Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This dataset contains dissolved oxygen time series in two formats: a combined table and individual tables by deployment. The combined table, “986667_v1_oxygen-time-series.csv,” includes the contents of all 60 CSV files contained within Oxygen_time_series-per-deployment.zip, along with deployment metadata from deployment_metadata.csv.

Optodes were deployed on moorings within the boundary currents entering and exiting the Labrador Sea, specifically, the Labrador Current in the western Labrador Sea (moorings C1_b, C2_b, C3_b, K7, K8, K9, K10, DSOW 2, and DSOW5), the West Greenland Current in the eastern Labrador Sea (LS1, LS3, LS4, LS5, LS6, LS7, and LS8), and the East Greenland Current in the western Irminger Sea (moorings  CF1, CF3, CF4, CF5, CF6, CF7, M1, M2, and M3). These moorings were part of the Overturning in the Subpolar North Atlantic Program (OSNAP) mooring array.  Optodes were set to sample every 15 minutes and were deployed from June 2020 - June 2022.  LS1, LS3, LS4, LS5, LS6, LS7, and LS8 in the eastern Labrador Sea. Depths of oxygen data collection on the moorings ranged from as shallow as 50 m to as deep as 3500 m, selected to cover the seasonally-stratified, near-surface waters, Labrador Sea Water, Northeast Atlantic Deep Water, and Denmark Strait Overflow Water masses.

Moored optode oxygen time series processing, calibration, and validation protocols are described in detail in Miller et al. (2024; 10.3389/fmars.2024.1441976). All oxygen time series were corrected for the instantaneous pressure response (Bittig et al., 2018; 10.3389/fmars.2017.00429) and "irreversible" drift using calibrated oxygen profiles collected on "cal-dip" casts, which are shipboard conductivity-temperature-depth-oxygen (CTD-oxygen) casts on which the optodes are strapped to the CTD rosette and dual CTD-oxygen and optode-oxygen profiles are obtained, and  "cal-casts", calibrated CTD-oxygen casts taken in the vicinity of the in-water optodes both upon mooring deployment and upon mooring recovery. Optodes deployed at depths greater than 1000 m were checked and where applicable, corrected for pressure-related "reversible" drift. Calibrated oxygen time series were validated against cal-cast profiles external to the calibration process as well as BGC-Argo oxygen profiles collated within a 100 km radius of each mooring.

* 60 csv files for the oxygen time series (one per deployment) were zipped and attached to this dataset as supplemental file Oxygen_time_series-per-deployment.zip.
* The tables within the 60 csv files were concatenated into the combined table

In the combined table 986667_v1_oxygen-time-series.csv the following changes were also made:
* Additional metadata added from a supplied file "Metadata_with_added_filenames.xlsx"
* Date converted to ISO 8601 format
* Column "TIME" converted to ISO 8601 DateTime with timezone (UTC) format and renamed "ISO_DateTime_UTC"

Supplemental file "deployment_metadata.csv" added from contents of submitted file "Metadata_with_added_filenames.xlsx"
* Duplicate serial number column removed
* Dates converted to ISO format
* Space removed from value in Filename column "CF6_ 1500m_sn204363.csv" so it matches the provided file

NSF Award Abstract:
Every winter, frigid winds blowing eastward from the North American continent cool the surface waters of the Labrador Sea, which is situated between Canada and Greenland. As the ocean cools, oxygen and carbon dioxide are mixed from the atmosphere into a thick layer of water that ultimately spreads southward to fill a large volume of the North Atlantic and beyond. The presence of this water mass prevents the North Atlantic anywhere from becoming completely devoid of oxygen. Vertical mixing in the Labrador Sea also redistributes carbon dioxide into the deep ocean, where it can remain for hundreds of years, preventing it from contributing to the greenhouse effect. Yet, the processes governing the uptake of gases by the ocean are not well understood or quantified. Given that, over the last century, the ocean has become steadily more depleted in oxygen while also absorbing a large fraction of anthropogenic carbon dioxide, observing gas exchange processes is essential for understanding and predicting the evolution of the ocean and climate system. The circulation of the Labrador Sea has been monitored since 2014 with an array of instrumented cables extending from the seafloor to nearly the ocean surface. This project adds gas sensors to this array to investigate the rates and processes governing gas exchange. Through this project, a student and postdoc will be trained in interdisciplinary oceanography with a rich network of international collaborators. Responding to the need to increase public ocean literacy, the project scientists will work with University of Rhode Island’s Inner Space Center to broadcast live, interactive science sessions to educators at partner high schools and will follow-up with in-person science cafés at three participating schools.

Given the unique role of the Labrador Sea in providing a pathway for oxygen (O2) and carbon dioxide (CO2) to enter the intermediate depths of the ocean, a quantification and mechanistic understanding of the gas uptake and transport in the basin is a leading scientific priority. Oxygenation of Labrador Sea water prevents large-scale hypoxia from developing anywhere in the Atlantic Ocean and anthropogenic CO2 storage in the basin is the highest in the global ocean. The assumption that, in the Atlantic Ocean, O2 and CO2 uptake and their variability are tied to the dynamics of heat loss and the overturning circulation pervades the literature but has never been evaluated on the basis of direct observations. Thus, GOHSNAP (Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program) addresses this gap and the urgent need to better understand interactions between gas uptake, transport, and the overturning circulation. Specifically, this program will provide a continuous 2-year record of the trans-basin, full water column transport of O2 across the southern boundary of the Labrador Sea, leveraging the mooring infrastructure of the US-lead, international Overturning in the Subpolar North Atlantic Program (OSNAP). The addition of O2 sensors at various depths on this array, supplemented by observations collected by autonomous platforms will allow for the quantification of O2 export from the Labrador Sea. The data will further be used to empirically model carbon concentrations and estimate carbon export. Proposed instruments will also measure the mixed layer O2 and pCO2 for two winters, from which air-sea gas exchange will be calculated and compared against analogous observations in the convective interior of the Labrador Sea.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.