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The timing of ice ages over the past ∼2,600 thousand years (kyr) follows pacing by cyclical changes in three aspects of Earth's orbit that influence the solar energy received as a function of latitude and season. Explaining the large magnitude of the climate changes is challenging, particularly so across the period of time from ∼1,250 to 750 ka—the Mid-Pleistocene Transition or MPT. The average repeat time of ice age cycles changed from an earlier 41-kyr rhythm to longer and more intense glaciations at a spacing of about 100 kyr. Explaining this change is very difficult because there was no corresponding change in the orbital pacing that would trigger a change in timing. While the first generation of hypotheses looked largely to changes in the behavior of Northern Hemisphere ice sheets, more recent work integrates ice behavior with new data capturing the evolution of other important aspects of past climate. A full explanation is still lacking, but attention increasingly focuses on the ocean carbon cycle and atmospheric CO2 levels as the crucial agents involved in the MPT. ▪ The pattern of climate changes connected to the ice ages of the past few million years changed radically between about 1,250 and 750 thousand years ago, a time known as the Mid-Pleistocene Transition or MPT. ▪ While the glacial cycles were ultimately triggered by cyclical changes in Earth's orbit, the changes across the MPT came from changes in the Earth system itself, most likely in the form of a change in the carbon cycle. ▪ The dramatic change in many essential aspects of climate—ice volume, temperature, rainfall on land, and many others—in the absence of an external change suggests how important feedbacks are to the climate system.

The Miocene Climatic Optimum (MCO) from ~17 to 14 million years ago (Ma) represents an enigmatic reversal in Cenozoic cooling. A synthesis of marine paleotemperature records shows that the MCO was a local maximum in global sea surface temperature superimposed on a period from at least 19 Ma to 10 Ma, during which global temperatures were on the order of 10°C warmer than at present. Our high-resolution global reconstruction of ocean crustal production, a proxy for tectonic degassing of carbon, suggests that crustal production rates were ~35% higher than modern rates until ~14 Ma, when production began to decline steeply along with global temperatures. The magnitude and timing of the inferred changes in tectonic degassing can account for the majority of long-term ice sheet and global temperature evolution since 20 Ma.

The prevailing mid-latitude westerly winds, known as the westerlies, are a fundamental component of the climate system because they have a crucial role in driving surface ocean circulation1 and modulating air–sea heat, momentum and carbon exchange1–3. Recent work suggests that westerly wind belts are migrating polewards in response to anthropogenic forcing4,5. Reconstructing the westerlies during past warm periods such as the Pliocene epoch, in which atmospheric carbon dioxide (CO2) was about 350 to 450 parts per million6 and temperatures were about 2 to 4 degrees Celsius higher than today7, can improve our understanding of changes in the position and strength of these wind systems as the climate continues to warm. Here we show that the westerlies were weaker and more poleward during the warm Pliocene than during glacial periods after the intensification of Northern Hemisphere glaciation (iNHG), which occurred around 2.73 million years ago8. Our results, which are based on dust and export productivity reconstructions, indicate that major ice sheet development during the iNHG was accompanied by substantial increases in dust fluxes in the mid-latitude North Pacific Ocean, especially compared to those in the subarctic North Pacific. Following this shift, changes in dust and productivity largely track the glacial–interglacial cycles of the late Pliocene and early Pleistocene epochs. On the basis of this pattern, we infer that shifts in the westerlies were primarily driven by variations in Plio-Pleistocene thermal gradients and ice volume. By combining this relationship with other dust records9–11 and climate modelling results12, we find that the proposed changes in the westerlies were globally synchronous. If the Pliocene is predictive of future warming, we posit that continued poleward movement and weakening of the present-day westerlies in both hemispheres can be expected. Analysis of dust from marine sediments in the North Pacific shows that warm periods during the Pliocene witnessed weaker and more poleward westerlies than during subsequent glacial periods.

The Yorktown Formation records paleoclimate conditions along the mid-Atlantic Coastal Plain during the mid-Piacenzian Warm Period (3.264 to 3.025 Ma), a climate interval of the Pliocene in some ways analogous to near future climate projections. To gain insight into potential near future changes, we investigated Yorktown Formation outcrops and cores in southeastern Virginia, refining the stratigraphic framework. We analyzed 485 samples for alkenone-based sea surface temperature (SST) and productivity estimates from the Holland and Dory cores, an outcrop at Morgarts Beach, Virginia, and the lectostratotype of the Yorktown Formation at Rushmere, Virginia, and analyzed planktonic foraminferal assemblage data from the type section. Using the structure of the SST record, we improved the chronology of the Yorktown Formation by establishing the maximum age ranges of the Rushmere (3.3–3.2 Ma) and Morgarts Beach (3.2–3.15 Ma) Members. SST values for these members average ~26 °C, corroborating existing sclerochronological data. Increasing planktonic foraminifer abundance, productivity, and species diversity parallel increasing SST over the MIS M2/M1 transition. These records constitute the greatest temporal concentration of paleoecological estimates within the Yorktown Formation, aiding our understanding of western North Atlantic temperature patterns, seasonality and ocean circulation during this interval. We provide a chronologic framework for future studies analyzing ecological responses to profound climate change.

Correlation does not necessarily imply a causation, but in climatology and paleoclimatology, correlation is used to identify potential cause-and-effect relationships because linking mechanisms are difficult to observe. Confounding by an often unknown outside variable that drives the sets of observables is one of the major factors that lead to correlations that are not the result of causation. Here we show how autoregressive (AR) models can be used to examine lead-lag relationships—helpful in assessing cause and effect—of paleoclimate variables while addressing two other challenges that are often encountered in paleoclimate data: unevenly spaced data and switching between regimes at unknown times. Specifically, we analyze multiple paleoclimate proxies, sea surface temperature (SST), C37, $$ \delta^{15} N $$ , and %N from the central Peru margin to find their correlations and changes in their variability over the Holocene epoch. The four proxies are sampled at high-resolution from the same core but are not synchronously sampled at all possible locations. The multidimensional records are treated as evenly spaced data with missing values, and the missing values are filled by the Kalman filter expected values. We employ hidden Markov models (HMM) and autoregressive HMM (AR-HMM) to address the potential that the degree of variability and the correlations between these proxies change over time. The HMM, which is not autoregressive, shows instantaneous correlations between observables in two regimes. However, our investigation of lead-lag relationships using the AR-HMM shows that the cross-correlations do not indicate a causal link. Each of the four proxies has predictability on decadal timescales, but none of the proxies is a good predictor of any other proxy, so we hypothesize that a common unobserved variable—or a set of variables—is driving the instantaneous relationships among these four proxies. These findings suggest that the variability at this site is remotely driven by processes such as those causing the Pacific Decadal Oscillation (PDO), rather than locally driven by processes such as upwelling influences on temperature and vertical mixing of nutrients.

The Miocene climate was dynamic, oscillating between major glaciation events and greenhouse conditions (the so-called Miocene Climatic Optimum or MCO). However, forcing factors responsible for climatic transitions from one state to another are not fully understood, partly because palaeoclimatological records from northern mid to high latitudes are scarce.To better resolve climatic changes of the Miocene epoch in the northern middle latitudes we studied a unique, nearly complete sedimentary record (Sdr. Vium borehole) spanning the upper Aquitanian to the Tortonian of the North Sea Basin. Newly obtained sea surface temperatures (SSTs) from our Miocene core revealed that the North Sea Basin was up to 20°C warmer than today, reaching the temperature maximum during the worldwide MCO (Herbert et al. 2020). Our high-resolution δ13C, TOC and C/N records, as well as elemental detrital ratios (Si/Al, Zr/Rb, Zr/Al) derived from XRF reveal important changes in the source of organic matter and detrital coarse fraction of the sediment. During the Miocene the location of the Sdr. Vium borehole was situated in a proximal setting, with water depths varying between 0 and ~200 m, partly due to advancing and retreating delta lobes and partly due to relative sea level changes. We observe that the depositional environment had a large impact on our record. By far the most important of these changes is a condensed interval associated with phosphatization, pyritization, and glauconite, associated with a major shift from a dark brown, organic-rich, bioturbated silty clay with thin sand lenses (the Hodde Formation) towards a green and brown clay with high concentrations of green glaucony pellets of fine sand grade (the Ørnhøj Formation). This shift is related to the subsidence of the North Sea Basin and marks the onset of a sediment-starvation in the basin.

We demonstrate that the precipitation record on the Chinese Loess Plateau during the middle Piacenzian (3.264–3.025 Ma) has strong 20-kyr precessional cycles, challenging past knowledge about East Asian monsoon variations at the orbital timescales.

International audience; Paleoproductivity is reconstructed across a Mediterranean benchmark record, the Early/Middle Pleistocene Montalbano Jonico section, cropping out in southern Italy. High-resolution coccolithophore and alkenone data (C37 and C37:2/C38:2 ratio) were collected in order to extend the data set on Mediterranean paleoproductivity pattern and forcing mechanisms. The multi-proxy record indicates low productivity during glacial and stadial phases and enhanced productivity during interglacial and interstadials. Increased surface water turbidity, cold-water temperature and polar-subpolar low salinity water incursion appear as the dominant controls for low productivity during Marine Isotope Stage (MIS) 20. Enhanced productivity during MIS 19c was sustained by warmer surface waters, coupled with a seasonal precipitation regime, providing higher nutrient availability. Productivity increases during interstadials with respect to stadials, in relation with enhanced land-derived nutrient input through river discharge during wetter winters. The productivity scenario we propose is similar to those reconstructed from deep-sea records in the central and western Mediterranean during Dansgaard-Oeschger oscillations over the last 70 ka. This indicates that similar forcing mechanisms acted on productivity dynamics on a regional scale over different times. We suggest that migration of the westerly wind system over the Mediterranean and the polar water inflow influenced productivity on a regional scale. The acquired data set provides new evidences on the environmental significance of the C37:2/C38:2 ratio and on its relation with surface water productivity.

Alkenones are biomarkers produced solely by algae in the order Isochrysidales that have been used to reconstruct sea surface temperature (SST) since the 1980s. However, alkenone-based SST reconstructions in the northern high latitude oceans show significant bias towards warmer temperatures in core-tops, diverge from other SST proxies in down core records, and are often accompanied by anomalously high relative abundance of the C37 tetra-unsaturated methyl alkenone (%C37:4). Elevated %C37:4 is widely interpreted as an indicator of low sea surface salinity from polar water masses, but its biological source has thus far remained elusive. Here we identify a lineage of Isochrysidales that is responsible for elevated C37:4 methyl alkenone in the northern high latitude oceans through next-generation sequencing and lab-culture experiments. This Isochrysidales lineage co-occurs widely with sea ice in marine environments and is distinct from other known marine alkenone-producers, namely Emiliania huxleyi and Gephyrocapsa oceanica. More importantly, the %C37:4 in seawater filtered particulate organic matter and surface sediments is significantly correlated with annual mean sea ice concentrations. In sediment cores from the Svalbard region, the %C37:4 concentration aligns with the Greenland temperature record and other qualitative regional sea ice records spanning the past 14 kyrs, reflecting sea ice concentrations quantitatively. Our findings imply that %C37:4 is a powerful proxy for reconstructing sea ice conditions in the high latitude oceans on thousand- and, potentially, on million-year timescales., Some algae produce compounds called alkenones that can reconstruct sea surface temperature through geological time, but in high latitudes unknown species complicate use of this proxy. Here the authors find a lineage of sea ice algae that produces alkenones and can be used as a paleo-sensor for sea ice abundance.

This study shows the first Mediterranean high-resolution record of alkenone-derived sea surface temperature (SST) in the marine sediments outcropping at the Ideale section (IS) (southern Italy, central Mediterranean) from late marine isotope stage (MIS) 20 - through early MIS 18. The SST pattern evidences glacial-interglacial up to submillennial-scale temperature variation, with lower values (~13 °C) in late MIS 20 and substage 19b, and higher values (up to 21 °C) in MIS 19c and in the interstadials of MIS 19a. The SST data are combined with the new calcareous plankton analysis and the available, chronologically well-constrained carbon and oxygen isotope records in the IS. The multi-proxy approach, together with the location of the IS near the Italian coasts, the lower circalittoral-upper bathyal depositional setting, and high sedimentation rate allow to document long-and short-term paleoenvironmental modifications (sea level, rainfall, inorganic/organic/fresh water input to the basin), as a response to regional and global climate changes. The combined proxies reveal the occurrence of a terminal stadial event in late MIS 20 (here Med-HTIX), and warm-cold episodes (here Med-BATIX and Med-YDTIX) during Termination IX (TIX), which recall those that occurred through the last termination (TI). During these periods and the following ghost sapropel layer (insolation cycle 74, 784 ka) in the early MIS 19, high frequency internal changes are synchronously recorded by all proxies. The substage MIS 19c is warm but quite unstable, with several episodes of paleoenvironmental changes, associated with fluctuating tropical-subtropical water inflow through the Gibraltar Strait, variations of the cyclonic regime in the Ionian basin, and the southward shift of westerly winds and winter precipitation over southern Europe and Mediterranean basin. Three high-amplitude millennial-scale oscillations in the patterns of SST and calcareous plankton key taxa during MIS 19a are interpreted as linked to changes in temperature as well as in salinity due to periodical water column stratification and mixing. The main processes involved in the climate variability include changes in oceanographic exchanges through the Gibraltar Strait during modulations of Atlantic meridional overturning circulation and/or variations in atmospheric dynamics related to the influence of westerly and polar winds acting in the paleo-Ionian basin. A strong climate teleconnection between the North Atlantic and Mediterranean is discussed, and a prominent role of atmospheric processes in the central Mediterranean is evidenced by comparing data sets at the IS with Italian and extra-Mediterranean marine and terrestrial records.

The warm Pliocene serves as an analogue for predicted warming over the next century. However, large uncertainties exist for atmospheric circulation and land surface conditions during the Pliocene. Dust transported by wind to locations of accumulation (terrestrial or marine) can provide a record of wind intensity and/or direction. Few dust flux records spanning the Plio-Pleistocene exist. As such, there is ample opportunity to use marine sediments to reconstruct changes in atmospheric conditions during a warmer-than-present world, as well as across the onset/intensification of Northern Hemisphere Glaciation (NHG). During this time, East Asia’s interior, the second largest source of mineral dust today, experienced aridification, occurring alongside a major reorganization of the subarctic North Pacific circulation which led to stratification of the surface ocean. Here, we present two North Pacific marine sediment records of extraterrestrial (ET) 3He-derived terrigenous dust flux proxies (4HeTerr and Th), along with a record of multiple paleoproductivity proxies (Baxs, Opal, and C37Total) for the period spanning ~2.5-4.5 Ma. Our results show that dust flux to the western North Pacific was relatively low and constant through the Pliocene up until ~2.7 Ma, with minor peaks during cooler phases from ~2.9-3.1 Ma. At ~2.7 Ma, concurrent with the intensification of NHG and formation of a permanent halocline cap in the subarctic North Pacific, dust fluxes increase dramatically. The central North Pacific record shows a less drastic shift in dust, but generally displays higher fluxes after ~3 Ma. Dust fluxes in East Asia and the North Pacific are consistent during this time interval, as are global dust fluxes from the North Atlantic, South Atlantic and North Pacific. Western North Pacific dust, SST, and paleoproductivity records point to northward-shifted and weakened Northern Hemisphere westerlies during the warm Pliocene, with evidence for strengthening and southward movement of the westerlies during glacials after ~2.7 Ma. Changes in both winds and dust production mechanisms are likely working in tandem to produce the coherent global dust signals.

The Sahel region is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in the Sahel and are implicated in both the major drought of the late 20th century and extreme droughts associated with the Heinrich events of the last glacial. To better understand how Sahelian hydroclimate may respond to SST variability in a warmer world, we turn to the Pliocene epoch, when atmospheric CO2 levels were comparable to present. We studied sediments from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our new dust accumulation rates and X-ray fluorescence core scan data indicate that there were major shifts between highly arid conditions and humid intervals with vegetated or “Green Sahara” conditions over much of northern Africa, driven by both solar insolation and glacial-interglacial variability. We also report three unusually long Plio-Pliocene humid intervals (each lasting ca. 100 kyr) characterised by very low dust emissions, that we term “Green Sahara Megaperiods (GSMPs)”. All three of these GSMPs occur at times when insolation variability was weak, resulting in values close to the long-term mean. This observation strongly suggests that factors other than insolation drove the sustained humidity of GSMPs. We present paired alkenone SST estimates and multi-species planktonic foramaniferal isotope records from 3.5–2.3 Myr ago to explore the extent to which the GSMPs were accompanied by intervals of extended warmth in the surface waters of the North Atlantic Ocean.

The El Niño-Southern Oscillation (ENSO) is a driver of global atmosphere-ocean dynamics, but projections of frequency and magnitude in different climate states remain uncertain. Palaeoclimate records offer the potential to improve our understanding of ENSO behaviour but most are fragmentary, suffer low resolution, and/or typically do not cover periods warmer than present day. The Last Interglacial (129-116 kyr BP) was the most recent period during which global temperatures were close to 21st century projections, and potentially provides insights into operation of climate modes of variability in the future. Here we report a continuous, inter-annually resolved record of hydroclimate spanning 220-80 ka from Lynch’s Crater in tropical northeast Australia, a region highly sensitive to ENSO. Our reconstruction is based on a micro-X-ray fluorescence (XRF)-generated elemental profile at 200 µm resolution, combined with loss-on-ignition, magnetic susceptibility, and pollen analysis. We find that during globally warmer periods (including super-interglacial Stage 5e, and 5c), there are significantly larger amplitudes in high-frequency ENSO spectral range (3-8 years), which are absent from the record during the glacial stages MIS6 and MIS4. Our results imply an ENSO dependence on mean climate, with enhanced ENSO variance during interglacials globally warmer than present. These results are consistent with climate model projections for a future slowdown of the Walker circulation and more extreme El Niño events under greenhouse warming.

The composite section from ODP Site 846 has provided key data sets for Pliocene stable isotope and paleoclimatic time series. We document here errors in primary data sets for stable isotopes and alkenone-derived sea surface temperature estimates (SST) in the late Pliocene interval containing the M2 glaciation (ca. 3.250–3.3 Ma) by tying high resolution core measurements to a continuous downhole conductivity log. In addition, we provide new stable isotopic and alkenone measurements that correlate well to the revised splices of color reflectance and gamma ray attenuation porosity evaluator data. A new composite splice is proposed, along with composite isotope and alkenone time series that should be integrated into revised Pliocene paleoclimatic stacks.

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.

A period of continental aridification and ecosystem change occurred about seven million years ago. A global sea surface temperature reconstruction identifies cooling temperatures and a strengthened meridional temperature gradient at this time.

It is difficult to untangle the mixed influences of high- and low-latitude climate forcing in the eastern equatorial Pacific (EEP). Here we test the hypothesis that the Southern Ocean drove change in the EEP via subsurface intermediate waters during the last deglaciation. We use the δ18O signature of benthic foraminifera to reconstruct water density changes during the last 25 kyr at three intermediate water depths (370 m, 600 m, and 1000 m) in the EEP. Carbonate δ18O records a combined signature of temperature and salinity and is therefore more closely related to density than temperature or salinity alone. We find that benthic foraminiferal δ18O values decreased first in the subsurface, simultaneously with rising temperatures over Antarctica, and propagated up to the surface within ~3 kyr. The early subsurface response initiated a rapid decrease in density stratification over the upper water column as indicated by reduced δ18O gradients between surface and intermediate depths. Stratification of the upper water column remained low through the termination, with stratification minima reached during Heinrich Stadial 1 and the Younger Dryas (YD), synchronous with the two-part deglacial rise in atmospheric CO2. Centennial-scale shifts toward heavier δ18O signatures at 370 and 600 m during the YD indicate short-lived shifts in the Subantarctic Mode Water/Antarctic Intermediate Water boundary to shallower intermediate depths. We suggest that decreased density gradients during the deglaciation accelerated vertical mixing across the EEP, and potentially the entire South Pacific subtropical gyre, which enhanced CO2 delivery from depth to the surface ocean and atmosphere.

The eastern equatorial Pacific cold tongue was only weakly developed to nonexistent before ~4.3 million years ago., The timing and mechanisms of the eastern equatorial Pacific (EEP) cold tongue development, a salient feature of the tropical ocean, are intensely debated on geological time scales. Here, we reconstruct cold tongue evolution over the past 8 million years by computing changes in temperature gradient between the cold tongue and eastern Pacific warm pool. Results indicate that the cold tongue remained very weak between 8 and 4.3 million years ago, implying much weaker zonal temperature gradients prevailing during the late Miocene–Pliocene, but then underwent gradual intensification with apparently increasing sensitivity of the cold tongue to extratropical temperature changes. Our results reveal that the EEP cold tongue intensification was mainly controlled by extratropical climate.

Correlation does not necessarily imply a causation, but in climatology and paleoclimatology, correlation is used to identify potential cause-and-effect relationships because linking mechanisms are difficult to observe. Confounding by an often unknown outside variable that drives the sets of observables is one of the major factors that lead to correlations that are not the result of causation. Here we show how autoregressive (AR) models can be used to examine lead-lag relationships – helpful in assessing cause and effect – of paleoclimate variables while addressing two other challenges that are often encountered in paleoclimate data: unevenly spaced data; and switching between regimes at unknown times. Specifically, we analyze multidimensional paleoclimate proxies, sea surface temperature (SST), C37, ∂15N, and %N from the central Peru margin to find their correlations and changes in their variability over the Holocene epoch. The four proxies are sampled at high-resolution but are not synchronously sampled at all possible locations. The multidimensional records are treated as evenly spaced data with missing parts, and the missing values are filled by the Kalman filter expected values. We employ hidden Markov models (HMM) and autoregressive HMM (AR-HMM) to address the potential that the degree of variability and the correlations between in these proxies appears to show changes over time. The HMM, which is not autoregressive, shows instantaneous correlations between observables in two regimes. However, our investigation of lead-lag relationships using the AR-HMM shows that the cross-correlations do not indicate a causal link. Each of the four proxies has predictability on decadal timescales, but none of the proxies is a good predictor of any other, so we hypothesize that a common unobserved variable – or a set of variables – is driving the instantaneous relationships among these four proxies, revealing probable confounding without prior knowledge of potential confounding variable(s). These findings suggest that the variability at this site is remotely driven by processes such as those causing the Pacific Decadal Oscillation, rather than locally driven by processes such as increased or decreased vertical mixing of nutrients.

The Atlantic–Mediterranean water exchange is a component of global ocean circulation capable of influencing deep water formation in the North Atlantic, yet it is poorly constrained for the time period preceding the intensification of Northern Hemisphere Glaciation (NHG). The sea surface temperature (SST) gradient between the Atlantic and Mediterranean sides of the Strait of Gibraltar can shed light on the communication between the two basins. IODP Site U1387 in the Gulf of Cadiz provides the first alkenone based reconstruction of SST for the Atlantic waters that flowed into the Mediterranean Sea during the Pliocene. This site reflects open ocean North Atlantic subtropical temperature trends while the published SST records from the Rossello composite section (Sicily) in the Mediterranean reflect the addition of regional, continentally-influenced signals from Europe and Northern Africa. The Mediterranean, in particular, may be influenced by high latitude Northern hemisphere climatic evolution. In the modern regime the sites discussed in this work have comparable SST and uninhibited surface connection; however, change in local heat loss/gain over the Mediterranean due to variability in latent heat loss and obstructed connection can result in a gradient between the sites in the Pliocene. The Pliocene surface waters of the Gulf of Cadiz and the Mediterranean Sea were as much as 7 °C warmer than the modern average of ~ 19–20 °C. The reconstructed temperatures show a ~ 1 °C cooling for the Atlantic side of the Strait of Gibraltar from ~ 6 Ma to ~ 2.7 Ma and increasingly cooler glacials. The long-term SST record from Site U1387 provides a basis for future studies into the hydrological balance of the Mediterranean and the temperature component of Mediterranean Outflow Water (MOW) density. We compared SST on either side of Gibraltar between ~ 3.4–2.7 Ma and found that between ~ 2.7 and ~ 3.1 Ma the Mediterranean and Atlantic surface waters show comparable average temperatures and comparable variance.

Temperature reconstructions from a shallow core (375 m) from the Peru Margin are used to test the influence of Subantarctic Mode Water (SAMW) on the eastern equatorial Pacific (EEP) thermostad and thus the effect of southern high latitude climate on interior ocean heat content (OHC). Temperature estimates, based on Mg/Ca measurements of planktonic and benthic foraminifera (Neogloboquadrina dutertrei and Uvigerina spp., respectively) show higher temperatures in the early Holocene, a cooling of ∼ 2 ° by 8 kyr B.P. and after relatively stable temperatures to the present. The temperature signal is similar in direction and timing to a rather robust Holocene climate signal from the southern high latitudes suggesting it originated there and was advected to the core site in the EEP. Based on the N. dutertrei and Uvigerina Mg/Ca temperature and δ13C records we conclude that SAMW acted as a conduit transporting the southern high latitude climate to the interior of the equatorial Pacific. We propose that the early Holocene warmth is related to a southward migration of the Subtropical Front, which enhanced the influence of warm subtropical water in the region of SAMW formation and was then transported to the EEP thermostad. The early Holocene warmth recorded in the EEP thermostad has a muted sea surface temperature expression indicating this mechanism is important for sequestering heat in the ocean interior.

In the Late Miocene, grasslands proliferated, succulent plants diversified in the mid-latitudes, and the desert-like conditions appeared in the Sahara. Despite this major environmental change on land, the coeval deep-sea oxygen isotope record does not provide evidence for significant high latitude cooling or continental ice growth, making it difficult to relate widespread terrestrial environmental change to global climatic changes. A U 37 K ′ –derived sea surface temperature (SST) reconstruction spanning 13 to 6 Ma from uplifted hemipelagic sediments in Northern Italy provides the first continuous mid-latitude temperature record with which to compare the evolution of aridity and biotic events at similar latitudes in Northern Africa and Pakistan. Between 13 and 8.8 Ma, Mediterranean SST lay near the upper limit of the alkenone temperature proxy (∼28 °C), exceeding modern SST at the site by as much as 10 °C. Throughout the record, sapropel layers correspond to local SST maxima, suggesting that Late Miocene hydrological conditions in the Mediterranean responded to insolation forcing via mechanisms similar to those documented for the Plio-Pleistocene. Mediterranean SST cooled rapidly beginning at ∼8 Ma, with an episode of intense cooling to ∼19 °C between 7.2 Ma and 6.6 Ma, followed by a rebound to ∼25 °C preceding the Messinian Salinity Crisis at 5.9 Ma. These observations establish, for the first time, a direct relationship between increasing aridity in the Northern hemisphere mid-latitudes and significant cooling. Evidently, this cooling was not accompanied by significant growth in continental ice volume. The extreme warmth and subsequent cooling of the Mediterranean Sea are not well-represented in current Late Miocene climate models, which our results suggest underestimate regional warmth prior to the Late Miocene cooling. Evidence of secular cooling during the Late Miocene gives new support to the much-debated link between a possible decline in atmospheric CO2 levels and Late Miocene changes in vegetation on land.

We present a composite time series of Mediterranean sea surface temperature (SST) and marine biomarker accumulation for the time span from 3.5 to 1.525 Ma, based on alkenone unsaturation and concentration from hemipelagic sediments outcropping in southern Italy and Sicily. Paleotemperature data define three regimes: a late Pliocene climate on average 4 – 5 ° C warmer than modern, a latest Pliocene to early Pleistocene onset of 41 kyr cycles, and a major increase in the range of glacial–interglacial temperature change at ∼ 1.84 Ma that shortly precedes the former definition of the Plio-Pleistocene boundary in the Crotone sequence. Pliocene sea surface temperature (SST) cycles are dominated by precession, with a ∼ 1.5 ° C range. Obliquity-related rhythms influence SST significantly shortly after ∼ 2.8 Ma (equivalent to MIS G10) and dominate after ∼ 2.51 Ma (equivalent to MIS 100). However, little, if any, long-term cooling occurred on an interglacial basis until after ∼ 1.85 Ma . Alkenone concentrations provide a good proxy for the accumulation of marine organic matter, and primarily reflect regional hydrology. Organic sedimentation, including the formation of layers highly enriched in organic matter (“sapropels”) was paced throughout by precessional variations despite changes in both average regional temperature, and the shift in temperature variance to the 41 kyr obliquity cycle in the latest Pliocene and early Pleistocene. Our reconstruction therefore highlights the intermingling of both hemispheric-wide changes in temperature and regional variations in the hydrological cycle that combined to force major evolutionary changes in the fauna and flora of northern Africa and the southern Mediterranean in late Pliocene to mid-Pleistocene time.

Orbital-scale precipitation isotope records can elucidate climate forcing mechanisms and provide benchmarks for climate model validation. The ability to differentiate the influence of temperature, seasonality, and vapor transport history on precipitation isotope proxies is critical to both objectives. We present a 300 k.y. leaf wax hydrogen isotope record from the South China Sea with the effects of local condensation temperature removed (δ 2 H wax– T ). δ 2 H wax– T reflects annually integrated precipitation δ 2 H in the Pearl River catchment of southeast China. Depleted δ 2 H wax– T lags minimum precession (P min ) by 1.0 ± 0.7 k.y., reflecting the influence of maximum summer insolation and minimum winter insolation, with a minor influence of global ice volume, which lags P min by 3.3 ± 0.4 k.y. In contrast, annually integrated cave δ 18 O minima in central China, 1000 km north of our site, lag P min by 2.7 ± 0.3 k.y., in phase with ice volume minima. This phase indicates that precipitation δ 18 O in central China is more strongly influenced by ice volume forcing at the precession band, with a lesser influence of Northern Hemisphere insolation. Our new δ 2 H wax– T data demonstrate that precipitation isotopes in Asia have strong regional variability. Interpreting water isotope records within the context of regionally varying temperature, seasonality, and sensitivity to changing glacial boundary conditions is imperative to understanding Asian hydroclimatic change.

There was minimal cooling in the North Atlantic Ocean during the Oligocene inception of the Antarctic ice sheet, according to a sediment record. This finding suggests asynchronous climate changes in the Northern and Southern hemispheres.

[1] Marine biological export productivity declined in high-latitude regions in the North Pacific and Southern Ocean 2.7 million years ago, in parallel with the intensification of Northern Hemisphere glaciation. Here we present data from the North Atlantic, which show a similar but time-transgressive pattern of high-latitude productivity decline from 3.3 to 2.5 Ma, with productivity decreasing first at 69°N, hundreds of thousands of years before it declined at 58°N. We propose that the cumulative data are best explained by an equatorward migration of the westerly winds, which caused a southward shift in the zone of Ekman divergence and upwelling-associated major nutrient supply over this time interval. We suggest that a similar equatorward migration of the westerly winds may also help explain the productivity changes observed in other high-latitude regions, particularly the Southern Ocean. At 2.7 Ma, equatorial and temperate Atlantic sites began to show orbitally paced productivity pulses, consistent with a shoaling and meridional contraction of the nutrient-poor “warm sphere” that characterizes the low latitude upper ocean. This timing coincides with observed productivity changes in Southern Ocean, consistent with previous findings that the Southern Ocean exerts a strong influence on the fertility of the low-latitude Atlantic. Finally, we propose that the unique basin geometry of the North Atlantic caused deep water formation in this region to remain relatively stable despite equatorward migration of winds and ocean fronts.