The Intertropical Convergence Zone (ITCZ) is a low-pressure band near the equator where the Northern and Southern hemisphere trade winds converge, characterized by heavy rainfall. The ITCZ typically moves seasonally, migrating north during the Northern hemisphere summer, and south during the Southern hemisphere summer, but there has also been a clear overall southward shift of the ITCZ since 1850. This project uses data from the latest Coupled Model Intercomparison Project (CMIP6) historical simulations to investigate this southward shift, made clear by changing precipitation patterns across the hemispheres. This shift could be caused by aerosols, which preferentially cooled the Northern hemisphere. It is known that the ITCZ is drawn toward the hemisphere with more heating, so this project explores and breaks down the global energy budget over the historical period simulated in the models (1850-2014) to further understand the causes of this shift.

Microbes can impact mineral solubility and the mobility of economically or environmentally important aqueous species, such as uranium and cadmium. Understanding bacteria’s influence on heavy metals is essential to predict how dissolved contaminants are transported in the environment. Shewanella putrefaciens strain CN32 can impact the mobility of uranium through the adsorption of uranium (VI) and through metabolic processes to induce uranium (VI) reduction and precipitation. Although these S. putrefaciens processes have been identified, we still lack a thorough identification of the functional groups on the bacterial surface implicated in the retardation of uranium and likely other heavy metals. Identification of these functional groups is critical to understanding the binding environment of contaminants on S. putrefaciens and hence the stability of such surface complexes. Using batch sorption experiments and Fourier Transform Infrared Spectroscopy (FTIR) we identified proton ionizable functional groups on the S. putrefaciens CN32 surface, which are the sites of metal adsorption. These results will be combined with data from adsorption experiments to develop thermodynamic parameters for the prediction of heavy metal interactions with S. putrefaciens, a ubiquitous marine microbe. Ultimately, incorporating microbial interactions into geochemical transport models will give geologists more predictive power to understand the movement of contaminants in the environment.

Since the Industrial Revolution, human-caused (anthropogenic) emissions of greenhouse gases and pollutants, including sulfur, have changed the composition of the Arctic atmosphere. Greenhouse gas emissions and climate feedbacks have resulted in an Arctic amplification, the phenomenon of rapidly warming Arctic temperatures and of sea-ice extent declining at a rate of 7.2% per decade since the 1980s. Other anthropogenic emissions, such as sulfur aerosols, can reflect sunlight and increase cloud cover, temporarily decreasing temperatures. Since the 1980s, clean air policies have reduced the emissions of sulfur aerosols, which have contributed to Arctic amplification. The majority of Arctic sulfate aerosols come from anthropogenic emissions, but natural sources include sea salt, volcanoes, or biological activity. Sea-ice algae produce dimethylsulfide (DMS), which converts to sulfate aerosols through oxidation in the atmosphere. With the decline in sea-ice extent, the habitats of Arctic biota such as algae are diminishing, and it is unclear how declining sea ice will affect biogenic sulfate aerosols and DMS emissions in the future. Here we investigate the relationship between sea-ice extent decline and DMS emissions thorough analysis of an ice core collected in Summit, Greenland to understand the relative contribution of biological activity to Arctic aerosol abundance. To analyze the biogenic sulfate in the ice core, we concentrate ice core meltwater samples, precipitate sulfate in the concentrated sample solution, measure the sulfur isotopes on a stable isotope mass spectrometer, and run GEOS-Chem model simulations to interpret the observed trends. The isotopes of sulfur in sulfate indicate what portion of the atmospheric sulfate aerosols result from biological activity. We hypothesize that biogenic sulfate has decreased with declining sea-ice extent due to the reduction of sea-ice habitats for sea-ice algae. The response of Arctic sulfate aerosol abundance to the decline of sea ice holds implications for the future of Arctic amplification.

We analyze simulations from over 25 climate models that allow us to visualize and understand how these models predict global averaged precipitation rate. Despite large improvements in climate model physics, there remain large differences among models in the global average precipitation, on the order of +/- 10%. The climate model simulations are from the Coupled Model Intercomparison Project 6 (CMIP6) which are being run for the next major Intergovernmental Panel on Climate Change report. Understanding the factors that determine the global precipitation in recent years can help us understand and interpret climate simulations of the future. The global average precipitation must be equal to the global average evaporation, and each of these individual components is additionally constrained by an energy balance equation. Evaporative cooling of the surface is balanced by radiation and sensible heat flux. The condensational heating of the atmosphere associated with precipitation is balanced by radiative cooling and sensible heat flux. These 3 balance equations provide a theoretical framework for analyzing the climate models. Our main analysis approach consists of plotting time series and contour plots of the terms in these equations, which we then compare with global precipitation. Our goal is to come up with a scientific explanation of the differences in precipitation across models, which will then allow us to better predict changes in global and regional precipitation in a warming climate.

 With lightning serving as a threat to life and property, understanding the factors that contribute to its frequency are important. Lightning forms when ice particles within clouds separate into lighter and heavier pieces, which creates charge separation in the cloud. If the updraft (a region of vertically moving air) within the cloud causes the distance between the positively- and negatively-charged regions of cloud to be large enough, an electric current flows to cancel this difference in charge. Convection associated with cold air outbreaks over the Northeast Pacific Ocean can occasionally produce lightning. These cold air outbreaks are extensions of larger synoptic scale systems (i.e. extratropical cyclones) that are powered by strong horizontal temperature gradients, the gradients themselves are defined by fronts. It is in the areas of colder air aloft, behind the cold front, where convection can occur. Unfortunately, limited observations in this region make it difficult for forecast models to accurately predict these electrically-active storms. Lightning data from the World Wide Lightning Location Network (WWLLN) is used during the wintertime months of November–March from 2015–2018 to relate the density of cloud-to-ground lightning strikes to the cold air outbreak events classified by anomalies of height from the climatological mean using the European Center for Medium-Range Weather Forecast (ECMWF) Re-Analysis (ERA5) dataset. This dataset is also used to calculate atmospheric instability in order to quantify the ability of the atmosphere to support convection. Finally, satellite measurements of cloud top height are used to evaluate whether a relationship exists between cloud depth and lightning frequency. Preliminary results suggest an increase in lightning activity as post-frontal convection associated with these cold air outbreaks makes landfall onto the West Coast. The findings from this study will benefit forecasting post-frontal convection over oceanic regions and their effects as the storms move over land.

The health of marine ecosystems is often determined by water chemistry balance and the levels of nutrients. Nutrients, such as nitrates, are essential to primary productivity. When they are present in excess, nutrients can lead to harmful algal blooms (HABS), eutrophication, and hypoxic conditions at depth due to phytoplankton decomposition. With decreasing dissolved oxygen, respiring plants and animals are at risk. Because of the potential negative impacts to the ecosystem, it is crucial to monitor these factors. We investigated the health of Possession Sound through levels of nitrate, dissolved oxygen (DO), and phytoplankton densities to investigate changes over time and indications of eutrophication. We hypothesized that the plankton populations would be less dense in areas with low DO levels and denser in areas with high nitrates. We used long-term water quality monitoring data collected by Ocean Research College Academy (ORCA) from 2014-2019 from five different sampling locations. Overall, trends from 2014 - 2019 showed that there was no linear correlation between nitrates, DO, and phytoplankton densities. It appeared that plankton density generally alternated every other year between highs and lows. Seasonally, DO was higher in the spring and summer, and Nitrates were higher in the fall and winter. Phytoplankton appeared to be greatest in the spring, with 2014 and 2018 having the largest blooms. Over time, nutrient levels changing can greatly affect the marine ecosystem in Possession Sound by creating an environment for excess plankton and algae blooms to occur and potentially harming fish populations. By observing a smaller sample of oceanic environments, we can see what could potentially occur in the open ocean if human influence goes unchanged.

Members of the genus Psychrobacter, within the class Gamma-proteobacteria, generally live in very cold marine habitats. These bacteria can be found in Arctic and Antarctic sea ice and sediments, in deep-sea environments, and in permafrost containing relic marine sediments (cryopeg). Each of these environments provides a different combination of temperature and salinity, with different strains of Psychrobacter spp. potentially adapted to grow at different rates depending on environmental source and in situ conditions. I am exploring the growth characteristics of two Psychrobacter spp., each isolated from a different extreme environment. Psychrobacter sp. nov. strain CB7C was isolated from cryopeg brine (originally at –6°C and 140 ppt), and Psychrobacter sp. nov. strain 7E was isolated from winter sea ice brine (originally at –12°C and 128 ppt). We incubated strain CB7C in duplicate at 57 different sets of temperature and salinity conditions, including 19 temperatures, ranging from –7 to 12°C, and salinities of 35, 75, and 120 ppt. The strain was grown in a complex medium, Marine Broth 2216 (at 50% organic strength), adjusted to desired salinity. At regular intervals during the incubations optical density was measured, with cell counts made at start and end. Calculated growth rates and cell yields for CB7C varied across the different temperatures for each salinity. At higher salinity, the temperature at which the bacteria showed maximal growth shifted downwards, a result consistent with in situ conditions (lower temperatures at higher salinities) but novel in microbiology. By conducting similar incubations with strain 7E I will be able to compare growth patterns of the two isolates across a wide set of temperatures and salinities and determine if results with CB7C are singular or represent a more common trait amongst Psychrobacter strains, helping to explain their prevalence under such extreme conditions.