Here, we compare the ocean overturning circulation of the early Eocene (47–56 Ma) in eight coupled climate model simulations from the Deep‐Time Model Intercomparison Project (DeepMIP) and investigate the causes of the observed inter‐model spread. The most common global meridional overturning circulation (MOC) feature of these simulations is the anticlockwise bottom cell, fed by sinking in the Southern Ocean. In the North Pacific, one model (GFDL) displays strong deepwater formation and one model (CESM) shows weak deepwater formation, while in the Atlantic two models show signs of weak intermediate water formation (MIROC and NorESM). The location of the Southern Ocean deepwater formation sites varies among models and relates to small differences in model geometry of the Southern Ocean gateways. Globally, convection occurs in the basins with smallest local freshwater gain from the atmosphere. The global MOC is insensitive to atmospheric CO2 concentrations from 1× (i.e., 280 ppm) to 3× (840 ppm) pre‐industrial levels. Only two models have simulations with higher CO2 (i.e., CESM and GFDL) and these show divergent responses, with a collapsed and active MOC, respectively, possibly due to differences in spin‐up conditions. Combining the multiple model results with available proxy data on abyssal ocean circulation highlights that strong Southern Hemisphere‐driven overturning is the most likely feature of the early Eocene. In the North Atlantic, unlike the present day, neither model results nor proxy data suggest deepwater formation in the open ocean during the early Eocene, while the evidence for deepwater formation in the North Pacific remains inconclusive.
Here, we compare the ocean overturning circulation of the early Eocene (47–56 Ma) in eight coupled climate model simulations from the Deep‐Time Model Intercomparison Project (DeepMIP) and investigate the causes of the observed inter‐model spread. The most common global meridional overturning circulation (MOC) feature of these simulations is the anticlockwise bottom cell, fed by sinking in the Southern Ocean. In the North Pacific, one model (GFDL) displays strong deepwater formation and one model (CESM) shows weak deepwater formation, while in the Atlantic two models show signs of weak intermediate water formation (MIROC and NorESM). The location of the Southern Ocean deepwater formation sites varies among models and relates to small differences in model geometry of the Southern Ocean gateways. Globally, convection occurs in the basins with smallest local freshwater gain from the atmosphere. The global MOC is insensitive to atmospheric CO2 concentrations from 1× (i.e., 280 ppm) to 3× (840 ppm) pre‐industrial levels. Only two models have simulations with higher CO2 (i.e., CESM and GFDL) and these show divergent responses, with a collapsed and active MOC, respectively, possibly due to differences in spin‐up conditions. Combining the multiple model results with available proxy data on abyssal ocean circulation highlights that strong Southern Hemisphere‐driven overturning is the most likely feature of the early Eocene. In the North Atlantic, unlike the present day, neither model results nor proxy data suggest deepwater formation in the open ocean during the early Eocene, while the evidence for deepwater formation in the North Pacific remains inconclusive.
“…took this sample and observed extensive core depletion and disruption. We assume that disruption and displacement explain the pre-PETM-like values (Pardo et al 1997;Katz et al 2003;Nunes and Norris 2006;D'Haenens et al 2012;Bornemann et al 2014Bornemann et al , 2016Gutjahr et al 2017). rmcd, revised meters composite depth.…”
Section: Resultsmentioning
confidence: 99%
“…Gray inset lines indicate maximum size-δ 13 C slope (same across all panels). C, Published foraminiferal and bulk carbonate δ 13 C data (Pardo et al 1997; Katz et al 2003; Nunes and Norris 2006; D'Haenens et al 2012; Bornemann et al 2014, 2016; Gutjahr et al 2017). rmcd, revised meters composite depth.Figure 4.Abundance and isotopic data for foraminifera from ODP Site 690.…”
Under stress, corals and foraminifera may eject or consume their algal symbionts (“bleach”), which can increase mortality. How bleaching relates to species viability over warming events is of great interest given current global warming. We use size-specific isotope analyses and abundance counts to examine photosymbiosis and population dynamics of planktonic foraminifera across the Paleocene–Eocene thermal maximum (PETM, ~56 Ma), the most severe Cenozoic global warming event. We find variable responses of photosymbiotic associations across localities and species. In the NE Atlantic (DSDP Site 401) PETM, photosymbiotic clades (acarininids and morozovellids) exhibit collapsed size-δ13C gradients indicative of reduced photosymbiosis, as also observed in Central Pacific (ODP Site 1209) and Southern Ocean (ODP Site 690) acarininids. In contrast, we find no significant loss of size-δ13C gradients on the New Jersey shelf (Millville) or in Central Pacific morozovellids. Unlike modern bleaching-induced mass mortality, populations of photosymbiont-bearing planktonic foraminifera increased in relative abundance during the PETM. Multigenerational adaptive responses, including flexibility in photosymbiont associations and excursion taxon evolution, may have allowed some photosymbiotic foraminifera to thrive. We conclude that deconvolving the effects of biology on isotope composition on a site-by-site basis is vital for environmental reconstructions.
“…Small samples such as foraminifera may be analyzed without embedding or sectioning, and high-sample throughput means that the technique is relatively inexpensive. Laser spot sizes are typically 20-80 µm in diameter, with 5 µm possible (Lazartigues et al, 2014), enabling repeat measurements of individual chambers or seasonality reconstruction in long-lived organisms with incremental growth layers (Bougeois et al, 2014;Evans et al, 2013). Because each laser pulse removes less than 100 nm of material on carbonates (Griffiths et al, 2013), depthprofiling through the sample has an effective resolution of < 0.5 µm when using a fast wash-out ablation cell (Müller et al, 2009).…”
Section: Recommended Methodologies For Mg/camentioning
Abstract. The early Eocene (56 to 48 million years ago) is inferred to have
been the most recent time that Earth's atmospheric CO2 concentrations
exceeded 1000 ppm. Global mean temperatures were also substantially warmer
than those of the present day. As such, the study of early Eocene climate provides insight
into how a super-warm Earth system behaves and offers an opportunity to
evaluate climate models under conditions of high greenhouse gas forcing. The
Deep Time Model Intercomparison Project (DeepMIP) is a systematic
model–model and model–data intercomparison of three early Paleogene time
slices: latest Paleocene, Paleocene–Eocene thermal maximum (PETM) and early
Eocene climatic optimum (EECO). A previous article outlined the model
experimental design for climate model simulations. In this article, we
outline the methodologies to be used for the compilation and analysis of
climate proxy data, primarily proxies for temperature and CO2. This
paper establishes the protocols for a concerted and coordinated effort to
compile the climate proxy records across a wide geographic range. The
resulting climate “atlas” will be used to constrain and evaluate climate
models for the three selected time intervals and provide insights into the
mechanisms that control these warm climate states. We provide version 0.1 of
this database, in anticipation that this will be expanded in subsequent
publications.
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