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Photosynthesis and respiration occur widely on Earth's surface, and the [sup.18]O/[sup.16]O ratio of the oxygen produced and consumed varies with climatic conditions. As a consequence, the history of climate is reflected in the deviation of the [sup.18]O/[sup.16]O of air ([[delta].sup.18] [O.sub.atm]) from seawater [[delta].sup.18]O (known as the Dole effect). We report variations in [[delta].sup.18] [O.sub.atm] over the past 60,000 years related to Heinrich and Dansgaard-Oeschger events, two modes of abrupt climate change observed during the last ice age. Correlations with cave records support the hypothesis that the Dole effect is primarily governed by the strength of the Asian and North African monsoons and confirm that widespread changes in tow-latitude terrestrial rainfall accompanied abrupt climate change. The rapid [[delta].sup.18][O.sub.atm] changes can also be used to synchronize ice records by providing global time markers.

Relatively brief periods of severe paleoenvironmental change during the Jurassic and Cretaceous were associated with the widespread accumulation of organic-rich marine deposits, termed oceanic anoxic events (OAEs). These intervals involved abrupt global warming of ~5-10 [degrees]C, higher rates of continental weathering, elevated extinction rates, and large-scale perturbations to the global carbon cycle. The major OAEs also overlapped temporally the emplacement of large igneous provinces. However, despite being known as OAEs, the extent of seawater anoxia at those times is undefined and the causative processes remain unclear. Here we show how changes in seawater molybdenum isotope ratios (a proxy for seawater anoxia) during the Toarcian (Early Jurassic) OAE define the onset and expansion of oxygen deficient conditions. Our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically, broadly in line with precession-driven changes in [[delta].sup.13][C.sub.org]. Despite their intermittent occurrence over geological history, OAEs have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day. Keywords: Toarcian, Jurassic, molybdenum, oceanic anoxic event, carbon cycle.

Cells exposed to low oxygen concentrations respond by initiating defense mechanisms, including the stabilization of hypoxia-inducible factor (HIF) 1α, a transcription factor that upregulates genes such as those involved in glycolysis and angiogenesis. Nitric oxide and other inhibitors of mitochondrial respiration prevent the stabilization of HIF1α during hypoxia. In studies of cultured cells, we show that this effect is a result of an increase in prolyl hydroxylase--dependent degradation of HIF1α. With the use of Renilla luciferase to detect intracellular oxygen concentrations, we also demonstrate that, upon inhibition of mitochondrial respiration in hypoxia, oxygen is redistributed toward nonrespiratory oxygen-dependent targets such as prolyl hydroxylases so that they do not register hypoxia. Thus, the signaling consequences of hypoxia may be profoundly modified by nitric oxide., HIF plays a major role in the response of tissues to low partial pressures of [O.sub.2] (1). The protein stability of the α subunit (HIF1α) of this heterodimeric transcription factor [...]

Aroma compounds (acetoin and diacetyl) are produced by Lactococcus lactis subsp. lactis biovar diacetylactis CNRZ 483 in fresh unripened cheese at different initial oxygen concentrations (0, 21, 50 and 100% of the medium saturation by oxygen). These compounds are produced in maximum number only after all the citrate is consumed. The quantity of diacetyl and acetoin produced by L. lactis increases in the presence of oxygen.