RIDDER, Allison ('98) (Advisor: Amy Leventer)
The problem of exactly how much of the global warming trend now seen is due to man and how much is a natural increase in temperature is a major question in today's debate on the greenhouse effect. The existence and timing of the Little Ice Age (LIA) is signigicant, as it is possible that the cooling of ~1400 to 1900 AD, has been masking the record of anthropogenic warming in the world (Kreutz 1997). The short gravity core PD95-10 GC3, which was collected from the Palmer Deep Basin in the Antarctic Peninsula, is a link between the already studied PD92-30 core data and a global record of sea ice distribution and paleoproductivity from an analysis of polar diatoms (Leventer et al., 1996). The top of that core was disturbed during coring so a short gravity core, PD95-10 GC3, was retrieved with the goal of keeping the sediment-water interface intact. PD95-10 GC3 has been correlated to PD92-30 by a comparison of the magnetic susceptibility (amount of magnetic material in a layer) and distinctive diatom layering so the short core can be added to the chronology of the Antarctic paleoclimate record represented by PD92-30 and the diatom distribution can be added to the greater body of LIA information.
Based on quantitative analysis of the diatom distribution in PD95-10 GC3 the core was divided into two sections. Above 120cm, predominantly unstratified conditions in the water column were suggested by low diatom ratios of Fragilariopsis cylindrus and Fragilariopsis curta to Thalassiosira antarctica and low numbers of Corethron criophilum, Proboscia spp. and Rhizosolenia spp., which indicate less sea ice melt and increased windiness (Leventer et al. 1996). Below 120 cm, there was a marked increase in water column stratification, indicators include a high ratio of F. cylindrus + F. curta to T. antarctica and highly concentrated Corethron, Proboscia and Rhizosoleia layers. The trend to toward less stratification and increased windiness above 120 cm are characteristic of the period known as the Little Ice Age ~1400-1900 AD. In Antarctica the record for this time perid is paricularly important because when coordinated with LIA work done in other parts of the world, the global nature of the period can be firmly established and it's impact on the theories of global warming evaluated.
