Linking surface phytoplankton to sinking carbon flux
The export of phytoplankton to the deep ocean is an important pathway for carbon sequestration, but the amount and types of phytoplankton exported from the surface ocean to the mesopelagic are poorly constrained for most ecosystems. My postdoctoral work in the Carbon Flux Ecology lab at MBARI investigates the links between surface ocean phytoplankton communities and sinking carbon flux. Using samples collected from the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaigns, I compare phytoplankton community composition in the surface and deep ocean to consider export mechanisms and carbon sequestration efficiency for different phytoplankton taxa.
Through this work, I will address the following questions: How are phytoplankton taxa distributed between different carbon pools at depth? What is the flux mechanism for different taxa based on the distribution of phytoplankton taxa across particle types and sizes? Which phytoplankton contribute the most to carbon transport away from the surface ocean in each ecosystem? And finally, can we create predictive models to link surface phytoplankton community composition to carbon export flux?
Global surface ocean phytoplankton community composition
My dissertation work characterized phytoplankton community structure in the global surface ocean using a combination of in situ methods (pigments, flow cytometry, bio-optics, cell imaging, and metabarcoding) and remote sensing data. This work began by compiling a large, quality-controlled dataset of phytoplankton pigments measured with High Performance Liquid Chromatography (HPLC; Kramer and Siegel, 2019) to examine the distribution of pigments on global scales, as well as to consider the strengths and limitations of using HPLC pigment data for satellite algorithm validation. The next steps of this project involved linking these HPLC pigment observations to in situ measurements of hyperspectral remote sensing reflectance (Kramer et al., 2022). The code for the resulting Spectral Derivative Pigments (SDP) algorithm, which is being adapted as a NASA Plankton Aerosol Cloud and ocean Ecosystem (PACE) product, can be found on my GitHub.
I believe it is essential to develop quality-controlled, validated remote sensing algorithms to describe phytoplankton communities from space. My work focuses on hyperspectral reflectance data in anticipation of NASA's Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) sensor launch in January 2024. I also believe that it is important to compare the performance and information content of different in situ methods used to describe phytoplankton community composition and for algorithm validation, which I explored more in my final dissertation chapter (Kramer et al., in review). My undergraduate thesis work at Bowdoin College, my dissertation work, and my side projects all contribute to this goal of in situ method intercomparison.
EXport Processes in the Ocean from RemoTe Sensing (EXPORTS)
EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) is a NASA field campaign to describe and quantify the export of carbon from the upper ocean to the deep ocean using in situ technology and remote sensing. I participated in both EXPORTS cruises as a member of the science team: in the North Pacific Ocean to Station P in August and September 2018 and in the North Atlantic to the Porcupine Abyssal Plain (PAP) observatory site in May 2021. I have also participated in a number of projects related to EXPORTS, including method comparisons for biogeochemical variables (Graff et al. accepted at Elementa), efforts to characterize phytoplankton community composition across methods (Kramer et al. in review), and laboratory work to process samples collected at sea.
North Atlantic Aerosols and Marine Ecosystems Study (NAAMES)
The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) was a five year NASA field campaign examining the North Atlantic annual phytoplankton bloom over four seasons/bloom phases. I participated in the 4th NAAMES cruise in March and April 2018 as a member of the science team. Since then, I have collaborated with other NAAMES team members on projects to characterize phytoplankton community composition from HPLC pigments (Kramer et al., 2020a), to compare estimates of phytoplankton size from pigment-based methods vs. flow cytometry and cell imaging (Chase et al., 2020), and to consider the role of phytoplankton community composition in net primary productivity (Fox et al., 2020; 2022) or viral infection of cells measured on NAAMES (Diaz et al., 2021).
Wildfire impacts on ocean ecosystems
In late 2016, a group of UCSB graduate students in the Interdepartmental Graduate Program in Marine Science (IGPMS) wrote a proposal to the UC Ship Funds program for a research cruise onboard R/V Sally Ride to examine the daily patterns of phytoplankton, zooplankton, and bacteria in the Santa Barbara Channel, CA. When we were granted the funding in early 2017, we had no way of knowing that the Thomas Fire (one of the largest wildfires in California history, and the largest at the time) would break out just days before we left port. We quickly pivoted our science goals to examine the impacts of smoke and ash on the biogeochemistry of the SBC. This project has led to several talks, a commentary in Oceanography, and a research article examining the interactions between wildfire ash and phytoplankton community composition (Kramer et al., 2020b). Potential impacts of wildfire smoke and ash on marine ecosystems remains an area of active interest for me (see: Kramer et al., 2023), particularly as an organizer of the 2022 C-SAW OCB scoping workshop.
This project also encouraged me to include artists in existing and future fieldwork. The artists on our ACIDD cruise (Gad Girling, Celia Jacobs, and Dustin Hayes) created an exceptional documentary (Aquatic Cathartic) that was honored at the DC Environmental Film Festival, as well as the Migrations magazine.