Live sub-surface oceanographic observations from an NDBC station's water-quality sensors: at each reported depth, water temperature, conductivity, salinity, dissolved oxygen as both saturation percent and concentration in ppm, chlorophyll, turbidity, pH, and redox potential. This is the water-column counterpart to noaa_marine_get_conditions, which returns surface meteorological and wave data — use this tool for what the water is doing below the surface, that one for weather and sea state at the buoy. It returns the most recent observation as one reading per reported depth, and most stations report a single depth while some report several at the same time; sensor coverage is sparse, most stations populating only water temperature and salinity, and any value the station did not report comes back null rather than a fabricated zero, as do latitude and longitude for a station absent from the NDBC active-stations list. Sub-surface sensors are on only a subset of NDBC stations, so find one with noaa_marine_find_stations using source="ndbc" and types=["water_quality"], which filters on NDBC's own water-quality catalog flag — the flag and actual .ocean availability drift, so this tool reads any station that serves the file and returns observations_not_found for one that does not.