According to a new study, global warming has a direct effect on the ocean’s net primary production (NPP) at the base of the food web and also on the seasonal timing of plankton blooms.
The study has been reported in Nature’s Climate Change journal.
In contrast to the familiar situation on land, where climate change has been forecasted to expand the growing season of plants on average as a result of the CO2 fertilization effect and earlier thawing of spring snow in high latitudes, the seasonal response of plankton in the ocean has remained a mystery.
To help answer this question, a group of climate scientists from the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea, Princeton University, the University of California Los Angeles, and the Geophysical Fluid Dynamics Laboratory (GFDL), in the US, examined global warming supercomputer model simulations that were performed with a realistic Earth system model.
To separate the human-induced effect on plankton seasonality in the coming eight decades, from the naturally happening chaotic changes, the researchers ran the model 30 times with growing greenhouse gas concentrations and vaguely different starting conditions.
The review of these alleged large ensemble simulations disclosed that global warming will have a considerable effect on the timing of future plankton blooms and that such variations will become detectable against the backdrop of natural changes, thereby reaching no-analog conditions by the end of 21st century.
Upon being subjected to such conditions, there may be a mismatch in the timing of the life cycles of phytoplankton and zooplankton that tend to feed on them. This causes an effect on the complete seasonally-paced clockwork of the marine food web.
The study denotes that such effects could be especially severe for high-productivity regions in the high latitudes of the Northern Hemisphere.
The basic controls on future alterations in the timing of marine phytoplankton productivity derive in large part from a powerful coupling of the growth and fall of ocean primary producers and zooplankton that act as predators.
Seasonal variations in ambient environmental factors like light levels, temperature, and nutrient concentrations (alleged “bottom-up” controls) and various predators (top-down controls) cause phytoplankton to flourish and decline; in turn, the predator populations react quickly to the abundance of phytoplankton.
The authors discovered that planetary warming could interrupt this fragile coupling between external environmental factors and zooplankton responses. This results in 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,” states Dr. Karl J. Stein, a co-author of the study.
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. 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.
Dr. Ryohei Yamaguchi, Study Lead Author, Center for Climate Physics, Institute for Basic Sciences
Yamaguchi, R., et al. (2022) Trophic level decoupling drives future changes in phytoplankton bloom phenology. Nature Climate Change. doi.org/10.1038/s41558-022-01353-1.