CONSISTENCY OF TOWING SPEED AND SAMPLING DEPTH FOR THE CONTINUOUS PLANKTON RECORDER

The mean annual towing speed of the Continuous Plankton Recorder (CPR) varied systematically between 1946 and 1991. By mounting a pressure t ransducer on the CPR to record towing depth, it was shown, however, th at changes in towing speed did not cause a significant change in towin g depth, although the mean towing depth (6.7 m, SD = 1.7 m, N = 77) wa s shallower than the previously assumed towing depth of 10 m. Thus the observed changes in towing speed are unlikely to have caused disconti nuities in the CPR time-series by affecting sampling depth.