EGU21-12470, updated on 04 Mar 2021
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Effects of lead width variation, re-freezing and mixing events on lead water structure in the central Arctic

Daiki Nomura1, Alison Web2, Yuhong Li3, Manuel Dall’osto4, Katrin Schmidt5, Elise Droste6, Emelia Chamberlain7, Yusuke Kawaguchi8, Jun Inoue9, Ellen Damm10, and Bruno Delille11
Daiki Nomura et al.
  • 1Hokkaido University, Hakodate, Japan (
  • 2University of Warwick, UK
  • 3Third Institute of Oceanography, MNR, China
  • 4Institute of Marine Science, Spain
  • 5University of Plymouth, UK
  • 6University of East Anglia, UK
  • 7University of California, San Diego, USA
  • 8University of Tokyo, Japan
  • 9National Institute of Polar Research, Japan
  • 10Alfred Wegener Institute, Germany
  • 11University of Liege, Belgium

We undertook a lead survey during the international drift campaign MOSAiC, Leg 5 (from 22 August to 17 September 2020) to understand the effects of lead width variation, re-freezing, and mixing events on lead water vertical structure. At the beginning of the survey period, the freshwater layer was occupied for the top 1 m depth and there were strong vertical gradients in temperature, salinity, and dissolved oxygen (DO) within 1 m depth: from 0.0°C to –1.6°C for temperature, from 0.0 to 31.4 psu for salinity, and 10.5 to 13.5 mg L–1 for DO. A strong DO minimum layer corresponded with a salinity of 25 psu, and usually occurred at the freshwater–seawater interface at approx. 1 m depth, most likely as a result of an accumulation of organic matter and ongoing degradation/respiration processes at this interface. However, during the survey period, these strong gradients weakened and reduced the freshwater layer thickness (FLT). In the first half of the sampling period (until 4 September), FLT changed due to variations in lead width: as lead width increased, FLT decreased due to a stretching of the freshwater layer. In the second half of the sampling period, FLT was controlled by the surface ice formation (re-freezing) and mixing processes along the lower boundary of the freshwater layer. Surface ice formation removed freshwater and the formation of surface ice (about 0.2 m thick) explains 20% of the reduction of FLT. The remaining 80% of the reduction of FLT was due to the mixing process within the water column that was initiated by cooling and re-freezing. This mixing process diluted the salinity from 31.6 to 29.3 psu in the water below freshwater layer towards the end of the survey period. Our results indicate that lead water structure can change rapidly and dynamically and that this has significant effects on the biogeochemical exchange between lead systems and the atmosphere.

How to cite: Nomura, D., Web, A., Li, Y., Dall’osto, M., Schmidt, K., Droste, E., Chamberlain, E., Kawaguchi, Y., Inoue, J., Damm, E., and Delille, B.: Effects of lead width variation, re-freezing and mixing events on lead water structure in the central Arctic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12470,, 2021.