Technical note: Determining Arctic Ocean cold halocline and cold halostad layer depths based on vertical stability

• Main Authors: Metzner, Enrico P., Salzmann, Marc
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; Arctic; Arctic Ocean; Canada; Greenland; Svalbard; canada basin; Sea ice
• Online Access: https://doi.org/10.5194/egusphere-2023-106; https://noa.gwlb.de/receive/cop_mods_00065077; https://egusphere.copernicus.org/preprints/egusphere-2023-106/egusphere-2023-106.pdf

The Arctic Ocean cold halocline layer (CHL) separates the cold surface mixed layer (SML) from the underlying warm Atlantic water, and thus provides a precondition for sea ice formation. Here, we introduce a new method in which the CHL base depth is diagnosed from vertical stability and compare it to two existing methods. Vertical stability directly affects vertical mixing and heat exchange. When applied to measurements from ice-tethered profilers, ships, and moorings, the new method for estimating the CHL base depth provides robust results with few artifacts. Comparatively large differences between our new method and two existing methods for detecting the CHL base depth were found in regions which are most prone to a CHL retreat in a warming climate. CHL base depth exhibits a seasonal cycle with a maximum depth in winter and also spring, when the SML depth is also at its maximum, but the amplitude of the CHL base depth's seasonal cycle is lower than for the SML for all three methods as expected. We also propose a novel method for detecting the cold halostad layer and study the seasonal cycle employing conservative assumptions to avoid a misclassification (including a lower bound of 50 m for the thickness). Detection of a cold halostad layer was largely confined to the Canada Basin and to the regions off the eastern coast of Greenland and also Svalbard.