Air carrier First Officer reported ATC issued a low altitude alert during approach after the Captain established a high rate of descent to regain glide path. The flight crew corrected and returned to a stabilized approach.

Narrative

On descent into LAX we were on the Ironman arrival and had the RNAV RNP Z 24R approach loaded into the FMS. We anticipated connecting DAHJR on the approach/arrival together as we had done nearly every time during the previous flights into LAX during this trip. ATC advised us that they were too busy to accommodate the RNAV and told us to expect the visual approach. On downwind they told us to descend to 2;600 at 210kts which we did and extended flaps to 1. While still at a relatively high altitude; approach told us to turn base. At this point the CA (PF) selected 200kts manual speed and called for flaps 2 and continued descending in Vertical Navigation Mode and Flight Level Change (VFLC). We could see the airport and knew we were high so he verbalized that he would square off his base turn to give us more time to descend. Right after that; approach gave us a turn to final which cancelled that plan we had made. At this point we were still too high and I was thinking we would probably end up going around. The Captain (CA) called for the gear down and additional flaps. I know he was using spoilers but I don't remember when or how much they were used. The Visual Glide Path (VGP) was still well below us so the CA disconnected the autopilot and manually pitched down to catch it. At this point the VSI increased as he focused on getting the glideslope. The RAD ALT called out 2500 feet and I assumed he would start to arrest his descent but he did not do so quickly enough. I remember at 1700 feet AGL seeing -2100FPM. I tried to think of what to say that would convey the issue I was seeing and all I could think to say was 'sink rate' and he acknowledged but I don't think he fully understood me or the situation. ATC also called us to warn us of a 'Low altitude alert' which I think was caused by the excessive descent rate. The CA had the spoilers stowed by 1200 feet and we were on glideslope at this point. I believe the rest of the approach was within the stabilized approach criteria after this point.