Ocean pastures have a close-knit relationship with pastures on land. They are both defined by their plant life, the grass and plankton of their pastures.
On land grass grows in mineral rich dirt and thirsts for rain to thrive. In ocean pastures it’s plankton that grows in water thirsting for minerals to thrive. We all know the oceans give up water that later falls upon the land as rain helping pastures grow. But it’s news to most that the plant life of ocean pastures actually help make that rain; giving back to the land a measure of mineral bounty the land has sent to it in the form of dust in the wind. It is one of Nature’s Yin and Yang phenomena.
Scientists at the Weizmann Institute in Israel led by Dr. Hezi Gildor of the Institute’s Environmental Sciences and Energy Research Department have studied ocean pastures and revealed this potential link through computer models designed to examine how nature’s complex web of interacting elements determines global climates.
Plankton pastures in the oceans are often filled with such abundance that they can be tracked from orbiting satellites. Space agencies track plankton because they make up the bottom most levels of the marine food chain, and the health of the entire ocean depends on them.
Gildor’s group has modeled two major groups of plankton: plant-like phytoplankton, which, like their rooted cousins, take up sunlight, carbon dioxide and nutrients and convert them into sugars using chlorophyll; and zooplankton, animal-like organisms that live off the phytoplankton. Ordinarily the grazing population grows at the expense of its “plankton grass” until the latter’s dwindling amounts can no longer sustain it.
Oscillation patterns are seen in global climate systems as well. The western Pacific Ocean is a case in point. The amount of rainfall in this tropical region swings through a cycle every 40-50 days, and the temperature of the surface water beneath oscillates in a more or less corresponding cycle. (Interestingly, even small rises in this region’s oceanic surface temperature can affect weather all across the globe, leading, through a complicated set of interactions, to such far-flung climatic phenomena as rain in India or floods in South America.)
Gildor and colleagues at Columbia University in New York wondered whether these two cycles – of oceanic temperature levels and plankton populations – might somehow be connected.
Their key clue was the phytoplankton’s chlorophyll. Built to absorb light, chlorophyll consumes a portion of the warming sunlight that penetrates the ocean’s surface. When conditions are right, plankton in ocean pastures can be so dense they effectively shade the water below. Therefore, changes in phytoplankton numbers will affect sea water temperatures.
The team put together a computer simulation based on existing models of three dynamic systems: the atmosphere, ocean water and plankton. They then ran the model to simulate ten months of weather over the tropical Pacific, alternately with and without the plankton component, to see if there were any differences between the two situations.
Their study hints that the plankton cycle interacts with changing atmospheric conditions, such as cloud formation. Clouds disrupt the normal flow of energy from the sun into the water and from the water back out toward space. As a result, cloud formation affects weather stability along a simple scale: When the level of cloud interference in the atmosphere is low, weather patterns tend to be stable (characterized by un-changing rainfall levels), whereas a high level of cloud interference is characterized by increased instability, in which the system swings between periods of heavy rainfall and clear skies.
A Plankton Butterfly Effect
But put the phytoplankton into this equation and the scales shift even further. Gildor showed that at the mid-cloud range, where the weather is usually stable, the presence of phytoplankton (due to the natural “ups” of its population cycle) affects the system, driving it toward increased instability. Moreover, as the level of cloud interference rises into the realm of instability, the plankton further influence rainfall patterns, significantly cutting the transition period from clear skies to rain.
“It turns out that not only the flap of a butterfly’s wings in Brazil that can set off a tornado in Texas, but plankton in the Western Pacific can cause rain in India,” says Gildor.
Cracking the Ice Age
In related research, Gildor has applied his computer models to examine the history of ice ages on Earth. In the “Sea-Ice-Switch” model, developed together with Prof. Eli Tziperman of the same department, ice forming on the ocean’s surface was found to play a major role in regulating the switch from climatic heating to cooling and back.
Such models are judged by how well they explain existing climate records. Gildor and Tziperman have successfully used the model to explain the mechanism that makes ice sheets advance and retreat; why recent ice ages took place in cycles of 100,000 years, whereas over a million years ago the cycles lasted only 41,000 years; and why CO2 levels in the atmosphere decreased as the ice advanced. The Ice Ages may have been just another Plankton butterfly effect. Read more on the link between ocean pasture plankton and ice ages here.
Dr. Gildor’s Weizmann Institute research (and source of this posting) is supported by the Sussman Family Center for the Study of Environmental Sciences and the Sir Charles Clore Prize – the Clore Foundation.