An ocean of tears

Back in the MOOC it's now late in week 3, and I've not really been keeping up. Sunday afternoon and Ive still got 3 activities, the quiz and the summary reflection to do. Not because I've been lazy, but because I've spent a lot of time debating with @DavidStark, one of the leading course 'sceptics'. However, that's not what this post is about (maybe later...).

Here, I'm responding to activity 1.9, which asks us to discuss, for one of the major causes of change in the oceans: effect on marine organisms; economic effects; effective solutions. I've chosen ocean acidification, and – naturally – I mean to attempt a systems model. My first draft is below. All the information I've used for this comes from the course activities, mainly from Dr Ceri Lewis's video.

System description. Within the oceans there is a natural system of buffers and feedbacks that has, for millions of years, kept a remarkably stable pH of about 8.2. This balance is maintained chiefly because the waters are saturated with respect to carbonate CO₃. Many marine organisms, especially invertebrates, have evolved to suit this level of mild alkalinity and would be critically endangered in a more acid environment.

System environment. This system exists within a boundary defined primarily by the atmosphere, the shoreline and sub-surface rocks. There is also an interface with the many human influences on the oceans, including flotsam, jetsam and fuel spill from marine vessels. I've treated the effects of human land-based activities as being mediated mainly by the atmosphere (human-generated gases) and the shoreline (waste and detritus). I've treated solar radiation as mediated by the atmosphere.

System inputs. From the atmosphere, gases (mainly CO₂ and O₂?), fresh water (rain) and heat (radiation). From the shoreline, fresh water, weathering of carbonate rocks (CO₃), river sediments, and a wide range of agricultural, industrial and other human waste and detritus – field run-off, treated and untreated sewage, plastic litter, oil spill and more. From human marine activity, roughly the same kinds of materials minus the agricultural element. From sub-surface rocks, more carbonate weathering and some volcanic gases from deep sea vents (SO₂ and other toxic gases).

System outputs. To the atmosphere, oxygen (mainly from phytoplankton) and heat (mainly by convection). To land-based and marine humans, a large quantity of biomass, mainly in the form of fish and shellfish for food.

Sub-systems. The main sub-systems of interest for this analysis are: the aquatic ecosystem, but particularly those invertebrates that make use of carbonate for their shells or skeletons; the carbonate buffer system.

Feedback and control. {Not sure I've got all this bit right}. When CO₂ dissolves in water, it reacts with H₂O to produce carbonic acid H₂CO₃, which quickly ionises into H⁺ and HCO₃⁻. Extra H⁺ ions make the water more acidic, but this is balanced by dissolved CO₃⁻⁻ which reacts with H⁺ to produce more bicarbonate. Much of the dissolved CO₂ comes from the atmosphere, and as CO₂ concentrations rise there then they also rise in the oceans.

Discussion. Provided seawater remains saturated with respect to CO₃, any extra H⁺ ions can be absorbed. But there are already signs in some places that this is beginning to change, and within the foreseeable future the water may not remain saturated everywhere. Aquatic invertebrates may be unable to cope with the consequent increase in H⁺ ions. The most obvious effect is that as the acidity level rises it will begin to dissolve their shells. In weak acid, this will not be a fast process, but it may be life threatening over time. In addition, many invertebrate larvae will be impaired in their development as it becomes harder for them to form skeletons. This is likely to mean fewer larvae maturing to the adult phase. For humans, the consequences are less clear. But these invertebrates are extemely numerous and occupy important niches at the bottom of the food chain. Many other marine animals depend on them, including some that we depend on for our food. It's also a given in any ecological system that any disturbance can have completely unforeseen consequences. Loss of biodiversity is in itself a possible threat to all other species involved in a given ecosystem. It seems clear that this changing balance is likely to be problematic for many species including our own. The cause also seems clear: rising levels of anthropogenically produced CO₂. Does that mean the solution is clear too? Well, yes: control the rise in anthropogenically produced CO₂. Simple!