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Ellen Thomas

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
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Book ChapterDOI
Ellen Thomas1
01 Jan 2007
TL;DR: In this article, the extinction of deep-sea benthic foraminifera was linked to a global feature of the end-Paleocene environmental change, i.e., rapid global warming.
Abstract: Deep-sea benthic foraminifera live in the largest habitat on Earth, constitute an important part of its benthic biomass, and form diverse assemblages with common cosmopolitan species. Modern deep-sea benthic foraminiferal assemblages are strongly infl uenced by events affecting their main food source, phytoplankton (a relationship known as bentho-pelagic coupling). Surprisingly, benthic foraminifera did not suffer signifi cant extinction at the end of the Cretaceous, when phytoplankton communities underwent severe extinction. Possibly, bentho-pelagic coupling was less strong than today in the warm oceans of the Cretaceous‐Paleogene, because of differences in the process of food transfer from surface to bottom, or because more food was produced chemosynthetically on the seafl oor. Alternatively, after the end-Cretaceous extinction the food supply from the photic zone recovered in less time than previously thought. In contrast, deep-sea benthic foraminifera did undergo severe extinction (30%‐50% of species) at the end of the Paleocene, when planktic organisms show rapid evolutionary turnover, but no major extinction. Causes of this benthic extinction are not clear: net extinction rates were similar globally, but there is no independent evidence for global anoxia or dysoxia, nor of globally consistent increase or decrease in productivity or carbonate dissolution. The extinction might be linked to a global feature of the end-Paleocene environmental change, i.e., rapid global warming. Cenozoic deep-sea benthic faunas show gradual faunal turnover during periods of pronounced cooling and increase in polar ice volume: the late Eocene‐early Oligocene, the middle Miocene, and the middle Pleistocene. During the latter turnover, taxa that decreased in abundance during the earlier two turnovers became extinct, possibly because of increased oxygenation of the oceans, or because of increased seasonality in food delivery. The Eocene-Oligocene was the most extensive of these turnovers, and benthopelagic coupling may have become established at that time.

252 citations

Journal ArticleDOI
TL;DR: In this paper, the authors review 30 years of accumulated data, interpretation and speculation about the Antarctic Circumpolar Current (ACC), deriving mainly from DSDP and ODP drilling in the Southern Ocean and conclude that the presence of a siliceous biofacies cannot be claimed as evidence of the existence of a continuous, deep-reaching oceanic front and therefore of an ACC.

249 citations

01 Jan 1990
TL;DR: In this article, the authors show that the extinction of deep-sea benthic foraminifers in the latest Paleocene may have been caused by a change in formational processes of the deep to intermediate waters of the oceans.
Abstract: Upper abyssal to lower bathyal benthic foraminifers from ODP Sites 689 (present water depth 2080 m) and 690 (present water depth 2941 m) on Maud Rise (eastern Weddell Sea, Antarctica) are reliable indicators of Maestrichtian through Neogene changes in the deep-water characteristics at high southern latitudes. Benthic foraminiferal faunas were divided into eight assemblages, with periods of faunal change at the early/late Maestrichtian boundary (69 Ma), at the early/late Paleocene boundary (62 Ma), in the latest Paleocene (57.5 Ma), in the middle early Eocene to late early Eo­ cene (55-52 Ma), in the middle middle Eocene (46 Ma), in the late Eocene (38.5 Ma), and in the middle-late Miocene (14.9-11.5 Ma). These periods of faunal change may have occurred worldwide at the same time, although specific first and last appearances of deep-sea benthic foraminifers are commonly diachronous. There were minor faunal changes at the Cretaceous/Tertiary boundary (less than 14°7o of the species had last appearances at Site 689, less than 9% at Site 690). The most abrupt benthic foraminiferal faunal event occurred in the latest Paleocene, when the diversity dropped by 50% (more than 35% of species had last appearances) over a period of less than 25,000 years; after the extinction the diversity remained low for about 350,000 years. The highest diversities of the post-Paleocene occurred during the middle Eocene; from that time on the diversity de­ creased steadily at both sites. Data on faunal composition (percentage of infaunal versus epifaunal species) suggest that the waters bathing Maud Rise were well ventilated during the Maestrichtian through early Paleocene as well as during the latest Eocene through Recent. The waters appeared to be less well ventilated during the late Paleocene as well as the late middle through early late Eocene, with the least degree of ventilation during the latest Paleocene through early Eo­ cene. The globally recognized extinction of deep-sea benthic foraminifers in the latest Paleocene may have been caused by a change in formational processes of the deep to intermediate waters of the oceans: from formation of deep waters by sinking at high latitudes to formation of deep to intermediate water of the oceans by evaporation at low latitudes. Benthic foraminiferal data (supported by carbon and oxygen isotopic data) suggest that there was a short period of in­ tense formation of warm, salty deep water at the end of the Paleocene (with a duration of about 0.35 m.y.), and that less intense, even shorter episodes might have occurred during the late Paleocene and early Eocene. The faunal record from the Maud Rise sites agrees with published faunal and isotopic records, suggesting cooling of deep to intermediate waters in the middle through late Eocene.

243 citations

Journal ArticleDOI
31 Aug 2017-Nature
TL;DR: Boron isotope data are presented that show that the ocean surface pH was persistently low during the PETM, and enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system.
Abstract: The Palaeocene–Eocene Thermal Maximum1,2 (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates3. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming1,3,4,5. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data—a proxy for seawater pH—that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event6,7. We find strong evidence for a much larger (more than 10,000 petagrams)—and, on average, isotopically heavier—carbon source than considered previously8,9. This leads us to identify volcanism associated with the North Atlantic Igneous Province10,11, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system12.

237 citations


Cited by
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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

Journal ArticleDOI
27 Apr 2001-Science
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

Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
17 Jan 2008-Nature
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