Alaska compendium of ocean profile data [ACOD]: Archival CTD and nutrient hydrography from NOAA's EcoFOCI, EMA, and predecessor programs

This oceanographic data product represents a multi-decade collection of shipboard hydrography in Alaska waters, sampled by select programs of the US National Oceanic and Atmospheric Administration (NOAA).  Data types include basic physical (temperature and salinity) and chemical (dissolved nutrient) properties collected as profiles from oceanographic research vessels.  The geographic extent includes coastal and offshore areas of the Gulf of Alaska, Bering Sea, and the Chukchi Sea.  Temporal coverage is 1974-2021 (temperature and salinity) or 2001-2021 (nutrient data).  Data in this product were collected under programs associated with the NOAA Pacific Marine Environmental Laboratory (PMEL) and Alaska Fisheries Science Center (AFSC).  Three major data collection efforts are represented: (1) the Ecosystems and Fisheries-Oceanography Coordinated Investigations (EcoFOCI) program (PMEL and AFSC); (2) the Ecosystem Monitoring and Assessment program led by AFSC and supported by EcoFOCI; and (3) historical data collected between the founding of PMEL in 1973 and the beginning of EcoFOCI in 1984.  Data were pooled across cruises and years into a concatenated, single-point-of-access product, with additional quality control applied to cruise records, profile data, and nutrient data.  Simple derived quantities and indexing are included for ease of use.  The data product is fully described in Mordy et al. (2025, "A compendium of temperature and salinity profiles and discrete nutrients from selected NOAA programs in Alaska," Scientific Data).

Methods
Sampling methods and instrumentation have varied across years and sources.  Temperature and salinity profiles (1974-2021) were collected using profiling Conductivity and Temperature with Depth (CTD) instruments.  Early CTD data quality in highly stratified waters was often compromised due to rapid profiling through a sharp thermocline; salinity data prior to April 1987 are of lower quality in some cruises and should be used with care.  Since approximately 1988, the sampling instrument of choice has been the SeaBird Electronics (SBE) 911plus system.  On some earlier EMA cruises (prior to 2018), an SBE25 was used.  Sampling during the EcoFOCI program involved standardized descent rates that increase with depth, filtering and binning to standard 1 dbar resolution, additional post-processing to ensure data integrity, and consistent rules for surface interpolation.  Salinity was reported in units of parts per thousand prior to August 1995 and PSS-78 thereafter.  Dissolved inorganic nutrient data (2001-2021; phosphate, silicic acid, nitrate, nitrite, and ammonium) were sampled by PMEL/EcoFOCI or EMA.  Samples were collected at discrete depths from Niskin bottles attached to the CTD rosette and were measured using autoanalyzers with segmented flow.  Samples were processed by PMEL or at the University of Washington Marine Chemistry Laboratory for EMA data 2003-2011.  Protocols utilized at all locations were comparable and included calibration of labware, preparation of primary and secondary standards, and corrections for blanks, refractive index and carryover. Ammonium was analyzed on most, but not all cruises.