There are many artists with this name:

1) Arca is an experimental project by Alejandro Ghersi, a Venezuelan electronic producer, mixing engineer and DJ. Arca does not take many categories for granted. His fondness for what he calls “in-between states” extends to gender, genre, emotion, and form itself. Mutability and ambivalence guide the sound of his music — the atmospheres he creates often contain abrasive percussive blasts, metal-shop whine, the screech of subway brakes, the whine of jet engines overheating. Anthropomorphic and animalistic sounds abound —mewling cats, mooing cows, anguished screams, the grunts and groans of orgasm, commingling pleasure and terror and beauty and ugliness in the most thrilling ways possible.

He's also been credited for his writing/producing efforts on Björk's Vulnicura, FKA Twigs' EP2 as well as for his collaborations with Dean Blunt, Mica Levi and Kelela amog others.

https://soundcloud.com/arca1000000

2) arca is a french project initiated by Joan Cambon and Sylvain Chauveau at the beginning of the year 2000. Arca is a reference to the portuguese writer Fernando Pessoa, the word "arca" means "chest" in Portuguese (Pessoa left most of his writings inside a chest that was discovered after he died).
arca is inspired by music, cinema, literature, photographs, daily occidental sounds…
Arca uses warm electronic sounds, mixed with organic instruments and rainy guitars to draw melancholic landscapes.

3) Arca (or ArcA) is a Chilean musical project initially created by Camilo Lillo. Working with Luis Araneda, an old friend of his, in another musical project, Camilo decided to invite Luis as vocalist and lyricist on the "ArcA" project.
Arca grabs different sounds on different styles inside the metal universe, and mixing them on to create the sound that they want.

Currently, they're working on their EP which will be released on Jan 2011 Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.