Sections of Intact Polar Diacylglycerolipids in the South Atlantic Reflect Dissolved Phosphorus and Nitrogen Distributions

The molecular composition of planktonic cell membranes is highly dynamic. It has been recognized for some time that membrane lipids in plankton cultured in phosphorus-depleted media contain fewer phospholipids than plankton cultured in phosphorus-replete media. However, only recently has this shift in membrane lipids been documented in the ocean. We collected plankton for membrane lipid analysis from surface waters along two zonal transects in the South Atlantic, approximately along 13S and 23S. Plans are also in place to collect samples along 40S this autumn. The data we have collected thus far show that the molecular composition of the planktonic community varies considerably, and that shifts in the relative abundance of phospholipids are correlated with shifts in the dissolved nutrient field. Although the correlation was considerably tighter in the 13S transect than in the 23S transect, the data suggest that the allocation of nitrogen and phosphorus in membranes reflects an adaptation that could affect the molecular distribution of around 1 Tg of nitrogen and phosphorus. The approach of analyzing organic molecules along sections has the potential to provide new insights on the biogeochemical cycles of major nutrients in the sea.