Carnival Corp. has received a federal grand jury subpoena asking the cruise line operator to produce documents and records concerning environmental matters, according to a regulatory filing. The Miami-based company received the subpoena on Aug. 22, 2000 from a grand jury sitting in the U.S. District Court for the Southern District of Florida. Carnival disclosed the news in a quarterly filing on Friday with the Securities and Exchange Commission. "At present we know very little about why the subpoena came to us and what the U.S. attorney is looking for," Carnival said in a statement. "Once that becomes apparent, we may be able to comment further."