Spanish police say that Martin-Artajo, a Spanish citizen, turned himself in Tuesday at a Madrid police station.
Martin-Artajo is wanted by the United States along with former JP Morgan trader Julien Grout. The pair allegedly falsified the market value of an investment portfolio to cover up its losses from JP Morgan management.
This caused the bank to overstate their 2012 first-quarter earnings by several hundred million dollars, prosecutors claim.
Losses eventually amounted to some $6 billion. The London trades, drawn on federally insured deposits, prompted renewed concerns over the stability of big banks. These are the first criminal charges brought in connection with the losses.
Bruno Iksil, another trader on their team, became known as the "London Whale" and escaped prosecution by providing evidence to U.S. authorities and promising to testify.
Charges against Martin-Artajo and Grout include wire fraud, falsifying books, records and Securities and Exchange Commission filings, and conspiracy.