The physics of rising air/bubbles displacing water below sealevel

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Homework Statement


Air accending from seabed reaches a fixed cap where it accumulates (e.g. an upside-down bucket). How can the air displace the water initially in the cap as it accumulates? What are the forces involved and how can it be explained?

The cap/bucket is sylinder shaped w/diameter 0,5m and height 1m hence the crossection area is 0,196 m2


Homework Equations


Buyoancy, the
Fb = (ρw- ρa)g Va =

Force= pressure* area F=PA
Pressure= ρgh



The Attempt at a Solution



Air is forced towards the top of bucket with the force at any height of (ρa=pM/RT kg/m3 - 1020 kg/m3)* 9,81* volume of air

I am thinking that bubbles of air accends and is trapped in the bucked it must have the energy to "push" some water out to take its place. It could be a relation to the fact that the water it is displacing is pressurizing the air, but how could this create the force to actually displace the water (which have the same pressure?)

Please guide me in the right direction, at least in the principles and logic I should seek to apply.


BR,

KIm
 
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Discussion

Do you not think that the bubble is ALREADY displacing water the entire time it rises, not just when it gets trapped in the bucket?