While the effects of climate change on terrestrial ecosystems have already been studied extensively, its impact on marine ecosystems remains largely a mystery. On land, due to CO2 fertilization and the earlier thawing of spring snow in high altitudes, climate change is expected to significantly extend the growing season of plants. But what will its effects be on the seasonal response of plankton populations in the oceans?
A new study published in the journal Nature Climate Change has found that global warming will have a substantial influence on the timing of future phytoplankton blooms. By analyzing climate change supercomputer model simulations conducted with a highly realistic Earth system model, the researchers discovered that such shifts in the timing of plankton blooms will become clearly detectable against the backdrop of natural variations by the end of the 21st century.
To better differentiate the anthropogenic effect on plankton seasonality from naturally occurring chaotic variations, the team ran the computer model 30 times, with rising greenhouse gas concentrations and slightly different initial conditions.
The factors controlling changes in the timing of phytoplankton productivity largely derive from the complex relation between the ocean’s primary producers and the zooplankton that act as predators. Seasonal changes in ambient environmental factors such as temperature, light levels, or nutrient concentrations (the so-called “bottom-up” controls), together with the number of predators (“top-down” controls) make phytoplankton thrive or decline. In turn, predator populations respond quickly to the phytoplankton abundance.
The study results suggest that climate change will most likely disrupt this delicate coupling between external environmental factors and zooplankton responses, causing seasonal shifts in the blooming of phytoplankton. “The additional level of predator/prey interactions makes the ocean’s response more complex than the response of land plants, where the control is mostly bottom-up,” said study co-author Dr. Karl J. Stein, an assistant researcher at the IBS Center for Climate Physics (ICCP).
Thus, the mismatch in the timing of the life cycles of phytoplankton and zooplankton that feed on them may impact the entire seasonally-paced clockwork of the marine food web, particularly in the high-productivity regions of the Northern Hemisphere’s high latitudes.
“Our study demonstrates the power of large ensemble computer model simulations to understand how ecosystems respond to future climate change, in this case their seasonality,” said study lead author Dr. Ryohei Yamaguchi, a climate expert at ICCP. “Having established the timing and underlying mechanisms of future plankton bloom changes, we will address further whether such changes will have a negative impact on future food security,” he concluded.