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During the Pliocene, atmospheric CO.sub.2 concentrations (pCO.sub.2) were probably sometimes similar to today's, and global average temperature was â¼3 °C higher than preindustrial. However, the relationships and phasing between variability in climate and pCO.sub.2 on orbital timescales are not well understood. Specifically, questions remain about the nature of a lag of pCO.sub.2 relative to benthic foraminiferal [delta].sup.18 O in late Pliocene Marine Isotope Stage (MIS) M2 (3300 ka), which was longer than during the Pleistocene. Here, we present a multiproxy paleoceanographic reconstruction of the late Pliocene subtropical-subantarctic zone. New dinoflagellate cyst assemblage data are combined with previously published sea surface temperature reconstructions to reveal past surface conditions, including latitudinal migrations of the subtropical front (STF) over the late Pliocene at Ocean Drilling Program (ODP) Site 1168, offshore of western Tasmania. We observe strong oceanographic variability at the STF over glacial-interglacial timescales, especially the interval (3320-3260 ka) across MIS M2. By providing tight and independent age constraints from benthic foraminiferal [delta].sup.18 O, we find that, much more than benthic [delta].sup.18 O or local SST, latitudinal migrations of the STF are tightly coupled to global pCO.sub.2 variations across the M2. Specifically, a northerly position of the STF during the MIS M2 deglaciation coincides with generally low pCO.sub.2 . We postulate that the Southern Ocean CO.sub.2 outgassing varied strongly with migrations of the STF and that this in part accounted for the variability in pCO.sub.2 across MIS M2.

While orbital forcing‐induced weakening of the Atlantic meridional overturning circulation (AMOC) potentially facilitated glacial initiation during the Quaternary glacial‐interglacial cycles, this mechanism has remained to be confirmed by atmosphere‐ocean general circulation models (AOGCMs). Our simulations with an AOGCM demonstrate that without any freshwater hosing, a complete AMOC collapse can be achieved through precessional forcing alone under high eccentricity and relatively low atmospheric CO2 level (pCO2). Crucially, the multi‐millennial timescale required for full AMOC response to precessional forcing suggests that the orbital acceleration techniques in AOGCM simulations, often adopted to save computation time, likely obscured detection of these abrupt AMOC transitions in previous studies.

It has been previously proposed that glacial inception represents a bifurcation transition between interglacial and glacial states and is governed by the nonlinear dynamics of the climate-cryosphere system. To trigger glacial inception, the orbital forcing (defined as the maximum of summer insolation at 65° N and determined by Earth's orbital parameters) must be lower than a critical level, which depends on the atmospheric CO.sub.2 concentration. While paleoclimatic data do not provide a strong constraint on the dependence between CO.sub.2 and critical insolation, its accurate estimation is of fundamental importance for predicting future glaciations and the effect that anthropogenic CO.sub.2 emissions might have on them. In this study, we use the novel Earth system model of intermediate complexity CLIMBER-X with interactive ice sheets to produce a new estimation of the critical insolation-CO.sub.2 relationship for triggering glacial inception. We perform a series of experiments in which different combinations of orbital forcing and atmospheric CO.sub.2 concentration are maintained constant in time. We analyze for which combinations of orbital forcing and CO.sub.2 glacial inception occurs and trace the critical relationship between them, separating conditions under which glacial inception is possible from those where glacial inception is not materialized. We also provide a theoretical foundation for the proposed critical insolation-CO.sub.2 relation. We find that the use of the maximum summer insolation at 65° N as a single metric for orbital forcing is adequate for tracing the glacial inception bifurcation. Moreover, we find that the temporal and spatial patterns of ice sheet growth during glacial inception are not always the same but depend on the critical insolation and CO.sub.2 level. The experiments evidence the fact that during glacial inception, ice sheets grow mostly in North America, and only under low CO.sub.2 conditions are ice sheets also formed over Scandinavia. The latter is associated with a weak Atlantic Meridional Overturning Circulation (AMOC) for low CO.sub.2 . We find that the strength of AMOC also affects the rate of ice sheet growth during glacial inception.

The Western Pacific Warm Pool (WPWP) exhibits different glacial-interglacial climate variability compared to high latitudes, and its sea surface temperatures are thought to respond primarily to changes in greenhouse forcing. To better characterize the orbital-scale climate response covering the WPWP, we constructed a planktonic [delta].sup.18 O stack (average) of 10 previously published WPWP records of the last 800 kyr, available at

The Greater Cape Floristic Region (GCFR) of South Africa is a biodiversity hotspot of global significance, and its archeological record has substantially contributed to the understanding of modern human origins. For both reasons, the climate and vegetation history of southwestern South Africa is of interest to numerous fields. Currently known paleoenvironmental records cover the Holocene, the last glacial-interglacial transition and parts of the last glaciation but do not encompass a full glacial-interglacial cycle. To obtain a continuous vegetation record of the last Pleistocene glacial-interglacial cycles, we studied pollen, spores and micro-charcoal of deep-sea sediments from IODP Site U1479 retrieved from SW of Cape Town. We compare our palynological results of the Pleistocene with previously published results of Pliocene material from the same site. We find that the vegetation of the GCFR, in particular fynbos and afrotemperate forest, responds to precessional forcing of climate. The micro-charcoal record confirms the importance of fires in the fynbos vegetation. Ericaceae-rich and Asteraceae-rich types of fynbos could extend on the western part of the Paleo-Agulhas Plain (PAP), which emerged during periods of low sea level of the Pleistocene.

Deglaciations are characterized by the largest natural changes in methane (CH.sub.4) and nitrous oxide (N.sub.2 O) concentrations of the past 800 000 years. Reconstructions of millennial- to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH.sub.4 and N.sub.2 O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of â¼100 years. Our data permit the identification of centennial-scale fluctuations during the transition from glacial to interglacial levels. At â¼134 000 and â¼129 000 years before present (hereafter ka), both CH.sub.4 and N.sub.2 O increased on centennial timescales. These abrupt rises are similar to the fluctuations associated with the Dansgaard-Oeschger events identified in the last glacial period. In addition, gradually rising N.sub.2 O levels at â¼130 ka resemble a pattern of increasing N.sub.2 O concentrations on millennial timescales characterizing the later part of Heinrich stadials. Overall, the events in CH.sub.4 and N.sub.2 O during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation and glacial cycle, suggesting that the processes leading to changes in emission during the transitions were similar but their timing differed.

The sulfur biogeochemical cycle plays a key role in regulating Earth’s surface redox through diverse abiotic and biological reactions that have distinctive stable isotopic fractionations. As such, variations in the sulfur isotopic composition (δ34S) of sedimentary sulfate and sulfide phases over Earth history can be used to infer substantive changes to the Earth’s surface environment, including the rise of atmospheric oxygen. Such inferences assume that individual δ34S records reflect temporal changes in the global sulfur cycle; this assumption may be well grounded for sulfate-bearing minerals but is less well established for pyrite-based records. Here, we investigate alternative controls on the sedimentary sulfur isotopic composition of marine pyrite by examining a 300-m drill core of Mediterranean sediments deposited over the past 500,000 y and spanning the last five glacial–interglacial periods. Because this interval is far shorter than the residence time of marine sulfate, any change in the sulfur isotopic record preserved in pyrite (δ34Spyr) necessarily corresponds to local environmental changes. The stratigraphic variations (>76‰) in the isotopic data reported here are among the largest ever observed in pyrite, and are in phase with glacial–interglacial sea level and temperature changes. In this case, the dominant control appears to be glacial–interglacial variations in sedimentation rates. These results suggest that there exist important but previously overlooked depositional controls on sedimentary sulfur isotope records, especially associated with intervals of substantial sea level change. This work provides an important perspective on the origin of variability in such records and suggests meaningful paleoenvironmental information can be derived from pyrite δ34S records.

During the Mid-Pleistocene Transition (MPT; â¼ 1.2-0.8 Myr ago) the dominant periodicity of glacial cycles increased from 41 kyr to an average of 100 kyr, without any appreciable change in the orbital pacing. As the MPT is not a linear response to orbital forcing, it must have resulted from feedback processes in the Earth system. However, the precise mechanisms underlying the transition are still under debate.

South American summer monsoon (SASM) strength tracks insolation on orbital timescales, linking global climate and continental hydrology. However, whether local water availability also responds to global climate forcings is unclear. Here, we present water balance records from Lake Junín, an Andean lake within the SASM domain. Local water balance and SASM strength is inferred from triple oxygen isotopes of lake carbonates during two interglacial periods (Marine Isotope Stage (MIS) 15, 621–563 ka; the Holocene, 11.7–0 ka). We find SASM strength and water balance both follow the precession‐pacing of local summer insolation, with the driest conditions occurring at Lake Junín under weakened SASM conditions (and vice versa). Further, the largest variations occurred during MIS 15, when insolation was more variable than the Holocene. These results suggest that global climate influences South American hydrology on both the local and continental scales, with implications for tropical water resources, the atmospheric greenhouse effect, and ecosystem dynamics.

High‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce seasonally resolved climate records from subarctic‐Canada using micron‐scale measurements of oxygen isotopes (δ18O) in speleothems with apparent annual growth bands from three interglacial periods—Marine Isotope Stages (MIS) 11, 9, and 5e. We find 3‰ lower δ18O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ18O and suggest low MIS 11 δ18O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. Our study highlights the potential for high‐latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them. Plain Language Summary Few climate records pre‐dating the last ice age exist from high‐latitude North America, which inhibits our understanding of how regions with permafrost responded to past warming and how they might change in the future. Here, we help fill this data gap by using six speleothems (cave mineral deposits) from a cave in the Northwest Territories, Canada to produce climate records that span thousands of years during former warm periods of Earth's history. We find that speleothems that grew during an exceptionally warm super‐interglacial period 400,000 years ago have 3‰ lower oxygen isotope (δ18O) values compared to those that grew during a likely cooler interglacial 125,000 years ago. We explore potential explanations for the difference in δ18O across interglacials, and suggest that lower δ18O values during warmer periods reflect greater infiltration of cool‐season precipitation with longer annual ground thaw durations. This study highlights the importance of high‐latitude speleothems to provide detailed climate records beyond the range available from Greenland ice cores. Key Points Long high‐latitude terrestrial climate records are rare in the Northern Hemisphere High‐latitude speleothems can provide ultra‐high‐resolution climate records beyond the reach of Greenland ice cores Mean oxygen isotopes of Arctic and subarctic speleothems likely are controlled by annual ground thaw durations