The Bank of Montreal announced today it is booking $320 million in writedowns arising from the turmoil in global credit markets.

BMO said the charges, to be booked in the fourth quarter ended October 31, are expected to amount to $210 million after tax.

The “valuation adjustments” at BMO Capital Markets include $170 million on trading and structured credit-related positions and preferred shares, $135 million on Canadian asset-backed commercial paper and $15 million on Links Finance Corp. and Parkland Finance Corp. structured investment vehicles (SIV).

The SIV writedown represents 21% of BMO’s $70-million investment in Links and Parkland. The bank also said it will take part in the effort to rescue these SIVs by contributing up to $1.6 billion.

In addition, BMO said “its strategy to reduce its commodities portfolio continued through the fourth quarter,” with losses of $25 million pre-tax.

The bank said these charges will be partly offset by a $110 million pre-tax gain on the sale of the bank’s MasterCard International Inc. shares.

The bank said there will be a charge of $185 million, or $120 million after tax, “to increase the liability for future customer redemptions related to its loyalty rewards program” in the MasterCard business of its Canadian personal and commercial banking segment.

In total, “These items will lower earnings per share in the fourth quarter by approximately 50¢,” the bank said.

BMO’s fourth-quarter results will be released November 27.