Trying to assess the likely effects of the upcoming changes in climate on the diverse ecosystems of the globe is a tricky business, since, unlike our ancestors who saw the end of the ice age and its widespread impacts, we have no direct experience of such events. The clearest lessons we can infer come from the geological record of times past in which similar conditions to those expected in our future occurred.
One commonly discussed event is the sudden abrupt warming associated with the Paleocene Eocene thermal maximum (seehttp://tinyurl.com/povhewl andhttp://tinyurl.com/qfqtkc4), but new research based on fieldwork along the coast of Yorkshire in England has given us an older analogue in the deeper past, analysing the effect of events similar to those that may be coming on marine ecosystems 180 million years ago in the early Jurassic.
The event saw global warming, gradual oxygen depletion in the seas, and an accompanying marine extinction event (which we already discussed in relation to the gem jet which is found in the dead zone of black shale that marks the extinction, seehttp://tinyurl.com/m99r5ag) that wiped out a quarted of all marine organisms.
The team correlated detailed stratigraphic (ie layer by layer) fossil counts through the period covering the extinction, gleaning further detailed environmental information from both sedimentology and geochemistry on the conditions under which the sediments (and their enclosed fossils) were deposited. They also correlated their field data with published information on ancient ocean temperatures, oxygen levels and sea level.
The results revealed drastic changes to ecosystems, and that while the seas eventually recovered, the new ecological networks that returned were quite different to their predecessors. They conclude from the changing environmental conditions they encountered through the different layers of rock and the story that they revealed that if global warming becomes too severe and long lasting, a marine extinction is likely and we cannot predict what will replace the vanished ecosystems.
This most detailed analysis of the Toarcian event shows how the ecosystems changed in response to the changes in conditions that had already been inferred from earlier studies. It seems like the response echoed that of modern marine life forms confronted with lowered oxygen levels. Though the species are different, similar patterns and ecological stages were found.
Marine ecosystems are already under threat, and not just from warming. Ocean acidification (also linked to CO2 emissions) and habitat pressure are already wreaking havoc amongst coral ecosystems worldwide, and the warming looks like it is going to add several further stresses to the delicate and balanced structures that life forms in the seas of the world. It would be a crying shame to see the past of the Toarcian repeat itself, knowing what we now do, and still (just about) in a position to change our ways, however painful that may prove.
Image credit, nacreous iridescent ammonites in Jurassic shale from the UK: Cobalt123
http://www.timesofmalta.com/articles/view/20130221/environment/Ocean-life-is-under-threat.458514 http://www.plymouth.ac.uk/pages/view.asp?page=39880 Original paper, free access: http://www.plosone.org/article/info%3Adoi/10.1371/journal.pone.0056255
