Long-term stabilization of reflective foams in sea water

Abstract

This work explores the challenge of making persistent foams in salt water to provide high reflectance. While stable foam is essential in the food industry and in fire fighting, this is the first work aimed at combining foam persistence with reflectance. One application is the use of oceanic foams to increase planetary albedo: extending foam lifetime moderates the energy required to maintain large areas of 'ocean mirror'. Two compositions to produce such foams in seawater are described. The first is based on high methyl ester pectin-type A gelatin complexes which produced foams with a reflectance of $0.5. The second produces stable foams using cellulose ethers and iota carrageenan gelling agents. These foams gelled in the presence of sea water to give measured reflectance of 0.65-0.75. Both had lifetimes, without wave action, beyond three months at which point the experiment ended. In contrast, single protein species such as gelatin B, whey protein isolate and albumin produced short-lived foams. Foam stability was measured by recording liquid drainage and foam height as a function of time. In the event that climate interventions are needed, such additives would be appropriate for nutrient-deficient ocean regions that support low levels of marine life.

The G4Foam Experiment: global climate impacts of regional ocean albedo modification

“…The reflectance of the foam was about 50 %, which is comparable to that of whitecaps. The creation of these stable microbubbles makes enhancing ocean albedo in this manner "feasible" (Aziz et al, 2014). However, there are a number of other potential risks associated with microbubble deployment, even if the feasibility issues are set aside.…”

“…Aziz et al identified foam lifetime of 3 months or more per microbubble as lasting long enough that the input of energy to create the microbubbles would not be prohibitive. After experimenting with protein-only solutions, Aziz et al (2014) added high methyl ester pectin to type A gelatin and created a foam in salt water, which was still intact and stable at the cessation of the experiment after 3 months. The reflectance of the foam was about 50 %, which is comparable to that of whitecaps.…”

“…Ocean albedo modification gained attention when Seitz (2010) suggested that since air-water and airsea interfaces are similarly refractive, dispersing microbubbles onto the surface of the ocean would reflect sunlight in much the same way as cloud droplets do. While engineering refractive or stable foams is commonly done and applied in both food science and firefighting, engineering a stable and refractive foam appropriate for a geoengineering scheme appeared fanciful until Aziz et al (2014) produced a long-lasting refractive foam made with biodegradable and non-toxic additives. Aziz et al identified foam lifetime of 3 months or more per microbubble as lasting long enough that the input of energy to create the microbubbles would not be prohibitive.…”

“…Robock (2011) also pointed out that a cooler ocean would serve as a more effective CO 2 sink, helping to offset the CO 2 increase that comes about as a feedback of warming. Other potentially attractive attributes of this technique include the possibility that it could be deployed exclusively in the 20 % of the world's oceans that are not biologically active (Aziz et al, 2014) and therefore have little impact on the biosphere, and that there would be no risk to ozone in the stratosphere. (a) Net clear-sky SW flux at top of atmosphere, which includes the effects of changes in radiation caused by changes in ocean surface albedo or land albedo (ice and snow), as well as stratospheric aerosols (stratospheric geoengineering) and (b) time series of global mean temperature.…”

“…Further study of the properties of the foam, including in ocean water with some turbulence, could provide information that would allow future modeling of the foam to include albedo fluctuations. This is the G4Foam experiment, which simulates a particular implementation of an idealized form of the technology described by Aziz et al (2014), where stable reflective foam, suitable for use as SRM in ocean regions with limited nutrients that support little marine life, is made in the laboratory.…”