Bucking the trend among Australia's major banks towards wholesale debt funding that has lengthening maturity profiles, new 364-day certificate of deposit markets are emerging in the UK and in the domestic Australian markets.This reverses a shift that has been apparent since the advent of the GFC, where Australia's major banks began steadily reducing their reliance on short term wholesale funding and lengthening the maturity profile of funds raised in wholesale markets. Indeed, the implementation of the Net Stable Funding Ratio from January 1 2018 will likely be the culmination of the process.Nevertheless, short term funding remains a sizeable component of the wholesale funding mix. But since July 2014 new regulations have started to restrict the primary source of such funds for the banks and new markets have had to be developed. The US certificate of deposit market was by far the preferred source of short term wholesale funding for the major banks and Westpac, in particular. And prime money market funds were significant investors in this market.Available figures on the use of the market are limited to certificates of deposit issued for 364 days. As certificates of deposit can also be issued for lesser periods, the figures available will understate market usage.In 2013, the major banks sold more than US$13 billion of 364 day certificates of deposit. In 2014 the volume sold dropped to just under US$11 billion and last year and for the year to date the figure is a little over US$5 billion for each.Westpac has accounted for 65 per cent to more than 90 per cent of the issuance recorded during each period.Market usage is falling because of changes imposed on prime money market funds by the US Securities and Exchange Commission.At the height of the GFC many prime money market funds found themselves in substantial difficulty, with investor redemptions rampant and the value of assets held volatile. There was an unwritten rule that the net asset value of the funds would never fall below US$1.00 and that funds invested could be redeemed within 24 hours.However, the NAV of some funds did indeed fall below US$1.00. The funds broke the buck, as the saying goes on Wall Street.The Securities and Exchange Commission adopted new regulations in July 2014, to make life more tenable for prime money market funds and to adjust investor expectations.From October this year, prime money market funds will calculate a 'floating NAV'. Reflecting the fact that the assets of these funds comprise investments in commercial paper, large certificates of deposits and floating rate notes, among other short term securities, NAV will be calculated to four decimal points (one-hundredth of one cent), rather than two decimal points, as has been the practice to date.The intention is to capture minute fluctuations in funds' NAV and thereby introduce volatility to NAV. Managing to a stable NAV will be virtually impossible and investors will need to recognise the inevitability of this outcome.Further, the SEC will allow the funds to impose "fees and gates" if a fund's weekly liquidity