Benthic respiration experiments

Paul Renaud
Akvaplan-niva AS

Elisabeth Alve
University of Oslo

Arunima Sen
NORD University

It is easy to forget, but breathing is not a one-sided coin. The carbon dioxide we exhale is just as important for life as its more fêted counterpart, oxygen. It is what photosynthetic organisms need to fix food for themselves and the rest of the living planet. In the verticality of the ocean, the seafloor represents the last stop for the generation of carbon dioxide. What the seabed breathes and exhales loops back to feed the rest of the ocean.

In order to better understand the cycling of carbon and nutrients in the Arctic, the Nansen Legacy benthos group is measuring the breathing rates of the seafloor community. This involves bringing up cores of the seafloor, saturating them with oxygen, sealing them tight to prevent oxygen from entering and escaping, and measuring oxygen concentration every few hours over the course of a couple of days. This gives the rate at which oxygen is being used up, and carbon dioxide is being generated. A fundamental measurement like this can provide insight into larger scale processes like how food is produced in the ocean and how it moves between different parts of the marine food chain.

The experimental setup is also expanded to estimate how marine carbon cycles will change in the future. The experiments are conducted in dark, refrigerated rooms to mimic the dark, cold seafloor. However, bottom water temperatures are expected to rise. Therefore,  batches of experiments are conducted at higher temperatures.

With rising temperatures comes melting sea ice in the Arctic. While this makes life difficult for animals like polar bears, it makes life easier for the algae that live at the ocean’s surface. Without ice blocking their access to sunlight, they can grow wild, literally turning the ocean green. More algal life and food at the surface should trickle down to the seafloor as well. To simulate this situation  another batch of experiments stimulated by adding algal food to the sediment cores.

In short, these experiments aim at revealing more about the circle of life as well as providing a window into the future at a time of rapid change in the Arctic.