Seafloor Biomass and Climate Change

By: Patrick Goebel, RJD Intern

The bottom of the ocean is a dark and mysterious place. It was first believed that this was a lifeless barren dessert. However, in recent years our understanding of this wasteland has changed. Submersible submarines, baited cameras and core samples have shown that life can survive at these deep depths. Animals and organisms have adapted to low temperatures, extreme pressure and minimal food. On the ocean seafloor, there is a plethora of organisms that play a vital role in the marine ecosystem. The vast majority of these organisms depend on the upper ocean as a source of energy. Energy on the seafloor is derived from particulate organic carbon (POC) from the upper ocean.

A recent article, Global reductions in seafloor biomass in response to climate change, predicts that biomass will decrease in response to climate change. Eight fully coupled earth system models were used to construct a multi-model mean of export flux. The model used two different Representative Concentration Pathways, one moderate and one high. The export flux estimates are used in conjunction with published empirical relationships to predict changes in benthic biomass (Jones et al 2013).

The article predicts that the upper ocean biomass will decrease in response to climate change, which will result in a decrease of POC that is transferred to the ocean floor.  Benthic communities are already limited by food supply and further depletion could change the diversity and structure of these communities. The total seafloor biomass is predicted to decrease by 5.2%. There will also be a shift in benthic infauna toward smaller size classes. Macrofauna will decrease far more than meiofuanal and megafaunal. This is most likely due to the greater energy demand of macrofauna.

Change in Biomass % over 90 yrs (Jones et al 2013)

Since not all oceans are the same, some will experience a decrease while others will experience an increase. The Atlantic, Pacific and Indian oceans are predicted to see a reduction in POC flux and biomass. However, the Southern and Artic Ocean are projected to experience biomass increases. There are many canyons, seamounts and cold-water corals located in these oceans that will largely be affected. More than 80% of potential deep-water biodiversity hotspots known around the world, including canyons, seamounts, and cold-water coral reefs, are projected to experience negative changes in biomass.

In conclusion, there will generally be a decrease in POC as a result of anthropogenically induced warming. However, there are other factors, such as, decreased oxygen, change in pH, and fishing pressure that could also have a negative impact on seafloor biomass.  These factors will likely contribute to a decrease in seafloor biomass and cause for under representation of the 5.2% decrease. The loss or decrease of benthic communities will have a negative impact on the ocean ecosystem, as these communities play a vital role in contributing to elemental cycling, benthic remineralization and carbon sequestration (Jones et al 2013).

Jones, D. O., Yool, A., Wei, C. L., Henson, S. A., Ruhl, H. A., Watson, R. A., & Gehlen, M. (2013). Global reductions in seafloor biomass in response to climate change. Global change biology.