“PACE is a mission that will use the unique vantage point of space to study some of the smallest things that can have the biggest impact.” — Karen St. Germain, director of NASA’s Earth Science Division
The skies above us are teeming with tiny particles of dust, sea salt, smoke, and human-made pollutants. The seas, oceans, and lakes around us are teeming with microscopic, plant-like organisms. In both cases, individual bits of these tiny living and inanimate particles are too small for your eye to see. But when billions to trillions of them aggregate in one place, we can see them from space. And these little things make a vast difference for life on Earth.
The particles in the air are known to atmospheric scientists as aerosols. Though the spray cans you might use for paint or hairspray do contain aerosols, the ones PACE will study are the flecks of carbon that rise from wildfires and smokestacks; the fine, dusty minerals that get lofted from deserts into the sky by strong winds; the nitrates and sulfates spewed by cars, trucks, and ships in their exhaust; and the salty spray from crashing waves and strong winds blowing over the ocean.
Why study them? Because those particles influence air quality, sometimes making it unhealthy to breathe, especially if you have asthma or heart and lung conditions. Pollution and smoke don’t observe borders – we all share Earth’s air — so it’s important to know something about the sources and types of particles floating around us. On the positive side, the bits of mineral dust or smoky aerosols can sometimes fertilize the ocean, providing nutrients for phytoplankton to bloom.
Aerosols also affect weather and climate. Tiny particles in the air reflect sunlight, and how much they reflect affects how much the land and ocean surfaces heat up. Aerosols also “seed” the formation of clouds: they provide surfaces on which water droplets form (condensation nucleii) as they aggregate into clouds. One of the great unknowns in our models of climate change is what role will aerosols will play in changing rainfall and snowfall patterns and in the heating or cooling of our atmosphere.
Though NASA has been studying aerosols from space for decades — observing where they are and the abundance of them — PACE and its SPEXone and HARP2 polarimeters will change the game. The instruments will tell us the shape and size of aerosols, helping us answer questions about where they come from and how they might influence other parts of the Earth system.
The other little things that PACE will examine have names like diatoms, coccolithophores, cyanobacteria, algae, and dinoflagellates. To borrow and mangle a quote from one of my favorite movie characters — Annie Savoy in Bull Durham — if you have three phytoplankton, they can’t do much. But if you have 300 billion of them, they can build a cathedral. Well, maybe not a cathedral, but they can develop into vast blooms that have a profound impact on life on this ocean planet.
Phytoplankton grow constantly on Earth and just about anywhere there are open, sunlit patches of water. When conditions are right, the growth of these microscopic cells can blossom to scales that are visible from orbit for days to weeks.
Phytoplankton are to the ocean what grasses and ground cover are to land: primary producers, a basic food source for other life, and the main carbon recycler for the marine environment. They are floating, plant-like organisms that soak up sunshine, sponge up nutrients, and create their own food (energy).
Why do we need to study these tiny organisms with PACE? While humans don’t really consume phytoplankton for food, the little floaters are fuel for the zooplankton, fish, and shellfish that we do eat. We also need to care about phytoplankton because they can influence water quality and human health. Some species of phytoplankton produce toxins that are dangerous to humans and animals; others can grow in such abundance that they crowd out other species or deplete the water of necessary oxygen.
Speaking of oxygen, phytoplankton produce a lot of it. Somewhere between 20 and 50 percent of the oxygen on Earth — some in our air, a lot in the ocean — is made by phytoplankton as they use photosynthesis to turn sunlight, carbon dioxide, and nutrients into sugars. In the process, they also draw carbon dioxide out of the atmosphere and, in time, sink it to the bottom of the ocean.
Better understanding the phytoplankton in the ocean will help us better understand the fisheries that feed us and our economy, and it can ultimately help us work toward cleaner waterways.
NASA and its research partners have been studying phytoplankton from space for decades, but mostly with just a few wavelengths of light. I am looking forward to the colors, textures, and details we will see with PACE’s OCI hyperspectral imager. As the PACE science team likes to say: we have been coloring the ocean with a box of 8 crayons, and now we are about to get a box with 128 shades of color. The leap in detail will allow scientists to better spot where phytoplankton are, but also figure out who (what species) they are.
And when PACE data are combined with observations from our recently launched SWOT mission — which studies the shape and movement of the surface of the ocean — it will be like going from the Earth-observing equivalent of the Hubble Space Telescope to the new James Webb Space Telescope.
Learn more about phytoplankton with these resources:
PACE Phytoplankton Exploration
The Insanely Important World of Phytoplankton
NASA Wants to Identify Phytoplankton Species from Space: Here’s Why.
As the Seasons Change, Will the Plankton?
Phytoplankton May Be Abundant Under Antarctic Sea Ice
Learn more about aerosols with these resources:
Just Another Day on Aerosol Earth
New NASA Satellite to Unravel Mysteries About Clouds, Aerosols
Global Transport of Smoke from Australian Bushfires
A few paths in life are short and direct; more of them are long and winding.
This week, a SpaceX Falcon 9 rocket will launch from Cape Canaveral Space Force Station carrying the PACE satellite, short for Plankton, Aerosol, Cloud ocean Ecosystem. Once in orbit 676 kilometers (420 miles) above our planet, the newest addition to NASA’s fleet of Earth-observers will look at the oceans and land surfaces in more than 100 wavelengths of light from the infrared through the visible spectrum and into the ultraviolet. It will also examine tiny particles in the air by looking at how light is reflected and scattered (using a method like looking through polarized sunglasses).
The combination of measurements from the new satellite will give scientists and citizens a finely detailed look at life near the ocean surface, the composition and abundance of aerosols (such as dust, wildfire smoke, pollution, and sea salt) in the atmosphere, and how both influence and are affected by climate change.
For NASA and the ocean science community, the PACE launch will be the culmination of 9 or 46 years of work, depending on when you start counting. For me, it will be the culmination of something that started in 1950.
“There is a greater than 50 percent chance I will burst into tears at the launch,” said Jeremy Werdell, a satellite oceanographer at NASA’s Goddard Space Flight Center since 1999 and project scientist for PACE since 2015. “We are standing on the shoulders of previous missions and the people who led them. And it has been a long and remarkable journey.”
NASA’s first attempt at measuring ocean color dates back to the Coastal Zone Color Scanner (CZCS) instrument, which flew on the Nimbus 7 satellite from 1978-1986. In 1997, the agency launched the Sea-viewing Wide Field-of-view Sensor on the OrbView-2 satellite. SeaWiFS collected ocean data until 2010 and fundamentally changed our understanding of phytoplankton—microscopic, floating, plant-like organisms that are the grass of the sea. That sensor is an ancestor of the new Ocean Color Instrument (OCI) on PACE.
Other instruments and teams have observed the colors of the ocean. The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA’s Terra and Aqua satellites have been flying since 2000 and 2002, complementing and extending the record started by SeaWiFS. More recently, the Visible Infrared Imaging Radiometer Suite (VIIRS) instruments on the Suomi-NPP, NOAA-20, and NOAA-21 satellites have provided a broad view of ocean color. And several other instruments — like the Hyperspectral Imager for the Coastal Ocean (which flew on the space station), HawkEye (on the SeaHawk CubeSat), and the Ocean Radiometer for Carbon Assessment (which was flown on NASA research planes) — helped researchers test new ways to look at the sea.
For atmospheric scientists, the path to PACE also traces back across decades. In the late 1970s, the Advanced Very High Resolution Radiometer (AVHRR) provided some of the first looks at aerosol optical depth, a measure of how much dust and particles were floating in our skies. Later scientists began measuring such particles daily and around the world with the Multi-angle Imaging SpectroRadiometer and MODIS instruments on Terra. The OMI instrument on the Aura satellite, and its successor OMPS on Suomi-NPP, provided other unique views of aerosols. A HARP instrument flew on a CubeSat from 2019-2022 and provided a direct test of the technology that now flies on PACE as HARP2.
The origin of PACE itself sort of started around 2007. NASA and other federal agencies asked the U.S. National Research Council to study and suggest new tools and measurements for studying Earth from space. Their report (known as a “decadal survey“) recommended a mission that ultimately led to the A(erosol) and C(loud) components of the PACE mission. The inspiration for new ocean color sensors then arose from a NASA climate initiative proposed in 2010.
By 2012, NASA scientists and engineers were starting to sketch out rough ideas for PACE, and the wider science community dug into the details in 2014. By 2015, NASA Goddard started hiring for a new mission—including Jeremy Werdell—and by 2016, the agency had announced the formal development of a PACE mission.
Between that moment in 2016—known as Key Decision Point A—and this week’s launch there have been thousands of hours of work by hundreds of people…including many months working through a global pandemic…and the methodical, thoughtful testing of every idea, every design, and every part.
For me, the road to the PACE launch has also been long.
I have spent 21 years of my life working for NASA, and yet this will be my first launch. I feel blessed to spend my days working with incredibly talented, visionary, and smart people. This launch feels like the culmination of a lifetime geeking out on Earth and space science. Several threads of my life will all tie together this week.
In 1950, a 7th grader in Newark, New Jersey, won an essay contest by writing about a trip to the Moon. My father was fascinated by science fiction—he still is—and by journalism. He followed America’s developing space program with interest and, in 1969, his youngest son was born two weeks after the Apollo 11 Moon landing. Though no one can remember clearly, I like to say my parents named me for Michael Collins, who quietly orbited the Moon for 21 hours while Neil Armstrong and Buzz Aldrin made the headlines below. (My mother often reminded me that she went through a similar 20+ painstaking hours of labor waiting for me to show up.)
On my first job as a magazine writer, I wrote in 1992 about the Mission to Planet Earth—first an international conference, then an early name for what became NASA’s Earth Observing System. I visited NASA’s Jet Propulsion Laboratory in 1994 to research my graduate thesis and by 1997 I had joined NASA Goddard, where I stayed for five years writing about space weather and space physics.
But then I traded one institution of exploration for another, leaving to write about ocean science for Woods Hole Oceanographic Institution (WHOI). It was during those years on Cape Cod that I learned a boatload about phytoplankton and harmful algae. I spent 11 days at sea in 2005 on the research vessel Oceanus, helping scientists gather water samples to track a pesky, toxic phytoplankton called Alexandrium fundyense. After decades visiting the ocean, I was living by it and learning about it daily.
I rejoined NASA in 2008 and eventually joined Earth Observatory. Circumstances and generous colleagues allowed me to keep living by the sea, and so I brought my love of the ocean into my reporting. I also passed that love of the ocean and space to my children: Two have become marine biologists who study plankton, and one is an aerospace engineer working on satellites.
After so many years of my life intersecting with NASA and the sea, it just feels right that my first rocket launch should be a satellite that will bring us new eyes on Planet Ocean.
It doesn’t take a lot of technology to see that the ocean is blue. And when it comes to the blueness of the ocean, it doesn’t get much more blue than where I am. I’m sitting on the research vessel Nathaniel B. Palmer—the largest icebreaker that supports the United States Antarctic Program—on an oceanographic expedition across the South Pacific Ocean, my current home, office, and laboratory. On this voyage, however, the Palmer has broken no ice.
Our Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) P06 campaign departed Sydney, Australia, on July 3, successfully ending the first leg of this journey on August 16 in Papeete, French Polynesia (Tahiti). This is where our team from NASA Goddard Space Flight Center (Scott Freeman, Michael Novak, and I) joined dozens of other scientists, graduate students, marine technicians, officers and crew members, for the second and final leg that will end in the port of Valparaiso, Chile, on September 30. The GO-SHIP program is part of the long history of international programs that have criss-crossed the major ocean basins, gathering fundamental hydrographic data that support our ever-growing understanding of the global ocean and its role in regulating the Earth’s climate, and of the physical and chemical processes that determine the distribution and abundance of marine life. This latter topic regarding the ecology of the ocean is what brings our Goddard team along for the ride.
The P06 ship track, for the most part, follows along 32.5° of latitude south. That route places our course just south of the center of the South Pacific Gyre—the largest of the five major oceanic gyres, which form part the global system of ocean circulation. The Gyre—on average—holds the clearest, bluest ocean waters of any other ocean basin. This blueness is the macroscopic expression of its dearth of ocean life. We have seen nary a fish nor other ships since we departed Tahiti—this is not a major shipping route. Oceanic gyres are often called the deserts of the sea. On land, desert landscapes are limited in their capacity to support life by the availability of water. Here, lack of water is not the issue. Water, however, is at least the co-conspirator in keeping life from flourishing. Physics, as it turns out, is what holds the key to this barren waterscape.
This map (above) shows the MODIS chlorophyll climatology with the ship track superimposed.
Due to the physics of fluids on a rotating sphere, such as our planet, the upper ocean currents slowly rotate counterclockwise around the edges of the center of the Gyre–as a proper Southern Hemisphere gyre should—and a fraction of that flow is deflected inward, towards its center. With water flowing towards the center from all directions, literally piling up and bulging the surface of the ocean–albeit, by just a few centimeters across thousands of miles–gravity pushes down on this pile of water. This relentless downward push puts a lock on life. The pioneers of life in the ocean, the tiny microscopic plants, known as phytoplankton, which drift in the currents, and grow on a steady mineral diet of carbon dioxide, nitrogen and phosphorus, and a dash of iron—and expel oxygen gas as a by-product, to the great benefit of life on Earth—must obtain most of their material sustenance from the ocean below. Layers of denser water trap the nitrogen and phosphorus-rich water at depth, keeping it too far down, where not enough light can reach it to spark the engine of photosynthesis that allows plants to grow.
Why are we here and where does NASA come into this story? Since the late 1970s, NASA has pursued—experimentally at first, and now as a sustained program—measuring the color of the oceans from Earth-orbiting satellites as a means to quantify the abundance of microscopic plant life. Microbiology from space, in a way. Formally, though, we call it “ocean color remote sensing.” Whizzing by at altitudes of several hundred miles, atop of the atmosphere, bound to polar orbits that allow satellites to scan the entire surface of the globe every couple of days, carrying instrument payloads of meticulously engineered spectro-radiometers—cameras capable of measuring the quantity and quality, or color, of the light that reaches its sensors. This is where our work aboard the R/V Palmer comes into the story. The data the satellites beam down from orbit do not directly measure how much plant life there is in the ocean. Satellite instruments give us digital signals that relate to the amount of light that reached their sensors. It is up to us to translate—to calibrate—those signals into meaningful, and accurate, measurements of plant life—or temperature, salinity, sediment load, sea level height, wind and sea surface roughness, or any other of the many environmental or geophysical variables satellite sensors can help us detect at the surface of the ocean. To properly calibrate a satellite sensor and validate its data products, we must obtain field measurements of the highest possible quality. That is what our team from NASA Goddard is here to do.
Around midday, typically the time of the ocean color satellite flying over our location, we perform our measurements and collect samples. We measure the optical properties of the water with our instruments to compare what we see from the R/V Palmer to what the satellites measure from their orbit above Earth’s atmosphere. At the same time that we perform our battery of optical measurements, we also collect phytoplankton samples to estimate their abundance, species composition as well as the concentration of chlorophyll-a, the green pigment common to most photosynthesizing organisms like plants, including phytoplankton. By collecting these two types of measurements at once, light and microscopic plant abundance, we are able to build the mathematical relationships that make the validation of the satellite data products possible.
The optical instrument being lowered into the South Pacific Ocean. Credit: Lena Schulze/FSU
Scott Freeman of NASA works with a R/V Nathaniel Palmer crew member to prepare an instrument for deployment over the side of the ship to collect opHcal measurements. Credit: Lena Schulze/FSU
Mike Novack of NASA studies the optical and biological characteristics of seawater samples in the ship’s laboratory. Credit: Joaquin Chavez/NASA
The waters of the South Pacific Gyre are an ideal location for gathering validation quality data, perhaps one the most desirable to do so, because there are few complicating factors and sources of uncertainty that blur the connection we want to establish between the color of the water and phytoplankton life abundance. Our measurements will extend NASA’s ocean chlorophyll-a dataset to some of the lowest values on Earth. The water here is blue; in fact, it’s the bluest ocean water on Earth.
This false-color image is a composite, assembled from data acquired by the the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite between September 10-17, 2017. Yellow represents areas with the highest chlorophyll concentrations and purples are the lowest. Credit: Norman Kuring/NASA
Plankton comes from the greek word planktos, meaning wanderer. It does not define a specific organism, but rather a specific life style. Plankton consist of all organisms dispersed in water that are passively driven by water currents or are subject to passive sinking process. Some of those organisms have an ability to produce oxygen and sugars using sunlight and CO2, just like terrestrial plants do. We call them phytoplankton (greek: phyton -plant ).
Phytoplankton are the wandering meadows of the ocean and an important base of the food web. Most of the phytoplankton are smaller than the width of the single human hair. They are feeding the hungry ocean, and the phytoplankton composition determines the diversity of organisms developing on the higher trophic levels like fish, birds and mammals. It is not only important for organisms living in the ocean, but it is crucial for all life on Earth. Consider the size of the oceans covering our blue planet for a moment – the amount of phytoplankton every second breath that we take the oxygen is produced by phytoplankton.
This is microscopic picture of a diatom called Leptocylindrus, a kind of phytoplankton. Phytoplankton feeds the ocean, and the phytoplankton composition determines the diversity of organisms developing on the higher trophic levels like fish, birds, and mammals. Colleen Durkin
When it comes to phytoplankton, it is not just the quantity, but also the quality that matters. You may wonder how can researchers sample something that we cannot see that exists in an environment where we cannot be in? How can we catch something that is passively driven by currents and changing all the time? How can we get the insight of the abundance of some particles that are unevenly dispersed in an ocean? Since the discovery of the microscope scientists have been trying to find answers to those questions.
Here, on R/V Falkor we are combining traditional methods of phytoplankton analysis – such as preservation of water for later, onshore analysis under a microscope – with the new, recently developed methods of onboard image analyses. Discrete samples are taken with the Niskin bottles at the specified depth. The sampling depth is chosen according to the physical, chemical and biological characteristics of the water column that are measured by the instruments mounted on the rosette, and controlled from the science control room. Once the rosette is on deck, the samples are taken from the Niskin bottles and prepared to be either stored until they return to land, or analyzed on board. The great advantage of the onboard image analysis is that it lends an instantaneous snapshot of the phytoplankton composition and abundance, which allows you to adapt your sampling strategy and use the time spent on the ship in a better, more productive way.
Discrete samples are taken with the Niskin bottles in each CTD cast, at specific depths. The sampling depth is chosen according to the physical, chemical, and biological characteristics of the water column. SOI/Mónika Naranjo González
The flow-through system onboard the R/V Falkor allows us for continuous sampling of the surface water for physical, chemical and biological properties, including phytoplankton composition with Imaging Flow Cytobot. This amazing instrument samples from the flow-through system every 20 minutes, and takes images of particles contained in 5 mL (100 drops) of seawater. Therefore, as we steam through the Pacific or as we stop to conduct some other measurements, we are continuously gathering high-spatial information about phytoplankton abundance and composition. The advantage of taking images vs. looking at the cells through the microscope is that you can always go back to your sample if needed. That helps us that help to have comparable results and minimizes the error of phytoplankton counting and taxonomy misidentification.
The Imaging Flow Cytobot is one of the state-of-the-art technologies used on the current expedition. As Falkor sails, a pump runs seawater through the instrument, which takes pictures of all the particles present. SOI/Ivona Cetinić
Will the modern methods of high-resolution imaging ever substitute traditional microscopy? I would say – no. While continuous sampling techniques give us amazing insight into the spatial distribution of the phytoplankton and inform best sampling strategies, classical microscopy gives us insight into the detailed morphological characteristics that are needed to be seen from multiple angles to really be understood. The phytoplankton taxonomy is under constant revision and change as the new methodologies develop. With more knowledge and deeper insight, we do find answers to existing questions, but we also encounter more questions that need to be answered. The combination of the traditional and modern methods is the best strategy to understand the secrets of these beautiful oceanic wonders.
A radiometer installed in the bow of Falkor takes color measurements from both seawater and sky. SOI/Kristen Carlson
Earth’s ocean is vast and deep, and we still need to study many things about it. To investigate and quantify biological and chemical processes, for instance, we need to determine the concentration and size of particles (living and non-living organisms) floating in the water, dissolved materials, and the diversity of organisms such as the microscopic photosynthetic phytoplankton. Their study requires both direct measurements by deploying instruments at sea or analyzing water samples, and satellite remote sensing.
Particles and dissolved organic materials scatter and absorb the sunlight that enters the ocean, which alters the ocean’s color. For instance, the first site that we sampled contained low abundances of particles including phytoplankton and dissolved organic materials, which translated to clear blue waters. Higher abundances of phytoplankton result in greener seas because of their chlorophyll pigments.
Since 1978, NASA has applied satellite remote sensing to study phytoplankton. The image depicts chlorophyll concentrations in the ocean. NASA/Norman Kuring
Since 1978, NASA has applied satellite remote sensing to study phytoplankton though its experimental Coastal Zone Color Scanner. Several other sensors followed from 1997 to the present. By 2022, NASA expects to launch the next generation ocean color satellite sensor for the Plankton, Aerosol, Cloud, and Ocean Ecosystem (PACE) which is currently being developed. This PACE sensor will provide unprecedented detail on the color spectrum and intensity of the light exiting the ocean’s surface, which will be used to infer a lot of information about our oceans, including the concentration and size of particles and dissolved organic materials, the diversity of phytoplankton, and rates of phytoplankton growth within the ocean’s sunlit surface layer.
To successfully apply the capabilities of the PACE sensor requires the development of relationships between ocean data (such as chlorophyll-a) and how it affects the color and the amount of light that will be measured by the satellite. One of our goals for participating on the Sea to Space Particle Investigation in the northeastern Pacific Ocean aboard Falkor is to collect biological, chemical and optical measurements in order to build these relationships.
To be able to do so, much of our work at sea involves development and evaluation of new methods and measurement capabilities to ensure that the data collected are of sufficient quality for application with satellite remote sensing. For example, to quantify phytoplankton growth rates, we are conducting experiments with phytoplankton and measuring the oxygen produced and carbon dioxide consumed over time.
Only satellite remote sensing can provide the comprehensive data sets across space and time needed to study the state of Earth’s vast ocean. The ocean moderates our weather, provides food, medicine, energy resources, recreation, and many other benefits. Improving our understanding of the ocean will help us better predict how it will change in the future.
Antonio Mannino, Oceanographer, installs a Coulometer in Falkor’s wet lab to measure particle productivity in water samples collected during the expedition. SOI/Mónika Naranjo González
