Diatom-inferred records of paleo-climate and paleo-hydrogeology from lakes in regions of different climate.

摘要

I comparatively investigated mid-to-late Holocene paleo-climate and paleo-hydrogeology in three regions with different climates (Alaska, New Mexico, and Alabama) using diatom frustules as the primary proxy sampled from lake sediment cores. This cross-regional research differs from previous paleo-limnology syntheses because it was designed a priori to simultaneously decipher differential environmental conditions using uniform measurements of the same proxy types with equal environmental sensitivities across spatial scales. Data were analyzed with a combination of multivariate ordination and time series bandwidth analysis to identify significant bifurcation points between periods of changing environmental conditions.;Each study region demonstrated different environmental changes through time. Diatom community dynamics in Alaska were significantly correlated with temperatures, indicating that diatom community structure is a validated temperature change surrogate. In New Mexico, diatom dynamics were significantly correlated with both precipitation and solar intensity, suggesting that diatoms are validated surrogates of solar-modulated drought. Additionally, the diatoms indicated that the study lake was susceptible to drought-induced acidification. In Alabama, the combination of diatoms and sedimentary organic matter elucidated oxbow lake evolution and fluctuations in coastal plain water tables. These changes were potentially caused by alterations in precipitation and eustatic sea levels following the last glaciation. Similar interpretations of mid-Holocene hydrogeology have been reported elsewhere in the coastal plain.;This cross-regional research demonstrated differential proxy responses between each climate region. More importantly, it also suggested reasons why uniform methods elucidated varying responses across broad spatial scales. Global climate change has the potential to affect different regional climates very differently from each other. My intersite research indicated that each region did not capture a ubiquitous global climate pressure. Instead, each region experienced asynchronous climate changes through time. This research is an important first step and a valuable approach in discerning climate change responses among different regions that could, subsequently, be applied more broadly across other regions and lead to improved climate change analyses.