Reply #32: Hardly - I'm a member of AGU and a biogeochemist [View All]

[jpak]

and I know what I'm talking about.

Also I worked with DMS and DMSP (the precursor to DMS) as part of my dissertation work (and published it) and most recently collaborated with other researchers measuring DMS fluxes in the Ross Sea (Antarctica) Polynya Pheocystis bloom.

DMS concentrations at the height of the bloom were so high you could smell it on deck. It also permeated the ship's freshwater supply. We drank it and showered with it for the better part of a month.

As far as the so-called DMS/CCN feedback mechanism is concerned, it's principal proponent R. J. Charlson has retracted his support for it.

Charlson, R. L. (1995) The Vanishing Climate Role of Dimethyl Sulfide. In: G.M. Woodwell and F.T. MacKenzie (eds) Biotic Feedbacks in the Global Climate System, Will the Warming Feed the Warming? Oxford Press pp. 251-252.

To be short, there is no greenhouse climate mechanism that would stimulate ocean productivity. Ocean productivity - and DMS production will decrease as the ocean warms. A strengthening thermocline will decrease diffusive upwelling of nutrients over large areas of the ocean and reduction in surface water pH will adversely affect coccolithophorids, forams and calcareous macroalgae. Marine primary production, photosynthetic draw-down of atmospheric CO2 and DMS emissions will decline. Furthermore, as the ocean warms, the solubility of CO2 in seawater will decline and result in a net release of CO2 to the atmosphere.

Again, all the marine biotic climate feed backs are positive, and it's old news to the climate community - and no one promotes the DMS/CCN feedback mechanism today (except maybe Lovelock).

As far as carbon sinks in natural terrestrial systems are concerned, there is little evidence that CO2 fertilization will result in a substantial negative feedback. Elevated CO2 might stimulate some C3 plant growth over the short term (days months), but on longer time scales, nutrient limitation will not allow plant communities to exploit elevated levels of CO2.

Elevated temperatures may also stimulate terrestrial respiration, releasing CO2 to the atmosphere, and canceling any potential negative feedbacks from CO2 stimulated primary production. The jury is still out on that though...

As far as weathering is concerned, it is widely recognized that soil microbes,vascular plants and lichens do play a role in soil and rock weathering. It is also widely recognized that weathering proceeds quite well without the aid of biota.

During the Neoproterozoic glaciations (the so-called Snowball Earth period), sea ice and glaciers covered nearly the entire planet (even the tropics) and effectively shutdown marine photosynthesis. These glacial periods terminated when CO2 released from volcanism reached concentrations high enough to cause "super-greenhouse" conditions. In these transition periods, deglaciation and sea ice retreat were catastrophic. Elevated global temperatures and CO2 concentrations combined with an accelerated hydrological cycle greatly increased weathering on the continents. This in turn, resulted in a rapid decrease in atmospheric CO2 and the massive deposition of carbonates (the so-called cap carbonates) in the ocean - and ultimately the rapid return of Snowball Earth conditions.

And all this occurred without any biologically assisted weathering on the continents.

So there...

:P