Fred Pearce: North Atlantic is world's 'climate superpower' (Tsonis et al., synchronised chaos -- NAO is pacemaker of major climate shifts)

North Atlantic is world's 'climate superpower'

by Fred Pearce, New Scientist, February 17, 2009

IF EVER there was a superpower of the oceans, the North Atlantic, with its ability to control global weather systems, is it. The bad news is that this region also happens to be especially sensitive to the effects of climate change, so what is happening there could affect the world.

The planet's climate goes through periodic convulsions that affect every region simultaneously. The most recent were in the early 1940s and mid-1970s. The latter coincided with the start of more frequent El Niño events in the Pacific and a strong global warming trend.

In past studies, Anastasios Tsonis and colleagues at the University of Wisconsin-Milwaukee have shown statistically that climate features like El Niño and the North Atlantic Oscillation (NAO), which drives weather across Europe, become synchronised for a few decades, before the links abruptly break down and a new pattern emerges. They call it "synchronised chaos."

Now their modelling studies have shown the action is always driven from the North Atlantic. Tsonis says the NAO is "without exception the common ingredient... the pacemaker of major climate shifts" (Geophysical Research Letters, DOI: 10.1029/2008GL036874).

The findings may be seized on by deniers of man-made climate change as evidence of the scale of natural climate variability. Tsonis argued two years ago that accelerated global warming since the 1970s could be due partly to a natural climate shift (Geophysical Research Letters, DOI: 10.1029/2007GL030288).

But the findings will leave most climate scientists more worried. Today's climate is changing most dramatically in the far North Atlantic, with record warming and ice loss in recent years. If the climate's "tipping point" resides in these waters, then nature's synchronised chaos could unleash unexpectedly sudden and severe consequences.

Link to article: http://www.newscientist.com/article/mg20126955.400-north-atlantic-is-worlds-climate-superpower.html

Rhiannon L. Mather et al., Phosphorus cycling in the North and South Atlantic Ocean subtropical gyres

Letter abstract

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Nature Geoscience 1, 439 - 443 (2008); Published online: 22 June 2008 | doi:10.1038/ngeo232

Subject Category: Oceanography

Phosphorus cycling in the North and South Atlantic Ocean subtropical gyres

Rhiannon L. Mather¹, Sarah E. Reynolds^1,4, George A. Wolff¹, Richard G. Williams¹, Sinhue Torres-Valdes², E. Malcolm S. Woodward³, Angela Landolfi^2,4, Xi Pan², Richard Sanders² & Eric P. Achterberg²

Despite similar physical properties, the Northern and Southern Atlantic subtropical gyres have different biogeochemical regimes. The Northern subtropical gyre, which is subject to iron deposition from Saharan dust¹, is depleted in the nutrient phosphate, possibly as a result of iron-enhanced nitrogen fixation². Although phosphate depleted, rates of carbon fixation in the euphotic zone of the North Atlantic subtropical gyre are comparable to those of the South Atlantic subtropical gyre³, which is not phosphate limited. Here we use the activity of the phosphorus-specific enzyme alkaline phosphatase to show potentially enhanced utilization of dissolved organic phosphorus occurring over much of the North Atlantic subtropical gyre. We find that during the boreal spring up to 30% of primary production in the North Atlantic gyre is supported by dissolved organic phosphorus. Our diagnostics and composite map of the surface distribution of dissolved organic phosphorus in the subtropical Atlantic Ocean reveal shorter residence times in the North Atlantic gyre than the South Atlantic gyre. We interpret the asymmetry of dissolved organic phosphorus cycling in the two gyres as a consequence of enhanced nitrogen fixation in the North Atlantic Ocean⁴, which forces the system towards phosphorus limitation. We suggest that dissolved organic phosphorus utilization may contribute to primary production in other phosphorus-limited ocean settings as well.

1. Department of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow Street, Liverpool, L69 3GP, UK
2. National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK
3. Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH, UK
4. Present address: Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, 4600 Elkhorn Avenue, Norfolk, VA, USA (S.E.R.); Leibniz-Institut für Meereswissenschaften, Marine Biogeochemical Modelling, Düsternbrooker Weg 20, D-24105 Kiel, Germany (A.L.)

Correspondence to: George A. Wolff¹; e-mail: Wolff@liv.ac.uk

Link to abstract: http://www.nature.com/ngeo/journal/v1/n7/abs/ngeo232.html