1. Multi-Proxy Evidence for Environmental Change During the Last Two Glacial-Interglacial Cycles from Core BL00-1, Bear Lake, Utah-Idaho

2. Darrell Kaufman R. Scott Anderson Jordon Bright Steven Colman Walter Dean Richard Forester Chip Heil, Jr Katrina Moser Marith Reheis Joseph Rosenbaum Kathleen Simmons (Northern Arizona U) (U Minnesota) (US Geological Survey) (U Rhode Island) (U Utah) (US Geological Survey)

3. NE Basin and Range Within the Bonneville drainage basin Bear Lake

4. N Uinta Mountains Setting Bear River Bear River enters Bear Lake valley 13 km north of lake Local inflow primarily (95%) from Bear River Range and subsurface Glaciated headwaters –Uintas –Bear River Range SLC

5. Lake nearly balanced hydrologically Bear River diverted into Bear Lake via canals ca. 1912 AD Affords a whole-lake experiment to understand a major hydrologic shift Inflow/outflow Bear River Range 10 km

6. TDS (1912 AD) = ~ 1060 mg L -1 TDS (2000 AD) = 550 mg L -1 Mesosaline / alkaline Surface area = 280 km 2 Maximum depth = 63 m Bear River Range - Paleozoic limestone & dolomite Bear Lake Plateau - Mesozoic limestone & sandstone - Mantled by Tertiary Wasatch Fm Bear Lake 10 km Bear River Range Bear Lake Plateau

7. Gravity cores in 1996 by U Minnesota & USGS GLAD800 drilling in 2000 by USGS (U Minnesota & DOSECC) Coring

8. Sediment wedge thickens toward basin-bounding fault >250 m of well-layered sediment BL00-1: 55 m water depth; two adjacent cores Colman et al. Seismics

9. ; 120 m long Lithology Marl Aragonitic Silty clay Tephra 120 m long massive gray silty clay with variable CaCO 3 contents ranging from calcareous silty clay to marl

10. MS correlations with 14 C age in BL96-2 U/Th age on aragonite –128 ka Tentative magnetic excursions –Laschamp (41 ka) –Blake (121 ka) –7  (236 ka) Correlations with Devils Hole  18 O –Peak isotope stages Colman et al. Chronology Depth (m) “tuned” model

11. 50 cm sample spacing Aragonite precipitated prior to historic diversion High-Mg calcite precipitated following diversion Aragonite inferred to form in closed-basin lake (e.g., Holocene) Rapid accumulation of magnesium in lake water poisons calcite lattice and forces aragonite precipitation CaCO 3 (%) Carbonate mineralogy Dean et al. 1 5a 5c 5e 7a 7c 7e

12. Abundance (%) QuartzDolomite Age (ka) Allogenic input Quartz dominates stream- sediment input Calcite and dolomite influence bulk carbonate composition Qtz/dolo deceases over aragonite-rich intervals Dean et al. CaCO 3

13.  18 O (‰ PDB) Bulk-sediment CaCO 3 Candona Cytherissa Oxygen isotopes 30 cm sample spacing + 90 ostracode samples Enriched  18 O coincides with major aragonite zones Bulk sediment  18 O is otherwise relatively uniform Higher variability in ostracode  18 O Bright et al.

14. Oxygen & carbon isotopes 1:1 Candona  18 O nearly always higher than enclosing bulk sediment More uniform bulk-sediment  18 O reflects allogenic influence O and C isotopes correlate strongly in aragonite intervals (‰)

15. Sr isotopes 1.3 m sample spacing Bear River water dominates Sr budget 87 Sr/ 86 Sr < 0.710 over most of core implies presence of Bear River water during the past 250 ka 87 Sr/ 86 Sr of CaCO 3 rocks = 0.7093 ± 0.0002 (n = 18) 87 Sr/ 86 Sr pre-diversion lake Simmons et al. < 0.710 > 0.710 0.709 Simmons et al.

16. Lake hydrologic status: Peak interglaciation Lake retracted into closed basin Aragonite precipitated Low detritial mineral component High  18 O Strongly covariant O & C isotopes High 87 Sr/ 86 Sr Occurred during OIS 1, 5e, and 7a Low effective moisture High % desert shrub and juniper

17. Lake hydrologic status: Glaciation Lake transgressed, captured Bear R Filled to northern threshold Carbonate content influenced by allogenic component Low  18 O Weakly covariant O & C isotopes Low 87 Sr/ 86 Sr Cytherissa lacustris associated with polar/sub-polar air masses High % pine, spruce & sagebrush

18. Lake hydrologic status Intermediate Bear River and Bear Lake connected via wetlands Influence of Bear River buffered Variable influence on sediment deposited at the core site

19. Conclusions Multi-proxy data document millennial-scale fluctuations in hydrology and environment during last 250 ka Fluctuations reflect variations in water and sediment discharged from the glaciated headwaters and processes that influence sediment delivery to the core site, including lake-level changes Most pronounced change resulted from re-arrangements of drainage, controlled by both climatic and non-climatic factors