It not only put an end to the dinosaurs – how the asteroid impact also killed many marine animals is now highlighted in a study: Poisonous algae could have contaminated the water 66 million years ago. According to simulations, the consequences of the impact triggered processes in the oceans that briefly led to an explosion of algae. Some species are notorious as poison producers in waters. Extensive algal blooms could also have contributed to marine mass extinction, the scientists explain.
The Cretaceous Period ended with a tremendous bang: in the area of the Mexican peninsula Yucatan, a huge asteroid crashed into the earth 66 million years ago. As a result, firestorms probably raced around the planet and enormous amounts of dust and ash got into the atmosphere. It is believed that the associated darkening and cooling had devastating effects on terrestrial ecosystems. The paleontological finds from the time of the impact also clearly show that the inferno was associated with a dramatic mass extinction. The dinosaurs were the most famous victims – but in addition to land creatures, many marine animals also disappeared from the stage of evolution.
According to this, the oceans ultimately offered little protection from the effects of the cosmic bomb. “The exact connections between the impact and the changes in the marine biosphere are still unclear,” says Julia Brugger from the Potsdam Institute for Climate Impact Research (PIK). What could have happened in the oceans 66 million years ago, she and her colleagues have now investigated using an improved Earth system model. By taking numerous influencing factors into account, it can simulate how the marine biosphere might have reacted to changes in the climate and nutrient supply as a result of the Chicxulub impact, the scientists explain.
Impact consequences with fertilizing effect
As they report, the new model simulations show how the processes of ocean circulation changed dramatically as a result of the effects of dust and sulfate aerosols in the atmosphere: The blockade of sunlight led to a cooling of the surface water, which made it denser and heavier. These water masses then sank into the depths, creating an opposing process: warmer water from deeper ocean layers flowed to the surface of the ocean. A well-known aspect of deep water then came into play: It has comparatively high levels of mineral substances with a fertilizing effect.
“At the same time, essential nutrients, especially iron, were brought into the oceans from the atmosphere, namely through the dust that was blown into the air by the impact of the iron-rich asteroid,” says co-author Georg Feulner from PIK. The inflow of nutrients could then have led to an effect that is also known from today’s waters when fertilizers are introduced: algae multiply explosively. This is exactly what the model simulation shows for the time after the impact, the researchers report.
Initially, a drastic collapse in the biomass produced by algae due to the initial darkness and cold is evident. But when it got lighter again, the algae growth assumed an oversized extent, according to the model calculations: “Biomass production reached a peak for a short time with a maximum value that was about a factor of seven higher than before the impact,” says Feulner. Although the peak of algae multiplication only lasted a few years according to the model simulation, the increased productivity persisted and only returned to the level before the impact after around 500 years.
Contaminated water?
As the scientists explain, this could have created significant problems for marine organisms of the time. Because blue-green algae (cyanobacteria) in particular are known to release substances that can have fatal effects. “It is likely that the algal blooms produced toxic substances that led to massive changes in marine life,” says Brugger. In conjunction with the various other adverse effects as a result of the impact – such as the sudden darkening, cooling and moderate ocean acidification – the study thus provides further information on how the asteroid impact contributed to the mass extinction of many marine species, according to the scientist.
The researchers see the references to the processes of the past also having a meaning for the view of today’s developments: “66 million years ago the Chicxulub impact caused rapid environmental disturbances and exposed the earth’s biosphere to a multitude of stresses, which eventually became one led to great mass extinctions, ”says Feulner. Today, however, humans are behind the drastic changes in the environment. “Although the drivers of current global warming and the modern biodiversity crisis are completely different, the past can teach us how a combination of simultaneous pressures can seriously damage life on earth,” said the scientist.
Source: Potsdam Institute for Climate Impact Research, specialist article: Geophysical Research Letters, doi: 10.1029 / 2020GL092260