Swiss needle cast (SNC) is a fungal disease of Douglas-fir (Pseudotsuga menziesii) that has recently become prevalent in coastal areas of the Pacific Northwest. We used growth measurements and stable isotopes of carbon and oxygen in tree-rings of Douglas-fir and a non-susceptible reference species (western hemlock, Tsuga heterophylla) to evaluate their use as proxies for variation in past SNC i...

Swiss needle cast (SNC) is a fungal disease of Douglas-fir (Pseudotsuga menziesii) that has recently become prevalent in coastal areas of the Pacific Northwest. We used growth measurements and stable isotopes of carbon and oxygen in tree-rings of Douglas-fir and a non-susceptible reference species (western hemlock, Tsuga heterophylla) to evaluate their use as proxies for variation in past SNC i...

A 1.5‰ to 2‰ carbon isotope excursion immediately above the clay layer that defines the Cretaceous-Tertiary (K/ T) boundary has been reported in marine sediments world wide. This paper reports a similar 1.5‰ to 2.8‰ carbon isotope excursion recorded by C3 land plants from three temporally-controlled, stratigraphically-constrained terrestrial sections in the Western Interior of North America (Ga...

We conducted experiments to determine isotope changes in the deposit-feeding chironomid larvae Chironomus acerbiphilus during feeding, starvation and metamorphosis. Isotope changes in chironomid larvae occurred mainly during growth and rarely afterward. This finding indicates that chironomid isotope turnover mainly occurs in conjunction with growth and suggests that chironomid larvae only break...

Models describing the evolution of the partial pressure of atmospheric oxygen over Phanerozoic time are constrained by the mass balances required between the inputs and outputs of carbon and sulfur to the oceans. This constraint has limited the applicability of proposed negative feedback mechanisms for maintaining levels of atmospheric O(2) at biologically permissable levels. Here we describe a...

In C4 plants, carbonic anhydrase (CA) facilitates both the chemical and isotopic equilibration of atmospheric CO2 and bicarbonate (HCO3-) in the mesophyll cytoplasm. The CA-catalyzed reaction is essential for C4 photosynthesis, and the model of carbon isotope discrimination (Delta13C) in C4 plants predicts that changes in CA activity will influence Delta13C. However, experimentally, the influen...

Carbon and nitrogen isotope signatures (delta(13)C and delta(15)N) of animal tissues provide information about the diet and, hence, the environment in which the animals are living. Hair is particularly useful as it provides a stable archive of temporal (e.g. seasonal) fluctuations in diet isotope composition. It can be sampled easily and with minimal disturbance from living subjects. However, d...

Stable isotope analysis has become a standard ecological tool for elucidating feeding relationships of organisms and determining food web structure and connectivity. There remain important questions concerning rates at which stable isotope values are incorporated into tissues (turnover rates) and the change in isotope value between a tissue and a food source (discrimination values). These gaps ...

Fossil-wood carbon-isotope data are presented for the Wessex Formation, a non-marine unit within the Lower Cretaceous (Valanginian–Barremian) Wealden Group of the Isle of Wight and Dorset, southern England. The carbon-isotope values have a range ( C c. 26.6 to 19.8‰) that is consistent with that expected for Mesozoic C3 plants. Consideration of the Isle of Wight fossil-wood carbon-isotope data ...

Pattern contrast discrimination is typically studied with simultaneous onset of the base contrast (C) and added contrast (delta C) patterns. I measured contrast discrimination functions at pattern offset. A brief (30 msec) localized, spatially narrow-band D6 test stimulus was delta C. The onset of delta C was simultaneous with the offset of a large, 500 msec cosine pattern (the base contrast C)...