Chemical Oceanography

Students and Postdocs


Kenny Bolster

Advisor: James Moffett
B.S.A. Chemistry (Russian language minor), University of Texas
PhD Student Department of Earth Sciences, University of Southern California

I study the chemical reactions of iron within anoxic parts of the ocean. I've worked on developing improved methods to measure chemical compounds that I'm interested in. I measure the distributions of different iron compounds throughout the oxygen deficient zone off the Pacific coast of Southern Mexico, and do incubations to measure rates of reactions. I'm trying to understand how iron gets transported away from the coast in these areas and affects ecosystems on a global scale. I also do work at USC's research station on Catalina Island, studying chemical reactions driven by light at the ocean surface, and I've been experimenting with using a quadcopter drone to collect surface samples without disturbing the water surface or bringing contamination from a boat.

Planned Thesis Title: Anaerobic Iron Cycling in a Marine Oxygen Deficient Zone

Recent Cruises

  • RB 16-03, NOAAS Ronald H. Brown, March 29- April 25, 2016
  • Ho Ho HODZ, R/V Sikuliaq, December 28, 2016 - January 16, 2017

Natalya Evans

Advisor: James Moffett
B.S. in Chemistry with emphasis on Materials Chemistry
PhD Student Department of Earth Sciences, University of Southern California

I investigate reactive intermediates across redox gradients, such as sulfide formed within reducing microenvironments in large sinking particles in Oxygen Deficient Zones or benthic Fe(II) fluxes in hypoxic waters. My research focuses on quantifying the abundance of these compounds, often in picomolar or nanomolar concentrations, and identifying the master variables that control their abundances. Since these compounds can originate from different source mechanisms, such as reducing shelf sediments, reducing microenvironments, or background biotic processes, I often work to decouple physical transport processes and incorporate biogeochemical modeling into my work for a thorough description of sulfide and Fe(II) chemistry. Water masses serve as a useful basis for understanding physical transport, both in regards to local chemistry as well as climate change-driven deoxygenation, which is vitally important.

Recent Cruises
  • R/V Falkor June 22 - July 21, 2018
  • R/V Kilo Moana, Sept. 21 - Oct. 22 2019, KM1919 and KM1920

Alexis Floback

Advisor: James Moffett
B.S. Marine Biology, Biology (chemistry, marine ecology minor), Nova Southeastern University
Ph.D. Student, Marine and Environmental Biology, University of Southern California

I’m interested in studying the intersection of chemical and biological oceanography, specifically the synergy between trace metal micronutrient distributions and biologic taxa in seawater. I spent my first year characterizing the rare earth distribution in the Arabian Sea oxygen deficient zone. Additionally, I have been working on trace metal clean culturing of SAR11, the most abundant heterotrophic bacteria in the ocean, to investigate the trace metal quotas of SAR11. Much of my thesis will focus on investigating the offshore transport of metals and SAR11 clade distribution off of the seasonally hypoxic Oregon coast on a series of cruises aboard the R/V Oceanus.

Babak Hassanzadeh

Advisor: Laura Gó-Consarnau & Sergio Sañ-Wilhelmy labs

B.S. Chemistry (UCLA)
USC Provost Fellow

My research involves studying proteorhodopsin photosystems in marine microbial communities. Proteorhodopsin is a light-driven proton pump which contributes to the proton motive force across a membrane and therefore cellular energy supply. Genomic studies have shown that proteorhodopsin is present in more than half of the bacterial taxa in the ocean; however its ecological role is poorly understood, mainly due to the lack of appropriate methods for quantifying this photosystem. I have played an integral role in developing a new, high-throughput analytical technique to quantify proteorhodopsin in natural microbial assemblages by measuring the retinal chromophore as a proxy. Using this technique, my goal is to investigate how light and nutrient availability in different oceanic regimes influence the abundance of proteorhodopsin, in particular relative to the well studied pigment, chlorophyll-a. Ultimately, our understanding of how sunlight is utilized within microbial communities may change as a result of our increasing knowledge about proteorhodopsin abundances and its ecological role.

Cruise Experience: Sep 2016-Dec 2017: monthly cruises at SPOT (San Pedro Ocean Time Series); Feb . Mar 2018: R/V Atlantis, tropical Atlantic Ocean

Rachel Kelly

Advisor: Seth John
B.A. Marine Science (Chemistry Minor), University of South Carolina
Ph.D. Student, Earth Sciences Department, University of Southern California

My research includes observing the metal limitations of several species of marine bacteria, so far from the genera Vibrio and Cellulophaga. Additionally, I study how those metal limitations may or may not affect the bacteria's viral dynamics (e.g. latent period, burst size) by conducting one-step phage growth experiments. I also look for metal limitation in natural marine environments by conducting in situ Fe and Zn additions. I'm interested in trying to quantitatively measure how much iron is recycled back into the microbial loop through lysates in the viral shunt. I hope to use these lab and field measurements to enhance computer models that represent the marine microbial loop and the viral shunt.

Recent Cruises

  • MESO-SCOPE cruise, Hawaii, June 26th - July 14th 2017
  • Ho Ho HODZ cruise, Hawaii, December 28th , 2016- January 16th , 2017

Nathaniel Kemnitz

My name is Nathan Kemnitz and I am a second year Master’s student in the Earth Sciences department at USC. I have undergraduate degrees in Geology and Chemistry and I want to use my knowledge I gained from my undergrad courses to studying our oceans. My current Master’s research focuses on measuring naturally occurring radioisotopes in the ocean as to answer important oceanographic question. Below is a recent abstract I presented this year.

227Ac along C-Disk-IV Transects in the Northeast Pacific


227Ac (t1/2=22 yrs) is directly produced by decay of 231Pa (t1/2=32,000 yrs). 231Pa is scavenged in the water column by falling particulates that carry it to sediments, where it decays to its more soluble daughter. 227Ac diffuses out of deep-sea sediments and mixes upward, so it can be used as a tracer for deep ocean diapycnal mixing. Five 227Ac profiles were measured in the Northeast Pacific during the C-Disk-IV Cruise (Chief Scientists, Berelson and Adkins) aboard the R/V Kilo Moana during August 2017, along a transect from Hawaii to Alaska. Profiles of excess 227Ac were fit with a 1-D vertical model to determine diapycnal eddy diffusivity in an effort to describe deep ocean mixing and give insight into deep water circulation pathways throughout this region.

Planned thesis title: Actinium-227 fluxes from the Seabed as a Constraint on Deep Ocean Mixing

Hengdi Liang

Advisor: Seth John Undergraduate Institution: Nanjing University (China)

Arriving in John's lab in 2017, Hengdi's research involves the use of mathematical and computer modeling to understand ocean circulation and biogeochemical processes. Her first project is designing a GUI for Awesome OCIM using MATLAB, then combining models and observations to explore the distribution of trace elements in the ocean.

Erin McParland

Advisor: Naomi Levine
B.S. Marine Science (Chemistry Minor), University of South Carolina
Ph.D. Candidate, Marine and Environmental Biology, University of Southern California

My thesis seeks to understand the cycling of dissolved organic matter and its relation to upper ocean carbon and sulfur cycling, with a focus on the climatically active marine phytoplankton metabolite, DMSP (dimethylsulfoniopropionate). DMSP is a labile compound with a dissolved pool that can be that can be turned over multiple times a day and satisfy a significant amount of marine bacterial carbon and sulfur demands. I use laboratory mono-culture studies and natural mixed community deckboard incubations to probe the response of phototrophs to different environmental cues and measure the resulting change of DMSP production. In particular, I am interested in understanding how different nutrient stressors (N and B12) and the presence of heterotrophic partners alter the production of DMSP. Understanding regulation of DMSP production is key to understanding its contribution to organic carbon cycling and its role in climate regulation.

Cruise Experience:
ProteOMZ, R/V Falkor (28 days Hawaii to Tahiti)
Reefs to Rainforest, R/V Investigator (29 days circumnavigation of the Great Barrier Reef)
Subarctic DMS(P) cycling, R/V Oceanus (20 days Seward, Alaska to Corvallis, Oregon)

Rin Moriyasu

Advisor: James Moffett
Undergraduate Institution: B.A Chemistry, Whitman College PhD Student, Biology department, University of Southern California

I am a first year graduate student working in the Moffett lab. During my time at my undergraduate institution, I worked on quantifying the inclusion of water in biogenic aragonite of Scleractinian corals. Currently, I am studying the lability of copper in the water column in the hopes that it brings insight into copper cycling in marine ecosystems.

Xuening Wen

Advisor: Naomi Levine

My research focuses on the interactions between upper ocean physical dynamics and biogeochemical cycling. Specifically, I am working on estimating shifts in phytoplankton community composition, and the resulting impact on carbon cycling, driven by a patchy physical environment. The first step of my research is to couple a probabalistic modelling framework of fine-scale episodic upper ocean dynamics with vertical structure.

Jessica Zaiss-Bowman

Advisor: Naomi Levine

Phytoplankton are responsible for nearly half of all photosynthesis on the planet and as such play a vital role in the global carbon cycle. Rising global temperatures will certainly influence phytoplankton primary productivity as previously investigated in steady state laboratory experiments and poorly parameterized, global climate models. However, only a few studies have investigated how spatiotemporal temperature variability, not just mean state, affects productivity. For my research I will incorporate data from lab experiments and remote sensing to develop a better model for primary productivity that includes the effect of temperature variability, as well as changes in the mean state.


Nick Hawco

Advisor: Seth John
Simons Postdoctoral Fellow
Ph.D. MIT/WHOI Joint Program in Chemical Oceanography (2017)

All life on earth needs iron and the oceans are no exception. I want to know exactly how much iron a healthy ocean needs. At sea, Iâ collected hundreds of seawater samples to find out how iron enters, cycles, and eventually leaves in the ocean. In the lab, I grow phytoplankton in bottles and measure their iron requirements. Its only by comparing the supply and demand of iron and other nutrients that we can predict how life in the oceans will change in the future.

Recent cruise experience
  • R/V Kaâikai-O-Kanaloa, HOT-LAVA cruise. North Pacific Ocean, July 2018
  • R/V Falkor, EDDIES cruise. North Pacific Ocean, March-April 2018
  • R/V Kilo Moana, MESOSCOPE cruise. June-Jul 2017
  • R/V Marcus G. Langseth, Gradients 2.0 cruise. May-June 2017

Paulina Pinedo-Gonzalez

Advisor: Seth John
Postdoctoral Researcher

A significant portion of my research is focused on generating new data on some biologically essential and anthropogenic metals in a wide variety of marine environments (i.e. North Pacific, Southern, and Arctic Oceans) to investigate the physico-chemical and biological influences that interact to control metal biogeochemistry in the ocean. I am also interested in applying trace metal isotopes as proxies to understand the cycling of metals in the ocean (i.e. Fe, Cd, Zn, and Pb isotopes). This research involves the analysis of a suite of dissolved and soluble trace-metals in seawater using trace-metal-clean techniques, HR-ICP-MS, and MC-ICP-MS.

Emily Zakem

Advisor: Naomi Levine

I am interested in the relationships of microbial ecology and global biogeochemistry. My research combines knowledge of microbial metabolisms and the physical transport within the earth system to gain a mechanistic understanding of biogeochemical cycling. I am specifically interested in the microbially-mediated marine nitrogen and oxygen cycles, with the goal of better understanding the distributions of nitrogen, oxygen, and other nutrients in the context of current ocean warming and deoxygenation. I use modeling as a tool to integrate micro- and global-scale processes.