411 research outputs found
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Uses and Misuses of the Journal Impact Factor
The second in a series of articles published in OSU This Week by members of the Faculty Senate Library Committee regarding threats to an open and sustainable system of scholarly communication and potential solutions. Article describes what journal impact factors are and how they are determined and makes recommendations for their proper use.Keywords: Scholarly publishing, Scholarly communication, Journal impact factorsKeywords: Scholarly publishing, Scholarly communication, Journal impact factor
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Introduction to special section : Coastal Advances in Shelf Transport
The Coastal Ocean Advances in Shelf Transport (COAST) program conducted an
interdisciplinary study of coastal upwelling off central Oregon during summer 2001.
Two intensive field efforts during May–June and August 2001 were coordinated with
ocean circulation, ecosystem, and atmospheric modeling of the region. A primary
goal was to contrast the coastal ocean response to wind forcing in a region of relatively
simple alongshore bottom topography versus that associated with a substantial submarine
bank. In this overview we provide background motivation for the COAST project
and summarize the major research findings
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Seasonal and across-shelf trends of the phytoplankton community of the Oregon coastal environment
This project, part of the Northeast Pacific GLOBEC Long Term Observation Project (NEPGLOBEC-
LTOP), constitutes the first multi-year study of phytoplankton variability in the Oregon coastal
environment. The work divides into two studies: analysis of interseasonal change and analysis of detailed
changes within the summer upwelling period. In the first study, I found that the majority of variability in
phytoplankton biomass in this system is due to changes in the abundance of chain forming diatoms,
particularly diatoms of the genera Chaetoceros and Skeletonema. The abundance of nanoflagellates (<10
μm) remains constant across the shelf. They dominate the phytoplankton community in the offshore
stations and larger cells, usually diatoms, are added inshore. Cyanobacteria, though numerically
abundant, never comprise more than approximately 10% of phytoplankton biomass.
Variation within the summer phytoplankton bloom over the shelf was analyzed based on results
from the four NEP-GLOBEC-LTOP summer cruises between August 1998 and July 2001. Nutrient
concentrations during the summer upwelling blooms show a linear decrease with increasing temperature
from 8 to 12° C. Over this range of temperatures, total Chl a and phytoplankton biomass increase, though
not significantly, and the % Chl a >10 μm remains high (>50 %). Above 12° C, when inorganic nutrients
are depleted or greatly reduced, total Chl a and % Chl a >10 μm decrease. The diatom genera
Chaetoceros and Skeletonema are also responsible for the majority of the variability in phytoplankton
stock during the summer phytoplankton bloom. Dinoflagellates, although present, are consistently less
abundant than diatoms
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Ammonium uptake and regeneration rates in a coastal upwelling regime
Ammonium uptake and regeneration rates were measured in time course experiments with 15N as a tracer. Both ammonium uptake and regeneration rates measured over 12 to 18 h remained essentially constant. However, as the length of the incubations increased the amount of usable data decreased dramatically due to substrate depletion and recycling of 15N. Mass balance calculations indicated that 22 to 51 % of the ammonium removed from the dissolved pool was not recovered in the particulate fraction. This appeared to be a more serious problem at 0 and 8 m (47%) than at 25 m (22%). As a result, ammonium uptake rates were probably underestimated. At 0, 12, and 20 m uptake rates either balanced or exceeded regeneration rates, while at 8 and 25 m net regeneration occurred. The fastest rates were measured during upwelling-induced phytoplankton blooms, intermediate rates characterized post-bloom conditions and the lowest rates coincided with an active upwelling event. Ammonium uptake rates were highest during the upwelling season (11 to 17 mmol N m-2 d-1) and lowest during the non-upwelling season (3 mmol N m-2 d-1), whereas regeneration rates did not differ significantly between seasons (11 to 20 mmol N m-2 d-1 ).Keywords: Ammonium uptake, Coastal upwelling, Ammonium regeneratio
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Production and partitioning of organic matter during simulated phytoplankton blooms
Few studies have examined the partitioning of organic matter in upwelling systems, despite the fact that these systems play a key role in carbon and nitrogen budgets in the ocean. We examined the production and partitioning of phytoplankton-derived organic matter in deck incubations off Oregon during the upwelling season. During exponential growth of the phytoplankton, ≥78% of total accumulated organic matter was in particulate (POM) form. This suggests that dissolved organic matter (DOM) is a small fraction of primary production during the exponential growth of coastal phytoplankton blooms. After nitrate depletion, carbon-rich (C:N ≥ 16) DOM accumulated in incubations dominated by the diatom Chaetoceros sp., accounting for 38% (±8.5%) of accumulated total organic carbon (TOC) and 24% (±8%) of accumulated total organic nitrogen (TON). However, in a bloom dominated by the diatom Leptocylindrus minimus, a relatively smaller amount of DOM accumulated, accounting for only 15% of accumulated TOC and 7% of accumulated TON. On the basis of measured concentrations of nitrate and accumulated TOC, ~70%–157% more carbon was fixed than would be predicted by Redfield stoichiometry (referred to as "excess carbon fixation"), with 20%–69% of the excess carbon fixation occurring after nitrate depletion. The accumulation of carbon-rich DOM and excess carbon fixation suggests that nitrate assimilation (i.e., new production) might not equate to net production of POM in coastal upwelling systems
Two coastal upwelling domains in the northern California Current system
A pair of hydrographic sections, one north and one south of Cape Blanco at 42.9N, was sampled in five summers (1998–2000 and 2002–2003). The NH line at 44.6N lies about 130 km south of the Columbia River, and spans a relatively wide shelf off Newport, Oregon. The CR line at 41.9N off Crescent City, California, lies 300 km farther south and spans a narrower shelf. Summer winds are predominantly southward in both locations but the southward winds are stronger on the CR line. Sampling included CTD/rosette casts (to measure temperature, salinity, dissolved oxygen, nutrients, chlorophyll), zooplankton net tows and continuous operation of an Acoustic Doppler Current Profiler. We summarize and compare July-August observations from the two locations. We find significant summer-season differences in the coastal upwelling domains north and south of Cape Blanco. Compared to the domain off Newport, the domain off Crescent City has a more saline, cooler, denser and thicker surface mixed layer, a wider coastal zone inshore of the upwelling front and jet, higher nutrient concentrations in the photic zone and higher phytoplankton biomass. The southward coastal jet lies near the coast (about 20–30 km offshore, over the shelf) on the NH line, but far from shore (about 120 km) on the CR line; a weak secondary jet lies near the shelf-break (35 km from shore) off Crescent City. Phytoplankton tend to be light-limited on the CR line and nutrient-limited on the NH line. Copepod biomass is high (15 mg C m−3) inshore of the mid-shelf on both NH and CR lines, and is also high in the core of the coastal jet off Crescent City. The CR line shows evidence of deep chlorophyll pockets that have been subducted from the surface layer. We attribute these significant differences to stronger mean southward wind stress over the southern domain, to strong small-scale wind stress curl in the lee of Cape Blanco, and to the reduced influence of the Columbia River discharge in this region
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Cold halocline, increased nutrients and higher chlorophyll off Oregon in 2002
Observed changes in the nutrient levels in the halocline of the California Current during 2002 indicated a natural eutrophication that was accompanied by increased chlorophyll and oxygen in surface water. Decreased oxygen in the lower water column over the shelf indicated that much of the phytoplankton production was respired rather than passed on to higher trophic levels. In 2002 the halocline water was >1ºC colder than usual and 0.5ºC colder than any previous observation. Four transect lines off the coast of Oregon show a 50% increase in nitrate, phosphate and silicate at 33 psu in 2002 compared to 1998–2001. The increase in nutrients resulted in a 2-fold increase in chlorophyll standing stocks during the summer of 2002 compared with the preceding four years. A significant portion of the increased production was subsequently respired resulting in low oxygen water over the shelf
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Assessment of macroalgal nitrogen limitation in a seasonal upwelling region
The relationship between nitrogen (N) availability and the growth of macroalgae in a seasonal upwelling region (Yaquina Head, Oregon, USA) was investigated. Water column nutrient concentrations were relatively high and stable during the winter, decreased in early spring, and were highly variable in the summer and early fall. Periods of high nutrient availability due to upwelling commenced in May and alternated with periods of low nutrient availability until September. Dissolved inorganic nitrogen (DIN) concentration was a poor predictor of N limitation of macroalgal growth due to the ability of macroalgae to store N for continued growth when ambient DIN concentrations were low. The relationship between growth and internal N content for Pelvetiopsis limitata (Phaeophyta:Fucaceae) and Ulva rigida (Chlorophyta:Ulvales) depended on the N source and culture conditions. Results of an in situ N enrichment experiment indicated that P. limitata growth may have been N-limited in April and May. A nitrogen budget for P. limitata indicated that NH+4 was the major N source for growth at Yaquina Head, due to its rapid uptake, despite the greater abundance of NO-3. The critical N value (tissue N level during the transition from N limiting to non-N limiting conditions) for growth of U. rigida on NO-3 (≤2.4 % dry wt) was much lower than that for growth on NH+4 (3.0 % dry wt). Ammonium was the major N source for growth of U. rigida at Yaquina Head, and growth was probably N-limited in April and May, as indicated by the critical N level for growth on NH: Growth of U. rigida may also have been intermittently N-limited between upwelling events. Problems with the use of critical N levels and nutrient monitoring to assess N limitation are discussed. Use of critical tissue N levels is complicated by variations in this parameter with the N source used for growth
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