HISTORY OF SEDIMENTATION IN BEAR LAKE, UTAH AND IDAHO, USA, OVER THE LAST 240,000 YEARS: LINKS TO PACIFIC CLIMATE

Sediments deposited over the last 240,000 years in Bear Lake, Utah/Idaho are predominantly calcareous silty clay, with calcite as the dominant carbonate mineral. The abundance of siliciclastic sediment indicates that Bear River usually was connected to Bear Lake. However, aragonitic marl intervals were deposited during the Holocene and the last two interglacial intervals, equivalent to marine isotope stages (MIS) 5 and 7. During these interglacial periods, Bear River was disconnected from Bear Lake and the lake became more saline. These high-carbonate, aragonitic intervals coincide with warm interglacial continental climates, warm Pacific SSTs, increased coastal upwelling under the California Current, and increased organic productivity, all recorded in marine sediments on the California margin. This implies that the subtropical North Pacific high-pressure system that today is dominant in the North Pacific during the summer and drives the California Current had a longer residence time off northern California during interglacials. During the last three glacial intervals (MIS 2, 4, and 6), the Aleutian low-pressure system, presently dominant in the North Pacific during the winter, had a longer residence time off northern California, producing storms and precipitation that increased the flow of Bear River. This increased precipitation during the last glacial maximum (MIS2) also increased the levels of Lake Bonneville and Lake Lahontan in the Great Basin of western United States. On the California margin, the California Current upwelling system was greatly reduced during glacial intervals. Sediments deposited on the California margin during glacial intervals indicate that organic productivity was considerably lower than during interglacials. These climatic patterns over the North Pacific are recorded in Bear Lake by river-borne detrital clastic sediments deposited during glacial intervals, and carbonate sediments, dominated by aragonite, deposited during the more arid interglacials.