Guaymas Basin 9-12kYrBP Leaf Wax Isotopes and Precipitation Reconstructions Bhattacharya, T.; Tierney, J.E.; Addison, J.A.; Murray, J.W. Bhattacharya, T. Tierney, J.E. Addison, J.A. Murray, J.W. Monsoon earth science/paleoclimate/paleoceanography (delta 2H,C30 n-alkanoic acid,null,per mil VSMOW,null,paleoceanography,corrected,gas chromatography|isotope ratio mass spectrometry,N,corrected for ice volume) earth science/paleoclimate/paleoceanography (delta 2H,C30 n-alkanoic acid,null,per mil VSMOW,null,paleoceanography,null,gas chromatography|isotope ratio mass spectrometry,N,null) earth science/paleoclimate/paleoceanography (delta 13C,C30 n-alkanoic acid,null,per mil VSMOW,null,paleoceanography,null,gas chromatography|isotope ratio mass spectrometry,N,null) earth science/paleoclimate/paleoceanography (delta 2H,C30 n-alkanoic acid,null,per mil VSMOW,null,paleoceanography,null,gas chromatography|isotope ratio mass spectrometry,N,corrected for ice volume) earth science/paleoclimate/climate reconstructions|paleoceanography (depth,null,null,centimeter,null,climate reconstructions|paleoceanography,null,null,N,null) earth science/paleoclimate/climate reconstructions|paleoceanography (precipitation,delta 2H,unspecified margin of error,percent,Jul-Sep,climate reconstructions|paleoceanography,null,Bayesian inference,N,error for Mean percent July-September rainfall) earth science/paleoclimate/climate reconstructions|paleoceanography (precipitation,delta 2H,null,percent,Jul-Sep,climate reconstructions|paleoceanography,null,Bayesian inference,N,Mean percent July-September rainfall) earth science/paleoclimate/climate reconstructions|paleoceanography (age,null,null,calendar year before present,null,climate reconstructions|paleoceanography,null,null,N,null) earth science/paleoclimate/paleocean earth science/paleoclimate/paleocean (NH-8P>LATITUDE 22.23>LONGITUDE -107.05) (MD02-2515>LATITUDE 27.4835>LONGITUDE -112.0743) (MD02-2517>LATITUDE 27.48>LONGITUDE -112.07) (JPC-56>LATITUDE 27.47>LONGITUDE -112.1) The North American monsoon, the dominant source of rainfall for much of the arid US Southwest, remains one of the least understood monsoon systems. The late Pleistocene evolution of this monsoon is poorly constrained, largely because glacial changes in winter rainfall obscure summer monsoon signatures in many regional proxy records. Here, we develop deglacial records of monsoon strength from isotopic analyses of leaf wax biomarkers in marine sediment cores. Reconstructions indicate a regional decrease in monsoon rainfall during the Last Glacial Maximum, and that the deglacial trajectory of the North American monsoon closely tracks changes in North American ice cover. In climate model simulations, North American ice cover shifts the westerlies southwards, favouring the mixing of cold, dry air into the US Southwest. This process, known as ventilation, weakens the monsoon by diluting the energy fluxes required for convection. As the ice sheet retreats northwards, the monsoon strengthens, and local ocean conditions may play a larger role in regulating its intensity. We conclude that on glacial-interglacial timescales, ice-sheet-induced reorganizations of atmospheric circulation have a dominant influence on the North American monsoon. STUDY NOTES: Stable isotope (dD and d13C) data on leaf waxes, plus summer (July-September) monsoon precipitation percent reconstructions from 4 sediment cores collected in the Guaymas Basin, Gulf of California, for the interval 9-12 kYrBP. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Bhattacharya, T. Investigator : Tierney, J.E. Investigator : Addison, J.A. Investigator : Murray, J.W. 2018-09-03 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/24890 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018md022515.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018jpc56.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018md022517.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018nh-8p.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018md022515.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018jpc56.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018md022517.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018nh-8p.txt English https://www.ncdc.noaa.gov/paleo/study/24890 https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018md022515.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018jpc56.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018md022517.txt https://www1.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/bhattacharya2018/bhattacharya2018nh-8p.txt Tripti Bhattacharya, Jessica E. Tierney, Jason A. Addison, James W. Murray2018Ice-sheet modulation of deglacial North American monsoon intensificationNature Geoscience10.1038/s41561-018-0220-7https://www.nature.com/articles/s41561-018-0220-7 START YEAR: 24266 cal yr BP * END YEAR: 1460 cal yr BP -112.1 22.23 -107.05 27.4835