A Reconstruction of the Response of the Water Balance in Western United States Lake Basins to Climatic Change
Changes in the water balance are among the most serious potential consequences of global climate change. Predicting future water balance fluctuations is dependent on understanding the causes of past fluctuations. In arid, hydrologically closed basins, the water balance can be quantified as the ratio of water surface area in the terminal sink or sinks to the basin drainage area. In this study, we have used the oxygen isotope content of carbonate minerals precipitated from lake waters to reconstruct lake surface-area history. We have developed a numerical water-balance and isotope-balance model to simulate the lake’s isotopic evolution and thus produced a lake surface-area history.
We have reconstructed the surface-area history of two basins in the southwestern United States. At the Plains of San Agustin, New Mexico, we used the oxygen isotope content of ostracode valves to achieve a high-resolution reconstruction of the interval 36 to 15 ka (thousand years before present). At Searles Lake, California, we used oxygen isotopes in inorganic carbonate minerals to produce a water-balance history for the period 1,180 to 10 ka. Comparing the Searles record with the marine oxygen isotope chronology shows the single strongest influence on the water balance is global glacial/interglacial cycles. Thus water-balance changes can be linked directly to global climatic change.
However, we also see patterns that differ from those of the global glacial cycles. We detect unexplained long-term trends of humid and arid water balance with an apparent periodicity of about 400 kyr. We also observe that the water balance seems to be characterized by relatively stable humid and arid modes, with rapid, unstable transitions between these modes.