Global warming may cause major marine oxygen depletion.Scientists investigating the changing conditi

Global warming may cause major marine oxygen depletion.Scientists investigating the changing conditions as the globe warmed 5 degrees Celsius during the several thousand year transition into the current interglacial epoch at the end of the last ice age (a rise similar to the outer limits predicted for the end of only this century) have come up with unsettling data suggesting that a period of extreme oxygen depletion in the sea accompanied the transition. Reversing the geological maxim of the present being the key to the past when investigating geological processes, in climatology the past is seen as the key to the future. They seek analogous events in the past to what might be expected from man-made global warming, and using what they can glean make predictions for the future.The event encompassed the period between 17,000 and 10,000 years ago, and was revealed by a detailed analysis of sediment cores taken across the Pacific Ocean. The cores showed the sea bottom footprint of oceanic dissolved oxygen loss, which was presumably accompanied by large dead zones in the sea and a redistribution of marine life due to changes in habitats. The transition was abrupt and basin wide (From the sub arctic to Chile), and penetrated the water column from the surface to a depth of three kilometres. It accompanied other signs of a changing climate such as increased temperature and atmospheric carbon or sea level rise.One common factor in all warm periods, from interglacials to the Mesozoic, it a tendency for the system to steer towards stratified oceans, with a thin oxygenated rind stirred by winds and currents and a mostly anoxic zone filling the depths. The longer the warm period, the more established and stable this Earth system becomes.If temperatures rise by the same amount in a short time, the effects are unpredictable, since the event would be unprecedented in geological history. Major changes are already occurring to marine oxygen levels and distribution, some due to agricultural runoff causing plankton blooms that suck the oxygen out of the surface layers. Oxygen levels are falling in every ocean basin, and the size of the risk that we seem to be taking just increased by another large notch.Most of the ocean ecosystem depends on oxygenated water, as do the fisheries that we depend on for protein. They are already affected by fisheries migrating as their habitat zones change, overfishing, pollution and dead zones due to excess agricultural runoff. Recent research from Tasmania is exploring the southerly migration of many commercial species and its implications for the future.Add in the increased acidification of the oceans due to the dissolved CO2 forming carbonic acid which is already affecting some shellfish populations (see our past coverage at http://on.fb.me/1C3moNZ), the fisheries and ecosystems of the world ocean are probably heading for a battering over the course of this century.LozImage credit: NASAOriginal paper, free access: http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0115246http://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/jan/29/new-research-reveals-extreme-oxygen-loss-in-oceans-during-past-climate-changehttp://www.theguardian.com/environment/2015/jan/29/australian-fish-moving-south-as-climate-changes-say-researchers -- source link

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