02 June, 2009

Diatoms are cool and hot, trust me on this

Has this ever happened to you, when you know what you are talking about but unfortunately [dumb ass!] cannot articulate at the time? It happened to me yesterday in a staff meeting, no less. As I lay in bed drifting off to sleep last night, the relevant info - dimethyl sulfide, of course! - that had been locked away in storage in the nether regions of my brain hit me like a bolt of lightening.

My organization has a journal club - once a month, we devote a part of our regular staff meeting to covering oceans-relevant studies and news from pre-assigned journals. I think it's a brilliant idea - from what I understand, it's a tradition borrowed from medical school (but I haven't verified this) - and makes staying on top of a number of journals much easier than any one person could do on her/his own.

While summarizing the microbial oceanography content from the May 14 Nature Insight, I included the what-I-thought-to-be-common-knowledge remark that "diatoms, as you know, are responsible for cloud production."

"Um, no we don't know" was the immediate response.

My colleagues were eager for an explanation, and the intricacies of phytoplanktonic life were momentarily eluding me. All I could say was, "I don't recall the precise biological and chemical processes, but, trust me, diatoms are linked to cloud formation and the regulation of temperature. I'll get back to you on this."

Here is the plain-speak answer I should have been able to articulate:

A. The picture that would have been worth 1,000 words. (courtesy of Oceanworld)

Phytoplankton such as diatoms emit dimethyl sulfide or DMS, a component in the "smell of the sea." Some of this gas ends up in the atmosphere, where it oxidizes and forms particles around which water can condense and form cloud droplets. The reflectivity of clouds (or their albedo) is influenced by the number of these condensation particles. According to my now totally outdated Environmental Science textbook (I see it's currently in its tenth edition), as the ocean warms more DMS is produced. Clouds block sunlight, so more DMS means more potential clouds to block sunlight. This, in turn, would result in a cooling effect, however, less solar energy means less active phytoplankton, which means less DMS and thus less cloud condensation particles. Hot, cold, hot, and so on...

In other words, what we have is a nice little feedback mechanism that is thought to help regulate temperature and keep it within a suitable range for life. Under normal conditions and all other things being equal, which of course we know they are not. (For more on diatoms and the regulation of planetary temperature, see Science Progress.)

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