The influence of surfactants on the mechanisms of ocean bubble generation, and the consequences for air-sea gas transfer.

Lead Research Organisation: University College London
Department Name: Mechanical Engineering

Abstract

This project will examine how natural ocean substances affect the production of bubbles in the ocean. Bubbles are important for many of the processes that happen in the top few metres of the ocean. They are mostly generated by breaking waves, and although the larger ones rise to the surface very quickly and burst, the smaller bubbles can remain trapped in the ocean for several minutes. Both large and small bubbles are important for the transfer of gas from the atmosphere to the ocean, since they provide lots of surface area where the gas inside the bubble can touch the ocean and may dissolve in it. Breaking waves generate a considerable amount of background noise in the ocean, because every newly-formed bubble emits a pulse of sound. Bubbles can also absorb and redirect sound that comes from other sources, and so knowledge of the bubbles present is important for understanding how sonar pulses and other sound from below the surface bounces off the top of the ocean. As modelling of weather and the effect of high winds and storms improves, an increasing level of detail is needed to understand the physics of the ocean surface properly. We now understand that very small events like bubble production can make a significant difference to larger processes in the ocean like gas absorption, so knowledge of the number and size of bubbles that exist in the ocean is becoming increasingly important. Bubbles underneath breaking waves are formed because of the intense turbulence that exists for the first second or two after wave breaking. This turbulence will distort the bubbles and may break a large bubble into two or more smaller bubbles. These smaller bubbles may fragment in turn, and the process continues until the turbulence is no longer strong enough to break the bubbles up. In addition, bubbles may bump into each other and coalesce, making larger bubbles out of two smaller ones. All these processes determine how many bubbles there are just after a wave breaks and how big they are, and then this fixed population of bubbles rises and dissolves and changes more slowly with time. The distortion of a bubble depends on the strength of the turbulence and the way the bubble surface behaves. The surface tends to reduce the distortion and so prevent the bubble breaking up. Previous research has investigated bubble splitting in clean fresh water and salt water, but natural ocean water contains many other substances, which are generated by the small organisms in the water (for example algae, tiny plants and tiny animals). Many of these substances will stick to bubble surfaces and may change how the bubble surface behaves, including the probability of splitting and rejoining. This fellowship project will look at single bubbles splitting into two bubbles and pairs of bubbles joining together to form one bigger bubble in turbulence, and compare what happens with and without the natural ocean chemicals present. Then, artificial waves will be generated and allowed to break in a wave tank with and without the additional chemicals , so that we can see the changes in the number and size of bubbles that are caused by the chemicals. Finally, the bubbles in real breaking waves at sea will be studied to look for the same effects. The overall results will help us understand how the natural chemistry of the ocean could affect how the ocean and the atmosphere interact. Ocean chemistry can be very different in different regions of the ocean, and this is not currently taken into account in the measurement of natural bubble populations and their effects.

Publications

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Related Projects

Project Reference Relationship Related To Start End Award Value
NE/H016856/1 04/10/2010 22/11/2013 £305,156
NE/H016856/2 Transfer NE/H016856/1 01/12/2013 30/09/2014 £93,184
 
Title Presented a range of BBC TV programmes, on general physics and earth science 
Description I'm including these because NERC gave me a no-cost extension to my fellowship specifically in order to make these possible, and I'm very grateful for that. Orbit: Earth's Extraordinary Journey, a three-part series on BBC Two. (March 2012), co-presented with Kate Humble. Operation Iceberg, a two-part series on BBC Two (October 2012) The Transit of Venus, BBC Two (June 2012) Horizon[13] Stargazing Challenges, (BBC Two) Dara Ó Briain's Science Club, two series of 6 programmes each (BBC Two) The Secret Life of the Sun, BBC Two (July 2013) Pop! The Science of Bubbles, BBC Four, April 2013 The £10 Million Challenge, a Horizon to launch the Longitude Prize 2014 (BBC2) What's Wrong with Our Weather?, July 2014, Horizon, BBC2, co-presented with meteorologist John Hammond Super Senses: The Secret Power of Animals, 3x1hr programmes on BBC2 I also have a regular column in BBC Focus magazine and was shortlisted for columnist of the year at the 2014 PPA Awards 
Type Of Art Film/Video/Animation 
Year Produced 2013 
Impact Visibility of a female scientist in a very male-dominated area, significant contribution to public understanding of these topics. 
 
Description Very little is known about how air bubbles break up in turbulent water. Experiments from this fellowship are currently being continued by a PhD student, and the data collected is challenging our existing understanding of the bubble break-up process. This is important in a range of fields, particularly oceanography (my focus) and also for industrial processes and medical bioreactors (a topic that I collaborate on).
Exploitation Route This is mainly of use to the oceanography community and those interested in the design of shaken and stirred bioreactors. We are building fundamental understanding, so it does not yet have an immediate real-world use for others outside the academic community. However, it will contribute to our understanding of weather and climate.
Sectors Environment

 
Description Departmental studentship
Amount £80,000 (GBP)
Organisation University College London 
Sector Academic/University
Country United Kingdom
Start 12/2014 
End 12/2017
 
Description Participation in large-scale theatre performance discussing our research 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact I and two PhD students were part of an immersive theatre experience called New Atlantis, which was open to the public for seven nights. The aim of the performance was to get the audience to consider climate change and water issues, by directly engaging with researchers in a theatrical situation. We took real equipment and real data, and were one of several groups of researchers participating in the performance.

http://www.theartsdesk.com/theatre/new-atlantis-crystal
Year(s) Of Engagement Activity 2015
URL http://www.newhamrecorder.co.uk/entertainment/theatre/immersive_victoria_docks_play_gives_chance_to_...