While Fjords are not particular common, and account for just 0.1% of the ocean surface area, they store 11-12% of the oceans carbon. Put differently, there are thought to be roughly 18 million tons of carbon stored in fjords around the world. To put it in perspective, that is a similar area to a speck of zest compared to the whole orange.
Importantly though, this carbon storage is not permanent. It is relatively delicate. They are carbon sinks during interglacial periods, but become carbon sources during glacial periods.
Now it is true that many humans are concerned that we have already basically released enough carbon to stop the next glacial period, but this is still something that we are not sure about. What is clear, is that fjord carbon storage is more of a reactionary force. As temperatures fall, and these fjords freeze, their carbon storage is released.