Rocket Specific Impulse vs Jet Engine Specific Impulse

[Juhannuskokko]

I really can't seem to wrap my head around why the specific impulse on a rocket is so much lower than that on a jet. I know a jet engine has a larger supply of oxygen, but I don't see why that has such a huge effect.
I also know exhaust velocity plays a large part, but I would have thought that a rocket has higher-velocity exhaust.

 

[Dr. Courtney]

https://en.wikipedia.org/wiki/Specific_impulse

The bigger part is that jets have much larger exhaust velocities. A small part is that rockets carry their own oxidizers, so the mass includes the oxidizer in rocket specific impulse calculations, but not jet engine specific engine calculations.

 

[PeterDonis]

jets have much larger exhaust velocities

I think you mean effective exhaust velocity, not actual exhaust velocity, correct? As the Wikipedia article you linked to notes, the two can differ for jet engines by orders of magnitude.