November 25, 2013

Historical varying hydrothermal oceanic heating; any resultant climate effect?

Assuming hydrothermal vents have been operative over long periods of time, have they had a significant effect on oceanic heating, and thus on planetary scale climate?  An ocean’s average lifetime is perhaps 100-150 million years (?); but the entire oceanic volume might cycle through such vent system over a much shorter time frame, such as perhaps less than 1 million years? Such vents are thought to contribute principally or significantly to oceans’ saltiness. Then if oceans’ volume recycles through such vent system, then wouldn’t this also contribute significantly to heating of such volume? Such a persistent heat buffer process would not seem consistent with a snowball earth model. Is such heat buffer process a principle modulator of long term climate regulation? Might the Paleocene Eocene Thermal Maximum (35-55 Myrs ago) be due to a transient increased heat egress from such hydrothermal vent system, vis-a-vis increased rate (flux) throughput i.e. circulation? Might such oceanic heating (of transient varying flux) secondarily result in methane hydrates release from oceanic sediments; thus further enhancement of atmospheric heating (although transient, since atmospheric half-life of 7 years)? In a contrasting model, any 100,000 year Milankovitch climate cycle mechanism could not be due to a change in eccentricity of Earth’s orbit, since curvature change is not possible, since the Sun’s mass and relative location remains essentially changed.

How might one test such model? What is the current overall average temperature of oceans? 72% surface area x average depth gives total oceanic volume. Then specific heat (~4x atmospheric specific heat) x oceanic volume equals heat capacity. Would 5-7 degrees Celsius increase in average temperature for total volume, suffice to affect the atmosphere (climate) over long term of 20 million years? Considering all vents in say clusters of 20, how many clusters (i.e. how long a portion of ridges along spreading centers etc.), and over how long a period of time (continuous or intermittent), would be required to initiate and maintain such temperature and heat capacity increase? Calculable? Changing flux (flow), and not the temperature, of some percentage of vents, might seem more reasonable. Perhaps one could use metal concentration in sediments for ~55 million year strata level (and for intervals over subsequent 20 million year strata?), from drilling perhaps near Iceland or other sites? That is, such metalicity concentration would serve as a proxy for increased past flux from such vents, in comparison to controls at other times and/or for more remote sites. However 55 million year strata is not very deep; wherein poor pressure of water, and hence mixing of metals etc. would have to be considered. Would drilling into basalt also present problems? Currently, is there observed variation in temperature and flux for any such vents? If there is, might this also suggest possible longer term variation in temperature and flux? Thus vis-a-vis this approach, might one have another model (plausible?) addressing the etiology of a considered planetary wide Paleocene Eocene Thermal Maximum?  TMM


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