Primary Production in the Glacial North-Atlantic and North Pacific Oceans

THE conditions controlling primary production are very different in the modern North Atlantic and North Pacific oceans1, a difference that is reflected in the composition of diatom fossils in surface sediments. By contrast, I report here evidence that during the last glacial interval the diatom assemblage, and by extrapolation the primary production, was very similar in the two regions. The modern analogues of these assemblages occur in sediments of Baffin Bay and the Sea of Okhotsk, both highly productive seas where ice is present. I infer that during the last glacial interval plankton biomass was at least as high as it is today in the North Atlantic, and was as much as an order of magnitude higher in the North Pacific. The glacial assemblage occurs in lithologies dominated by ice-rafted detritus, which is generally believed to indicate the presence of icebergs2-6. I hypothesize that the presence of numerous icebergs, possibly associated with sea ice, supported high production by physical mechanisms (such as turbulent mixing and enhanced density stratification) and/or biogeochemical ones (such as supply of major or trace nutrients).