Biogeochemistry

The latest special report published by the IPCC in the fall of 2019 on oceans and the cryosphere shows that these environments are among those most vulnerable to climate change. The temperature last summer exceeded 18°C on several occasions, while seasonal normals range from -3°C to 0°C. Both ocean and coastal ecosystems, made up of interactions between water, ice and the atmosphere, are being disrupted. 


Biogeochemistry is looking at the flows of the elementary elements of life (oxygen, carbon, metals, nutrients, etc.) that are exchanged, consumed and produced by the various organisms present in these ecosystems. To better understand the links between these organisms, regular water and ice samples should be taken both at sea and on land. These samples must be taken according to standardized protocols, using specific equipment and stored in such a way as not to damage the components of the environment before their analysis in the laboratory. In particular, this makes it possible to compare real ecosystems with those that are being modelled.

 

Most of these elementary elements are not "bare" in water or ice but are encapsulated by molecules: ligands. These ligands are produced by different organisms in the environment in different ways and allow them to assimilate, store, use and reject these elements according to their needs. By analyzing the ligands, we can better understand the interactions that bind the different species in the environment, whether they are in a competitive or mutual aid situation. For example, we are currently trying to analyse the links between phytoplankton and bacteria. They are the base of the food chain and the carbon cycle. (Research in progress at IMAS in Hobart - Tasmania).


This is a crucial issue: the Southern Ocean is one of the main areas of exchange between surface and deep waters. This makes it the main heat sink and a major atmospheric carbon sink. Understanding how life there is organized will allow us to better assess the changes that are taking place now, and to better predict what these zones of life will be like in the future.

The challenge is both local and global: these ecosystems will be among those that will have undergone the greatest changes, but also those that will have one of the greatest impacts on the global climate of the future.