Less ice and more sunlight will drastically alter the Arctic Ocean

Over the last quarter century, the Arctic has witnessed a dramatic reduction in summer sea ice, shrinking by more than one million square kilometers. This transformation has left extensive parts of the Arctic Ocean ice-free during the summer months with a significant increase in sunlight exposure. 

This phenomenon has drawn the attention of the scientific community worldwide, who are keenly observing its impact on sunlight penetration and the resultant effects on the marine ecosystems of the far north.

Increased sunlight availability on the Arctic seafloor

Karl Attard, a prominent marine scientist and assistant professor in the Department of Biology at the University of Southern Denmark, is at the forefront of a global research initiative that delves into the implications of increased sunlight availability on the photosynthetic activity of the Arctic seafloor, a region less studied in this context. 

The team’s research places a spotlight on the Arctic Ocean’s extensive shelf regions. These areas of the seafloor, which are relatively shallow and seldom exceed depths of 200 meters, account for about half the Arctic Ocean’s surface area. This makes them particularly intriguing for studying how seafloor ecosystems adjust as sea ice continues to recede.

Photosynthetic activity 

Primary producers like microalgae, seaweeds, and seagrasses, which are capable of photosynthesis, rely on sunlight along with water, carbon dioxide, and nutrients. These organisms are foundational to the ocean’s food web, underpinning commercially vital fisheries and supporting large predators such as polar bears.

Given the expanding areas of the seafloor now exposed to sunlight, one might intuitively expect an increase in the abundance of these primary producers. However, the experts reached a counterintuitive result. 

Sunlight reaching the Arctic seafloor 

“It might seem reasonable to assume that the abundance of primary producers on the seafloor in the shallower regions of the Arctic Ocean would increase as more sunlight reaches the bottom,” noted Attard.

“In fact, our research suggests that since 2003, the seafloor area exposed to sunlight has been increasing rapidly at around 47,000 square kilometers per year. 

Curiously, however, we do not see an increase in the total amount of sunlight reaching the Arctic seafloor.”

This observation, based on two decades of satellite data, indicates that despite the expanded ice-free areas, there isn’t a corresponding increase in sunlight reaching the seafloor.

Decrease in water transparency 

The study reveals that water transparency in many parts of the Arctic Ocean has decreased, impeding sunlight from penetrating to the seafloor. 

Sunlight that enters the ice-free ocean is rapidly absorbed by phytoplankton, sediments, and dissolved substances, thus limiting its reach to the ocean floor. Despite these regions now being ice-free and receiving sunlight at the surface, the models predict variable impacts on primary production across different areas.

The decline in water clarity is attributed to the influx of river water, carrying sediments from distant regions like Mongolia or central North America, into the Arctic Ocean. These sediments, along with dissolved organic molecules, cloud the water, reducing sunlight penetration.

Sunlight availability and primary production

The researchers’ models reveal regional disparities in biomass production on the newly exposed ocean floor, with some areas experiencing an increase in primary production while others not. 

“The question then arises: why does sunlight availability and primary production increase in some areas while diminishing in others?” Attard said. “Unfortunately, our models do not provide a clear answer as to what specifically is driving this change, and obtaining this information necessitates investigating individual regions and validating our models with more observational data.”

“The latest models suggest that seaweeds and eelgrass will establish themselves on the shallow coastal seafloor and will expand into the Arctic Ocean as the ice further diminishes and water temperature increases. Here too, more observations are needed to test the uncertainties in the models,” he added.

Complex interactions 

This study underscores the complex interplay between climate change, sunlight availability, and primary production in the Arctic Ocean. As the Arctic continues to warm, the influx of species from lower latitudes might lead to a more productive marine environment than currently exists, albeit at the expense of the Arctic’s unique character. 

“Our study suggests that the impacts of climate change on sunlight availability and primary production in the Arctic Ocean are complex. Additionally, as the Arctic Ocean continues to warm, we may witness more species migrating from lower latitudes, potentially leading to a more productive marine environment than what exists today – at the cost of losing what is special for the Arctic,” Attard concluded. 

The study is published in the journal Proceedings of the National Academy of Sciences.

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