Application of the clumped isotope paleothermometer in soil carbonates to new estimates of Pleistocene glacial-interglacial temperature change in the Central Rocky Mountains Nicole Sarieddine 1 ([email protected]), Katharine Huntington 1 , Adam Hudson 2 , Julia Kelson 1 , Andy Schauer 1 1 Department of Earth and Space Sciences, University of Washington, Seattle; 2 USGS, Lakewood, CO 1. Introduction o Learning about how past climates have responded to changes in carbon dioxide concentrations is important to understand how our current climate will respond to atmospheric changes. o Extensive studies have tried to constrain the warming that occurred after the Last Glacial Maximum (LGM, ~20,000 years ago) and have estimated the temperature change from the LGM to today to be 5-10º C. o In this study we: o Measure the clumped oxygen and carbon isotopes of soil carbonate samples collected in the Central Rocky Mountains from the LGM and today to develop a more precise estimate of the amount of warming since the LGM. o Investigate the time of year soil carbonates form, which is important for interpreting the soil temperature recorded by clumped isotopes. 2. Carbonate clumped isotope thermometry o Measures ratio of “clumped” heavy isotopologues in carbonate minerals o Proportion of “clumped” molecules increases with decreasing temperature o Calculate temperature of soil carbonate formation from clumping (Δ47) using an empirical calibration (Kelson et al., 2017) Δ 47 = 13 + 16 +18 4. Clumped isotope temperature results o We expected clumped isotope temperature estimates from the LGM and today to differ by 5-10°C (based on climate models, Braconnot et al., 2007) if the carbonates formed in the same season. o However, LGM and modern clumped temperatures are within error of each other (LGM: 9 ± 1°C; modern: 10 ± 2 °C), indicating the samples formed in different seasons 0 2 4 6 8 10 12 14 -25,000 -20,000 -15,000 -10,000 -5,000 0 Temperature (°C) Time (BP) ▵47 Measured Temperatures LGM vs Present Day δ 13 C δ 18 O Δ47 13 C 18 O 16O O 3. Analytical methods o We measure clumping in CO 2 derived from carbonate o Digested 10 soil carbonate samples (3 replicates each) in phosphoric acid to produce CO 2 o Purified CO 2 cryogenically using an automated vacuum line o Analyzed purified CO 2 on a MAT 253 mass spectrometer References Hudson, Adam. "Research Proposal-Mendenhall Opportunity #15-27." Proposal. 2017; Kelson JR, et al., (2017). Towards a university carbonate clumped isotope calibration: diverse synthesis and preparatory methods suggest a single temperature relationship. Geochimica et Cosmochimica Acta 197, 104-131. doi:10.1016/j.gca.2016.10.010. Braconnot, P., et al., Results of PMIP2 coupled simulations of the Mid-Holocene and Last Glacial Maximum – Part 1: experiments and large-scale features, Clim. Past, 3, 261-277, https://doi.org/10.5194/cp-3-261-2007, 2007. 6. Implications for LGM Climate o Because of the apparent change in the season of carbonate formation, we are unable to discern a meaningful temperature difference between the LGM and present day. o However, the change in carbonate seasonality implies that timing of seasonal precipitation was different in the LGM. No summer monsoon in LGM? 5. Discussion – Temperature interpretation o Modern carbonate temperatures of 10° resemble fall or spring soil and air temperatures o If LGM was 5-10°C cooler than modern à the 10 °C soil carbonate samples from the LGM formed in the summer We use the clumped isotope temperature to reconstruct climate. However, the temperatures recorded by the soil carbonates are seasonally dependent, because carbonate formation depends on seasonal rainfall/soil drying. Soil carbonate nodule “Clumped” carbonate ion Clumped mass-47 CO2 from carbonate -15 -10 -5 0 5 10 15 20 25 30 January February March April May June July August September October November December Temperature (°C) Modern Day Soil and Air Temperature from Dead Cholla Site Soil Temperature (°C) Air Temperature (°C) Hypothetical LGM Soil Temperature (°C) Prepping the samples in the prep-line Mass Spectrometer Expected LGM Temperature Measured LGM Temperature Measured Modern Day Temperature
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Application of the clumped isotope paleothermometer in soil carbonates to new estimates of Pleistocene glacial-interglacial temperature change in the
Central Rocky Mountains Nicole Sarieddine1 ([email protected]), Katharine Huntington1, Adam Hudson2, Julia Kelson1, Andy Schauer1
1Department of Earth and Space Sciences, University of Washington, Seattle; 2USGS, Lakewood, CO
1. Introductiono Learning about how past climates have responded to changes
in carbon dioxide concentrations is important to understand how our current climate will respond to atmospheric changes.
o Extensive studies have tried to constrain the warming that occurred after the Last Glacial Maximum (LGM, ~20,000 years ago) and have estimated the temperature change from the LGM to today to be 5-10º C.
o In this study we:o Measure the clumped oxygen and carbon isotopes of
soil carbonate samples collected in the Central Rocky Mountains from the LGM and today to develop a more precise estimate of the amount of warming since the LGM.
o Investigate the time of year soil carbonates form, which is important for interpreting the soil temperature recorded by clumped isotopes.
2. Carbonate clumped isotope thermometryo Measures ratio of “clumped” heavy isotopologues in carbonate
minerals
o Proportion of “clumped” molecules increases with decreasing temperature
o Calculate temperature of soil carbonate formation from clumping (Δ47) using an empirical calibration (Kelson et al., 2017)
Δ47 = 13 + 16 +18
4. Clumped isotope temperature resultso We expected clumped isotope temperature estimates
from the LGM and today to differ by 5-10°C (based on climate models, Braconnot et al., 2007) if the carbonates formed in the same season.
o However, LGM and modern clumped temperatures are within error of each other (LGM: 9 ± 1°C; modern: 10 ± 2 °C), indicating the samples formed in different seasons
0
2
4
6
8
10
12
14
-25,000 -20,000 -15,000 -10,000 -5,000 0
Tem
pera
ture
(°C)
Time (BP)
▵47 Measured Temperatures LGM vs Present Day
δ13C
δ18O
Δ47
13C
18O
16O
O
3. Analytical methodso We measure clumping in CO2 derived from carbonateo Digested 10 soil carbonate samples (3 replicates each)
in phosphoric acid to produce CO2o Purified CO2 cryogenically using an automated
vacuum lineo Analyzed purified CO2 on a MAT 253 mass
spectrometer
References
Hudson, Adam. "Research Proposal-Mendenhall Opportunity #15-27." Proposal. 2017; Kelson JR, et al., (2017). Towards a university carbonate clumped isotope calibration: diverse synthesis and preparatory methods suggest a single temperature relationship. Geochimica et Cosmochimica Acta 197, 104-131. doi:10.1016/j.gca.2016.10.010. Braconnot, P., et al., Results of PMIP2 coupled simulations of the Mid-Holocene and Last Glacial Maximum – Part 1: experiments and large-scale features, Clim. Past, 3, 261-277, https://doi.org/10.5194/cp-3-261-2007, 2007.
6. Implications for LGM Climate o Because of the apparent change in the season of carbonate
formation, we are unable to discern a meaningful temperature difference between the LGM and present day.
o However, the change in carbonate seasonality implies that timing of seasonal precipitation was different in the LGM. No summer monsoon in LGM?
5. Discussion – Temperature interpretationo Modern carbonate temperatures of 10° resemble fall or spring
soil and air temperatureso If LGM was 5-10°C cooler than modern à the 10 °C soil
carbonate samples from the LGM formed in the summer
We use the clumped isotope temperature
to reconstruct climate.
However, the temperatures recorded by the soil carbonates are seasonally dependent, because carbonate formation depends on seasonal rainfall/soil drying.
Soil carbonate nodule
“Clumped” carbonate ion
Clumped mass-47 CO2 from carbonate
-15-10
-505
1015202530
Janua
ry
Febru
aryMa
rch April
May
June
July
Augu
st
Septe
mber
Octob
er
Nove
mber
Dece
mber
Tem
pera
ture
(°C)
Modern Day Soil and Air Temperature from Dead Cholla Site
SoilTemperature(°C)
AirTemperature(°C)
HypotheticalLGM SoilTemperature(°C)
Prepping the samples in the prep-line
Mass Spectrometer
Expected LGM Temperature
Measured LGM Temperature
Measured Modern Day Temperature
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