Not, of course, to be confused with Joan Clarke, the British cryptanalyst and numismatist who worked with Alan Turing during WWII! (Note the spelling of her name.)

Or with the British pediatrician, Joan B. Clarke, who turned to writing sci-fi novels in the 1960s and 1970s.

One of her more popular books (for adults) seems to be "Latitudes of Melt" (2000). Description:

"This bountiful, magical novel opens with the discovery by two fishermen of a baby floating in a cradle on an ice pan in the North Atlantic off the coast of Newfoundland in 1912. To the small fishing community into which the foundling is adopted, Aurora, as they name her with her shock of white hair, one blue eye and one brown is clearly enchanted. But it is not until Aurora is herself an old woman that she learns the heart-wrenching story behind her miraculous survival on the ice."

https://www.cbc.ca/news/canada/newfoundland-labrador/joan-clark-nl-obit-1.6812307
(it's a long one, with photos of her and her books)

William Ping · CBC · Posted: Apr 16, 2023

Excerpts:

Joan Clark, an acclaimed author who spent much of her life in Newfoundland and Labrador, has died.

Born in 1934, Clark wrote more than 15 books, including novels such as An Audience of Chairs, Latitudes of Melt, and Eiriksdottir: A Tale of Dreams and Luck. Her work has been translated into at least six other languages and published around the world.

"She was a very vital force within the cultural and literary community of Newfoundland," said Kevin Major, one of Clark's friends and a fellow writer in St. John's.

"She had a beautiful way with words and it was a privilege to know her and just to share personally in some of the time that she spent in Newfoundland.."...

....In 1988, Clark published her first novel for adults, The Victory of Geraldine Gull, about a Swampy Cree community in Hudson Bay. It went on to garner nominations for some of Canada's highest literary honours, including the Governor General's Award and the Books In Canada First Novel Award.

Clark is also the only writer who has received both the Marian Engel Award, recognizing her body of work in adult fiction, and the Vicky Metcalf award, in honour of her contributions to children's literature. Clark received the Order of Canada in 2010, for her work in the literary arts communities in Alberta and Newfoundland. As well, she was a two time winner of the BMO Winterset Award, which celebrates excellence in Newfoundland and Labrador writing...

....Another milestone in Clark's career was Deanne Foley's 2019 film adaptation of An Audience of Chairs. Filmmaker Rosemary House adapted the book into a screenplay and worked on the film for seven years. She had known Clark as a friend of her parents and Clark had encouraged her to adapt one of her books into a film. House said Clark was impressed with the finished result..

"She just loved it and was thrilled to see it go to screen," she said.

As both a friend and a colleague, House said she has fond memories of Clark..

"Lovely, smart, intelligent, creative, she had a great smile," House said. "And her husky voice. She was just a lovely person who I think had a very good life and enjoyed her work tremendously. She was pretty fabulous."...

https://www.kirkusreviews.com/author/joan-clark/
(two Kirkus reviews)

https://www.goodreads.com/author/show/189002.Joan_Clark
(reader reviews)

https://groups.google.com/g/rec.arts.books.childrens/c/xYIapIsq8LA/m/Rjnk24WNQrcJ
(birthday post from 2014 - the links still work)

Excerpts:

From "Contemporary Authors":

"...Wild Man of the Woods and The Moons of Madeleine were originally
conceived as one story. However, in recognizing how differently boys
and girls handle conflict, Clark opted to break the tale into two
separate books that focus on cousins who travel to each other's homes
for the summer. In Wild Man of the Woods Stephen leaves Calgary to
visit his aunt, uncle, and cousin Louie in Inverary in the Canadian
Rockies. Madeleine, Louie's sister, visits Stephen's family in Calgary,
and her experiences are detailed in The Moons of Madeleine. For both
children, the summer is filled with experiences that cause them to
gain in maturity. Stephen deals with being bullied through the use
of a mythical mask that brings about a violent climax. Madeleine,
on the other hand, copes with her beloved grandmother's illness, as
well as her own confused adolescent feelings, during an escape to the
cave of the First Woman and an introduction to the continuity of the
circle of life..."

WRITINGS:
FOR YOUNG PEOPLE

Girl of the Rockies, illustrated by Douglas Philips, Ryerson Press
(Toronto, Ontario, Canada), 1968.

Thomasina and the Trout Tree, illustrated by Ingeborg Hiscox, Tundra
Books (Toronto, Ontario, Canada), 1971.
The Hand of Robin Squires, illustrated by William Taylor and Mary
Cserepy, Clarke, Irwin (Toronto, Ontario, Canada), 1977.

The Leopard and the Lily (fable), illustrated by Velma Foster,
Oolichan Books (Lantzville, British Columbia, Canada), 1984.
Wild Man of the Woods, Penguin Books Canada (Markham, Ontario,
Canada), 1985.
The Moons of Madeleine, Viking Kestrel (Markham, Ontario, Canada),
1987.

The Dream Carvers, Viking (Toronto, Ontario, Canada), 1995.
Leaving Home, illustrated by Cherrisa Bonine, Your Book, 1996.
The Word for Home, Viking (Toronto, Ontario, Canada), 2002.
Snow, illustrated by Kady McDonald Delton, Vintage Canada (Toronto,
Ontario, Canada), 2006.
Road to Bliss, 2009.

OTHER

From a High Thin Wire (short stories), NeWest Press (Edmonton,
Ontario, Canada), 1982.
The Victory of Geraldine Gull (adult novel), Macmillan of Canada
(Toronto, Ontario, Canada), 1988.
Swimming toward the Light (short stories), Macmillan of Canada
(Toronto, Ontario, Canada), 1990.
Eiriksdottir: A Tale of Dreams and Luck (adult novel), Macmillan
of Canada (Toronto, Ontario, Canada), 1994.
Latitudes of Melt (adult novel), Knopf (Toronto, Ontario, Canada),
2000, Soho (New York, NY), 2002.
An Audience of Chairs (adult novel), Knopf (Toronto, Ontario,
Canada), 2005.
The Birthday Lunch, 2015.

On top of those British authors, it seems that "Joan Clark" was used as a pseudonym in the 1930s by, of all people, Mildred Benson, who helped write the Nancy Drew series! (Benson was almost 30 years older than Clark.)

https://www.goodreads.com/author/show/5415434.Mildred_Benson

Under that name, Benson wrote the Penny Nichols mysteries.