My Bookmarks on Science & Technology, Climate Change, Astrobiology, Genetics, Evolution

July 1, 2008 – Original Source: Dot Earth, The New York Times
By Andrew C. Revkin

The heat from sea-bed volcanoes in the Arctic Ocean is kept isolated from the surface by layers of intervening water, experts say. A cross-section of the Gakkel Ridge as compiled by Henry Dick, co-chief scientist on the Arctic Mid-Ocean Ridge Expedition. (Credit: Paul Oberlander / Woods Hole Oceanographic Institution)

There was an eruption of assertions in recent days that the increasing summer retreats and thinning of Arctic Ocean sea ice might be a result not of atmospheric warming but instead all the heat from the recent discovered volcanoes peppering the Gakkel Ridge, one of the seams in the deep seabed at the top of the world.

Several experts said it was not plausible from the get-go, but for the sake of due diligence, I queried a heap of the Arctic oceanographers and climate and ice experts I’ve gotten to know since my North Pole journey in 2003. They uniformly reject the idea that heat from the bottom — either from the general geothermal activity beneath the seabed or the occasional outbursts of lava or vents — could have a significant impact on the veneer of floating, drifting ice on the surface.

The deep saltier, warmer water is largely isolated from the cold, fresher waters near the surface, they say. I’ve listed some responses below, with more to come. I’m in transit and can’t transliterate some of the techno-speak at the moment, but wanted to get this post up while the issue is still burbling in the blogosphere.

Here are the views of these scientists:

Peter Winsor, Woods Hole Oceanographic Institution:

I have had similar questions from the general public recently. On our recent Arctic expedition named AGAVE to the Gakkel Ridge (~85N) in 2007 we found evidence of recent explosive volcanic eruptions. However, most of the heat flow at the Gakkel Ridge seems to be diffusive and slowly seeping out. In any case, heat releases from the Arctic sea floor do not get higher up in the water column than, typically, ~500-1000 m from the ocean floor due to constantly mixing with ambient water on its way up (so-called entrainment). There is also a background heat source due to the constant cooling of the Earth’s interior. This slow-simmering geothermal heat flow is actually able to mix the very weakly stratified bottom waters of the Arctic. So, heat is released from volcanic activity, both from explosive larger events and more broad diffusive events, and in addition, from background geothermal heating. None of these will have any impact on the Arctic sea ice as the heat is trapped in the deep ocean and is unable to communicate with the upper ocean and sea ice. However, heat store in the Atlantic Layer (temperature maxima at ~300 m) and in waters of Pacific origin (maxima at ~50 m depth in the western Arctic) are prime candidates for releasing heat to the underside of the Arctic ice.

I hope this helps and let me know if you want more info.

Cheers, Peter


Jamie Morison, University of Washington
(I went with Dr. Morison and the rest of the North Pole Environmental Observatory team to the North Pole sea ice in 2003):

It occurs to me that we have primary evidence that heat from the bottom is not reaching the ice. Temperature profiles from virtually everywhere in the Arctic Ocean display a maximum temperature at a depth from 200-400 [meters]. This is associated with the Atlantic Water entering the basin from the Norwegian Sea. Fundamental laws of physics require that below the depth of this maximum, the heat flux is downward. Very near the bottom temperatures have been found to increase with depth indicating a small upward heat flux from geothermal sources, which help to heat only the very deepest water.

The heat flux above the Atlantic temperature maximum is upward. The rate of this flux of Atlantic Water heat flux is variable depending on depth of the maximum and overlying stratification (stratification is controlled by salinity in the Arctic Ocean). Treshnikov estimated it from Atlantic Water heat content to be a couple of Watt/m2 in much of the Euarasian Basin. It is smaller farther from Fram Strait and greater near Fram Strait. How this flux changes is potentially very important to the ice cover. Changes in geothermal heat flux are not.

Jamie


Timothy Stanton, Naval Postgraduate School
(was on team I accompanied to the North Pole):

Andy,

I agree with Jamie – the thermal structure is dominated by the Atlantic water maximum temperature which is trapped in a strongly stratified upper ocean. We have just submitted a paper to JGR that looks at these upper ocean fluxes measured with thermal microstructure and CTD for the year-long SHEBA experiment. This shows upward fluxes through the top of the pycnocline of about 1 watt in the Beayfort Sea, and 2-3 watts over the Chukchi Shelf, an area influenced by the Pacific inflow. The other replies suggest volcano input is comparable to the background geothermal flux, which in turn is much less than the fluxes through the pycnocline from the warm Atlantic water, and to a lesser extent, the Pacific inflow.

Tim

Associate Research Professor Tim Stanton
Code OC/St, Department of Oceanography
833 Dyer Road, Room 329C, Building 232
Naval Postgraduate School
Monterey, CA 93943


Jeff Severinghaus, Scripps Institution of Oceanography

I get this question too – and my usual response is to say, the average heat added from volcanoes to the ocean is of order 0.1 Watt per square meter. But the heat added (or removed) to the ocean from the sun and atmosphere is of order 100 Watt per square meter. So it is very hard for volcanoes to compete. Someone probably has much better estimates than these.

– Jeff

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