Warm and wet conditions in the Arctic region during Eocene Thermal Maximum 2

Several episodes of abrupt and transient warming, each lasting between 50,000 and 200,000 years, punctuated the long-term warming during the Late Palaeocene and Early Eocene (58 to 51 Myr ago) epochs1,2. These hyperthermal events, such as the Eocene Thermal Maximum 2 (EMT2) that took place about 53.5 Myr ago2, are associated with rapid increases in atmospheric CO2 content. However, the impacts of most events are documented only locally86. Here we show, on the basis of estimates from the TEX 86 ′ proxy, that sea surface temperatures rose by 3-5 C in the Arctic Ocean during the EMT2. Dinoflagellate fossils demonstrate a concomitant freshening and eutrophication of surface waters, which resulted in euxinia in the photic zone. The presence of palm pollen implies5 that coldest month mean temperatures over the Arctic land masses were no less than 8 C, in contradiction of model simulations that suggest hyperthermal winter temperatures were below freezing6. In light of our reconstructed temperature and hydrologic trends, we conclude that the temperature and hydrographic responses to abruptly increased atmospheric CO2 concentrations were similar for the ETM2 and the better-described Palaeocene-Eocene Thermal Maximum7,8, 55.5 Myr ago. © 2009 Macmillan Publishers Limited. All rights reserved

Lymphocyte apoptosis in murine <it>Pneumocystis </it>pneumonia

<p>Abstract</p> <p>Background</p> <p>Apoptosis of lymphocytes is important in the termination of an immune response to infection but has also been shown to have detrimental effects in animal models of systemic infection and sepsis. We sought to characterize lymphocyte apoptosis in an animal model of pneumonia due to <it>Pneumocystis murina</it>, an infection localized to the lungs.</p> <p>Methods</p> <p>Control mice and mice depleted of CD4+ lymphocytes were inoculated with <it>Pneumocystis</it>. Apoptosis of lung and spleen lymphocytes was assayed by flow cytometry and PCR assay of apoptotic proteins.</p> <p>Results</p> <p>In control mice, apoptosis of lung lymphocytes was maximal just after the infection was cleared from lung tissue and then declined. However, in CD4-depleted mice, apoptosis was also upregulated in recruited lymphocytes in spite of progressive infection. In splenic lymphocytes, apoptosis was observed early at 1 week after inoculation and then declined. Apoptosis of lung lymphocytes in control mice was associated with a decrease in mRNA for Bcl-2 and an increase in mRNA for Bim. In CD4-depleted mice, lavaged CD8+ cells did change intracellular Bcl-2 but showed increased mRNA for Bim.</p> <p>Conclusion</p> <p>Apoptosis of both pulmonary and extrapulmonary lymphocytes is part of the normal host response to <it>Pneumocystis </it>but is also triggered in CD4-deficient animals with progressive infection. In normal mice apoptosis of pulmonary lymphocytes may serve to terminate the immune response in lung tissue. Apoptosis of lung lymphocytes takes place via both the intrinsic and extrinsic apoptotic pathways and is associated with changes in both pro- and anti-apoptotic proteins.</p

Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

The Palaeocene/Eocene thermal maximum, ~55 million years ago, was a brief period of widespread, extreme climatic warming, that was associated with massive atmospheric greenhouse gas input. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition. We show that sea surface temperatures near the North Pole increased from 18°C to over 23°C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations, but the absolute polar temperatures that we derive before, during and after the event are more than 10°C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms—perhaps polar stratospheric clouds or hurricane-induced ocean mixing – to amplify early Palaeogene polar temperatures