Search

Your search keyword '"Phelps, Samuel R."' showing total 15 results
Start Over Author "Phelps, Samuel R."
15 results on '"Phelps, Samuel R."'

1. Oligocene-early Miocene paradox of pCO2 inferred from alkenone carbon isotopic fractionation and sea surface temperature trends.

Author

Guitián, José, Phelps, Samuel R., Wijker, Reto S., Polissar, Pratigya J., Arnold, Laura, and Stoll, Heather M.

Abstract

Atmospheric carbon dioxide decline is hypothesized to drive the progressive cooling over the Cenozoic. However, at multimillion-year timescales during the Oligocene to Miocene time interval the existing reconstructions, most based on the phytoplankton carbon isotopic fractionation (εp) proxy, differ from what is expected to drive the climate observations. Here, we produce two new long-term records of εp over the Oligocene to early Miocene time interval from widely separated locations at IODP Site 1406 and ODP 1168 and increase the resolution of determinations at the equatorial Atlantic ODP 925. These new results confirm a global footprint of εp shift occurring during this interval. Abrupt 3 ‰ declines are found from 27 to 24.5 Ma and 24 to 22.5 Ma, and minimum εp is attained at 19 Ma. Between 28.7 and 29.7 Ma at IODP 1406, a higher resolution sampling reveals orbital scale 100 kyr cyclicity in εp. Making use of alkenone-based sea surface temperature (SST) estimates and benthic δ18O estimated extracted from the same samples, we perform a direct comparison with εp to evaluate the relationship with climate dynamics. We observe that across the long Oligocene to early Miocene interval the two sites' relationships contrast with what is expected if CO2 was the main driver of εp and average earth surface temperature evolution was registered at the local surface SST and global benthic δ18O. Moreover, at orbital timescale, εp and benthic δ18O appear to follow an inverse relationship, although located within the multimillion-year period with the strongest direct correlation between these variables (>25.5 Ma). To evaluate the physiological, non- CO2 influences on εp, we use modern cultures to evaluate the impact of changing cell size and growth rate on the trends in εp. Although at specific time intervals, those drivers seem to explain part of the εp divergence with SST or benthic δ18O, most periods remain largely divergent, particularly the late Oligocene warming. We infer that a common CO2 forcing is likely the dominant control on the coherent temporal trends in εp at widely separated sites, which experienced contrasting temperature evolution and likely experienced different variations in nutrient availability. While CO2 changes likely caused significant changes in radiative forcing, SST variation at the examined sites may have been conditioned by regional heat transport, and the relationship between benthic δ18O and εp could reflect variable phasing between ice growth and global temperature. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

5. Oldest evidence of abundant C 4 grasses and habitat heterogeneity in eastern Africa

Author

Peppe, Daniel J., primary, Cote, Susanne M., additional, Deino, Alan L., additional, Fox, David L., additional, Kingston, John D., additional, Kinyanjui, Rahab N., additional, Lukens, William E., additional, MacLatchy, Laura M., additional, Novello, Alice, additional, Strömberg, Caroline A. E., additional, Driese, Steven G., additional, Garrett, Nicole D., additional, Hillis, Kayla R., additional, Jacobs, Bonnie F., additional, Jenkins, Kirsten E. H., additional, Kityo, Robert M., additional, Lehmann, Thomas, additional, Manthi, Fredrick K., additional, Mbua, Emma N., additional, Michel, Lauren A., additional, Miller, Ellen R., additional, Mugume, Amon A. T., additional, Muteti, Samuel N., additional, Nengo, Isaiah O., additional, Oginga, Kennedy O., additional, Phelps, Samuel R., additional, Polissar, Pratigya, additional, Rossie, James B., additional, Stevens, Nancy J., additional, Uno, Kevin T., additional, and McNulty, Kieran P., additional

Published
2023
Full Text
View/download PDF

7. Toward a Cenozoic history of atmospheric CO 2

Author

Hönisch, Bärbel, Royer, Dana L., Breecker, Daniel O., Polissar, Pratigya J., Bowen, Gabriel J., Henehan, Michael J., Cui, Ying, Steinthorsdottir, Margret, McElwain, Jennifer C., Kohn, Matthew J., Pearson, Ann, Phelps, Samuel R., Uno, Kevin T., Ridgwell, Andy, Anagnostou, Eleni, Austermann, Jacqueline, Badger, Marcus P. S., Barclay, Richard S., Bijl, Peter K., Chalk, Thomas B., Scotese, Christopher R., de la Vega, Elwyn, DeConto, Robert M., Dyez, Kelsey A., Ferrini, Vicki, Franks, Peter J., Giulivi, Claudia F., Gutjahr, Marcus, Harper, Dustin T., Haynes, Laura L., Huber, Matthew, Snell, Kathryn E., Keisling, Benjamin A., Konrad, Wilfried, Lowenstein, Tim K., Malinverno, Alberto, Guillermic, Maxence, Mejía, Luz María, Milligan, Joseph N., Morton, John J., Nordt, Lee, Whiteford, Ross, Roth-Nebelsick, Anita, Rugenstein, Jeremy K. C., Schaller, Morgan F., Sheldon, Nathan D., Sosdian, Sindia, Wilkes, Elise B., Witkowski, Caitlyn R., Zhang, Yi Ge, Anderson, Lloyd, Beerling, David J., Bolton, Clara, Cerling, Thure E., Cotton, Jennifer M., Da, Jiawei, Ekart, Douglas D., Foster, Gavin L., Greenwood, David R., Hyland, Ethan G., Jagniecki, Elliot A., Jasper, John P., Kowalczyk, Jennifer B., Kunzmann, Lutz, Kürschner, Wolfram M., Lawrence, Charles E., Lear, Caroline H., Martínez-Botí, Miguel A., Maxbauer, Daniel P., Montagna, Paolo, Naafs, B. David A., Rae, James W. B., Raitzsch, Markus, Retallack, Gregory J., Ring, Simon J., Seki, Osamu, Sepúlveda, Julio, Sinha, Ashish, Tesfamichael, Tekie F., Tripati, Aradhna, van der Burgh, Johan, Yu, Jimin, Zachos, James C., Zhang, Laiming, Hönisch, Bärbel, Royer, Dana L., Breecker, Daniel O., Polissar, Pratigya J., Bowen, Gabriel J., Henehan, Michael J., Cui, Ying, Steinthorsdottir, Margret, McElwain, Jennifer C., Kohn, Matthew J., Pearson, Ann, Phelps, Samuel R., Uno, Kevin T., Ridgwell, Andy, Anagnostou, Eleni, Austermann, Jacqueline, Badger, Marcus P. S., Barclay, Richard S., Bijl, Peter K., Chalk, Thomas B., Scotese, Christopher R., de la Vega, Elwyn, DeConto, Robert M., Dyez, Kelsey A., Ferrini, Vicki, Franks, Peter J., Giulivi, Claudia F., Gutjahr, Marcus, Harper, Dustin T., Haynes, Laura L., Huber, Matthew, Snell, Kathryn E., Keisling, Benjamin A., Konrad, Wilfried, Lowenstein, Tim K., Malinverno, Alberto, Guillermic, Maxence, Mejía, Luz María, Milligan, Joseph N., Morton, John J., Nordt, Lee, Whiteford, Ross, Roth-Nebelsick, Anita, Rugenstein, Jeremy K. C., Schaller, Morgan F., Sheldon, Nathan D., Sosdian, Sindia, Wilkes, Elise B., Witkowski, Caitlyn R., Zhang, Yi Ge, Anderson, Lloyd, Beerling, David J., Bolton, Clara, Cerling, Thure E., Cotton, Jennifer M., Da, Jiawei, Ekart, Douglas D., Foster, Gavin L., Greenwood, David R., Hyland, Ethan G., Jagniecki, Elliot A., Jasper, John P., Kowalczyk, Jennifer B., Kunzmann, Lutz, Kürschner, Wolfram M., Lawrence, Charles E., Lear, Caroline H., Martínez-Botí, Miguel A., Maxbauer, Daniel P., Montagna, Paolo, Naafs, B. David A., Rae, James W. B., Raitzsch, Markus, Retallack, Gregory J., Ring, Simon J., Seki, Osamu, Sepúlveda, Julio, Sinha, Ashish, Tesfamichael, Tekie F., Tripati, Aradhna, van der Burgh, Johan, Yu, Jimin, Zachos, James C., and Zhang, Laiming

Abstract

The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO 2 ) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO 2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO 2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO 2 thresholds in biological and cryosphere evolution. Editor’s summary The concentration of atmospheric carbon dioxide is a fundamental driver of climate, but its value is difficult to determine for times older than the roughly 800,000 years for which ice core records are available. The Cenozoic Carbon dioxide Proxy Integration Project (CenCO2PIP) Consortium assessed a comprehensive collection of proxy determinations to define the atmospheric carbon dioxide record for the past 66 million years. This synthesis provides the most complete record yet available and will help to better establish the role of carbon dioxide in climate, biological, and cryosphere evolution. — H. Jesse Smith

Published
2023
Full Text
View/download PDF

12. Hydrologic Changes Drove the Late Miocene Expansion of C4 Grasslands on the Northern Indian Subcontinent.

Author

Polissar, Pratigya J., Uno, Kevin T., Phelps, Samuel R., Karp, Allison T., Freeman, Katherine H., and Pensky, Jennifer L.

Subjects
TROPICAL dry forests, MIOCENE Epoch, GRASSLAND soils, GRASSLANDS, HYDROGEN isotopes, CARBON 4 photosynthesis
Abstract

Modern tropical and subtropical C4 grasslands and savannas were established during the late‐Miocene and Pliocene, over 20 Myr after evolutionary originations of the C4 photosynthetic pathway. This lag suggests environmental factors first limited and then favored C4 plants. Here, we examine the timing and drivers for the establishment of C4 grasslands on the Indian Subcontinent using carbon and hydrogen isotope signatures of plant‐wax n‐alkanes recovered from turbidites in the Bengal Fan. Like prior studies, we find C4 ecosystems in the Ganges‐Brahmaputra catchment first emerged at 7.4 Ma and subsequently expanded between 6.9 to ∼6.0 Ma. Hydrogen isotope values varied from 10.2 to 7.4 Ma and then increased after 7.4, which suggests intermittent drying began before the establishment of C4 grasslands with further drying at the onset of C4 expansion. Synthesis of published plant fossil data from the Siwalik Group of the Himalayan foreland basin documents an ecosystem trajectory from evergreen tropical forests to seasonally deciduous forests, and then expansive C4 grasslands. This trajectory coincided with a seasonally uneven drying trend due to both increased evaporation of plant leaf and soil waters and reduced rainfall, as identified in soil carbonate and tooth enamel data sets. Collectively the fossil, biomarker, and isotopic evidence reveal the development of modern C4 ecosystems on the Indian Subcontinent followed a series of ecosystem transformations driven by drying and fire feedbacks, and possibly declining atmospheric pCO2, beginning at 10.2 Ma and strengthening through the late Miocene. Key Points: Late Miocene expansion of C4 grasslands in the Bengal Fan catchment followed prior ecological change from evergreen to dry deciduous forestsSynthesis of isotopic and ecological records from Himalayan foreland basin reveals ecological change and multifaceted hydrologic change preceded C4 grassland expansionSeasonal reduction in rainfall and increased evaporation promoted ecosystem change, accelerated by ecological feedbacks [ABSTRACT FROM AUTHOR]

Published
2021
Full Text
View/download PDF

13. Synchronous rise of African C4ecosystems 10 million years ago in the absence of aridification

Author

Polissar, Pratigya J., Rose, Cassaundra, Uno, Kevin T., Phelps, Samuel R., and deMenocal, Peter

Abstract

Grasslands expanded globally during the late Cenozoic and the development of these ecosystems shaped the evolution of many faunal groups, including our hominin ancestors. The emergence of these ecosystems has been dated in many regions, but the origins of the iconic African C4savannah grasslands remain poorly known, as do the causal factors that led to their establishment. Here we document their origins with the distinct carbon isotope signature from the hot-, arid- and low-CO2-adapted C4grasses that dominate modern savannahs and grasslands. We use the carbon isotope values of leaf-wax molecules in deep-sea drill cores to measure the rise of African C4ecosystems. We also reconstruct African palaeohydroclimate change from leaf-wax hydrogen isotope values and dust deposition rates in these cores. We find that C4-dominated ecosystems expanded synchronously across Northwestern and East Africa after 10 million years ago. This was not accompanied by substantial changes in palaeohydrology or dust deposition, precluding aridification as a causal factor. The expansion of C4grasses was coincident, however, with dramatic high-latitude cooling and increased pole–Equator temperature gradients. We suggest that declining atmospheric CO2levels were a direct cause of the C4grassland expansion.

Published
2019
Full Text
View/download PDF

14. Toward a Cenozoic history of atmospheric CO2

Author

Hönisch, Bärbel, Royer, Dana L., Breecker, Daniel O., Polissar, Pratigya J., Bowen, Gabriel J., Henehan, Michael J., Cui, Ying, Steinthorsdottir, Margret, McElwain, Jennifer C., Kohn, Matthew J., Pearson, Ann, Phelps, Samuel R., Uno, Kevin T., Ridgwell, Andy, Anagnostou, Eleni, Austermann, Jacqueline, Badger, Marcus, Barclay, Richard S., Bijl, Peter K., Chalk, Thomas B., Scotese, Christopher R., de la Vega, Elwyn, DeConto, Robert M., Dyez, Kelsey A., Ferrini, Vicki, Franks, Peter J., Giulivi, Claudia F., Gutjahr, Marcus, Harper, Dustin T., Haynes, Laura L., Huber, Matthew, Snell, Kathryn E., Keisling, Benjamin A., Konrad, Wilfried, Lowenstein, Tim K., Malinverno, Alberto, Guillermic, Maxence, Mejía, Luz María, Milligan, Joseph N., Morton, John J., Nordt, Lee, Whiteford, Ross, Roth-Nebelsick, Anita, Rugenstein, Jeremy K. C., Schaller, Morgan F., Sheldon, Nathan D., Sosdian, Sindia, Wilkes, Elise B., Witkowski, Caitlyn R., Zhang, Yi Ge, Anderson, Lloyd, Beerling, David J., Bolton, Clara, Cerling, Thure E., Cotton, Jennifer M., Da, Jiawei, Ekart, Douglas D., Foster, Gavin L., Greenwood, David R., Hyland, Ethan G., Jagniecki, Elliot A., Jasper, John P., Kowalczyk, Jennifer B., Kunzmann, Lutz, Kürschner, Wolfram M., Lawrence, Charles E., Lear, Caroline H., Martínez-Botí, Miguel A., Maxbauer, Daniel P., Montagna, Paolo, Naafs, B. David A., Rae, James W. B., Raitzsch, Markus, Retallack, Gregory J., Ring, Simon J., Seki, Osamu, Sepúlveda, Julio, Sinha, Ashish, Tesfamichael, Tekie F., Tripati, Aradhna, van der Burgh, Johan, Yu, Jimin, Zachos, James C., Zhang, Laiming, Hönisch, Bärbel, Royer, Dana L., Breecker, Daniel O., Polissar, Pratigya J., Bowen, Gabriel J., Henehan, Michael J., Cui, Ying, Steinthorsdottir, Margret, McElwain, Jennifer C., Kohn, Matthew J., Pearson, Ann, Phelps, Samuel R., Uno, Kevin T., Ridgwell, Andy, Anagnostou, Eleni, Austermann, Jacqueline, Badger, Marcus, Barclay, Richard S., Bijl, Peter K., Chalk, Thomas B., Scotese, Christopher R., de la Vega, Elwyn, DeConto, Robert M., Dyez, Kelsey A., Ferrini, Vicki, Franks, Peter J., Giulivi, Claudia F., Gutjahr, Marcus, Harper, Dustin T., Haynes, Laura L., Huber, Matthew, Snell, Kathryn E., Keisling, Benjamin A., Konrad, Wilfried, Lowenstein, Tim K., Malinverno, Alberto, Guillermic, Maxence, Mejía, Luz María, Milligan, Joseph N., Morton, John J., Nordt, Lee, Whiteford, Ross, Roth-Nebelsick, Anita, Rugenstein, Jeremy K. C., Schaller, Morgan F., Sheldon, Nathan D., Sosdian, Sindia, Wilkes, Elise B., Witkowski, Caitlyn R., Zhang, Yi Ge, Anderson, Lloyd, Beerling, David J., Bolton, Clara, Cerling, Thure E., Cotton, Jennifer M., Da, Jiawei, Ekart, Douglas D., Foster, Gavin L., Greenwood, David R., Hyland, Ethan G., Jagniecki, Elliot A., Jasper, John P., Kowalczyk, Jennifer B., Kunzmann, Lutz, Kürschner, Wolfram M., Lawrence, Charles E., Lear, Caroline H., Martínez-Botí, Miguel A., Maxbauer, Daniel P., Montagna, Paolo, Naafs, B. David A., Rae, James W. B., Raitzsch, Markus, Retallack, Gregory J., Ring, Simon J., Seki, Osamu, Sepúlveda, Julio, Sinha, Ashish, Tesfamichael, Tekie F., Tripati, Aradhna, van der Burgh, Johan, Yu, Jimin, Zachos, James C., and Zhang, Laiming

Abstract

The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO2) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO2 thresholds in biological and cryosphere evolution.

15. Toward a Cenozoic history of atmospheric CO 2 .

Author

Hönisch B, Royer DL, Breecker DO, Polissar PJ, Bowen GJ, Henehan MJ, Cui Y, Steinthorsdottir M, McElwain JC, Kohn MJ, Pearson A, Phelps SR, Uno KT, Ridgwell A, Anagnostou E, Austermann J, Badger MPS, Barclay RS, Bijl PK, Chalk TB, Scotese CR, de la Vega E, DeConto RM, Dyez KA, Ferrini V, Franks PJ, Giulivi CF, Gutjahr M, Harper DT, Haynes LL, Huber M, Snell KE, Keisling BA, Konrad W, Lowenstein TK, Malinverno A, Guillermic M, Mejía LM, Milligan JN, Morton JJ, Nordt L, Whiteford R, Roth-Nebelsick A, Rugenstein JKC, Schaller MF, Sheldon ND, Sosdian S, Wilkes EB, Witkowski CR, Zhang YG, Anderson L, Beerling DJ, Bolton C, Cerling TE, Cotton JM, Da J, Ekart DD, Foster GL, Greenwood DR, Hyland EG, Jagniecki EA, Jasper JP, Kowalczyk JB, Kunzmann L, Kürschner WM, Lawrence CE, Lear CH, Martínez-Botí MA, Maxbauer DP, Montagna P, Naafs BDA, Rae JWB, Raitzsch M, Retallack GJ, Ring SJ, Seki O, Sepúlveda J, Sinha A, Tesfamichael TF, Tripati A, van der Burgh J, Yu J, Zachos JC, and Zhang L

Abstract

The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO 2 ) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO 2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO 2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO 2 thresholds in biological and cryosphere evolution.

Published
2023
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results