A warm, stratified, and restricted Labrador Sea across the Middle Eocene and its Climatic Optimum

Margot J. Cramwinckel; Helen K. Coxall; Kasia K. Śliwińska; Marcel Polling; Dustin T. Harper; Peter K. Bijl; Henk Brinkhuis; James S. Eldrett; Alexander J.P. Houben; Francien Peterse; Stefan Schouten; Gert Jan Reichart; James C. Zachos; Appy Sluijs

doi:10.1029/2020PA003932

A warm, stratified, and restricted Labrador Sea across the Middle Eocene and its Climatic Optimum

Margot J. Cramwinckel^*, Helen K. Coxall, Kasia K. Śliwińska, Marcel Polling, Dustin T. Harper, Peter K. Bijl, Henk Brinkhuis, James S. Eldrett, Alexander J.P. Houben, Francien Peterse, Stefan Schouten, Gert Jan Reichart, James C. Zachos, Appy Sluijs

^*Corresponding author for this work

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

Abstract

Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long-term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX₈₆. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low-latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.

Original language	English
Article number	e2020PA003932
Journal	Paleoceanography and Paleoclimatology
Volume	35
Issue number	10
DOIs	https://doi.org/10.1029/2020PA003932
Publication status	Published - Oct 2020

Funding

This research used samples and data provided by the International Ocean Discovery Program (IODP) and its predecessors. This work was carried out under the program of the Netherlands Earth System Science Centre (NESSC), financially supported by the Dutch Ministry of Education, Culture and Science (Ministerie van Onderwijs, Cultuur en Wetenschap). M. J. C. thanks ECORD for the ECORD Research Grant to visit UCSC. M. J. C. and A. S. thank the Ammodo Foundation for funding unfettered research of laureate AS. H. K. C.'s contributions were supported by a Royal Society University Research Fellowship and the Bolin Centre for Climate Research, Stockholm. K. K. Ś. acknowledges funding from the Danish Council for Independent Research/Natural Sciences (DFF/FNU) Grant 11‐107497. P. K. B. and A. S. thank the European Research Council for Starting Grant 802835 OceaNice and Consolidator Grant 771497 SPANC, respectively. We thank Max Hoi Wong for technical support in generating the benthic foraminifera stable isotope data. We thank Jan van Tongeren and Klaas Nierop (Utrecht University Geolab) and Colin Carney, Brandon Cheney, and Rob Franks (UC Santa Cruz lab) for laboratory assistance and analytical support. We thank the two anonymous referees for their constructive reviews, which helped improve the manuscript.

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Cramwinckel, M. J., Coxall, H. K., Śliwińska, K. K., Polling, M., Harper, D. T., Bijl, P. K., Brinkhuis, H., Eldrett, J. S., Houben, A. J. P., Peterse, F., Schouten, S., Reichart, G. J., Zachos, J. C., & Sluijs, A. (2020). A warm, stratified, and restricted Labrador Sea across the Middle Eocene and its Climatic Optimum. Paleoceanography and Paleoclimatology, 35(10), Article e2020PA003932. https://doi.org/10.1029/2020PA003932

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title = "A warm, stratified, and restricted Labrador Sea across the Middle Eocene and its Climatic Optimum",

abstract = "Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long-term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX86. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low-latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.",

author = "Cramwinckel, {Margot J.} and Coxall, {Helen K.} and {\'S}liwi{\'n}ska, {Kasia K.} and Marcel Polling and Harper, {Dustin T.} and Bijl, {Peter K.} and Henk Brinkhuis and Eldrett, {James S.} and Houben, {Alexander J.P.} and Francien Peterse and Stefan Schouten and Reichart, {Gert Jan} and Zachos, {James C.} and Appy Sluijs",

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Cramwinckel, MJ, Coxall, HK, Śliwińska, KK, Polling, M, Harper, DT, Bijl, PK , Brinkhuis, H, Eldrett, JS, Houben, AJP, Peterse, F , Schouten, S , Reichart, GJ, Zachos, JC & Sluijs, A 2020, 'A warm, stratified, and restricted Labrador Sea across the Middle Eocene and its Climatic Optimum', Paleoceanography and Paleoclimatology, vol. 35, no. 10, e2020PA003932. https://doi.org/10.1029/2020PA003932

TY - JOUR

T1 - A warm, stratified, and restricted Labrador Sea across the Middle Eocene and its Climatic Optimum

AU - Cramwinckel, Margot J.

AU - Coxall, Helen K.

AU - Śliwińska, Kasia K.

AU - Polling, Marcel

AU - Harper, Dustin T.

AU - Bijl, Peter K.

AU - Brinkhuis, Henk

AU - Eldrett, James S.

AU - Houben, Alexander J.P.

AU - Peterse, Francien

AU - Schouten, Stefan

AU - Reichart, Gert Jan

AU - Zachos, James C.

AU - Sluijs, Appy

PY - 2020/10

Y1 - 2020/10

N2 - Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long-term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX86. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low-latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.

AB - Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long-term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX86. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low-latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea.

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SN - 2572-4517

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JO - Paleoceanography and Paleoclimatology

JF - Paleoceanography and Paleoclimatology

IS - 10

M1 - e2020PA003932

ER -

A warm, stratified, and restricted Labrador Sea across the Middle Eocene and its Climatic Optimum

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