University of Maine

About: University of Maine is a education organization based out in Orono, Maine, United States. It is known for research contribution in the topics: Population & Ice sheet. The organization has 8637 authors who have published 16932 publications receiving 590124 citations. The organization is also known as: University of Maine at Orono.

Thermal acclimation induces adaptive changes in subcellular structure of fish skeletal muscle.

Abstract: Stereological analyses of electron micrographs were used to quantify physiologically important ultrastructures of slow-twitch oxidative (red) and fast-twitch glycolytic (white) muscle fibers from striped bass (Morone saxatilis) acclimated to 25 and 5 degrees C. The fraction of cell volume occupied by the mitochondria [volume density, Vv (mit,f)] of red fibers increases from 0.286 +/- 0.018 to 0.448 +/- 0.024 between 25 and 5 degrees C; Vv (mit,f) of white fibers increased from 0.027 +/- 0.003 and 0.040 +/- 0.004 at 25 and 5 degrees C, respectively. Because of a concomitant increase in the mass of oxidative muscle, acclimation from 25 to 5 degrees C results in an increase in total mitochondrial volume per 100 g body wt from 2.58 to 6.73 cm3 in oxidative muscle and from 2.46 to 3.40 cm3 in fast glycolytic muscle. Mitochondria of red fibers are in more clustered arrays after cold acclimation. Size and cristae surface densities of individual mitochondria are not affected markedly by acclimation, suggesting true cold-induced proliferation rather than enlargement of organelles. Harmonic means of intermitochondrial spacing in red fibers decreases from 2.64 to 1.43 micron between 25 and 5 degrees C. This reduces diffusion path lengths between sarcoplasmic and mitochondrial compartments proportionately, compensating for decreases in diffusivity of aqueous solutes. Intracellular lipid droplets of red fibers markedly increase in volume density from 0.006 +/- 0.003 at 25 degrees C to 0.079 +/- 0.014 at 5 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Subsurface maxima of phytoplankton and chlorophyll: Steady-state solutions from a simple model

Abstract: In oligotrophic lakes and oceans, the deep chlorophyll maximum may form independently of a maximum of phytoplankton biomass, because the ratio of chlorophyll to phytoplankton biomass (in units of carbon) increases with acclimation to reduced light and increased nutrient supply at depth. Optical data (beam attenuation as proxy for phytoplankton biomass and chlorophyll fluorescence and absorption as proxies for chlorophyll concentration) and conventional measurements of biovolume, particulate organic carbon, and chlorophyll from two oligotrophic systems (Crater Lake, Oregon, and Sta. ALOHA in the subtropical North Pacific Ocean) are presented and show a vertical separation of the maxima of biomass and chlorophyll by 50‐80 m during stratified conditions. We use a simple mathematical framework to describe the vertical structure of phytoplankton biomass, nutrients, and chlorophyll and to explore what processes contribute to the generation of vertical maxima. Consistent with the observations, the model suggests that biomass and chlorophyll maxima in stable environments are generated by fundamentally different mechanisms. Maxima in phytoplankton biomass occur where the growth rate is balanced by losses (respiration and grazing) and the divergence in sinking velocity, whereas the vertical distribution of chlorophyll is strongly determined by photoacclimation. A deep chlorophyll maximum is predicted well below the particle maximum by the model. As an interpretation of these results, we suggest a quantitative criterion for the observed coexistence of vertically distinct phytoplankton assemblages in oligotrophic systems: the vertical position at which a species occurs in highest abundance in the water column is determined by the ‘‘general compensation depth’’— that is, the depth at which specific growth and all loss rates, including the divergence of sinking/swimming and vertical mixing, balance. This prediction can be tested in the environment when the divergence of sinking and swimming is negligible.

Regional estimates of the export flux of particulate organic carbon derived from thorium-234 during the JGOFS EqPac program

Abstract: The upper ocean 234Th activity distribution at 77 stations was measured between 12°N and 10°S, and 95°W and 170°W in the spring and autumn of 1992. A regional scavenging model was used to estimate vertical export of particulate 234Th. Given the relatively high upwelling rates in this region, particularly at equatorial latitudes near 140°W, it was necessary to include upwelling of 234Th in our model in order to quantify particulate export. Using this export flux and the measured organic C or N to 234Th ratio on particles, one can empirically determine POC and PON fluxes for this region. The estimated particulate organic C flux varies spatially and temporally within this region, ranging from 1 to 7 mmol C m−2 day−1, with enhanced export occurring over the equator. Fluxes are also enhanced along 95°W coincident with a low temperature/high nutrient peak at 4°S. Along 140°W, particulate organic C export from the upper 100 m is on the order of 2 mmol C m−2 day−1 at latitudes beyond 4°N and 4°S, with an equatorial peak of 3–5 mmol C m−2 day−1 in both spring and fall. These results suggest that a relatively small per cent of the total production is exported locally on sinking particles (particle export/primary production C 234 Th ratios. Given the measured C N ratio, particulate N fluxes from the upper 100 m would be 6 times lower than for POC.

The Amundsen Sea Low: Variability, Change, and Impact on Antarctic Climate

Abstract: The Amundsen Sea Low (ASL) is a climatological low pressure center that exerts considerable influence on the climate of West Antarctica. Its potential to explain important recent changes in Antarctic climate, for example in temperature and sea ice extent, means that it has become the focus of an increasing number of studies. Here, we summarize current understanding of the ASL, using reanalysis datasets to analyze recent variability and trends, and ice-core chemistry and climate model projections to examine past and future changes in the ASL, respectively. The ASL has deepened in recent decades, affecting the climate through its influence on the regional meridional wind field, which controls the advection of moisture and heat into the continent. Deepening of the ASL in spring is consistent with observed West Antarctic warming and greater sea ice extent in the Ross Sea. Climate model simulations for recent decades indicate that this deepening is mediated by tropical variability while climate model projections through the 21st century suggest that the ASL will deepen in some seasons in response to greenhouse gas concentration increases.