First paper published from cruise results reveals widespread submesoscale instabilities within the ACC

Kate Adams, the SMILES observational post-doc, has recently published the first paper arising directly from the SMILES cruise. The paper details our observations of the submesoscale structures found around the periphery of the eddy and highlights their potential importance to vertical circulation at fronts.

Kate writes, ‘At the start of the 2015 SMILES research cruise, we took measurements onboard the RRS James Clark Ross of a meander along the Antarctic Circumpolar Current. As the cruise went on we monitored this meander with daily snapshots of sea surface temperature and sea surface height that were sent to us from the Plymouth Marine Laboratory (NEODAAS). Over time the meander grew sharper and more pronounced and the team decided to perform a drifter-following survey along the front defining the edge of the meander. Our hypothesis was that submesoscale motions, with length scales of only 1 km, may be active along this sharp front as has been found in numerical modeling studies. So, three drifters were released in the northwest corner of the meander and followed with the ship towing an instrument package capable of measuring conductivity, temperature and depth (CTD).

To the surprise of everyone onboard, the meander separated from the ACC during the survey and formed a cold-core cyclonic eddy. We developed a mathematical framework for the vertical velocity along the drifter track which showed vigorous upwelling and subsequent downwelling. Rapid changes in temperature and salinity suggest that modification of mode water may occur during the formation of mesoscale eddies on time scales ~ 1 day. Eddies in the Southern Ocean are important for transporting heat, nutrients and also energy to the north and south of the ACC. The observations and analyses of the drifter-following survey dataset are detailed in a recent accepted manuscript in the Journal of Physical Oceanography.


K.Adams, P.Hosegood, J. Taylor, J.Sallée, S.Bachman, R.Torres and M.Stamper 2017: Frontal circulation and submesoscale variability during the formation of a Southern Ocean mesoscale eddy. J.Phys. Oceanogr. doi:10.1175/JPO-D-16-0266.1, in press.

Link: http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-16-0266.1

Figure 1. Vertical cross-front sections of (a) potential density anomaly (kg m-3), (b) temperature (◦C), (c) salinity, (d) along-front velocity and (e) cross-front velocity for Seasoar legs N to S. The start time since the start of leg N is reported above (a) in hours. Sections are oriented such that cross-front distance increases away from the meander and eddy center. Mixed layer depth (MLD) defined as a 0.01 kg m-3 density difference from the surface is white in (a). The drifter location during each leg is at cross-front distance = 0 and depth = 50 m, shown at the intersection of gray lines in (c) and (d) (Figure 7 in Adams et al., 2017).