CTD: Conductivity, Temperature, Depth

The Winched Shallow Profiler engulfed in soft sunlight rises up 30 m beneath the ocean's surface. Located at the Slope Base site it is measuring nutrients, dissolved oxygen and carbon dioxide concentrations, seawater acidity, temperature and chlorophyll concentrations at high temporal and spatial resolution, controlled from >200 miles onshore through the Internet at the University of Washington. Credit: NSF-OOI/UW/ISS; V15.

A CTD is an instrument used to determine how conductivity (C) and temperature (T) measurements in the ocean vary relative to depth (D) and is a primary tool for measuring physical properties of the ocean.  Salinity is determined from electrical conductivity and is a measurement of the concentration of salt and other inorganic compounds in seawater.  Salinity and temperature are two of the most basic measurements used by ocean scientists.  The CTD temperature and salinity measurements are both used to determine seawater density, which is a primary driving force for major ocean currents.

CTDs are installed at Axial Base - near the seafloor (MJ03A), on the 200 m Shallow Profiler mooring including the Platform Interface Assembly (PC03A) and on the Science Pod, and on the Deep Profiler vehicle (DP03A). A CTD near the seafloor was installed in 2017 in the ASHES hydrothermal field as part of an NSF award to Dr. William Chadwick at NOAA-PMEL.

CTD instruments are also at the Slope Base site near the seafloor (MJ01A), on the 200 m Shallow Profiler mooring including the Platform Interface Assembly (PC01A) and on the Science Pod (SF01A) , and on the Deep Profiler vehicle (DP01A). At the Offshore site 600 m site they are a component of the Benthic Experiment Platform (LJ01C), the 200 m Shallow Profiler mooring including the Platform Interface Assembly (PC01B) and on the Science Pod (SF01B), and on the Deep Profiler vehicle (DP01B). At the Cable Oregon Shelf site, they are on the Benthic Experiment Platform (LJ01D)

CTDs were supplied by Sea-Bird; the models are SBE 16plusV2 and SBE 52MP (Deep Profiler vehicles).