A Slowdown in Earth’s Rotation Could Have Affected the Oxygen Content of the Atmosphere - SciTechDaily

A scuba diver observes the purple, white and green microbes covering rocks in Lake Huron’s Middle Island Sinkhole.

“But when studying mats of cyanobacteria in the Middle Island Sinkhole in Lake Huron in Michigan, which live under conditions resembling early Earth, I had an idea.”.

Arrow and red circle indicate the location of several submerged Lake Huron sinkholes, including the Middle Island Sinkhole.

The water in the Middle Island Sinkhole, where groundwater seeps out of the lake bottom, is very low in oxygen.

“Life on the lake bottom is mainly microbial, and serves as a working analog for the conditions that prevailed on our planet for billions of years,” says Bopi Biddanda, a collaborating microbial ecologist from the Grand Valley State University.

Purple microbial mats in the Middle Island Sinkhole in Lake Huron, June 2019.

When Brian Arbic, a physical oceanographer at the University of Michigan, heard about this diel microbial dance, he raised an intriguing question: “Could this mean that changing daylength would have impacted photosynthesis over Earth’s history?”.

A burbot fish resting on rocks covered in purple and white microbial mats inside the Middle Island Sinkhole in Lake Huron.

Geomicrobiologist Judith Klatt, formerly a postdoctoral researcher in Greg Dick’s U-M laboratory and now at the Max Planck Institute for Marine Microbiology, scrapes a microbial mat from the top of a sediment core collected at the Middle Island Sinkhole in Lake Huron.

Credit: Jim Erickson, University of Michigan News.

After noting the stunning similarity between the pattern of Earth’s oxygenation and rotation rate over geological timescales, Klatt was fascinated by the thought that there might be a link between the two – a link that went beyond the “late riser” photosynthesis lag observed in the Middle Island sinkhole.

“I realized that daylength and oxygen release from microbial mats are related by a very basic and fundamental concept: During short days, there is less time for gradients to develop and thus less oxygen can escape the mats,” Klatt hypothesized.

U-M geomicrobiologist and oceanographer Greg Dick, left, and U-M environmental engineering alumnus Kirk Olsen examine one of the sediment cores collected from the Middle Island Sinkhole in Lake Huron.

Credit: Jim Erickson, University of Michigan News.

Based on an open-source software developed by Chennu for this study, they investigated how sunlight dynamics link to oxygen release from the mats.  “Intuition suggests that two 12-hour days should be similar to one 24-hour day.

But the release of oxygen from bacterial mats does not, because it is limited by the speed of molecular diffusion.

Scuba divers in dry suits prepare to enter the frigid waters of Lake Huron to collect microbial mat samples at the Middle Island Sinkhole in September 2017.

Temperatures at the bottom of the sinkhole, where groundwater rich in sulfur and low in oxygen seeps into the lake bottom, can be in the low 40s Fahrenheit.

Credit: Jim Erickson, University of Michigan News!

To understand how the processes occurring within a day can impact long-term oxygenation, Klatt and her colleagues incorporated their results into global models of oxygen levels.

The analysis suggests that the increased oxygen release due to daylength change could have boosted oxygen levels globally?

Scuba diver leaps from the stern of the R/V Storm before descending to the bottom of the Middle Island Sinkhole roughly 80 feet below, in September 2017.

Hence, increasing daylength could have boosted benthic net productivity sufficiently to impact atmospheric oxygen levels.

Are you suggesting that the demise of dinosaurs was caused by a decline in oxygen levels