Predator-induced life-history shifts in a freshwater snail

The snail Physella virgata virgata, a widely distributed freshwater pulmonate, was observed to change its life-history characteristics in the presence of the crayfish Orconectes virilis in spring-fed Oklahoma streams. These changes were apparently initiated by a water-borne cue released when crayfish fed on conspecific snails. In the presence of the cue, snails exhibited rapid growth rates and little reproduction until they reached a size of about 10 mm after 8 months. In the absence of the cue, snails typically grew to about 4 mm (3.5 months) and then began reproduction. The chemically inducible shift indicates that the life histories of these snails are phenotypically plastic. By increasing the variance associated with size and age of maturity, prey may increase the likelihood of coexisting with seasonal predators.     

Cyclic variation and solar forcing of Holocene climate in the Alaskan subarctic

High-resolution analyses of lake sediment from southwestern Alaska reveal cyclic variations in climate and ecosystems during the Holocene. These variations occurred with periodicities similar to those of solar activity and appear to be coherent with time series of the cosmogenic nuclides 14C and 10Be as well as North Atlantic drift ice. Our results imply that small variations in solar irradiance induced pronounced cyclic changes in northern high-latitude environments. They also provide evidence that centennial-scale shifts in the Holocene climate were similar between the subpolar regions of the North Atlantic and North Pacific, possibly because of Sun-ocean-climate linkages.     

Arctic research in the national interest

The Arctic Research and Policy Act of 1984 was designed to advance arctic research in the national interest. Some of the research fields that require attention are weather and climate; national defense; renewable and nonrenewable resources; transportation; communications and spacedisturbance effects; environmental protection; health, culture, and socioeconomics; and international cooperation. A research framework recommended by the Arctic Research Commission includes, in order of priority, integrated investigations to understand: (i) the Arctic Ocean (including the marginal seas, sea ice, and seabed) and how the ocean and atmosphere operate as coupled components of the arctic system; (ii) the coupled atmosphere and land components and how their interaction governs the terrestrial environment; and (iii) the high-latitude upper atmosphere and its extension into the magnetosphere with emphasis on predicting and mitigating effects on communications and defense systems. A separate recommendation is for high priority research to resolve the major health, behavioral, and cultural problems related to the arctic environment. Recommendations are also made concerning support services and management.     

Oceanographic Phenomena in the Arctic Basin

Roots of decapitated sunflower plants absorbed iron from the ferric chelate of ethylenediamine di(o-hydroxyphenylacetic acid), leaving most of the acid in the nutrient solution. The chelating capacity of the nutrient solution increased as iron was absorbed by the plants. Most of the absorbed iron was found in the plant exudate.     

Glacial/interglacial changes in subarctic north pacific stratification

Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.     

High concentrations of toxaphene in fishes from a subarctic lake

Concentrations of toxaphene and other organochlorine compounds are high in fishes from subarctic Lake Laberge, Yukon Territory, Canada. Nitrogen isotope analyses of food chains and contaminant analyses of biota, water, and dated lake sediments show that the high concentrations of toxaphene in fishes from Laberge resulted entirely from the biomagnification of atmospheric inputs. A combination of low inputs of toxaphene from the atmosphere and transfer through an exceptionally long food chain has resulted in concentrations of toxaphene in fishes that are considered hazardous to human health.     

Molecular analysis of plant migration and refugia in the Arctic

The arctic flora is thought to have originated during the late Tertiary, approximately 3 million years ago. Plant migration routes during colonization of the Arctic are currently unknown, and uncertainty remains over where arctic plants survived Pleistocene glaciations. A phylogenetic analysis of chloroplast DNA variation in the purple saxifrage (Saxifraga oppositifolia) indicates that this plant first occurred in the Arctic in western Beringia before it migrated east and west to achieve a circumpolar distribution. The geographical distribution of chloroplast DNA variation in the species supports the hypothesis that, during Pleistocene glaciations, some plant refugia were located in the Arctic as well as at more southern latitudes.     

Self-organized patchiness and catastrophic shifts in ecosystems

Unexpected sudden catastrophic shifts may occur in ecosystems, with concomitant losses or gains of ecological and economic resources. Such shifts have been theoretically attributed to positive feedback and bistability of ecosystem states. However, verifications and predictive power with respect to catastrophic responses to a changing environment are lacking for spatially extensive ecosystems. This situation impedes management and recovery strategies for such ecosystems. Here, we review recent studies on various ecosystems that link self-organized patchiness to catastrophic shifts between ecosystem states.     

Dynamics of recent climate change in the Arctic

The pattern of recent surface warming observed in the Arctic exhibits both polar amplification and a strong relation with trends in the Arctic Oscillation mode of atmospheric circulation. Paleoclimate analyses indicate that Arctic surface temperatures were higher during the 20th century than during the preceding few centuries and that polar amplification is a common feature of the past. Paleoclimate evidence for Holocene variations in the Arctic Oscillation is mixed. Current understanding of physical mechanisms controlling atmospheric dynamics suggests that anthropogenic influences could have forced the recent trend in the Arctic Oscillation, but simulations with global climate models do not agree. In most simulations, the trend in the Arctic Oscillation is much weaker than observed. In addition, the simulated warming tends to be largest in autumn over the Arctic Ocean, whereas observed warming appears to be largest in winter and spring over the continents.     

Tritium Tracer in Arctic Problems

Tritium measurements in the Arctic Ocean confirm a marked near-surface stratification. Sea water at 400 meters' depth, however, is less than 3 years old, suggesting a contribution to this water mass due to sinking along the continental shelf. The top ice layer on the Ward Hunt Island ice field is older than 25 years.     

Frequent long-distance plant colonization in the changing Arctic

The ability of species to track their ecological niche after climate change is a major source of uncertainty in predicting their future distribution. By analyzing DNA fingerprinting (amplified fragment-length polymorphism) of nine plant species, we show that long-distance colonization of a remote arctic archipelago, Svalbard, has occurred repeatedly and from several source regions. Propagules are likely carried by wind and drifting sea ice. The genetic effect of restricted colonization was strongly correlated with the temperature requirements of the species, indicating that establishment limits distribution more than dispersal. Thus, it may be appropriate to assume unlimited dispersal when predicting long-term range shifts in the Arctic.     

Simulating Arctic climate warmth and icefield retreat in the last interglaciation

In the future, Arctic warming and the melting of polar glaciers will be considerable, but the magnitude of both is uncertain. We used a global climate model, a dynamic ice sheet model, and paleoclimatic data to evaluate Northern Hemisphere high-latitude warming and its impact on Arctic icefields during the Last Interglaciation. Our simulated climate matches paleoclimatic observations of past warming, and the combination of physically based climate and ice-sheet modeling with ice-core constraints indicate that the Greenland Ice Sheet and other circum-Arctic ice fields likely contributed 2.2 to 3.4 meters of sea-level rise during the Last Interglaciation.     

Shallow scattering layer in the subarctic pacific ocean: detection by high-frequency echo sounder

Shallow scattering layers consisting mainly of Calanus cristatus were detected on a trans-Pacific crossing to depths of 60 meters with a high-frequency echo sounder. Biomass estimates of these layers indicate concentrations of zoo-plankton that are greater and more extensive than previously reported in the open ocean.     

Climate change and distribution shifts in marine fishes

We show that the distributions of both exploited and nonexploited North Sea fishes have responded markedly to recent increases in sea temperature, with nearly two-thirds of species shifting in mean latitude or depth or both over 25 years. For species with northerly or southerly range margins in the North Sea, half have shown boundary shifts with warming, and all but one shifted northward. Species with shifting distributions have faster life cycles and smaller body sizes than nonshifting species. Further temperature rises are likely to have profound impacts on commercial fisheries through continued shifts in distribution and alterations in community interactions.     

Resistance shifts accompanying the evoked cortical response in the cat

Clicks and flashes that evoke an electrical response from the auditory or visual cortex also evoke a resistance shift in the tissue. The resistance shift, a drop followed by a rise in resistance, closely follows the temporal pattern of the electrical response recorded simultaneously through the same electrodes. While several experimental manipulations produce corresponding changes in the amplitudes of both electrical response and resistance shift, the resistance shift is more sensitive to alterations in cortical temperature and anesthetic level. The two responses behave distinctly differently as a function of the depth of the electrode in the cortex.