- Author: Brenda Altman
Today the day's sunshine is close to its maximum, it's solstice time. When the sun is directly over the Tropic of Cancer 23.5 degrees north latitude, the axis of the earth is tilted to its maximum so the northern hemisphere gets its maximum number of daylight hours. Daylight hours are getting longest. The rhythm of the sun, the solar day drives circadian rhythms.
At Summer solstice in the northern polar region there is less intensity of solar radiation but twenty-four hours of light. At the pole you could take a picture of the sun making a round trip across the sky at, you guessed it, 23.5 degrees in the sky from the horizon. Solar radiation is not as intense there as it is at the tropic of Cancer, but there is 24 hours of sunlight.
I lived in Alaska for a number of years and witnessed this incredible phenomenon at Prudhoe Bay Alaska, 250 miles north of the Arctic Circle, 77. 2269 degrees north latitude in July. The sun appeared to circle the sky like it was 10:00 a.m. all day!
It was hard to get any sleep. I had all this energy. It's interesting, to note, even in Anchorage 850 miles south of Prudhoe Bay, in the summer you can fall asleep at 8:00 p.m. take a short nap for an hour wake up refreshed and panic because it looks like you're late for work because your watch says 9 o'clock. I've been there, the joke was on me!
All living things have internal biological clocks called circadian rhythms. There rhythms fluctuate with the seasons. That's why you have more energy in the summer, your circadian clock has made changes to the sun's rhythm. A disruption in latitude or longitude can have serious effects on ones circadian clock.
In the spring, plants respond to the sunlight and warmth of solar radiation by releasing hormones to sprout and seed. In their nest, insects respond to their circadian clocks by hatching and looking for food. Hopefully the plants and pollinators clocks will coincide and they can reproduce and thrive. As described above, humans can have their circadian clocks disrupted by moving across several latitude or longitude lines in a short time period. We get up at the wrong time, we're hungry, we're wide awake at night when all the stores are closed etc.… A catastrophic event such as a prolonged overcast of the sun from wildfire smoke can have plants opening up their stomata at the wrong time. The Circadian clock will tell a plant its daytime, and to maximize photosynthesis. It will waste precious energy stores not produce enough food and perhaps even die. 65 million years ago circadian rhythms were totally disrupted when an asteroid hit the earth at Chicxulub covering the sky with dust. Plants died because they could not photosynthesize and all the dinosaurs died off it was the end of the Cretaceous period.
Even a minor disruption like an solar eclipse can disrupt a circadian clock.
Another way you can disrupt the circadian clock is temperature. The circadian clocks in plants can be disruptive with temperature changes. We as gardeners know this and use this to our advantage using green houses, grow lights and warming beds to push plants off their circadian cycles and bud earlier than they normally would in the environment outdoors. In other words, we move the sun and its radiation to them rather than the other way, when we travel across longitude or latitude lines.
Climate change also changes the temperature and disrupts circadian plant and insect rhythms because the changes are subtle, we may not even notice them. The plants may sprout earlier because it's warm but there is not enough solar radiation to sustain its early growing stage. Insects emerge only to find the plants past their pollination stage.
Dr. Pamela Menegazzi, Department of Neurobiology and Genetics of the University of Wurburg, writes. “Circadian clocks with periodicity of about 24 hours enable animals to adapt to the day and night cycles. However, if these clocks are too rigid, this could be a disadvantage when adapting to weakly rhythmic environments like the polar regions.”
Diversity within the plant and insect worlds could provide organisms that could adapt to changing environmental factors that affect circadian rhythms.
As gardeners we are on the front lines of climate change and circadian rhythms. Observe which plants are thriving are the pollinators present? Provide diverse plants for all kinds of pollinators. Observe which crops do well in the warmer conditions and which do not. All this is vital information we can give to scientists and to each other so we can live well and thrive.
University of Wurzburg. “What drives circadian rhythms at the poles?” ScienceDaily. ScienceDaily, 4 November 2019. www.sciencedaily.com/releases/2019/11/191104141656.htm.