The Effects of an early Eocene Paleogene Hyperthermal on the Benthic Ocean

Deep-sea benthic foraminiferal turnover across early Eocene hyperthermal events at Northeast Atlantic DSDP Site 550

Authors:

Arreguín-Rodríguez et al

Abstract:

Several extreme warming events, called hyperthermals, superimposed the warming trend of the early Paleogene. Deep-sea benthic foraminifera suffered major extinction during the most severe of those events, the Paleocene–Eocene Thermal Maximum, but their response to the following, less severe hyperthermals has been documented at very few locations. We evaluate and compare the benthic foraminiferal assemblages across ETM2 and H2 events at DSDP Site 550 in the NE Atlantic Ocean. The CIE and carbonate dissolution were more severe during ETM2 than during the H2 event.

Early Eocene benthic foraminiferal assemblages were moderately diverse and strongly dominated by calcareous taxa, and they consisted of mixed infaunal and epifaunal morphogroups. They responded similarly to ETM2 and H2 events, showing a decrease in absolute abundance, an increase in the relative abundance of agglutinated taxa, indicative of more carbonate-corrosive waters, and a marked decrease in the percentage of Bolivinoides decoratus, suggesting a lower food supply during hyperthermals. However, some differences in their response were also noted. Oligotrophic taxa such as Nuttallides truempyi and Quadrimorphina profunda increased in relative abundance during early ETM2, whereas Globocassidulina subglobosa and Osangularia sp. 1, opportunistic species which may indicate pulsed food inputs, peaked during the H2 event. We conclude that both hyperthermal events represent a general disruption of an overall meso-oligotrophic environment, with less food reaching the seafloor combined with increased CaCO3 corrosivity of bottom waters. We did not find clear evidence for decreasing primary productivity during the hyperthermal events, and the apparent low food delivery to the seafloor may have been related to an increase in benthic foraminiferal metabolic rates due to the higher temperatures, with a more severe lack of food during ETM2 than during H2. The benthic foraminiferal response thus appears to be scaled to the magnitude of hyperthermals.

Evidence of a Hyperthermal Caused Paleocene Paleogene Biotic Event

Terrestrial evidence for a two-stage mid-Paleocene biotic event

Authors:

Hyland et al

Abstract:

Marine records of the Paleocene indicate a series of hyperthermal events characterized by significant climatic and carbon cycle variability, but there are few comparable continental records. The mid-Paleocene biotic event (MPBE) is a recently described interval defined by a rapid negative carbon isotope excursion and major short-term changes in marine ecosystems, but it is as yet unclear whether the event was globally important. Here we present the first terrestrial paleoenvironmental record of the MPBE based on paleosols that document rapid and short-lived increases in temperature and precipitation and resultant shifts in plant assemblages concomitant with substantial carbon isotope excursions. The new record indicates that carbon cycle changes during the early late Paleocene may have resulted in a two-stage transient hyperthermal event that caused a significant perturbation to both the regional climate and terrestrial ecology of South America in addition to the major biotic event (MPBE) previously recognized in marine records. Overall, this suggests that the MPBE may have been a global climate event with far-reaching environmental impacts in both the marine and terrestrial realms.

Enhanced Primary & Bacterial Productivity During Paleocene-Eocene Thermal Maximum

Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean

Authors:

Savian et al

Abstract:

Earth's climate experienced a warming event known as the Middle Eocene Climatic Optimum (MECO) at ~ 40 Ma, which was an abrupt reversal of a long-term Eocene cooling trend. This event is characterized in the deep Southern, Atlantic, Pacific and Indian Oceans by a distinct negative δ18O excursion over 500 kyr. We report results of high-resolution paleontological, geochemical, and rock magnetic investigations of the Neo-Tethyan Monte Cagnero (MCA) section (northeastern Apennines, Italy), which can be correlated on the basis of magneto- and biostratigraphic results to the MECO event recorded in deep-sea sections. In the MCA section, an interval with a relative increase in eutrophic nannofossil taxa (and decreased abundances of oligotrophic taxa) spans the culmination of the MECO warming and its aftermath and coincides with a positive carbon isotope excursion, and a peak in magnetite and hematite/goethite concentration. The magnetite peak reflects the appearance of putative magnetofossils, while the hematite/goethite apex is attributed to an enhanced detrital mineral contribution, likely as aeolian dust transported from the continent adjacent to the Neo-Tethys Ocean during a drier, more seasonal climate during the peak MECO warming. Based on our new geochemical, paleontological and magnetic records, the MECO warming peak and its immediate aftermath are interpreted as a period of high primary productivity. Sea-surface iron fertilization is inferred to have stimulated high phytoplankton productivity, increasing organic carbon export to the seafloor and promoting enhanced biomineralization of magnetotactic bacteria, which are preserved as putative magnetofossils during the warmest periods of the MECO event in the MCA section. Together with previous studies, our work reinforces the connection between hyperthermal climatic events and the occurrence (or increased abundance) of putative magnetofossils in the sedimentary record.

Rapid and Sustained Surface Ocean Acidifcation During the Paleocene-Eocene Thermal Maximum?

Rapid and sustained surface ocean acidification during the Paleocene-Eocene Thermal Maximum

Authors:

Penman et al

Abstract:

The Paleocene-Eocene Thermal Maximum (PETM) has been associated with the release of several thousands of petagrams of carbon (Pg C) as methane and/or carbon dioxide into the ocean-atmosphere system within ~10 thousand years (ky), on the basis of the co-occurrence of a carbon isotope excursion (CIE), widespread dissolution of deep sea carbonates, and global warming. In theory, this rapid carbon release should have severely acidified the surface ocean, though no geochemical evidence has yet been presented. Using boron-based proxies for surface-ocean carbonate chemistry, we present the first observational evidence for a drop in the pH of surface and thermocline seawater during the PETM. Planktic foraminifers from a drill site in the North Pacific (ODP Site 1209) show a ~0.8‰ decrease in boron isotopic composition (δ11B) at the onset of the event, along with a 30-40% reduction in shell B/Ca. Similar trends in δ11B are present in two lower resolution records from the South Atlantic and Equatorial Pacific. These observations are consistent with significant, global acidification of the surface ocean lasting at least 70 ky and requiring sustained carbon release. The anomalies in the B records are consistent with an initial surface pH drop of ~0.3 units, at the upper range of model-based estimates of acidification.

How Fast was the Onset of the Paleocene-Eocene Thermal Maximum? Was a Comet to Blame?!?!

A Comet Caused the PETM!

Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum

Authors:

Wright et al

Abstract:

The Paleocene/Eocene thermal maximum (PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE’s onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). These couplets have corresponding δ18O cycles that imply a climatic origin. Seasonal insolation is the only regular climate cycle that can plausibly account for δ18O amplitudes and layer counts. High-resolution stable isotope records show 3.5‰ δ13C decrease over 13 couplets defining the CIE onset, which requires a large, instantaneous release of 13C-depleted carbon. During the CIE, a clear δ13C gradient developed on the shelf with the largest excursions in shallowest waters, indicating atmospheric δ13C decreased by ∼20‰. Our observations and revised release rate are consistent with an atmospheric perturbation of 3,000-gigatons of carbon (GtC).

No! It Did NOT!

Onset of carbon isotope excursion at the Paleocene-Eocene thermal maximum took millennia, not 13 years

Authors:

Zeebee et al

Abstract:

The Paleocene-Eocene thermal maximum (PETM) may represent the best paleo-analog for rapid and massive carbon release to the ocean and atmosphere. Thus, constraining the carbon release rate at its onset is critical. Wright and Schaller (1) use records from apparently rhythmically layered shelf sediments to argue that the layering is annual and that the onset of the carbon isotope excursion (CIE, fingerprint for carbon release) in the surface ocean was complete in 13 y. Using basic carbon cycle and climate considerations, we show this is not feasible. In fact, Wright and Schaller’s isotope records indicate that the CIE onset took at least several millennia. This finding rules out a cometary origin of the carbon release.

Yes, it did!

Reply to Pearson and Nicholas, Stassen et al., and Zeebe et al.: Teasing out the missing piece of the PETM puzzle

Authors:

Wright et al

Abstract:

Understanding the Paleocene-Eocene Thermal Maximum (PETM) critically depends on knowing the rate at which the perturbation carbon was released. In our report (1) we argue that the layered Marlboro Clay may provide this important constraint. Our strongest evidence in support of the rapid release of carbon at the onset of the PETM is the differential response of the %CaCO3 and δ13C in the Millville core. The sharp %CaCO3 decrease occurred over 4 mm, compared with the δ13C decrease over an interval of 25 cm (figure 3 in ref. 1). Temporal differences are predicted by a rapid (instantaneous) release of light carbon, which would lower the surface ocean Graphic in a matter of months, in contrast to the carbon isotopic equilibrium exchange, which occurs on the scale of a decade (2) and can only be recorded in a core with a high sedimentation rates (1). Based on the rhythmic bedding in the Marlboro Clay, we argue that the drop in %CaCO3 occurred in less than a year and the δ13C equilibrium was on the order of a decade.

My guess is probably not given all we know of the PETM.

Sea Levels Changes During Paleocene–Eocene Thermal Maximum (PETM) in Spain Due to Tectonomagmatic Activity in the North Atlantic?

Sea-level changes across the Paleocene–Eocene interval in the Spanish Pyrenees, and their possible relationship with North Atlantic magmatism

Authors:

Pujalte et al

Abstract:

The issue of whether major and rapid global sea-level changes existed on a preglacial Earth can be resolved by the detailed study of the Paleocene–Eocene (P–E) interval, where a large and rapid carbon isotope excursion linked to an important global warming event, the Paleocene Eocene Thermal Maximum, allows for high-resolution correlation between terrestrial, coastal and marine settings. Based primarily on outcrop and borehole information from the Tremp-Graus Basin in the southern Spanish Pyrenees, it is shown that a sea-level fall of at least 20 m occurred less than 75 kyr prior to the PETM. This forced a seaward displacement of the shoreline of ca. 20 km, a widespread incision of valleys in the alluvial plains and the subaerial exposure and excavation of the adjacent marine carbonate platform. The subsequent sea-level rise caused the infilling of the incised valleys, a process completed before the onset of the PETM, and continued rising during and after the event, leading to the aggradation of the alluvial plain and eventually to the transgression of the whole Tremp-Graus Basin. However, the sea level did not regain its pre-fall position until near the end of the PETM. Therefore, although rising, the sea level was comparatively low in the southern Pyrenean area during most of the PETM. The pre-PETM sea-level fall has been reported in other basins of the southern Pyrenees, in the North Sea area, the Austrian Alps and in Egypt, and the subsequent sea-level rise has been documented in widely separated sites around the Earth, an evidence of their global (eustatic) scope. The causal mechanism(s) of the pre-PETM sea-level fall is (are) unresolved, although glacioeustasy may have played a role. The subsequent sea-level rise was most likely caused by tectonomagmatic activity in the North Atlantic.

Paleocene-Eocene Thermal Maximum Benthic Adaptations in

Surviving rapid climate change in the deep sea during the Paleogene hyperthermals

Authors:

1. Laura C. Foster (a)
2. Daniela N. Schmidt (a)
3. Ellen Thomas (b,c)
4. Sandra Arndt (d)
5. Andy Ridgwell (d)

Affiliations:

a. Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom;

b. Department of Geology and Geophysics, Yale University, New Haven, CT 06520;

c. Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459; and

d. School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, United Kingdom

Abstract:

Predicting the impact of ongoing anthropogenic CO2 emissions on calcifying marine organisms is complex, owing to the synergy between direct changes (acidification) and indirect changes through climate change (e.g., warming, changes in ocean circulation, and deoxygenation). Laboratory experiments, particularly on longer-lived organisms, tend to be too short to reveal the potential of organisms to acclimatize, adapt, or evolve and usually do not incorporate multiple stressors. We studied two examples of rapid carbon release in the geological record, Eocene Thermal Maximum 2 (∼53.2 Ma) and the Paleocene Eocene Thermal Maximum (PETM, ∼55.5 Ma), the best analogs over the last 65 Ma for future ocean acidification related to high atmospheric CO2 levels. We use benthic foraminifers, which suffered severe extinction during the PETM, as a model group. Using synchrotron radiation X-ray tomographic microscopy, we reconstruct the calcification response of survivor species and find, contrary to expectations, that calcification significantly increased during the PETM. In contrast, there was no significant response to the smaller Eocene Thermal Maximum 2, which was associated with a minor change in diversity only. These observations suggest that there is a response threshold for extinction and calcification response, while highlighting the utility of the geological record in helping constrain the sensitivity of biotic response to environmental change.