Freshwater input and vertical mixing in the Canada Basin’s seasonal halocline: 1975 versus 2006-2012

• Published in: Journal of Physical Oceanography
• Main Authors: Rosenblum, Erica, Stroeve, Julienne, Gille, Sarah T, Tremblay, L Bruno, Lique, Camille, Fajber, Robert, Galley, Ryan, Barber, David, Loureiro, Thiago, Lukovich, Jennifer
• Other Authors: Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU]Sciences of the Universe [physics]; Arctic; Canada; canada basin; Sea ice
• Online Access: https://hal.science/hal-04203741; https://hal.science/hal-04203741/document; https://hal.science/hal-04203741/file/phoc-JPO-D-21-0116.1.pdf; https://doi.org/10.1175/JPO-D-21-0116.1

The seasonal halocline impacts the exchange of heat, energy, and nutrients between the surface and the deeper ocean, and it is changing in response to Arctic sea ice melt over the past several decades. Here, we assess seasonal halocline formation in 1975 and 2006-2012 by comparing daily, May to September, below-ice salinity profiles collected in the Canada Basin. We evaluate differences between the two time periods using a one-dimensional (1D) bulk model to quantify differences in freshwater input and vertical mixing. The 1D model metrics indicate that two separate factors contribute similarly to stronger stratification in 2006-2012 than in 1975: (1) larger surface freshwater input and (2) less vertical mixing of that freshwater. The first factor is mainly important in August-September, consistent with a longer melt season in recent years. The second factor is mainly important from June until mid-August, when similar levels of freshwater input in 1975 and 2006-2012 are mixed over a different depth range, resulting in different stratification. These results imply that decadal changes to ice-ocean dynamics, in addition to freshwater input, significantly contribute to the stronger seasonal stratification in 2006-2012 than in 1975. The findings highlight the need for near-surface process studies to elucidate the roles of lateral processes and ice-ocean momentum exchange on vertical mixing.