Mass extinctions, atmospheric sulphur and climatic warming at the K/T boundary

A connection has recently been proposed between cloud albedo over the oceans and the release of dimethyl sulphide (DMS) by marine algae. DMS acts as a precursor for most of the cloud condensation nuclei (CCN) in the marine atmosphere¹. The mass extinctions at the Cretaceous/Tertiary (K/T) boundary include about 90% of marine calcareous nannoplankton^2,3, and carbon isotope data show that marine primary productivity as a whole was drastically reduced for at least several tens of thousands of years, and perhaps up to a million years after the extinction event^4-6. The elimination of most marine calcareous phytoplankton would have meant a severe decrease in DMS production, leading to a drastic reduction in CCN and hence marine cloud albedo. Here we examine the possible climatic effects of a drastic decrease in CCN associated with a severe reduction in the global marine phytoplankton abundance. Calculations suggest that a reduction in CCN of more than 80%, and the resulting decrease in marine cloud albedo, could have produced a rapid global warming of 6°C or more. Oxygen isotope analyses of marine sediments from many parts of the world have been interpreted as indicating a marked warming coincident with the demise of calcareous nannoplankton at the K/T boundary. Decreased marine cloud albedo, and resulting high sea surface temperatures could have been a factor in the maintenance of low productivity in the 'Strangelove Ocean' period following the K/T extinctions.