107 research outputs found
Recommended from our members
Role of Trichodesmium spp. in the productivity of the subtropical North Pacific Ocean
The concentrations of filamentous diazotroph Trichodesmium spp., present as free trichomes and in colonial assemblages, were measured at approximately monthly intervals at Stn ALOHA (22°45'N, 158°00'W) between October 1989 and December 1992. The average abundance of filaments in the upper 45 m of the water column was highly variable ranging from 1.1 to 7.4 X 10⎠trichomes mâŸÂł and from 0.02 to 1.4 X 10ÂČ colonies mâŸÂł. Colonies were composed, on average, of 182 filaments accounting for 12% of total (free filament plus colonies) Trichodesmium biomass. Low densities of single trichomes were associated with, but not restricted to, deep mixing events and winter periods. During 1991 and 1992 the concentration of Trichodesmium spp. present in the water column increased relative to the pre 1991 observations. This increase coincided with increases in photosynthetic carbon assimilation and in the molar ratio of N:P of suspended particulate matter in the upper 45 m of the water column. However, the change in Trichodesmium biomass alone does not account for the change observed in autotrophic carbon assimilation and elemental biomass composition Trichodesmium spp. comprised, on average, 18% of the chlorophyll a, 4% of the photosynthetic carbon assimilation, 10% of the particulate nitrogen and 5% of the particulate phosphorus. We also estimate that Trichodesmium dinitrogen fixation accounted for, on average, at least 27%, of the new production at this study site. These observations, combined with primary production experiments conducted on isolated colonies, suggest that phytoplankton production is enhanced due to the release of NHââș and dissolved organic nitrogen by Trichodesmium spp. during episodes of nitrogen fixation.Article appears in Marine Ecology Progress Series and is copyrighted by Inter Research.Keywords: Nutrients, Productivity, Trichodesmium, Nitrogen fixation, Time-serie
Recommended from our members
Parameterizing the natural fluorescence kinetics of Thalassiosira weissflogii
We examined variability in the natural fluorescence yield of a neritic diatom, Thalassiosira weissflogii, in continuous cultures. In this species, kinetics in natural fluorescence yield over time scales less than a photoperiod were characterized by sharp decreases, occurring at irradiance intensities that presumably coincide with the onset of nonphotochemical fluorescence quenching by interconvertible xanthophylls. The irradiance at which these decreases occurred, and the concomitant degree of quenching involved, varied systematically in these cultures as a function of dilution rate and irradiance intensity, independent of biomass. Similar diurnal kinetics in natural fluorescence yield were observed in phytoplankton assemblages in a coastal transition region in the Gulf of Alaska. An empirical parameterization was developed to quantify these diurnal kinetics in terms of the magnitude of this increased quenching and the irradiance at which it occurred, in order to track the behavior of these kinetics over longer time scales of days to weeks
Recommended from our members
Physiological Response of Crocosphaera watsonii to Enhanced and Fluctuating Carbon Dioxide Conditions
We investigated the effects of elevated pCOâ on cultures of the unicellular Nâ-fixing cyanobacterium Crocosphaera watsonii
WH8501. Using COâ-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions
approximating current atmospheric COâ concentrations (~400 ppm) as well as COâ levels corresponding to low- and high-end
predictions for the year 2100 (~750 and 1000 ppm). Following acclimation to COâ levels, the concentrations of
particulate carbon (PC), particulate nitrogen (PN), and cells were measured over the diurnal cycle for a six-day period
spanning exponential and early stationary growth phases. High rates of photosynthesis and respiration resulted in
biologically induced pCOâ fluctuations in all treatments. Despite this observed pCOâ variability, and consistent with previous
experiments conducted under stable pCOâ conditions, we observed that elevated mean pCOâ enhanced rates of PC
production, PN production, and growth. During exponential growth phase, rates of PC and PN production increased by
~1.2- and ~1.5-fold in the mid- and high-COâ treatments, respectively, when compared to the low-COâ treatment. Elevated
pCOâ also enhanced PC and PN production rates during early stationary growth phase. In all treatments, PC and PN cellular
content displayed a strong diurnal rhythm, with particulate C:N molar ratios reaching a high of 22:1 in the light and a low of
5.5:1 in the dark. The pCOâ enhancement of metabolic rates persisted despite pCOâ variability, suggesting a consistent
positive response of Crocosphaera to elevated and fluctuating pCOâ conditions
Recommended from our members
Flexible elemental stoichiometry in Trichodesmium spp. and its ecological implications
We conducted laboratory experiments to assess the bioelemental plasticity of cultures of Trichodesmium
IMS101 under phosphorus (P)-replete, P-restricted, and light-limited conditions. The results reveal a high degree
of stoichiometric flexibility. Specifically, Trichodesmium IMS101 is capable of growth with carbon (C) : nitrogen
(N) : P ratios of Câ
ââ
屉
â : Nââ±ââ : Pâ, approximately six times higher than would be predicted by the Redfield
reference ratio (Câââ : Nââ : Pâ), thus signifying low cellular P quotas relative to C and N. Luxury consumption of
P occurs rapidly after periods of prolonged P restriction, under both light and dark conditions, resulting in
substantial increases in P quotas and reductions of C : N : P ratios (Cââ±â : Nââ±â : Pâ). Comparisons of
laboratory culture data to our field observations from the Northwest Atlantic and the North Pacific indicate that,
while natural populations of Trichodesmium exhibit persistently low P content relative to C and N
(Câââ±ââ
: N â
â±â : Pâ), the highest and lowest C : P and N : P ratios recorded in the laboratory are rarely
observed in nature. We have also performed laboratory experiments intended to simulate the energetic and
nutritional extremes that would occur as naturally migrating populations of Trichodesmium sink out of the
euphotic zone into P-rich regions of the upper disphotic zone. The duration of dark survival for this isolate is on
the order of 3â6 d, after which time cells are unable to recover from light deprivation. This finding provides
a constraint on the temporal scale of vertical migration.Individual authors are also free to post PDF copies of their work published in ASLO journals on their individual or institutional websites. It is not necessary to request permission from ASLO so long as such postings are not used for commercial purposes
Recommended from our members
Autonomous observations of in vivo fluorescence and particle backscattering in an oceanic oxygen minimum zone
The eastern South Pacific (ESP) oxygen minimum zone (OMZ) is a permanent hydrographic feature located directly off the coasts of northern Chile and Peru. The ESP OMZ reaches from coastal waters out to thousands of kilometers offshore, and can extend from the near surface to depths greater than 700 m. Oxygen minimum zones support unique microbial assemblages and play an important role in marine elemental cycles. We present results from two autonomous profiling floats that provide nine months of time-series data on temperature, salinity, dissolved oxygen, chlorophyll a, and particulate backscattering in the ESP OMZ. We observed consistently elevated backscattering signals within low-oxygen waters, which appear to be the result of enhanced microbial biomass in the OMZ intermediate waters. We also observed secondary chlorophyll a fluorescence maxima within low-oxygen waters when the upper limit of the OMZ penetrated the base of the photic zone. We suggest that autonomous profiling floats are useful tools for monitoring physical dynamics of OMZs and the microbial response to perturbations in these areas.This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/home.cfm. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law
Recommended from our members
Light driven seasonal patterns of chlorophyll and nitrate in the lower euphotic zone of the North Pacific Subtropical Gyre
The euphotic zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long-term oligotrophic habitat assessment; 22Âș45âČN, 158Âș00âČW) transects the nearly permanently stratified upper thermocline. Hence, seasonal changes in solar radiation control the balance between photosynthesis and respiration in this lightlimited region. Combining profiles of radiance reflectance, algal pigments, and inorganic nutrients collected between January 1998 and December 2000, we explore the relationships between photosynthetically available radiation (PAR), phytoplankton biomass (chlorophyll a), and the position of the upper nitracline in the lower euphotic zone. Seasonal variations in the water-column PAR attenuation coefficient displace the 1% sea-surface PAR depth from approximately 105 m in winter to 121 m in summer. However, the seasonal depth displacement of isolumes (constant daily integrated photon flux strata) increases to 31 m due to the added effect of changes in sea-surface PAR. This variation induces a significant deepening of the DCML during summertime with a concomitant increase in chlorophyll a and the removal of 36 mmol m22 inorganic nitrogen [NOâ3 NOâ2] in the 90â200-m depth range, equivalent to approximately 34% of the annual flux of particulate nitrogen collected in sediment traps placed at 150 m. We conclude that in this oceanic region the annual light cycle at the base of the euphotic zone induces an increase in the phototrophic biomass analogous to a spring bloom event
Recommended from our members
Jet stream intraseasonal oscillations drive dominant ecosystem variations in Oregonâs summertime coastal upwelling system
Summertime wind stress along the coast of the northwestern United States typically exhibits intraseasonal oscillations (ISOs) with periods from â15 to 40 days, as well as fluctuations on the 2- to 6-day âweather-bandâ and 1-day diurnal time scales. Coastal upwelling of cool, nutrient-rich water is driven by extended periods of equatorward alongshore winds, and we show that the â20-day ISOs in alongshore wind stress dominated the upwelling process during summer 2001 off Oregon. These wind stress ISOs resulted from northâsouth positional ISOs of the atmospheric jet stream (JS). Upper-ocean temperature, phytoplankton, and zooplankton varied principally on the â20-day time scale as well, and these correlated with the ISOs in alongshore wind stress and JS position, even though there also were weather-band stress fluctuations of comparable magnitude. Such wind stress ISOs are typical along Oregon in the summer upwelling season, occurring in 10 of 12 years examined, including 2001. We present a previously unreported direct connection from the atmospheric JS to oceanic primary and secondary production on the intraseasonal time scale and show the leading importance of ISOs in driving this coastal upwelling ecosystem during a typical summer.Keywords: coastal variability, coastal marine ecosystems, marine ecology, wind-driven ocean upwellin
Recommended from our members
Summer surface waters in the Gulf of California: Prime habitat for biological Nâ fixation
We report significant rates of dinitrogen (Nâ) fixation in the central basins of the Gulf
of California (GC) during JulyâAugust 2005. Mixing model estimates based upon
ÎŽÂčâ”N values of particulate matter in the surface mixed layer indicate that Nâ fixation
provides as much as 35% to 48% of the phytoplankton-based nitrogen demand in the
central Guaymas and Carmen basins. Microscopic analyses identify the responsible
genera as the Nâ-fixing endosymbiont, Richelia intracellularis, with lesser contributions
from the large nonheterocystous diazotroph Trichodesmium. Analyses of remotely sensed
chlorophyll a and sea surface temperature indicate that primary production levels are
elevated in regions of the GC where oceanographic conditions are ideal in summertime
for the growth of Nâ-fixing organisms. These findings suggest that biological Nâ fixation
must be taken into account when assessing past and present nitrogen dynamics in this
environmentally important region.Keywords: nitrogen fixation, Gulf of California, remote sensin
Recommended from our members
Using lasers to probe the transient light absorption by proteorhodopsin in marine bacterioplankton
We constructed an experimental apparatus that used lasers to provide the probe beams for measuring the transient absorption kinetics of bacterioplankton that contain proteorhodopsin, a microbial protein that binds retinal and is analogous to animal rhodopsin. With this approach we were able to observe photocycles characteristic of functioning retinylidene ion pumps. Using light from lasers instead of broadband sources as transmittance probe beams can be advantageous when examining optically dense, highly scattering samples such as concentrated microbial cultures. Such a laser-based approach may prove useful in shipboard studies for identifying proteorhodopsin in whole cell suspensions concentrated from seawater.This paper was published in Applied Optics and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/ao/home.cfm. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law
Recommended from our members
Analysis of a Method to Estimate Chlorophyll-a Concentration from Irradiance Measurements at Varying Depths
A model to estimate chlorophyll-a concentration and yellow substance absorption at 440 nm from irradiance measurements made at varying depths is examined. The derivation of the model, requiring irradiance measurements at three wavebands, is presented and tested on data collected in oligotrophic (with low chlorophyll concentrations) waters and in coastal waters (with both high and low chlorophyll concentrations). The results indicate excellent quantitative agreement with chlorophyll-a concentration and yellow substance absorption measurements. A sensitivity analysis of the model shows it to be highly sensitive to pressure sensor precision, the accuracy of the value used for the mean cosine of the downwelling radiance distribution, and the irradiance sensor measurement error. However, provided that these factors are taken into account, accurate estimates of chlorophyll-a concentrations in case I (phytoplankton-dominated) waters using a single (or multiple) irradiance sensor with three wavebands can be derived. This model can be applied to irradiance data from a variety of deployment methods including profilers, bottom-tethered moorings, subsurface drifters, and towed platforms
- âŠ