New research indicates extreme oxygen loss in oceans during prior climate episodes, warning of present risks to oceans

By Magdalena A K Muir

Recent research indicates that vast stretches of the ocean i abruptly lost oxygen during the transition out of the last ice age that occurred 17,000 to 10,000 years ago. This transition period was the most recent example of large-scale global warming. This is important as past climate events provide information for understanding what is currently happening to the modern climate and oceans system. For this research, marine sediment core records across the Pacific Ocean were used to reconstruct the subsurface footprint of dissolved oxygen loss during abrupt global climate warming. The research found that entire ocean basins can abruptly lose dissolved oxygen in sync with other global-scale climate change indicators: temperature rise, atmospheric carbon concentration increases, and sea level rise.

Visualization of the extent of low-oxygen seafloor at 14,000 years ago mid-way through the deglaciation. The gray shading along the coastline is the paleoshoreline, or rather where the shoreline would been when sea level was 85 meters lower than today. Red seafloor is associated with severe hypoxia and orange seafloor is associated with intermediate hypoxia.

Visualization of the extent of low-oxygen seafloor at 14,000 years ago mid-way through the deglaciation. The gray shading along the coastline is the paleoshoreline, or rather where the shoreline would been when sea level was 85 meters lower than today. Red seafloor is associated with severe hypoxia and orange seafloor is associated with intermediate hypoxia

Most marine organisms need oxygen to live. Most marine life, from salmon, crabs, to shellfish, uses oxygen and many forms are intolerant of low oxygen seawater. Low oxygen zone are often referred to as “dead zones” as many species are unable to survice. Only extremophiles -worms, bacteria, and specialized urchins and bivalves – are able to live in these  these  environments. Importantly, few commercially species of fish or shellfish can live within the low oxygen zones.

From the Subarctic Pacific to the Chilean margin in the Southern Hemisphere, there was evidence of extreme oxygen loss  from the shallow upper ocean to about 3,000 meters deep in some regions. The transition from the last ice age to today’s warmer climate substantially reduced the oxygenated regions of the global ocean and changed marine life and ecosystems.

Low oxygen zones were not found in the upper ocean in the glacial world. Afte deglaciation occurred with the loss of massive glaciers and the rise of global temperatures,, ocean systems  responded. Upper ocean ecosystems, or those  connected to the surface ocean and with high concentrations of dissolved oxygen, were compressed towards the ocean surface. Below these oxygenated ecosystems, vast low oxygen zones or “dead zones” developed.

These are real, challenging and critical issues that fisheries and conservation and oceans managers will have to address in in the coming decades. As the lead author in the journal article, Sara Moffit, states in the Guardian article: “The immense risk of ocean oxygen loss in a future of climate change essentially dwarfs the existing modern paradigms of ecosystem-level conservation and management action.”

Further information:

Guardian news article by S Moffitt (one of the authors of the journal article), New research reveals extreme oxygen loss in oceans during past climate change
http://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/jan/29/new-research-reveals-extreme-oxygen-loss-in-oceans-during-past-climate-change

Open access journal article, Moffitt SE, Moffitt RA, Sauthoff W, Davis CV, Hewett K, et al. (2015) Paleoceanographic Insights on Recent Oxygen Minimum Zone Expansion: Lessons for Modern Oceanography. PLoS ONE 10(1): e0115246. doi:10.1371/journal.pone.0115246  http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0115246

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