Polar Night and Midnight Sun Photosynthesis

Did you know?
That carbon can be dissolved in water (DOCs – Dissolved Organic Carbon), occur as particles (POCs – Particulate Organic Carbon), and as blocks of peat and soil falling from a river or pond bank into the water.
Because of the midnight sun, carbon capture in some green plants can occur 24 hours per day in midsummer.
Wet areas store most carbon because decomposition microbes work more slowly in the absence of oxygen (see stories 6.2 and 6.3)
In wet areas, microbes release methane rather than CO2 – a more powerful gas!
Did you know that when flowers and plants were allowed in hospitals, the nurses would take them out each night and put back in the morning: Why? Because they were producing CO2 at night but not absorbing CO2 in photosynthesis. In the Arctic, that wouldn't be necessary because it is light all day round during midsummer– The Arctic is the land of the midnight sun. (See graphic below).
Photosynthesis is limited by low temperatures. As the Arctic summer is short, photosynthesis is slower there so it is important that plants photosynthesize longer in the continuous light of summer days.

Polar Night and Midnight Sun Photosynthesis
Photosynthesis is the key to most life on Earth. Plants, algae and bacteria use photosynthesis to turn sunlight and carbon dioxide into energy to grow and the by-product – oxygen – allows us and other animals on Earth to breathe.
Sunlight + Carbon Dioxide + Water = Oxygen + Energy (sugars)
The amount that plants photosynthesize changes throughout the days and the seasons, sometimes happening faster and sometimes slower. Can you think of what might cause plants to photosynthesize more slowly? Check out this video from NASA showing how the vegetation breathing changes around the world within one year.

Most plants do not photosynthesize at night because they need sunlight. However, in some places, in certain times, plants are able to photosynthesize at night! In the Arctic and Antarctic, there are two periods of time when the sun either doesn't set or doesn't rise – this is known as the Polar Night and the Midnight Sun. The reason for these two unusual events is because the Earth's axis is not vertical and the tilt away from, or closer to the sun means that the polar regions are either away from the sun longer each day in winter or closer to the sun each day in summer.

Get Active!
Some Arctic plants track the sun as it moves around the sky. Outside the Arctic, sun flowers do this. Plant one and watch it grow and change direction during the day.
Arctic photosynthesis during
a Midnight Sun day

Draw an arrow from the sun to the leaf when photosynthesis is happening, draw a thicker arrow if you think photosynthesis is happening faster during one of the time frames.
1. Is there a time where photosynthesis is not happening in the Arctic during the midnight sun?
No, not for many plants as they can photosynthesise throughout 24 hours during the midnight sun.
2. Is photosynthesis happening at night?
Yes, for many plants as night time during the midnight sun is not dark.
3. Why do you think this might be?
Plants need light to photosynthesise. Plants such as mosses can use even very low light levels.
4. Why are plants photosynthesising less at night than at mid-day even though there is the midnight sun?
Even though the sun is visible at night time, it is low in the sky, just above the horizon, so the light energy is spread over a bigger area of ground with less light available at any one spot than when the sun is higher in the sky. Shine a torch on a spot on a flat surface from above and from the side. See how the beam is spread over a bigger area as you lower the torch, spreading the same light energy over more space.