Decline in microbial genetic richness in the western Arctic Ocean

The Arctic region is experiencing climate change at a much faster rate than the rest of the world. Melting ice sheets, runoff from thawing permafrost and other factors are rapidly changing the composition of the Arctic Ocean's water. And that change is being experienced all the way down to the microbial level.

In a Concordia-led study published in the journal ISME Communications, researchers analyzed archival samples of bacteria and archaea populations taken from the Beaufort Sea, bordering northwest Canada and Alaska.

The samples were collected between 2004 and 2012, a period that included two years -- 2007 and 2012 -- in which the sea ice coverage was historically low.

The researchers looked at samples taken from three levels of water: the summer mixed layer, the upper Arctic water below it and the Pacific-origin water at the deepest level.

The study examined the microbes' genetic composition using bioinformatics and statistical analysis across the nine-year time span.

Using this data, the researchers were able to see how changing environmental conditions were influencing the organisms' structure and function.

The researchers found subtle but statistically significant changes in the communities they studied.

"We observed a general overall loss in diversity of species across all the different water masses," says David Walsh, a professor in the Department of Biology and the paper's corresponding author.

"We also saw changes in the composition of the microbial community, meaning there were different species after the 2007 sea ice minimum than before."

However, the periods of population richness decline changed between the ocean's layers of water.

Sudden decline in the fresher summer mixed water level, between 3-9 meters deep, was observed in 2005-2007.

The upper Arctic water, between 16-78 metres, saw declines in 2010-2012, while the deeper Pacific water layer, between 49-154 meters, experienced a two-step decline -- once between 2005-2007 and again between 2010-2012.

Small beginnings

The researchers are taking care not to overemphasize the results of their findings, saying the changes, while significant, remain slight.

But with the summer Arctic ice cover shrinking steadily year over year, the data does hint at possible trends that may be visible in upcoming population studies in more recent years.

"With the warming and freshening of the Arctic Ocean comes a decrease of nutrients that are important for photosynthesis, which produces the organic matter that serves as energy and carbon sources for the marine food web," Walsh explains.

"This shift risks strengthening what is known as the microbial loop, in which the energy and carbon that would normally go into higher trophic levels -- meaning zooplankton and then fish -- is rapidly recycled by microorganisms. This ecosystem is already dominated by microbial processes, which will only get stronger as this system continues."

"This study provides us with a baseline idea of what is happening in the Arctic," says co-author Arthi Ramachandran, PhD 23. "The Arctic is warming four times faster than the rest of the world, which makes it a fascinating ecosystem to study. The oceans are all interconnected, and the physical barriers of these oceans are becoming much less defined."

Looking into the ocean's warmer, fresher future

The researchers are now planning a metagenomic study that extends the time series to cover periods of even more intense sea ice minima.

They hope to fully sequence the organisms' genomes to further understand the microbial communities' diversity and function in the environment.

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New research explains 'Atlantification' of the Arctic Ocean

New research by an international team of scientists explains what's behind a stalled trend in Arctic Ocean sea ice loss since 2007. The findings indicate that stronger declines in sea ice will occur when an atmospheric feature known as the Arctic dipole reverses itself in its recurring cycle.

The many environmental responses to the Arctic dipole are described in a paper published online today in the journal Science. This analysis helps explain how North Atlantic water influences Arctic Ocean climate. Scientists call it Atlantification.

The research is led by professor Igor Polyakov of the University of Alaska Fairbanks College of Natural Science and Mathematics. He is also affiliated with the International Arctic Research Center at UAF.

Co-authors include Andrey V. Pnyushkov, research assistant professor at the International Arctic Research Center; Uma S. Bhatt, atmospheric sciences professor at the UAF Geophysical Institute and UAF College of Natural Science and Mathematics; and researchers from Massachusetts, Washington state, Norway, and Germany.

"This is a multidisciplinary view on what's going on in the Arctic and beyond," Polyakov said of the new research. "Our analysis covered the atmosphere, ocean, ice, changing continents and changing biology in response to climate change."

A wealth of data, including direct instrumental observations, reanalysis products and satellite information going back several decades, shows that the Arctic dipole alternates in an approximately 15-year cycle and that the system is probably at the end of the present regime.

In the Arctic dipole's present "positive" regime, which scientists say has been in place since 2007, high pressure is centered over the Canadian sector of the Arctic and produces clockwise winds. Low pressure is centered over the Siberian Arctic and features counterclockwise winds.

This wind pattern drives upper ocean currents, with year-round effects on regional air temperatures, atmosphere-ice-ocean heat exchanges, sea-ice drift and exports, and ecological consequences.

The authors write that, "Water exchanges between the Nordic seas and the Arctic Ocean are critically important for the state of the Arctic climate system" and that sea ice decline is "a true indicator of climate change."

In analyzing oceanic responses to the wind pattern since 2007, the researchers found decreased flow from the Atlantic Ocean into the Arctic Ocean through the Fram Strait east of Greenland, along with increased Atlantic flow into the Barents Sea, located north of Norway and western Russia.

The new research refers to these alternating changes in the Fram Strait and the Barents Sea as a "switchgear mechanism" caused by the Arctic dipole regimes.

The researchers also found that counterclockwise winds from the low-pressure region under the current positive Arctic dipole regime drive freshwater from Siberian rivers into the Canadian sector of the Arctic Ocean.

This westward movement of freshwater from 2007 to 2021 helped slow the overall loss of sea ice in the Arctic compared to 1992 through 2006. The freshwater layer's depth increased, making it too thick and stable to mix with the heavier saltwater below. The thick layer of freshwater prevents the warmer saltwater from melting sea ice from the bottom.

The authors write that the switchgear mechanism regulating inflows of sub-Arctic waters has "profound" impacts on marine life. It can lead to potentially more suitable living conditions for sub-Arctic boreal species near the eastern part of the Eurasian Basin, relative to its western part.

"We are beyond the peak of the currently positive Arctic dipole regime, and at any moment it could switch back again," Polyakov said. "This could have significant climatological repercussions, including a potentially faster pace of sea-ice loss across the entire Arctic and sub-Arctic climate systems."

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Unprecedented look at what influences sea ice motion in the Arctic

A new study led by researchers at Brown offers fresh insights into the forces above and beneath the ocean surface that influence how sea ice moves and disperses in the Arctic Ocean, which is warming at over twice the rate of the global average.

The in-depth analysis reveals how local tidal currents strongly affect the movement of the ice along its journey and provides an unprecedented look at how the makeup of the seafloor is causing some of the most abrupt changes.

Data from the study can be applied to improve complex computer simulations used for forecasting Arctic sea ice conditions, and in the long-term, the results may help clarify how climate change is altering the Arctic and inform future climate predictions.

"The ice is clearly feeling the influence of the bottom of the ocean," said Daniel Watkins, a postdoctoral researcher at Brown and lead author of the new study published in Geophysical Research Letters. "The landscape at the ocean floor, like canyons and continental shelves, affects tides and other ocean currents. And as it drifts, the sea ice passes over many different undersea features. We see sharp changes in the dynamics of the sea ice as soon as it gets to those undersea features."

Using data from largest ever drifting sea-ice buoy array, along with 20 years of satellite images, the researchers examined sea ice motion as it drifted from the Arctic Ocean through a deep-water passage called the Fram Strait and eventually into the Greenland Sea. The analysis revealed the seafloor's impact on some of the most abrupt changes affecting the sea ice, like dramatic gains in speed or motions that force the ice to pack in close together or even break apart.

"What we see with this dataset is a transition from the central Arctic, where the ice is mostly moving as a whole and following wind patterns, to areas where we're seeing much stronger impacts of ocean currents," Watkins said.

The Arctic is the fastest warming part of the globe and it has long been understood that sea ice in the region plays an important role in the planet's climate. For instance, the ice acts like a reflective surface deflecting how much sunlight is absorbed by the Earth. As it disappears, more sunlight is absorbed, leading to a warmer planet. Many scientists also expect that as Arctic ice vanishes, weather across the Northern Hemisphere will be impacted, producing periods of bitter cold, punishing heat waves and disastrous floods.

With the study, the researchers wanted to delve deeper into the changes happening in this critically important part of the Earth. Much of the data for the study was gathered during the largest polar expedition in history -- the Multidisciplinary drifting Observatory for the Study of Arctic Climate.

Comprehensive research reveals sudden increases in ice speed

During the expedition, teams of researchers took turns spending a year drifting with the sea ice aboard a massive German icebreaker in the Arctic Ocean. Watkins was there for two weeks in October 2019 to help install a network of autonomous sensors around the base camp. While there, Watkins coordinated helicopter flights to remote patches of sea ice, worked with analysts to find suitable sites for instruments and buoys and deployed them on the ice.

Throughout the year-long expedition, a total of 214 buoys were deployed, including 51 during Watkins' tenure on the expedition. The study is based on GPS data transmitted from a set of 108 of the buoys that drifted from the central Arctic through the Fram Strait and into the Greenland Sea.

The major focus was on what are known as marginal ice zones in the Greenland Sea and Fram Strait, which is the transition zone between the open, ice-free ocean and the pack ice of the central arctic.

As part of their analysis, the group also analyzed satellite measurements taken from 2003 to 2020 to put the data the buoys gathered over the year adrift into historical context. The satellite data helped confirm sharp changes in ice velocity and ice motion that could only be explained by the seafloor's influence on the sea ice.

For instance, looking at the data from an area northeast of Svalbard, Norway, the researchers noticed the speed of the ice suddenly increased even though the wind hadn't changed. That meant the ice was getting pushed by the ocean currents, so the team delved deeper to find where this happens and how. They found that the sea ice speeds up where the Transpolar Drift Stream, one of the Arctic's Ocean major currents, ends and the fast-moving East Greenland Current, which forms due to a combination of the Earth's rotation and the edge of the continental shelf on the seafloor, begins. The analysis shows how the sea ice responds to different ocean currents and that the sea floor plays a role.

"In the beginning of this journey, there was almost no difference in the drift speed across the whole set of buoys," Watkins said. "Then there's essentially one day where the wind died down and the ice ran into the that boundary current and it just took off. It was like a one-day-to-the-next change in what was pushing the ice."

As next steps, the researchers plan to work with model developers to help implement the data from the study into forecasts of how the ice will move and where it will end up. They also plan to further develop an ice floe tracking tool to track the motion of individual pieces of ice. The tool would help researchers see details of ice motion that are invisible to standard approaches.

"We're hoping to understand the changing ice physics in a warming Arctic and use it to help make our models of those physics better," Watkins said.

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Meltwater influences ecosystems in the Arctic Ocean

In the summer months, sea ice from the Arctic drifts through Fram Strait into the Atlantic. Thanks to meltwater, a stable layer forms around the drifting ice atop the salty seawater, producing significant effects on biological processes and marine organisms. In turn, this has an effect on when carbon from the atmosphere is absorbed and stored, as a team of researchers led by the Alfred Wegener Institute has now determined with the aid of the FRAM ocean observation system. Their findings have just been published in the journal Nature Communications.

Oceans are one of the largest carbon sinks on our planet, due in part to the biological carbon pump: just below the water's surface, microorganisms like algae and phytoplankton absorb carbon dioxide from the atmosphere through photosynthesis. When these microorganisms sink to the ocean floor, the carbon they contain can remain intact for several thousand years. As experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have now discovered, the meltwater from sea-ice floes can delay this process by four months.

From the summer of 2016 to the summer of 2018, the FRAM (Frontiers in Arctic Marine Monitoring) ocean observation system continually gathered data in Fram Strait (between Greenland and Svalbard). Dense clusters of moorings were installed at two sites in the strait in order to monitor as many aspects of the coupled physical-biological processes in the water as possible. Physical, biogeochemical and acoustic sensors throughout the water column and on the ocean floor, as well as devices that gathered water and sediment samples for subsequent laboratory analysis, were used. "For the first time, for two entire years we were able to comprehensively monitor not only the seasonal developments of microalgae and phytoplankton, but also the complete physical, chemical and biological system in which these developments take place," says Dr Wilken-Jon von Appen, a climate researcher at the AWI and first author of the study.

During this period, the sea-ice export reached two extremes: in the summer of 2017, an extraordinarily large amount of ice was transported out of the Arctic through Fram Strait. This produced a great deal of low-saline meltwater and a pronounced stratification of the water. In contrast, uncharacteristically little ice was transported out of the Arctic in the summer of 2018, which meant there was very little meltwater and therefore no pronounced, salinity-based stratification. The processes involved in the biological carbon pump progressed so differently during these two extremes that the experts refer to them as two different regimes: the meltwater regime (summer of 2017) and the mixed-layer regime (summer of 2018).

Meltwater regime in the summer of 2017

The first algal and phytoplankton blooms appeared on 15 May, when the atmosphere began warming the ocean. In the summer of 2017 a great deal of ice drifted through Fram Strait, producing large quantities of meltwater. "This low-saline water lay atop the saltwater without mixing," says von Appen. "And the stratification between 0 and 30 metres was ten times as intense as between 30 and 55 metres." Consequently, very few nutrients made their way upwards from the deeper water layers, while very little carbon made its way to the seafloor. Phytoplankton growth, which is the first step in the biological carbon pump, took place almost exclusively in the top 30 metres. This intense stratification only collapsed in mid-August, when the atmosphere no longer warmed the water's surface. The majority of the biomass drifted down from the upper layer between September and November, was more than three months old, and was too lacking in nutrients to interest fauna at the ocean floor. In the meltwater regime, during the bloom the microorganisms were able to fix up to 25 grams of carbon per square metre.

Mixed-layer regime in the summer of 2018

The spring and summer of 2018 were another story entirely: conditions were relatively ice-free, which meant less meltwater and less intense stratification of the seawater. A mixed layer formed to a depth of ca. 50 metres. With the first of May came the first diatom blooms; at the same time, the numbers of zooplankton, and of the fish that primarily feed on them, began to rise. Thanks to their faeces, only two to three weeks after the start of the bloom, organic carbon reached depths of up to 1200 metres. Four to seven weeks after the start of the bloom -- almost four months earlier than in the summer of 2017 -- the biomass reached the seafloor. This material was rich in nutrients, attracting five times more fish and benthic fauna than in the meltwater summer. During the bloom, the algae were able to fix roughly 50 grams of carbon per square metre, twice as much as in the meltwater regime.

Despite all these differences between the two regimes, the biological carbon pump wasn't necessarily more productive in the summer of 2018: "We found that, in the summer of 2017, the majority of the organic carbon didn't reach the seafloor until after September," says von Appen. "If you look at the period between early May and late November, the carbon export in the mixed-layer regime was only a third higher than in the meltwater regime." Rather, the pronounced stratification in 2017 promoted longer-term growth over several months, since carbon and nutrients were trapped in the upper layers. In contrast, the ice-free situation in 2018 produced a brief, intense bloom and rapid export, providing food and carbon for deep-sea ecosystems on the ocean floor. As such, the latter would seem to particularly benefit from the summertime conditions in the mixed-layer regime; in the meltwater regime, the intense stratification blocks nutrient input in the summer and deep water mixing in the winter.

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The moon controls the release of methane in Arctic Ocean

 It may not be very well known, but the Arctic Ocean leaks enormous amounts of the potent greenhouse gas methane. These leaks have been ongoing for thousands of years but could be intensified by a future warmer ocean. The potential for this gas to escape the ocean, and contribute to the greenhouse gas budget in the atmosphere, is an important mystery that scientists are trying to solve.

The total amount of methane in the atmosphere has increased immensely over the past decades, and while some of the increase can be ascribed to human activity, other sources are not very well constrained.

A recent paper in Nature Communications even implies that the moon has a role to play.

Small pressure changes affect methane release

The moon controls one of the most formidable forces in nature -- the tides that shape our coastlines. Tides, in turn, significantly affect the intensity of methane emissions from the Arctic Ocean seafloor.

"We noticed that gas accumulations, which are in the sediments within a meter from the seafloor, are vulnerable to even slight pressure changes in the water column. Low tide means less of such hydrostatic pressure and higher intensity of methane release. High tide equals high pressure and lower intensity of the release" says co-author of the paper Andreia Plaza Faverola.

"It is the first time that this observation has been made in the Arctic Ocean. It means that slight pressure changes can release significant amounts of methane. This is a game-changer and the highest impact of the study." Says another co-author, Jochen Knies.

New methods reveal unknown release sites

Plaza Faverola points out that the observations were made by placing a tool called a piezometer in the sediments and leaving it there for four days.

It measured the pressure and temperature of the water inside the pores of the sediment. Hourly changes in the measured pressure and temperature revealed the presence of gas close to the seafloor that ascends and descends as the tides change. The measurements were made in an area of the Arctic Ocean where no methane release has previously been observed but where massive gas hydrate concentrations have been sampled.

"This tells us that gas release from the seafloor is more widespread than we can see using traditional sonar surveys. We saw no bubbles or columns of gas in the water. Gas burps that have a periodicity of several hours won't be identified unless there is a permanent monitoring tool in place, such as the piezometer." Says Plaza Faverola

These observations imply that the quantification of present-day gas emissions in the Arctic may be underestimated. High tides, however, seem to influence gas emissions by reducing their height and volume.

"What we found was unexpected and the implications are big. This is a deep-water site. Small changes in pressure can increase the gas emissions but the methane will still stay in the ocean due to the water depth. But what happens in shallower sites? This approach needs to be done in shallow Arctic waters as well, over a longer period. In shallow water, the possibility that methane will reach the atmosphere is greater." Says Knies.

May counteract the temperature effects

High sea-level seems thus to influence gas emissions by potentially reducing their height and volume. The question remains whether sea-level rise due to global warming might partially counterbalance the effect of temperature on submarine methane emissions.

"Earth systems are interconnected in ways that we are still deciphering, and our study reveals one of such interconnections in the Arctic: The moon causes tidal forces, the tides generate pressure changes, and bottom currents that in turn shape the seafloor and impact submarine methane emissions. Fascinating!" says Andreia Plaza Faverola.

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