While we often hear about the important role of anthropogenic carbon dioxide emissions in today’s climate, much of our understanding of current and future climate is based on Earth’s long history of climate change. Many factors affect the carbon cycle – carbon moves between the atmosphere, oceans, rocks, soil and living things. Between 7.6 and 5.4 million years ago, the planet experienced a period of severe cooling known as the Late Miocene Cooling. This was accompanied by great changes in plant and animal communities both on land and in the oceans. Until recently, this cooling was explained by the leaching of carbon dioxide from the atmosphere as a result of the silicate erosion of the Himalayas.
Scientists suggest another factor contributing to this – a significant increase in volcanism in the Andes about seven million years ago. They explain that the Andes are positioned to ash the Pacific and Atlantic oceans, provide nutrients to the world’s oceans, and give impetus to the rapid development of life. Tiny marine organisms called diatoms used these nutrients to thrive, and marine mammals such as whales evolved. Given their massive size, large numbers of marine mammals can store a lot of carbon. Whales dump their waste into shallow waters, giving nutrients back to diatom communities, and the cycle continues.
“But maybe that was the case when they themselves contributed to their deaths,” explains one of the study’s authors. Too many nutrients in the water can lead to toxic algal blooms, a possible stressor contributing to the extinction that follows the spring of life. Another possibility is that the ashes of ongoing volcanism may have poisoned the air.
The researchers plan to look in the future for evidence to distinguish between these possible extinction factors.