NASA Sets the PACE for Advanced Studies of Earth's Changing Climate
The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission will deliver the most
comprehensive look at global ocean color measurements in NASA's history. Not only will PACE monitor the health of our ocean, its
science data will expand atmospheric studies by sensing our skies over an exceptionally broad spectrum
Movement in the ocean is a complex interplay of currents and eddies. High above earth's surface, satellite sensors specifically tuned to see colors of the ocean reveal the presence of life: swirls and streaks as beautiful as masterpiece paintings. Beyond their beauty, these images provide valuable information about biological and chemical processes in our ocean.
Marine ecosystems depend on the health and productivity of single-celled organisms called phytoplankton. These algae either swim weakly or not at all. They spend their lives suspended in seawater, at the mercy of the ocean's motion. With dissolved carbon dioxide readily available, phytoplankton need only two additional things to survive: sunlight and nutrients.
Phytoplankton contain a pigment called "chlorophyll." It absorbs red and blue wavelengths of sunlight and reflects the green, giving the ocean a blue-green color. Through the process of photosynthesis, chlorophyll allows phytoplankton to store and convert the sun's energy to build their cells, while releasing oxygen. Over time, ocean phytoplankton have produced about half the oxygen in the atmosphere.
The nutrients needed by phytoplankton -- including phosphates, nitrates, silicates, and iron -- can come from dead plants and animals that fall to the seafloor. So the challenge is to stay in the sunlit upper ocean and still get nutrients that are sinking due to gravity. Phytoplankton thrive in places where seawater gets stirred up regularly: where deeper, more nutrient-rich cold water is brought to the surface.
PACE data will help researchers estimate the rates at which phytoplankton are absorbing carbon dioxide and producing oxygen. Since phytoplankton are key to reducing levels of carbon dioxide in our atmosphere, changes in their populations can affect climate. When scientists observe variations in phytoplankton populations, they can investigate how those changes connect to other parts of the ocean and climate systems.
Carbon takes many forms: from invisible gases to billions of living things. Society has come to depend on carbon-based resources and the energy harnessed within their chemical bonds. For centuries, burning of fossil fuels has moved hydrocarbons from deep underground to Earth's atmosphere. And our vast ocean has helped to keep Earth in balance by absorbing carbon dioxide gas. But we are now seeing that this process, which affects all of our lives, may have its limits.
When carbon cycles from land or the ocean into the atmosphere as carbon dioxide, it acts like a blanket, trapping heat and raising temperatures on Earth. In natural balance and along with other natural "greenhouse" gases such as water vapor, this process has maintained the planet at habitably comfortable temperatures.
In the ocean, phytoplankton take in dissolved carbon dioxide and use it for photosynthesis. Phytoplankton and the animals that eat them store carbon in their cells, moving it deeper in the ocean when they die. Bacteria decompose most of the dead matter, converting it back into carbon dioxide. The rest can settle to the seafloor and become buried for many, even millions, of years.
The more carbon dioxide from human activity that is stored in the ocean, the less is stored in the atmosphere to trap heat near Earth's surface and raise temperatures. Even though the ocean serving as a vast natural carbon reservoir sounds like a good thing, scientists are concerned about the biological impacts of increased carbon dioxide levels in the ocean, specifically a series of chemical reactions collectively known as "ocean acidification."
Scientists will use PACE data to observe the productivity of ocean ecosystems and gauge the amount of carbonate in the surface water. By comparing these data with information from ships and buoys, they will be able to monitor crucial changes in the health of our ocean.
The atmosphere and ocean are inextricably linked. Earth relies on atmospheric circulation and ocean currents to regulate the distribution of heat. Thus deciphering the ocean-atmosphere conversation is key to predicting the future of our climate.
The amount of sun's heat reaching the ocean surface is tied to clouds and aerosols, tiny airborne particles and liquids suspended in our atmosphere. On the other hand, ocean itself can be a strong source of atmospheric aerosols, influencing climate though direct obstruction of sunlight as well as changes to clouds' reflective properties.
There are significant gaps in scientific understanding on how clouds are formed and behave in remote marine environments. This information is crucial because Earth's heat balance is dominated by clouds over the ocean.
Ocean ecosystems also depend on fluxes between the atmosphere and ocean. Phytoplankton growth at the ocean's surface relies on the availability of sunlight and nutrients. In the open ocean, airborne dust can deliver nutrients that trigger phytoplankton blooms.
As our climate warms, changes in patterns of atmospheric input of dust will affect phytoplankton populations far from land. Moreover, continued use of fertilizers will deliver more nitrogen to marine ecosystems, particularly near coasts, with potential impacts on phytoplankton growth.
PACE's broad spectral coverage will also provide extended data records on clouds and aerosols which, according to the Intergovernmental Panel on Climate Change (2007), are the largest uncertainty in our understanding of physical climate.
The 2007 Report, Earth Science and Application from Space: National Imperatives for the Next Decade, called for "societal needs to guide scientific priorities more effectively."
In response, PACE Applications will partner with public and private organizations on ways to apply data from PACE and its scientific findings in their decision-making activities and services, helping to improve the quality of life and strengthen the economy.
PACE observations will benefit a broad spectrum of people, including:
Operational users in various tribal, local, state, federal, and international agencies
The combination of high-quality, global atmospheric and oceanic observations provided by the PACE mission will provide direct benefits to society in the major NASA application areas of Oceans, Water Resources, Disasters, Climate, Ecological Forecasting, and Human Health & Air Quality.
What are the biomass and compositions of ocean ecosystems? How and why are they changing?
How and why are Earth's biological and geochemical cycles changing?
How is matter exchanged between the land and ocean? How does this exchange influence coastal ecosystems?
How do aerosols influence the ocean?
How do ocean biological and light-related chemical processes the ocean affect the atmosphere?
How does the ocean's motion affect biology and geochemistry (and vice versa)?
What are the distributions of habitats and ecosystems along the coasts?
How do variations in biological and geochemical factors impact the biodiversity of coastal estuaries, tidal wetlands, and large lakes?
How does material that originated on land affect the compositions of phytoplankton communities?
How do the types of phytoplankton communities affect the cycling of organic matter?
How do processes such as sedimentation, degradation of materials by light, and respiration affect the cycling of organic matter along the coasts?
What are the long-term changes in aerosol and cloud properties?
How are these properties related to year-to-year variations in climate?
How do aerosols affect radiative forcing (i.e., difference between sunlight absorbed by the Earth and the energy radiated back to space)?
To what extent is aerosol-based radiative forcing is caused by human activity?
How do aerosols influence ocean ecosystems, biological and geochemical cycles?
Major Areas of Activity
PACE will extend climate records by collecting key global data using a design-to-cost approach
PACE's wide spectral coverage will provide a wide variety of atmospheric and ocean science products
PACE will help improve climate studies, fisheries management, Harmful Algal Bloom forecasts, and more
PACE will benefit from numerous ship-based and airborne studies being conducted worldwide
Broadening the Spectrum
Unlike previous U.S. ocean color sensors (i.e., "heritage" sensors), the PACE Ocean Color Instrument will provide continuous
high-spectral-resolution observations from the ultraviolet (UV) to near infrared (i.e., 350 – 800 nanometers), plus several short-wave
infrared (SWIR) bands. PACE's broad spectral coverage will unveil a variety of new products to aid our understanding of the atmosphere
For example, UV wavelengths will reveal the distributions of aerosols that absorb sunlight. In the ocean, UV data will help discriminate
between living and non-living components of the upper ocean. Visible wavelengths will be used to identify the composition of phytoplankton
communities. These micro-organisms not only serve as the base of the marine food web, they remove carbon dioxide from the atmosphere
and produce much of the oxygen we breathe.
Finally, SWIR bands will support studies of clouds and aerosols, key pieces to solving the climate change puzzle.
PACE will provide systematic observations and continuity for ongoing ocean color research, systematic observations of aerosol and clouds
in the climate record, and enhanced ocean color remote sensing over a broad spectrum. The long-term record of observations of advanced
ocean biology, ecology, and biogeochemistry will directly benefit society by monitoring the extent and impacts of climate change.