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Ocean acidification (OA) during the Paleocene-Eocene thermal maximum (PETM) likely caused a biocalcification crisis. The calcium isotope composition (δ44/40Ca) of primary carbonate producers may be sensitive to OA. To test this hypothesis, we constructed the first high-resolution, high-precision planktic foraminiferal δ44/40Ca records before and across the PETM. The records employ specimens of Morozovella spp. collected from Ocean Drilling Program Sites 1209 (Shatsky Rise, Pacific Ocean) and 1263 (Walvis Ridge, Atlantic Ocean). At Site 1209, δ44/40Ca values start at −1.33‰ during the Upper Paleocene and increase to a peak of −1.15‰ immediately before the negative carbon isotope excursion (CIE) that marks the PETM onset. Values remain elevated through the PETM interval and decrease into the earliest Eocene. A shorter-term record for Site 1263 shows a similar trend, although δ44/40Ca values are on average 0.22‰ lower and decrease shortly after the CIE onset. The trends support neither diagenetic overprinting, authigenic carbonate additions, nor changes in the δ44/40Ca value of seawater. Rather, they are consistent with a kinetic isotope effect, whereby calcite δ44/40Ca values inversely correlate with precipitation rate. Geologically rapid Ca isotope shifts appear to reflect the response of Morozovella to globally forced changes in the local carbonate geochemistry of seawater. All data combined suggest that the PETM-OA event occurred near the peak of a gradual reduction in seawater carbonate ion concentrations during a time of elevated atmospheric pCO2, potentially driven by North Atlantic igneous province emplacement.

Stratigraphic features of the carbon isotope excursion (CIE) marking the Paleocene-Eocene Thermal Maximum (PETM; ca. 55.8 Ma) are used to study ocean-climate change and carbon cycling during this ancient global warming event. Yet discrepancies in its timing and amplitude exist between bulk-carbonate and planktic-foraminifera δ13C records. Here we examine these disparities through the lens of δ13C compositions of size-segregated planktic shells across the pre-CIE to CIE transition in the iconic PETM section of Ocean Drilling Program Site 690 in the Weddell Sea. Our results show that the stratigraphic position of the CIE onset is dependent upon shell size, which we attribute to preferential mixing of smaller shells with pre-CIE δ13C values up into the overlying CIE interval. Hence, the transitory loss of size-dependent δ13C signatures in photosymbiotic planktic foraminifera is a taphonomic artifact, not a geochemical signal of symbiont “bleaching” during the PETM. Our results also indicate that many salient features of the Site 690 bulk-carbonate δ13C record are aberrations caused by size-dependent sediment mixing, and as such, should not be viewed as primary signals of ocean-climate change during what is arguably one of the best ancient analogs for future ocean-climate change.

The Paleocene-Eocene thermal maximum, a transient global warming event, is character- ized by extensive evidence of a more active hydrological cycle. This includes a widespread pulse of kaolinite accumulation on continental margins, viewed as the by-product of either enhanced chemical weathering consistent with much more humid conditions and/or increased erosion of previously deposited laterites. The former would be more consistent with year- round humid conditions, whereas the latter might be indicative of extreme seasonal precipi- tation patterns. To assess these hypotheses, we present a new high-resolution clay mineral assemblage and oxygen isotope record from Bass River, a site on the New Jersey margin (east coast of North America), which shows a sharp rise in the abundance of kaolinite beginning a few thousand years before the onset of the carbon isotope excursion (CIE). The δ 18 O of the

In conjunction with increasing benthic foraminiferal δ 18 O values at the Eocene–Oligocene transition (EOT; ca. 34 Ma), coarse-grained ice-rafted debris (IRD; >425 μm) appears abruptly alongside fossil fish teeth with continentally derived neodymium (Nd) isotope ratios (e Nd ) in Kerguelen Plateau (Southern Ocean) sediments. Increased Antarctic weathering flux, as inferred from two steps to less radiogenic e Nd values, coincides with two steps in benthic foraminiferal δ 18 O values. These results indicate that two distinct surges of weathering were generated by East Antarctic ice growth during the EOT. Weathering by ice sheets during a precursor glaciation at 33.9 Ma did not produce significant IRD accumulation during the first e Nd shift. Glacial weathering was sustained during a terrace interval between the two steps, probably by small high-elevation ice sheets. A large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca. 33.7 Ma. Rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions. Parallel changes in Antarctic weathering flux and deep-sea carbonate accumulation suggest that ice-sheet expansion during the EOT had a direct impact on the global carbon cycle; possible mechanisms include associated changes in silicate weathering on the East Antarctic craton and enhanced fertilization of Southern Ocean waters, both of which warrant further investigation.

Sea-surface temperature (SST) estimates of ~30 °C from planktic foraminifera and archaeal membrane lipids in bathyal sediments in the Canterbury Basin, New Zealand, support paleontological evidence for a warm subtropical to tropical climate in the early Eocene high-latitude (55°S) southwest Pacific. Such warm SSTs call into question previous estimates based on oxygen isotopes and present a major challenge to climate modelers. Even under hypergreenhouse conditions (2240 ppm CO2), modeled summer SSTs for the New Zealand region do not exceed 20 °C.

The Paleocene–Eocene thermal maximum (PETM) ca. 55.5 Ma was a geologically brief interval characterized by massive influx of isotopically light carbon, extreme changes in global climate, and profound variations in Earth system processes. An outstanding issue is whether it was an isolated event, or the most prominent example of a recurring phenomenon. Recent studies of condensed deep-sea sections support the latter, but this finding remains uncertain. Here we present and discuss lithologic and carbon isotope records across two lower Eocene outcrops on South Island, New Zealand. The PETM manifests as a marl-rich horizon with a significant negative carbon isotope excursion (CIE). Above, in sediment deposited between 54 and 53 Ma, are four horizons with similar though less pronounced expressions. Marl beds of all five horizons represent increased terrigenous sedimentation, presumably linked to an accelerated hydrological cycle. Five corresponding clay-rich horizons and CIEs are found in deep-sea records, although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution. The presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 C-depleted carbon during the early Eocene.

The evolutionary recovery of planktic foraminifera from the Cretaceous-Paleogene mass extinction was closely linked to recovery of the marine carbon system. Both the evolutionary recovery and the biogeochemical recovery occurred in two stages. The second stage of evolutionary radiation peaked nearly four million years after the extinction, immediately after the abrupt final recovery of the organic flux to deep waters. The timing of these events suggests that the final postextinction recovery of planktic foraminiferal diversity was directly contingent on the final recovery of the marine carbon cycle. This second radiation was defined by the diversification of tropical photosymbiotic forms that dominated low- and mid-latitude assemblages long into the Eocene. We hypothesize that this diversification was a result of the reappearance of oligotrophic oceans as the organic flux from the surface ocean to deep water fully recovered from the mass extinction.

Abrupt global warming and profound perturbation of the carbon cycle during the Paleocene-Eocene Thermal Maximum (PETM, ca. 55 Ma) have been linked to a massive release of carbon into the ocean-atmosphere system. Increased phytoplankton productivity has been invoked to cause subsequent CO2 drawdown, cooling, and environmental recovery. However, interpretations of geochemical and biotic data differ on when and where this increased productivity occurred. Here we present high-resolution nannofossil assemblage data from a shelf section (the U.S. Geological Survey [USGS] drill hole at Wilson Lake, New Jersey) and an open-ocean location (Ocean Drilling Program [ODP] Site 1209, paleoequatorial Pacific). These data combined with published biotic records indicate a transient steepening of shelf-offshelf trophic gradients across the PETM onset and peak, with a decrease in open-ocean productivity coeval with increased nutrient availability in shelf areas. Productivity levels recovered in the open ocean during the later stages of the event, which, coupled with intensified continental weathering rates, may have played an important role in carbon sequestration and CO2 drawdown.

Here we report on mid-Oligocene globally synchronous Arctic dinoflagellate migration events, calibrated against chron C9n. We show that sudden appearances and marked abundance increases of the Arctic taxon Svalbardella at lower and middle latitudes coincide with the Oi-2b benthic δ18O glacial episode, dated as ca. 27.1 Ma. These unprecedented migrations are taken to indicate anomalously strong surface-water cooling during Oi-2b time, in turn associated with strong concomitant Antarctic ice-sheet growth and sea-level lowering. We estimate the duration of these unique Svalbardella migrations and the associated episode of profound cooling as 500 k.y. Our records suggest a close link between this distinct Oligocene glaciation episode, strong sea-level fall, and the classic lower-upper Oligocene, or Rupelian-Chattian, boundary, dating this boundary as ca. 27.1 Ma.

Dramatic warming and upheaval of the carbon system at the end of the Paleocene Epoch have been linked to massive dissociation of sedimentary methane hydrate. However, testing the Paleocene-Eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events. The cause of the Paleocene-Eocene thermal maximum carbon isotope excursion remains speculative, primarily due to uncertainties in the timing and duration of the Paleocene-Eocene thermal maximum. We present new high-resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from Ocean Drilling Program Site 690 (Weddell Sea, Southern Ocean), demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface-water warming. Both of these findings support the thermal dissociation of methane hydrate as the cause of the Paleocene-Eocene thermal maximum carbon isotope excursion. Furthermore, the data reveal that the methane-derived carbon was mixed from the surface ocean downward, suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation.

Planktonic foraminiferal oxygen isotope records from the western and eastern tropical Pacific and Atlantic Oceans suggest a southward shift in the Intertropical Convergence Zone toward its modern location between 4.4 and 4.3 Ma. A concomitant shift in the carbon isotope compositions of Atlantic benthic foraminifera provides strong evidence for an increased thermohaline overturn at this time. We suggest that the southward shift of the Intertropical Convergence Zone and associated change in trade-wind circulation altered equatorial surface hydrography, increased the advection of warmer and more saline surface waters into the subtropical and North Atlantic, and contributed to thermohaline overturn.

Two recently drilled Caribbean sites contain expanded sedimentary records of the late Paleocene thermal maximum, a dramatic global warming event that occurred at ca. 55 Ma. The records document significant environmental changes, including deep-water oxygen deficiency and a mass extinction of deep-sea fauna, intertwined with evidence for a major episode of explosive volcanism. We postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the Earth’s environment.

The planktonic foraminiferal generaMorozovellaandAcarininarapidly (in ;10 k.y.) diversified during the late Paleocene thermal maximum (LPTM), giving rise to such morphotypes asM. allisonensis(new species),M. africana, andA. sibaiyaensis. Single-specimen isotopicanalysisconfirmsthatM.allisonensisandA.sibaiyaensisarerestrictedtotheLPTM carbon isotope excursion recorded at Ocean Drilling Program Site 865 (equatorial Pacific Ocean). The short-lived (50 to several 100 k.y.) ‘‘excursion’’ taxa attest to the ephemeral effectsoftheLPTMonthecalcareousplankton.Single-specimenoxygenisotopedatashow that evolution of M. allisonensis and A. sibaiyaensis was accompanied by migration to deeper water depths. AncestralM. velascoensisandA. soldadoensiswere extremely rare or absent during the early stages of the LPTM, but immigrated back into the study area to coexist with their descendants in later LPTM horizons. Photosymbiosis may have facilitatedthemorozovellidandacarininiddiversificationsduringtheoligotrophicconditionsof the LPTM.

Sedimentological and stable isotope data from a pelagic sequence recovered from the southern Indian Ocean provide the most convincing evidence to date for short-term expansion of a large ice sheet on Antarctica during the earliest Oligocene (∼36 Ma). Terrigenous debris identified as ice-rafted in origin on the basis of textural, compositional, and size criteria is present at the same stratigraphic level as the ubiquitous early Oligocene oxygen isotope shift. The highest benthic foraminiferal δ18O values (>3.0‰) of the Paleogene occur in samples from within the ice-rafted debris interval. These values are similar to those recorded by Holocene benthic foraminifera, implying that the ice sheet may have attained a volume similar to that of the present-day ice sheet on Antarctica. The stratigraphic distribution of ice-rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka.

Exposed near Braggs, Alabama, is one of the few well-studied, nearly continuous shallow-marine Cretaceous/Tertiary boundary sections; it allows a glimpse of the biotic and environmental changes that occurred in the latest Cretaceous to earliest Paleocene. Paleomagnetic, strontium isotopic, and biostratigraphic data closely constrain the age of a series of lithologic, geochemical, and biotic variations and suggest that no more than 100–200 ka could be missing at the boundary. A major reduction in macrofaunal diversity associated with lithofacies changes occurs prior to but within 300 ka of the nannofossil-defined boundary. Approximately 40% of the apparent faunal reduction is attributed to the “Lazarus effect.” Faunal and floral assemblages, trends in carbon isotopic composition of benthic invertebrates, and lithologic characteristics indicate that a latest Maestrichtian regression culminated near the boundary (Chron C29R; Micula murus zone), significantly later than recent estimates. Water depths at this site remained shallow during the subsequent early Paleocene (zone NP1) transgression and did not reach depths equivalent to those of the late Maestrichtian until zone NP2. Relatively minor climatic changes across the boundary are suggested by a ≤4 °C cooling trend seen in the oxygen-isotope paleotemperatures. A high-resolution 87 Sr/ 86 Sr record from well-preserved macrofossil calcite shows a pattern of smooth variation and elevated values near the boundary; however, the early Paleocene “spike” of other workers was not found.