Goldman Sachs' head of oil and agricultural trading, Karl Robijns, is retiring from the firm, an internal memo seen by Reuters showed. London-based Robijns, who first joined Goldman as an oil trader in 1998, has headed the bank's global oil, refined products, and agricultural trading since last year. "Karl has had a substantial commercial impact on our market-leading commodities franchise," said the memo from Goldman's co-heads of securities - Isabelle Ealet, Ashok Varadhan and Pablo Salame. Robijns is the latest high-profile commodities executive to leave a bank, as the industry wrestles with lower profits, increased regulation and reduced volatility in the sector.