News and research

Oceans’ microscopic plants known as diatoms capture carbon dioxide via biophysical pathways

Diatoms are tiny unicellular plants — no bigger than half a millimeter — which inhabit the surface water of the world’s oceans where sunlight penetration is plenty. Despite their modest size, they are one of the world’s most powerful resources for removing carbon dioxide (CO2) from the atmosphere. They currently remove, or “fix,” 10-20 billion metric tons of CO2 every year by the process of photosynthesis. But not much is known about which biological mechanisms diatoms use, and whether these processes might become less effective with rising ocean acidity, temperatures, and, in particular, CO2 concentrations. A new study shows that diatoms predominantly use one pathway to concentrate CO2 at the vicinity of carbon fixing enzyme and that this continues to operate even at higher CO2 concentrations.

“We show that marine diatoms are super smart in fixing atmospheric CO2 even at the present-day level of CO2 — and the variability in surface seawater CO2 levels did not impact the gene expression and abundance of the five key enzymes used in carbon fixation,” says the group leader of the study, Dr Haimanti Biswas from the National Institute of Oceanography-CSIR (Council of Scientific and Industrial Research), India. “This answers a key question about how marine diatoms may respond to the future increase in atmospheric CO2 levels.”

Centric diatoms

The plant kingdom has evolved a wide range of mechanisms for concentrating CO2 from the air, or water, and transforming it into organic carbon. In this way, plants convert CO2 into glucose and other carbohydrates, which they use as building blocks and energy storage. But these different mechanisms have varied strengths and weaknesses. Somewhat ironically, the only carbon-fixing enzyme, RuBisCO, is notoriously inefficient at fixing CO2 and hence plants need to keep CO2 levels high In the vicinity of this enzyme.

To better understand which mechanism diatoms use to concentrate CO2, Biswas and her collaborators, Drs Chris Bowler and Juan Jose Pierella Karluich from the Institut de Biologie de I’Ecole Normale Supérieure, Paris, France, mined a data set from the Tara Oceans research expedition. The international Tara expedition collected marine plankton samples from around the world over several years (2009 to 2013). These included more than 200 metagenomes (which show the abundance of the genes responsible for the five key enzymes) and over 220 metatranscriptomes (showing expression of the genes for the five key enzymes) from diatoms of different size classes.

Biswas and her collaborators were particularly interested in how often the genes of five key carbon-fixing enzymes are present, and whether there were any differences in their abundance and expression levels depending on location and conditions. Across all of the samples measured, one enzyme was roughly ten times more abundant than any of the other enzymes. This enzyme — called carbonic anhydrase — is especially informative because it also confirms that diatoms are actively pumping in dissolved CO2 inside the cell, as opposed to biochemically transforming CO2 first.

The team also observed complex different patterns of the key enzymes’ gene expression, which varied depending on latitude and temperature. The researchers hope to learn more using new datasets from more widely-traveled future expeditions.

“So far, our study indicates that despite variability in CO2 levels, these tiny autotrophs are highly efficient in concentrating CO2 inside the cell,” says Biswas. “That’s the probable reason for their ability to fix nearly one-fifth of the global carbon fixation on earth.”

More information: https://www.frontiersin.org/articles/10.3389/fpls.2021.657821/full

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

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

Record-high Arctic freshwater will flow to Labrador Sea, affecting local and global oceans

Freshwater is accumulating in the Arctic Ocean. The Beaufort Sea, which is the largest Arctic Ocean freshwater reservoir, has increased its freshwater content by 40% over the past two decades. How and where this water will flow into the Atlantic Ocean is important for local and global ocean conditions.

A new study shows that this freshwater travels through the Canadian Archipelago to reach the Labrador Sea, rather than through the wider marine passageways that connect to seas in Northern Europe. The open-access study was published in Nature Communications.

“The Canadian Archipelago is a major conduit between the Arctic and the North Atlantic,” said lead author Jiaxu Zhang, a UW postdoctoral researcher at the Cooperative Institute for Climate, Ocean and Ecosystem Studies. “In the future, if the winds get weaker and the freshwater gets released, there is a potential for this high amount of water to have a big influence in the Labrador Sea region.”

The finding has implications for the Labrador Sea marine environment, since Arctic water tends to be fresher but also rich in nutrients. This pathway also affects larger oceanic currents, namely a conveyor-belt circulation in the Atlantic Ocean in which colder, heavier water sinks in the North Atlantic and comes back along the surface as the Gulf Stream. Fresher, lighter water entering the Labrador Sea could slow that overturning circulation.

A simulated red dye tracer released from the Beaufort Gyre in the Artic Ocean (center top) shows freshwater transport through the Canadian Arctic Archipelago, along Baffin Island to the western Labrador Sea, off the coast of Newfoundland and Labrador, where it reduces surface salinity.

“We know that the Arctic Ocean has one of the biggest climate change signals,” said co-author Wei Cheng at the UW-based Cooperative Institute for Climate, Ocean and Atmosphere Studies. “Right now this freshwater is still trapped in the Arctic. But once it gets out, it can have a very large impact.”

Fresher water reaches the Arctic Ocean through rain, snow, rivers, inflows from the relatively fresher Pacific Ocean, as well as the recent melting of Arctic Ocean sea ice. Fresher, lighter water floats at the top, and clockwise winds in the Beaufort Sea push that lighter water together to create a dome.

When those winds relax, the dome will flatten and the freshwater gets released into the North Atlantic.

“People have already spent a lot of time studying why the Beaufort Sea freshwater has gotten so high in the past few decades,” said Zhang, who began the work at Los Alamos National Laboratory. “But they rarely care where the freshwater goes, and we think that’s a much more important problem.”

Using a technique Zhang developed to track ocean salinity, the researchers simulated the ocean circulation and followed the Beaufort Sea freshwater’s spread in a past event that occurred from 1983 to 1995.

Their experiment showed that most of the freshwater reached the Labrador Sea through the Canadian Archipelago, a complex set of narrow passages between Canada and Greenland. This region is poorly studied and was thought to be less important for freshwater flow than the much wider Fram Strait, which connects to the Northern European seas.

In the model, the 1983-1995 freshwater release traveled mostly along the North American route and significantly reduced the salinities in the Labrador Sea — a freshening of 0.2 parts per thousand on its shallower western edge, off the coast of Newfoundland and Labrador, and of 0.4 parts per thousand inside the Labrador Current.

The volume of freshwater now in the Beaufort Sea is about twice the size of the case studied, at more than 23,300 cubic kilometers, or more than 5,500 cubic miles. This volume of freshwater released into the North Atlantic could have significant effects. The exact impact is unknown. The study focused on past events, and current research is looking at where today’s freshwater buildup might end up and what changes it could trigger.

“A freshwater release of this size into the subpolar North Atlantic could impact a critical circulation pattern, called the Atlantic Meridional Overturning Circulation, which has a significant influence on Northern Hemisphere climate,” said co-author Wilbert Weijer at Los Alamos National Lab.

More information: https://www.nature.com/articles/s41467-021-21470-3

Will climate change outpace species adaptation?

Species evolve heat tolerance more slowly than cold tolerance

Many species might be left vulnerable in the face of climate change, unable to adapt their physiologies to respond to rapid global warming. According to a team of international researchers, species evolve heat tolerance more slowly than cold tolerance, and the level of heat they can adapt to has limits.

In a study published in the Nature Communications, McGill professor Jennifer Sunday and her co-authors wanted to understand how species’ thermal limits have evolved. To examine variation across the tree of life, the researchers developed the largest available database compiling thermal tolerances for all types of organisms (GlobTherm database).

Migrating mullet

The researchers found that first and foremost, a species’ thermal tolerance is linked to the current climate where they live. “It’s logical that thermal limits mostly match a species’ present-day climate but tracing the evolutionary history of thermal limits can reveal how species got to be where they are today,” says Sunday, an Assistant Professor in the Department of Biology.

The researchers also found that tolerance to cold has evolved much faster than tolerance to heat, particularly in endotherms as compared to ectotherms and plants. Endothermic animals are those that generate metabolic heat to regulate their own body temperature – for example, mammals and birds – while ectothermic animals are those that regulate their body temperature using external heat sources, like reptiles, fishes and invertebrates.

One cause of this disparity could be that heat tolerance has reached an evolutionary barrier, called an ‘attractor,’ beyond which further evolution is constrained or selected against. “This is very concerning because it suggests that the vast majority of species will not be able to adapt fast enough to survive the unprecedented rate of contemporary climate change,” says co-author Joanne Bennett of Leipzig University and University of Canberra.

The results of this study are particularly relevant to conservation management, say the researchers. Protecting and creating areas that provide refuges for biodiversity from upper temperature extremes is a key strategy for conservation managers.

More information: DOI: https://doi.org/10.1038/s41467-021-21263-8

United Nations Launches New Flagship Report On State Of The Ocean

The Second World Ocean Assessment (WOA II)

The Second World Ocean Assessment (WOA II) is the major output of the second cycle of the Regular Process for Global Reporting and Assessment of the States of the Marine Environment, including Socioeconomic Aspects. It is the newest outcome of the only integrated assessment of the world’s ocean at the global level covering environmental, economic and social aspects.

WOA II is a collective effort of interdisciplinary writing teams made up of more than 300 experts from around the world, including scientists from the Plymouth Marine Laboratory and the University of Plymouth. It provides scientific information on the state of the marine environment in a comprehensive and integrated manner to support decisions and actions for the achievement of Sustainable Development Goals, in particular goal 14, as well as the implementation of the United Nations Decade of Ocean Science for Sustainable Development.

The report catalogues a swathe of impacts on what UN secretary general António Guterres said was the planet’s “life support system”.

Sea levels were rising, coasts were eroding, waters were heating and acidifying and the number of deoxygenated “dead zones” was rising.

Martin Edwards and Michael Moore from Plymouth Marine Laboratory who contributed to the section on human health and the oceans said “there is strong evidence of an increase in the spread of pathogens related to climate warming (e.g., Vibrio) and there is some evidence related to an increase in some harmful algal bloom species related to climate warming is some regional areas around the world. Increasingly the spread of non-indigenous species have also started to be considered as one of the major threats to global marine ecosystems through impacts on the ecosystem’s structure, function and services.

Marine litter was present in all marine habitats, the report said, and overfishing was costing societies billions. About 90% of mangrove, seagrass and marsh plant species were threatened with extinction, the report said.

The report said there had been progress in protecting more marine areas, but there were still many scientific knowledge gaps to be filled.

Specifically for the pelagic environment, climate change during the course of the twenty-first century is expected to continue to drive changes in the upper ocean that have an impact on the diversity and productivity of plankton assemblages on the regional to global scales.

  • These changes include an expansion of the subtropical gyres, ocean warming and acidification, decreases in salinity, increases in vertical stratification and decreases in inorganic nutrient supplies to the euphotic zone in the open ocean. Predicted biological responses to those changes on a global scale include the following:
  • Primary production  is likely to decrease and the relative abundance of picophytoplankton is likely to increase at the expense of microplankton diatoms. These trends are likely to propagate through food webs resulting in decreases in the ocean’s carrying capacity for fisheries and in its capacity to sequester carbon through the biological pump.
  • Plankton food webs in the polar oceans and coastal upwelling regions will be the most affected by ocean acidification, owing to the high solubility of CO2 in cold waters.

Get the report here: https://www.un.org/regularprocess/woa2launch

Rise of marine predators reshaped ocean life as dramatically as sudden mass extinctions

Evolutionary arms races between marine animals overhauled ocean ecosystems on scales similar to the mass extinctions triggered by global disasters, a new study shows.

Scientists at Umeå University in Sweden and the Florida Museum of Natural History used paleontological databases to build a multilayered computer model of the history of marine life over the last 500 million years. Their analysis of the fossil record closely echoed a seminal 1981 study by paleontologist J. John Sepkoski – with one key difference.

Sepkoski’s ground-breaking statistical work showed abrupt ocean-wide changes in biodiversity about 490 and 250 million years ago, corresponding to two mass extinction events. These events divided marine life into what he called “three great evolutionary faunas,” each dominated by a unique set of animals.

But the new model reveals a fourth.

The fierce fight for survival that played out between predatory marine animals and their prey about 250 to 66 million years ago may have been an equally powerful force, reshaping ocean diversity into what we see today. This third grand transition was much more gradual than its predecessors and driven by organisms, rather than external processes.

“What we learned is that not all major shifts in animal life have been related to mass extinction events,” said study lead author Alexis Rojas, who earned his Ph.D. at the University of Florida. Rojas is now a postdoctoral researcher at the Integrated Science Lab, a hub dedicated to interdisciplinary research at Umeå University.

Jeff Gage/Florida Museum of Natural History

Many scientists have long held the view that external factors such as volcanic activity, asteroid impacts or changes in climate are the primary drivers of major shifts in the Earth’s biosphere, said study co-author Michal Kowalewski, Rojas’ doctoral adviser and the Florida Museum Thompson Chair of Invertebrate Paleontology.

“The fossil record tells us that some of the key transitions in the history of life were rapid changes triggered by abrupt external factors. But this study shows that some of those major transitions were more gradual and may have been driven by biological interactions between organisms,” he said.

More information: Rojas, A., Calatayud, J., Kowalewski, M. et al. A multiscale view of the Phanerozoic fossil record reveals the three major biotic transitions. Commun Biol 4, 309 (2021). https://doi.org/10.1038/s42003-021-01805-y

Climate change has reduced ocean mixing far more than expected

The ocean is dynamic in nature, playing a crucial role as a planetary thermostat that buffer global warming. However, in response to climate change, the ocean has generally become stabler over the past 50 years. Six times stabler, in fact, than previously estimated–as shown by a new study that researchers from the CNRS, Sorbonne University, and IFREMER have conducted within the scope of an international collaboration.* Warming waters, melting glaciers, and disrupted precipitation patterns have created an ocean surface layer cut off from the depths. Just as oil and water separate, so this division of surface and deeper waters limits oceanic mixing, making it harder for the ocean to mitigate climate change. Furthermore, climate change has strengthened winds, which has thickened the ocean surface layer by 5 to 10 m per decade over the last half century. This has hindered vital access to light for most marine organisms within it. Published in Nature, these findings underscore the consequences of climate change and anthropogenic phenomena for the ocean, the life it harbours, and its capacity to remain a global thermostat into the future.

This work calls for reconsideration of the drivers of ongoing shifts in marine primary production, and reveals stark changes in the world’s upper ocean over the past five decades.

More information: Sallée, JB., Pellichero, V., Akhoudas, C. et al. Summertime increases in upper-ocean stratification and mixed-layer depth. Nature 591, 592–598 (2021). https://doi.org/10.1038/s41586-021-03303-x

UK waters are home again to the bluefin tuna

Atlantic bluefin tuna have returned to UK waters and can once again be seen during the summer and autumn months.

Their numbers appear to be increasing, following a long period of absence linked to population decline, according to research led by Cefas and the University of Exeter.

Marine scientists in the UK and Ireland have analysed multiple datasets, spanning a 16-year period, to document the increase in bluefin, which arrive into the waters of the Celtic Seas and off South West England, the Scilly Isles, and North West Ireland to feed in late summer and autumn.

The research is part of the Defra-funded “Thunnus UK” research project.

Thunnus UK was established to improve knowledge of this species, as an essential first step in ensuring a positive future for Atlantic bluefin tuna around the UK.

Central to the project’s success has been a concerted effort to share and combine important data on where people have observed Atlantic bluefin tuna.

This will help to identify where and when these fish are found in UK waters.

Nearly 1,000 unique observations were recorded between 2013 and 2018 by citizen scientists, scientists, fishers and eco-tour leaders.

Researchers found that Atlantic bluefin tuna begin to arrive in May and stay as late as January.

However, peak numbers were recorded between August and October each year.

The research draws on five key data sources:

  • The general public: A total of 80 sightings recorded by the public and submitted to http://www.thunnusuk.org
  • Eco-tourism: three eco-tourism vessels collecting data on more than 1600 boat tours off the SW coast of England between 2008 and 2018.
  • Opportunistic scientific surveys: 40 days of surveys with >2500 km of effort conducted by Cefas and University of Exeter experts off the Northwest Coast of Ireland and SW England in 2016 and 2018.
  • Fisheries independent surveys: (1) data collected by MarineLife during the Peltic survey by Cefas between 2013 and 2015, and (2) data collected by the Irish Whale and Dolphin Group during the Irish Marine Institute’s Celtic Sea Herring Acoustic Survey between 2014 and 2018
  • Bycatch in commercial fisheries: Bluefin tuna were accidentally caught (bycatch) in the Irish commercial fishery for albacore tuna between 2003 and 2017.

Lead author Tom Horton, of the University of Exeter, said: “Atlantic bluefin tuna are once again a feature in nearshore waters off the UK and Ireland.

We’ve been able to document this story by using data from a wide variety of sources. We need to work together to ensure a future for Atlantic bluefin tuna, both in the UK and Ireland and more broadly throughout their range in the Atlantic Ocean. This is a really exciting study and the return of these fish suggest an important role in the UK’s ecosystem.

Are cold winters in Europe caused by melting sea-ice in the Arctic?

They are diligently stoking thousands of bonfires on the ground close to their crops, but the French winemakers are fighting a losing battle. An above-average warm spell at the end of March has been followed by days of extreme frost, destroying the vines with losses amounting to 90 percent above average. The image of the struggle may well be the most depressingly beautiful illustration of the complexities and unpredictability of global climate warming. It is also an agricultural disaster from Bordeaux to Champagne.

Nasa

It is the loss of the Arctic sea-ice due to climate warming that has, somewhat paradoxically, been implicated with severe cold and snowy mid-latitude winters.

“Climate change doesn’t always manifest in the most obvious ways. It’s easy to extrapolate models to show that winters are getting warmer and to forecast a virtually snow-free future in Europe, but our most recent study shows that is too simplistic. We should beware of making broad sweeping statements about the impacts of climate change.” Says professor Alun Hubbard from CAGE Center for Arctic Gas Hydrate, Environment and Climate at UiT The Arctic University of Norway.

Melting Arctic sea ice supplied 88% of the fresh snow

Hubbard is the co-author of a study in Nature Geoscience examining this counter-intuitive climatic paradox: A 50% reduction in Arctic sea-ice cover has increased open-water and winter evaporation to fuel more extreme snowfall further south across Europe.

The study, led by Dr. Hanna Bailey at the University of Oulu, Finland, has more specifically found that the long-term decline of Arctic sea-ice since the late 1970s had a direct comparison to one specific weather event: “Beast from the East”—the February snowfall that brought large parts of the European continent to a halt in 2018, causing £1bn a day in losses.

Researchers discovered that atmospheric vapor traveling south from the Arctic carried a unique geochemical fingerprint, revealing that its source was the warm, open-water surface of the Barents Sea, part of the Arctic Ocean between Norway, Russia, and Svalbard. They found that during the “Beast from the East,” open-water conditions in the Barents Sea supplied up to 88% of the corresponding fresh snow that fell over Europe.

Climate warming is lifting the lid off the Arctic Ocean

“What we’re finding is that sea-ice is effectively a lid on the ocean. And with its long-term reduction across the Arctic, we’re seeing increasing amounts of moisture enter the atmosphere during winter, which directly impacts our weather further south, causing extreme heavy snowfalls. It might seem counter-intuitive, but nature is complex and what happens in the Arctic doesn’t stay in the Arctic.” says Bailey.

When analyzing the long-term trends from 1979 onwards, researchers found that for every square meter of winter sea-ice lost from the Barents Sea, there was a corresponding 70 kg increase in the evaporation, moisture, and snow falling over Europe.

“This study illustrates that the abrupt changes being witnessed across the Arctic now, really are affecting the entire planet,” says professor Hubbard.

Their findings indicate that within the next 60 years, a predicted ice-free Barents Sea will likely become a significant source of increased winter precipitation—be it rain or snow—for Europe.

More information: Hannah Bailey et al, Arctic sea-ice loss fuels extreme European snowfall, Nature Geoscience (2021). DOI: 10.1038/s41561-021-00719-y

Provided by UiT The Arctic University of Norway

New research paper on overwintering zooplankton in the North Sea

New open access paper published in Progress in Oceanography Overwintering distribution, inflow patterns and sustainability of Calanus finmarchicus in the North Sea.

The modelled abundance (1000 individual/m2) of overwintering C. finmarchicus in the North Sea

Some of the highlights include:

•High overwintering biomass in Norwegian Trench and north-west North Sea shelf.

•Inflow accounts for 41% of North Sea biomass and drives interannual variability.

•Norwegian Trench and East Shetland Atlantic Inflow are important inflow pathways.

C. finmarchicus in the North Sea is not self-sustained but dependent on the inflow.

•Biomass carried by East Shetland Atlantic Inflow decreases over 2000–2016.

Abstract: Calanoid copepods are key taxa in the North Sea as they are the main food source for many fish stocks, such as herring, mackerel and cod. In this study we use an individual-based model for Calanus finmarchicus embedded in the NORWegian ECOlogical Model system (NORWECOM) to investigate important population parameters such as biomass and abundance, distribution and interannual variability of the overwintering population, as well as the inflow of C. finmarchicus into the North Sea from adjacent areas for the 2000–2016 period. The modelled spatial–temporal patterns of C. finmarchicus abundance is comparable with the Continuous Plankton Recorder (CPR) Survey data in the northern North Sea. The simulated annual mean biomass of C. finmarchicus amounts to 0.94 million-tonnes of carbon. High overwintering biomass appears in the Norwegian Trench as well as in the north-west shelf region of the North Sea. A decreasing trend in the overwintering biomass has been detected on the path of the East Shetland Atlantic Inflow (ESAI) over the simulated period. The inflow of C. finmarchicus biomass into the North Sea from the north constitutes on average 41% of the annual mean biomass in the North Sea during the simulated 17 years, and thus determines the interannual variability of the biomass. We conclude that the C. finmarchicus population in the North Sea is not self-sustained and is highly dependent on the inflow of C. finmarchicus from the Faroe-Shetland Channel and south of the Norwegian Sea. C. finmarchicus enter the North Sea via three branches of the North Atlantic current with variable depths depending on seasons and topography. Beside the western flank of the Norwegian Trench (carrying 57% of the inflow biomass), we suggest that the ESAI is also an important agent carrying 37% of the total C. finmarchicus inflow biomass through the shelf area into the north-west of the North Sea. The annual mean outflow biomass is larger than the inflow biomass (0.52 versus 0.39 million-tonnes carbon per year), which indicates that the North Sea serves as a feeding ground and growth region for C. finmarchicus. This study is a first step towards a better understanding and quantification of the exchange of C. finmarchicus between the open seas, coastal waters and the fjords.

Get the open access paper here: