Oceans around the globe have become darker over the last two decades, leaving researchers fearful for their marine inhabitants, according to a new study.

Professor Thomas Davies of the University of Plymouth said in a study published in the Global Change Biology journal there is growing concern for the marine ecosystem.

Satellite data from NASA's Ocean Color Web data portal showed 21% of the planet’s oceans had darkened between 2003 and 2022.

According to Davies, the majority of marine life lives in the photic zones of the ocean, which is where sufficient light penetrates to stimulate photobiological processes.

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The photic zone, which is 200 meters deep, is where global nutrients and carbon budgets sustain the planetary fish markets.

This is the area where light reaches marine life that lives closer to the surface of the ocean.

These ocean inhabitants rely on both the moonlight and sunlight for hunting, mating, reproduction and other important milestones.

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The upper level of the ocean is where microscopic organisms and different types of plankton live.

With the oceans beginning to darken, it will cause creatures that rely on light to begin moving closer to the surface, potentially creating a cramped living space.

Using satellite data and an algorithm-derived measure of the attenuation of light in seawater, Davis was able to measure how deep each photic zone was around the world.

Among the darker oceans, 9% of their photic zones were 50 meters more shallow, and 3% of the oceans' photic zones were 100 meters more shallow.

The reasoning behind the darkening of oceans far offshore is less clear.

Global warming and changes in ocean currents are thought to be involved in this phenomenon, according to the study.

Despite an overall darkening, about 10% of oceans, or 37 million square kilometers, have become lighter over the past 20 years, the study found.

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It also found that most coastal areas have seen an increase in light. However, the study found that this does not translate into a net reduction in photic zone depth near shorelines.

Davies predicts the implications of ocean darkening could be severe for marine food webs, global fisheries and carbon and nutrient budgets.

State Department spokesperson Tammy Bruce indicated Thursday that the increased scrutiny the Trump administration is placing on foreign student visas will not be a "one-time" check, but rather a process that lasts the entire time foreign students remain studying in the country. 

Bruce was peppered with questions at a Thursday press briefing about the Trump administration's plans for increased vetting for foreign students. The briefing came amid news that the Trump administration has paused new student visa appointments at embassies across the globe. The Trump administration also indicated this week it would begin "aggressively" revoking the visas of Chinese students that pose national security threats, and has plans to implement expanded social media vetting for foreign student visas. 

"Everyone who's here on a visa has to recognize – certainly it is what they've seen over the last few months – that America takes their visa seriously, that vetting is not a one-time process – it's continuing," Bruce said in response to questions about what the new scrutiny and vetting will entail. "When things, if things happen, if you get arrested, if there's some kind of an issue, it's probably going to be seen at some point," Bruce added.

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"There's an interest in making sure that those who are here from China on a visa understand that we are taking our national security seriously," she continued. "And, if everything's fine, terrific. But, that will be a vetting that certainly continues and is important."

Citing national security concerns, Bruce did not reveal many details about what the new scrutiny on foreign students will look like. However, she did tell reporters that the student visa interviews will likely resume "sooner-than-later," once a formalized process has been agreed upon. 

Bruce framed the new student visa scrutiny as part of President Donald Trump's "America First" agenda aimed at reducing alleged political indoctrination on campuses and ensuring that American students can receive the highest quality education possible without interference.

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"There's a reason why people come here – it's because of what the country represents. Yes, the excellence of our schools. And we want to keep it that way," Bruce told reporters Thursday.

"We want parents who send their children, whether they be from a different country or America – to an American university – that they can recognize their child when that child returns home … making sure that everyone who does want to send their child to a school in this country can do so knowing that they're going to be safe, they're going to be able to get into a building and not held hostage in a library because it's been occupied, or that they're going to be able to actually learn things that you're paying that kind of money for."