RATIONALE

We currently witness in the Arctic:

1) a decrease in summer ice cover that exposes sea surface to solar radiation and physical forcings,

2) permafrost thawing and increased river runoff, both leading to an increase in the export to the ocean of organic carbon previously sequestered in the Tundra, and

3) an increase in ultraviolet radiation.

These three phenomena favour a growing mineralization of organic carbon through photo-oxidation and bacterial activity, amplifying the increase in atmospheric CO₂. At the same time, the exposure of a larger fraction of ocean surface to sun light and the increase in nutrients brought by rivers lead to larger autotrophic production and sequestration of organic carbon. Will the Arctic Ocean become a new net source of CO₂ originating from organic carbon that was sequestered in the permafrost (analogous to the combustion of fossil fuel), or a stronger biological sink of CO₂ leading to more sequestration of carbon in the sediments? To predict the balance of these processes, we will conduct an extensive study in the Mackenzie River / Beaufort Sea system in July, August and September 2009 onboard the Canadian research icebreaker CCGS Amundsen. The spatial distribution of organic carbon stocks (living and detrital) in the water column and sediments will be determined on the shelf and beyond. The magnitude and variability of organic carbon mineralization through photo-oxidation and bacterial activity, and production through photosynthesis will be determined. These targeted studies will allow the monitoring of these processes using remote sensing in the coming years and decades. A detailed study of microbial biodiversity will be conducted to describe the different biocenoses and biotopes and to anticipate their response to climate change. Diagnostic models of the studied processes (primary production, bacterial activity and light-driven mineralization of organic matter) will be combined with a coupled physical-biological ecosystem model, and applied using outputs from global climate models to assess the fate of the associated carbon fluxes in the Arctic Ocean during the next decades under different climate change scenarios. Additionally, a retrospective approach will be followed to partly answer the Malina questions, based on the analysis of geochemical proxies in the past 1000-y sediments.

 

CONTEXT

The Arctic has attracted growing attention from scientists, the public, and policy makers, because it is an environment where the effects of global climate change are accumulating and increasing.  A group of specialists (Arctic Climate Impact Assessment; http://www.acia.uaf.edu/) recently published a 1042-page document including an inventory of climate changes and their major impacts on oceanic and terrestrial environments:

1. Temperature rise. The air temperature has risen almost twice as fast in the Arctic as compared to the rest of the world during the last few decades in response to the increase in greenhouse gases in the atmosphere. In a scenario for moderate emissions, an increase in the average annual temperature of up to 7 °C is predicted above the Arctic Ocean during the next century. According to Zhang (2005), the average temperature of the top 700 m of the water column has increased by 0.097 °C in the World Ocean, and by 0.203 °C in the Arctic Ocean since 1960.

2. Increase of ultraviolet radiation.  The amount of atmospheric ozone above the Arctic during the spring, has decreased by 10 to 15 % since 1979.  While the stratospheric concentrations of anthropogenic chlorinated and brominated compounds are currently stable, there are other factors (e.g. effects of other gases that result in a greenhouse effect, changes in atmospheric circulation, decrease of the stratospheric temperature, growth of stratospheric clouds) that could maintain, or even aggravate, the reduction of stratospheric ozone over the coming decades.  Ultraviolet radiation is increasing in parallel with the reduction of the ozone layer.

3. Melting of sea ice. The figure shows the September ice extent for 2008. The summer ice cover over the Arctic Ocean decreased by 20% over the last 26 years (Stroeve et al. 2005). Recent developments has further enhanced this trend (read more here). It is predicted that the perennial sea ice will disappear almost completely in the first half of this century (Holland et al. 2006, Serreze et al. 2007). This phenomenon will have three direct consequences: i) exposure of the water column to solar radiation, ii) exposure of the ocean surface to atmospheric forcing (heat exchange, physical forcing), and iii) changes in surface salinity.  The reduction of Arctic ice cover (oceanic and continental) will cause a local acceleration of heating (positive feedback) and largely explains the strength of climate change in the Arctic in comparison to the rest of the world.

4. Thawing of permafrost and coastal erosion. The peat bogs in the high latitudes contain up to a third of the global organic carbon stored in soils. The majority was formed since the last glacial maximum and contains 26% of the planetary organic carbon sequestered during this period (Smith et al. 2004). The permafrost, which represents 25% of the continental surface of the northern hemisphere, has been observed to have undergone a temperature increase since the 1960s and, in many places, a gradual thaw. This thaw drives the mobilization of the sequestered organic carbon, a part of which is oxidized by bacterial action. This anaerobic activity is a major source of methane, a gas with a greenhouse effect 23 to 63 times more important than that of CO₂ (per molecule). Another part of the mobilized carbon could be transported by streams towards rivers and the ocean. The available data to date on the ¹⁴C content of the organic material transported by Siberian rivers indicates, however, that this material is relatively young (<100 years) and that the transport towards the Arctic Ocean of the terrestrial organic carbon sequestered in the tundra is not yet apparent (Amon and Meon, 2004 ; Benner et al., 2004). Coastal erosion, exacerbated by the mechanical action of waves which increases as sea ice diminishes, contributes significantly to the export of organic terrestrial carbon towards the ocean (Grigoriev et al., 2004).

5. Changes in river flow. The catchment basin for the Arctic Ocean extends over a surface area one and a half times larger that the ocean itself. The Arctic Ocean receives 10% of the global contribution of freshwater although it represents only 1% of the volume of the World Ocean. It is thus the ocean basin most influenced by the input of freshwater. From 1936 to 1999, the freshwater inputs to the Arctic Ocean have increased by 7% (Peterson et al. 2002), resulting mainly from an increase in precipitation. By 2080, this increase could reach 24 to 31% (Arnell 2005), which corresponds to an increase of 0.037 to 0.048 Sverdrups, and is close to the threshold of 0.06-0.15 Sverdrups of freshwater entering the Atlantic Ocean beyond which the formation of deep water could be suspended (Rahmstorf 2002). This phenomenon will be strongly amplified by ice melt in Greenland.

6. Changes in ocean circulation. The reduction in ice cover and the increasing inputs of freshwater are the main phenomena that could lead to major changes in the thermohaline and geostrophic circulation of the Arctic Ocean. In turn, these, affecting mainly the formation of deepwater, will influence the global distribution of energy and particularly the climate of Europe.

The phenomena observed locally in the Arctic in response to climate change are not only harbingers of the impact of climate change at the global scale – like the canary was to the miners, to use the expression of ACIA - but also of certain direct impacts of climate change on the global scale.

1. Surface albedo. The polar icecaps play an important role in the global heat budget. The reduction of summertime snow and ice cover in the Arctic will contribute not only to an increase in atmospheric and oceanic temperatures at the global scale, but will also directly affect large-scale atmospheric and oceanic circulation. The reduction in albedo will create a positive feedback.

2. Greenhouse gas emissions. The thaw of permafrost leads to greenhouse gas emissions, such as carbon dioxide and methane, resulting from bacterial action. The organic material exported to the ocean by rivers is in part respired by marine bacteria and photo-oxidized by solar radiation. Considering the importance of the pool of organic carbon sequestered in the permafrost (approximately 1000 times greater than the annual reduction set in the objectives of the Kyoto Accord) and the rapidity with which its temperature evolves, it is possible that the thaw of permafrost will accelerate climate change (positive feedback).

While the heating and thawing of permafrost is almost unavoidable, its outcome remains however uncertain. In fact, an increase in the temperature of permafrost could also lead to the colonization of the tundra by plant species typical of the boreal forest, that would sequester the permafrost’s organic carbon in another form. However, several studies predict a net loss of carbon for the terrestrial arctic ecosystems (Mack et al. 2004; Freeman et al. 2004). As for the terrestrial organic carbon exported to the Arctic Ocean by rivers or by coastal erosion, its fate offshore is not well understood. The Arctic Ocean receives about 10% of the terrestrial organic carbon input of the World Ocean (Rachold et al. 2004), and this fraction is very likely to increase (Frey and Smith 2005). Most of the particulate organic carbon (POC) is deposited near the coast, over and just beyond the continental shelf. As for dissolved organic carbon (DOC), more than half is exported towards the Atlantic Ocean via the Canadian Arctic Archipelago and Fram Strait (Benner et al. 2005). The remainder is photo-oxidized by UV radiation as CO and CO₂ (Bélanger et al. 2006), and oxidized by marine bacteria within the Arctic Ocean (Hansell et al., 2004).

It is clear that all of the environmental changes triggered by climate change have an impact on primary productivity. In fact, the melt of sea ice, favoring the penetration of solar radiation into the water column, and the increased input of nutrients by rivers will be favorable to an increase in primary productivity (see for instance Gobeil et al. 2001). At the scale of the Arctic, primary productivity could well increase and compensate for, perhaps even overtake, the increase in oxidation of organic carbon of terrestrial origin.

These changes to pelagic marine ecosystems, which also include a measurable increase in the water temperature, will lead to, as observed for terrestrial tundra ecosystems, (e.g. Sturm et al. 2001), changes in microbial communities, such as the bacteria and phytoplankton. This evolution of biodiversity, which could occur quite rapidly, would have consequences for primary productivity and bacterial activity.

 

OBJECTIVES

The general objective of the proposed study is to determine the impact of climate change on the fate of terrestrial carbon exported to the Arctic Ocean, on the photosynthetic production of organic carbon, and on microbial diversity.

More specifically, we will attempt to answer the following 10 questions:

• What is the importance and form (particulate vs. dissolved) of the terrestrial organic material transported to the Arctic Ocean by rivers?

• What are the transport pathways of this material in the coastal zone and offshore?

• What is the chemical composition of the terrestrial organic material exported and what transformations occur during transport from rivers ⇒ coast ⇒ open ocean?

• What is the importance of photo-oxidation of organic material in the pelagic environment (production of CO and CO₂)?

• What is the impact of photodegradation on the chemical composition and bioavailability of terrestrial organic material?

• What is the importance of bacterial activity in the pelagic environment and its impact on the fate of terrestrial organic material?

• What is the impact of coloured dissolved organic material on primary productivity (e.g. release of nutrients, shading)?

• What is the importance of primary productivity and how is it affected by nutrients and light?

• How will these processes evolve in response to climate change (principally ice cover and UV)?

• What will be the impact of these changes on the biodiversity of bacteria and marine phytoplankton and, in turn, on carbon fluxes?

The physical environment of the Arctic Ocean will change in two fundamental ways as a consequence of climate change. First, the perenial sea ice will recede which will result in major modification of the planetary heat budget and, second, the increase in precipitation over the Arctic Ocean watershed, combined with deeply modified atmospheric forcing on the ocean surface, will impact the formation of deep-water. This in turn may affect regional climates outside the Arctic. These physical processes are under study by several international initiatives, among which the EC project Damocles (http://www.damocles-eu.org/) led by the French scientist Jean-Claude Gascard represents probably the most extensive effort.

Malina’s ambition is to address the biological and photochemical impact of another major physical consequence of climate change in Arctic: the drastic switch in the light regime encountered by the ocean surface layers. Simply put, because of ice cover, presently in the summer, the surface waters of much of the arctic are essentially dark; with the ice receding, these waters will be illuminated 24 hours a day.  Beyond warming the water when penetrating the water column, light interacts with the plankton and the colored organic matter in solution. Thus influencing the most fundamental source of energy in the ecosystem: photosynthesis. Beyond photosynthesis, photo-oxidation and, indirectly, bacterial activity will also be impacted. The predicted increased export of organic matter by rivers draining the permafrost amplifies the potential consequences of this change in the light climate of the Arctic Ocean surface waters. Indeed, just like fossil fuels, the carbon contained in the permafrost is “sequestered” carbon. A potential positive feedback of climate change is that it may trigger the oxidation of that sequestered carbon, adding a natural process to human activity in releasing even more CO₂.

It is unavoidable that the whole marine ecosystem of the Arctic will be affected by the above changes. But in Malina, we propose to focus on the above three processes (photosynthesis, photooxidation of organic matter and bacterial activity) because they form the basis of the cascade of possible effects. Our project is a massive and exhaustive effort to documenting these processes and predicting their vulnerability to anticipated climate change. Some data exist on those processes, and a number of ongoing international projects include, among others, the study of some of those processes. But here, we propose to deploy at once the effort required to build a self-consistent data set and to obtain a body of knowledge sufficiently large (beyond a critical size) to significantly improve our present understanding of the fluxes in this remote ecosystem, and to further our capacity to predict future changes. Therefore, the impact of Malina on Arctic science should truly be considerable. It will complement efforts to assess the most important impacts of climate change on the Arctic Ocean.

WORK DESCRIPTION

The ultimate goal of Malina is to determine the fate of 3 light-related processes over the current century in response to climate change in the Arctic Ocean. These processes - primary production, bacterial activity and organic matter photo-oxidation - play a major role in the organic ↔ inorganic carbon fluxes. The current state of the art does not allow estimating these fluxes as a function of environment factors such as light, nutrients, temperature, and organic matter composition and concentration, in the Arctic marine environment.

Therefore, to reach our goal, we conducted as the first phase of the Malina project a major oceanographic cruise (see expedition page). This cruise represents the most intensive effort ever focused on documenting extensively light propagation and the three above-mentioned processes in the Arctic Ocean. The geographic region of the Arctic Ocean that is of particular interest in this study is the continental shelf of the Mackenzie River in the Beaufort Sea. The Mackenzie is the river in the Arctic that exports the most organic particulate matter, and is the third most important for the export of total organic carbon (dissolved and particulate) of terrestrial origin (Rachold et al. 2004). During recent decades, this region has experienced a significant reduction in summertime ice cover (Barber and Hanesiak 2004) and an increase in ultraviolet radiation (Bélanger et al. 2006), and the study by Arora & Boer (2001) predicts a strong increase of freshwater inputs if the anthropogenic emissions of CO₂ were to double. The choice of this study area is also motivated by the particularly intensive research efforts between 2002 and 2004 in this region carried out by Canada, the United States, Japan, and other countries (including France) within the framework of the international CASES project (Canadian Arctic Shelf Exchange Study).The results of this work as well as other research projects during the last two decades in this region form an excellent foundation for the more focused study that we propose in this document.

In the second phase of the Malina project, our goal will be to predict the response of primary production, bacterial activity and organic matter photo-oxidation to climate change in the Arctic, over the next several decades. To this end, we will embed the developed diagnostic models into a coupled biological-physical ecosystem model. The latter will then be forced using outputs from global climate models in order to determine the fate of the above carbon fluxes, for different climate change scenarios. Additionally, a retrospective approach, based on the analysis of marine sediments, will be used to answer some of the Malina questions.

Finally, the third phase of the Malina project will consist in developing the tools (algorithms and protocols) necessary for running our diagnostic models using remote sensing data (ice, clouds, ozone, ocean color, SST, wind), in the frame of a long-term continuous monitoring. Changes are occurring so quickly in the Arctic that their impact on the marine ecosystem may be detectable at the decadal time scale. It is not our intent to conduct such a monitoring in the frame of the Malina project, but to implement what is necessary to launch such a monitoring from space.

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EXPECTED RESULTS AND POTENTIAL IMPACTS

The legacy of Malina will be:

• First, an extensive and self-consistent data set for future research.  The size and completeness of that data set will be in itself a major contribution.

• Diagnostic models for primary production, bacterial activity and photo-oxidation, appropriate for predictive modelling and monitoring for the arctic environement.  There is a general need for better modelling of « biology » in coupled biological-physical ocean models.  Malina aims at partly filling this gap.

• An assessment of the fate of carbon fluxes in the Arctic Ocean over the next decades.  Will the Arctic ocean become a major source of biologically and photochemically produced CO₂, a major biological sink of carbon, or will these processes be somewhat balanced?

• A better view on biodiversity of the microbial community and how it could be affected by climate change.

• Earth observation remote sensing provides great potential for monitoring the ocean, both at the level of physical and biological properties, and is a great source of data for feeding models.  In a remote and hardly accessible environment such as the Arctic, remote sensing represents the best and cheapest technology for monitoring but, presently, largely underused.  Because polar orbiting setellites revisite arctic regions at a much high frequency than lower latitudes it makes remote sensing even more useful. One significant legacy of Malina will be the protocols and algorithms necessary to monitor the three processes above over the open waters of the Arctic Ocean.

Furthermore, through our tight collaboration with the Canadian Arcticnet and CFL projects (more at the ABOUT US > COORDINATION tab), we hope to contribute to the ongoing effort toward transferring knowledge to Arctic local communities.  Indeed, we intend to participate in the Schools On Board program of those two projects, where scientists take part to dedicated cruises of the Arcticnet program (one 42-day leg every year) to teach various aspects of oceanography to high-school students.

 

 

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