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Global climate change and North American mammalian evolution
- John Alroy, Paul L. Koch, James C. Zachos
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- Journal:
- Paleobiology / Volume 26 / Issue S4 / 2000
- Published online by Cambridge University Press:
- 26 February 2019, pp. 259-288
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We compare refined data sets for Atlantic benthic foraminiferal oxygen isotope ratios and for North American mammalian diversity, faunal turnover, and body mass distributions. Each data set spans the late Paleocene through Pleistocene and has temporal resolution of 1.0 m.y.; the mammal data are restricted to western North America. We use the isotope data to compute five separate time series: oxygen isotope ratios at the midpoint of each 1.0-m.y. bin; changes in these ratios across bins; absolute values of these changes (= isotopic volatility); standard deviations of multiple isotope measurements within each bin; and standard deviations that have been detrended and corrected for serial correlation. For the mammals, we compute 12 different variables: standing diversity at the start of each bin; per-lineage origination and extinction rates; total turnover; net diversification; the absolute value of net diversification (= diversification volatility); change in proportional representation of major orders, as measured by a simple index and by a G-statistic; and the mean, standard deviation, skewness, and kurtosis of body mass. Simple and liberal statistical analyses fail to show any consistent relationship between any two isotope and mammalian time series, other than some unavoidable correlations between a few untransformed, highly autocorrelated time series like the raw isotope and mean body mass curves. Standard methods of detrending and differencing remove these correlations. Some of the major climate shifts indicated by oxygen isotope records do correspond to major ecological and evolutionary transitions in the mammalian biota, but the nature of these correspondences is unpredictable, and several other such transitions occur at times of relatively little global climate change. We conclude that given currently available climate records, we cannot show that the impact of climate change on the broad patterns of mammalian evolution involves linear forcings; instead, we see only the relatively unpredictable effects of a few major events. Over the scale of the whole Cenozoic, intrinsic, biotic factors like logistic diversity dynamics and within-lineage evolutionary trends seem to be far more important.
Millennial-scale variations in western Sierra Nevada precipitation during the last glacial cycle MIS 4/3 transition
- Jessica L. Oster, Isabel P. Montañez, Regina Mertz-Kraus, Warren D. Sharp, Greg M. Stock, Howard J. Spero, John Tinsley, James C. Zachos
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- Journal:
- Quaternary Research / Volume 82 / Issue 1 / July 2014
- Published online by Cambridge University Press:
- 20 January 2017, pp. 236-248
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Dansgaard–Oeschger (D–O) cycles had far-reaching effects on Northern Hemisphere and tropical climate systems during the last glacial period, yet the climatic response to D–O cycles in western North America is controversial, especially prior to 55 ka. We document changes in precipitation along the western slope of the central Sierra Nevada during early Marine Oxygen Isotope Stages (MIS) 3 and 4 (55–67 ka) from a U-series dated speleothem record from McLean's Cave. The timing of our multi-proxy geochemical dataset is coeval with D–O interstadials (15–18) and stadials, including Heinrich Event 6. The McLean's Cave stalagmite indicates warmer and drier conditions during Greenland interstadials (GISs 15–18), signified by elevated δ18O, δ13C, reflectance, and trace element concentrations, and less radiogenic 87Sr/86Sr. Our record extends evidence of a strong linkage between high-latitude warming and reduced precipitation in western North America to early MIS 3 and MIS 4. This record shows that the linkage persists in diverse global climate states, and documents the nature of the climatic response in central California to Heinrich Event 6.
Stable isotopic signals and photosymbiosis in Late Paleocene planktic foraminifera
- Steven D'Hondt, James C. Zachos, Gretchen Schultz
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- Journal:
- Paleobiology / Volume 20 / Issue 3 / Summer 1994
- Published online by Cambridge University Press:
- 08 February 2016, pp. 391-406
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Late Paleocene planktic foraminifera exhibit strong positive correlations between carbon isotopic values and test mass, but negative correlations between oxygen isotopic values and test mass. Based on analogy with modern taxa, these trends are probably ecotypic and may or may not apply to an ontogenetic series. Among Acarinina and Morozovella species, the magnitude and direction of these trends resemble those of modern planktic foraminifera with dinoflagellate photosymbionts. This is consistent with current models of photosymbiosis and calcification in planktic foraminifera and suggests that Acarinina and Morozovella relied heavily on photosymbionts for nutrition.
Acarinina and Morozovella species resemble modern, strongly photosymbiotic taxa in their association with low and mid latitude nearsurface water masses. However, their test morphologies differ greatly from those of extant taxa that bear obligate photosymbionts. Earliest Paleocene taxa that exhibit a similar paleohabitat association and similar size-related isotopic trends are characterized by still different test morphologies. These comparisons suggest that (1) throughout geologic time, strong reliance on photosymbiont activity has been closely linked to habitat, but not to test morphology; (2) photosymbiosis has been a common and convergently evolved strategy of planktic foraminifera over geologic time, and (3) modern relationships between planktic foraminiferal test morphology and photosymbiont dependence are largely an artifact of geologically recent phylogenetic relationships and shared ecologic strategies.
Intersite comparison suggests that the stable isotopic signals of narrowly constrained size fractions of a late Paleocene Acarinina or Morozovella species can be used to reconstruct the magnitude and direction of relative variation in equilibrium stable isotopic values throughout its geographic and temporal range. This is supported by analogy with extant photosymbiotic taxa. However, since photosynthetic depletion of 12C leaves 13C-enriched HCO3-for calcification, the carbon isotopic values of Acarinina and Morozovella tests may have been consistently greater than paleoseawater values. Failure to account for this effect could lead to overestimation of late Paleocene marine productivity.
Cretaceous foraminifera and the evolutionary history of planktic photosymbiosis
- Steven D'Hondt, James C. Zachos
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- Journal:
- Paleobiology / Volume 24 / Issue 4 / Fall 1998
- Published online by Cambridge University Press:
- 08 February 2016, pp. 512-523
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Ecotypic correlations between stable isotopic signals and skeletal size indicate that some Late Cretaceous serial planktic foraminifera were strongly photosymbiotic. In contrast, coeval trochospiral planktic foraminifera do not exhibit the isotope/size signatures that typify strongly photosymbiotic species. Comparison to Cenozoic taxa demonstrates that photosymbiosis has recurred throughout planktic foraminiferal history and has evolved independently in superfamilies characterized by very different gross skeletal morphologies. The historical contingency of that evolution is illustrated by the consequences of the Cretaceous/Paleogene mass extinction, which terminated the Cretaceous lineages of photosymbiotic planktic foraminifera but did not permanently extinguish photosymbiont reliance by planktic foraminifera.
3 - Comparison of zonal temperature profiles for past warm time periods
- from Part 1 - Approaches to the study of paleoclimates
- Edited by Brian T. Huber, Smithsonian Institution, Washington DC, Kenneth G. Macleod, University of Missouri, Columbia, Scott L. Wing, Smithsonian Institution, Washington DC
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- Book:
- Warm Climates in Earth History
- Published online:
- 06 July 2010
- Print publication:
- 02 December 1999, pp 50-76
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Summary
ABSTRACT
A standard explanation for past warm time periods involves higher atmospheric CO2 levels. However, model simulations indicate that the zonal temperature response to a CO2 perturbation is significantly different from observations in the geologic record: model-predicted temperatures are higher in low latitudes and lower in high latitudes than revealed by observations. Although changes in ocean heat transport have been invoked to account for such discrepancies, it is also necessary to subject zonal temperature profiles, particularly tropical sea surface temperature (SST) estimates, to error analysis in order to test for robustness of conclusions. Herein we conduct such an analysis and demonstrate that it is difficult to generalize about the tropical SST pattern in low latitudes during warm periods. Three time periods (Pliocene, Eocene, Cenomanian) indicate tropical SSTs not significantly different from the present, while two time periods (Miocene and Maastrichtian) suggest cooler tropical SSTs. Diagenesis may be responsible for some of the cooler tropical temperature estimates. Analysis of uncertainties in δ O-based paleotemperature estimates suggests that random non-dissolution-related uncertainties are in the order of 2–3 °C for individual specimens. However, averaging of Holocene core top samples yields zonal mean temperature estimates in the tropics that agree with observations to within 0.5–1.0 °C. Although there is a potential for pre-Pleistocene uncertainties of 2–4 °C in tropical SSTs (due to diagenesis and salinity/alkalinity changes from CO2 variations), careful screening of samples should produce a smaller non-random uncertainty of +1.5 to –3.0 °C for the zonal average from multiple sites.
5 - Deep-sea environments on a warm earth: latest Paleocene-early Eocene
- from Part II - Case studies: latest Paleocene–early Eocene
- Edited by Brian T. Huber, Smithsonian Institution, Washington DC, Kenneth G. Macleod, University of Missouri, Columbia, Scott L. Wing, Smithsonian Institution, Washington DC
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- Book:
- Warm Climates in Earth History
- Published online:
- 06 July 2010
- Print publication:
- 02 December 1999, pp 132-160
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Summary
ABSTRACT
Latest Paleocene–early Eocene high-latitude surface and global deep-ocean waters were warmer than those of today by up to 15 °C; planktonic foraminiferal and nannofossil assemblages suggest that primary oceanic productivity was low. Low oceanic productivity is also indicated by geochemical evidence that the supply of nutrients to the oceans may have been low. Climate modeling suggests that oceanic and atmospheric circulation may have been sluggish at low temperature gradients, leading to low rates of upwelling of nutrients. Benthic foraminiferal data, by contrast, suggest that the food supply to the deep sea floor in open-ocean settings was larger than that in Recent oceans, in agreement with the speculation that a larger fraction of organic carbon was buried. The benthic foraminiferal evidence might be explained by more efficient food transfer to the bottom in poorly oxygenated, warm deep waters. Possibly the pelagic microbial loop was more active at the higher temperatures, leading to enhanced zooplankton productivity and thus enhanced food supply. Or possibly the benthic faunas do not indicate a high average food supply, but a more continuous and less seasonally pulsed supply than that today. Environmental interpretation of early Eocene benthic foraminiferal faunas is difficult not only because they differ substantially from Recent ones but also because the faunas had been decimated by a massive extinction during an episode of rapid warming, the Late Paleocene Thermal Maximum (LPTM), with a duration of between 25 and 200000 ka.
Isotopic evidence for paleoclimatic and paleoatmospheric variations from the Paleogene Bighorn Basin sequence
- Paul L. Koch, David L. Dettman, James C. Zachos
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- Journal:
- The Paleontological Society Special Publications / Volume 6 / 1992
- Published online by Cambridge University Press:
- 26 July 2017, p. 170
- Print publication:
- 1992
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Land mammal faunas changed dramatically from the late Paleocene to the Eocene. This interval was marked by substantial paleoceanographic changes, including marine warming, and mass extinction of benthic foraminifera. Yet study of the impact of marine events on continental climates and faunas is problematic, due to imprecision in marine/continental correlation.
Oxygen isotope measurements of paleosol carbonates, mammals, and bivalves from the Paleogene Bighorn Basin can be used to estimate mean annual temperature (MAT). The δ18O of paleosol carbonate is controlled by two factors: the δ18O of the groundwater from which it crystallizes, and the temperature during crystallization. Because mammals and bivalves secrete mineral in a biologically-restricted range of temperatures, their isotopic compositions serve as proxy indicators of surface water δ18O. The difference in δ18O between these proxy indicators of water and paleosol carbonate is used to calculate MAT through application of standard oxygen isotope thermometry relationships. Calculated temperatures vary significantly throughout the interval, with high values (>20°) in the late Paleocene, lower values in the earliest Eocene (10–20°), and renewed warmth later in the Early Eocene.
In modern temperate regions, MAT and the δ18O of precipitation are closely correlated. Estimates for Paleocene/Eocene surface waters from tooth apatite and bivalves range from −8 to −12± (SMOW). Today, precipitation with values this low is usually found in cold regions (0–10°). These temperature estimates are too low in light of other isotopic and paleobotanical indicators, which suggest very warm temperatures in the Bighorn Basin during the Paleogene. We hypothesize that vapor transport to the region was substantially different than at present. A potential model may be Amazonia, where wet season air masses lose up to 80% of their water vapor as they move across the basin, resulting in 18O-depleted rainfall despite a warm climate.
Variations in δ13C provide a tool for marine/continental correlation. Carbon in tooth apatite and soil carbonate is derived from plants, which fix atmospheric CO2. Atmospheric CO2 is, in turn, in isotopic equilibrium with marine carbonate. Because of these links, marine carbonate, land plants, land mammals, and soil carbonate should exhibit coupled carbon isotope variations. In the Paleogene, when C3 plants dominated floras, isotopic variations due to shifting floral composition, such as those documented in the Miocene Siwalik Sequence, could not occur. Paleogene continental and marine carbon isotope records are tightly coupled. In particular, there is an unusual marine carbon isotope excursion immediately preceding the Paleocene/Eocene boundary, which corresponds precisely to the major paleoceanographic changes and the extinction of benthic foraminifera. Tooth apatite and soil carbonate from the Paleogene Bighorn Basin also record this excursion, which occurs at the base of the Wasatchian, where perrisodactyls, artiodactyls, and modern primates first appear. Carbon isotopes allow tight marine/continental correlation of the Paleocene/Eocene boundary, and demonstrate that major biologic and climatic events at this time were globally synchronous.