The 'deadly trio' - a triple whammy

Having individually discussed all three consequences of the global carbon perturbation, ocean warming, acidification and deoxygenation, this post will bring everything together and discuss them in terms of the deadly trio. Bijma et al. named them as such because these ‘big three’ have been associated with most of Earth’s five global mass extinctions and, therefore, can easily be considered deadly (2013). This is extremely worrying when you realise that they are all present in our ocean today and are occurring at a much faster rate than has ever occurred in the past 55 million years!

It is this rate that is the critical factor of any carbon perturbation. In the past, carbon perturbations occurred slowly and were sustained over thousands of years, but now, we are releasing the same amount of carbon, just on a much shorter timescale. Resultantly, the Earth system’s capacity to buffer the changes has been exceeded and organisms are now threatened by unprecedented evolutionary pressure (Bijma et al., 2013). As previously discussed, the ocean’s uptake of CO₂ is now outstripping its ability to absorb the carbon - it has exceeded the supply of cations required for the reactions. This decreased buffering capacity has caused a reduction in pH, decreasing the ocean’s saturation state and detrimentally impacting many marine calcifiers (Cai et al.,2011). Simultaneously, the ocean has warmed, which has enhanced stratification and further decreased its ability to absorb CO₂ (Tyrell, 2011). This has lowered the oceans dissolved oxygen content, first due to oxygen’s decreased solubility in warmer waters and secondly, through the reduced ventilation of the ocean interior owing to increased stratification (Keeling et al., 2010). Although I have previously discussed each stressor individually, it is clear they occur simultaneously in the ocean and interact with one another to create synergistic effects.

Together, the deadly trio are not only considerably affecting the productivity and efficiency of our ocean, but are threatening marine life as we know it. Bijma et al. argues that if we do nothing to change the current carbon perturbation, we can expect serious consequences for the marine ecosystem, worse than occurred during the Paleocene-Eocene Thermal Maximum extinction (PETM) (2013). This is the most recent major extinction event that occurred approximately 55 million years ago and is considered to be the closest analogue to current ocean acidification. The current carbon perturbation will undoubtedly continue to have huge implications for the Earth, its ocean and for us, the human population and if we are to do anything to save our ocean from the deadly trio, Gruber argues our starting point is reducing CO₂ emissions (2011).