Climate cycles, geomorphological change, and the interpretation of soil and ecosystem development

We evaluated changes in temperature and precipitation associated with climate change, subsidence, and erosion on a chronosequence of sites across Hawaii. The sites range in age from 0.3 to 4100 ky, and the current temperature and precipitation are similar at all sites. Interpretations of fossil pollen records suggest that cooler, dryer conditions prevailed in windward Hawaii during the last glacial period. If the previous glacial periods were similar, the 20-, 150-, and 1400-ky-old sites would have spent 60% or more of their development under relatively cool and dry conditions, whereas the 0.3- and 2.1-ky-old sites have experienced only the warmer, wetter climate of the present interglacial. Subsidence and erosion have also affected the temperature and precipitation of these sites over time; in the past, some of them have been in the dry air above the trade wind inversion or in the lee of larger mountains. Combining these components of change, we estimate that the average temperature over the history of Pleistocene-aged sites (20, 150, and 1400 ky) was up to 2.2 degreesC cooler and that the average precipitation was only about 50% of current values. Under current conditions, it would take only 230 ky for as much water to leach through the 1400-ky-old site as we calculate has leached over 1400 ky. Incorporating more reasonable assumptions about environmental history has the potential to allow more powerful interpretations of chronosequence data and thereby improve the predictive potential of models of soil and ecosystem development.