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Abstract Starting in 2012, the eastern subpolar North Atlantic experienced the strongest surface freshening in the past 120 years. It is yet unknown whether this salinity anomaly propagated downward into the water column and affected the properties of the boundary currents of the subpolar gyre, which could slow down the overturning. Here, we investigate the imprint of this salinity anomaly on the warm and saline Irminger Current (IC) in the decade thereafter. Using daily mooring data from the IC covering the period 2014–2022 combined with hydrographic sections across the adjacent basins from 1990, the evolving signal of the salinity anomaly over the water column and its imprint on the transport variability is studied. We find that due to the salinity anomaly, the northward freshwater transport of the IC increased by 10 mSv in summer 2016 compared to summer 2015. In 2018, the salinity anomaly covered the water column down to 1,500 m depth. Hydrographic sections across the basin showed that this recent freshening signal spread across the Irminger Sea. Overall, the freshwater transport of the IC increased by a factor of three between 2014–2015 and 2021–2022. The associated density decrease over the upper 1,500 m of the water column resulted in an increase in the northward transport of waters lighter thanσ₀ = 27.55 kg m⁻³from 1.7 to 4.2 Sv. This change in northward IC transport by density class may impact the characteristics of the overturning in the Northeastern Atlantic, its strength and the density at which it peaks. 

Increasing interest in the deployment of optical oxygen sensors, or optodes, on oceanographic moorings reflects the value of dissolved oxygen (DO) measurements in studies of physical and biogeochemical processes. Optodes are well-suited for moored applications but require careful, multi-step calibrations in the field to ensure data accuracy. Without a standardized set of protocols, this can be an obstacle for science teams lacking expertise in optode data processing and calibration. Here, we provide a set of recommendations for the deployment andin situcalibration of data from moored optodes, developed from our experience working with a set of 60 optodes deployed as part of the Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program (GOHSNAP). In particular, we detail the correction of drift in moored optodes, which occurs in two forms: (i) an irreversible, time-dependent drift that occurs during both optode storage and deployment and (ii) a reversible and pressure-and-time-dependent drift that is detectable in some optodes deployed at depths greater than 1,000 m. The latter is virtually unidentified in the literature yet appears to cause a low-bias in measured DO on the order of 1 to 3µmol kg⁻¹per 1,000 m of depth, appearing as an exponential decay over the first days to months of deployment. Comparisons of our calibrated DO time series against serendipitous mid-deployment conductivity-temperature-depth (CTD)-DO profiles, as well as biogeochemical (BGC)-ARGO float profiles, suggest the protocols described here yield an accuracy in optode-DO of ∼1%, or approximately 2.5 to 3µmol kg⁻¹. We intend this paper to serve as both documentation of the current best practices in the deployment of moored optodes as well as a guide for science teams seeking to collect high-quality moored oxygen data, regardless of expertise. 

This dataset contains bottle-calibrated dissolved oxygen (DO) profiles collected from Conductivity Temperature Depth (CTD) casts during cruises in 2020 (AR45) and 2022 (AR69-03) to recover and redeploy Overturning in the Subpolar North Atlantic Program (OSNAP) moorings in the Labrador Sea and western Irminger Sea. DO profiles were used in conjunction with oxygen bottle measurements (Winklers) to produce a post-cruise oxygen-calibrated CTD product for scientific use as part of Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program (GOHSNAP), which has added moored oxygen sensors to the OSNAP mooring array, beginning in 2020. This documentation contains overviews of CTD data collection and processing and of the oxygen sensor calibration method. For each cruise, we provide a summary of relevant cruise events, oxygen sensor calibration results, and issues/problems associated with oxygen data collected. 

This dataset contains discrete sample measurements of dissolved oxygen, dissolved inorganic carbon, and total alkalinity collected during cruises in 2020 (AR45) and 2022 (AR69-03) to recover and redeploy Overturning in the Subpolar North Atlantic Program (OSNAP) moorings in the Labrador Sea and western Irminger Sea. Samples in this dataset were collected as part of Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program (GOHSNAP), which has added moored oxygen sensors to the OSNAP mooring array, beginning in 2020. We provide the discrete sample measurements alongside salinity- and oxygen- calibrated Conductivity Temperature Depth (CTD) and oxygen sensor data from the depths where Niskin bottles were closed for sample collection.