Tag: climate change

Phytoplankton and climate change in the North Atlantic

Featured by oceanecology, posted in Research article

A team of UK and French scientists have shown dramatic changes in the abundance of phytoplankton in the North Atlantic over the last 60 years driven primarily by climate variability and North Atlantic warming. In particular, the scientists focused on the important group of phytoplankton collectively known as diatoms. This major phytoplankton group contributes approximately one-fifth of all of Earth’s photosynthesis and up to 30-40% of the global marine primary production each year. As such diatoms are extremely important contributors to marine primary production and to the ocean carbon cycle. In the North Atlantic and its adjacent seas, primary production is primarily driven by these diatoms which produce vast spring blooms that cover the whole ocean every year and fuel the highly productive marine food-webs found there. They also transfer a significant part of the produced energy as carbon to the deep ocean contributing to a significant drawdown of carbon from the atmosphere.

Microscopic image of diatoms. Copyright Charles Kreb

In the study the authors showed that anthropogenic warming and climate variability (including natural climate oscillations and wind) over a multidecadal scale have had important consequences for the productivity and spatial/temporal dynamics of these phytoplankton.  The authors used multidecadal diatom abundance data (>60 years) for large areas of the North Atlantic and the North Sea to show significant spatial and temporal correlations over these scales between diatoms and climate variability. They also examined 50 phytoplankton species individually to investigate seasonal and life-cycle (phenology) patterns at the species level. In summary, the study found that climate warming is having a huge impact on the total abundance of diatoms and species in the North Atlantic over the period of this study. 

Martin Edwards from Plymouth Marine Laboratory who led the study said ‘some of the most important findings in this study include showing an increasing diatom population in northerly systems, but deceasing populations in more southerly systems. We also discovered major phase shifts in diatom abundance synchronous with multidecadal trends in Atlantic climate variability that occurred after the mid-1990s’.  

Phytoplankton bloom in the Northeast Atlantic observed from space. Copyright Nasa

Over the whole area of study there has been an increase in phytoplankton biomass during spring and autumn (where diatoms dominate) with increasing temperatures in cooler regions but a decrease in phytoplankton biomass in warmer regions.  The authors suggest that this is possibly due to increased phytoplankton metabolic rates caused by warming temperatures in colder regions but conversely a decrease in nutrient supply in warmer regions (where warming can enhance stratification and limit nutrient replenishment and hence diatom growth in the surface layers).  Gregory Beaugrand from CRNS in France and a co-author of the study also said ‘that the that autumnal diatom abundance is positively correlated with Sea Surface Temperatures and the increase in Northern Hemisphere Temperatures seen over the last few decades’. The study also found that regional climate warming in some areas of the North Sea has been linked to an increase in certain diatoms that are associated with Harmful Algal Blooms (HABs). Diatom growth in such well mixed areas may be enhanced by temperature as these regions are not inhibited by stratification and hence nutrient availability. These dramatic changes in such a fundamental primary producer for marine food-webs in the North Atlantic will have large on-going ramifications for other marine life from fish to whales found in these oceans.

More information: Edwards, M., Beaugrand, G., Kléparski, L. et al. Climate variability and multi-decadal diatom abundance in the Northeast Atlantic. Commun Earth Environ 3, 162 (2022). https://doi.org/10.1038/s43247-022-00492-9

Deep ocean warming as climate changes

by oceanecology, posted in News, Research article

Much of the “excess heat” stored in the subtropical North Atlantic is in the deep ocean (below 700m), new research suggests.

Oceans have absorbed about 90% of warming caused by humans. The study found that in the subtropical North Atlantic (25°N), 62% of the warming from 1850-2018 is held in the deep ocean.

The researchers – from the University of Exeter and the University of Brest – estimate that the deep ocean will warm by a further 0.2°C in the next 50 years.

Ocean warming can have a range of consequences including sea-level rise, changing ecosystems, currents and chemistry, and deoxygenation.

“As our planet warms, it’s vital to understand how the excess heat taken up by the ocean is redistributed in the ocean interior all the way from the surface to the bottom, and it is important to take into account the deep ocean to assess the growth of Earth’s ‘energy imbalance’,” said Dr Marie-José Messias, from the University of Exeter.

“As well as finding that the deep ocean is holding much of this excess heat, our research shows how ocean currents redistribute heat to different regions.

“We found that this redistribution was a key driver of warming in the North Atlantic.”

The researchers studied the system of currents known as the Atlantic Meridional Overturning Circulation (AMOC).

AMOC works like a conveyer belt, carrying warm water from the tropics north – where colder, dense water sinks into the deep ocean and spreads slowly south.

The findings highlight the importance of warming transferring by AMOC from one region to another.

Dr Messias said excess heat from the Southern Hemisphere oceans is becoming important in the North Atlantic – now accounting for about a quarter of excess heat.

The study used temperature records and chemical “tracers” – compounds whose make-up can be used to discover past changes in the ocean.

The paper, published in the Nature journal Communications Earth & Environment, is entitled: “The redistribution of anthropogenic excess heat is a key driver of warming in the North Atlantic.”

More information: Messias, MJ., Mercier, H. The redistribution of anthropogenic excess heat is a key driver of warming in the North Atlantic. Commun Earth Environ 3, 118 (2022). https://doi.org/10.1038/s43247-022-00443-4

Warming oceans are getting louder

by oceanecology, posted in News, Research article

FASTER SOUND TRANSMISSION IN THE OCEANS DUE TO CLIMATE CHANGE WILL CHANGE THE UNDERWATER SOUNDSCAPE MARINE ORGANISMS RELY ON FOR SURVIVAL AND REPRODUCTION IN COMING DECADES.

Climate change will significantly alter how sound travels underwater, potentially affecting natural soundscapes as well as accentuating human-generated noise, according to a new global study that identified future ocean “acoustic hotspots.” These changes to ocean soundscapes could impact essential activities of marine life.

In warmer water, sound waves propagate faster and last longer before dying away.

“We calculated the effects of temperature, depth and salinity based on public data to model the soundscape of the future,” said Alice Affatati, an bioacoustics researcher at the Memorial University of Newfoundland and Labrador in St. John’s, Canada, and lead author of the new study.

Warmer oceans mean sound will travel faster, impacting marine animals who depend on sounds to find each other and eat. The largest effect on the underwater speed of sound can be expected east of Greenland and off Newfoundland in the Atlantic, according to a new study in the AGU journal Earth’s Future.
Credit: NOAA

Two hotspots, in the Greenland Sea and a patch of the northwestern Atlantic Ocean east of Newfoundland, can expect the most change at 50 and 500 meter depths, the new study projected. The average speed of sound is likely to increase by more than 1.5%, or approximately 25 meters per second (55 miles per hour) in these waters from the surface to depths of 500 meters (1,640 feet), by the end of the century, given continued high greenhouse gas emissions (RCP8.5).

“The major impact is expected in the Arctic, where we know already there is amplification of the effects of climate change now. Not all the Arctic, but one specific part where all factors play together to give a signal that, according to the model predictions, overcomes the uncertainty of the model itself,” said author Stefano Salon, a researcher at the National Institute of Oceanography and Applied Geophysics in Trieste, Italy.

The ocean soundscape is a cacophony of vibrations produced by living organisms, natural phenomena like waves and cracking ice, and ship traffic and resource extraction. Sound speed at 50 meters depth ranges from 1,450 meters per second in the polar regions to 1,520 meters per second in equatorial waters (3,243 to 3,400 miles per hour, respectively).

Many marine animals use sound to communicate with each other and navigate their underwater world. Changing the sound speed can impact their ability to feed, fight, find mates, avoid predators and migrate, the authors said.

CHANGING SOUNDSCAPES

In addition to the notable hotpots around Greenland and in the northwestern Atlantic Ocean, the new study found a 1% sound speed increase, more than 15 meters per second, at 50 m in the Barents Sea, northwestern Pacific, and in the Southern Ocean (between 0 and 70E), and at 500 m in the Arctic Ocean, Gulf of Mexico, and southern Caribbean Sea.

Temperature, pressure with increasing depth and salinity all affect how fast and how far sound travels in water. In the new study, the researchers focused on hotspots where the climate signal stood out clearly from the model uncertainty and was larger than seasonal variability.

The new study also modeled common vocalisations, under the projected future conditions, of the North Atlantic right whale, a critically endangered species inhabiting both north Atlantic acoustic hotspots. The whales’ typical “upcall” at 50 Hertz is likely to propagate farther in a warmer future ocean, the researchers found.

“We chose to talk about one megafauna species, but many trophic levels in the ocean are affected by the soundscape or use sound,” Affatati said. “All these hotspots are locations of great biodiversity.”

Future work will combine the global soundscape with other maps of anthropogenic impacts in the oceans to pinpoint areas of combined stressors, or direct needed observational research.

“With complicated problems like climate change, to combine different approaches is the way to go,” said author Chiara Scaini, an environmental engineer at the National Institute of Oceanography and Applied Geophysics.

More information: Affatati, A., Scaini, C., & Salon, S. (2022). Ocean sound propagation in a changing climate: Global sound speed changes and identification of acoustic hotspots. Earth’s Future, 10, e2021EF002099. https://doi.org/10.1029/2021EF002099

The Ocean Decade at COP 26

by oceanecology, posted in News, Uncategorized

COP26 is the 2021 United Nations climate change conference

For nearly three decades the UN has been bringing together almost every country on earth for global climate summits – called COPs – which stands for ‘Conference of the Parties’. In that time climate change has gone from being a fringe issue to a global priority. Specifically part of the COP conference is focused on our oceans and seas. Part of the COP discussions includes the ‘Ocean Decade’.

What is the Ocean Decade?


The Ocean Decade provides a ‘once-in a-lifetime’ opportunity to create a new foundation across the
science-policy interface to strengthen the management of the ocean and coasts for the benefit of humanity and to mitigate the impacts of climate change. The Ocean Decade Implementation Plan outlines ten Decade Challenges, representing the most immediate and pressing needs of the Decade.

Link to the plan below:

Marine Plankton helps produce clouds, but existing clouds keep new ones at bay

by oceanecology, posted in News, Research article

Marine plankton breathe more than 20 million tons of sulfur into the air every year, mostly in the form of dimethyl sulfide (DMS). In the air, this chemical can transform into sulfuric acid, which helps produce clouds by giving a site for water droplets to form. Over the scale of the world’s oceans, this process affects the entire climate.

But new research from the University of Wisconsin–Madison, the National Oceanic and Atmospheric Administration and others reveals that more than one-third of the DMS emitted from the sea can never help new clouds form because it is lost to the clouds themselves. The new findings significantly alter the prevailing understanding of how marine life influences clouds and may change the way scientists predict how cloud formation responds to changes in the oceans.

NOAA

 By reflecting sunlight back into space and controlling rainfall, clouds play significant roles in the global climate. Accurately predicting them is essential to understanding the effects of climate change.

More information: Novak et al PNAS October 19, 2021 118 (42) e2110472118; https://doi.org/10.1073/pnas.2110472118

Predicting the future of cod stocks in the North Atlantic

by oceanecology, posted in Research article

New fisheries management planning tool developed with fewer stocks expected

The future of cod stocks in the North Sea and the Barents Sea may be much easier to predict than before. This is the result of an international research project led by the Helmholtz-Zentrum Hereon and its Institute of Coastal Systems – Analysis and Modeling. For the first time, the team has succeeded in predicting the development of stocks for ten years in advance, taking into account both changes due to climate and fishing. Traditionally, fisheries experts provide catch recommendations for about a year in advance, on the basis of which fishing quotas are negotiated and set internationally. This involves first estimating the size of current cod stocks and then calculating how much cod can be caught in the coming year without endangering the stocks as well as harvesting the stock optimally. The climatic change, long-term changes in water temperature, circulation and mixing, which have a decisive influence on how well cod reproduce, are not included in this prediction, so that the development of stocks can only be predicted in the short term.

Cod stocks will probably decrease in the future: Photo: David Young via Fotolia

Warm North Sea causes stress

As the experts around climate modeler Vimal Koul und Corinna Schrum of Hereon now write in the journal Nature Communications Earth and Environment, they have taken temperature into account in their calculations. For the North Sea, the climate forecast continues to predict temperatures at a high level, so that cod stocks are unlikely to recover or reach earlier levels. As a result, catches are expected to remain low. Things look better for the Barents Sea, where stocks can be managed sustainably.

For the researchers, the challenge was that climate models cannot calculate how much fish there will be in the oceans in the future. They only provide information about expected temperatures. “So we first had to develop a program that translates water temperature into fish quantities,” says Vimal Koul. Among other things, this took into account the ocean temperature in the North Atlantic. The researchers were then able to run their prediction model. The model starts with today’s conditions – the current temperature conditions and the current carbon dioxide content of the atmosphere, and can then calculate how the situation will change as carbon dioxide concentrations increase. The future temperatures are then translated into expected fish abundance and stock sizes.

To test how reliably the model works, it was first compared with real fish data from the 1960s to the present. As it turned out, it was able to correctly estimate fish stocks for the ten-year periods since the early 1960s. In this respect, the researchers led by Vimal Koul can assume that the current view of the coming ten years is also correct.

Fishing intensity taken into account

Another interesting aspect of the study is that the team of climate modelers, fisheries biologists and oceanographers took four different fishing scenarios into account. This allowed them to determine how cod stocks would fare if they were fished at different levels – from intensive to sustainable. In this respect, the results of the current study are very practical. “The 10-year estimates will help the fishing industry better plan catches in the future – so that cod stocks are fished sustainably and gently despite changes in climate,” says Vimal Koul. The new 10-year calculation model could also help fishing companies in their strategic planning – by providing a secure basis for investments in new vessels or processing facilities.

More information: Koul, V., Sguotti, C., Årthun, M. et al. Skilful prediction of cod stocks in the North and Barents Sea a decade in advance. Commun Earth Environ 2, 140 (2021). https://doi.org/10.1038/s43247-021-00207-6

IPBES/IPCC Report: Tackling the biodiversity and climate crises together

by oceanecology, posted in News

Unprecedented changes in climate and biodiversity, driven by human activities, have combined and increasingly threaten nature, human lives, livelihoods and well-being around the world. Biodiversity loss and climate change are both driven by human economic activities and mutually reinforce each other. Neither will be successfully resolved unless both are tackled together.

This is the message of a new IPES/IPCC report, published by 50 of the world’s leading biodiversity and climate experts. This is the first time that the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) and the Intergovernmental Panel on Climate Change (IPCC) – two intergovernmental bodies have collaborated together.

The report finds that previous policies have largely tackled biodiversity loss and climate change independently of each other, and that addressing the synergies between mitigating biodiversity loss and climate change, while considering their social impacts, offers the opportunity to maximize benefits and meet global development goals.

Among the most important available actions identified in the report are:

  • Stopping the loss and degradation of carbon- and species-rich ecosystems on land and in the ocean, especially forests, wetlands, peatlands, grasslands and savannahs; coastal ecosystems such as mangroves, salt marshes, kelp forests and seagrass meadows; as well as deep water and polar blue carbon habitats. The report highlights that reducing deforestation and forest degradation can contribute to lowering human-caused greenhouse gas emissions, by a wide range from 0.4-5.8 gigatonnes of carbon dioxide equivalent every year.
A multifunctional ’scape across land, freshwater and marine biomes, including
large, intact wilderness spaces (blue circles), shared spaces (yellow circles) and
anthromes (red circles).

New study shows a 50% decline in Krill abundance in the North Atlantic

Featured by oceanecology, posted in Uncategorized

North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift

A team of UK and French scientists have shown a huge decline in North Atlantic krill over the last 60 years driven primarily by climate variability and North Atlantic warming. Krill, are extremely abundant crustaceans present throughout the world’s oceans. In the North Atlantic, krill are numerically a significant component of the biomass of marine ecosystems particularly in the more boreal and Arctic waters of the North Atlantic. They are an important source of food for commercially exploited fish species, squid and marine mammals such as baleen whales and therefore represent a crucial component in North Atlantic food webs.

50% decline in krill abundance

Examining the data that used long-term observations of krill, the team led by Martin Edwards from Plymouth Marine Laboratory (PML) showed that across the whole North Atlantic basin there has been a 50% decline in krill abundance over the last 60 years. The findings, published in the journal Communications Biology https://www.nature.com/articles/s42003-021-02159-1 show this widespread and abrupt decline has been associated with the warming climate of the North Atlantic observed over the last six decades. This warming has particularly accelerated since the mid 1990s where there was an abrupt shift to warmer conditions in Atlantic waters.

Close up of krill, photo by Brett Wilks

Accelerated pace of changes in the Arctic

In the sub-polar regions of the North Atlantic, where krill are most abundant, concern is growing at the accelerated pace of these changes and the increasing ‘Atlantification’ (i.e warmer more saline Atlantic waters) of these more northern waters and their detrimental effects on Arctic systems. The Arctic sea regions, in particular, are experiencing the strongest warming on the planet (nearly three times as fast as the planetary average) and the loss of sea ice in recent decades has been very rapid. Many regional seas that were once considered as being inhabited exclusively by Arctic flora and fauna have become more influenced by more southerly species as these species move northward as the Arctic warms.

Martin Edwards said ‘as ocean temperature rise, we generally expect species distributions to track towards historically cooler regions in line with their preferred habitats. In this case we would expect the krill populations to simply shift northward to avoid the warming environment and find new habitats in cooler regions of the North Atlantic. However, this study shows for the first time in the North Atlantic that marine populations do not simply just shift their distributions northward due to shifting isotherms to re-establish new geographic habitats’.

Angus Atkinson also from PML said ‘while krill has declined in abundance by 50%, its core latitudinal distribution at ~55 oN has remained markedly stable over the 60 year period’. The study showed that the isotherms for the warmer temperatures are shifting steadily northwards, the cooler isotherms remain in place with an 8 degree difference in average latitudes of the 7-8°C and 12-13°C isotherms in 1958-1967 but only 4 degrees of latitude between the same temperatures in 2008-2017. This ‘habitat squeeze’ and a potential habitat loss of 4 degrees of latitude could be the main driver in the decline of krill populations seen in this study.  This highlights that, as the temperature warms, not all species will be able to tract isotherms as they shift northward and there will be particular species that will win or lose when establishing new habitats as more northerly regions like the Barents Sea and Arctic Ocean become increasingly warmer and ‘Atlantified’.

Humpback whale feeding on krill. Photo by Jean Tresfon

One of the main reasons for the lack of northerly movement is because the centre of krill populations is found in the North West Atlantic (south and east of Greenland) and populations can become spatially constrained due to ocean currents and strong thermal boundaries such as the polar front limiting their northward expansions.  Here, unlike the North East Atlantic which has unimpeded northward flow into the Norwegian and Barents Seas, this region is latitudinally stalled by the sub-polar gyre circulation which is geographically and temporally more robust and forms a thermal barrier to the rapid northward expansion of species.

Martin Edwards further added: ‘while temperature alone does not necessary explain all patterns observed in this study, as trophic interactions would also play an important role, we are currently exploring the mechanisms for these wide-scale changes. We also do not currently know the full ecological ramifications of this dramatic decline in krill but they would presumably have had major consequences for the rest of the marine food-web and will have important implications for ongoing fisheries in the North Atlantic’.

Get the Open Assess paper here: https://www.nature.com/articles/s42003-021-02159-1.pdf

Edwards, M., Goberville, E., Helaouet, P., Lindley, A., Atkinson, A., Burrows, M., Tarling, G. (2021). North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift. Commun Biol 4, 644. https://doi.org/10.1038/s42003-021-02159-1

Arctic Climate Change Update 2021: Arctic warming three times faster than the planet

by oceanecology, posted in News

Arctic Monitoring and Assessment Programme (AMAP)

The Arctic has warmed three times more quickly than the planet as a whole, and faster than previously thought according to the newly published ‘Arctic Climate Change update 2021’.

Arctic sea ice looks set to be an early victims of rising temperatures, with each fraction of a degree making a big difference: the chance of it disappearing entirely in summer is 10 times greater if Earth warms by 2 degrees Celsius above pre-industrial levels compared to 1.5C, the goal set by the 2015 Paris Accord.

The finding comes from the Arctic Monitoring and Assessment Programme (AMAP) in their new report.

In less than half a century, from 1971 to 2019, the Arctic’s average annual temperature rose by 3.1C, compared to 1C for the planet as a whole.

That’s more than previously suspected. In a 2019 report on Earth’s frozen spaces, the UN’s Intergovernmental Panel on Climate Change (IPCC) concluded that Arctic surface air temperature has likely increased “by more than double the global average”.

According to researchers, a turning point came in 2004 when the temperature in the Arctic surged for largely unexplained reason.

Since then, warming has continued at a rate 30 percent higher than in previous decades.

Warming has immediate consequences for the Arctic ecosystem, including changes in habitat, food habits and interactions between animals and the migration of some species.

The warming and freshening of the Arctic Ocean directly and indirectly affect the lifecycles of marine species, leading to changes in seasonality, range shifts, and broad changes in ocean ecosystems.

The decline in sea ice affects marine ecosystems through changes in the open water areas and increases in the length of the open water period (both of which affect phytoplankton and ice algae, including the timing of phytoplankton blooms), as well as under-ice productivity and diversity. These changes are having cascading effects through ecosystems, with widespread impacts on the distribution, seasonality, and abundance of a variety of species.

Migrating narwhals

Satellite data show an increasing trend in primary production in all regions of the Arctic Ocean over the past two decades, explained by complex changes in light and nutrient conditions. The consequences of warming near the ocean surface on primary producers in the surface and subsurface ocean layers are still poorly understood, and there is new evidence that dominant Arctic phytoplankton species may be able to adapt to higher temperatures.

Phytoplankton bloom in northern Norway. NASA

Changes in the Arctic Ocean gateways

Warmer waters from the Pacific and Atlantic are also pushing farther into the Arctic Ocean, with widespread impacts on ocean ecosystems. The composition of Arctic plankton communities that form the basis of marine food webs is changing, as are the distribution and abundance of a variety of invertebrate, fish, and marine mammal species.

Find the summary report here:

https://www.amap.no/documents/doc/arctic-climate-change-update-2021-key-trends-and-impacts.-summary-for-policy-makers/3508

Potentially toxic plankton algae may play a crucial role in the future Arctic

by oceanecology, posted in News, Research article

As the sea ice shrinks in the Arctic, the plankton community that produces food for the entire marine food chain is changing. New research shows that a potentially toxic species of plankton algae that lives both by doing photosynthesis and absorbing food may become an important player in the Arctic Ocean as the future sea ice becomes thinner and thinner.

Microscopic plankton algae, invisible to the naked eye, are the foundation of the marine food web, feeding all the ocean´s living creatures from small crustaceans to large whales. Plankton algae need light and nutrients to produce food by photosynthesis.

A thick layer of sea ice – sometimes covered with snow – can reduce how much sunlight penetrates into the water and stop the algae getting enough light. However, as the sea ice is becoming thinner and less widespread in the Arctic, more and more light is penetrating into the sea. Does this mean more plankton algae and thus more food for more fish, whales and seabirds in the Arctic? The story is not so simple.

More light in the sea will only lead to a higher production of plankton algae if they also have enough nutrients – and this is often not the case. With the recent increase in freshwater melt from Arctic glaciers and the general freshening of the Arctic Ocean, more and more fresh and nutrient-depleted water is running out into the fjords and further out into the sea. The fresher water lies on top of the more salty ocean and stops nutrients from the deeper layers from mixing up towards the surface where there is light. And it is only here that plankton algae can be active.

Mixotrophic algae play on several strings

However, a new study published in the journal Nature – Scientific Reports shows that so-called mixotrophic plankton algae may play a crucial role in the production of food in the Arctic Sea.

When the spring sets in in the Arctic, the metre-thick sea ice begins to melt. Melt ponds on the surface of the sea ice bring so much sunlight into the underlying seawater that the mixotrophic plankton algae start to grow dramatically. During an approx. 9-day period, the plankton can produce up to half of the total annual pelagic production in the high-Arctic fjord, Young Sound, in northeast Greenland. Several mixotrophic algae species are toxic. Photo credit: Lars Chresten Lund Hansen and Dorte H. Søgaard

Mixotrophic algae are small, single-celled plankton algae that can perform photosynthesis but also obtain energy by eating other algae and bacteria. This allows them to stay alive and grow even when their photosynthesis does not have enough light and nutrients in the water.

In northeast Greenland, a team of researchers measured the production of plankton algae under the sea ice in the high-Arctic fjord Young Sound, located near Daneborg.

“We showed that the plankton algae under the sea ice actually produced up to half of the total annual plankton production in the fjord,” says Dorte H. Søgaard from the Greenland Climate Research Centre, Greenland Institute of Natural Resources and the Arctic Research Centre, Aarhus University, who headed the study.

“Mixotrophic plankton algae have the advantage that they can sustain themselves by eating other algae and bacteria as a supplement to photosynthesis when there isn’t enough light. This means that they are ready to perform photosynthesis even when very little light penetrates into the sea. In addition, many mixotrophic algae can live in relatively fresh water and at very low concentrations of nutrients – conditions that often prevail in the water layers under the sea ice in the spring when the ice melts,” Dorte H. Søgaard explains.

Toxic algae kill fish

For nine days, the researchers measured an algal bloom driven by mixotrophic algae occurring under the thick but melting sea ice in Young Sound during the Arctic spring in July, as the sun gained more power and more melt ponds spread across the sea ice, gradually letting through more light.

The algae belong to a group called haptophytes. Many of these algae are toxic, and in this study they bloomed in quantities similar to those previously observed in the Skagerrak near southern Norway. Here, the toxic plankton algae killed large amounts of salmon in Norwegian fish farms.

“We know that haptophytes often appear in areas with low salinity – as seen in the Baltic Sea, for example. It is therefore very probable that these mixotrophic-driven algae blooms will appear more frequently in a more freshwater-influenced future Arctic Ocean and that this shift in dominant algae to a mixotrophic algae species might have a large ecological and socio-economic impact.” says Dorte H. Søgaard.

The researchers behind the project point out that it is the first time that a bloom of mixotrophic algae has been recorded under the sea ice in the Arctic.

More information: An under-ice bloom of mixotrophic haptophytes in low nutrient and freshwater-influenced Arctic waters.http://www.nature.com/articles/s41598-021-82413-y