Wind‐Driven Barotropic Velocity Dynamics on an Antarctic Shelf. Issue 5 (12th May 2020)

• Record Type: Journal Article
• Authors: McKee, Darren C.; Martinson, Douglas G.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 5(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-05-12
• Subjects: Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2019JC015771
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Reanalysis surface stress around the Antarctic continent is used to obtain the cross‐shelf sea surface height (SSH) gradient from the shallow water equations in the long‐wave limit, and the result is compared to the observed barotropic current sampled by current meters on the western Antarctic Peninsula shelf. Similar to the dynamics of SSH, intraseasonal velocity fluctuations (periods 3–100 days) largely consist of a circumpolar‐coherent wavenumber zero mode and of barotropic shelf waves; however, an important distinction from previous studies is the importance of second mode barotropic shelf waves in the velocity signal. Fluctuations with period 40–60 days are particularly energetic. This is partly due to strong fluctuations in the wavenumber zero mode at this period, as previously demonstrated in Drake Passage transport, but also due to excitement of the second mode barotropic shelf wave. After diagnosing the wind‐driven dynamics, some of their implications for shelf‐slope exchange are discussed. Firstly, it is shown that wintertime upwelling of warm water at a coastal canyon head is associated with a coastal SSH drop. Secondly, it is argued that the waves' subtle baroclinicity over the steep continental slope modifies isopycnal depth and affects shelf access to warm water. Plain Language Summary: An existing set of theoretical equations forced by winds along the Antarctic coastline is used to calculate the depth‐averaged current on the western Antarctic Peninsula shelf, and the result is compared to that measured by current meters. It is found that current variability on time scales longer than a few days but shorter than a season can be explained by the component of the winds that is uniform around the Antarctic continent summed with current variability generated by the winds over and east of the peninsula. Current variations with periods 40–60 days are particularly energetic and are driven by the component of the winds that is uniform around the continent in addition to winds in the southeastern Pacific sector. The large‐scale, wind‐driven fluctuations lead to upwelling of warm, deep water at the head of a coastal canyon. Key Points: On average, half of the intraseasonal velocity variance on the western Antarctic Peninsula shelf can be explained by wind‐driven dynamics The wind‐driven dynamics consist of a wavenumber zero mode and at least two barotropic shelf wave modes The large‐scale barotropic dynamics lead to upwelling of warm water at a coastal canyon head