I have enjoyed David Attenborough's latest series, Blue Planet 2, immensely with its breath-taking photography and extraordinary insight into the behaviour of sea creatures. There is no doubt it has deservedly been a great success with very high viewing figures. Unfortunately David has gone way over the top (near the end) in this final episode by showing hydrochloric acid reacting with sea shells and trying to compare this with the effect of adding extra CO2 to sea water. He failed to mention that sea water is alkaline and will remain so even if our emissions of CO2 were to carry on at their present rate for centuries. He also forgot to point out that shell fish can survive quite well alongside thermal vents bubbling CO2 in a constant stream.
It's a pity that Attenborough has done this as it diminishes his extremely high reputation as a trustworthy broadcaster. It may also serve to undermine his other valid claims that our oceans must stop being a dumping ground for plastic and other types of pollution.
It's a pity that Attenborough has done this as it diminishes his extremely high reputation as a trustworthy broadcaster. It may also serve to undermine his other valid claims that our oceans must stop being a dumping ground for plastic and other types of pollution.
Interesting that you left out the part where Attenborough asks the scientist how acidic the experiment was relative to the ocean. The scientist responds that it's much more acidic, but he's just using HCl for visual demonstration (given you're watching a TV show and cannot wait to see long-term dissolution).
ReplyDeleteYes he did say the hydrochloric acid was "more acidic than the ocean", but this was very misleading as the oceans are not ACIDIC at all - they are ALKALINE and so would not dissolve the shells at all! So why would he do a demonstration of something that is not happening and is never expected to happen?
ReplyDeleteThat's absolutely false. Alkalinity/acidity is a logarithmic scale and are just semantics. Shell dissolution depends on the concentration of calcium carbonate (CO3) in the ocean. There is a certain saturation state of CO3 in the ocean, dependent essentially on depth. When more CO2 is absorbed into the ocean, the pH declines as well as the concentration of CO3. We've already observed the CO3 concentration to be below the saturation concentration in certain coastal ecosystems. This leads to shells dissolving into the water since they are undersaturated. (Examples: http://science.sciencemag.org/content/320/5882/1490, http://rspb.royalsocietypublishing.org/content/281/1785/20140123.short).
ReplyDeleteI'm surprised you have a BSc in Applied Chemistry and cannot grasp the concept of relative pH and the saturation state of a calcium carbonate mineral.
The pH of the oceans varies slightly from place to place and even from day today. It is around 8.1 and is strongly buffered, meaning that it needs a vast amount of CO2 to change it by even one tenth of a pH unit. There is currently no serious threat to shell-fish and no likelihood of any. The terms acid and alkaline are not semantic, they are clearly defined and the oceans are alkaline.
ReplyDeleteCorrect, the oceans do have high alkalinity. Because pH is on a logarithmic scale, a 0.1pH change is significant. E.g. a 0.3-0.4pH change relates to a 150% increase in the H+ ion and 50% decrease in calcium carbonate ([CO3]). There currently is a threat to shellfish. Did you even look at the two studies I linked? We have collected snails off the coast of California and revealed shell dissolution from SEM imaging.
ReplyDeleteYes they are defined, but only in relation to the order of magnitude. Anything less than 10^(-7) [H+] is "acidic," but shells don't just suddenly start dissolving when it passes that threshold. You can have shell dissolution in the 7.9-8.0 range. All that matters is the [CO3] concentration relative to the saturation state.
I encourage you to educate yourself before making these posts: http://www.annualreviews.org/doi/abs/10.1146/annurev.marine.010908.163834
Greater than 10^(-7)*
ReplyDeleteI did try to read your links but the first two did not work. What you don't seem able to accept is that in the real oceans there has been little change in pH and so Mr Attenborough was exaggerating by using hydrochloric acid. Here is a good link to explain what is happening.
ReplyDelete