We will focus on the critical processes linked to climate variability and change that constrain marine ecosystem dynamics. Our special focus will be on the lower trophic levels. The ocean physics affects marine ecosystem at all trophic levels, particularly the ocean temperatures as all marine organisms have their specific thermal habitat niches. In this way, changes in ocean temperature affect species distributions in the world oceans. However, ocean temperature has only minor – or at best indirect – impacts on the basic biomass, i.e. the primary production in the ocean.
The onset of spring bloom, as well as the more or less sustained subsequent primary production, depends on light, wind forcing (stratification) and temperature. In regions of sea ice and freshwater influence, spring and summer heating can coincide with release of freshwater, which adds a haline stratification component to the thermal stratification. Mixed layer dynamics is therefore one of the most important physical processes driving the marine production.
Climate change alters the relative contribution of these governing processes. Projections of wind have large uncertainties due to different parameterizations in different models. It is uncertain whether extratropical cyclones in the North Atlantic have become stronger and/or more frequent. Also, many climate models predict a poleward shift of storm tracks in the northern hemisphere, which will have a large impact on the wind energy available for mixing the upper ocean.
Another limitation in global climate models is the coarse resolution that often prevent realistic transport of heat and thereby sea ice extent in the Artic regions. These differences in process representations could all feedback into the climate projection by altering the strength of biologicallymediated carbon sinks or emissions of marine aerosol precursors (e.g., dimethyl sulfate or DMS).
By comparing global against regional model outputs, we will also discern and identify dominant mechanisms driving the biases in primary production projected by global models. Here, we want to synthesize existing output from climate models and downscaling experiments and show how these simulations have provided new insights to the above-mentioned processes.
Key questions
- How do climate change and variability affect the marine ecosystem through bottom-up processes? What are the critical parameters influencing mixed layer depth, e.g. wind, hydrography?
- What are the strength and weaknesses of climate models to predict and project these? Which critical process in Earth system models need to be improved to reduce biases in the projected ocean productivity?
These questions have been investigated across different research themes at the Bjerknes Centre the recent years and in strategic internal projects as PARADIGM, BIGCHANGE, EMULATE and LOES, as well as in other national and international projects (ArcChange, EPOCASA, KeyClim, TRIATLAS, COMFORT).
Effects of climate variability and change on the marine ecosystem is a field of great interest to society. Ecosystem changes might have large consequences for biodiversity on a local scale and food security globally. It should therefore be of interest to the research community at the Bjerknes Centre and elsewhere to shed light on and synthesize the issues mentioned above. In this way models and corresponding predictions and projections of climate effects can be improved with respect to these processes.
Our focus will be mainly on subarctic marine ecosystems; however, the findings will be discussed in a global context. A potential increase of wind at low latitudes are likely to increase primary production due to increased supply of nutrients to the upper ocean. However, stronger winds at high latitudes might reduce stability and therefore delay the spring bloom. Eastern Boundary Upwelling Ecosystem (EBUE) provide the highest productivity in the global ocean on a very small area.
These important areas are not well resolved by global ESM which affects the total estimate of primary production. Local winds, driven by density differences between land and ocean, cause strong coastal upwelling of nutrients. Also here is the physical forcing crucial for understanding the uncertainty of both regional and global primary production.
Outcome
The main outcome of this project will be a synthesis paper evaluating how the physical drivers from both atmosphere and ocean influence primary production in a subarctic ecosystem, discussed in a global context. We will summarize how the key physical processes are resolved by global ESMs and regional downscaling experiments. Recommendations will also be discussed for further development of climate models.
Leader: Mari S. Myksvoll