Classic case of exposed sapwood rotting/drying too fast. You can dig right down as far as you want, but those will go into the heartwood, that's a guaranteed fact.
That said, they won't actually be a problem. Paint that section with a good thick paint or glue and let it season. When you get to shaping it, once the bow is roughed out to more or less final width measurements see if you can squeeze the cracks together using a vice or clamp. If you can, flood them with superglue and clamp the cracks shut. If you can't close them with pressure, flood them with a good quality 2 part epoxy. They're longitudinal so won't cause any problem with the bow itself. They're just a bit unsettling to look at!
This is what you'll end up with. This bow was somewhere around 100lb at finished weight and I didn't bother gluing these. Granted, the bow exploded in my face at full draw a while later, but that was due to something else, not the cracks. Honest!