Synthesis Product for Ocean Time-Series (SPOTS) – A ship-based biogeochemical pilot
Authors: Lange Nico , Fiedler Björn , Álvarez Marta , Benoit-Cattin Alice , Benway Heather , Buttigieg Pier L. , Coppola Laurent , Currie Kim , Flecha Susana , Honda Makio , Huertas I. Emma , Lauvset Siv K. , Muller-Karger Frank , Körtzinger Arne , O'Brien Kevin M. , Ólafsdóttir Sólveig R. , Pacheco Fernando C. , Rueda-Roa Digna , Skjelvan Ingunn , Wakita Masahide , White Angelicque , Tanhua Toste 
Published: July 2023

Abstract. The presented pilot for the “Synthesis Product for Ocean Time-Series” (SPOTS) includes data from 12 fixed ship-based time-series programs. The related stations represent unique marine environments within the Atlantic Ocean, Pacific Ocean, Mediterranean Sea, Nordic Seas, and Caribbean Sea. The focus of the pilot has been placed on biogeochemical essential ocean variables: dissolved oxygen, dissolved inorganic nutrients, inorganic carbon (pH, total alkalinity, dissolved inorganic carbon, and partial pressure of CO2), particulate matter, and dissolved organic carbon. The time-series used include a variety of temporal resolutions (monthly, seasonal, or irregular), time ranges (10 – 36 years), and bottom depths (80 – 6000 m), with the oldest samples dating back to 1983 and the most recent one corresponding to 2021. Besides having been harmonized into the same format (semantics, ancillary data, units), the data were subjected to a qualitative assessment in which the applied methods were evaluated and categorized. The most recently applied methods of the time-series programs usually follow the recommendations outlined by the Bermuda Time-Series Workshop report (Lorenzoni and Benway, 2013) which is used as the main reference for “biogeochemical best-practices”. However, measurements of dissolved oxygen and pH in particular, still show room for improvement. Additional data-quality descriptors include precision and accuracy estimates, indicators for data variability, and offsets compared to a reference and widely recognized data product for the global ocean: the “GLobal Ocean Data Analysis Project”. Generally, these descriptors indicate a high level of continuity in measurement quality within time-series programs and a good consistency with the GLobal Interior Ocean Carbon Data, even though robust comparisons to the latter are limited. The data are available as (i) a merged comma-separated file that is compliant with the World Ocean Circulation Experiment (WOCE) exchange format and ii) a format dependent on user queries via the ERDDAP server of the Global Ocean Observing System (GOOS). The pilot increases the data utility, findability, accessibility, interoperability, and reusability following the FAIR philosophy, enhancing the readiness of biogeochemical time-series. It facilitates a variety of applications that benefit from the collective value of biogeochemical time-series observations and forms the basis for a sustained time-series living data product, SPOTS, complementing relevant products for the global interior ocean carbon data (GLobal Ocean Data Analysis Project), global surface ocean carbon data (Surface Ocean CO2 Atlas; SOCAT), and global interior and surface methane and nitrous oxide data (MarinE MethanE and NiTrous Oxide product). Aside from the actual data compilation, the pilot project produced suggestions for reporting metadata, implementing quality control measures, and making estimations about uncertainty. These recommendations aim at encouraging the community to adopt more consistent and uniform practices for analysis and reporting and at updating these practices regularly. The detailed recommendations, links to the original time-series programs, the original data, their documentation, and related efforts are available on the SPOTS website. This site also provides access to the data product (DOI: 10.26008/1912/bco-dmo.896862.1, Lange et al., 2023) and ancillary data.