There are a couple of artists with this name:

1-) post trip hop/whatever artist from nyc, released 2 giveaways on uno
http://soundcloud.com/arca‑2

2-) arca is a french project iniatiated 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.

cinematique, 2001 — Les Disques du Soleil et de l'Acier / Chronowax
angles, 2003 — Les Disques du Soleil et de l'Acier / Chronowax
on ne distinguait plus les têtes, 2007 — Ici dAilleurs / Differ‑Ant


http://myspace.com/arcamusique

3-) Arca (or ArcA) is a Chilean musical project initally 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

http://www.myspace.com/projectarca

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