Merrill Lynch said on Wednesday that Osman Semerci, its global head of fixed income, currencies & commodities, has left the firm and been replaced by David Sobotka.
Sobotka has been head of Merrill's global commodities business since 2004.
A Merrill spokeswoman said Semerci and Dale Lattanzio of the company's structured credit unit have left the firm and that Sobotka will replace Semerci.
Merrill declined to comment on why the two executives are leaving the firm, but market speculation is that Merrill is taking a writedown from losses in the fixed income division.
"We're in a quiet period, and we can't talk it about," a spokeswoman told CNBC.
A Goldman Sachs analyst said on Sept. 26 that Merrill Lynch faces a $1.5 billion third-quarter loss on its fixed-income business, driven by $4 billion in asset write-downs connected to leveraged loans and mortgages.
On Sept. 14, Merrill warned that shaky credit markets forced it to reduce the value of securities linked to risky subprime mortgages and other products, a move that could hurt third-quarter profit.
Shares of the investment bank rose 0.5% to $76 Wednesday.
-- Reuters contributed to this report.