The Australian sharemarket fell to a four week low and back into the red for the year as the large cap miners succumbed to iron ore weakness and the retail giants were also hammered. The S&P/ASX 200 index fell 52.6 points, or 0.98 per cent, to the day's low of 5316.2 on volume 12 per cent above average as BHP Billiton, Rio Tinto, Woolworths and Wesfarmers all lost around 2 per cent as tumbling iron ore prices signalled strengthening domestic global growth headwinds.