Seawater sampling by an autonomous underwater vehicle: "Gulper" sample validation for nitrate, chlorophyll, phytoplankton, and primary production

Abstract

The effort and expense associated with sample and data collections for long oceanographic time series are, in part, driving the development of autonomous platforms, sensors and sample collectors. Here we validate basic oceanographic samples collected by an autonomous underwater vehicle with water sampler (AUV with "Gulper") by comparison with samples collected by a standard collection device, the conductivity-temperature-depth rosette with Niskin bottles. After elimination of a toxic material, "on-deck" and field comparisons show that Gulpers and Niskin bottles collect comparable nitrate, chlorophyll, phytoplankton species and 14C-based primary production (PP) samples and data. Gulper materials and lubricants, Gulper firing, field presence of the possibly toxic submarine, and the pressure and temperature cycling associated with the submarine's depth undulations all appear unimportant. However, 24 h sample hold periods for live samples within the Gulpers, as is necessary during many AUV deployments, appears to depress nitrate, chlorophyll and PP values somewhat (4-16%). While challenges remain, demonstration that the AUV and sampler can collect fundamental oceanographic samples is a critical step toward the broader use of such autonomous platforms.