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Exploring carbon export with ocean color

Sasha Kramer preparing a hyperpro radiometer on board the Paragon, along with other members of the Carbon Flux Ecology team.
Sasha Kramer preparing to deploy the HyperPro sensor, which measures something similar to what the PACE satelite sensor sees, but from a ship rather than from space! Image: Natalia Llopis Monferrer @ 2023 MBARI

Exploring carbon export with ocean color

Written by: Sasha Kramer (Simons Postdoctoral Fellow in Marine Microbial Ecology)

A true color image of phytoplankton in the California current. Areas with more phytoplankton have greener water.
A true color image of phytoplankton in the California current. Areas with more phytoplankton have greener water. Image: NASA

I recently attended a meeting where everyone was asked to summarize their work in haiku form. Here’s what I came up with:

Rainbow of pigments

Reflecting ocean colors–

Where cells become swirls.

My research before joining the Carbon Flux Ecology (CFE) lab could be described using those three lines. During my Ph.D. at the University of California, Santa Barbara, I studied the way that microscopic algal cells (i.e., phytoplankton) scatter and absorb light, and related these optical measurements to the type of phytoplankton community in the surface ocean. Phytoplankton change ocean color primarily through their differently-colored pigments, which they use to harvest light for growth via photosynthesis (like plants on land), or protect the cell from excess light, like sunscreen. When these tiny cells are in high enough abundance, they change the color of the ocean so much that we can see it from space using satellites.

Right now, we are really good at using ocean color satellites to know how much phytoplankton are in the surface ocean, but we can’t resolve which types of phytoplankton are there. In February 2024, NASA launched the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite—a new sensor that includes the Ocean Color Instrument to observe the surface ocean across the whole range of visible light and into the UV (i.e., the entire rainbow of colors). In grad school, I developed a model to describe the amount and types of 13 different phytoplankton pigments in the surface ocean using PACE data. We can describe five distinct types of phytoplankton with PACE from those pigment concentrations.

NASA's illustration of the PACE satellite
An artist’s rendition of the PACE satellite in space, including the Ocean Color Instrument (OCI). Image: NASA

So why do we care about different types of phytoplankton, anyway?! Different types of phytoplankton come in various shapes and sizes and contain different amounts of elements like carbon, silicon, and nitrogen. For instance, diatoms tend to have large cells that include a lot of carbon and are enclosed in a glass shell made of silicon, while cyanobacteria are tiny cells with relatively less carbon but can be superabundant in parts of the global ocean. By understanding the distribution of varying types of phytoplankton, we can better understand how these organisms contribute to marine food webs, cycle nutrients, and (most importantly in the CFE lab!) help transport surface ocean carbon to the deep sea.

My postdoc work in the CFE lab connects these different types of phytoplankton in the surface ocean and the amount of sinking carbon in the deep sea. We want to know how the phytoplankton that live at the sea surface, where they have enough light to photosynthesize and grow, are eventually transported to the mesopelagic. By using a combination of DNA data, microscope image data, and elemental analysis, we can tell the amount of carbon being exported in different types of particles, and the groups of phytoplankton found in each particle type.

Collage of diatom images collected by the imaging flow cytobot.
Images of diatoms collected using an Imaging FlowCytobot. Image: Sasha Kramer @ MBARI 2024

Eventually, we might be able to make models using PACE data that connect the global surface ocean to the amount of carbon export in the deep sea. This information will help us understand the impact of surface phytoplankton on the global biological carbon pump, which is an important process for buffering the amount of carbon in the atmosphere, particularly under anthropogenic climate change.

In the meantime, I’ll keep working on ways to describe my work through poetry. At the end of the day, I might prefer the haiku my friend came up with to describe my work through his eyes:

Phytoplankton float.

The ocean is their highway!

Tesla could never.