The Plight of the Plankton: Climate Change Forces Species to Move North
“By experience we find out a short way by a long wandering.” — Roger Ascham
Floating deep throughout the ocean column, there are tiny — sometimes microscopic drifters swaying and churning at the whims of waves and currents. Collectively known as plankton, this living brew of animals and plants, protozoa and archaea, bacteria and viruses, is a powerful force that has shaped the chemistry and geology of the Earth we know.
All planktonic species occupy unique positions in the food chain and play crucial roles in ocean processes and economic outcomes for humans. Tiny, planktonic animals respire carbon, pumping it out of the atmosphere and into the ocean, specks of fungi and bacteria remineralize organic matter, and free-floating photosynthesizers release valuable oxygen into the ocean and have been faithfully regulating the atmospheric balance of oxygen & carbon dioxide since the Pre-Cambrian Eon. Algae, which includes many planktonic species, form the base of the food chain. They are fed upon by small animals, which are a food source for fish, which can then be eaten or sold by human beings.
For plankton, job security — and life itself is completely dependent on complex interactions between the physical and living worlds. Sunlight piercing through the water, winds blowing phosphate & iron dust over the ocean, upwelling & downwelling, runoff from fertilizers, and importantly — sea temperature, all play a role in plankton survival.
Rising sea temperatures especially can influence not only where plankton live, but also how they interact with their environment. A recent study (published in Nature) at the University of Bremen found that climate change, which causes regions of ocean warming, is forcing some plankton to migrate North, which could threaten the integrity of their ecosystem.
Deep ocean sediments provide a physical record of some plankter’s extensive reign on planet Earth, which allows scientists to view how populations have changed over time. Foraminifera, or forams, are tiny planktonic organisms encased in calcium shells. When a foram dies, its tiny, hard shell sinks to the bottom of the ocean, at rest above the millions of other shells that came before it.
This build up over time preserves the history of forams that died centuries ago and has allowed researchers at the university to uncover how populations of forams are altered by climate change.
Lukas Jonkers, a post-doctoral fellow at the center (and the lead author of the published report), looked at pre-industrial sediments and compared them to sediments containing modern (between 1978–2013) foram shells. After taking nearly 4,000 sediment samples across the Northern Hemisphere, Jonkers found that modern foram communities didn’t look at all like the ones that left their mark in older sediments.
In fact, when he examined forams in old sediments further south, he found that modern foram communities in the north looked a lot like old foram communities that once lived in warmer, more southern waters. Astoundingly, modern species recorded in sediments near Greenland were some of the same species that once occupied pre-industrial waters in the south.
While there is currently no evidence for mass extinctions in foram communities, the pattern of migration is concerning because of plankton’s important role in the food chain. When a species moves to a new habitat, it has to survive long enough to adapt to the demands of its new ecosystem. Similarly, when plankton leave a region, they leave behind the organisms that once fed on them and enter a new race for survival with different actors and different appetites.
On a broader scale, the way plankton respond to climate change could have consequences for the long-term rhythm of Earth’s climate — especially if some species fail to thrive post-migration.
On Earth, there are natural oscillations in climate that occur with or without human influence. These cycles can operate on annual, decadal, centennial, or even millennial time scales. Millennial climate cycles are largely due to shifts in the Earth’s axial tilt, or obliquity, which changes what places receive solar radiation and how much. Cycles like these are also recorded in sediments, and while they usually don’t cause major temperature changes on their own, they can amplify the effects of warming and cooling.
Numerous factors, including but not limited to the circulation of the ocean and atmosphere, the carbon cycle, and biological activity all influence these oscillations. In an attempt to make sense of it all, Earth scientists use models to try and understand where the Earth’s climate has been and where it will end up. Usually, these models rely on changes in obliquity to recreate naturally observed climate cycles.
Researchers at the GEOMAR Helmholtz Centre for Ocean Research, Kiel decided to explore a different avenue when they studied a ~40,000-year climate cycle previously thought to reflect obliquity forcing (their findings can be found here). They used a model of the marine biome to simulate biogeochemical processes, like the oxidation & reduction (redox) reactions that control which elements get dissolved in ocean water.
In their model, two important ocean basins switched between iron-rich and sulfidic states, and between highly oxygenated and less oxygenated states. This change, which the researchers describe as a “redox see-saw” was enough to change the amount of carbon dioxide in the atmosphere and create a self-sustaining 40,000-year cycle. No orbital forcing required. This suggests that, along with being the backbone of the food web, plankton may play a role as climate drivers over longer time periods.
The extent to which plankton might drive climate and the longterm effects of foram migration are still yet to be seen, but because plankton and climate are so tightly interwoven, studying either party can reveal where the Earth’s physical and living systems are going and what our future might hold.
Click on the link below to learn more about the tiny, carnivorous microbes that teach scientists how predators feed on prey.
