Changing Arctic Ocean

Implications for marine biology and biogeochemistry

Photo: Snapshot of a GoPro movie taken to scan the underside of an ice floe on the ARAON 10B expedition 2019. The light penetration through the sea ice and snow is visible, as is some ice algae abundance in patches. The light penetration is larger under a melt pond in the back, behind which the keels of ice ridges reach into the water column.

The overarching aim of the Changing Arctic Ocean programme is to understand how the changing physical environment will affect the large-scale ecosystem structure and biogeochemical functioning of the Arctic Ocean.

The two key research challenges of the programme are the following:

  • To develop quantified understanding of the structure and functioning of Arctic ecosystems.
  • To understand the sensitivity of Arctic ecosystem structure, functioning and services to multiple stressors and the development of projections of the impacts of change.

The programme started in February 2017 with four large projects (Arctic PRIZE, ARISE, ChAOS, DIAPOD) funded by NERC. A further 12 projects joined the programme in July 2018, co-funded by NERC and the German Federal Ministry of Education and Research. Each one investigates different aspects of the Changing Arctic Ocean. Combined, the projects involve 32 research institutions and organisations in the UK and Germany, and more than 200 scientists.

The contribution of the sea ice physics section to this program are part of two of the projects in the CAO progamme (see boxes below): Eco-Light and Diatom-ARCTIC. Both projects are co-funded by the German Federal Ministry of Education and Research and by NERC.

Diatom- ARCTIC

Diatom Autecological Responses with Changes to Ice Cover

Sea ice algae are important primary producers, contributing to the base of the food chain in the Arctic Ocean. Their productivity and composition depend on the light, nutrient and salinity conditions present in the ice and underlying water column, all of which are likely to change in response to climate warming. Diatom-ARCTIC will characterize sea ice habitats in the Arctic and evaluate the biogeochemical and ecological contributions of the most prolific algal community – diatoms – within them. These insights will be applied to understand how the Arctic marine system will respond to ongoing changes that include thinning of sea ice, declines in nutrient inventories and freshening of Arctic Ocean surface waters. We will answer questions such as:

  • How do sea ice conditions vary over different spatial and temporal scales in the Arctic?
  • How do sea ice diatoms respond to variability in growth conditions?

The project integrates field observations of community composition, and those derived from innovative laboratory experiments targeted at single-species of ice algae, directly into a predictive biogeochemical model. Field observations will steer the set-up of laboratory experiments to identify photophysiological responses of individual diatom species over a range of key growth conditions: light, salinity and nutrient availability. Additional experiments will characterise algal lipid composition as a function of growth conditions – quantifying food resource quality as a function of species composition. Field and laboratory results will then be incorporated into the state-of-the-art BFM-SI biogeochemical model for sea ice algae, to enable simulating gross and net production in sea ice based on directly observed autecological responses. The model will be used to characterise algal productivity in different sea ice growth habitats present in the contemporary Arctic. By applying future climate scenarios to the model, we will also forecast ice algal productivity over the coming decades as sea ice habitats transform in an evolving Arctic.

Figure 1: A schematic of the sea-ice components of BFM-SI and the flow of matter between the components. The model is coupled with a pelagic component, and takes advantage of the same biological processes. A planned development of the model is to resolve 3 state variables for sea ice algae functional groups, which allows for simulating the autecological responses.

 

Literature:
BFM model documentation
 

Project publications: Lange, B. A., Haas, C., Charette, J., Katlein, C., Campbell, K., Duerksen, S., et al. ( 2019). Contrasting ice algae and snow‐dependent irradiance relationships between first‐year and multiyear sea ice. Geophysical Research Letters, 46, 10834– 10843. https://doi.org/10.1029/2019GL082873

 

 

 

Eco-Light

Ecosystem functions controlled by sea ice and light in a changing Arctic 

Eco-Light is a collaborative project of the British Antarctic Service (BAS), the sections Sea Ice Physics and Polar Biological Oceanography at the Alfred Wegener Institute (AWI), the University College London (UCL) and Ocean Atmosphere Systems GmbH (OASys).

The Arctic is warming more than twice as fast as any other region of our planet. This warming has led to quantifiable changes right across the Arctic on land, in the ocean and the atmosphere. The most dramatic changes are those associated with Arctic sea ice whose extent has decreased by around 50% in the last three decades. The Arctic is no longer a region dominated by a thick multi-year ice (MYI); it is now a regime controlled by thinner, more dynamic, first year ice (FYI). The Arctic is experiencing a shift from a year-round sea-ice cover to a seasonal regime. In fact, complex computer models predict that the Arctic Ocean is on track to become mostly ice free in summer within a few decades, if not earlier.

These changes have important implications for the Arctic marine ecosystem since its functioning is mainly driven by the seasonality and the physical properties of the sea ice. Our understanding of the functioning of the Arctic marine ecosystem has been overwhelmingly derived from a MYI setting, rather than the FYI dominated Arctic of recent years. Thus, our current state of knowledge of these processes and the validity of many of the parameterisations presently embedded in computer models become more questionable.

Light is one of the critical drivers of primary production in and under sea ice by acting as a trigger for sea-ice algae and phytoplankton blooms. Recent studies revealed that that the transition from MYI to FYI ice cover corresponds to an increase of 200% in light transmittance into the upper ocean. Therefore, if we are to understand and predict ecosystem function in this ‘new Arctic’, we must understand and correctly parameterise the light climate under this new FYI environment we find ourselves in today, and for the foreseeable future. To do this correctly we need a holistic approach that seamlessly brings biology, optics, sea ice and ocean physics, together with satellite remote sensing and cutting-edge modelling. Eco-Light embodies this approach.

Eco-Light will provide fundamental data to improve parameterisations of physical processes, as well as biogeochemical and ecosystem processes in the snow, sea ice and upper ocean. Questions like the following drive this research:

  • How does this new Arctic influence light penetration through ice and snow?
  • How will the ecosystem respond to changes in light conditions and food availability?

To tackle those science questions, we collaborate also with the Korean Polar Research Institute. In August 2019 we participated in an expedition to the Chukchi Sea in the Pacific region of the Arctic Ocean with the research vessel ‘ARAON’. Here, in-situ measurements of light transmission through sea ice and snow were taken, in conjunction with primary production data. In addition, a set of buoys were deployed, which were intended to measure light transmission and biological data over the course of a seasonal cycle (Fig. 1)

Figure 2: Pictures of the August 2019 ice station in the Chukchi Sea as part of the ARAON 10B expedition. (a) First ice floe visited, ponded MYI. (b) Remote ice floe visited during the first ice camp, ponded FYI. (c) 3rd ice floe visited during the second ice camp, mix of ponded FYI and MYI.

In addition to measurements, numerical models are used to simulate the changes in light transmission under the new Arctic conditions and the response of the in-ice and under-ice algae. At AWI we are using the Sea Ice Algae model SIMBA (Castellani et al., 2015), which is coupled to the coupled sea ice - ocean model FESOM. Driven with realistic atmospheric data (JRA55) we investigate the impact of different parameterizations of light transmission on the light which is available for primary production (PAR) and the effect on the sea ice algae. Figure 3 shows an example of the drastically different amount of PAR when we improve the way how in the model the transmission through very thin sea ice and snow is handled. Further observations and tests with models are necessary to improve those parameterizations, so that projections of the future development of the Arctic Ecosystem can be improved.

Figure 3: Snapshots of PAR at the sea ice bottom for the year 2012 at the end of May. Left:
with the parameter setting of Lebrun, Right: with the additionally corrected treatment of thin ice and snow. Notice the tremendous difference in under-ice PAR, showing the vital role of thin ice and snow.

Ecolight publications:
J. Stroeve, M. Vancoppenolle, G. Veyssiere, M. Lebrun, G. Castellani, M. Babin, M. Karcher, J. Landy, G. Liston and J.P. Wilkinson; A Multi-Sensor and Modeling Approach for Mapping Light under Sea Ice. Frontiers in Marine Science- Global Change in the future ocean. (submitted)

G. Veyssiere, G. Castellani, H. Flores, A. Hayward, M. Karcher, F. Kauker, J-H. Kim, M. Nicolaus, J. Stroeve, L. Valcic, J.P. Wilkinson, E.-J. Yang; Under-ice light field analysis in the Arctic Ocean. Arctic Special Issue, Phil Trans Royal Soc. (submitted)

Literature:
Castellani, G., M. Losch, B. A. Lange, and H. Flores (2017), Modeling Arctic sea-ice algae: Physical drivers of spatial distribution and algae phenology, J. Geophys. Res. Oceans, 122, doi:10.1002/2017JC012828.