Geochemical data from core collected from a deep trough on the outer shelf document a warmer marine condition with less sea ice cover in the lower unit and a colder condition with increased sea ice cover in the upper unit. The colder condition is inferred from a reduction in the total organic carbon content and C/N ratio. This geochemical change is paralleled by a change in the diatom assemblages, indicated by a shift from assemblages characterized by the relative abundance increase of Chaetoceros resting spore and typical sea-ice diatoms (Fragilariopsis curta and Fragilariopsis cylindrus) and stratified cold water species (Rhizosolenia antennata) in the lower unit to those by the relative abundance decrease of these diatoms in the upper unit. During the colder climate, the glacial restriction between the Weddell Sea and the northern South Shetland Islands seemed to hinder the influx of typical ice-edge blooms, dominant in the marginal ice zone of the northwest Weddell Sea, to the core site. Rather, the abundance of Actinocyclus actinochilus and Navicula glaciei, indigenous to coastal zone of the South Shetland Islands, increases significantly during this cold event due to the less dilution by the less influx of ice-edge blooms from the Weddell Sea. A 14C chronology of core WB2 indicates colder condition in the shelf around 330 years ago, coincident with the glacier advances at time of colder period in other high southern latitude regions during the Little Ice Age.