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The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.

Migration is an integral feature of modern mysticete whale ecology, and the demands of migration may have played a key role in shaping mysticete evolutionary history. Constraining when migration became established and assessing how it has changed through time may yield valuable insight into the evolution of mysticete whales and the oceans in which they lived. However, there are currently few data which directly assess prehistoric mysticete migrations. Here we show that calcite δ18O profiles of two species of modern whale barnacles (coronulids) accurately reflect the known migration routes of their host whales. We then analyze well-preserved fossil coronulids from three different locations along the eastern Pacific coast, finding that δ18O profiles from these fossils exhibit trends and ranges similar to modern specimens. Our results demonstrate that migration is an ancient behavior within the humpback and gray whale lineages and that multiple Pleistocene populations were undertaking migrations of an extent similar to those of the present day.

Geologically abrupt carbon perturbations such as the Palaeocene-Eocene Thermal Maximum (PETM, approx. 56 Ma) are the closest geological points of comparison to current anthropogenic carbon emissions. Associated with the rapid carbon release during this event are profound environmental changes in the oceans including warming, deoxygenation and acidification. To evaluate the global extent of surface ocean acidification during the PETM, we present a compilation of new and published surface ocean carbonate chemistry and pH reconstructions from various palaeoceanographic settings. We use boron to calcium ratios (B/Ca) and boron isotopes (δ11B) in surface- and thermocline-dwelling planktonic foraminifera to reconstruct ocean carbonate chemistry and pH. Our records exhibit a B/Ca reduction of 30-40% and a δ11B decline of 1.0-1.2‰ coeval with the carbon isotope excursion. The tight coupling between boron proxies and carbon isotope records is consistent with the interpretation that oceanic absorption of the carbon released at the onset of the PETM resulted in widespread surface ocean acidification. The remarkable similarity among records from different ocean regions suggests that the degree of ocean carbonate change was globally near uniform. We attribute the global extent of surface ocean acidification to elevated atmospheric carbon dioxide levels during the main phase of the PETM.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.

Geologically abrupt carbon perturbations such as the Palaeocene-Eocene Thermal Maximum (PETM, approx. 56 Ma) are the closest geological points of comparison to current anthropogenic carbon emissions. Associated with the rapid carbon release during this event are profound environmental changes in the oceans including warming, deoxygenation and acidification. To evaluate the global extent of surface ocean acidification during the PETM, we present a compilation of new and published surface ocean carbonate chemistry and pH reconstructions from various palaeoceanographic settings. We use boron to calcium ratios (B/Ca) and boron isotopes (δ11B) in surface- and thermocline-dwelling planktonic foraminifera to reconstruct ocean carbonate chemistry and pH. Our records exhibit a B/Ca reduction of 30-40% and a δ11B decline of 1.0-1.2‰ coeval with the carbon isotope excursion. The tight coupling between boron proxies and carbon isotope records is consistent with the interpretation that oceanic absorption of the carbon released at the onset of the PETM resulted in widespread surface ocean acidification. The remarkable similarity among records from different ocean regions suggests that the degree of ocean carbonate change was globally near uniform. We attribute the global extent of surface ocean acidification to elevated atmospheric carbon dioxide levels during the main phase of the PETM.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.

As the research interests and the focus of traditional earth scientists are transformed, so too must education in earth system science at colleges and universities across the country change. The required change involves not only the methods used to teach this new science, but also the essential place of the earth sciences in the panoply of disciplines as traditionally ordered by academic colleagues. With growing public and political awareness of the significant environmental problems facing the earth in the coming decades, and the realization that issues such as global warming require action on the part of individuals as well as governments, earth system science must establish its place in college curricula to ensure that a new generation of citizens and scientists is prepared to meet future challenges. In this article, the authors posit that strong research in earth system science and equally strong investments in both teaching the earth sciences and training a new generation of earth system scientists are not optional but essential.

Author(s): Katrin J. Meissner (corresponding author) [1]; Timothy J. Bralower (corresponding author) [2] On page 573, Gutjahr et al . [1] report a fundamental breakthrough in our understanding of a [...]

Lithified marine sediments are not equitably distributed through time, raising the possibility that lithification masks biological signals when data from unlithified and lithified sediments are compared or combined. Using mollusk-dominated assemblages from the early Cenozoic of the Gulf Coastal Plain, we find that lithification conceals small taxa, decreases taxonomic resolution, and exacerbates the undersampling of rare taxa. Lithified assemblages appear less diverse and have less even abundance distributions than coeval unlithified samples. These limitations cannot be overcome by standardization procedures, nor are they likely to be circumvented by collecting larger samples. The effects of this bias, however, can be mitigated by restricting analyses to a single lithification state or to specific size classes. Since lithification selectively obscures small taxa, the magnitude of this bias will be most severe when organisms are particularly small, such as in the aftermath of mass extinctions. In the study area, lithification artificially protracts the recovery period following the Cretaceons-Paleogene mass extinction by ~7 m.y.

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 C[O.sub.2] 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 openocean 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 C[O.sub.2] drawdown. Keywords: plankton, Paleocene, Eocene, paleoproductivity.

The Paleocene-Eocene Thermal Maximum (PETM) has been attributed to a rapid rise in greenhouse gas levels. If so, warming should have occurred at all latitudes, although amplified toward the poles, Existing records reveal an increase in high-latitude sea surface temperatures (SSTs) (8° to 10°C) and in bottom water temperatures (4° to 5°C. To date, however, the character of the tropical SST response during this event remains unconstrained. Here we address this deficiency by using paired oxygen isotope and minor element (magnesium/calcium) ratios of planktonic foraminifera from a tropical Pacific core to estimate changes in SST. Using mixed-layer foraminifera, we found that the combined proxies imply a 4° to 5°C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pC[O.sub.2] to levels three to four times as high as those estimated for the late Paleocene., The Paleocene-Eocene Thermal Maximum [55 million years ago (Ma)] was accompanied by a number of environmental perturbations, including mass extinction of benthic foraminifera (1), widespread appearance and proliferation of exotic [...]

The strontium isotope ratios ([sup.87]SF/[sup.86]Sr) of marine barite microcrystals separated from Cretaceous sedimentary deposits from Ocean Drilling Program and Deep Sea Drilling Project sites from the Pacific and Indian Oceans have been compared to the composite Sr isotope curve of McArthur et al. The barite in these cores accurately recorded the seawater [sup.87]Sr/[sup.86]Sr ratio, thereby reaffirming the composite Cretaceous strontium curve. Moreover, marine barite is a more reliable recorder of [sup.87]Sr/[sup.86]Sr than is carbonate in sedimentary deposits with high clay content, thereby providing an opportunity for Sr isotope stratigraphy and dating in carbonate-poor or diagenetically altered sections. We have used the barite-derived Sr isotope record to refine the biostratigraphic age models of the sites investigated. Keywords: barite, strontium isotopes, stratigraphy, Cretaceous.

How Much will global temperatures rise over the next century? How fast will ice sheets on Antarctica and Greenland melt and raise global sea level? Will rising temperature and acidification [...]

A distinctive mixture of reworked microfossils, impact-derived materials, and lithic fragments occurs in sediments at the Cretaceous-Tertiary boundary in the basinal Gulf of Mexico and Caribbean. We have named this mixture the Cretaceous-Tertiary boundary 'cocktail.' Lithologic and paleontologic evidence suggests that the cocktail was deposited by giant sediment gravity flows, apparently triggered by the collapse of continental margins around the Gulf of Mexico as a result of the Chicxulub impact. As most microfossils in the gravity-flow units are reworked, biostratigraphy provides only maximum ages. Recognition of the cocktail is a reliable way to identify Cretaceous-Tertiary boundary deposits in the basinal Gulf of Mexico and Caribbean.

This report is a documentation of data and certain ideas presented in:1) Bralower, T. J. and Thierstein, H. R., 1987. Organic carbon and metal accumulation in Holocene and mid-Cretaceous marine sediments : paleoceanographic significance. IN: Brooks, J. and Fleet, A. (eds.) Marine Petroleum Source Rocks , Special Publication of the Geological Society of London v. 24, p. 377-398. Blackwell, London.2) Bralower, T. J., and Thierstein, H. R., 1984. Low productivity and slow deep-water circulation in mid-Cretaceous oceans. Geology 12:614—618.Recent advances in dating techniques, bio-, chrono- and magneto-stratigraphic, have had important implications to our understanding of sedimentary processes. Accurate estimates of the duration of geologic time-slices have allowed the calculation of sedimentation and also accumulation rates. The accumulation rate of a sedimentary component is the rate at which it is removed from the oceanic system into the sedimentary reservoir. Comparisons of sedimentary accumulation rates of particular components with estimates of their oceanic input rates have greatly improved our knowledge of the overall budgets of these elements in the present day ocean.We have integrated and interpreted a large body of Holocene accumulation rate data, and compared it to the accumulation rates of similar components in certain Mid-Cretaceous intervals. Some of this data has been obtained from the literature. Numerous analyses have been made as a part of this study and the techniques and results are presented herein. This report also documents and extends certain aspects of our interpretation of organic carbon and transition metal accumulation.

The planktonic foraminiferal genera Morozovella and Acarinina rapidly (in [approximately]10 k.y.) diversified during the late Paleocene thermal maximum (LPTM), giving rise to such morphotypes as M. allisonensis (new species), M. africana, and A. sibaiyaensis. Single-specimen isotopic analysis confirms that M. allisonensis and A. sibaiyaensis are restricted to the LPTM 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 effects of the LPTM on the calcareous plankton. Single-specimen oxygen isotope data show that evolution of M. allisonensis and A. sibaiyaensis was accompanied by migration to deeper water depths. Ancestral M. velascoensis and A. soldadoensis were 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 facilitated the morozovellid and acarininid diversifications during the oligotrophic conditions of the LPTM.

We report on the effect of the end-Cretaceous impact event on the present-day deep microbial biosphere at the impact site. IODP-ICDP Expedition 364 drilled into the peak ring of the Chicxulub crater, México, allowing us to investigate the microbial communities within this structure. Increased cell biomass was found in the impact suevite, which was deposited within the first few hours of the Cenozoic, demonstrating that the impact produced a new lithological horizon that caused a long-term improvement in deep subsurface colonization potential. In the biologically impoverished granitic rocks, we observed increased cell abundances at impact-induced geological interfaces, that can be attributed to the nutritionally diverse substrates and/or elevated fluid flow. 16S rRNA gene amplicon sequencing revealed taxonomically distinct microbial communities in each crater lithology. These observations show that the impact caused geological deformation that continues to shape the deep subsurface biosphere at Chicxulub in the present day. [ABSTRACT FROM AUTHOR]