Seasonal Cycle of Phytoplankton Community Composition in the Coastal Upwelling System Off Central Oregon in 2009

Du, Xiuning; Peterson, William T.

doi:10.1007/s12237-013-9679-z

Cited by 40 publications

(31 citation statements)

References 51 publications

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“…Surface water (125ml) for Pseudo-nitzschia (PN) cell counts and phytoplankton community composition was fixed with acid Lugol’s solution (2% final concentration) immediately after collection. The procedures for phytoplankton species identification and enumeration were consistent with previous work [ 30 ]. PN cells were counted as three universally accepted size categories [ 21 ] using a light microscope: the ‘wide group’ species P .…”

Section: Methodsmentioning

confidence: 87%

“…Macronutrient concentrations and ratios of Si:N and N:P in May fell in the normal range compared to their long term records for the upwelling season [ 34 ]. However, despite “normal” nutrient concentrations, some of the diatoms that occur commonly during upwelling, e.g., Chaetoceros and Thalassiosira [ 30 ] were lacking and the phytoplankton community was rather simplified with low species richness. We suggest the unusually low diversity of the phytoplankton community was the result of rapid transition of nutrient concentrations from severe depletion to repletion and upwelling-associated turbulence (dispersal and loss to offshore) during the end of April to early May, conditions that may have favored only a handful of species ( S1 Table ).…”

Section: Discussionmentioning

confidence: 99%

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Initiation and Development of a Toxic and Persistent Pseudo-nitzschia Bloom off the Oregon Coast in Spring/Summer 2015

Peterson

Fisher

et al. 2016

PLoS ONE

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In spring/summer 2015, a toxic bloom by the diatom Pseudo-nitzschia (PN) occurred along the west coast of the United States which led to closures of the harvest of razor clams and Dungeness crabs. Twice monthly observations of temperature, salinity, nutrients, chlorophyll and phytoplankton species composition allowed us to track oceanographic conditions preceding and during the development of the bloom. PN cells were first detected during late winter 2015. A PN bloom was initiated following the onset of coastal upwelling in mid-April; subsequent peaks in May and June were sustained by episodic upwelling events and reached magnitudes of 105 cells/L and 106 cells/L, 40% and 90% of the total diatom abundance, respectively. The bloom temporarily crashed in July due to a lack of upwelling, but PN cells increased again in August due to a resumption of upwelling, albeit with lower magnitude. Macronutrient conditions prior to this bloom likely played a critical role in triggering the bloom and its toxicity (particularly silicic acid limitation stress). Nutrient stress preceding the toxic bloom was related to two oceanographic events: an anomalously warm and thick water mass that occupied the northern North Pacific from September 2014 through 2015 leading to a highly-stratified water column, and the drawdown of nitrate and silicic acid during an unusually intense winter phytoplankton bloom in February and early March 2015.

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Section: Methodsmentioning

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Initiation and Development of a Toxic and Persistent Pseudo-nitzschia Bloom off the Oregon Coast in Spring/Summer 2015

Peterson

Fisher

et al. 2016

PLoS ONE

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“…An optimal window (e.g. 3-10 days) of relaxation or reversal in the wind stress not only affects the primary production rate but also the microbial community composition and the biomass accumulation (Rutllant and Montecino, 2002;Wilkerson et al, 2006;Du and Peterson, 2009), and could even explain the hot N 2 O moments (short periods of disproportionately high rates) observed in this system . In this regard, clear variations in the alongshore wind stress (intensity and direction) were observed between sampling times, considering the 5 days preceding the sampling and the sampling day itself.…”

Section: Environmental Variabilitymentioning

confidence: 98%

Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem

2017

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Abstract. The upwelling system off central Chile (36.5 • S) is seasonally subjected to oxygen (O 2 )-deficient waters, with a strong vertical gradient in O 2 (from oxic to anoxic conditions) that spans a few metres (30-50 m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N 2 and/or N 2 O, were studied using 15 N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. Incubations were developed using water retrieved from the oxycline (25 m depth) and bottom waters (85 m depth) over the continental shelf off Concepción, Chile. Results of 15 N-labelled incubations revealed higher N removal activity during the austral summer, with denitrification as the dominant N 2 -producing pathway, which occurred together with anammox at all times. Interestingly, in both spring and summer maximum potential N removal rates were observed in the oxycline, where a greater availability of oxygen was observed (maximum O 2 fluctuation between 270 and 40 µmol L −1 ) relative to the hypoxic bottom waters (< 20 µmol O 2 L −1 ). Different pathways were responsible for N 2 O produced in the oxycline and bottom waters, with ammonium oxidation and dissimilatory nitrite reduction, respectively, as the main source processes. Ammonium produced by dissimilatory nitrite reduction to ammonium (DNiRA) could sustain both anammox and nitrification rates, including the ammonium utilized for N 2 O production. The temporal and vertical variability of δ 15 N-NO − 3 confirms that multiple N-cycling processes are modulating the isotopic nitrate composition over the shelf off central Chile during spring and summer. N removal processes in this coastal system appear to be related to the availability and distribution of oxygen and particles, which are a source of organic matter and the fuel for the production of other electron donors (i.e. ammonium) and acceptors (i.e. nitrate and nitrite) after its remineralization. These results highlight the links between several pathways involved in N loss. They also establish that different mechanisms supported by alternative N substratesPublished by Copernicus Publications on behalf of the European Geosciences Union. 4796A. Galán et al.: Vertical segregation among pathways mediating nitrogen loss are responsible for substantial accumulation of N 2 O, which are frequently observed as hotspots in the oxycline and bottom waters. Considering the extreme variation in oxygen observed in several coastal upwelling systems, these findings could help to understand the ecological and biogeochemical implications due to global warming where intensification and/or expansion of the oceanic OMZs is projected.

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“…In general, upwellingfavorable winds work with quasi-weekly upwelling pulses, consisting of an alternation in the winds and/or change in wind intensity; with respect to the southern hemisphere, this may vary from southerly and intense (active upwelling) to northern and decreased winds (upwelling relaxation) (Send et al 1987, Rutllant and Montecino 2002). Over a 5-to 10-day time scale this active-relaxing cycle affects both microbial communities and the accumulation of biomass, and primary production rates and microbial community composition (Rutllant and Montecino 2002, Wilkerson et al 2006, Du and Peterson 2009. For example, for effective Chl-a accumulation an optimal window of 3-7 days of relaxed winds was required following an upwelling pulse.…”

Section: N 2 O Exchange Across Air-sea Interfacementioning

confidence: 99%

Presence of nitrous oxide hotspots in the coastal upwelling area off central Chile: an analysis of temporal variability based on ten years of a biogeochemical time series

Farı́as

Besoain

García-Loyola

2015

Environ. Res. Lett.

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Seasonal and inter-annual variabilities of biogeochemical variables, including nitrous oxide (N 2 O), an important climate active gas, were analyzed during monthly observations between 2002 and 2012 at an ocean Time-Series station in the coastal upwelling area off central Chile (36°30.8′; 73°15′).Oxygen, N 2 O, nutrients and chlorophyll-a (Chl-a) showed clear seasonal variability associated with upwelling favorable winds (spring-summer) and also inter-annual variability, which in the case of N 2 O was clearly observed during the occurrence of N 2 O hotspots with saturation levels of up to 4849%. These hotspots consistently took place during the upwelling-favorable periods in 2004, 2006, 2008, 2010 and 2011, below the mixed layer (15-50 m depth) in waters with hypoxia and some − NO 2 accumulation. The N 2 O hotspots displayed excesses of N 2 O (ΔN 2 O) three times higher than the average monthly anomalies (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012). Estimated relationships of ΔN 2 O versus apparent oxygen utilization (AOU), and ΔN 2 O versus − NO , 3 suggest that aerobic ammonium oxidation (AAO) and partial denitrification are the processes responsible for high N 2 O accumulation in subsurface water. Chl-a levels were reasonably correlated with the presence of the N 2 O hotspots, suggesting that microbial activities fuelled by high availability of organic matters lead to high N 2 O production. As a result, this causes a substantial N 2 O efflux into the atmosphere of up to 260 μmol m −2 d −1 . The N 2 O hotspots are transient events or hot moments, which may occur more frequently than they are observed. If so, this upwelling area is producing and emitting greater than expected amounts of N 2 O and is therefore an important N 2 O source that should be considered in the global atmospheric N 2 O balance. OPEN ACCESS RECEIVED

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Seasonal Cycle of Phytoplankton Community Composition in the Coastal Upwelling System Off Central Oregon in 2009

Cited by 40 publications

References 51 publications

Initiation and Development of a Toxic and Persistent Pseudo-nitzschia Bloom off the Oregon Coast in Spring/Summer 2015

Initiation and Development of a Toxic and Persistent Pseudo-nitzschia Bloom off the Oregon Coast in Spring/Summer 2015

Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem

Presence of nitrous oxide hotspots in the coastal upwelling area off central Chile: an analysis of temporal variability based on ten years of a biogeochemical time series

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Seasonal Cycle of Phytoplankton Community Composition in the Coastal Upwelling System Off Central Oregon in 2009

Cited by 40 publications

References 51 publications

Initiation and Development of a Toxic and Persistent Pseudo-nitzschia Bloom off the Oregon Coast in Spring/Summer 2015

Initiation and Development of a Toxic and Persistent Pseudo-nitzschia Bloom off the Oregon Coast in Spring/Summer 2015

Vertical segregation among pathways mediating nitrogen loss (N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O production) across the oxygen gradient in a coastal upwelling ecosystem

Presence of nitrous oxide hotspots in the coastal upwelling area off central Chile: an analysis of temporal variability based on ten years of a biogeochemical time series

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Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem