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Paleontological reconstructions of plankton community structure during warm periods of the Cenozoic (last 66 million years) reveal that deep-dwelling 'twilight zone' (200-1000 m) plankton were less abundant and diverse, and lived much closer to the surface, than in colder, more recent climates. We suggest that this is a consequence of temperature's role in controlling the rate that sinking organic matter is broken down and metabolized by bacteria, a process that occurs faster at warmer temperatures. In a warmer ocean, a smaller fraction of organic matter reaches the ocean interior, affecting food supply and dissolved oxygen availability at depth. Using an Earth system model that has been evaluated against paleo observations, we illustrate how anthropogenic warming may impact future carbon cycling and twilight zone ecology. Our findings suggest that significant changes are already underway, and without strong emissions mitigation, widespread ecological disruption in the twilight zone is likely by 2100, with effects spanning millennia thereafter.

Abstract. The early Eocene (56 to 48 million years ago) is inferred to havebeen the most recent time that Earth's atmospheric CO2 concentrationsexceeded 1000 ppm. Global mean temperatures were also substantially warmerthan those of the present day. As such, the study of early Eocene climate provides insightinto how a super-warm Earth system behaves and offers an opportunity toevaluate climate models under conditions of high greenhouse gas forcing. TheDeep Time Model Intercomparison Project (DeepMIP) is a systematicmodel–model and model–data intercomparison of three early Paleogene timeslices: latest Paleocene, Paleocene–Eocene thermal maximum (PETM) and earlyEocene climatic optimum (EECO). A previous article outlined the modelexperimental design for climate model simulations. In this article, weoutline the methodologies to be used for the compilation and analysis ofclimate proxy data, primarily proxies for temperature and CO2. Thispaper establishes the protocols for a concerted and coordinated effort tocompile the climate proxy records across a wide geographic range. Theresulting climate “atlas” will be used to constrain and evaluate climatemodels for the three selected time intervals and provide insights into themechanisms that control these warm climate states. We provide version 0.1 ofthis database, in anticipation that this will be expanded in subsequentpublications.

The Palaeocene-Eocene Thermal Maximum (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data-a proxy for seawater pH-that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event. We find strong evidence for a much larger (more than 10,000 petagrams)-and, on average, isotopically heavier-carbon source than considered previously. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system.

The Early Eocene Climate Optimum (EECO, which occurred about 51 to 53 million years ago), was the warmest interval of the past 65 million years, with mean annual surface air temperature over ten degrees Celsius warmer than during the pre-industrial period. Subsequent global cooling in the middle and late Eocene epoch, especially at high latitudes, eventually led to continental ice sheet development in Antarctica in the early Oligocene epoch (about 33.6 million years ago). However, existing estimates place atmospheric carbon dioxide (CO2) levels during the Eocene at 500-3,000 parts per million, and in the absence of tighter constraints carbon-climate interactions over this interval remain uncertain. Here we use recent analytical and methodological developments to generate a new high-fidelity record of CO2 concentrations using the boron isotope (δ(11)B) composition of well preserved planktonic foraminifera from the Tanzania Drilling Project, revising previous estimates. Although species-level uncertainties make absolute values difficult to constrain, CO2 concentrations during the EECO were around 1,400 parts per million. The relative decline in CO2 concentration through the Eocene is more robustly constrained at about fifty per cent, with a further decline into the Oligocene. Provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the Eocene was similar to that of the late Quaternary period, this CO2 decline was sufficient to drive the well documented high- and low-latitude cooling that occurred through the Eocene. Once the change in global temperature between the pre-industrial period and the Eocene caused by the action of all known slow feedbacks (apart from those associated with the carbon cycle) is removed, both the EECO and the late Eocene exhibit an equilibrium climate sensitivity relative to the pre-industrial period of 2.1 to 4.6 degrees Celsius per CO2 doubling (66 per cent confidence), which is similar to the canonical range (1.5 to 4.5 degrees Celsius), indicating that a large fraction of the warmth of the early Eocene greenhouse was driven by increased CO2 concentrations, and that climate sensitivity was relatively constant throughout this period.

Electron backscatter diffraction (EBSD) analysis enables a unique perspective of the internal microstructure of foraminiferal calcite. Specifically, EBSD provides crystallographic data from within the test, highlighting the highly organised "mesocrystal" structure of crystallographically aligned domains throughout the test, formed by sequential deposits of microgranular calcite. We compared EBSD maps across the test walls of both poorly preserved and well-preserved specimens of the planktonic foraminifera species Globigerinoides ruber and Morozovella crater. The EBSD maps, paired with information about intra-test distributions of Mg/Ca ratios, allowed us to examine the effects of different diagenetic processes on the foraminifera test. In poorly preserved specimens EBSD data show extensive reorganisation of the biogenic crystal microstructure, indicating differing phases of dissolution, re-precipitation and overgrowth. The specimens with the greatest degree of microstructural reorganisation also show an absence of higher concentration magnesium bands, which are typical features of well-preserved specimens. These findings provide important insights into the extent of post-depositional changes, in both microstructure and geochemical signals that must be considered when utilising foraminifera to generate proxy archive data. [ABSTRACT FROM AUTHOR]

The purpose of this application, under Articles 23.9.3 and 81.2.2 of the Code, is to conserve the usage of the genus-group name TrilobatusSpezzaferri, Kucera, Pearson, Wade, Rappo, Poole, Morard & Stalder, 2015 for a genus of planktonic foraminifera from the global ocean and fossil record by partial suppression of its senior objective synonym TrilobigerinaPopescu, 1987. Partial suppression of the little-used senior name will allow conservation of the younger name that is in very widespread use. [ABSTRACT FROM AUTHOR]

Author(s): Marcus Gutjahr (corresponding author) [1, 2]; Andy Ridgwell [3, 4]; Philip F. Sexton [5]; Eleni Anagnostou [1]; Paul N. Pearson [6]; Heiko Plike [7]; Richard D. Norris [8]; Ellen [...]