Deciphering the State of the Late Miocene to Early Pliocene Equatorial Pacific

A. J. Drury; G. P. Lee; W. R. Gray; M. Lyle; T. Westerhold; Amelia E. Shevenell; C. M. John

doi:10.1002/2017PA003245

Deciphering the State of the Late Miocene to Early Pliocene Equatorial Pacific

A. J. Drury, G. P. Lee, W. R. Gray, M. Lyle, T. Westerhold, Amelia E. Shevenell, C. M. John

College of Marine Science

Research output: Contribution to journal › Article › peer-review

Abstract

The late Miocene&hyphen;early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here we present the first continuous late Miocene&hyphen;early Pliocene (8.0–4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0–3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest that mean sea surface temperatures (SSTs) are ~27.8 ± 1.1°C (1σ) between 6.4 and 5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2 and 6.1 Ma and an up to 3°C warming between 6.1 and 4.4 Ma, consistent with observed tropical alkenone paleo&hyphen;SSTs. Diverging fine&hyphen;fraction&hyphen;to&hyphen;foraminiferal δ13C gradients likely suggest increased upwelling between 7.1–6.0 and 5.8–4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene&hyphen;early Pliocene. Between 8.0–6.5 and 5.2–4.4 Ma, low east&hyphen;west δ18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5 and 5.7 Ma, with larger east&hyphen;west δ18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric p CO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction).

Original language	American English
Journal	Paleoceanography and Paleoclimatology
Volume	33
DOIs	https://doi.org/10.1002/2017PA003245
State	Published - Mar 1 2018

Keywords

planktic foraminifera stable isotope records
late Miocene to early Pliocene
equatorial Pacific mean state
surface ocean conditions
biogenic bloom
Mg/Ca sea surface temperature

Disciplines

Life Sciences

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Deciphering the State of the Late Miocene to Early Pliocene EquatFinal published version, 4.59 MBLicense: CC BY

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title = "Deciphering the State of the Late Miocene to Early Pliocene Equatorial Pacific",

abstract = " The late Miocene&hyphen;early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here we present the first continuous late Miocene&hyphen;early Pliocene (8.0–4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0–3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest that mean sea surface temperatures (SSTs) are ~27.8 ± 1.1°C (1σ) between 6.4 and 5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2 and 6.1 Ma and an up to 3°C warming between 6.1 and 4.4 Ma, consistent with observed tropical alkenone paleo&hyphen;SSTs. Diverging fine&hyphen;fraction&hyphen;to&hyphen;foraminiferal δ13C gradients likely suggest increased upwelling between 7.1–6.0 and 5.8–4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene&hyphen;early Pliocene. Between 8.0–6.5 and 5.2–4.4 Ma, low east&hyphen;west δ18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5 and 5.7 Ma, with larger east&hyphen;west δ18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric p CO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction).",

keywords = "planktic foraminifera stable isotope records, late Miocene to early Pliocene, equatorial Pacific mean state, surface ocean conditions, biogenic bloom, Mg/Ca sea surface temperature",

author = "Drury, {A. J.} and Lee, {G. P.} and Gray, {W. R.} and M. Lyle and T. Westerhold and Shevenell, {Amelia E.} and John, {C. M.}",

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doi = "10.1002/2017PA003245",

language = "American English",

volume = "33",

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T1 - Deciphering the State of the Late Miocene to Early Pliocene Equatorial Pacific

AU - Drury, A. J.

AU - Lee, G. P.

AU - Gray, W. R.

AU - Lyle, M.

AU - Westerhold, T.

AU - Shevenell, Amelia E.

AU - John, C. M.

PY - 2018/3/1

Y1 - 2018/3/1

N2 - The late Miocene&hyphen;early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here we present the first continuous late Miocene&hyphen;early Pliocene (8.0–4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0–3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest that mean sea surface temperatures (SSTs) are ~27.8 ± 1.1°C (1σ) between 6.4 and 5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2 and 6.1 Ma and an up to 3°C warming between 6.1 and 4.4 Ma, consistent with observed tropical alkenone paleo&hyphen;SSTs. Diverging fine&hyphen;fraction&hyphen;to&hyphen;foraminiferal δ13C gradients likely suggest increased upwelling between 7.1–6.0 and 5.8–4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene&hyphen;early Pliocene. Between 8.0–6.5 and 5.2–4.4 Ma, low east&hyphen;west δ18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5 and 5.7 Ma, with larger east&hyphen;west δ18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric p CO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction).

AB - The late Miocene&hyphen;early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here we present the first continuous late Miocene&hyphen;early Pliocene (8.0–4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0–3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest that mean sea surface temperatures (SSTs) are ~27.8 ± 1.1°C (1σ) between 6.4 and 5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2 and 6.1 Ma and an up to 3°C warming between 6.1 and 4.4 Ma, consistent with observed tropical alkenone paleo&hyphen;SSTs. Diverging fine&hyphen;fraction&hyphen;to&hyphen;foraminiferal δ13C gradients likely suggest increased upwelling between 7.1–6.0 and 5.8–4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene&hyphen;early Pliocene. Between 8.0–6.5 and 5.2–4.4 Ma, low east&hyphen;west δ18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5 and 5.7 Ma, with larger east&hyphen;west δ18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric p CO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction).

KW - planktic foraminifera stable isotope records

KW - late Miocene to early Pliocene

KW - equatorial Pacific mean state

KW - surface ocean conditions

KW - biogenic bloom

KW - Mg/Ca sea surface temperature

UR - https://digitalcommons.usf.edu/msc_facpub/597

U2 - 10.1002/2017PA003245

DO - 10.1002/2017PA003245

M3 - Article

VL - 33

JO - Paleoceanography and Paleoclimatology

JF - Paleoceanography and Paleoclimatology

ER -

Deciphering the State of the Late Miocene to Early Pliocene Equatorial Pacific

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