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The Paleocene–Eocene Thermal Maximum (PETM) is associated with climatic change and biological turnover. It shares features with the Oceanic Anoxic Events (OAEs) of the Mesozoic, such as transient global warming and biogeochemical perturbations. However, the PETM experienced a more muted expansion of marine anoxia compared to the Mesozoic OAEs (especially OAE2), with geographically limited evidence for photic zone euxinia (PZE). We explore the extent and drivers of marine deoxygenation during the PETM using biomarkers for water column euxinia and anoxia as well as an intermediate complexity Earth system model (cGEnIE). These reveal that the water column in the North‐East Peri‐Tethys became anoxic, with euxinic conditions reaching the photic zone (PZE) during the PETM. Our model shows that euxinia developed due to a global increase in the ocean nutrient inventory with concomitant oxygen consumption, similar to findings for OAE2. The particularly strong regional response in the NE Peri‐Tethys appears to arise from a combination of global CO2‐weathering forcing, regionally restricted circulation and upwelling of sulphidic thermocline waters. Unlike OAE2, anoxia and PZE do not become widespread in our PETM simulations, consistent with new and existing geochemical and biological proxy data. This globally muted response could result from reduced biogeochemical feedbacks to climate forcing relative to the mid‐Cretaceous climate. Our observations suggest that similar mechanisms operated in response to disparate Cenozoic (PETM) and Mesozoic (OAEs) transient global warming events, while also highlighting that background conditions are crucial in modulating the sensitivity of Earth's system to them. Plain Language Summary: Ancient global warming events can help us understand the impact(s) of current global warming. A response to many past global warming events has been the expansion of oxygen deficient waters in the ocean. This is also true for the Paleocene‐Eocene Thermal Maximum that occurred about 56 million years ago. Here we show that this decrease in oxygen was so dramatic in the Peri‐Tethys (a precursor to the Mediterranean Sea of today) that it extended into the photic zone and stimulated the growth of unusual bacteria that require both light and hydrogen sulfide. This did not appear to be a direct result of warming but rather an indirect result ‐ warming caused the delivery of nutrients that stimulated the production of organic matter, which consumed oxygen in the underlying waters when it sank and degraded. This has potential analogs throughout Earth history and potentially for the future, but our work also shows that the magnitude of this response will be governed by other factors, such as the restriction of circulation, biogeochemical feedbacks and location of upwelling zones. Key Points: Photic zone euxinia (PZE) occurred in the NE Peri‐Tethys during the Paleocene–Eocene Thermal MaximumPhotic zone euxinia was likely stimulated by an increase in the nutrient inventory rather than as a direct response to ocean warmingThe restriction of PZE to specific regions is governed by geography [ABSTRACT FROM AUTHOR]

The 2‐methylhopanes (2‐MeHops) are molecular fossils of 2‐methylbacteriohopanepolyols (2‐MeBHPs) and among the oldest biomarkers on Earth. However, these biomarkers' specific sources are currently unexplained, including whether they reflect an expansion of marine cyanobacteria. Here, we study the occurrence of 2‐MeBHPs and the genes involved in their synthesis in modern bacteria and explore the occurrence of 2‐MeHops in the geological record. We find that the gene responsible for 2‐MeBHP synthesis (hpnP) is widespread in cyano‐ and ⍺‐proteobacteria, but absent or very limited in other classes/phyla of bacteria. This result is consistent with the dominance of 2‐MeBHP in cyano‐ and ⍺‐proteobacterial cultures. The review of their geological occurrence indicates that 2‐MeHops are found from the Paleoproterozoic onwards, although some Precambrian samples might be biased by drilling contamination. During the Phanerozoic, high 2‐MeHops' relative abundances (index >15%) are associated with climatic and biogeochemical perturbations such as the Permo/Triassic boundary and the Oceanic Anoxic Events. We analyzed the modern habitat of all hpnP‐containing bacteria and find that the only one species coming from an undisputed open marine habitat is an ⍺‐proteobacterium acting upon the marine nitrogen cycle. Although organisms can change their habitat in response to environmental stress and evolutionary pressure, we speculate that the high sedimentary 2‐MeHops' occurrence observed during the Phanerozoic reflect ⍺‐proteobacteria expansion and marine N‐cycle perturbations in response to climatic and environmental change. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) is used to infer past changes in the state of the climate system. Here we use a combination of newly generated and published organic paleothermometer records, together with novel high‐resolution benthic foraminiferal δ18O stratigraphy, from four sites in the midlatitude North Atlantic (41–58°N) to reconstruct the long‐term evolution of the latitudinal SST gradient during the Pliocene and early Pleistocene (4.0 to 2.4 Myr), the last time atmospheric CO2 reached concentrations above 400 ppmv. We demonstrate that the latitudinal SST gradient in the North Atlantic nearly collapsed twice during this period. We conclude that the latitudinal SST gradient in the midlatitude North Atlantic has two end‐members: a maximum as existing at present and a minimum that existed during certain periods of the (late) Pliocene. Our results suggest that the 400‐ppmv Pliocene world was more dynamic than currently thought. Key Points: New SST records spanning Plio/Pleistocene from the North AtlanticReveal episodic collapse latitudinal SST gradient North AtlanticWe speculate that collapse is related to changes in Gateways [ABSTRACT FROM AUTHOR]

The extent and persistence of anoxia in the South Atlantic Ocean during its early opening phase in the Early Cretaceous is not well constrained, hindering a holistic understanding of the processes and mechanisms that drive past changes in water column redox conditions, as well as the impacts of such changes on marine ecosystems. Here we provide high-resolution geochemical records from Deep Sea Drilling Project Site 364 that document variations in redox conditions, chemocline depth, marine productivity, and marine ecosystem dynamics in the northern South Atlantic during the Aptian. We show that many of these parameters varied across discrete sedimentary cycles expressed in the Deep Sea Drilling Project 364 succession. Our data indicate that during the initial stages of basin development, anoxic and euxinic conditions were prevalent and occasionally extended into the upper water column. However, strong cyclicity in sedimentological and geochemical parameters imply that the anoxia/euxinia was not a persistent state. We argue that the water column redox conditions during the Aptian were driven by changes in the hydrological cycle, induced by variations in astronomical forcing. We suggest that the episodically amplified hydrological cycle not only enhanced nutrient availability and marine productivity, but might also have caused density-driven upper ocean stratification. The presence of black shales of similar age in other ocean basins suggests that this mechanism is broadly important for the formation of Early Cretaceous organic-rich successions. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 possibly doubled during Oceanic Anoxic Event (OAE) 1a, likely in response to submarine volcanic outgassing. Despite being important for our understanding of the consequences of carbon cycle perturbations, the response of the climate system to this increase in greenhouse forcing is poorly constrained. Here we provide a new sea-surface temperature (SST) record from the mid-latitude proto-North Atlantic based on the organic geochemical TEX86 paleothermometer. Using different calibrations, including the newly developed Bayesian Spatially-varying Regression (BAYSPAR) deep-time analogue approach, we demonstrate that SSTs increased by ∼2-4 °C during OAE 1a and decreased by ∼4-6 °C at its end, both simultaneous with changes in δ13Corg, which we argue reflects changes in pCO2. We demonstrate that a clear latitudinal SST gradient prevailed during OAE 1a, contrary to the generally accepted view that a nearly flat SST gradient existed during OAE 1a and the Early Cretaceous. These results are more consistent with climate model simulations of the Cretaceous that have failed to produce flat SST gradients. [ABSTRACT FROM AUTHOR]

Ocean Drilling Program (ODP) Site 982 provided a key sediment section at Rockall Plateau for reconstructing northeast Atlantic paleoceanography and monitoring benthic &dgr;18O stratigraphy over the late Pliocene to Quaternary onset of major Northern Hemisphere glaciation. A renewed holespecific inspection of magnetostratigraphic reversals and the addition of epibenthic &dgr;18O records for short Pliocene sections in holes 982A, B, and C, crossing core breaks in the &dgr;18O record published for Hole 982B, now imply a major revision of composite core depths. After tuning to the orbitally tuned reference record LR04, the new composite &dgr;18O record results in a hiatus, where the Kaena magnetic subchron might have been lost, and in a significant age reduction for all proxy records by 130 to 20 ky over the time span 3.2-2.7 million years ago (Ma). Our study demonstrates the general significance of reliable composite-depth scales and &dgr;18O stratigraphies in ODP sediment records for generating ocean-wide correlations in paleoceanography. The new concept of age control makes the late Pliocene trends in SST (sea surface temperature) and atmospheric pCO2 at Site 982 more consistent with various paleoclimate trends published from elsewhere in the North Atlantic. [ABSTRACT FROM AUTHOR]

The article examines the impacts of millennial-scale climate variability on global climate change. Among such millennial-scale variables are the Hudson Strait (HS) Heinrich Events and ice-rafting events in the North Atlantic from the Laurentide ice sheet (LIS). It proves that sea surface temperatures (SST) has no significant role in the occurrence of HS Heinrich(-like) Events. It cites the use of mineralogy and organic geochemistry in analyzing the characteristics of ice-rafting debris (IRD) and their role in HS Heinrich Events.

The article discusses the terrestrial higher plant leaf wax inputs to the North Atlantic Ocean in the late Pliocene era, as well as their effects on global climate change. It claims that the aeolian input of terrestrial material in the ocean coincided with the intensification of the Northern Hemisphere glaciation (NHG). It cites that continental ice sheets are major dust sources, which are said to play a key role in simulating a complete glacial cycle. It employs materials from the Integrated Ocean Drilling Project (IODP) to analyze if changes in aeolian input are related in the intensification of NHG.

The article discusses the global climate change, particularly in the North Atlantic region, during the late Pliocene period. It presents the study that reconstructed the orbitally resolved sea surface temperature (SST) and productivity records from the Integrated Ocean Drilling Project (IODP) during the late Pliocene and early Pleistocene to analyze climate change in the area. It examines such activities as Northern Hemisphere glaciation (NHG), North Atlantic Current (NAC) movement, and Northern Hemisphere ice sheet growth.

Ocean Drilling Program (ODP) Site 982 provided a key sediment section at Rockall Plateau for reconstructing northeast Atlantic paleoceanography and monitoring benthic δ18O stratigraphy over the Late Pliocene to Quaternary onset of major Northern Hemisphere Glaciation. A renewed hole-specific inspection of magnetostratigraphic events and the addition of epibenthic δ18O records for short Pliocene sections in holes 982A, B, and C, crossing core breaks in the δ18O record published for Hole 982B, now imply a major revision of composite core depths. After tuning to the orbitally tuned reference record LR04 the new composite δ18O record results in a hiatus, where the Kaena magnetic event might been lost, and in a significant age reduction for all proxy records by 130 to 20 ka over the time span 3.2-2.7million yr ago (Ma). Our study demonstrates the significance of reliable composite-depth scales and δ18O stratigraphies in ODP sediment records for ocean-wide correlations in paleoceanography and makes Late Pliocene trends found at Site 982 much better comparable to those published from elsewhere in the North Atlantic. [ABSTRACT FROM AUTHOR]

Variations in atmospheric circulation across the last deglaciation in the northernmost monsoon-influenced regions of Asia are not well constrained, highlighting a fundamental gap in our understanding of Asian climate. Here we reconstruct continental air temperatures for northeast China across the last deglaciation (past 16 k.y.), based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers in a sequence of the Hani peat (Jilin Province, northeast China). Our results indicate large (as much as 10 °C) oscillations in temperature in northeast China across the deglaciation, oscillations significantly larger than observed in other temperature records from low-latitude or same-latitude East Asia, but consistent with climate model simulations. This enhanced magnitude, as well as the timing of temperature variations, provides evidence for atmospheric teleconnections with high latitudes; in particular, we suggest that highlatitude cooling associated with Arctic ice expansion and changes in Atlantic Meridional Overturning Circulation enhanced the intensity and lowered the temperature of Eurasian mid-latitude westerlies and northwesterly winds over East Asia during the last glacial, delivering cold air masses to northeast China. During the deglaciation the westerlies and therefore delivery of cold air masses weakened, amplifying the deglacial warming in this region. We conclude that changes in North Atlantic climate had a particularly strong impact on the northernmost parts of the East Asian monsoon-influenced area. [ABSTRACT FROM AUTHOR]