Changes to the climate have had major impacts on the oceans and the biological systems that live there. A new study sheds more light on how fast these systems respond to changes. What the authors find is that short term climate changes can require 1,000 years for recovery. This means the current harm caused to the deep oceans by the changing climate will last for many centuries to come.

The new study, published in the Proceedings of the National Academy of Sciences by Dr. Sarah Moffitt and her colleagues is novel for a number of reasons. The researchers took core samples from ocean floor regions off the coast of California. The location was chosen in part because of the exceptional synchrony between sediment archives from offshore California and ice core records from the Greenland Ice sheet.

Dr. Sarah Moffitt. Photo credit: Wayne Freedman

The authors’ method was novel because they sampled many different types of creatures, not merely the single-celled organisms that are most commonly studied. In fact, the authors included Mollusca, Echinodermata, Arthropods, and Annelida samples (approximately 5,000 fossils). There was major “turnover” in these animals with only small changes to oxygen levels.

Using the ocean sediment core, the authors were able to travel back in time to the last deglaciation. They connected cooling and warming events to increases and decreases in the oxygen contained within the waters. Past events of abrupt warming, which occurred in decades to centuries and were accompanied by subsurface oxygen loss, significantly impacted the types and numbers of animals found within the sediments. Recovery from this abrupt, climate-forced disturbance can take 1,000 years.

Among the changes documented are expansions and intensification of oxygen poor regions. These regions, called “Oxygen Minimum Zones” get larger when the oceans warm. As these oxygen poor zones get larger, there is a predominance of animals that thrive in low-oxygen environments. Animals that need higher levels of oxygen suffer and die off.

It isn’t just that one ecosystem replaces another. Rather, a rich diversity of oxygen-loving biology is replaced by a much smaller diversity of low-population low-oxygen biology, and in particular single-celled organisms. In short, the ocean floor changes from a rainforest to a desert.

I asked Dr. Moffitt about her research and she said,

Past events of climate warming are informative laboratories to understand the ecological consequences of abrupt changes in ocean circulation and temperature. We demonstrated that marine ecosystems can be disrupted by climate events on the timescales of multiple decades, but a subsequent recovery can take a thousand years to be complete. Fundamentally, what you can take away from this research is the vulnerability of the deep sea – truly an enormous biome on the planet – to abrupt warming.

This research is important for us today because we are causing rapid changes to the environment of the ocean and the ocean floor. We can expect these changes to impact biodiversity of the open ocean and seafloor. We now know that it will take a very long time for those biological systems to recover, basically the changes will be permanent from our standpoint. All of this makes more clear the need to take action to preserve the quality of the ocean habitat for animals and plants that live there.