If you throw kelp into a bucket and let it rot that's the smell you get.
Liquifies and yow rotten eggs. Not a pleasant way to use kelp.
And fish guts is even worse
The smell you can't get rid of. Better to bury it and let it rot sweetly in the ground.
Here are some pics of the kelp I got this spring and the coarse kelp meal I made for my container tomatoes as I do every year. The seaweed was a mix of stuff what happened to be on the beach. It was a bit dry and on a sunny day I spread it out to get really crispy. Then I put a good pair of gloves on and crush it up with my hands. This seems to be the easiest way for me to deal with raw kelp. I have chopped it when fresh which is a lot of work. It is even worse to try chopping or breaking when it is half dried.. you have to get it really crispy dry and crush it in the moment. High humidity or a bit of fog and it will absorb the moisture and gets leathery and impossible to break again.
The other option is to bag and let it rot for a full year and then use the powder as a semi-soluble fert. This doesn't smell much at all either.