- Email: [email protected]
Pleistocene precipitation variability in the central Sierra Nevada: Stalagmite results and future directions
Abstracts / Quaternary International 310 (2013) 227–246
Here we constrain the upper vertical boundary of the California Margin Oxygen Minimum Zone (OMZ) through the past 15,000 years. The depth and intensity of the California Margin OMZ is responsive to events of rapid warming, however the spatial extent and underlying mechanism for the synchrony is not clear. We construct a depth transect within Santa Barbara Basin (34 150 N, 119 450 W) using a core from 418 m water depth (MV0811-15JC), and previously investigated cores from 481 m (MD022503) and 570 m (MD02-2504a) water depths. The transect spans 152 vertical meters and ends 32 m above basin's western sill depth. Isotope stratigraphy and radiocarbon dating (planktonic foraminiferal calcite) were used to generate an age model. Foraminiferal and invertebrate assemblages and sediment laminations reconstruct bottom water oxygenation. Oxygen isotopic values at all three sites record similar surface water d18O shifts over the deglaciation (1.5& magnitude; based upon planktonic foraminifera Globigerina bulloides) and a smaller but analogous d18O shift is seen in benthic records (0.5& magnitude; based on benthic foraminifera Uvigernia peregrina). The Bølling-Allerød lamination record indicates strong hypoxia below 480 m; however laminations are not preserved at 418 m. In contrast, benthic foraminiferal assemblages show similar responses (albeit more muted in the shallowest site) to low-oxygen concentrations during the Bølling-Allerød, with species Nonionella stella, Bolivina tumida, and Bulimina tenuata dominating at all three sites. Invertebrate fauna diversity and abundance exhibit taxa-specific synchronicity with respect to climate transition intervals, indicating cross-community responses to fluctuating oxygen concentrations. At core MV0811-15JC, 32 m above the western basin sill, the proxies in the Bølling-Allerød indicate marginally low oxygen conditions; strong enough to affect foraminiferal and invertebrate assemblages, yet not strong enough to preserve annual laminations like those seen in the deeper sites. These results indicate that OMZ waters ephemerally and intermittently shoaled above 418 m during the BøllingAllerød. URANIUM ISOTOPIC VARIATIONS IN MODERN SOILS AND DATED SOIL MINERALS: CALIBRATING A POTENTIAL PALEO-RAINFALL PROXY Jessica Oster, Katharine Maher, Daniel Ibarra. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA E-mail address: [email protected].
Dated secondary minerals, such as pedogenic carbonate and opal and speleothem, display substantial secular variations in initial (234U/238U) that may be related to environmental variability. (234U/238U) of secondary minerals should record the U isotopic value of the soil water or drip water from which they precipitate. Variation in soil water (234U/238U) may reflect changes in eolian inputs, infiltration rates, or weathering rates. Given this wide array of potential influences, distinguishing which processes led to initial (234U/238U) variability in the past can be challenging. Here we present preliminary results from a combined study of modern soil water chemistry from three soil sequences in Nevada and pedogenic mineral uranium isotopic variability from Fish Lake Valley, Nevada. Modern soil waters from Diamond Valley, Newark Valley, and Fish Lake Valley show significant initial (234U/238U) variability between sites, but are consistent along soil profiles. Soil water initial (234U/238U) values appear to be set in the Av layer and reflect soil parent material and grain size, and the degree of silicate versus carbonate weathering in the soil profile. Initial (234U/238U) values vary significantly along an elevation transect in Fish Lake Valley, with lower elevation soil waters displaying higher (234U/238U) values, possibly reflecting slower water infiltration rates due to less precipitation at lower elevations. The results of this modern soil water chemistry study were used to parameterize two types of models that investigate the relative effects of eolian input, a-recoil loss factor, and infiltration rate on soil water initial (234U/238U) values. Fish Lake Valley pedogenic opal displays substantial initial (234U/238U) variability (1.0-1.8) over the past 140,000 years, with generally lower values during past glacial periods, and higher values during interglacials. This variability could reflect generally wetter conditions during glacial periods, and drier conditions during interglacials.
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PLEISTOCENE PRECIPITATION VARIABILITY IN THE CENTRAL SIERRA NEVADA: STALAGMITE RESULTS AND FUTURE DIRECTIONS Jessica Oster a, Isabel Montañez b, Jerry Potter b. a Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA; b Department of Geology, University of California, Davis, CA 95616, USA E-mail address: [email protected].
U-series-calibrated paleoclimate records for stalagmites from two central Sierra Nevada foothills caves document precipitation changes that are approximately coeval with Greenland temperature changes during the last glacial period and deglaciation. The Moaning Cave isotopic and trace element stalagmite proxies record variations in precipitation between 16,500 and 8700 years ago that suggest drier and possibly warmer conditions during Northern Hemisphere warm periods and wetter and possibly colder conditions during high-latitude cool periods during the last deglaciation (Oster et al., 2009). New paleoclimate proxy records for a stalagmite from McLean's Cave, document changes in precipitation that are approximately coeval with interstadials and stadials associated with Dansgaard-Oeschger cycles between 68,000 and 56,000 years ago, during Marine Isotope Stages 4 and 3. The McLean's Cave stalagmite documents drier conditions in central California during Greenland interstadial events, signified by elevated d18O, d13C, grayscale, [Sr], and [Ba], and less radiogenic 87Sr/86Sr. Conversely, wetter conditions in California during Greenland stadials are signified by more negative d18O, d13C, lower grayscale, [Sr], and [Ba], and more radiogenic 87Sr/86Sr. The precipitation changes indicated by the Moaning and McLean's Cave records for the western Sierra Nevada are consistent with a broad picture of precipitation variability throughout the Northern Hemisphere in response to climate changes in the high northern latitudes, with the polar jet stream and Intertropical Convergence Zone shifting southward during Northern Hemisphere cold periods and northward during warm periods. Our new observations further support other paleoclimate records and models that link reduced precipitation in central California with changes in Arctic sea-ice extent and thermohaline circulation in the North Atlantic coincident with Arctic warming. We are further investigating these relationships by expanding our cave monitoring research and speleothem paleoclimate reconstructions to include other central and northern Sierra Nevada caves. We are also in the process of testing the linkage between high latitude climate conditions and California precipitation using the NCAR Community Climate System Model 3. Oster, J.L., Montañez, I.P., Sharp, W.D., Cooper, K.M., 2009. Late Pleistocene California droughts during deglaciation and Arctic warming: Earth and Planetary Science Letters, doi:10.1016/j.epsl.2009.10.003. FORAMINIFERAL SHELL THINNING OVER THE LAST 100 YEARS IN VARVED SEDIMENT FROM THE SANTA BARBARA BASIN, CALIFORNIA Lily Clayman a, James Weaver b, Arndt Dorothy Pak a, Schimmelmann c, Ingrid Hendy d. a Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; b Wyss Institute, Harvard University, Cambridge, MA 02138, USA; c Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA; d Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA E-mail address: [email protected].
Foraminiferal shell weights have been used as a proxy for calcite dissolution in marine sediments and to infer periods of past ocean acidification, assuming that lower shell weights are due to shell thinning in response to lower ocean water pH. Previous laboratory studies have shown that calcification rates of some species of planktonic foraminifera decrease in response to lower seawater carbonate ion concentrations, however, it is difficult to distinguish between post-depositional dissolution and reduced biogenic calcification. A 2009 box core collected from the center of Santa Barbara Basin (586 m water depth, 34 16.8470 N, 120 02.2680 W) has provided a high-resolution record of varved sediment since AD 1780. We present a record of size-normalized shell weights of the near-surface dwelling planktonic foraminifer Globigerina bulloides spanning the last 250
Here we constrain the upper vertical boundary of the California Margin Oxygen Minimum Zone (OMZ) through the past 15,000 years. The depth and intensity of the California Margin OMZ is responsive to events of rapid warming, however the spatial extent and underlying mechanism for the synchrony is not clear. We construct a depth transect within Santa Barbara Basin (34 150 N, 119 450 W) using a core from 418 m water depth (MV0811-15JC), and previously investigated cores from 481 m (MD022503) and 570 m (MD02-2504a) water depths. The transect spans 152 vertical meters and ends 32 m above basin's western sill depth. Isotope stratigraphy and radiocarbon dating (planktonic foraminiferal calcite) were used to generate an age model. Foraminiferal and invertebrate assemblages and sediment laminations reconstruct bottom water oxygenation. Oxygen isotopic values at all three sites record similar surface water d18O shifts over the deglaciation (1.5& magnitude; based upon planktonic foraminifera Globigerina bulloides) and a smaller but analogous d18O shift is seen in benthic records (0.5& magnitude; based on benthic foraminifera Uvigernia peregrina). The Bølling-Allerød lamination record indicates strong hypoxia below 480 m; however laminations are not preserved at 418 m. In contrast, benthic foraminiferal assemblages show similar responses (albeit more muted in the shallowest site) to low-oxygen concentrations during the Bølling-Allerød, with species Nonionella stella, Bolivina tumida, and Bulimina tenuata dominating at all three sites. Invertebrate fauna diversity and abundance exhibit taxa-specific synchronicity with respect to climate transition intervals, indicating cross-community responses to fluctuating oxygen concentrations. At core MV0811-15JC, 32 m above the western basin sill, the proxies in the Bølling-Allerød indicate marginally low oxygen conditions; strong enough to affect foraminiferal and invertebrate assemblages, yet not strong enough to preserve annual laminations like those seen in the deeper sites. These results indicate that OMZ waters ephemerally and intermittently shoaled above 418 m during the BøllingAllerød. URANIUM ISOTOPIC VARIATIONS IN MODERN SOILS AND DATED SOIL MINERALS: CALIBRATING A POTENTIAL PALEO-RAINFALL PROXY Jessica Oster, Katharine Maher, Daniel Ibarra. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA E-mail address: [email protected].
Dated secondary minerals, such as pedogenic carbonate and opal and speleothem, display substantial secular variations in initial (234U/238U) that may be related to environmental variability. (234U/238U) of secondary minerals should record the U isotopic value of the soil water or drip water from which they precipitate. Variation in soil water (234U/238U) may reflect changes in eolian inputs, infiltration rates, or weathering rates. Given this wide array of potential influences, distinguishing which processes led to initial (234U/238U) variability in the past can be challenging. Here we present preliminary results from a combined study of modern soil water chemistry from three soil sequences in Nevada and pedogenic mineral uranium isotopic variability from Fish Lake Valley, Nevada. Modern soil waters from Diamond Valley, Newark Valley, and Fish Lake Valley show significant initial (234U/238U) variability between sites, but are consistent along soil profiles. Soil water initial (234U/238U) values appear to be set in the Av layer and reflect soil parent material and grain size, and the degree of silicate versus carbonate weathering in the soil profile. Initial (234U/238U) values vary significantly along an elevation transect in Fish Lake Valley, with lower elevation soil waters displaying higher (234U/238U) values, possibly reflecting slower water infiltration rates due to less precipitation at lower elevations. The results of this modern soil water chemistry study were used to parameterize two types of models that investigate the relative effects of eolian input, a-recoil loss factor, and infiltration rate on soil water initial (234U/238U) values. Fish Lake Valley pedogenic opal displays substantial initial (234U/238U) variability (1.0-1.8) over the past 140,000 years, with generally lower values during past glacial periods, and higher values during interglacials. This variability could reflect generally wetter conditions during glacial periods, and drier conditions during interglacials.
239
PLEISTOCENE PRECIPITATION VARIABILITY IN THE CENTRAL SIERRA NEVADA: STALAGMITE RESULTS AND FUTURE DIRECTIONS Jessica Oster a, Isabel Montañez b, Jerry Potter b. a Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA; b Department of Geology, University of California, Davis, CA 95616, USA E-mail address: [email protected].
U-series-calibrated paleoclimate records for stalagmites from two central Sierra Nevada foothills caves document precipitation changes that are approximately coeval with Greenland temperature changes during the last glacial period and deglaciation. The Moaning Cave isotopic and trace element stalagmite proxies record variations in precipitation between 16,500 and 8700 years ago that suggest drier and possibly warmer conditions during Northern Hemisphere warm periods and wetter and possibly colder conditions during high-latitude cool periods during the last deglaciation (Oster et al., 2009). New paleoclimate proxy records for a stalagmite from McLean's Cave, document changes in precipitation that are approximately coeval with interstadials and stadials associated with Dansgaard-Oeschger cycles between 68,000 and 56,000 years ago, during Marine Isotope Stages 4 and 3. The McLean's Cave stalagmite documents drier conditions in central California during Greenland interstadial events, signified by elevated d18O, d13C, grayscale, [Sr], and [Ba], and less radiogenic 87Sr/86Sr. Conversely, wetter conditions in California during Greenland stadials are signified by more negative d18O, d13C, lower grayscale, [Sr], and [Ba], and more radiogenic 87Sr/86Sr. The precipitation changes indicated by the Moaning and McLean's Cave records for the western Sierra Nevada are consistent with a broad picture of precipitation variability throughout the Northern Hemisphere in response to climate changes in the high northern latitudes, with the polar jet stream and Intertropical Convergence Zone shifting southward during Northern Hemisphere cold periods and northward during warm periods. Our new observations further support other paleoclimate records and models that link reduced precipitation in central California with changes in Arctic sea-ice extent and thermohaline circulation in the North Atlantic coincident with Arctic warming. We are further investigating these relationships by expanding our cave monitoring research and speleothem paleoclimate reconstructions to include other central and northern Sierra Nevada caves. We are also in the process of testing the linkage between high latitude climate conditions and California precipitation using the NCAR Community Climate System Model 3. Oster, J.L., Montañez, I.P., Sharp, W.D., Cooper, K.M., 2009. Late Pleistocene California droughts during deglaciation and Arctic warming: Earth and Planetary Science Letters, doi:10.1016/j.epsl.2009.10.003. FORAMINIFERAL SHELL THINNING OVER THE LAST 100 YEARS IN VARVED SEDIMENT FROM THE SANTA BARBARA BASIN, CALIFORNIA Lily Clayman a, James Weaver b, Arndt Dorothy Pak a, Schimmelmann c, Ingrid Hendy d. a Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; b Wyss Institute, Harvard University, Cambridge, MA 02138, USA; c Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA; d Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA E-mail address: [email protected].
Foraminiferal shell weights have been used as a proxy for calcite dissolution in marine sediments and to infer periods of past ocean acidification, assuming that lower shell weights are due to shell thinning in response to lower ocean water pH. Previous laboratory studies have shown that calcification rates of some species of planktonic foraminifera decrease in response to lower seawater carbonate ion concentrations, however, it is difficult to distinguish between post-depositional dissolution and reduced biogenic calcification. A 2009 box core collected from the center of Santa Barbara Basin (586 m water depth, 34 16.8470 N, 120 02.2680 W) has provided a high-resolution record of varved sediment since AD 1780. We present a record of size-normalized shell weights of the near-surface dwelling planktonic foraminifer Globigerina bulloides spanning the last 250