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Your search keyword '"Esper, O. M."' showing total 10 results
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10 results on '"Esper, O. M."'

1. Late Miocene to Early Pliocene paleoceanographic evolution of the Central South Pacific: A deep-sea benthic foraminiferal perspective

Author

Das, S, Mahanta, N, Sahoo, B, Singh, R, Alvarez Zarikian, C, Tiwari, M, Vats, N, Nihal, Lamy, F, Winckler, G, Middleton, J, Arz, H, Gottschalk, J, Basak, C, Brombacher, A, Esper, O, Farmer, J, Herbert, L, Iwasaki, S, Lembke-Jene, L, Lawson, V, Lo, L, Malinverno, E, Michel, E, Moretti, S, Moy, C, Ravelo, A, Riesselman, C, Saavedra-Pellitero, M, Seo, I, Smith, R, Souza, A, Stoner, J, de Oliveira, I, Wan, S, Zhao, X, Das S. K., Mahanta N., Sahoo B., Singh R. K., Alvarez Zarikian C. A., Tiwari M., Vats N., Lamy F., Winckler G., Middleton J. L., Arz H. W., Gottschalk J., Basak C., Brombacher A., Esper O. M., Farmer J. R., Herbert L. C., Iwasaki S., Lembke-Jene L., Lawson V. J., Lo L., Malinverno E., Michel E., Moretti S., Moy C. M., Ravelo A. C., Riesselman C. R., Saavedra-Pellitero M., Seo I., Smith R. A., Souza A. L., Stoner J. S., de Oliveira I. V. M. P., Wan S., Zhao X., Das, S, Mahanta, N, Sahoo, B, Singh, R, Alvarez Zarikian, C, Tiwari, M, Vats, N, Nihal, Lamy, F, Winckler, G, Middleton, J, Arz, H, Gottschalk, J, Basak, C, Brombacher, A, Esper, O, Farmer, J, Herbert, L, Iwasaki, S, Lembke-Jene, L, Lawson, V, Lo, L, Malinverno, E, Michel, E, Moretti, S, Moy, C, Ravelo, A, Riesselman, C, Saavedra-Pellitero, M, Seo, I, Smith, R, Souza, A, Stoner, J, de Oliveira, I, Wan, S, Zhao, X, Das S. K., Mahanta N., Sahoo B., Singh R. K., Alvarez Zarikian C. A., Tiwari M., Vats N., Lamy F., Winckler G., Middleton J. L., Arz H. W., Gottschalk J., Basak C., Brombacher A., Esper O. M., Farmer J. R., Herbert L. C., Iwasaki S., Lembke-Jene L., Lawson V. J., Lo L., Malinverno E., Michel E., Moretti S., Moy C. M., Ravelo A. C., Riesselman C. R., Saavedra-Pellitero M., Seo I., Smith R. A., Souza A. L., Stoner J. S., de Oliveira I. V. M. P., Wan S., and Zhao X.

Abstract

The bottom water conditions in the Central South Pacific (CSP) and associated changes in the Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW) under warmer-than-present conditions need to be better understood. These water masses transfer their properties to the major ocean basins. We analyzed Late Miocene to Early Pliocene (5.6–3.6 Ma) marine sediment core sections from the CSP for benthic foraminifera, ice rafted debris (IRD), Ostracoda, planktic foraminifera Orbulina universa abundance, and organic geochemical proxies to assess the bottom water characteristics under warmer-than-present day conditions. A significant increase in IRD abundance between 5.3 and 4.9 Ma marks the Early Pliocene warm phase. The benthic foraminiferal assemblages indicate shifts in bottom water conditions over time in the CSP region. Between 5.6 and 5.3 Ma, predominantly oxygenated bottom water with moderate organic matter flux prevailed. This shifted to suboxic conditions with increased organic matter flux from 5.3 to 4.9 Ma. Subsequently, between 4.9 and 4.4 Ma, bottom water conditions alternated frequently between oxic and suboxic states. Enhanced bottom water formation and inflow of LCDW and AABW in the CSP during 4.4–4.0 Ma promoted oxygenated conditions, accompanied by low organic export flux. However, sluggish bottom water circulation from 4.0 to 3.6 Ma reverted to suboxic conditions, associated with increased carbon burial. Notably, productivity peaked intermittently between 5.3 and 3.6 Ma, as indicated by the occurrence of suboxic species assemblages and increase in the abundance of Orbulina universa, benthic microfauna (ostracods), and other paleoproductivity indicators.

Published
2024

2. Five million years of Antarctic Circumpolar Current strength variability

Author

Lamy, F, Winckler, G, Arz, H, Farmer, J, Gottschalk, J, Lembke-Jene, L, Middleton, J, van der Does, M, Tiedemann, R, Alvarez Zarikian, C, Basak, C, Brombacher, A, Dumm, L, Esper, O, Herbert, L, Iwasaki, S, Kreps, G, Lawson, V, Lo, L, Malinverno, E, Martinez-Garcia, A, Michel, E, Moretti, S, Moy, C, Ravelo, A, Riesselman, C, Saavedra-Pellitero, M, Sadatzki, H, Seo, I, Singh, R, Smith, R, Souza, A, Stoner, J, Toyos, M, de Oliveira, I, Wan, S, Wu, S, Zhao, X, Lamy F., Winckler G., Arz H. W., Farmer J. R., Gottschalk J., Lembke-Jene L., Middleton J. L., van der Does M., Tiedemann R., Alvarez Zarikian C., Basak C., Brombacher A., Dumm L., Esper O. M., Herbert L. C., Iwasaki S., Kreps G., Lawson V. J., Lo L., Malinverno E., Martinez-Garcia A., Michel E., Moretti S., Moy C. M., Ravelo A. C., Riesselman C. R., Saavedra-Pellitero M., Sadatzki H., Seo I., Singh R. K., Smith R. A., Souza A. L., Stoner J. S., Toyos M., de Oliveira I. M. V. P., Wan S., Wu S., Zhao X., Lamy, F, Winckler, G, Arz, H, Farmer, J, Gottschalk, J, Lembke-Jene, L, Middleton, J, van der Does, M, Tiedemann, R, Alvarez Zarikian, C, Basak, C, Brombacher, A, Dumm, L, Esper, O, Herbert, L, Iwasaki, S, Kreps, G, Lawson, V, Lo, L, Malinverno, E, Martinez-Garcia, A, Michel, E, Moretti, S, Moy, C, Ravelo, A, Riesselman, C, Saavedra-Pellitero, M, Sadatzki, H, Seo, I, Singh, R, Smith, R, Souza, A, Stoner, J, Toyos, M, de Oliveira, I, Wan, S, Wu, S, Zhao, X, Lamy F., Winckler G., Arz H. W., Farmer J. R., Gottschalk J., Lembke-Jene L., Middleton J. L., van der Does M., Tiedemann R., Alvarez Zarikian C., Basak C., Brombacher A., Dumm L., Esper O. M., Herbert L. C., Iwasaki S., Kreps G., Lawson V. J., Lo L., Malinverno E., Martinez-Garcia A., Michel E., Moretti S., Moy C. M., Ravelo A. C., Riesselman C. R., Saavedra-Pellitero M., Sadatzki H., Seo I., Singh R. K., Smith R. A., Souza A. L., Stoner J. S., Toyos M., de Oliveira I. M. V. P., Wan S., Wu S., and Zhao X.

Abstract

The Antarctic Circumpolar Current (ACC) represents the world’s largest ocean-current system and affects global ocean circulation, climate and Antarctic ice-sheet stability1–3. Today, ACC dynamics are controlled by atmospheric forcing, oceanic density gradients and eddy activity4. Whereas palaeoceanographic reconstructions exhibit regional heterogeneity in ACC position and strength over Pleistocene glacial–interglacial cycles5–8, the long-term evolution of the ACC is poorly known. Here we document changes in ACC strength from sediment cores in the Pacific Southern Ocean. We find no linear long-term trend in ACC flow since 5.3 million years ago (Ma), in contrast to global cooling9 and increasing global ice volume10. Instead, we observe a reversal on a million-year timescale, from increasing ACC strength during Pliocene global cooling to a subsequent decrease with further Early Pleistocene cooling. This shift in the ACC regime coincided with a Southern Ocean reconfiguration that altered the sensitivity of the ACC to atmospheric and oceanic forcings11–13. We find ACC strength changes to be closely linked to 400,000-year eccentricity cycles, probably originating from modulation of precessional changes in the South Pacific jet stream linked to tropical Pacific temperature variability14. A persistent link between weaker ACC flow, equatorward-shifted opal deposition and reduced atmospheric CO2 during glacial periods first emerged during the Mid-Pleistocene Transition (MPT). The strongest ACC flow occurred during warmer-than-present intervals of the Plio-Pleistocene, providing evidence of potentially increasing ACC flow with future climate warming.

Published
2024

3. Expedition 383 summary

Author

Lamy, F., Winckler, G., Alvarez Zarikian, C.A., and the Expedition 383 Scientists, Winckler, G, Lamy, F, Alvarez Zarikian, C, Arz, H, Basak, C, Brombacher, A, Esper, O, Farmer, J, Gottschalk, J, Herbert, L, Iwasaki, S, Lawson, V, Lembke-Jene, L, Lo, L, Malinverno, E, Michel, E, Middleton, J, Moretti, S, Moy, C, Ravelo, A, Riesselman, C, Saavedra-Pellitero, M, Seo, I, Singh, R, Smith, R, Souza, A, Stoner, J, Venancio, I, Wan, S, Zhao, X, Foucher McColl, N, Winckler, G., Lamy, F., Alvarez Zarikian, C. A., Arz, H. W., Basak, C., Brombacher, A., Esper, O. M., Farmer, J. R., Gottschalk, J., Herbert, L. C., Iwasaki, S., Lawson, V. J., Lembke-Jene, L., Lo, L., Malinverno, E., Michel, E., Middleton, J. L., Moretti, S., Moy, C. M., Ravelo, A. C., Riesselman, C. R., Saavedra-Pellitero, M., Seo, I., Singh, R. K., Smith, R. A., Souza, A. L., Stoner, J. S., Venancio, I. M., Wan, S., Zhao, X., Foucher McColl, N., Lamy, F., Winckler, G., Alvarez Zarikian, C.A., and the Expedition 383 Scientists, Winckler, G, Lamy, F, Alvarez Zarikian, C, Arz, H, Basak, C, Brombacher, A, Esper, O, Farmer, J, Gottschalk, J, Herbert, L, Iwasaki, S, Lawson, V, Lembke-Jene, L, Lo, L, Malinverno, E, Michel, E, Middleton, J, Moretti, S, Moy, C, Ravelo, A, Riesselman, C, Saavedra-Pellitero, M, Seo, I, Singh, R, Smith, R, Souza, A, Stoner, J, Venancio, I, Wan, S, Zhao, X, Foucher McColl, N, Winckler, G., Lamy, F., Alvarez Zarikian, C. A., Arz, H. W., Basak, C., Brombacher, A., Esper, O. M., Farmer, J. R., Gottschalk, J., Herbert, L. C., Iwasaki, S., Lawson, V. J., Lembke-Jene, L., Lo, L., Malinverno, E., Michel, E., Middleton, J. L., Moretti, S., Moy, C. M., Ravelo, A. C., Riesselman, C. R., Saavedra-Pellitero, M., Seo, I., Singh, R. K., Smith, R. A., Souza, A. L., Stoner, J. S., Venancio, I. M., Wan, S., Zhao, X., and Foucher McColl, N.

Abstract

The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and is constricted to its narrowest extent in the Drake Passage. Fresh and cold Pacific surface and intermediate water flowing through the Drake Passage (cold-water route) and warm Indian Ocean water masses flowing through the Agulhas region (warm-water route) are critical for the South Atlantic contribution to Meridional Overturning Circulation changes. Furthermore, physical and biological processes associated with the ACC affect the strength of the ocean carbon pump and therefore are critical to feedbacks linking atmospheric CO2 concentrations, ocean circulation, and climate/cryosphere on a global scale. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, there are no deep-sea drilling paleoceanographic records from the Pacific sector of the ACC. To advance our understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 recovered sedimentary sequences at (1) three sites in the central South Pacific (CSP) (U1539, U1540, and U1541), (2) two sites at the Chilean margin (U1542 and U1544), and (3) one site from the pelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Because of persistently stormy conditions and the resulting bad weather avoidance, we were not successful in recovering the originally planned Proposed Site CSP-3A in the Polar Frontal Zone of the CSP. The drilled sediments at Sites U1541 and U1543 reach back to the late Miocene, and those at Site U1540 reach back to the early Pliocene. High sedimentation rate s

Published
2021

4. Expedition 383 summary.

Author

Winckler, G., Lamy, F., Zarikian, C. A. Alvarez, Arz, H. W., Basak, C., Brombacher, A., Esper, O. M., Farmer, J. R., Gottschalk, J., Herbert, L. C., Iwasaki, S., Lawson, V. J., Lembke-Jene, L., Lo, L., Malinverno, E., Michel, E., Middleton, J. L., Moretti, S., Moy, C. M., and Ravelo, A. C.

Subjects
ANTARCTIC Circumpolar Current, CARBON cycle, BIOLOGICAL productivity, ICE sheets, PALEOCEANOGRAPHY
Abstract

The Antarctic Circumpolar Current (ACC), the world's strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and is constricted to its narrowest extent in the Drake Passage. Fresh and cold Pacific surface and intermediate water flowing through the Drake Passage (cold-water route) and warm Indian Ocean water masses flowing through the Agulhas region (warmwater route) are critical for the South Atlantic contribution to Meridional Overturning Circulation changes. Furthermore, physical and biological processes associated with the ACC affect the strength of the ocean carbon pump and therefore are critical to feedbacks linking atmospheric CO2 concentrations, ocean circulation, and climate/cryosphere on a global scale. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, there are no deep-sea drilling paleoceanographic records from the Pacific sector of the ACC. To advance our understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 recovered sedimentary sequences at (1) three sites in the central South Pacific (CSP) (U1539, U1540, and U1541), (2) two sites at the Chilean margin (U1542 and U1544), and (3) one site from the pelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Because of persistently stormy conditions and the resulting bad weather avoidance, we were not successful in recovering the originally planned Proposed Site CSP-3A in the Polar Frontal Zone of the CSP. The drilled sediments at Sites U1541 and U1543 reach back to the late Miocene, and those at Site U1540 reach back to the early Pliocene. High sedimentation rate sequences reaching back to the early Pleistocene (Site U1539) and the late Pleistocene (Sites U1542 and U1544) were recovered in both the CSP and at the Chilean margin. Taken together, the sites represent a depth transect from ~1100 m at Chilean margin Site U1542 to ~4070 m at CSP Site U1539 and allow investigation of changes in the vertical structure of the ACC, a key issue for understanding the role of the Southern Ocean in the global carbon cycle. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic-, carbonate-, and opalbased proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep-ocean variations and their relation to atmosphere and cryosphere changes. [ABSTRACT FROM AUTHOR]

Published
2021
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5. Site U1544.

Author

Lamy, F., Winckler, G., Zarikian, C. A. Alvarez, Arz, H. W., Basak, C., Brombacher, A., Esper, O. M., Farmer, J. R., Gottschalk, J., Herbert, L. C., Iwasaki, S., Lawson, V. J., Lembke-Jene, L., Lo, L., Malinverno, E., Michel, E., Middleton, J. L., Moretti, S., Moy, C. M., and Ravelo, A. C.

Subjects
OCEANOGRAPHY, OCEAN temperature, CARBON cycle, BIOLOGICAL productivity, ICE sheets
Published
2021
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6. Site U1541.

Author

Winckler, G., Lamy, F., Zarikian, C. A. Alvarez, Arz, H. W., Basak, C., Brombacher, A., Esper, O. M., Farmer, J. R., Gottschalk, J., Herbert, L. C., Iwasaki, S., Lawson, V. J., Lembke-Jene, L., Lo, L., Malinverno, E., Michel, E., Middleton, J. L., Moretti, S., Moy, C. M., and Ravelo, A. C.

Subjects
CARBON cycle, BIOLOGICAL productivity, ICE sheets, OCEAN temperature
Published
2021
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7. Expedition 383 methods.

Author

Winckler, G., Lamy, F., Zarikian, C. A. Alvarez, Arz, H. W., Basak, C., Brombacher, A., Esper, O. M., Farmer, J. R., Gottschalk, J., Herbert, L. C., Iwasaki, S., Lawson, V. J., Lembke-Jene, L., Lo, L., Malinverno, E., Michel, E., Middleton, J. L., Moretti, S., Moy, C. M., and Ravelo, A. C.

Subjects
ICE sheets, CARBON cycle, GLOBAL Positioning System, INFORMATION retrieval
Published
2021
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8. Site U1525.

Author

McKay, R. M., De Santis, L., Kulhanek, D. K., Ash, J. L., Beny, F., Browne, I. M., Cortese, G., de Sousa, I. M. Cordeiro, Dodd, J. P., Esper, O. M., Gales, J. A., Harwood, D. M., Ishino, S., Keisling, B. A., Kim, S., Laberg, J. S., Leckie, R. M., Müller, J., Patterson, M. O., and Romans, B. W.

Subjects
UNDERWATER exploration, SEDIMENTATION & deposition, PALEOCEANOGRAPHY, SUBMARINE topography, ICE sheets, OCEAN circulation
Published
2019
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9. Expedition 374 methods.

Author

McKay, R. M., De Santis, L., Kulhanek, D. K., Ash, J. L., Beny, F., Browne, I. M., Cortese, G., de Sousa, I. M. Cordeiro, Dodd, J. P., Esper, O. M., Gales, J. A., Harwood, D. M., Ishino, S., Keisling, B. A., Kim, S., Laberg, J. S., Leckie, R. M., Müller, J., Patterson, M. O., and Romans, B. W.

Subjects
UNDERWATER exploration, GLOBAL Positioning System, DRILLING platforms, ICE sheets
Published
2019
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10. Expedition 374 summary.

Author

McKay, R. M., De Santis, L., Kulhanek, D. K., Ash, J. L., Beny, F., Browne, I. M., Cortese, G., de Sousa, I. M. Cordeiro, Dodd, J. P., Esper, O. M., Gales, J. A., Harwood, D. M., Ishino, S., Keisling, B. A., Kim, S., Laberg, J. S., Leckie, R. M., Müller, J., Patterson, M. O., and Romans, B. W.

Subjects
ICE sheets, OCEAN currents, SCIENTIFIC expeditions, ATMOSPHERIC temperature, CLIMATE change
Published
2019
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