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Knapp S, Burls NJ, Dee S, Feng R, Feakins SJ, Bhattacharya T. A Pliocene Precipitation Isotope Proxy-Model Comparison Assessing the Hydrological Fingerprints of Sea Surface Temperature Gradients. PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY 2022; 37:e2021PA004401. [PMID: 37082439 PMCID: PMC10108060 DOI: 10.1029/2021pa004401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Revised: 12/14/2022] [Accepted: 12/15/2022] [Indexed: 05/03/2023]
Abstract
The Pliocene offers insights into future climate, with near-modern atmospheric pCO2 and global mean surface temperature estimated to be 3-4°C above pre-industrial. However, the hydrological response differs between future global warming and early Pliocene climate model simulations. This discrepancy results from the use of reduced meridional and zonal sea surface temperature (SST) gradients, based on foraminiferal Mg/Ca and Alkenone proxy evidence, to force the early Pliocene simulation. Subsequent, SST reconstructions based on the organic proxy TEX86, have found warmer temperatures in the warm pool, bringing the magnitude of the gradient reductions into dispute. We design an independent test of Pliocene SST scenarios and their hydrological cycle "fingerprints." We use an isotope-enabled General Circulation Model, iCAM5, to model the distribution of water isotopes in precipitation in response to four climatological SST and sea-ice fields representing modern, abrupt 4 × CO2, late Pliocene and early Pliocene climates. We conduct a proxy-model comparison with all the available precipitation isotope proxy data, and we identify target regions that carry precipitation isotopic fingerprints of SST gradients as priorities for additional proxy reconstructions. We identify two regions with distinct precipitation isotope (D/H) fingerprints resulting from reduced SST gradients: the Maritime Continent (D-enriched due to reduced convective rainfall) and the Sahel (wetter, more deep convection, D-depleted). The proxy-model comparison using available plant wax reconstructions, mostly from Africa, is promising but inconclusive. Additional proxy reconstructions are needed in both target regions and in much of the world for significant tests of SST scenarios and dynamical linkages to the hydrological cycle.
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Affiliation(s)
- Scott Knapp
- Department of Atmospheric, Oceanic, and Earth SciencesGeorge Mason UniversityFairfaxVAUSA
| | - Natalie J. Burls
- Department of Atmospheric, Oceanic, and Earth SciencesGeorge Mason UniversityFairfaxVAUSA
| | - Sylvia Dee
- Department of Earth, Environmental and Planetary SciencesRice UniversityHoustonTXUSA
| | - Ran Feng
- Department of GeosciencesUniversity of ConnecticutStorrsCNUSA
| | - Sarah J. Feakins
- Department of Earth SciencesUniversity of Southern CaliforniaLos AngelesCAUSA
| | - Tripti Bhattacharya
- Department of Earth and Environmental SciencesSyracuse UniversitySyracuseNYUSA
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Shi M, Worden JR, Bailey A, Noone D, Risi C, Fu R, Worden S, Herman R, Payne V, Pagano T, Bowman K, Bloom AA, Saatchi S, Liu J, Fisher JB. Amazonian terrestrial water balance inferred from satellite-observed water vapor isotopes. Nat Commun 2022; 13:2686. [PMID: 35562340 PMCID: PMC9106687 DOI: 10.1038/s41467-022-30317-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 04/26/2022] [Indexed: 11/09/2022] Open
Abstract
Atmospheric humidity and soil moisture in the Amazon forest are tightly coupled to the region’s water balance, or the difference between two moisture fluxes, evapotranspiration minus precipitation (ET-P). However, large and poorly characterized uncertainties in both fluxes, and in their difference, make it challenging to evaluate spatiotemporal variations of water balance and its dependence on ET or P. Here, we show that satellite observations of the HDO/H2O ratio of water vapor are sensitive to spatiotemporal variations of ET-P over the Amazon. When calibrated by basin-scale and mass-balance estimates of ET-P derived from terrestrial water storage and river discharge measurements, the isotopic data demonstrate that rainfall controls wet Amazon water balance variability, but ET becomes important in regulating water balance and its variability in the dry Amazon. Changes in the drivers of ET, such as above ground biomass, could therefore have a larger impact on soil moisture and humidity in the dry (southern and eastern) Amazon relative to the wet Amazon. The evolution of the Amazon forest is tightly coupled to its terrestrial water balance. Here, the authors show that forest biomass changes in the Amazon are a driver of the spatiotemporal variation of evapotranspiration, and such changes could have a larger impact on water availability in the dry regions (southern, eastern) of the Amazon.
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Affiliation(s)
- Mingjie Shi
- Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, USA. .,Pacific Northwest National Laboratory, 902 Battelle Blvd, Richland, WA, USA.
| | - John R Worden
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
| | - Adriana Bailey
- National Center for Atmospheric Research, Boulder, CO, USA
| | - David Noone
- University of Auckland, Auckland, New Zealand
| | - Camille Risi
- Laboratoire de Météorologie Dynamique, Paris, France
| | - Rong Fu
- University of California, Los Angeles, CA, USA
| | | | - Robert Herman
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Vivienne Payne
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Thomas Pagano
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Kevin Bowman
- Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, USA.,Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - A Anthony Bloom
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Sassan Saatchi
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Junjie Liu
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.,California Institute of Technology, Pasadena, CA, USA
| | - Joshua B Fisher
- Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, USA.,Schmid College of Science and Technology, Chapman University, 1 University Drive, Orange, CA, USA
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Risi C, Muller C, Blossey P. Rain Evaporation, Snow Melt, and Entrainment at the Heart of Water Vapor Isotopic Variations in the Tropical Troposphere, According to Large-Eddy Simulations and a Two-Column Model. JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 2021; 13:e2020MS002381. [PMID: 33868576 PMCID: PMC8047889 DOI: 10.1029/2020ms002381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 02/08/2021] [Accepted: 02/15/2021] [Indexed: 06/12/2023]
Abstract
We aim at developing a simple model as an interpretative framework for the water vapor isotopic variations in the tropical troposphere over the ocean. We use large-eddy simulations of disorganized convection in radiative-convective equilibrium to justify the underlying assumptions of this simple model, to constrain its input parameters and to evaluate its results. We also aim at interpreting the depletion of the water vapor isotopic composition in the lower and midtroposphere as precipitation increases, which is a salient feature in tropical oceanic observations. This feature constitutes a stringent test on the relevance of our interpretative framework. Previous studies, based on observations or on models with parameterized convection, have highlighted the roles of deep convective and mesoscale downdrafts, rain evaporation, rain-vapor diffusive exchanges, and mixing processes. The interpretative framework that we develop, valid in case of disorganized convection, is a two-column model representing the net ascent in clouds and the net descent in the environment. We show that the mechanisms for depleting the troposphere as the precipitation rate increases all stem from the higher tropospheric relative humidity. First, when the relative humidity is larger, less snow sublimates before melting and a smaller fraction of rain evaporates. Both effects lead to more depleted rain evaporation and eventually more depleted water vapor. This mechanism dominates in regimes of large-scale ascent. Second, the entrainment of dry air into clouds reduces the vertical isotopic gradient and limits the depletion of tropospheric water vapor. This mechanism dominates in regimes of large-scale descent.
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Affiliation(s)
- Camille Risi
- Laboratoire de Meteorologie DynamiqueIPSLCNRSEcole Normale SuperieureSorbonne UniversitePSL Research UniversityParisFrance
| | - Caroline Muller
- Laboratoire de Meteorologie DynamiqueIPSLCNRSEcole Normale SuperieureSorbonne UniversitePSL Research UniversityParisFrance
| | - Peter Blossey
- Department of Atmospheric SciencesUniversity of WashingtonSeattleWAUSA
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