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 investigated the links between surface ocean phytoplankton communities and sinking carbon flux (Kramer et al., 2025 The ISME Journal). Using samples collected from the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaigns, I compared phytoplankton community composition in the surface ocean to the phytoplankton found in sinking particles to consider export mechanisms and carbon sequestration efficiency for different taxa.
This work is continuing with support from a NASA EXPORTS phase II grant in collaboration with colleagues at MBARI, UMaine, and Bigelow. We are investigating flux mechanisms for different phytoplankton taxa, mechanistic links between zooplankton grazing and phytoplankton carbon export, and predictive models linking surface phytoplankton community composition (particularly that which is visible from space via PACE) to carbon export flux.
Global surface ocean phytoplankton community composition
Much of my work involves describing 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. I started with phytoplankton pigments, compiling a large, quality-controlled dataset of phytoplankton pigments measured with High Performance Liquid Chromatography (HPLC; Kramer and Siegel, 2019 JGR Oceans) to examine the distribution of pigments on global scales, and 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 Remote Sensing of Environment). 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 to create algorithms that can be applied to NASA's Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) satellite, which launched in February 2024. My approach to describing phytoplankton communities from space involves comparing the performance and information content of different in situ methods used to describe phytoplankton community composition and for algorithm validation (Kramer et al., 2024 L&O Methods). My work over the years has contributed to this goal of in situ method intercomparison, and I am continuing to investigate these questions as PACE data becomes available (Kramer et al., 2024 Optics Express).
Wildfire impacts on ocean ecosystems
In late 2016, a group of UCSB graduate students in the Interdepartmental Graduate Program in Marine Science (including me!) 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., 2020 JGR Oceans). Potential impacts of wildfire smoke and ash on marine ecosystems remains an area of active interest for me (e.g., Kramer et al., 2023 Frontiers in Marine Science), particularly as an organizer of the 2022 C-SAW OCB scoping workshop. I am curious to think about how wildfires impact marine ecology and biogeochemistry, particularly when our observations of these systems are constrained during these extreme events.
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, which have both helped us to share the impacts of this scientific research far beyond our resulting journal articles.
EXport Processes in the Ocean from RemoTe Sensing (EXPORTS)
EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) was a 2018 + 2021 NASA field campaign that aimed 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 also participated in a number of projects related to EXPORTS, including method comparisons for biogeochemical variables (Graff et al., 2023 Elementa), efforts to characterize phytoplankton community composition across methods (Kramer et al., 2024 L&O Methods) and relate those measurements to ecosystem productivity (Meyer et al., 2024 GBC), and laboratory work to process samples collected at sea. The relationships between surface ocean conditions and carbon export remain an active focus of my research.
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., 2020 Frontiers in Marine Science), to compare estimates of phytoplankton size from pigment-based methods vs. flow cytometry and cell imaging (Chase et al., 2020 L&O Methods), and to consider the role of phytoplankton community composition in net primary productivity (Fox et al., 2020 Frontiers; 2022 L&O Letters) or viral infection of cells measured on NAAMES (Diaz et al., 2021 Nature Communications). These fundamental questions in phytoplankton ecology, relating environmental change to community composition and physiology, remain a major area of interest for my current and future research directions.