LAKE LEVEL STUDIES | North America

Abstract

Numerous studies have recognized changes in the levels of North American lakes during the late Quaternary period. Analyses have been conducted on a wide range of lakes from large lakes in the Great Basin to small kettle lakes in the mid-continent. Here, we discuss the water-level histories inferred from lake-sediment cores collected in small lakes (generally <100 ha) that form a network of local paleoclimate records spanning the continent and showing regionally coherent patterns of change over the past 15 kyr. Many of the lakes formed with glacially formed basins and, thus, only represent the period since the last ice age. Nearly all of the lakes, whether in karst terrain in Florida, in glacial outwash and till in the central and northeastern United States, or in older glacial deposits in Alaska, depend in large part upon groundwater, and thus their levels reflect the balance of precipitation and evaporation that controls groundwater recharge. In this way, the lake levels tend to track centennial and longer changes in climate, although most studies have only identified multimillennial trends. Lakes from the Rocky Mountains to the Great Lakes were low during the mid-Holocene, often between 8 and 4 cal kyr BP. To the northwest in Alaska and the Yukon and to the east from Quebec to Florida, most lakes reached their lowest levels before 9 cal kyr BP and rose as conditions in the mid-continent dried. A second period of low levels at many lakes from Ontario to New Hampshire lasted from ca. 5 to ca. 2 cal kyr BP. Long-term ice-sheet retreat and changes in the seasonality of insolation may be the dominant controls on the regional histories with regional factors altering the expression of the responses.