Hexbyte Glen Cove Ocean currents predicted on Enceladus thumbnail

Hexbyte Glen Cove Ocean currents predicted on Enceladus

Hexbyte Glen Cove

Encased in an icy shell, the ocean on Enceladus appears to be churning. Credit: California Institute of Technology

Buried beneath 20 kilometers of ice, the subsurface ocean of Enceladus—one of Saturn’s moons—appears to be churning with currents akin to those on Earth.

The theory, derived from the shape of Enceladus’s , challenges the current thinking that the moon’s is homogenous, apart from some vertical mixing driven by the warmth of the moon’s core.

Enceladus, a tiny frozen ball about 500 kilometers in diameter (about 1/7th the diameter of Earth’s moon), is the sixth largest moon of Saturn. Despite its , Enceladus attracted the attention of scientists in 2014 when a flyby of the Cassini spacecraft discovered evidence of its large subsurface ocean and sampled water from geyser-like eruptions that occur through fissures in the ice at the . It is one of the few locations in the solar system with (another is Jupiter’s moon Europa), making it a target of interest for astrobiologists searching for signs of life.

The ocean on Enceladus is almost entirely unlike Earth’s. Earth’s ocean is relatively shallow (an average of 3.6 km deep), covers three-quarters of the planet’s surface, is warmer at the top from the sun’s rays and colder in the depths near the seafloor, and has currents that are affected by wind; Enceladus, meanwhile, appears to have a globe-spanning and completely subsurface ocean that is at least 30 km deep and is cooled at the top near the ice shell and warmed at the bottom by heat from the moon’s core.

Despite their differences, Caltech graduate student Ana Lobo (MS ’17) suggests that oceans on Enceladus have currents akin to those on Earth. The work builds on measurements by Cassini as well as the research of Andrew Thompson, professor of environmental science and engineering, who has been studying the way that ice and water interact to drive ocean mixing around Antarctica.

The oceans of Enceladus and Earth share one important characteristic: they are salty. And as shown by findings published in Nature Geoscience on March 25, variations in salinity could serve as drivers of the ocean circulation on Enceladus, much as they do in Earth’s Southern Ocean, which surrounds Antarctica.

Lobo and Thompson collaborated on the work with Steven Vance and Saikiran Tharimena of JPL, which Caltech manages for NASA.

Gravitational measurements and heat calculations from Cassini had already revealed that the ice shell is thinner at the poles than at the equator. Regions of thin ice at the poles are likely associated with melting and regions of thick ice at the equator with freezing, Thompson says. This affects the ocean currents because when salty water freezes, it releases the salts and makes the surrounding water heavier, causing it to sink. The opposite happens in regions of melt.

“Knowing the distribution of ice allows us to place constraints on circulation patterns,” Lobo explains. An idealized computer model, based on Thompson’s studies of Antarctica, suggests that the regions of freezing and melting, identified by the ice structure, would be connected by the ocean currents. This would create a pole-to-equator circulation that influences the distribution of heat and nutrients.

“Understanding which regions of the subsurface might be the most hospitable to life as we know it could one day inform efforts to search for signs of life,” Thompson says.

More information:
A pole-to-equator ocean overturning circulation on Enceladus, Nature Geoscience (2021). DOI: 10.1038/s41561-021-00706-3

Ocean currents predicted on Enceladus (2021, March 25)
retrieved 26 March 2021
from https://phys.org/news/2021-03-ocean-currents-enceladus.html

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Hexbyte Glen Cove Oil in the ocean photooxidizes within hours to days, new study finds thumbnail

Hexbyte Glen Cove Oil in the ocean photooxidizes within hours to days, new study finds

Hexbyte Glen Cove

Satellite image taken on May 9, 2010 of the Deepwater Horizon oil spill site in the Gulf of Mexico. Credit: MODIS on NASA’s AQUA satellite, 9 May 2010 @ 190848 UTC. Downlink and processed at the UM Rosenstiel School’s Center for Southeastern Tropical Advanced Remote Sensing (CSTARS)

A new study led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science demonstrates that under realistic environmental conditions oil drifting in the ocean after the DWH oil spill photooxidized into persistent compounds within hours to days, instead over long periods of time as was thought during the 2010 Deepwater Horizon oil spill. This is the first model results to support the new paradigm of photooxidation that emerged from laboratory research.

After an oil , oil droplets on the ocean surface can be transformed by a weathering process known as photooxidation, which results in the degradation of crude oil from exposure to light and oxygen into new by-products over time. Tar, a by-product of this weathering process, can remain in coastal areas for decades after a spill. Despite the significant consequences of this weathering pathway, photooxidation was not taken into account in oil spill models or the oil budget calculations during the Deepwater Horizon spill.

The UM Rosenstiel School research team developed the first oil-spill model algorithm that tracks the dose of solar radiation oil droplets receive as they rise from the deep sea and are transported at the ocean surface. The authors found that the weathering of oil droplets by solar light occurred within hours to days, and that roughly 75 percent of the photooxidation during the Deepwater Horizon oil spill occurred on the same areas where chemical dispersants were sprayed from aircraft. Photooxidized oil is known to reduce the effectiveness of aerial dispersants.

“Understanding the timing and location of this weathering process is highly consequential. said Claire Paris, a UM Rosenstiel School faculty and senior author of the study. “It helps directing efforts and resources on fresh oil while avoiding stressing the environment with chemical dispersants on oil that cannot be dispersed.”

“Photooxidized compounds like tar persist longer in the environment, so modeling the likelihood of photooxidation is critically important not only for guiding first response decisions during an oil spill and restoration efforts afterwards, but it also needs to be taken into account on risk assessments before exploration activities” added Ana Carolina Vaz, assistant scientist at UM’s Cooperative Institute for Marine and Atmospheric Studies and lead author of the study.

The study, titled “A Coupled Lagrangian-Earth System Model for Predicting Oil Photooxidation,” was published online on Feb 19, 2021 in the journal Frontiers in Marine Science. The authors of the paper include: Ana Carolina Vaz, Claire Beatrix Paris and Robin Faillettaz.

More information:
Ana C. Vaz et al, A Coupled Lagrangian-Earth System Model for Predicting Oil Photooxidation, Frontiers in Marine Science (2021). DOI: 10.3389/fmars.2021.576747

Oil in the ocean photooxidizes within hours to days, new study finds (2021, March 13)
retrieved 15 March 2021
from https://phys.org/news/2021-03-oil-ocean-photooxides-hours-days.html

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