Global mean surface temperature and climate sensitivity of the EECO, PETM and latest Paleocene

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The Miocene epoch (23.03-5.33 Ma) was a time interval of global warmth, relative to today.Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval-the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO 2 , and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO 2 (∼400-600 ppm), the MCO has been suggested as a particularly appropriate analog for future climate scenarios, and for assessing the predictive accuracy of numerical climate models-the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re-interpretation of proxies, which might mitigate the model-data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here, we review the state-of-the-art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modeling studies. Plain Language Summary During the Miocene time period (∼23-5 million years ago),Planet Earth looked similar to today, with some important differences: the climate was generally warmer and highly variable, while atmospheric CO 2 was not much higher. Continental-sized ice sheets were only present on Antarctica, but not in the northern hemisphere. The continents drifted to near their modernday positions, and plants and animals evolved into the many (near) modern species. Scientists study the Miocene because present-day and projected future CO 2 levels are in the same range as those reconstructed for the Miocene. Therefore, if we can understand climate changes and their biotic responses from the Miocene past, we are able to better predict current and future global changes. By comparing Miocene climate reconstructions from fossil and chemical data to climate simulations produced by computer models, scientists are able to test their understanding of the Earth system under higher CO 2 and warmer conditions than those of today. This helps in constraining future warming scenarios for the coming STEINTHORSDOTTIR ET AL.

Section: Introductionmentioning

confidence: 99%

The Miocene: The Future of the Past

Steinthorsdottir

Coxall

Boer

et al. 2021

268

179

“…We suggest that the closure/opening of the English Channel during the middle Eocene partially influenced the ocean temperatures and salinities recorded in the Hampshire Basin. In particular, we argue that in the lower part of the section the water temperature was mitigated by the intermittent introduction of colder North Sea water within the basin, explaining the cool and less saline waters recorded, in average comparable to the Norwegian‐Greenland Sea (Inglis et al., 2015, 2020). This was reversed upward when total or partial closure of the English Channel led to an increase of regional water temperatures and salinity, probably also influenced by increased evaporation, closer to the Atlantic sites (Cramwinckel et al., 2020).…”

Section: Discussionmentioning

confidence: 82%

Disentangling the Impact of Global and Regional Climate Changes During the Middle Eocene in the Hampshire Basin: New Insights From Carbonate Clumped Isotopes and Ostracod Assemblages

Marchegiano

John

2022

In 2013 the IPCC (Stocker et al., 2013) estimated up to 5°C global warming by 2100 associated with the rapid rise of anthropogenic atmospheric CO 2 . Coastal and shelf seas play an important role in the uptake of atmospheric CO 2 through a process known as the "continental shelf pump" (Thomas, 2004). Increased export productivity of continental shelves leads to the subtraction of CO 2 from the atmosphere and carbon sequestration in sediments at geological timescales (John et al., 2008). Precise evaluation of the effects of regional climate changes is therefore essential to accurately forecast climate scenarios as well as the ecological response of distinct geographic areas in a warmer world.Starting from the middle Eocene, the Earth entered a cooling phase that slowly brought the climate from a "greenhouse" to a "icehouse" state at the Eocene-Oligocene boundary. This broad climatic trend was interrupted by a short (∼500 ka) globally recorded warm event called Middle Eocene Climatic Optimum (MECO; ∼40 Ma) (Bohaty et al., 2009;Bohaty & Zachos, 2003) a potential deep-time analogue for current warming. During MECO, an increase of about 4-6°C of surface and deep sea water is interpreted based on the oxygen isotope composition of benthic foraminifers (δ 18 O carbonate ) from deep-sea cores (Bohaty et al., 2009;Bohaty & Zachos, 2003).The main recorded effects of the MECO in open, deep and large marine basins are the shallowing of the lysocline and the carbonate compensation depth (CCD) as evidenced by a global carbonate decrease caused by seawater acidification (Bohaty et al., 2009) and the reduced amount of nutrients and oxygenation in the sea-floor (Boscolo

“…Pre‐MECO SSTs at Site 647 are similar to those from the equatorial Atlantic Ocean and a few degrees lower than those from the (sub)tropical South Atlantic (Boscolo‐Galazzo et al, 2014; Cramwinckel et al, 2018) (Figure 9). They are distinctly higher than those from the Southwest Pacific Ocean (Bijl et al, 2010) and Norwegian‐Greenland Sea (Inglis et al, 2015, 2020; Liu et al, 2009). SSTs from the early‐middle (~48 Ma) and middle (~46 Ma) Eocene Arctic Ocean (~8–14°C) (Brinkhuis et al, 2006; Sangiorgi et al, 2008) are also much lower than the middle Eocene Labrador Sea, although coeval estimates are not available.…”

Section: Discussionmentioning

confidence: 84%

“…Compilation of middle Eocene TEX 86 ‐based sea surface temperatures. Site 647 (red) data plotted together with published TEX 86 data from the Atlantic basin: ODP Site 913, Norwegian‐Greenland Sea (gray) (Inglis et al, 2015, 2020; Liu et al, 2009); Kysing‐4 borehole, North Sea Basin (light blue) (Śliwińska et al, 2019); ODP Site 925, equatorial Atlantic Ocean (pink) (Liu et al, 2009); ODP Site 959, equatorial Atlantic Ocean (orange) (Cramwinckel et al, 2018); Site 1263, subtropical South Atlantic Ocean (purple) (Boscolo‐Galazzo et al, 2014); and South Dover Bridge, Atlantic coastal plain (blue) (Inglis et al, 2015). TEX 86 record from Site 1172 (green) (Bijl et al, 2009, 2010) added as a high southern latitude end‐member.…”

Section: Discussionmentioning

confidence: 99%

“…Importantly, Eocene boundary conditions were very different from today, with higher temperatures, intensified hydrological cycling, and a different shape and bathymetry of the Atlantic Ocean (e.g., Seton et al, 2012). Estimates of global mean temperature indicate this dropped from about 27–29°C in the early Eocene to 23–26°C during the middle Eocene and ~19°C during the late Eocene (Cramwinckel et al, 2018; Inglis et al, 2020). A warmer climate by itself results in enhanced hydrological cycling, with an increased contrast between regions of excess evaporation in the subtropics and excess precipitation at high latitudes (Held & Soden, 2006; Pierrehumbert, 2002).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Warm, Stratified, and Restricted Labrador Sea Across the Middle Eocene and Its Climatic Optimum

Cramwinckel

Coxall

Śliwińska

et al. 2020

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 TEX 86. 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.