Guy J. Harrington

Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor

A deep sleep in coal beds Deep below the ocean floor, microorganisms from forest soils continue to thrive. Inagaki et al. analyzed the microbial communities in several drill cores off the coast of Japan, some sampling more than 2 km below the seafloor (see the Perspective by Huber). Although cell counts decreased with depth, deep coal beds harbored active communities of methanogenic bacteria. These communities were more similar to those found in forest soils than in other deep marine sediments. Science, this issue p. 420; see also p. 376 Coal beds more than 2 kilometers below the seafloor host methanogenic bacteria related to those found in forest soils. [Also see Perspective by Huber] Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from <10 to ~104 cells cm−3. Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.

Floral response to rapid warming in the earliest Eocene and implications for concurrent faunal change

Abstract During the first 10–20 Kyr of the Eocene temperatures warmed by 4–8°C in middle and high latitudes, then cooled again over the succeeding ∼200 Kyr. Major changes in the composition of marine and terrestrial faunas, including one of the largest mammalian turnover events of the Cenozoic, occurred during this temperature excursion. To better understand the effects of rapid climatic change on continental biotas, we studied 60 fossil pollen samples collected from 900 m of section spanning approximately three million years of the late Paleocene and early Eocene; the samples come from the Fort Union Formation and Willwood Formation in the Bighorn Basin of northwestern Wyoming, paleolatitude approximately 47°N. There are 40 samples from the 500 m of rock deposited during the one million year interval centered on the Paleocene/Eocene boundary, although pollen was not preserved well in rocks representing the short warm interval at the base of the Eocene. Overall, the palynoflora shows moderate change in composition and diversity. Two pollen taxa clearly expanded their ranges to include North America in the first 400 Kyr of the Eocene, Platycarya (Juglandaceae), and Intratriporopollenites instructus (cf. Tilia), but they account for less than 5% of pollen grains in the early Eocene. There are no last appearances of common taxa associated with the Paleocene/Eocene boundary. The most noticeable palynological changes are the decrease in abundance of Caryapollenites spp. and Polyatriopollenites vermontensis (Juglandaceae), and the increase in abundance of Taxodiaceae (bald cypress family), Ulmaceae (elm family), and Betulaceae (birch family), particularly Alnipollenites spp. (alder). There are 22% more species in the Eocene samples than in the Paleocene samples; mean richness of Eocene samples is 17% higher than the mean of Paleocene samples. The mean evenness of Eocene samples is higher than that of Paleocene samples, but the difference is not significant. The modest level of floral change during the late Paleocene and early Eocene contrasts with the major taxonomic turnover and ecological rearrangement of North American mammalian faunas observed at the same time. Faunal change probably resulted from intercontinental range expansion across Arctic land bridges that became habitable as a result of high-latitude warming, so it is surprising that climatically sensitive plants did not also experience a major episode of interchange. The absence of fossil plants from the temperature excursion interval itself could prevent us from recognizing a transient shift in floral composition, but it is clear that the flora did not undergo a major and permanent restructuring like that seen in the mammals. The contrast between the moderate floral response to warming and the strong faunal response is consistent with the idea that interactions between immigrant and native taxa, rather than climate directly, were the primary cause of terrestrial biotic change across the Paleocene/Eocene boundary.

The palynology of the Cerrejón formation (Upper Paleocene) of northern Colombia

Abstract A palynological study of the Cerrejon Formation was conducted in order to date the formation and understand the floristic composition and diversity of a Paleocene tropical site. The Cerrejon Formation outcrops in the Cerrejon Coal Mine, the largest open cast coal mine in the world. Two cores (725 m) were provided by Carbones del Cerrejon LLC for study. Two hundred samples were prepared for palynology, and at least 150 palynomorphs were counted per sample where possible. Several statistical techniques including rarefaction, species accumulation curves, detrended correspondence analysis, and Anosim were used to analyze the floristic composition and diversity of the palynofloras. Palynomorph assemblages indicate that the age of the Cerrejon Formation and the overlying Tabaco Formation is Middle to Late Paleocene (ca. 60–58 Ma). Major structural repetitions were not found in the Cerrejon Formation in the Cerrejon coal mine, and there is little floral variation throughout. The floral composition, diversity, and lithofacies do not change significantly. Lithofacies associations and floral composition indicate deposition fluctuating from an estuarine-influenced coastal plain at the base to a fluvial-influenced coastal plain at the top. There are, however, significant differences in the composition and diversity of coal and siliciclastic samples. Coal palynofloras have fewer morphospecies, and a distinct and more homogeneous floral assemblage compared to assemblages from the intervening sisliciclastic strata, suggesting that tropical swampy environments supported fewer plant species and had a distinct vegetation adapted to permanently wet environments.

Paratropical floral extinction in the Late Palaeocene-Early Eocene

The Palaeocene–Eocene Thermal Maximum (PETM) at c. 55.8 Ma marks a transient (c. 100 ka duration) interval of rapid greenhouse warming that had profound effects on marine and terrestrial biota. Plant communities responded rapidly with major compositional turnover. The long-term effects on tropical vegetation communities that stem from the brief period of global warming are unclear. We present pollen data from the paratropical US Gulf Coast (eastern Mississippi, western Alabama and Georgia), which had background Palaeogene mean annual temperatures of 26–27 °C. Sporomorph data (pollen and spores) demonstrate that taxonomic diversity increases over c. 1 Ma in the Late Palaeocene but this trend is replaced, with the first occurrences of taxa that mark the Early Eocene, by a pronounced extinction into the Early Eocene (c. 20% of the palynoflora). Taxonomic diversity also decreases by up to 38% in the Early Eocene. The timing of the extinction is not clearly resolved but may be restricted to the earliest part of the Early Eocene. Two richness estimators (Chao 2 and Jackknife 2) both demonstrate that Late Palaeocene samples contain significantly more taxa than those in the Early Eocene. Extinction on the US Gulf Coast proves that ancient tropical ecosystems were highly susceptible to changes in diversity mediated directly or indirectly by environmental change even during equable greenhouse climates in the early Palaeogene.

Palynological evidence of vegetation dynamics in response to palaeoenvironmental change across the onset of the Paleocene‐Eocene Thermal Maximum at Cobham, Southern England

A high‐resolution palynological study is undertaken through the Cobham Lignite Bed (Cobham, Kent, UK) to investigate vegetation response to the rapid climate warming at the onset of the Paleocene‐Eocene thermal maximum (PETM). The lower laminated lignite records negative carbon isotope (δ 13C) excursions (CIE) (marking the PETM onset) in bulk organic material, n‐alkanes and, uniquely, also in hopanes. The upper blocky lignite represents an estimated 4–12 kya after PETM onset. Raw and rarefied palynomorph species richness measures are higher in the PETM but the difference is not statistically significant. Only five (of 24) common taxa have last appearance or major shifts in percentage occurrence close to the PETM onset. One of these, a triporate eudicot, occurs only in the maximum negative CIE sample and the immediately underlying sample, the former at very high percentages, an interesting feature of PETM onset. The palynomorph composition of Late Paleocene samples is significantly different from PETM samples. In the late Paleocene there is a close association of high abundances of Cicatricosisporites (Schizaeaceae) fern spores with microscopic and mesoscopic charcoal representing a low diversity fire prone fern and woody angiosperm community. By contrast, the PETM vegetation is characterised by the loss of ferns and cessation of fires, an increase in wetland plants (including cupressaceous conifers) and a more varied flowering plant community with palms and eudicots. These palynofloras thus indicate little response in plant species across the PETM onset but a major change in vegetation composition, linked to a switch in fire regime.

Palaeocene–Eocene paratropical floral change in North America: responses to climate change and plant immigration

The Initial Eocene Thermal Maximum (IETM) at c. 55 Ma represents a period of rapid global warming that lasted less than 200 ka. The response of vegetation to such an event, and particularly warm-adapted highly diverse vegetation types, is poorly understood. Using pollen floral, clay mineral and stable carbon isotope analyses of sediments from the upper Tuscahoma Formation on the eastern US Gulf Coast (eastern Mississippi and western Alabama), we document paratropical floral changes across the Palaeocene–Eocene boundary from the Wahalak #2 and lower Harrell cores. Data indicate strong changes in the abundance of kaolinite that correlate with changes in relative abundance of native pollen taxa. There is no evidence for a transient, extra-tropical flora on the US Gulf Coast that may characterize the IETM. Immigration and extinction are not associated with this event. Instead, Early Eocene plant immigration occurs in pulses and therefore is not associated directly with climate change during the IETM. The two cores share the same regional species pool but compositional differences are stronger between cores than they are either through changes in environment, increased soil erosion or chemical weathering, or through the introduction of non-native plants. Our data suggest that vegetation change across the Palaeocene–Eocene boundary is not a single event but rather a sequence of cascading events.

Floral Change during the Initial Eocene Thermal Maximum in the Powder River Basin, Wyoming

Rapid warming at the beginning of the Eocene (the Initial Eocene Thermal Maximum, or IETM) has been associated with modest changes in floral composition, mostly shifts in the relative abundances of taxa rather than large numbers of first or last appearances. Although floral change across the Paleocene-Eocene transition has been studied in many areas, few fossils demonstrably come from the ∼200 k.y.-long IETM. The rarity of fossils from the IETM permits two end-member hypotheses: (1) IETM floras were similar to, or intermediate in composition between, Paleocene and Eocene floras, or (2) they were distinct from both Paleocene and Eocene assemblages in having a high proportion of taxa that were temporary, thermophilic immigrants. The latter hypothesis is consistent with expectations developed from the study of late Quaternary floras, which demonstrate rapid northward range displacements in the wake of retreating continental glaciers. Here we report lithological, paleontological and isotopic evidence for a Paleocene-Eocene boundary section in the lower Wasatch Formation of the southwestern Powder River Basin, Wyoming. Pollen samples from within the IETM interval do not record immigrants from the south, making it unlikely that there were rapid, continental-scale range displacements during the IETM. Floral response consisted of shifts in the relative abundances of native taxa at the beginning of, or even prior to, the IETM, followed by immigration of taxa from outside of North America, probably Europe, near the end of, or possibly after, the IETM. 425 Wing, S.L., Harrington, G.J., Bowen, G.J., and Koch, P.L., 2003, Floral change during the Initial Eocene Thermal Maximum in the Powder River Basin, Wyoming, in Wing, S.L., Gingerich, P.D., Schmitz, B., and Thomas, E., eds., Causes and Consequences of Globally Warm Climates in the Early Paleogene: Boulder, Colorado, Geological Society of America Special Paper 369, p. 425–440.

Impact of Paleocene/Eocene Greenhouse Warming on North American Paratropical Forests

Abstract The Paleocene/Eocene boundary (c. 55.2 ma) represents transient greenhouse warming of <220 ky duration that had a critical impact upon North American mammals but an apparently limited impact upon subtropical plants. The effect of enhanced warming on biomes already tolerant of paratropical/tropical climate conditions is essentially unknown at the Paleocene/Eocene boundary because most research has centered on high latitude changes in plant turnover. Fossil pollen and spores from the US Gulf Coast allow an assessment of the impact that Paleocene/Eocene climate events had on a Paleo—paratropical/tropical vegetation type. Pollen data from two marginal marine sections either side of the boundary in Alabama, USA, demonstrate secular but subdued changes in composition that are manifest primarily as a restructuring of the vegetation type. Taxa found in the Paleocene remain dominant in the early Eocene (≥89% of taxonomic groups), and both extinction and immigration rates are moderate. Immigrants probably came from at least two different continents, Europe and South America, which implies a highly individualistic response of plant species from different Paleocene biomes to greenhouse warming. Diversity changes are not pronounced across the boundary, but within-sample diversity changes reflect a more heterogeneous, or possibly more successional, early Eocene vegetation type than the late Paleocene. This does not lead to greater between-sample diversity because the Paleocene palynofloras are moderately more diverse, if less heterogeneous at the within-sample level. Results imply that on time-scales of 105 years, Paleocene/Eocene warming is correlative with only minor compositional and diversity changes in paratropical vegetation types.

Terrestrial records of a regional weathering profile at the Paleocene-Eocene boundary in the Williston Basin of North Dakota

The “orange zone” within the Bear Den Member of the Golden Valley Formation (Williston Basin, North Dakota) represents a terrestrial weathering profile formed by intense pedogenesis during an ancient (ca. 55 Ma) global warming event referred to as the Paleocene-Eocene thermal maximum. Distinctive features of the orange zone include: (1) high abundances of kaolinite, (2) a strongly leached character with a bright orange iron-enriched horizon, (3) poor organic carbon preservation, and (4) ferric pans/pisoliths at its basal contact, equivalent to modern lateritic materials. Though conclusive evidence, such as a distinctive Paleocene-Eocene thermal maximum flora and/or definitive carbon isotope excursion, is lacking, the stratigraphic succession of palynofloral datums preserved within the upper part of the Bear Den orange zone is similar to that associated with the later stages of other terrestrial Paleocene-Eocene thermal maximum records from the U.S. Western Interior. Bulk δ 13 C org ratios decrease through the orange zone as well, but the magnitude of this isotopic decrease is less than that of the carbon isotope excursion. Thus, the collective evidence indicates that the early initial stages of the Paleocene-Eocene thermal maximum are either preserved within the barren, condensed interval of the lower orange zone or are missing altogether from the Williston Basin stratigraphy, and that the orange zone likely developed during the later recovery stages of the Paleocene-Eocene thermal maximum. The Williston Basin records generally agree with the tenet that continental weathering intensified during the Paleocene-Eocene thermal maximum. Moreover, these records indicate that the paleohydrology of the basin varied markedly and that sequestration of terrestrial organic carbon was greatly reduced as this transient global warming event unfolded.

Arctic plant diversity in the Early Eocene greenhouse

For the majority of the Early Caenozoic, a remarkable expanse of humid, mesothermal to temperate forests spread across Northern Polar regions that now contain specialized plant and animal communities adapted to life in extreme environments. Little is known on the taxonomic diversity of Arctic floras during greenhouse periods of the Caenozoic. We show for the first time that plant richness in the globally warm Early Eocene (approx. 55–52 Myr) in the Canadian High Arctic (76° N) is comparable with that approximately 3500 km further south at mid-latitudes in the US western interior (44–47° N). Arctic Eocene pollen floras are most comparable in richness with todays forests in the southeastern United States, some 5000 km further south of the Arctic. Nearly half of the Eocene, Arctic plant taxa are endemic and the richness of pollen floras implies significant patchiness to the vegetation type and clear regional richness of angiosperms. The reduced latitudinal diversity gradient in Early Eocene North American plant species demonstrates that extreme photoperiod in the Arctic did not limit taxonomic diversity of plants.