Overall I enjoyed this one. Strong character, good pacing. I liked how the narration jumped between the current story and flashbacks for the progressing setup, and especially how it was written in present tense for the current stuff and past tense for the flashbacks. (Although, that's one of my beefs, too, which I will get to.) I found the diving information to be interesting and informative without feeling info-dumpish.
Elle was a strong and willful character and I enjoyed seeing her stick it to anyone who tried to tell her she was wrong and foolish for pursuing her goal. And, although I think it was fully in-character for her to throw away the letter without reading it, the sentimentalist in me nearly cried out when she tossed it. I mean, obviously her father went to great lengths to get that message to her, I think the least she could do was give him a chance. Yes, he was a douche for leaving, and for not letting her stay with him, (which I didn't like, mostly because there's no REAL explanation as to WHY she can't stay. He got to stay, I think she should, too. But, I also like the ending of the story as is, so I won't push that too far.) But there was such little time for them to talk that maybe the letter explained things that he couldn't in the short time they had. Maybe he detailed a way for her to join him, maybe he had some plan to return to them later. Maybe he just wanted to say "I'm sorry" one more time. We'll/She'll never know.
The only other problem I had with this story is a structural one. For the entire tale, everything that happens on the boat with Barry and Al is written in present tense. The search for her father is happening
right now, and the flashbacks to her childhood are all written in past tense, because they already happened. I really liked this, it fit well with this story. So, what I can't figure out is why, when she goes through the portal and finds her dad, it reverts to past tense. I mean, this is still a part of the current story, the stuff that is happening
now. It's not a flashback, why is she thinking back on it? And then it reverts to present tense again when she goes to see Mark. I find this to be a major structural flaw that, for whatever reason, really bugs me. I get that once she goes through the portal there are no more flash backs and the rest of the story would all be present tense, which would ruin the back and forth flow of the story, but who cares? I think it would have been fine, and more true to the structure, to tell the remainder in present tense. My two cents.
One last thing:
In fact I am not sure as to the purpose of Mark in the story; I expected him to do more but they went their separate ways after her dad disappeared and he wasn't lost because of her obsession.
Well, it sounded like normal diving protocol says that she should have a diving partner, so she needed to have someone until that final scene at least. And I think he served a purpose in the story playing the straight man as a counterpoint to her obsessive compulsion. He also upped the tension in the final scenes because she had to return to the surface to get him more air, and then had to go back down by herself, which all would've been less tense if she hadn't had to do that. Maybe he served other narrative purposes too, but that was good enough for me.
I think, Unblinking, that you're mixing up Mark with Barry here. Mark wasn't at the final scene. But I think sykoticwit got it right in his response:
Aside from a generic diving partner (you never do high risk stuff like diving or climbing alone, safety in numbers and whatnot…) Mark was an example of what she gave up in her search for her father. After her father's disappearance she went from being an engaging and fun person to a driven person with one goal, finding her father, and she gave up her entire life for seven years in pursuit of that goal. Mark was a variation of her choosing her obsession over friends and family, and when she returned to him at the end, it was her finally admitting that her father was dead (metaphorically speaking, since he wasn't, you know, actually dead).
And Mark's character was laid out to be a bit of an introvert, (maybe slightly socially inept?) so it seems plausible to me that he may not have moved on after Elle became obsessed. It felt to me like he was a friend, and lover, who would always be there for her.
Man, why can't I write a review in less than a rant?