Author
Ellen Thomas
Other affiliations: University of Zaragoza, Scripps Institution of Oceanography, Yale University ...read more
Bio: Ellen Thomas is an academic researcher from Wesleyan University. The author has contributed to research in topics: Benthic zone & Foraminifera. The author has an hindex of 63, co-authored 225 publications receiving 21806 citations. Previous affiliations of Ellen Thomas include University of Zaragoza & Scripps Institution of Oceanography.
Papers published on a yearly basis
Papers
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TL;DR: For example, this article found that the species-richness gradient and increase in abundance of phytodetritus-exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply, especially at high latitudes.
Abstract: From late middle Eocene through earliest Oligocene, high-latitude regions cooled, and by the end of the period, continental ice sheets existed in Antarctica. Diversity of planktonic microorganisms declined, and modern groups of terrestrial vertebrates originated. Coeval faunal changes in deep-sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation. Cooling, however, occurred globally, whereas species richness declined at high latitudes and not in the tropics. The late Eocene and younger lower-diversity, high-latitude faunas typically contain common Epistominella exigua and Alabaminella weddellensis , opportunistic phytodetritus-exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor. We speculate that the species-richness gradient and increase in abundance of phytodetritus-exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply, especially at high latitudes.
232 citations
01 Jan 1998
TL;DR: In this paper, the Late Paleocene Thermal Maximum (LPTM) was used as a time of extinction of species in the benthic foraminiferal extinctions.
Abstract: During the Late Paleocene Thermal Maximum (LPTM) be nthic fbraminif'era at rniddle bathl'al and greater depths suffered extinct ion of 30-507c of species dul ing a lew thousand ycars. Extinct ion was less sevcrc at neri t ic to upper bathyal depths, where temporary changc-s in launal composit ion prevai led. Preextinct ion dcep-sea taunas were cosmopoli tan and diverse. and contained heavi ly calcif ied species. Imrnediate postextinct ion faunas were more variable geographical ly, exhibited low dil 'ersity. and were donrinated by thin-walled calcareous or agslut inated taxa, possibl l , because CaCO, dissolut ion increased global ly l iom nerit ic to abyssal dcpths just bcfbre the extinct ion. Thcse assernbla-ges were dontinatcd either by long-lived taxa sLrch as Nuttttllide.r truerrtpt ' ior by bul irninid taxa. the latter accompanicd by a-uglut inants in somc areas. Faunas donrinated by N. tmentpri rvere contnton in the Sor.rth Atlantic and at lower bathl'al through upper abyssal depth in the lndian Ocean. and might incl icate ol igotrophic condit ions as well as incrcased corrr)si \L-ness. Bul iminid-dominated launas might indicate high rates of deposit ion of organic matter or lor. l-oxygen condit ions. Such l lunas werc common globl l ly along continental rnargins. and locallv co-occun'ed u'ith sedimcntologic or planktonic taunal indicators of high procluct ivi tr . In the bathyal central Pacif ic. however. bul iminid-dominated faunas co-occun'ed with planktonic faunas suggestins ol i-sotl 'ophi ' . and thev could ref lect low-oxygen condit iorrs lesult in-u from sluggish ocean circulat ion. oxidation of cl issociated methanc hydrates. or r larming ol ' bathl 'al i rbyssal waters caused by a chan-ge in deep-sea circr.r lat ion. Alternatively, they could indicate that thc t iact ion ol 'organic matter rcaching the seafl(x)r increased as a rcsult of decreased occanic oxygenf,t ion. 214 Biogeography of the Late Paleocene Benthic Foraminiferal Extinction
231 citations
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TL;DR: An expanded and largely complete upper Paleocene to upper Eocene section was recovered from the pelagic cap overlying Allison Guyot, Mid-Pacific Mountains at Ocean Drilling Program (ODP) Site 865 (18o26'N, 179o33'W; paleodepth 1300-1500 m).
Abstract: An expanded and largely complete upper Paleocene to upper Eocene section was recovered from the pelagic cap overlying Allison Guyot, Mid-Pacific Mountains at Ocean Drilling Program (ODP) Site 865 (18o26'N, 179o33'W; paleodepth 1300-1500 m). Reconstructions show that the site was within a few degrees of the equator during the Paleogene. Because no other Paleogene sections have been recovered in the Pacific Ocean at such a low latitude, Site 865 provides a unique record of equatorial Pacific paleoceanography. Detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa (species of Acarinina, Morozovella, and Subbotina). We studied benthic foraminiferal isotopes at much lower resolution on species of Cibicidoides and Lenticulina, Nuttallides truernpyi and Gavelinella beccariiformis, because of their exceptional rarity. The 5180 and 513C stratigraphies from Site 865 are generally similar to those derived from other Paleocene and Eocene sections. The planktonic foraminiferal records at Site 865, however, include significantly less short-term, single-sample variability than those from higher-latitude sites, indicating that this tropical, oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability. Low-amplitude (0.1-0.8%o) oscillations on timescales of 250,000 to 300,000 years correlate between the/513C records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters. Peak sea surface temperatures of 24o-25oC occurred in the earliest Eocene, followed by a rapid cooling of 3-6oC in the late early Eocene. Temperatures remained cool and stable through the middle Eocene. In the late Eocene, surface water temperatures decreased further. Vertical temperature gradients decreased dramatically in the late Paleocene and were relatively constant through much of the Eocene but increased markedly in the late Eocene. Intermediate waters warmed through the late Paleocene, reaching a maximum temperature of 10oC in the early Eocene. Cooling in the middle and late Eocene paralleled that of surface waters, with latest Eocene temperatures below 5oC. Extinction patterns of benthic foraminifera in the latest Paleocene were similar to those observed at other Pacific sites and were coeval with a short-term, very rapid negative excursion in/513C values in planktonic and benthic taxa as at other sites. During this excursion, benthic foraminiferal/5180 values decreased markedly, indicating warming of 4 to 6oC for tropical intermediate waters, while planktonic taxa show slight warming (1 oC) followed by 2oC of cooling. Convergence of/5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion. These data are consistent with the hypothesis that equatorial Pacific surface waters were a potential source of warm, higher salinity waters which filled portions of the deep ocean in the latest Paleocene. Oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oC at the peak of the excursion, suggesting some fundamental change in global heat transport.
228 citations
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TL;DR: In this paper, the authors studied benthic foraminifera from the last 45 kyr in the >63 mu m size fraction in Biogeochemical Ocean Flux Studies (BOFS) cores at a time resolution of several hundreds to a thousand years.
Abstract: We studied benthic foraminifera from the last 45 kyr in the >63 mu m size fraction in Biogeochemical Ocean Flux Studies (BOFS) cores 5K (50 degrees 41.3'N, 21 degrees 51.9'W, depth 3547 m) and 14K (58 degrees 37.2'N, 19 degrees 26.2'W, depth 1756 m), at a time resolution of several hundreds to a thousand years. The deepest site showed the largest fluctuations in faunal composition, species richness, and benthic foraminiferal accumulation rates; the fluctuations resulted from changes in abundance of Epistominella exigua and Alabaminella weddellensis. In the present oceans, these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor. The ''phytodetritus species'' had very low relative abundances and accumulation rates during the last glacial maximum. A strong increase in absolute and relative abundance of E. exigua and A weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer Neogloboquadrina pachyderma (s), and the increase in abundance of warmer water planktonic species such as Globigerina bulloides. This strong increase in relative abundance of the ''phytodetritus species'' and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor (and thus probably of surface productivity) when the polar front retreated to higher latitudes. The abundance of ''phytodetritus species'' decreased during the Younger Dryas, but not to the low levels of fully glacial conditions. During Heinrich events (periods of excessive melt-water formation and ice rafting) benthic accumulation rates were very low, as were the absolute and relative abundances of the ''phytodetritus species'', supporting suggestions that surface productivity was very low during these events. In both cores Pullenia and Cassidulina species were common during isotope stages 2, 3 and 4, as were bolivinid, buliminid and uvigerinid species. High relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor. In our cores, relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates, and we can thus not interpret them as indicative of increased productivity during glacials. The percentage of these ''low oxygen'' species calculated on a ''phytodetritus species'' - free basis decreased slightly at deglaciation at 5K, but not at 14K. This suggests that decreased production of North Atlantic Deep Water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern North Atlantic at 3547 m depth, but not at 1756 m. In conclusion, major changes in deep-sea benthic foraminiferal faunas over the last 45,000 years in our cores from the northeastern Atlantic were the result of changes in surface water productivity, not of changes in deep water circulation; productivity was lower during the glacial, probably because of extensive ice cover.
212 citations
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01 Jan 2007TL;DR: The Palaeocene-Eocene Thermal Maximum (PETM) is a geologically brief episode of global warming associated with the palaeocene boundary as discussed by the authors. The PETM is characterized by a globally quasi-uniform 5-8 8C warming and large changes in ocean chemistry and biotic response.
Abstract: The Palaeocene–Eocene Thermal Maximum (PETM), a geologically brief episode of global warming associated with the Palaeocene–Eocene boundary, has been studied extensively since its discovery in 1991. The PETM is characterized by a globally quasi-uniform 5–8 8C warming and large changes in ocean chemistry and biotic response. The warming is associated with a negative carbon isotope excursion (CIE), reflecting geologically rapid input of large amounts of isotopically light CO2 and/or CH4 into the exogenic (ocean–atmosphere) carbon pool. The biotic response on land and in the oceans was heterogeneous in nature and severity, including radiations, extinctions and migrations. Recently, several events that appear similar to the PETM in nature, but of smaller magnitude, were identified to have occurred in the late Palaeocene through early Eocene, with their timing possibly modulated by orbital forcing. Although debate continues on the carbon source, the mechanisms that caused the input, the mechanisms of carbon sequestration, and the duration and pacing of the event, the research carried out over the last 15 years has provided new constraints and spawned new research directions that will lead to improved understanding of PETM carbon cycle and climate change. A distinct period of extreme global warmth was initiated close to the boundary between the Palaeocene and Eocene epochs, approximately 55.5 Ma ago (Gradstein et al. 2004). This event, termed the Palaeocene–Eocene Thermal Maximum (PETM), occurred during a time of generally warm, ‘greenhouse’ climate conditions, but stands out against the background warmth as an abrupt and short-lived spike in global temperatures. Evidence for global warming is preserved by the TEX86 0 temperature proxy (Sluijs et al. 2006; Zachos et al. 2006), oxygen isotope (dO) excursions in marine foraminiferal calcite (Fig. 1) (Kennett & Stott 1991; Thomas et al. 2002) and terrestrial carbonates (Koch et al. 1995), increased Mg/Ca values in planktonic and benthic foraminifera (Zachos et al. 2003; Tripati & Elderfield 2005), poleward migrations of (sub)tropical marine plankton (Kelly et al. 1996; Crouch et al. 2001) and terrestrial plant species (Wing et al. 2005), and mammal migrations across high northern latitudes (Bowen et al. 2002, 2006; Smith et al. 2006). Associated with the warming is a negative 2.5–6‰ carbon isotope (dC) excursion (CIE) (Kennett & Stott 1991; Koch et al. 1992; Thomas et al. 2002; Pagani et al. 2006), generally accepted to reflect the geologically rapid injection of C-depleted carbon, in the form of CO2 and/or CH4, into the global exogenic carbon pool (Fig. 1). The apparent conjunction between carbon input and warming has fuelled the hypothesis that increased greenhouse gas concentrations resulted in greenhouse warming during the PETM. The total amount of carbon input during the PETM, which is known to within an order of magnitude (Dickens et al. 1997; Zachos et al. 2005; Pagani et al. 2006), was about 4–8 times the anthropogenic carbon release from the start of the industrial era up From: WILLIAMS, M., HAYWOOD, A. M., GREGORY, F. J. & SCHMIDT, D. N. (eds)Deep-Time Perspectives on Climate Change: Marrying the Signal from Computer Models and Biological Proxies. The Micropalaeontological Society, Special Publications. The Geological Society, London, 323–349. 1747-602X/07/$15.00 # The Micropalaeontological Society 2007. to today (Marland et al. 2005), and comparable to that expected from gross anthropogenic emissions through the end of the 21st century (Intergovernmental Panel on Climate Change 2001). In association with carbon cycle and climatic change, the PETM also stands out as a time of major biotic restructuring. Given the probable ties between releases of near-modern levels of carbon-based greenhouse gases and PETM climatic and biotic change, the PETM has developed as a provocative geological case study in global change, and many of the event’s characteristics and mechanisms are under intensive study. A large volume of research on the PETM has appeared over the past decade (Fig. 2), and in this paper we aim to review and synthesize this material, including the duration and magnitude of carbon cycle perturbation, magnitude of warming, changes in ocean chemistry and marine and terrestrial biotic response. 167
211 citations
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28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。
18,940 citations
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TL;DR: This work focuses primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records.
Abstract: Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.
8,903 citations
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TL;DR: The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research as mentioned in this paper, and both are only imperfect analogs to current conditions.
Abstract: Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO2 conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions.
2,995 citations
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TL;DR: In this article, a new solution for the astronomical computation of the insolation quantities on Earth spanning from −250 m to 250 m was presented, where the most regular components of the orbital solution could still be used over a much longer time span, which is why they provided here the solution over 250 m.
Abstract: We present here a new solution for the astronomical computation of the insolation quantities on Earth spanning from -250 Myr to 250 Myr. This solution has been improved with respect to La93 (Laskar et al. [CITE]) by using a direct integration of the gravitational equations for the orbital motion, and by improving the dissipative contributions, in particular in the evolution of the Earth–Moon System. The orbital solution has been used for the calibration of the Neogene period (Lourens et al. [CITE]), and is expected to be used for age calibrations of paleoclimatic data over 40 to 50 Myr, eventually over the full Palaeogene period (65 Myr) with caution. Beyond this time span, the chaotic evolution of the orbits prevents a precise determination of the Earth's motion. However, the most regular components of the orbital solution could still be used over a much longer time span, which is why we provide here the solution over 250 Myr. Over this time interval, the most striking feature of the obliquity solution, apart from a secular global increase due to tidal dissipation, is a strong decrease of about 0.38 degree in the next few millions of years, due to the crossing of the resonance (Laskar et al. [CITE]). For the calibration of the Mesozoic time scale (about 65 to 250 Myr), we propose to use the term of largest amplitude in the eccentricity, related to , with a fixed frequency of /yr, corresponding to a period of 405 000 yr. The uncertainty of this time scale over 100 Myr should be about , and over the full Mesozoic era.
2,992 citations
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TL;DR: Past episodes of greenhouse warming provide insight into the coupling of climate and the carbon cycle and thus may help to predict the consequences of unabated carbon emissions in the future.
Abstract: Past episodes of greenhouse warming provide insight into the coupling of climate and the carbon cycle and thus may help to predict the consequences of unabated carbon emissions in the future.
2,771 citations