Ocean bubbles under high wind conditions – Part 2: Bubble size distributions and implications for models of bubble dynamics
-
Published:2022-05-03
Issue:3
Volume:18
Page:587-608
-
ISSN:1812-0792
-
Container-title:Ocean Science
-
language:en
-
Short-container-title:Ocean Sci.
Author:
Czerski HelenORCID, Brooks Ian M.ORCID, Gunn Steve, Pascal Robin, Matei Adrian, Blomquist ByronORCID
Abstract
Abstract. Bubbles formed by breaking waves in the open ocean
influence many surface processes but are poorly understood. We report here
on detailed bubble size distributions measured during the High Wind Speed
Gas Exchange Study (HiWinGS) in the North Atlantic, during four separate
storms with hourly averaged wind speeds from 10–27 m s−1. The
measurements focus on the deeper plumes formed by advection downwards (at 2 m depth and below), rather than the initial surface distributions. Our
results suggest that bubbles reaching a depth of 2 m have already evolved to
form a heterogeneous but statistically stable population in the top 1–2 m of the ocean. These shallow bubble populations are carried downwards
by coherent near-surface circulations; bubble evolution at greater depths is
consistent with control by local gas saturation, surfactant coatings and
pressure. We find that at 2 m the maximum bubble radius observed has a very
weak wind speed dependence and is too small to be explained by simple
buoyancy arguments. For void fractions greater than 10−6, bubble size
distributions at 2 m can be fitted by a two-slope power law (with slopes of
−0.3 for bubbles of radius <80 µm and −4.4 for larger sizes).
If normalised by void fraction, these distributions collapse to a very
narrow range, implying that the bubble population is relatively stable and
the void fraction is determined by bubbles spreading out in space rather
than changing their size over time. In regions with these relatively high
void fractions we see no evidence for slow bubble dissolution. When void
fractions are below 10−6, the peak volume of the bubble size
distribution is more variable and can change systematically across a plume
at lower wind speeds, tracking the void fraction. Relatively large bubbles
(80 µm in radius) are observed to persist for several hours in some
cases, following periods of very high wind. Our results suggest that local
gas supersaturation around the bubble plume may have a strong influence on
bubble lifetime, but significantly, the gas in the bubbles contained in the
deep plumes cannot be responsible for this supersaturation. We propose that
the supersaturation is predominately controlled by the dissolution of
bubbles in the top metre of the ocean, and that this bulk water is then
drawn downwards, surrounding the deep bubble plume and influencing its
lifetime. In this scenario, oxygen uptake is associated with deep bubble
plumes but is not driven directly by them. We suggest that as bubbles move
to depths greater than 2 m, sudden collapse may be more significant as a
bubble termination mechanism than slow dissolution, especially in regions of
high void fraction. Finally, we present a proposal for the processes and
timescales which form and control these deeper bubble plumes.
Funder
Natural Environment Research Council National Science Foundation
Publisher
Copernicus GmbH
Subject
Cell Biology,Developmental Biology,Embryology,Anatomy
Reference66 articles.
1. Al-Lashi, R. S., Gunn, S. R., and Czerski, H.: Automated Processing of
Oceanic Bubble Images for Measuring Bubble Size Distributions underneath
Breaking Waves, J. Atmos. Ocean. Tech., 33,
1701–1714, https://doi.org/10.1175/jtech-d-15-0222.1, 2016. 2. Al-Lashi, R. S., Gunn, S. R., Webb, E. G., and Czerski, H.: A Novel
High-Resolution Optical Instrument for Imaging Oceanic Bubbles, IEEE J. Ocean. Eng., 43, 72–82, https://doi.org/10.1109/joe.2017.2660099, 2018. 3. Anguelova, M. D. and Huq, P.: Characteristics of bubble clouds at various
wind speeds, J. Geophys. Res.-Oceans, 117, C03036,
https://doi.org/10.1029/2011jc007442, 2012. 4. Atamanchuk, D., Koelling, J., Send, U., and Wallace, D. W. R.: Rapid
transfer of oxygen to the deep ocean mediated by bubbles, Nat. Geosci.,
13, 232–237, https://doi.org/10.1038/s41561-020-0532-2, 2020. 5. Blenkinsopp, C. E. and Chaplin, J. R.: Void fraction measurements in
breaking waves, P. Roy. Soc. A-Math. Phy., 463, 3151–3170, https://doi.org/10.1098/rspa.2007.1901, 2007.
Cited by
5 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|