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Abstract The history of over 100 years of observing the ocean is reviewed. The evolution of particular classes of ocean measurements (e.g., shipboard hydrography, moorings, and drifting floats) are summarized along with some of the discoveries and dynamical understanding they made possible. By the 1970s, isolated and “expedition” observational approaches were evolving into experimental campaigns that covered large ocean areas and addressed multiscale phenomena using diverse instrumental suites and associated modeling and analysis teams. The Mid-Ocean Dynamics Experiment (MODE) addressed mesoscale “eddies” and their interaction with larger-scale currents using new ocean modeling and experiment design techniques and a suite of developing observational methods. Following MODE, new instrument networks were established to study processes that dominated ocean behavior in different regions. The Tropical Ocean Global Atmosphere program gathered multiyear time series in the tropical Pacific to understand, and eventually predict, evolution of coupled ocean–atmosphere phenomena like El Niño–Southern Oscillation (ENSO). The World Ocean Circulation Experiment (WOCE) sought to quantify ocean transport throughout the global ocean using temperature, salinity, and other tracer measurements along with fewer direct velocity measurements with floats and moorings. Western and eastern boundary currents attracted comprehensive measurements, and various coastal regions, each with its unique scientific and societally important phenomena, became home to regional observing systems. Today, the trend toward networked observing arrays of many instrument types continues to be a productive way to understand and predict large-scale ocean phenomena. 

Abstract Solute exclusion during sea ice formation is a potentially important contributor to the Arctic Ocean inorganic carbon cycle that could increase as ice cover diminishes. When ice forms, solutes are excluded from the ice matrix, creating a brine that includes dissolved inorganic carbon (DIC) and total alkalinity (A_T). The brine sinks, potentially exporting DIC andA_Tto deeper water. This phenomenon has rarely been observed, however. In this manuscript, we examine a ~1 yearpCO₂mooring time series where a ~35‐μatm increase inpCO₂was observed in the mixed layer during the ice formation period, corresponding to a simultaneous increase in salinity from 27.2 to 28.5. Using salinity and ice based mass balances, we show that most of the observed increases can be attributed to solute exclusion during ice formation. The resultingpCO₂is sensitive to the ratio ofA_Tand DIC retained in the ice and the mixed layer depth, which controls dilution of the ice‐derivedA_Tand DIC. In the Canada Basin, of the ~92 μmol/kg increase in DIC, 17 μmol/kg was taken up by biological production and the remainder was trapped between the halocline and the summer stratified surface layer. Although not observed before the mooring was recovered, this inorganic carbon was likely later entrained with surface water, increasing thepCO₂at the surface. It is probable that inorganic carbon exclusion during ice formation will have an increasingly important influence on DIC andpCO₂in the surface of the Arctic Ocean as seasonal ice production and wind‐driven mixing increase with diminishing ice cover.