The Arctic is not only at the top of the world but also tops the list of areas most impacted by climatic changes. With temperatures rising about 2-3 times faster than the global average, climate change manifests in the Arctic as a vast loss of sea ice. As the ice retreats, new commercial activities are initiated. Yet, the deep Arctic Basin is one of the least known realms on earth, and the ecosystems of many Arctic shelf seas are only rudimentary studied. Baseline knowledge for sustainable ecosystem-based management of the future seasonally ice-free Arctic seas is therefore urgently needed. The research project Nansen Legacy aims to close some of these knowledge gaps on the European Arctic side.
Sea ice reduction is most visible, but the human footprints are many
Satellites have documented the loss of sea ice in the Arctic during the past 40 years, and now sea ice is the most prominent and visual indicator of the effects of climate change. The present-day Arctic sea ice is thinner, younger, freezes up later in autumn, melts earlier in spring than just a few decades ago, and regulates the exchange between the ocean and the atmosphere differently from what it did in the past. With cracks in the isolating ice layer, processes like heat and CO2 exchange between the atmosphere and the ocean and light penetration into the Arctic Ocean are increasing drastically.
For Arctic inhabitants – people, animals, and other organisms – the severe implications of the sea ice changes are already being felt today. With the reduced sea ice cover, ice-associated organisms – from microscopic algae to seals and Inuit hunters – lose the platform they have previously depended upon. In addition, a warmer ocean and the increased CO2 level in the atmosphere result in higher CO2 concentrations in the ocean, which makes the Arctic Ocean more acidic. This affects tiny planktonic organisms such as the planktonic snail Limacina, whose protective calcareous shell is thinning in the more acidic water, increasing predation risk.
Further, emissions of human-derived contaminants far away from the pole impact the Arctic Ocean. When these contaminants are released into the air and water, they are transported to the remote Arctic by weather systems and ocean currents. When airborne contaminants precipitate with the moisture as snow, they can be released into the ocean during snowmelt, where they are then taken up by organisms and transferred through the Arctic food web. Due to bioaccumulation, exceptionally high concentrations of contaminants are found in the Arctic lipid-rich and long-lived organisms such as large fishes, birds, polar bears, marine mammals, and humans.
Another indirect effect of climate change is the northward distribution of species. Due to more extended ice-free periods and increased water temperature, boreal species can survive further north, occasionally replacing single Arctic species or entire communities. This has already been documented for microalgae, zooplankton communities, and boreal and sub-Arctic fish species. Along with the active or passive introduction of species by humans, like the Pacific snow crab in the Barents Sea, other human activities (e.g., trawl fisheries, petroleum activities, and maritime shipping) introduce new disturbances to the world’s northernmost marine ecosystems.
Responses to multiple changes are not straightforward
These examples clearly illustrate that the Arctic is not only exposed to a higher temperature but a variety of stressors. However, investigating the responses of species and ecosystems to multiple changes is difficult because the response of an organism to many stressors cannot be deducted from studying the response to a single stressor. That means responses to contaminants, for example, are often stronger if they are combined with increased temperatures, ocean acidification, and higher predation pressure. Further, responses and vulnerability most likely vary between organisms’ life stages and physiological processes, e.g., growth rate, food requirements, and fertility.
Scientific investigations of life in and under Arctic sea ice involves hard physical work. In recent years, efforts have been undertaken to synchronize scientific sampling schemes in order to make data from different regions and research projects directly comparable (Image credit: Christian Morel, The Nansen Legacy)
This complexity can be illustrated from exciting data from the Barents Sea. Time-series data on polar cod – a small Arctic cod species – reveals different responses to diminishing ice cover and increased seawater temperatures on both the individual level and species population dynamics. While the retreating sea ice had positive effects on the individual growth of polar cod in the Barents Sea due to higher food availability, low sea ice concentrations and high temperatures led to poorer recruitment of polar cod. Additionally, the invasion of boreal fish species from the south increases the risk of polar cod being eaten.
Henceforth, disentangling and understanding the multiple changes and stressors on the individual, population, and ecosystem levels is not straightforward. Internationally, major research efforts are underway to address the implications for Arctic ecosystems and to provide knowledge for sound sustainable management.
The Arctic Ocean is an incredibly heterogeneous sea
Adding yet another level of complexity, the Arctic Ocean is not one large homogenous sea. Instead, it consists of vastly differing marine regions with deep central basins surrounded by shallow shelf seas. These sub-regions are impacted differently by the warming climate, pollution, invasion of boreal species, and human activities.
Some of the most pronounced changes occur at the marine gateways to the Central Arctic Ocean, namely the Barents Sea region on the Atlantic side and the Bering Sea on the Pacific side. These areas are greatly influenced by warm water masses from the south. For example, the increasing inflow of relatively warmer water from the North Atlantic into the Barents Sea has largely altered the Barents Sea ecosystem over the last decades.
The decline of Arctic sea ice is the most prominent and visual indicator of the effects of climate change, yet it is not the only threat to the Arctic marine ecosystem. (Image credit: Christian Morel/christianmorel.net/The Nansen Legacy)
Research within the Nansen Legacy project has revealed the seasonally ice-covered northern Barents Sea to be at the epicenter of change, with early changes in summer ice, the strongest decline in winter ice at present, and predictions of potentially ice-free winters by the end of the century (given business as usual in CO2 release). Moreover, the changes here may propagate to other Arctic regions. The Nansen Legacy project focuses on investigating the complex dynamics and interactions of the climate and the ecosystem in the Barents Sea as well as the shelf and the deep basin of the European Arctic Ocean. It links its work with international research networks such as MOSAiC (www.mosaic-expedition.org) and the Synoptic Arctic Survey.
Only collaborations can generate the knowledge needed
The Synoptic Arctic Survey aims to bring together a large-scale picture of the status and change of the Arctic carbon cycle and marine ecosystems, including physical measurements (e.g., temperature, salinity), by conducting comparable ocean measurements at almost the same time in different Arctic regions. This fall, a Nansen Legacy expedition to the Central Arctic Ocean as part of the Synoptic Arctic Survey. We conducted the same measurements as researchers on the Swedish icebreaker Oden and the Canadian vessel Louis St. Laurent, at the same time, in different parts of the Arctic Ocean. Together with the findings of similar research expeditions (Japanese RV Mirai, Korean RV Aaron) in 2020, immense international efforts are invested in exploring the central Arctic Ocean.
Polar cod is an Arctic key fish species that has experienced extensive changes in its habitat. Understanding the effects of these changes on an individual and population level is an important task in the Nansen Legacy Project. (Image credit: Christian Morel, The Nansen Legacy)
Lack of time series and need for high-resolution spatial data
The high level of activity may partly hide the bitter truth that vast areas of the Arctic Ocean are greatly understudied, and only a few in situ long-time observations exist despite large-scale international efforts. Networks of autonomous underwater technology have emerged at lower latitudes during the past years, and steps are being taken to increase the in situ surveillance of the Arctic Ocean by this technology. This, however, requires solving basic technical challenges as navigation instruments become less accurate at high latitudes and sea ice makes safe operations difficult. Within the Nansen Legacy, marine technologists work jointly with physical, chemical, and biological oceanographers to solve these challenges, improve sensors, and develop adaptive mission management of underwater vehicles. For the following steps, multiple autonomous vehicles with complementary properties will collaborate by sharing status and data, providing marine researchers with highly needed high-resolution spatial and temporal data to understand the profound changes in the Arctic Ocean.
The planktonic snail Limacina helicina is one of the animals in the Arctic exposed to multiple stressors, such as increasing water temperatures and ocean acidification. Understanding the combined effect of these stressors is challenging but a prerequisite for sound management of Arctic ecosystems. (Image credit: Snorre Flo/UNIS)
Perspectives
The Arctic is amplifying the responses to climate change, and the impact and responses are complex. Collaborations like the Nansen Legacy across broad groups of science disciplines, including modelers, integrate our present understanding. Predicting future scenarios is essential to prepare and adapt to climate-induced changes and motivate societal changes to reduce our Arctic footprints. International collaboration is also key to optimizing our efforts in understanding the Arctic and making sure that the footprints of science activities are minimized. The technological development will enable the observational capacity needed to ensure that the Arctic communities can maintain a knowledge- and ecosystem-based management of this new emerging Arctic Ocean.
This feature appeared in Environment, Coastal & Offshore (ECO) Magazine's 2021 Winter edition, to read more access the magazine here.
