The relationship between primary production and export production in the ocean: Effects of time lags and temporal variability

We analyzed net primary production (NPP) and export production rates measured in the Southern Ocean (SO) and at Station ALOHA (22 degrees 45'N, 158 degrees 00'W) and discovered that in both cases there was a highly significant negative correlation between NPP and the ratio of export production to NPP (i.e., the export ratio). We show that in both cases this negative correlation can be explained by a time lag between the production and export of organic matter from the euphotic zone. The negative correlation appears (disappears) in simulated data if the estimates of the relationship between NPP and export production are based on measurements over timeframes that are comparable to or shorter (much longer) than the time lag between NPP and export production. At Station ALOHA, where data are available from a time series that extends back to 1988, the negative correlation disappears when the data are climatologies over monthly time intervals, which are long compared to the assumed lag of five days between the production and export of organic matter at low latitudes. We conclude that because of the temporal variability of NPP and the time lags between the production and export of organic matter, meaningful estimates of export ratios will need to be based on rates of NPP and export production averaged over timeframes that are long compared to the lag between production and export.