Climate projections for tropical low latitudes suggest temperatures will increase by 2°C this century, and precipitation will become more variable. The last interglacial (110-130ka), when average temperatures were ca.1-2°C above modern, represents the most recent time on Earth with conditions comparable to those predicted for the immediate future. The last interglacial provides a framework from which we can understand climatic responses to future warming. Little is known, however, about interglacial climate dynamics of the lowland Neotropics due to the lack of low-latitude paleoecological records. Furthermore, the few existing records from the warmest portion of the last interglacial in the Neotropics, MIS5e (128-115ka), reveal conflicting precipitation patterns with evidence for both wet and dry trends. Using a paleoecological record from Panama, we seek to answer the central research question: did Central America experience wet or dry conditions during the peak warmth of the last interglacial?
A 54-m core (EV08) was retrieved from El Valle, Panama in 2008 from what is now a paleolake. Diatom assemblages from EV08 taken every 5cm between 45 and 54m core depth (110-130ka) were compared with two glacial-aged cores from the same depositional basin. The changes in diatom assemblages at El Valle provided one of the oldest precipitation records from Central America.
Results/Conclusions
The dominant diatom of both glacial and interglacial periods was Aulacoseira granulata. Other species, e.g. Aulacoseira agassizi, Achnanthidium duthiei, and Nitzschia amphibia had distinctive patterns of abundance within the record, indicating a deepening of the lake during the last millennia of MIS5e. Low DCA scores through the interglacial suggest high similarities in species composition with low rates of species turnover (<2 std.). Cluster analysis revealed three diatom zones from the interglacial period, with ANOSIM separating the group from 118-123 ka as significantly different (p=0.001, R=0.76) from older and younger sequences. A decline in benthic species followed by the dominance of the centric planktonic species, A. agassizi, from 118-123 ka suggested an increase in lake level with reduced importance of stream inputs. These results were consistent with previous studies at El Valle, which revealed a continuous presence of a lake at the site through most of the glacial period, with shallowing only apparent during the Last Glacial Maximum (ca. 33 ka). The evidence for both a wet interglacial and glacial period, supported independent palynological findings that the humid environments of Central Panama were not interrupted by glacial aridity.