The study may have answered the mystery of the weak young sun, which shone 20% brighter in Archean times. Even though the Sun burned 20% brighter on early Earth, fossil evidence suggests our planet had warm, shallow oceans where stromatolites – microbial mats – thrived.
New research may have solved the “weak young sun problem”, demonstrating that saltier waters could have kept the earth from freezing more than 3 billion years ago.
(Photo: Photo by JOHAN ORDONEZ/AFP via Getty Images)
We all know that the composition of the atmosphere (especially the concentration of greenhouse gases) is critical to regulating Earth’s temperature, but what about the composition of the oceans? To study the influence of salinity, the researchers used an ocean-atmosphere general circulation model.
They show that saltier seas lead to warmer temperatures, partly because salt lowers the freezing point of salt water and limits the development of sea ice, but mainly because salt water has a density higher, which changes ocean circulation patterns and favors the transit of heat towards the poles.
According to them Archean scenario, current salinity levels result in a heavily glaciated globe with just a tiny band of open water near the equator. However, the rise in salinity to 40% higher than today indicated a warmer Archean land with typical surface temperatures of over 20 degrees Celsius, with ice only arriving seasonally at the poles. Geophysical Research Letters have published their findings.
Read also : Study shows how much ocean fjords release methane
Why is the ocean salty?
(Photo: Photo by Mario Tama/Getty Images)
The ocean takes its salt from two places: excess soil and openings in the bottom.
Terrestrial rocks are the main source of dissolved salts in salt water. Because rainwater on earth is slightly acidic, it erodes rocks. This causes ions to be released into streams and rivers, which eventually flow into the ocean. Many dissolved ions are extracted from water by ocean creatures. Others are not eliminated, causing their concentration to increase over time.
Hydrothermal fluids, which come from seafloor vents, are another source of salts in the ocean. Ocean water seeps through cracks in the seabed and is heated by magma from the Earth’s core. Heat sets off a chain of chemical reactions. Water tends to lose oxygen, magnesium, and sulfates while absorbing metals like iron, zinc, and copper from surrounding rocks.
The heated water is expelled through vents on the seabed, bringing in the metals. Some ocean salts form due to underwater volcanic eruptions that release minerals directly into the ocean.
What if the ocean froze?
The composition of the atmosphere, in particular the concentration of greenhouse gases, is well known to impact the Earth’s climate system. We show, using a climate model, that ocean composition can significantly influence surface temperature and ice cover. We focus on the amount of dissolved salt in seawater and find that saltier oceans lead to warmer climates.
These effects are minor today, but salt may have been an important part of early Earth’s habitability when the Sun was less bright.
The ice cover covering the oceans would block out most of the light in surface water. This would destroy seaweed, with consequences that would ripple through the food chain until the seas were nearly barren. Only deep-sea species living near hydrothermal vents could survive.
Because ice reflects more sunlight than water, the global climate would decrease dramatically, causing the earth to freeze. Plants would die from lack of water, which would reduce CO2 uptake; thus, the CO2 from the volcanoes would slowly build up in the atmosphere and warm the earth again – although the melting of the ice could take millions of years.
Related article: Climate change is affecting the composition of the ocean, making it harder for sea creatures to communicate
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