Optical measurements of bubble size distributions at 6-9 m depths generated by large-scale breaking waves in the Southern Ocean

Kaylan Randolph, University of Connecticut, kaylan.randolph@uconn.edu (Presenter)
Heidi Dierssen, University of Connecticut, heidi.dierssen@uconn.edu
Michael Twardowski, WET Labs, mtwardo@wetlabs2.com
Alejandro Cifuentes Lorenzen, University of Connecticut, alejandro.cifuentes@uconn.edu
Christopher Zappa, Lamont-Doherty Earth Observatory, zappa@ldeo.columbia.edu

Submerged bubble populations are recurrently introduced into the surface ocean by wind-generated breaking waves and can have long residence times in the water column. Bubble plumes influence the optical properties of the ocean and ocean color reflectance, the scavenging of organic material, mixing processes, and aerosol production. Optical techniques were used to determine bubble size distributions (BSDs) from 1-125 μm radius at 6-9 m depths under sustained high wind conditions (13-15 m s-1, Hs 3-5 m) and during large-scale wave breaking in the Southern Ocean as a part of the Southern Ocean Gas Exchange Experiment. Deep bubble plumes were identified using multiple instruments which measure the optical volume scattering function, in particular at the very near forward angles and at the critical scattering angle for bubbles between 60° and 80°. Upper ocean dynamics coupled with modeling results revealed intense wave breaking and the potential for deep penetration (6-9 m) of bubbles. Concomitant enhancements in particle size distribution and critical angle scattering during wave breaking events were used to differentiate the concentration of bubbles from other particles. To a first order, the bubble populations followed a power law distribution, decreasing from small to large sizes. A power law fit to the bubble size distributions produced mean slope values, ξ, of 3.6-4.7, within the range of previously published slopes, but slightly steeper. Concurrent measurements of the acoustic backscatter anomaly suggest that these measurements were at the base of the bubble plume, consistent with the presence of fewer bubbles and steeper slopes. The composition of bubbles in a 50 s wave breaking event revealed a general steepening trend in ξ over time, indicating a loss of larger bubbles. Organic material was present in the water column and likely provided an organic coating to stabilize bubbles.

Presentation Type:  Poster

Session:  Coupled Processes at Land-Atmosphere-Ocean Interfaces   (Mon 4:00 PM)

Associated Project(s): 

• Dierssen, Heidi: Differentiating sources of backscattering in the Southern Ocean: calcite, bubbles, and other optical constituents ...details

Poster Location ID: 71