North Atlantic surface ocean warming and salinization in response to middle Eocene greenhouse warming

Abstract

Quantitative reconstructions of hydrological change during ancient greenhouse warming events provide valuable insight into warmer-than-modern hydrological cycles but are limited by paleoclimate proxy uncertainties. We present sea surface temperature (SST) records and seawater oxygen isotope (δ 18 O sw ) estimates for the Middle Eocene Climatic Optimum (MECO), using coupled carbonate clumped isotope (Δ 47 ) and oxygen isotope (δ 18 O c ) data of well-preserved planktonic foraminifera from the North Atlantic Newfoundland Drifts. These indicate a transient ~3°C warming across the MECO, with absolute temperatures generally in accordance with trace element (Mg/Ca)–based SSTs but lower than biomarker-based SSTs for the same interval. We find a transient ~0.5‰ shift toward higher δ 18 O sw , which implies increased salinity in the North Atlantic subtropical gyre and potentially a poleward expansion of its northern boundary in response to greenhouse warming. These observations provide constraints on dynamic ocean response to warming events, which are consistent with theory and model simulations predicting an enhanced hydrological cycle under global warming.

Astronomical Pacing of Middle Eocene Sea‐Level Fluctuations: Inferences From Shallow‐Water Carbonate Ramp Deposits

“…Assuming sea‐level rise documented by elementary sequence #21 records a glacioeustatic forcing (i.e., ice‐volume effect on δ 18 O), and given a relationship of 0.10–0.13‰ per 10 m of sea‐level change (Pekar et al., 2003), the global negative OIE of the MECO of ∼1.0‰ would have a minimum of 0.3‰ glacioeustatic component, and correspondingly global temperature increase inferred from δ 18 O data would be ≤3°C (assuming a δ 18 O change of −0.23‰ per °C (Böhm et al., 2000)): much smaller than originally inferred (Bohaty et al., 2009; Bohaty & Zachos, 2003). While this would appear at odds with $${{\text{TEX}}_{86}}^{\mathrm{H}}$$ records that suggest a ∼3°C rise in the tropics (Cramwinckel et al., 2018) and up to ∼6°C in high latitudes (Cramwinckel et al., 2018), it would be consistent with $${{\text{TEX}}_{86}}^{\mathrm{H}}$$ records that show a much more muted 2°C change in temperature (Cramwinckel et al., 2020), or no change at all (van der Ploeg et al., 2023).…”

Surface Ocean Cooling in the Eocene North Atlantic Coincides With Declining Atmospheric CO2

“…Proxy‐based reconstructions during the Middle Eocene Climatic Optimum have argued that northward expansion of the North Atlantic subtropical gyre could also act as a mechanism to increase SSTs within the North Atlantic (Van Der Ploeg et al., 2023). However, details of the gyre heat transport and the impact of this large‐scale process on regional SSTs (especially near coastlines) requires further investigation.…”

“…We use the water isotope-enabled Community Earth System Model version 1.2 (iCESM1.2) (Zhu et al, 2019(Zhu et al, , 2020 to compare with our proxy reconstruction and to provide an independent estimate of δ 18 O sw . iCESM1.2 is able to closely replicate large-scale features of early Eocene climate, including: (a) enhanced global mean surface temperature estimates (Lunt et al, 2021;Zhu et al, 2019), (b) reduced meridional temperature gradients (Lunt et al, 2021), (c) changes in the hydrological cycle (Cramwinckel et al, 2023), and (d) the values and distribution of planktonic foraminifera δ 18 O values (Zhu et al, 2020). It is also the only DeepMIP model that has water isotopes enabled (Zhu et al, 2020).…”

“…Our data compilation spans three regions: (a) the equatorial Atlantic (0-30°N/S) (Cramwinckel et al, 2018;Inglis et al, 2015;Liu et al, 2009;Y. G. Zhang et al, 2013), (b) the northwest Atlantic (30-50°N) (this study; Cramwinckel, Coxall, et al, 2020;Inglis et al, 2015;Keating-Bitonti et al, 2011;van der Ploeg et al, 2023) and (c) the southwest Pacific (>50°S) (Bijl et al, 2009(Bijl et al, , 2013Cramwinckel, Woelders, et al, 2020;Crouch et al, 2020;Hollis et al, 2009;Inglis et al, 2015;Liu et al, 2009) (Figure 3; Supporting Information S1). Inglis et al, 2015;Zhang et al, 2013), (b) North Atlantic (this study; Inglis et al, 2015;de Bar et al, 2019), and (c) the southwest Pacific (Bijl et al, 2009(Bijl et al, , 2013Crouch et al, 2020;Hollis et al, 2009;Inglis et al, 2015).…”

North Atlantic Drift Sediments Constrain Eocene Tidal Dissipation and the Evolution of the Earth‐Moon System

“…The middle Eocene is a time of gradual global cooling, interrupted by a remarkable warm event called the Middle Eocene Climatic Optimum (MECO) (Bohaty & Zachos, 2003;Bohaty et al, 2009). The MECO is marked by large temperature, sea level and salinity variations in the North Atlantic, the Arctic Ocean and the North Sea (e.g., Cramwinckel et al, 2020;Marchegiano & John, 2022;van der Ploeg et al, 2023). The contourite drift deposit sequences of International Ocean Discovery Program (IODP) Site U1408 and Site U1410 (Newfoundland Ridge, North Atlantic, IODP Expedition 342, Figure 1) provide a high-resolution paleoceanographic archive throughout this time interval and have the potential to supply a test for Earth-Moon dynamics and the evolution of the solar system.…”