Carbon Cycling: Transformations in Ocean, Coasts, and Great Lakes Research

NOAA explores and investigates ocean habitats and resources, providing scientific results to help manage and understand fisheries, conserve and protect our coasts, and build a stronger economy through marine products and businesses, such as biotechnology and sustainable aquaculture. NOAA also looks for changes in the oceans due to natural and human activities.

Oceans—these vast expanses of water are intricately linked to our weather, climate, commerce, the food we eat, and so much more.

Since the mid-19th century, NOAA and its predecessors have been studying our oceans, coasts, and Great Lakes, to unlock their mysteries and help us manage the ocean and coastal resources on which we depend. One of these mysteries is how carbon cycles through our Earth system. The ocean carbon cycle is the circulation of carbon, primarily carbon dioxide, from the atmosphere to the ocean and from the ocean to the atmosphere. In this cycle, the ocean absorbs human-produced carbon dioxide that would otherwise end up in the atmosphere and ultimately affect global climate. The uptake of carbon dioxide by the ocean also changes the acidity of ocean water, which can impact marine animals and plants.

Explorer at Labadee

The Explorer of the Seas is a volunteer observing ship from which carbon dioxide measurements are taken. Here, it is anchored off the Labadee Resort in Haiti. Click image for larger view.

Research into the ocean carbon cycle spans many of NOAA’s programs because it requires studying the atmosphere and the physical, biological, and chemical characteristics of the oceans. The results of this research are applicable to everything from ocean life to climate change. By exploring how this cross-cutting research has evolved over the last 15 to 20 years, we can perhaps gain an appreciation of how some of NOAA’s laboratories involved in ocean research (or “wet labs”) are evolving to meet the needs of today.


Getting Started: The World Ocean Circulation Experiment

While NOAA has been sampling atmospheric carbon since the 1950s, it is only since the 1980s that we have been collecting similar carbon data for the oceans.

During the 1980s and 1990s, scientists from two of NOAA’s research laboratories, the Atlantic Oceanographic and Meteorological Laboratory (AOML) and the Pacific Marine Environmental Laboratory (PMEL), participated in a program called the World Ocean Circulation Experiment (WOCE). Although this experiment focused on ocean currents and heat content of the ocean, scientists also collected carbon dioxide samples during WOCE cruises. These samples were collected using conductivity, temperature, and density (or CTD) sensors and measuring instruments called rosettes.

Throughout the duration of the WOCE, researchers collected approximately 70,000 carbon dioxide samples from the Atlantic, Pacific, and Indian oceans.

From these samples, scientists were able to increase their knowledge of ocean currents and heat content of the ocean. This was a significant increase to the amount of data scientists previously had on the ocean and the experiment significantly improved the way scientists understand the ocean.

Conductivity, Temperature, and Density (CTD) sensor

Scientists prepare an instrument called a conductivity, temperature, and density (or CTD) sensor for deployment. Click image for larger view.

As part of the WOCE, surveys are scheduled on a decadal repeat cycle (every 10 years) because of the length of time that it takes for the uptake of carbon dioxide to measurably change the carbon content in the oceans.  When scientists first began to study the ocean carbon cycle, surveys were done as frequently as possible to establish a benchmark. Now, scientists are able to select specific locations to sample in order to get an idea of the decadal time scale of the carbon cycle.  At first scientists took many samples in order to get an idea of what carbon levels were common in the oceans. After this benchmark was established, they were able to sample less frequently because carbon content changes slowly in the world oceans. Scientists are now able to select fewer sampling sites, allowing them to avoid the expense of taking frequent ship-board measurements.


This is Now…

Deploying the Conductivity, Temperature, and Density (CTD) sensor

Here, scientists deploy a conductivity, temperture, and densty (or CTD) sensor from a research ship.

Today, AOML and PMEL remain the main NOAA contributors to ocean carbon cycle research. Investigators at AOML and PMEL have worked closely over the past 15 years to gather data on the ocean carbon system. AOML researchers collect and study samples from the Atlantic and Indian Oceans, whereas PMEL samples in the Pacific Ocean. Scientists from both labs are involved in a range of research, building upon the work of the WOCE and earlier carbon cycling research to increase our understanding of the ocean carbon cycle.


A Global Sampling Network

Components of CO2 instrument

Close-up of the components of an instrument that measures carbon dioxide concentration onboard a voluntary observer ship. Click image for larger view.

Today, AOML and PMEL have several projects focused on the ocean carbon cycle.  One project involves creating a global ocean carbon dioxide sampling network by gathering measurements of surface carbon dioxide levels from vessels such as the NOAA research vessels, the Ronald H. Brown and Ka’Imimoana, as well as from volunteer observing ships.  This project allows researchers to study the exchange of carbon dioxide between the ocean and the atmosphere.  Water column measurements are also taken to find the amount of total carbon content in seawater, to determine changes over time.



PMEL has started to build a network of carbon dioxide sensors on coastal and open ocean moorings. One such network is the Tropic Atmosphere-Ocean (TAO) array in the equatorial Pacific.

Tropical Atmosphere Ocean instrumentation buoy

A buoy in the TAO/TRITON array, located in the equatorial Pacific.

The TAO project, in collaboration with Japan’s Triangle Trans-Ocean Buoy Network (TRITON), supports a series of buoys in the Pacific basin that provide vital data to oceanographers and meteorologists. This includes high-resolution time series measurements that provide information on the variability of carbon cycle time scales on several time levels.  The TAO/TRITON array consists of about 70 moorings in the tropical Pacific, covering three times the area of the continental United States.

The TAO/TRITON array plays a large role in the El Niño/Southern Climate Oscillation Observing system. Data from the array are used for research and forecasting of El Niño and La Niña, which originate in the tropical Pacific through ocean-atmosphere interactions. El Niño and La Niña are the strongest year-to-year fluctuations of the climate system, affecting the lives and livelihoods of millions around the world. The TAO/TRITON array is one of the most visible and successful ocean observing systems ever developed for climate and will also provide valuable information for understanding the ocean carbon cycle.



The Climate Variability and Predictability (CLIVAR) program is an international, interdisciplinary research effort within the World Climate Research Program. CLIVAR focuses on improved understanding of the variability and predictability of the varying components of the climate system. CLIVAR researchers, including NOAA scientists, investigate dynamic physical processes in the climate system, which occur on seasonal, inter-annual, decadal and centennial time-scales.

US CLIVAR, the component of CLIVAR managed by the United States, hopes to leave as its legacy improved predictive capability of coupled ocean-atmospheric climate models. Carbon dioxide is one parameter that is important to capture in these models.

Currently, researchers from AOML and PMEL are performing carbon dioxide measurements on CLIVAR/carbon dioxide hydrographic cruises. Fifteen to 20 cruise tracks are sampled once every 10 years to monitor decadal changes. This strategy differs from the earlier, more frequent participation on WOCE cruises that enabled scientists to get a good idea of where to take samples. The new strategy was implemented because carbon content in the oceans cycles slowly, so there is no need for more frequent cruises. Therefore, in order to get the best science in the most cost effective manner, scientists selected fewer cruise tracks to be samples every 10 years.

The CLIVAR/ Carbon Dioxide Repeat Hydrography program began in 2003 and cruises will continue thru 2012.  During this time two to three cruise tracks will be sampled a year by NOAA and the National Science Foundation and different areas will be done at different times.

Ronald  H. Brown, NOAA research ship

The Ronald H. Brown is one of the NOAA research ships used to gather carbon dioxide data.

Researchers have already gained new insights from the CLIVAR carbon dioxide samples. They have learned that biological carbon cycling at mid-water depths appears to have changed in several ocean basins.  One of the main ways that carbon is cycled in the oceans is through biological organisms. The change in biological carbon cycling at mid-depths is a way to measure the activity of marine organisms. The causes, whether a manifestation of human-induced climate change or natural variability, are not fully understood.

The CLIVAR/ Carbon Dioxide Hydrographic program is jointly funded by NOAA, which funds one-third and also supplies ships one-third of the time, and by the National Science Foundation, which funds the other two-thirds of the project and two-thirds of the ship-time.



Over the years, NOAA scientists have been working to increase our understanding of how carbon cycles through our oceans. Since the implications of the global ocean carbon cycle are far-reaching—from impacting marine life to global climate—this research is connected to the entire Earth system and is just one example of how the NOAA of today is working to find answers that solve the problems that affect our everyday lives.

Contributed by Erica Rule and Cassandra Lopez, NOAA's Office of Oceanic and Atmospheric Research