The singer and songwriter’s ninth album, “Did You Know That There’s a Tunnel Under Ocean Blvd,” asks big, earnest questions and isn’t afraid to get messy.“I wrote you a note, but I didn’t send it,” Lana Del Rey sings on her rangy ninth album, “Did You Know That There’s a Tunnel Under Ocean Blvd” — a 16-song, 78-minute collection as sprawling, hypnotic and incorrigibly American as an interstate highway.Many of the tracks have the run-on, handwritten feel of letters never mailed, and this particular one, the fluttering piano ballad “Sweet,” is addressed to a paramour who seems unwilling to go as deep as the 37-year-old Del Rey. “Lately we’ve been making out a lot,” she sings, spinning her signature, soft-serve swirl of the sacred and profane, “not talking ’bout the stuff that’s at the very heart of things.”More than any of its predecessors, this Del Rey album is about the very heart of things. Its themes and lyrical preoccupations are philosophical and weighty: the existence of God; the afterlife; the precise moment the soul leaves the body; the concessions of marriage and motherhood; fate; familial bonds; and, on the strikingly melancholy centerpiece “Fingertips,” recent scientific progress into the attainment of eternal life. “God, if you’re near me, send me three white butterflies,” she sings three-quarters into the LP, in a voice that’s almost childlike in its surging sincerity. Throughout “Ocean Blvd,” an artist who arrived on the scene sounding like a nihilist is now searching and sincerely self-scrutinizing, sending earnest questions into a possible void.The album’s title itself suggests hidden depths beneath picturesque surfaces — something Del Rey knows a thing or two about. When she debuted with the 2011 viral hit “Video Games” and an awkward, excessively maligned “Saturday Night Live” performance, the musician born Elizabeth Grant was dismissed by some skeptics as nothing more than a pretty face, all retro artifice and pouty pastiche. But as she’s sharpened her pencil, most powerfully on the eerie 2014 LP “Ultraviolence” and her sublime 2019 album “Norman _____ Rockwell!,” Del Rey has proved to be an expert chronicler of her own interiority as well as a larger, more diffuse cultural subconscious. Del Rey, at her best, has a finger not just on the pulse, but somewhere beneath the flesh.And she is occasionally at her best here. “Ocean Blvd” is Del Rey’s strongest and most daring album since “Rockwell,” though it’s also marked by uneven pacing and occasional overindulgence. On an excellent four-song opening stretch, Del Rey establishes the album’s unhurried pace and her connection to that fabled tunnel, a sealed-up, subterranean bit of West Coast architecture — one of the few places in California where the sun can’t shine. “I can’t help but feel somewhat like my body marred my soul,” Del Rey croons on the mournful, gorgeously string-kissed title track.A few songs later, on the shape-shifting nightmare “A&W,” she finds an even darker line of inquiry: “Look at my hair, look at the length of it and the shape of my body,” she sings atop a droning, monotonous chord progression that conjures early Cat Power. “If I told you that I was raped, do you really think that anybody would think I didn’t ask for it?” The line is more shocking for the vaporous, ultra-femme falsetto in which she delivers it — as if the ballerina inside a music box opened her mouth and sang.Part of the thrill of Del Rey’s music is the sense that she can and will say absolutely anything, regardless of who it may offend. She makes a somewhat clumsy admission of her own white privilege on “Grandfather Please Stand on the Shoulders of My Father While He’s Deep-Sea Fishing”: “I’m blue, I’m green, regrettably also a white woman/But I have good intentions even if I’m one of the last ones.” The line is complicated by the fact that, save for her brief forays into hip-hop on her grab-bag 2017 album “Lust for Life,” “Ocean Blvd” is more conversant with Black music than any other entry in her discography. Gospel is a particular touchstone. Some of the first voices heard on the record are Melodye Perry and Pattie Howard, onetime backing singers for Whitney Houston; later, the jazz musician Jon Batiste accompanies Del Rey on the pirouetting duet “Candy Necklaces” and stays, to testify, on a fiery three-minute interlude.At this unfettered stage in her career, Del Rey’s music is driven by a tension between freedom and structure; her greatest material finds its quivering equilibrium. Two six-minute compositions in the middle of “Ocean Blvd,” though, test the limits of Del Rey’s penchant for free verse. “Kintsugi,” an aching meditation on the deaths of several family members, mostly works; it’s discursive and diaristic, but a repeated refrain borrowed from Leonard Cohen (“that’s how the light gets in”) is an effective anchor. “Fingertips,” despite containing some of the record’s most piercing lyrics, simply drifts. The return of meter, on the elegant “Paris, Texas,” comes as a relief.Partly based on a piano-driven instrumental track by the indie composer SYML, “Paris, Texas” is one of 11 songs that Del Rey co-produced with Jack Antonoff, who has become a trusted collaborator. A handful of songs also evolved out of impromptu Sunday jam sessions that Del Rey’s boyfriend at the time, the film producer and amateur guitarist Mike Hermosa, recorded on his phone; a few of them (“Peppers,” “Let the Light In”) have a playful, flirtatious feel. (“When we broke up,” Del Rey said in a recent Rolling Stone U.K. interview, “I was like, ‘You know at some point we’re going to talk about the fact that you have half of this album.’” He is credited as a writer on five songs.)“Ocean Blvd” closes with a trio of those lighter and more irreverent tracks that stray from the heart of things, giving the album’s concluding moments the sense of a cosmic shrug: “Get high, drop acid, never die,” she sings in responses on the final track. But she also seems to have embraced the more superficial pleasures of gaudy, earthly delights. “Peppers” is at once inane and irresistible (“me and my boyfriend listen to the Chili Peppers”). Del Rey has asked God for guidance and accepted Anthony Kiedis’s scat-nonsense as the answer. What could be more Californian than that?That three-song suite that concludes “Ocean Blvd” can certainly feel like an anticlimax, or a retreat from the existential questions posed in its opening movement. But it’s also a perfect distillation of the duality that makes Del Rey’s 21st-century siren songs so singular. Nine albums into her career, she has become a musical mermaid, capable of breathing as easily on the surface as she can in the ocean’s darkest depths. More