Ocean Breathing

INTRODUCTION

Beneath the ocean surface, an extraordinary process is taking place on a planetary scale. Microscopic organisms known as phytoplankton capture sunlight and use photosynthesis to convert carbon dioxide and water into organic matter, releasing oxygen in the process.

Although most phytoplankton are invisible to the naked eye, together they form one of the most important biological systems on Earth. Scientists estimate that roughly half of Earth’s oxygen production comes from the ocean, with photosynthetic plankton responsible for most of it.

Phytoplankton also form the foundation of most marine food webs. Their growth supports zooplankton, fish and ultimately many of the larger animals associated with healthy ocean ecosystems.

At the same time, phytoplankton are deeply connected to the global carbon cycle. By absorbing carbon dioxide during photosynthesis and transferring carbon through marine ecosystems, they help connect the atmosphere, surface ocean and deep sea.

The ocean may appear blue and empty from above, but at microscopic scale it contains a vast living system helping power life across our planet.

WHY IT MATTERS

Ocean photosynthesis helps sustain the atmosphere. Phytoplankton, algae and photosynthetic bacteria collectively contribute an enormous share of global oxygen production. NOAA estimates that roughly half of the oxygen produced on Earth comes from the ocean.

Phytoplankton support marine food webs. These microscopic primary producers convert sunlight into biological energy. That energy moves through marine ecosystems as phytoplankton are consumed by zooplankton and other organisms, eventually supporting fish, seabirds and marine mammals.

They are part of Earth’s carbon system. During photosynthesis, phytoplankton absorb carbon dioxide. Some of this carbon moves through the food web, while some can eventually be transported into deeper ocean waters through processes collectively associated with the biological carbon pump.

Changes at microscopic scale can have enormous consequences. Because phytoplankton sit at the base of marine ecosystems, changes in their abundance, distribution or species composition can influence organisms far above them in the food web.

Understanding phytoplankton therefore means understanding one of the fundamental biological connections between the ocean, atmosphere, climate and life on Earth.

KEY FACTS

About half of Earth’s oxygen production comes from the ocean. Most of that marine oxygen production comes from photosynthetic plankton.

Phytoplankton are the foundation of most marine food webs. They transform sunlight and nutrients into biological energy that supports life throughout the ocean.

Phytoplankton contribute around 45% of global primary production despite representing less than 1% of Earth’s photosynthetic biomass.

Phytoplankton absorb carbon dioxide through photosynthesis. They are an important part of the ocean’s biological carbon pump, which helps transfer carbon through the ocean system.

Scientists can observe phytoplankton from space. Satellites measure ocean colour and chlorophyll concentrations, allowing researchers to monitor phytoplankton abundance, blooms and changes across enormous areas of the ocean.

Phytoplankton are extraordinarily diverse. They include organisms such as diatoms, dinoflagellates, coccolithophores and photosynthetic cyanobacteria, each playing different roles in marine ecosystems and biogeochemical cycles.

Main Threats

Ocean warming is changing phytoplankton habitats. Temperature influences metabolism, growth, nutrient availability and the structure of marine ecosystems. As the ocean warms, suitable conditions for different phytoplankton groups can shift geographically and seasonally.

Changes in ocean circulation can alter nutrient supply. Phytoplankton require nutrients as well as sunlight. Changes in mixing, currents and upwelling can affect how nutrients from deeper waters reach the sunlit surface ocean.

Ocean acidification changes marine chemistry. As the ocean absorbs additional atmospheric carbon dioxide, seawater chemistry changes. Different phytoplankton groups may respond differently, potentially altering marine communities and carbon cycling.

Pollution and excess nutrients can destabilize coastal ecosystems. Agricultural runoff, wastewater and other nutrient inputs can trigger excessive algal growth. When large blooms decay, decomposition can consume oxygen and contribute to low-oxygen conditions.

Some phytoplankton blooms can become harmful. Certain species naturally produce toxins, and under favorable conditions they can form harmful algal blooms that affect marine wildlife, fisheries, aquaculture and human health.

Multiple pressures can interact. Warming, changing nutrient availability, acidification, deoxygenation and pollution do not occur independently. Together they can reshape plankton communities and the marine ecosystems that depend on them.

SOLUTIONS

Reduce greenhouse-gas emissions. Limiting global warming is fundamental to reducing long-term changes in ocean temperature, chemistry, circulation and ecosystem structure.

Reduce nutrient and chemical pollution. Better wastewater treatment, improved agricultural practices and stronger pollution controls can reduce excessive nutrient inputs and harmful coastal algal blooms.

Protect functioning marine ecosystems. Healthy food webs, coastal habitats and marine biodiversity can make ecosystems more resilient to environmental change.

Expand ocean observation. Satellites, research vessels, autonomous floats, sensors and biological sampling allow scientists to monitor phytoplankton and detect changes across local and global scales.

Improve our ability to identify phytoplankton. Different species respond differently to environmental change. New satellite instruments, microscopy, genetic analysis and environmental DNA can help scientists understand which organisms are present — not simply how much chlorophyll exists in the water.

Connect ocean science with climate policy. Phytoplankton demonstrate that microscopic biological processes can influence planetary systems. Protecting ocean function therefore needs to be part of wider climate, biodiversity and pollution strategies.

Invest in long-term research. Ocean ecosystems are changing over decades. Continuous observations are essential for separating natural variability from long-term trends and understanding what those changes mean for marine life and people.

WHAT YOU CAN DO

Understand the connection. The oxygen cycle, climate system and marine food web are deeply connected to microscopic life in the ocean. Learning about phytoplankton is an important first step toward understanding why ocean health matters.

Reduce your climate impact. Energy use, transport and consumption contribute to greenhouse-gas emissions that affect ocean temperature and chemistry. Supporting the transition toward low-carbon energy helps address these pressures at their source.

Prevent pollution from reaching waterways. Plastics, chemicals, fertilizers and other pollutants can travel through rivers and drainage systems before eventually reaching coastal waters and the ocean.

Support ocean science. Satellite missions, research expeditions, monitoring programs and long-term datasets are essential for understanding how marine ecosystems are changing.

Support responsible environmental policy. Strong climate policy, water-quality regulation, pollution prevention and marine conservation all contribute to protecting the systems on which phytoplankton and wider marine ecosystems depend.

Share credible ocean science. Many of the planet’s most important organisms cannot be seen without a microscope. Helping others understand the role of phytoplankton can make an otherwise invisible part of Earth’s life-support system visible.

Think beyond individual action. Personal choices matter, but protecting planetary ocean processes requires governments, industries, scientists and communities to work together at scale.

SOURCES

NOAA Ocean Service — How Much Oxygen Comes From the Ocean?
Overview of marine oxygen production and the role of photosynthetic plankton. National Ocean Service
NOAA — How Much Oxygen Comes From the Ocean?

NOAA Ocean Service — What Are Plankton?
Introduction to phytoplankton, photosynthesis and their role in marine ecosystems. National Ocean Service
NOAA — What Are Plankton?

NOAA Fisheries — Phytoplankton of the Northeast U.S. Shelf Ecosystem
Information on primary production, marine food webs, carbon cycling and phytoplankton research. NOAA Fisheries
NOAA Fisheries — Phytoplankton

NASA Science — A Sea Aswirl With Chlorophyll
Explains satellite observations of phytoplankton, chlorophyll, oxygen production and the biological carbon pump. NASA Science
NASA Science — A Sea Aswirl With Chlorophyll

NASA — Identifying Phytoplankton Species From Space
Explains phytoplankton diversity, global primary production and why identifying different phytoplankton communities matters. NASA
NASA — Phytoplankton From Space

Smithsonian Ocean — Phytoplankton
Accessible scientific overview of phytoplankton as the foundation of ocean food webs. ocean.si.edu
Smithsonian Ocean — Phytoplankton

Ocean Photosynthesis & Phytoplankton