The ocean and atmosphere interact through air-sea exchanges of heat and energy across the air-sea interface. These air-sea fluxes have important implications on global weather and climate patterns. Because estimation of covarying turbulent variations is not feasible in Numerical Weather Prediction (NWP) models, the turbulent air-sea exchanges are typically estimated using bulk air-sea flux algorithms based on state variables. However there are large differences in the values estimated by different NWP and even when they agree, without a reference data set, it may be that all NWP are equally biased. For this project, I used in situ observations collected by Saildrone Uncrewed Surface Vehicles (USV) in the central tropical Pacific to assess bulk flux estimates from multiple atmospheric reanalyses including NCEP Climate Forecast System Reanalysis (CFSR), ECMWF Reanalysis v5 (ERA5), NCEP/NCAR Reanalysis 1 (NCEP1), and NCEP/DOE Reanalysis 2 (NCEP2). Preliminary results, based upon hourly, spatially-interpolated, co-located values that are then made into 24-hour “daily” averages, indicate that all of the reanalyses had a strong correlation with USV observations for net heat flux and net SWR, but the correlation was much weaker (0.5 to 0.7) for other flux components and very weak (~0.25) for the net longwave radiation for NCEP1 and NCEP2. The root mean square errors for the 24-hour-averaged differences were 55 to 66 W/m^2 for solar radiation and 20 to 30 W/m^2 for latent heat flux. In my analysis of my results, I looked at the differences region by region for each of the flux components and state variables as well as for each of the products. As Saildrone technology becomes more widely used and more intercomparison studies such as this are conducted, observations from Saildrones could eventually be integrated into NWP models, possibly improving forecast accuracy.

Metabolites are small organic compounds that are the products of cellular metabolism and the building blocks of macromolecules. The analysis of a multitude of metabolites in a sample simultaneously is known as metabolomics and is a powerful tool for understanding microbial interactions in the ocean. In particular, metabolomics provides a way to investigate how marine communities vary in composition during shifts in environmental conditions. The North Pacific Subtropical Gyre (NPSG) is a region where inorganic nitrogen availability limits phytoplankton productivity and microorganisms rely partially on diazotrophs for fixed nitrogen in the surface ocean. Because N2 fixation is often iron-limited, bioavailable iron should control fixed nitrogen levels in the gyre. Here, we tested this hypothesis by collecting metabolomic samples during a large-volume incubation in which tanks were amended with various nutrient combinations of iron, nitrogen, and phosphate during a month-long incubation. It was expected to stimulate a diazotroph bloom by limiting the incubation for nitrogen. In these nitrogen-limited tanks, we expect to see a strong metabolic response to the absence of fixed nitrogen, followed by the ingrowth of nitrogen fixers with their own metabolite fingerprints as the experiment progresses. I will compare metabolomes of incubations to those of phytoplankton cultures, including the nitrogen-fixing cyanobacteria UCYN-A and Trichodesmium. I will also use the incubation's nutrient concentration and microbial community metabolomics to test the hypothesis that altering nutrient supply ratios (Fe: N: P) in the NPSG microbial population will result in metabolite shifts. As the critical link between inorganic matter and the formation of the organic material that powers the ocean’s food chains and biological carbon pump, metabolomics provides a way to better understand the critical role that nitrogen fixation plays in regulating the taxonomy and biochemistry of the world’s largest biomes.

About one-quarter of photosynthetically fixed carbon is cycled through the marine microbial community in the form of metabolites, the intermediate compounds or products of metabolic processes. Marine heterotrophic bacteria are largely responsible for consuming these metabolites as a source of carbon, energy, and nutrients, yet little is known about transporter affinity and uptake kinetics of bacteria for abundant substrates. Homarine is a small, nitrogen-containing, zwitterionic metabolite that is produced by the cyanobacterium Synechococcus as well as some diatoms and haptophytes, where it is thought to function as an osmolyte. Dissolved homarine is present in the ocean at very low concentrations (~1.1 nM in Puget Sound). I hypothesize that these low concentrations are the result of high affinity bacterial transporters for homarine. Homarine can be used as a sole carbon and nitrogen source for OBi1, a marine bacterium isolated from Puget Sound. In this study, I investigate the uptake kinetics of homarine by OBi1 in the lab using the Michaelis-Menten model. I compare the uptake kinetics of OBi1 to similar homarine uptake experiments in the Salish Sea in June 2019. I expect that OBi1 will have a high affinity for homarine uptake and will take up homarine at nanomolar concentrations. I also anticipate that the marine microbial community in Puget Sound will have similar uptake kinetics to those observed with OBi1. Understanding the uptake kinetics of homarine by marine bacteria sheds light on the cycling of homarine in marine environments like Puget Sound and can help us understand the processes that keep the dissolved homarine concentration so low.

Cyanobacteria are tiny photosynthetic microbial organisms responsible for producing roughly an eighth of the oxygen we breathe. Synechococcus is a model cyanobacteria, meaning the species has characteristics making it easy to study and modify. As a scientific community, we don’t know the function or purpose of many genes expressed by Synechococcus. The goal of this project is to determine the function of particular genes hypothesized to be important to the adaptive survival of Synechococcus in different environments. We are approaching this by building a start-to-finish gene characterization method, starting with computational analysis to identify genes of interest, followed by knocking out, or disabling these genes and observing the effect on the growth of the culture. On the computational side, I’m now analyzing residual gene expression, using that information to characterize gene clusters, and analyzing external data to infer genetic context. On the laboratory side, I’ve characterized the growth of the un-modified base strains and developed procedures for genetic modification. Identifying the function of Synechococcus genes allows scientists to better study the response of Synechococcus to varying environments, which is especially important in a changing climate. Increasing understanding of the molecular mechanisms of Synechococcus also opens the door to genome engineering for the production of biofuels, plastics, and other commodities, or for using Synechococcus as a tool for bioremedial carbon sequestration. Additionally, the genes of Synechococcus are similar to those in other related oceanic microbes such as Prochlorococcus, the most ubiquitous photosynthetic organism in the world. For all these reasons, Synechococcus is an important model organism, and a deeper understanding of its biology will bolster our sparse understanding of marine genomics.

Cyanobacteria are ancient single-celled photosynthetic organisms, prevalent throughout Earth's oceans. Over billions of years, cyanobacteria have evolved genes that enable them to survive across a diversity of adverse, ever-changing environmental conditions. However, researchers are faced with the problem of not understanding the role of many of these genes. This research project entails tracking down the function of some high variance genes in marine Synechococcus, an important model organism and a genus of cyanobacteria. We will test gene function by generating knockout strains in which a gene of interest is inactivated, and testing the growth of these mutant strains in various conditions. In particular, our project focuses on the importance of the flavodoxin gene, which codes for an electron transport protein that is involved in photosynthesis and is expressed in response to iron scarcity. This gene inactivation is done with a plasmid, which is a genetic structure in bacteria that can replicate itself independent of bacterial chromosomal replication, that’s enabled to knock out the flavodoxin I gene when inserted into Synechococcus cells. We insert the plasmid into our Synechococcus cells and once the DNA is taken up by the cell, we then use CRISPR technology to remove the gene. Successfully creating the flavodoxin knockout of Synechococcus establishes the procedures necessary for generating knockouts of other genes that could be expressed in similar patterns as flavodoxin. Ultimately, this research furthers our understanding of how Synechococcus’ genes allow it to adapt to various environments and contributes to ongoing research on how organisms might withstand the pressures of Earth’s ever-changing climate.