Automated nutrient analyses in seawater

Whitledge, Terry E.; Malloy, S.C.; Patton, Charles J.; Wirick, Creighton D.

doi:10.2172/5433901

Cited by 167 publications

(88 citation statements)

References 7 publications

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“…For nutrient determination, lo-ml aliquots of culture were stored frozen in acid-washed, 20-ml polycarbonate scintillation vials. Concentration of [nitrate + nitrite] was determined using a Technicon II Auto-Analyzer and the protocol of Whitledge et al (1986).…”

Section: Methodsmentioning

confidence: 99%

Effects of darkness on multi‐excitation in vivo fluorescence and survival in a marine diatom

Murphy

Cowles

1997

Limnology & Oceanography

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Surveys of the California Current System in 1993 revealed high concentrations of photosynthetic pigment biomass at -200-m depth, well below the euphotic zone. The deep fluorescence feature contained an estimated 2.2 X 10J metric tons of carbon and contained -2.5 times the amount of chloroph,yll observed in surface waters directly above it. Deep phytoplankton assemblages may be a signature of water mass subduction, suggesting the possibility of using phytoplankton as water mass tracers. These field observations led to a laboratory study of the fluorescence characteristics of autotrophic cells as possible indices of acclimation to extended periods of darkness. In vivo multiexcitation Chl a fluorescence of the diatom Thalassiosira weissflogii was mlsnitored for 2 months of total darkness. Numbers of living and dead cells were determined using the vital stain flucarescein diacetate (FDA). By the end of the dark incubation period, in vivo Chl a fluorescence and fluorescence per cell had leveled off to -45% and 65% of initial values, respectively. The contribution of accessory pigments to Chl a fluorescence, expressed as multiexcitation fluorescence ratios, was higher in the dark than prior to transfer to darkness but showed no significant changes during 2 months of darkness. The FDA assay indicated that -85% of the cells were alive for at least the first 3 weeks during the first dark experiment and for the entire 2 months of 1 second dark incubation. Cell numbers decreased to 65% of initial values and then grew exponentially upon reexplsure to a light: dark photoperiod. Our results for T. weissjlogii suggest that extended light limitation of photosynthesis does not preclude the survival of subducted phytoplankton assemblages and the consequent accumulation of Chl a at depths below the euphotic zone. If these results extend to natural assemblages, it is not possible to estimate advective time scales based on a maximum persistence time of pigment fluorescence below the euphotic zone. Nevertheless, the deep phytoplankton assemblage we observed provides evidence for water mass subduction and suggests that large, intermittent pulses of phytoplankton carbon are a part of cross-shelf exchange and vertical flux from surface waters to depth in this region.

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Section: Methodsmentioning

confidence: 99%

Effects of darkness on multi‐excitation in vivo fluorescence and survival in a marine diatom

Murphy

Cowles

1997

Limnology & Oceanography

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“…Ammonium concentrations were measured onboard using a phenol-hypochlorite protocol similar to that described by Whitledge et al [1981]; ammonium in the deep BS was always close to detection limits. The concentration of dissolved O 2 was determined by Winkler titration.…”

Section: Sample Collection and Hydrochemical Analysesmentioning

confidence: 99%

Origin of the deep Bering Sea nitrate deficit: Constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes

Lehmann¹,

Sigman

McCorkle

et al. 2005

Global Biogeochemical Cycles

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[1] On the basis of the normalization to phosphate, a significant amount of nitrate is missing from the deep Bering Sea (BS). Benthic denitrification has been suggested previously to be the dominant cause for the BS nitrate deficit. We measured water column nitrate 15 N/ 14 N and 18 O/ 16 O as integrative tracers of microbial denitrification, together with pore water-derived benthic nitrate fluxes in the deep BS basin, in order to gain new constraints on the mechanism of fixed nitrogen loss in the BS. The lack of any nitrate isotope enrichment into the deep part of the BS supports the benthic denitrification hypothesis. On the basis of the nitrate deficit in the water column with respect to the adjacent North Pacific and a radiocarbon-derived ventilation age of $50 years, we calculate an average deep BS (>2000 m water depth) sedimentary denitrification rate of $230 mmol N m À2 d À1 (or 1.27 Tg N yr À1 ), more than 3 times higher than high-end estimates of the average global sedimentary denitrification rate for the same depth interval. Pore water-derived estimates of benthic denitrification were variable, and uncertainties in estimates were large. A very high denitrification rate measured from the base of the steep northern slope of the basin suggests that the elevated average sedimentary denitrification rate of the deep Bering calculated from the nitrate deficit is driven by organic matter supply to the base of the continental slope, owing to a combination of high primary productivity in the surface waters along the shelf break and efficient down-slope sediment focusing along the steep continental slopes that characterize the BS.

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“…Samples were analyzed with an Alpkem autoanalyzer on board ship using the methods of Whitledge et al (1981).…”

Section: Nutrient Analysismentioning

confidence: 99%

Phytoplankton growth, microzooplankton herbivory and community structure in the southeast Bering Sea: insight into the formation and temporal persistence of an Emiliania huxleyi bloom

Olson

Strom

2002

Deep Sea Research Part II: Topical Studies in Oceanography

143

108

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Using the seawater dilution technique, we measured phytoplankton growth and microzooplankton grazing rates within and outside of the 1999 Bering Sea coccolithophorid bloom. We found that reduced microzooplankton grazing mortality is a key component in the formation and temporal persistence of the Emiliania huxleyi bloom that continues to proliferate in the southeast Bering Sea. Total chlorophyll a (Chl a) at the study sites ranged from 0.40 to 4.45 mg C l À1 . Highest phytoplankton biomass was found within the bloom, which was a mixed assemblage of diatoms and E. huxleyi. Here, 75% of the Chl a came from cells >10 mm and was attributed primarily to the high abundance of the diatom Nitzschia spp. Nutrient-enhanced total phytoplankton growth rates averaged 0.53 d À1 across all experimental stations. Average growth rates for >10 mm and o10 mm cells were nearly equal, while microzooplankton grazing varied among stations and size fractions. Grazing on phytoplankton cells >10 mm ranged from 0.19 to 1.14 d À1 . Grazing on cells o10 mm ranged from 0.02 to 1.07 d À1 , and was significantly higher at non-bloom (avg. 0.71 d À1 ) than at bloom (avg. 0.14 d À1 ) stations. Averaged across all stations, grazing by microzooplankton accounted for 110% and 81% of phytoplankton growth for >10 and o10 mm cells, respectively. These findings contradict the paradigm that microzooplankton are constrained to diets of nanophytoplankton and strongly suggests that their grazing capability extends beyond boundaries assumed by size-based models. Dinoflagellates and oligotrich ciliates dominated the microzooplankton community. Estimates of abundance and biomass for microzooplankton >10 mm were higher than previously reported for the region, ranging from 22,000 to 227,430 cells l À1 and 18 to 164 mg C l À1 . Highest abundance and biomass occurred in the bloom and corresponded with increased abundance of the large ciliate Laboea, and the heterotrophic dinoflagellates Protoperidinium and Gyrodinium spp. Despite low grazing rates on phytoplankton o10 mm within the bloom, the abundance and biomass of small microzooplankton (o20 mm) capable of grazing E. huxleyi was relatively high at bloom stations. This body of evidence, coupled with observed high grazing rates on large phytoplankton cells, suggests the phytoplankton community composition was strongly regulated by herbivorous activity of microzooplankton. Because grazing behavior deviated from size-based model predictions and was not proportional to microzooplankton biomass, alternate mechanisms that dictate levels of grazing activity were in effect in the southeastern Bering Sea. We hypothesize that these mechanisms included morphological or chemical signaling between phytoplankton and micrograzers, which led to selective grazing pressure. r

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Automated nutrient analyses in seawater

Cited by 167 publications

References 7 publications

Effects of darkness on multi‐excitation in vivo fluorescence and survival in a marine diatom

Effects of darkness on multi‐excitation in vivo fluorescence and survival in a marine diatom

Origin of the deep Bering Sea nitrate deficit: Constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes

Phytoplankton growth, microzooplankton herbivory and community structure in the southeast Bering Sea: insight into the formation and temporal persistence of an Emiliania huxleyi bloom

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