by (i) positive correlations between 14C content and OC% (and surface area) and (ii) negative correlations between 14C content and grain size (and bottom shear stress). Hydrodynamic processes influence 14C content due to both OC aging during lateral transport and accompanying selective degradation of OM associated with sediment (re) mobilization, these effects being superimposed on the original 14C characteristics of carbon source. Our observations support the hypotheses of Blair and Aller (2012, https://doi.org/10.1146/annurev‐marine‐120709‐142717) and Leithold et al. (2016, https://doi.org/10.1016/j.earscirev.2015.10.011) that hydrodynamically driven sediment translocation results in greater OC 14C depletion in broad, shallow marginal seas common to passive margin settings than on active margins. On a global scale, this may influence the extent to which continental margins act as net carbon sources and sinks. Our findings thus suggest that hydrodynamic processes are important in shaping the nature, dynamics, and magnitude of OC export and burial in passive marginal seas