FORAMINIFERAL Mg/Ca AND δ 18 O RECORDS IN THE MUD AERA OF THE EAST CHINA SEA DURING THE LAST 8 000 YEARS AND THEIR PALAEOENVIRONMENTAL IMPLICATIONS: FORAMINIFERAL Mg/Ca AND δ 18 O RECORDS IN THE MUD AERA OF THE EAST CHINA SEA DURING THE LAST 8 000 YEARS AND THEIR PALAEOENVIRONMENTAL IMPLICATIONS