Carbon Isotopes in Pinus elliotti cellulose from Big Pine Key, Florida: Indicators of Seasonal Precipitation, ENSO and Disturbance Events.

Abstract:

Long-term, high-resolution paleoclimate data has never been more important as a means of putting global climate change in context. The inherent complexities of natural climate variability require a very long paleoproxy record that spans many cycles of overlapping multi-scale climate oscillations, such as the Atlantic Multidecadal Oscillation (AMO) and the El Niño-Southern Oscillation (ENSO), in order to distinguish the true effects of climate change. The tropical region has important linkages to global climate regulation and its annual stability makes it highly sensitive to climate change. It is predicted that tropical ecosystems will experience greater climate-related stress than those located at the poles. Yet, this region has an underrepresentation of high-resolution terrestrial paleoclimate records, such as those derived from the tree ring archives. South Florida, like many areas of the subtropics, has few tree species that are suitable for dendrochronological studies due to non-visible or seasonally inconsistent ring production.

 This study examines the potential of Pinus elliottii trees from Big Pine Key as a high-resolution terrestrial paleoclimate proxy for South Florida. The trees were difficult to cross-date using standard dendrochronology techniques. Instead, a chronology extending from 1927 to 2005 was developed by cross-dating patterns in the δ¹³C records. There is a strong, but complex, correlation between δ¹³C, ENSO and the AMO. The δ¹³C record trends with ENSO during the cool phase of the AMO, but there is an inverse relationship between δ¹³C and ENSO during the warm phases. The transition in the relationship between δ¹³C and ENSO occurs about 5 years before the AMO phase shift. In addition, preliminary analysis shows that about 45% of the variance in the carbon isotope chronology is related to precipitation and the ENSO signal is captured through the timing of that precipitation. During El Niño years, there is an increase in dry season precipitation, so a decrease in δ¹³C is witnessed in the latewood; whereas during La Niña years, when winters and springs are drier but the summer precipitation is close to normal, there is a decrease in the δ¹³C of the earlywood. These P. elliottii trees show promise as a paleoclimate proxy for precipitation, ENSO and the AMO in subtropical Florida.