The ocean plays an integral role in the global carbon cycle and serves as the largest planetary reservoir for carbon. As more anthropogenic CO2 is released to the atmosphere it is essential to understand and quantify the impact of elevated pCO2 on the ocean’s role in the uptake, transfer, and transformation of carbon as well as cascading effects on biogeochemical processes. Direct observations are limited in space and time due to shortage of autonomous technology available to effectively monitor the aqueous carbon dioxide system at seasonal, interannual, and longer timescales. This dissertation describes novel sensors that are being developed and implemented to expand available marine biogeochemical observations.

The first two chapters describe the development of a solid state sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity of seawater for monitoring the aqueous carbon dioxide system. This novel sensor requires no external reagents, has low power consumption, and meets the rugged demands required for integration with autonomous platforms. Chapter 1 focuses on the development and analytical assessment of the working sensor. Chapter 2 provides a more detailed description of all the processes and methods that were explored in reaching the working sensor described in Chapter 1.

Chapters 3 and 4 both use profiling floats equipped with existing biogeochemical sensing technology deployed through the Southern Ocean Carbon and Climate Observations and Modeling project to look at biogeochemical processes in the Southern Ocean. SOCCOM is a pilot program that will hopefully lead to global scale array of biogeochemical sensors on profiling floats. In Chapter 3, the influence of sea ice on the relative role of physical versus biological components of the pH and O2 signal is explored. While Chapter 3 primarily focuses on organic biogeochemical processes, Chapter 4 focuses on the role of CaCO3 reactions in the Southern Ocean carbon budget.

Introduction: An aortoenteric fistula (AEF) is an abnormal connection between the aorta and the gastrointestinal tract that develops due to a pathologic cause. It is a rare, but life-threatening, cause of gastrointestinal (GI) bleeding. Although no single imaging modality exists that definitively diagnoses AEF, computed tomography angiography (CTA) of the abdomen and pelvis is the preferred initial test due to widespread availability and efficiency. 

Case Report: Many deaths occur before the diagnosis is made or prior to surgical intervention. We describe a case of a patient with a history of aortic graft repair who presented with active GI bleeding.

Conclusion: Although CTA can make the diagnosis of AEF, it cannot adequately rule it out. In patients with significant GI bleeding and prior history of aortic surgery, vascular surgery should be consulted early on, even if CTA is equivocal.

Declines in amphibian populations have been reported throughout the world in recent years. Chytridiomycosis, a disease of amphibians caused by the chytrid fungus, Batrachochytrium dendrobatidis, is one of a number of factors that have been shown to contribute to these population declines. B. dendrobatidis is associated with rapid population declines and local extinctions of populations of mountain yellow-legged frog, Rana muscosa, in some areas of the California Sierra Nevada mountains, however in other areas R. muscosa populations are persisting in the presence of this fungal pathogen. We conducted field surveys and laboratory experiments to investigate several factors that may explain these different population-level outcomes of B. dendrobatidis. Our field surveys revealed that R. muscosa at persistent sites are carrying very low fungal loads, which lead to sub-clinical infections. At these sites, B. dendrobatidis is having no detectable effect on adult R. muscosa survival (although subadults may be experiencing high disease-induced mortality), and some adults are apparently losing the infection. At sites experiencing frog population crashes, a large fraction of R. muscosa adult are carrying extremely high fungal loads, and very few infected adults are surviving over the course of a summer, or between years. We found no consistent differences in temperature profiles between the two types of sites. Our laboratory experiments detected no difference in transmission rate or virulence of fungal strains from persistent versus die-off sites. We are investigating differences in susceptibility of frogs from the two types of sites in an experiment currently underway.

Background: America is in the midst of a syphilis epidemic. The CDC documented 207,255 new cases of syphilis in 2022, representing the highest incidence of disease observed since 1950 and a 17.3% increase from 2021. Treponemal central nervous system (CNS) invasion is estimated to occur in approximately 25-60% of infections, however, the current standard of care for non-neurologic syphilis does not provide antimicrobial dosing sufficient to achieve CNS clearance. This raises concern for a preventable burden of neurologic morbidity secondary to treponemal CNS persistence and subsequent neurosyphilis. Our central hypothesis is that individuals with a history of syphilis infection will experience greater odds of neurologic morbidity relative to their uninfected counterparts.

Methods: A preliminary 10-year retrospective analysis (01/2013-12/31/2022) of deidentified electronic medical records (EMR) from an academic health system was undertaken. The exposure of interest consisted of grouped ICD-10 codes representative of syphilis infection, with neurologic outcomes defined as ICD-10 diagnoses reflective of the principle clinical manifestations of neurosyphilis. Exploratory analysis of psychiatric outcomes was performed understanding psychiatry to be a property emergent of neurology. Unadjusted, bivariate analysis was performed for preliminary assessment of exposure-outcome association.

Results: 3,619,941 distinct patient EMR were included in the final analysis. 5,943 patients were found to have a diagnosis of syphilis. Patients with a history of syphilis had a higher prevalence of diabetes mellitus (DM), hyperlipidemia (HLD), and HIV relative to patients without a history of syphilis. Additionally, patients with syphilis exposure were found to have significantly higher odds of neurologic morbidity outcomes including stroke (OR = 5.14; 95%CI = 4.71-5.61), dementia (OR = 20.68 ; 95%CI = 19.27–22.19 ), sensorineural hearing loss (OR= 5.75; 95% CI= 5.07-6.2), and blindness (OR= 15.74 ; 95%CI = 14.31-16.54) relative to unexposed patients. Exposed patients also had significantly higher odds of psychiatric morbidity across all mental health outcomes assessed. Sensitivity analysis was performed whereby bivariate exposure-outcome associations were reassessed within a cohort restricted to patients without the potential confounding diagnoses of DM, HLD, and HIV. All neurologic and psychiatric outcomes studied were observed to retain significance during confounder-restricted sensitivity analysis.

Conclusion: Syphilis infection was associated with significantly increased odds of neurologic and psychiatric morbidity across all outcome measures queried after controlling for several potential confounders. These data are concerning as they suggest the possibility of a clinically significant limitation to the neurologic coverage provided by the current standard of care for non-neurologic syphilis. We plan to more rigorously evaluate our hypothesis in a follow-up study that will utilize multivariate logistic regression analysis to more precisely determine the independent effect of syphilis exposure while adjusting for a number of potential confounders.