123 research outputs found
Quantitative and Qualitative Effects of Phosphorus on Extracts and Exudates of Sudangrass Roots in Relation to Vesicular-Arbuscular Mycorrhiza Formation
Possible Interruption of Malaria Transmission, Highland Kenya, 2007â2008
Annual insecticide spraying and artemisinin combination therapy may stop transmission
Surface freshening in the Arctic Ocean's Eurasian Basin : an apparent consequence of recent change in the wind-driven circulation
Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C00D03, doi:10.1029/2011JC006975.Data collected by an autonomous ice-based observatory that drifted into the Eurasian Basin between April and November 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008. Sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0.5 m of liquid freshwater to the ocean (comparable to the freshening by melting estimated for those previous years), while the observed change in upper-ocean salinity over the melt period implies a freshwater gain of about 0.7 m. Results of a wind-driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the Eurasian Basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the Beaufort Gyre. This flux is likely associated with a 2009 shift in the large-scale atmospheric circulation to a significant reduction in strength of the anticyclonic Beaufort Gyre and the Transpolar Drift Stream.This work was
funded by the National Science Foundation Office of Polar Programs Arctic
Sciences Section under awards ARCâ0519899, ARCâ0856479, and ARCâ
0806306
Membrane-Mediated Decrease in Root Exudation Responsible for Phorphorus Inhibition of Vesicular-Arbuscular Mycorrhiza Formation
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The Dynamics and Impact of Ocean Acidification and Hypoxia: Insights from Sustained Investigations in the Northern California Current Large Marine Ecosystem
Coastal upwelling ecosystems around the world are defined by wind-generated currents that bring deep, nutrient-rich waters to the surface ocean where they fuel exceptionally productive food webs. These ecosystems are also now understood to share a common vulnerability to ocean acidification and hypoxia (OAH). In the California Current Large Marine Ecosystem (CCLME), reports of marine life die-offs by fishers and resource managers triggered research that led to an understanding of the risks posed by hypoxia. Similarly, unprecedented losses from shellfish hatcheries led to novel insights into the coastal expression of ocean acidification. Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) scientists and other researchers in the CCLME responded to the rise of OAH with new ocean observations and experiments. This work revealed insights into the expression of OAH as coupled environmental stressors, their temporal and spatial variability, and impacts on species, ecological communities, and fisheries. Sustained investigations also deepened the understanding of connections between climate change and the intensification of hypoxia, and are beginning to inform the ecological and eco-evolutionary processes that can structure responses to the progression of ocean acidification and other pathways of global change. Moreover, because the severity of the die-offs and hatchery failures and the subsequent scientific understanding combined to galvanize public attention, these scientific advances have fostered policy advances. Across the CCLME, policymakers are now translating the evolving scientific understanding of OAH into new management actions
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Wind-driven inner-shelf circulation off central Oregon during summer
Velocity measurements from 17 deployments of moored acoustic Doppler current
profilers obtained during four summer upwelling seasons are used to describe the crossshelf
divergence of Ekman transport in the inner shelf off Oregon. For each deployment
the measured surface and bottom cross-shelf transports were compared with estimates
of the theoretical Ekman transports to find the fraction of full theoretical Ekman transport
present. In general, in 15 m of water at 1â2 km offshore, measured transport was 25% of
the full Ekman transport. Measured transports reached full Ekman transport 5â6 km
offshore in 50 m of water. This result indicates that the region of active upwelling marked
by the divergence of Ekman transport was limited to a narrow region along the coast. With
small wind stress curl and no major headlands in the region, no along-shelf trends
in the transport fractions were observed. Average transport fractions at each station were
similar from year to year with one exception. The interannual variability seen at this
particular site was most likely a result of local along-shelf bathymetric features. In
addition, a weak linear relationship was found between the ambient stratification and the
fraction of full Ekman transport. Reduced cross-shelf transport occurred at times of
decreased stratification. This type of ââshutdownââ of the inner-shelf cross-shelf circulation
has significant biological implications, sequestering production in the nearshore and
reducing larval cross-shelf transport
Combined electroejaculation and in vitro fertilization in the evaluation and treatment of anejaculatory infertility
Seven couples underwent combined electroejaculation and in vitro fertilization for anejaculatory infertility after a failed regimen of electroejaculation and intrauterine insemination. Two pregnancies resulted, one proceeding to a term vaginal delivery and one ending in a 6-week spontaneous abortion. Poor sperm binding and no fertilization were seen in two of the couples. Fertilization of the oocytes but no subsequent pregnancy were seen in the other three couples. Combined in vitro fertilization and gamete intrafallopian transfer was performied in four of the couples. The combination of electroejaculation and in vitro fertilization offers the opportunity to evaluate the female pelvis, observe the sperm-oocyte interaction, and achieve a pregnancy in couples with anejaculatory infertility.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44644/1/10815_2005_Article_BF01133886.pd
Intercomparison of snow depth retrievals over Arctic sea ice from radar data acquired by Operation IceBridge
Since 2009, the ultra-wideband snow radar on Operation IceBridge (OIB; a NASA airborne mission to survey the polar ice covers) has acquired data in annual campaigns conducted during the Arctic and Antarctic springs. Progressive improvements in radar hardware and data processing methodologies have led to improved data quality for subsequent retrieval of snow depth. Existing retrieval algorithms differ in the way the airâsnow (aâs) and snowâice (sâi) interfaces are detected and localized in the radar returns and in how the system limitations are addressed (e.g., noise, resolution). In 2014, the Snow Thickness On Sea Ice Working Group (STOSIWG) was formed and tasked with investigating how radar data quality affects snow depth retrievals and how retrievals from the various algorithms differ. The goal is to understand the limitations of the estimates and to produce a well-documented, long-term record that can be used for understanding broader changes in the Arctic climate system. Here, we assess five retrieval algorithms by comparisons with field measurements from two ground-based campaigns, including the BRomine, Ozone, and Mercury EXperiment (BROMEX) at Barrow, Alaska; a field program by Environment and Climate Change Canada at Eureka, Nunavut; and available climatology and snowfall from ERA-Interim reanalysis. The aim is to examine available algorithms and to use the assessment results to inform the development of future approaches. We present results from these assessments and highlight key considerations for the production of a long-term, calibrated geophysical record of springtime snow thickness over Arctic sea ice
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Delayed upwelling alters nearshore coastal ocean ecosystems in the northern California current
Wind-driven coastal ocean upwelling supplies nutrients to the
euphotic zone near the coast. Nutrients fuel the growth of phytoplankton,
the base of a very productive coastal marine ecosystem
[Pauly D, Christensen V (1995) Nature 374:255â257]. Because
nutrient supply and phytoplankton biomass in shelf waters are
highly sensitive to variation in upwelling-driven circulation, shifts
in the timing and strength of upwelling may alter basic nutrient
and carbon fluxes through marine food webs. We show how a
1-month delay in the 2005 spring transition to upwelling-favorable
wind stress in the northern California Current Large Marine Ecosystem
resulted in numerous anomalies: warm water, low nutrient
levels, low primary productivity, and an unprecedented low recruitment
of rocky intertidal organisms. The delay was associated
with 20- to 40-day wind oscillations accompanying a southward
shift of the jet stream. Early in the upwelling season (MayâJuly) off
Oregon, the cumulative upwelling-favorable wind stress was the
lowest in 20 years, nearshore surface waters averaged 2°C warmer
than normal, surf-zone chlorophyll-a and nutrients were 50% and
30% less than normal, respectively, and densities of recruits of
mussels and barnacles were reduced by 83% and 66%, respectively.
Delayed early-season upwelling and stronger late-season
upwelling are consistent with predictions of the influence of global
warming on coastal upwelling regions.Keywords: coastal ocean upwelling, coastal marine ecosystems, marine ecology, climate variabilit
Ice and ocean velocity in the Arctic marginal ice zone: Ice roughness and momentum transfer
The interplay between sea ice concentration, sea ice roughness, ocean stratification, and momentum transfer to the ice and ocean is subject to seasonal and decadal variations that are crucial to understanding the present and future air-ice-ocean system in the Arctic. In this study, continuous observations in the Canada Basin from March through December 2014 were used to investigate spatial differences and temporal changes in under-ice roughness and momentum transfer as the ice cover evolved seasonally. Observations of wind, ice, and ocean properties from four clusters of drifting instrument systems were complemented by direct drill-hole measurements and instrumented overhead flights by NASA operation IceBridge in March, as well as satellite remote sensing imagery about the instrument clusters. Spatially, directly estimated ice-ocean drag coefficients varied by a factor of three with rougher ice associated with smaller multi-year ice floe sizes embedded within the first-year-ice/multi-year-ice conglomerate. Temporal differences in the ice-ocean drag coefficient of 20â30% were observed prior to the mixed layer shoaling in summer and were associated with ice concentrations falling below 100%. The ice-ocean drag coefficient parameterization was found to be invalid in September with low ice concentrations and small ice floe sizes. Maximum momentum transfer to the ice occurred for moderate ice concentrations, and transfer to the ocean for the lowest ice concentrations and shallowest stratification. Wind work and ocean work on the ice were the dominant terms in the kinetic energy budget of the ice throughout the melt season, consistent with free drift conditions. Overall, ice topography, ice concentration, and the shallow summer mixed layer all influenced mixed layer currents and the transfer of momentum within the air-ice-ocean system. The observed changes in momentum transfer show that care must be taken to determine appropriate parameterizations of momentum transfer, and imply that the future Arctic system could become increasingly seasonal
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