Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

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Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

[1] We present a 53-Myr stack (the “LR04” stack) of benthic δ18O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm This is the first benthic δ18O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene We also present a new LR04 age model for the Pliocene-Pleistocene derived from tuning the δ18O stack to a simple ice model based on 21 June insolation at 65°N Stacked sedimentation rates provide additional age model constraints to prevent overtuning Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 53 Myr and in the precession band for more than half of the record The LR04 stack contains significantly more variance in benthic δ18O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic Finally, the relative phases of the stack's 41- and 23-kyr components suggest that the precession component of δ18O from 27–16 Ma is primarily a deep-water temperature signal and that the phase of δ18O precession response changed suddenly at 16 Ma

/pdf/a-pliocene-pleistocene-stack-of-57-globally-distributed-n5iphe7mt2.pdf

A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

We present here a new solution for the astronomical computation of the insolation quantities on Earth spanning from -250 Myr to 250 Myr. This solution has been improved with respect to La93 (Laskar et al. [CITE]) by using a direct integration of the gravitational equations for the orbital motion, and by improving the dissipative contributions, in particular in the evolution of the Earth–Moon System. The orbital solution has been used for the calibration of the Neogene period (Lourens et al.  [CITE]), and is expected to be used for age calibrations of paleoclimatic data over 40 to 50 Myr, eventually over the full Palaeogene period (65 Myr) with caution. Beyond this time span, the chaotic evolution of the orbits prevents a precise determination of the Earth's motion. However, the most regular components of the orbital solution could still be used over a much longer time span, which is why we provide here the solution over 250 Myr. Over this time interval, the most striking feature of the obliquity solution, apart from a secular global increase due to tidal dissipation, is a strong decrease of about 0.38 degree in the next few millions of years, due to the crossing of the  resonance (Laskar et al. [CITE]). For the calibration of the Mesozoic time scale (about 65 to 250 Myr), we propose to use the term of largest amplitude in the eccentricity, related to , with a fixed frequency of /yr, corresponding to a period of 405 000 yr. The uncertainty of this time scale over 100 Myr should be about , and  over the full Mesozoic era.

/pdf/a-long-term-numerical-solution-for-the-insolation-quantities-4jg807k9xu.pdf

A long-term numerical solution for the insolation quantities of the Earth

Past episodes of greenhouse warming provide insight into the coupling of climate and the carbon cycle and thus may help to predict the consequences of unabated carbon emissions in the future.

/pdf/an-early-cenozoic-perspective-on-greenhouse-warming-and-yffl0bpyf1.pdf

An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics

We review Phanerozoic sea-level changes [543 million years ago (Ma) to the present] on various time scales and present a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 ± 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 10 4 - to 10 6 -year scale, but a link between oxygen isotope and sea level on the 10 7 -year scale must be due to temperature changes that we attribute to tectonically controlled carbon dioxide variations. Sea-level change has influenced phytoplankton evolution, ocean chemistry, and the loci of carbonate, organic carbon, and siliciclastic sediment burial. Over the past 100 My, sea-level changes reflect global climate evolution from a time of ephemeral Antarctic ice sheets (100 to 33 Ma), through a time of large ice sheets primarily in Antarctica (33 to 2.5 Ma), to a world with large Antarctic and large, variable Northern Hemisphere ice sheets (2.5 Ma to the present).

/pdf/the-phanerozoic-record-of-global-sea-level-change-14696qrujw.pdf

The Phanerozoic Record of Global Sea-Level Change

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018PA003327

Water Column Stratification in the Antarctic Zone of the Southern Ocean During the Mid-Pleistocene Climate Transition

Alkenone mass accumulation rates (MARs) provide a proxy for export productivity in the northwestern Pacific (Ocean Drilling Program Site 1208) spanning the late Pliocene through early Pleistocene (3.0-1.8 Ma). We investigate changes in productivity associated with global cooling during the onset and expansion of Northern Hemisphere glaciation (NHG). Alkenone MARs vary on obliquity time-scales throughout, but the amplitude increases at 2.75 Ma concurrent with the intensification of NHG and cooling of the sea surface by 3 °C. The obliquity-scale variations in alkenone MARs parallel shipboard measurements of sediment color reflectance (%) with higher MARs significantly correlated (>95%) with darker (opal-rich) intervals. Variations in both lead benthic foraminiferal δ18O values by 1.5-2 kyr, suggesting that export productivity may be a contributing factor, rather than a response, to the extent of continental glaciation. The biological pump is therefore a plausible mechanism for transferring atmospheric CO2 into the deep ocean during the onset of NHG and the ensuing obliquity dominated climate regime. Obliquity-scale correlation between productivity and magnetic susceptibility is consistent with a link via westerly winds delivering terrigenous sediments and mixing the upper water column. Alkenone MARs also contain a ~400 kyr modulation. Because this periodicity is a multiple of the residence time of carbon in the ocean, it may reflect inputs of new nutrients associated with eccentricity forced changes in the terrestrial biosphere and weathering. We ascribe these findings to interactions between the East Asian winter monsoon and productivity in the North Pacific Ocean, perhaps contributing to Plio-Pleistocene climate change.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016PA002955

Paleoproductivity in the northwestern Pacific Ocean during the Pliocene-Pleistocene climate transition (3.0–1.8 Ma)

Published benthic foraminiferal Mg/Ca records have been compiled that span the latest Oligocene through Miocene, including new data for the South Atlantic. This synthesis, the first such of Mg/Ca data, necessitates consideration of uncertainties and limitations and provides a general perspective on the evolution of deep-sea temperatures over this period. Published Mg/Ca records show temperature patterns through the Miocene that are consistent with those first synthesized by Kennett (1985) utilizing isotope and other data. Accordingly, the early Miocene was an interval of relative warmth culminatinginaclimaticoptimumat � 16Mathatwascharacterizedbythewarmest(Mg-derived) temperatures of the past 20 million years. After the climatic optimum, palaeotemperatures dropped by 3‐4 � C during the second major advance of Antarctic ice between � 15Ma and 13Ma. For the late Miocene, between 11 and 8.5Ma, a distinct increase in benthic foraminiferal Mg/Ca ratios at two Atlantic sites provides evidence for deep to intermediate water circulation changes. Thereafter, temperatures close to modern are recorded at all sites. Assuming constant seawater Mg/Ca ratios through time, it can be concluded that the early Miocene climate was generally warmer than today and that by the late Miocene temperatures approached modern values.

A synthesis of Late Oligocene through Miocene deep sea temperatures as inferred from foraminiferal Mg/Ca ratios

Surface water hydrography of the Kuroshio Extension during the Pliocene–Pleistocene climate transition

We explore the use of the coiling direction of planktic foraminifer Globorotalia truncatulinoides in sediment cores from the northwestern subtropical Atlantic Ocean as a proxy for variations in the intensity of the western boundary of the subtropical gyre over the past 280 kyr. Core-top sediments from the study region are dominated by the left coiling variety consistent with the deep permanent thermocline at the study sites (KNR140-37PC and Ocean Drilling Program Site 1059). Downcore G. truncatulinoides (sinistral) maxima occur in conjunction with 14 out of the 25 (Northern and Southern Hemisphere) precession maxima contained in the study interval. The agreement between the dominance of left coiling tests and the precession index of the Southern Hemisphere, in particular, supports a link between a deep thermocline in the northwestern subtropical Atlantic and northward flow of equatorially sourced warm surface currents, a situation analogous to the Late Holocene. Interglacial marine oxygen isotope stage (MIS) 5 lacks G. truncatulinoides (s) minima attesting to the relative stability of the western boundary during an interval of prolonged global warmth. G. truncatulinoides (s) disappear during the glacial extremes of MIS 2, 6, and 8 implying a weaker western boundary current at these times. Our results support that the coiling direction of this species is sensitive to variations in hydrography of the western boundary of the subtropical gyre. Because of the association between G. truncatulinoides (s) and precession maxima in both hemispheres, results support the importance of oceanic heat transport in half-precession climate variability in the North Atlantic.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016PA002927

Exploring Globorotalia truncatulinoides coiling ratios as a proxy for subtropical gyre dynamics in the northwestern Atlantic Ocean during Late Pleistocene Ice Ages

Katharina Billups

Papers

Water Column Stratification in the Antarctic Zone of the Southern Ocean During the Mid-Pleistocene Climate Transition

Paleoproductivity in the northwestern Pacific Ocean during the Pliocene-Pleistocene climate transition (3.0–1.8 Ma)

A synthesis of Late Oligocene through Miocene deep sea temperatures as inferred from foraminiferal Mg/Ca ratios

Surface water hydrography of the Kuroshio Extension during the Pliocene–Pleistocene climate transition

Exploring Globorotalia truncatulinoides coiling ratios as a proxy for subtropical gyre dynamics in the northwestern Atlantic Ocean during Late Pleistocene Ice Ages