photo of the Chilean coast Comments

If you have a question or comment for the scientists during the research expedition, please email us at We will respond with a video or written post.


Questions from students at Kalama Intermediate School, Maui

Teacher: Davilla Riddle
Kalama Intermediate, Maui, Hawai‘i

Click on the student’s name to jump to the answers to their questions.

Questions from Reilly:

  1. Why are you going from Peru to Easter island? Is there specific reason?
  2. What is there a normal amount of CO2 in the water?
  3. How deep does the robot go under water?

Questions from Alesha:

  1. What type of marine microbes are essential for habitat on our planet?
  2. Why did you choose Chile and Easter Island to take water samples?
  3. What is “Surface PAR”?

Questions from Jordan C.:

  1. How does the ocean get nutrients?
  2. Why are you using satellite images? What do these satellite images show?

Questions from Jamielyn:

  1. What is the purpose of this trip?
  2. What are you going to Easter Island?
  3. If the experiment is for the University of Hawai‘i, why is the boat starting off of South America?

Questions from Beau:

  1. Why is the amount of chlorophyll-a going down as you go into deeper water?
  2. What is PAR?
  3. What dos PAR have to do with chlorophyll-a?

Questions by Reilly

Why are you going from Peru to Easter Island? There are several reasons. One of them is that we are trying to see how life in the ocean changes when you go from one of the most productive marine regions in the world — the coast of Northern Chile and Peru, to one of the poorest — the center of the South Pacific Ocean surrounding Easter Island. By sampling these regions, which can be considered as extreme environments, and the gradient between them, we hope to learn how microbes adapt to these extreme conditions.

What is the normal amount of CO2 in the water? Physics tell us that surface waters try to be in equilibrium with the atmosphere regarding the concentration of gases. For this reason, we expect the concentration of CO2 in surface waters to be close to that in the atmosphere, around 390 ppm (parts per million). Imagine that if you had 10,000 marbles representing the composition of the atmosphere, 7,808 would correspond to nitrogen gas, 2,095 to oxygen and less than 4 to CO2, the rest of the marbles corresponding to water and other minor gases. The surface of the ocean tends to have a CO2 that is close to 390 ppm. However, photosynthesis in the water will remove CO2 and release oxygen as plants grow, lowering slightly the concentration of CO2 in surface waters. Some of these plants (microalgae) will support life in the surface of the ocean. However, some of the organic matter they have made will sink as a rain of particles into the deep ocean where they will be respired. As you know, respiration will consume oxygen and release CO2. So, the deep ocean tends to have high concentrations of CO2 due to the constant respiration of organic matter at depth. This transfer of CO2 from surface waters into the deep layers of the ocean is called the “biological pump.”

There is also another factor that affects the distribution of CO2 in the surface of the ocean and is that cold water can hold twice as much CO2 than warm waters. For this reason, in polar regions like the Arctic and the Southern Oceans, surface waters can collect more CO2. As warm surface currents travel from the tropics move toward the poles, such as the Gulf stream, they get colder and collect CO2. Eventually, these cold waters become dense (heavy) and sink below the surface, trapping CO2. This process is termed the “solubility pump.” But, where does all this CO2 trapped by the biological and solubility pumps end up? Eventually, the deep waters in the ocean will come back to the surface in what we call upwelling regions, such as the Coast of Chile that we just visited or the Equatorial Pacific. When these waters reach the surface of the ocean, they still have high concentrations of CO2 that will be release into the atmosphere. In these upwelling regions the CO2 in surface waters can be very high, reaching values close to 900 ppm.

How deep does the robot go under water? I assume that you are asking how deep can our sampling rosette go. The rosette itself, with its bottles and the CTD (conductivity, temperature and depth sensor) can go as deep as we need, depending of the length of cable that we have to lower it to the bottom of the ocean, which in this region is close to 4 kilometers. However, some of the additional instruments on the rosette, such our light (also called PAR) sensor, can only go down to 2 km depth. Below that depth the pressure becomes too great and the instrument would be crushed if we forgot to remove it from the rosette.

[ Top of page ]

Questions from Alesha

What types of marine microbes are essential for habitat in our planet? This is a great question that is hard to answer. Rather than thinking about specific microbes, maybe it is easier to think about the essential processes they drive, such as photosynthesis, respiration, nitrogen fixation, and others. From this perspective, life in our planet would be very different without microalgae and bacteria that are responsible for photosynthesis and the production of oxygen in the sea. Also, if the nutrients that are stored when cells grow were not release when they die, then we would eventually run out of nutrients. For this reason, we need other microbes that will re-mineralize the organic matter so that nutrients can be released and become available again for microalgae and other microbes to grow (think about the compost and how it can be used to put nutrients into a garden). Also, only a few microbes are able to convert nitrogen gas (abundant in the atmosphere and ocean) into a form that can be used by all living forms. These microbes, termed nitrogen fixers (or diazotrophs) are important because they replenish the ocean of biologically available nitrogen.

Why did you choose Chile and Easter Island to take water samples? See our answer to Reilly’s question #1.

What is surface PAR? PAR stands for Photosynthetically Available Radiation. This is a fancy term to describe the range of light that most photosynthetic organisms can use to drive photosynthesis. The sun emits radiation in a broad range, usually measured in terms of wavelength (nanometer), frequency (Hertz) or energy (Watts). Some of the radiations with high energy are called gamma-rays, x-rays, ultraviolet and we cannot see them. Another range of radiation with lower energy is the infrared, which warms us. The radiation in between the ultraviolet and the infrared is the visible. It ranges between 400 nm and 750nm and is the one that allows us to see. Blue is approximately 450nm, green is 520nm, yellow is around 600 nm and red around 700 nm. A nanometer (nm) is equal to 1 inch divided by 25,400,000!!! The Phosynthetically Available Radiation (PAR) is very similar to the visible range (from 400 to 700 nm) and we have instruments to measure the amount of sun energy in this range that reaches the surface of the ocean. This is what we call Surface PAR.

[ Top of page ]

Questions by Jordan C.

How does the ocean get nutrients? Great question, Jordan. Most of the nutrients we find in the ocean come from the weathering of rocks on land. Over millions of years the grinding of rocks by water on land filled the oceans with nutrients such as phosphorus or iron. Nitrogen is a special case because some organisms can use nitrogen gas dissolved in the ocean and convert it into a form that can be used by the rest of the organisms in the ocean.

Why are you using satellite images? What do these images show? I tend to imagine satellites as very high poles from where I can see the surface of the ocean. When you are onboard a ship it is difficult to see if the surface of the ocean is changing around you. If you climb to the top of a ship mast you may see a few hundred yards around you. But, satellites can provide you with images from large areas of the ocean surrounding you. Depending on the sensors onboard the satellites, we can obtain information regarding the temperature in the surface of the ocean (we call it SST which stands for Sea Surface Temperature), the concentration of chlorophyll a (chl a) and other ocean color products such as suspended material in the water. We can also derive wind speed and direction, see how the surface of the ocean changes, and now there is a new sensor that may provide information regarding how the concentration of salt (or salinity) in surface waters change.

The satellite images we have been posting online help us see how temperature was changing along our cruise track. More important, they also provided with us information regarding the spatial distribution of chlorophyll in our study region (red indicates high chlorophyll and blue-violet represent areas with very low chlorophyll values; you must be careful when comparing information from two different images because the color scale for the chlorophyll changes; always look at the scale which is the color bar next to the image, it will tell you what the colors mean). Knowing how the concentration changes along out transect allows us to decide in advance where we will locate our stations in order to ensure that we sample areas with high, medium and low chlorophyll.

And why do we want to sample regions with different concentrations of chlorophyll? Because chlorophyll a is the pigment responsible for photosynthesis and, in general terms, the concentration of chlorophyll in surface waters gives an indication about how much phytoplankton is there.

[ Top of page ]

Questions from Jamielyn

What is the purpose of our trip? One of our main goals during this trip is to characterize the diversity of microbes in the surface waters (upper 1000 meters) of this oceanic region, how this diversity changes from nutrient rich waters along the coast of Chile, to the nutrient depleted area surrounding Easter Island. In addition, we study how these microbes, which we call primary producers, capture energy from the sun and use it to take up from the environment elements such carbon, nitrogen, phosphorus, iron, to grow and multiply. Other organisms will eat the primary producers and some of the material and energy will make it all the way into large organisms such as fishes, whales, birds. Other material will be respired and remineralized by microbes allowing nutrients to go back into the system. Another small portion will sink into deep water or even to the bottom of the ocean where it can serve as food for organisms living at great depth. We are trying to understand how life in this ocean affects the flow of energy and elements.

We have been working North of the Hawaiian Island for over 21 years, going to Station ALOHA, 60 miles north of O‘ahu, ten times a year and making some of the same measurements we are making in this cruise. And even if the ocean around Hawai‘i and Easter Island look very much the same, there are some very important differences in the balance of nutrients and total amount of microbial biomass that we still do not completely understand. By studying and comparing both systems, the one off Hawai‘i and the one of Easter Island, we hope to better understand what drives these differences.

[ Top of page ]

Questions from Beau

Why does the amount of chlorophyll a decreases as you go into deep waters? When we move from coastal waters into the deep open ocean chlorophyll goes down in surface waters because it becomes more difficult to replenish the needed nutrients for plants to grow. In the coastal waters of Chile and Peru, the currents make that deep water, rich in nutrients, move to the surface where there is plenty of light for microalgae to grow. However, when you move away from the coast the upper ocean becomes well stratified because the sun tends to warm the surface of the ocean and warm water is lighter (less dense) than cold water. The greater the change in density, the harder is to bring deep nutrient rich water to the surface to support large amounts of phytoplankton to grow.

But chlorophyll concentration also changes with the vertical depth. In coastal waters it is high at the surface and decreases with depth. The reason for this is that at depth there is no light and plants that get their energy from the sun cannot survive. If you look closely to depth profiles of chlorophyll a in the open ocean stations (far away from the coast) you will notice that the chlorophyll a will display a maximum value at the depth where the Photosynthetically Available Radiation (PAR) becomes very small. And below this depth the chlorophyll will decrease. This increase of chlorophyll at depth is due to the same reason why the leaves of bushes and small trees in a forest have a darker green color than the leaves in the tall trees. The tall trees get lots of light so they do not need much chlorophyll to capture the amount of light they need to grow and survive. However, if you are a plant living in the shade, you need to increase the amount of chlorophyll and other pigments on your leaves in order to bbe able to capture enough light to grow. The same happens in the ocean: Phytoplankton living in surface waters do not need much chlorophyll to capture light photons but, the deeper we go, the less light there is and phytoplankton cells will increase their pigment concentrations to capture as much light as they can. However, there is a point where there is so little light that it is not possible for plants to grow. At this point the chlorophyll a concentration starts to deceases with depth.

What is PAR? See my answer to Alesha.

What does PAR have to do with chlorophyll a? PAR provides us with an estimate of the amount of light available for microbes to carry on photosynthesis and chlorophyll a is the main pigment responsible for photosynthesis. Hence, plants will produce chlorophyll a in response to the amount of light that is available.


[ Top of page ]