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David M. Karl - One of the best experts on this subject based on the ideXlab platform.
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Particle distributions and dynamics in the Euphotic Zone of the North Pacific Subtropical Gyre
Journal of Geophysical Research: Oceans, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (
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particle distributions and dynamics in the Euphotic Zone of the north pacific subtropical gyre
Journal of Geophysical Research, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (<202 µm) in the upper Euphotic Zone (25–75 m), as estimated using an empirical formula to transform particle volume to carbon concentrations. Over the entire vertical layer considered (20–180 m), the largest contribution to particle volume corresponded to particles between 3 and 10 µm in diameter. Although the exponent of a power law parameterization suggested that larger particles had a lower relative abundance than in other regions of the global ocean, this parameter and hence conclusions about relative particle abundance are sensitive to the shape of the size distribution and to the curve fitting method. Results on the vertical distribution of particles indicate that different size fractions varied independently with depth. Particles between 1.25 and 2 µm reached maximal abundances coincident with the depth of the chlorophyll a maximum (averaging 121 ± 10 m), where eukaryotic phytoplankton abundances increased. In contrast, particles between 2 and 20 µm tended to accumulate just below the base of the mixed layer (41 ± 14 m). Variability in particle size tracked changes in the abundance of specific photoautotrophic organisms (measured with flow cytometry and pigment concentration), suggesting that phytoplankton population dynamics are an important control of the spatiotemporal variability in particle concentration in this ecosystem.
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Microbial respiration in the Euphotic Zone at Station ALOHA
Limnology and Oceanography, 2015Co-Authors: Sandra Martínez-garcía, David M. KarlAbstract:Measurements of the temporal and vertical variability of microbial community respiration (MCR) in the Euphotic Zone (0–200 m) at Station ALOHA were made using the in vivo INT method to constrain oxygen and carbon cycling at this oceanic site. Mean ( ± 1 SE) MCR was higher in the upper (0–100 m) (0.89 ± 0.05 mmol O2 m−3 d−1) than in the lower (100–200 m) portion of the Euphotic Zone (0.52 ± 0.05 mmol O2 m−3 d−1). Respiration in the 0.8 μm size-fraction relative to respiration in the 0.2–0.8 μm size-fraction was on average 1.4 ± 0.1. Variability in MCR was observed on both daily and monthly time scales, suggesting that respiration is a dynamic process throughout the year at Station ALOHA. MCR in the 0.2–0.8 μm size fraction was more variable than > 0.8 μm MCR. Despite significant vertical and temporal variability in MCR, the Euphotic Zone depth-integrated (0–200 m) MCR was relatively constant (134.8 ± 11.8 mmol O2 m−2 d−1) throughout the period of observation. Oxygen consumption via MCR always exceeded O2 production extrapolated from 14C-primary production estimation, assuming a photosynthetic quotient of 1.13 mol O2 produced : mol CO2 fixed. MCR plus particulate carbon export from the Euphotic Zone for the period November 2011–October 2012 at Station ALOHA can be used to set a lower limit of ∼ 45 mol C m−2 yr−1 for gross primary production.
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A role for nitrite in the production of nitrous oxide in the lower Euphotic Zone of the oligotrophic North Pacific Ocean
Deep Sea Research Part I: Oceanographic Research Papers, 2014Co-Authors: Samuel T. Wilson, Daniela A. Del Valle, Mariona Segura-noguera, David M. KarlAbstract:Abstract Understanding the role of the oceans in the Earth's changing climate requires comprehension of the relevant metabolic pathways which produce climatically important trace gases. The global ocean represents one of the largest natural sources of nitrous oxide (N 2 O) that is produced by selected archaea and/or bacteria during nitrogen (N) metabolism. In this study, the role of nitrite (NO 2 − ) in the production of N 2 O in the upper water column of the oligotrophic North Pacific Subtropical Gyre was investigated, focusing primarily on the lower Euphotic Zone where NO 2 − concentrations at the primary NO 2 − maximum reached 195 nmol L −1 . Free-drifting sediment trap arrays were deployed to measure N cycle processes in sinking particulate material and the addition of selected N substrates to unpreserved sediment traps provided an experimental framework to test hypotheses regarding N 2 O production pathways and controls. Sinking particles collected using NO 2 − -amended, unpreserved sediment traps exhibited significant production of N 2 O at depths between 100 and 200 m. Subsequent stable isotope tracer measurements conducted on sediment trap material amended with 15 NO 2 − yielded elevated δ 15 N values of N 2 O, supporting N 2 O production via a NO 2 − metabolism pathway. Experiments on seawater collected from 150 m showed N 2 O production via NO 2 − metabolism also occurs in the water-column and indicated that the concentration of NO 2 − relative to NH 4 + availability may be an important control. These findings provide evidence for the production of N 2 O via nitrifer-denitrification in the lower Euphotic Zone of the open ocean, whereby NO 2 − is reduced to N 2 O by ammonia-oxidizing microorganisms.
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light driven seasonal patterns of chlorophyll and nitrate in the lower Euphotic Zone of the north pacific subtropical gyre
Limnology and Oceanography, 2004Co-Authors: Ricardo M. Letelier, David M. Karl, Mark R Abbott, Robert R. BidigareAbstract:The Euphotic Zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long-term oligotrophic habitat assessment; 228459N, 1588009W) 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 m 22 inorganic nitrogen [NO 1 NO ] in the 90‐200-m depth range, 22 32 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.
Robert R. Bidigare - One of the best experts on this subject based on the ideXlab platform.
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Particle distributions and dynamics in the Euphotic Zone of the North Pacific Subtropical Gyre
Journal of Geophysical Research: Oceans, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (
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particle distributions and dynamics in the Euphotic Zone of the north pacific subtropical gyre
Journal of Geophysical Research, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (<202 µm) in the upper Euphotic Zone (25–75 m), as estimated using an empirical formula to transform particle volume to carbon concentrations. Over the entire vertical layer considered (20–180 m), the largest contribution to particle volume corresponded to particles between 3 and 10 µm in diameter. Although the exponent of a power law parameterization suggested that larger particles had a lower relative abundance than in other regions of the global ocean, this parameter and hence conclusions about relative particle abundance are sensitive to the shape of the size distribution and to the curve fitting method. Results on the vertical distribution of particles indicate that different size fractions varied independently with depth. Particles between 1.25 and 2 µm reached maximal abundances coincident with the depth of the chlorophyll a maximum (averaging 121 ± 10 m), where eukaryotic phytoplankton abundances increased. In contrast, particles between 2 and 20 µm tended to accumulate just below the base of the mixed layer (41 ± 14 m). Variability in particle size tracked changes in the abundance of specific photoautotrophic organisms (measured with flow cytometry and pigment concentration), suggesting that phytoplankton population dynamics are an important control of the spatiotemporal variability in particle concentration in this ecosystem.
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light driven seasonal patterns of chlorophyll and nitrate in the lower Euphotic Zone of the north pacific subtropical gyre
Limnology and Oceanography, 2004Co-Authors: Ricardo M. Letelier, David M. Karl, Mark R Abbott, Robert R. BidigareAbstract:The Euphotic Zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long-term oligotrophic habitat assessment; 228459N, 1588009W) 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 m 22 inorganic nitrogen [NO 1 NO ] in the 90‐200-m depth range, 22 32 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.
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Accessory pigments versus chlorophyll a concentrations within the Euphotic Zone: A ubiquitous relationship
Limnology and Oceanography, 2000Co-Authors: Charles C. Trees, Robert R. Bidigare, Dennis K. Clark, Michael Ondrusek, James L. MuellerAbstract:Remotely sensed chlorophyll a (Chl a) concentrations are determined by the ratio of upwelled radiances within the Soret band of Chl a (443 nm) and at 550 nm. Absorption at wavelengths outside this band (.460 nm) is dominated by accessory pigments and for the successful measurement of Chl a (e.g., 490 : 550 nm and 520 : 550 nm ratios) early Coastal Zone Color Scanner investigators speculated that these accessory pigments must covary with Chl a, although routine methods to measure these pigments had not yet been developed. Nearly 7,000 (high performance liquid chromatography) pigment samples, collected within the Euphotic Zone, were measured to test the consistency of the relationship between accessory pigments and Chl a. Despite the various sampling periods (1985‐1998) and numerous geographic locations, consistent patterns have emerged in the ratios of the log accessory pigments to log total Chl a (TCHLA 5 Chl a, Chl a allomer, Chl a epimer, and chlorophyllide a). There were strong log-linear relationships within cruises for these ratios with an average r 2
Louis Legendre - One of the best experts on this subject based on the ideXlab platform.
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Water Column Biogeochemistry below the Euphotic Zone
Ocean Biogeochemistry, 2003Co-Authors: Paul Tréguer, Louis Legendre, Richard T. Rivkin, Olivier Ragueneau, Nicolas DittertAbstract:The main focus of the International JGOFS research inititiatives was on the cycling of carbon and of associated elements within the surface layer, and their downward export from the upper ocean. Relatively few coordinated measurements and experiments were made below the photic Zone so our understanding and modeling of the biogeochemistry of the ocean’s interior is still in its infancy. However from the numerous data acquired in the 1990s during JGOFS and JGOFS-like process studies it is possible to extract sufficient information to make preliminary statements about the biogeochemistry of the water column below the Euphotic Zone. An important preliminary result of these studies is that we now are beginning to realize that the biogeochemistry of the surface ocean, of the ocean’s interior, and of the surface sediments appears to be more coupled than was thought fifteen years ago.
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Chlorophyll a to estimate the particulate organic carbon available as food to large zooplankton in the Euphotic Zone of oceans
Journal of Plankton Research, 1999Co-Authors: Louis Legendre, Josée MichaudAbstract:In order to optimize the sustained exploitation of marine renewable resources, a major objective of modern biological oceanography is to quantify, model and predict the flux of biogenic carbon (BC) from phytoplankton towards large metazoans. The present paper explains why the concentrations of sestonic particulate organic carbon ((POC)) provide estimates of the BC that can be used as food by large (i.e. meso- and macro-) zooplankton, and can thus be channelled towards large metazoans. Because of this, the wealth of existing (POC) data provide first-order estimates of the BC available to large zooplankton. The paper also derives, from a large set of data from the litera- ture, general relationships between chlorophyll a concentrations ((Chl)) and (POC) in the Euphotic Zone of oceans. These empirical relationships can be used to compute (POC) from (Chl) and thus obtain from the latter, which is easy to determine in the field or derive from remotely sensed images of ocean colour, estimates of the BC that is available as food to large zooplankton.
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Flux of particulate organic material from the Euphotic Zone of oceans: Estimation from phytoplankton biomass
Journal of Geophysical Research: Oceans, 1998Co-Authors: Louis LegendreAbstract:A major objective of modem biological oceanography is to quantify, model, and predict the downward flux of biogenic carbon. Previous papers have documented an empirical relationship between the sinking flux of particulate organic material from the Euphotic Zone (S) and phytoplankton biomass (B), in oceans, and suggested that S could be estimated directly from B. The present paper investigates, using a mathematical model and data from the literature, the relationship between S and B. Calculations show that S is determined mostly by B and also by p (instantaneous coefficient of net phytoplankton production minus Euphotic Zone heterotrophic community respiration and incorporation in the pelagic food web). The regression S = f(B) accounts for 90% of the variation in S. In remote sensing, B is derived from ocean color, phytoplankton production (P) is derived from B, and S is derived from P. Within that context, the biomass approach could be used as an additional means to constrain the estimates of S.
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Pathways of carbon cycling in the Euphotic Zone: the fate of largesized phytoplankton in the Northeast Water Polynya
Journal of Plankton Research, 1998Co-Authors: S. Pesant, Louis Legendre, Michel Gosselin, Carin J. Ashjian, B. C. Booth, Kendra L. Daly, Louis Fortier, Hans-jürgen Hirche, Josée Michaud, Ralph E. H. SmithAbstract:The fate of large-sized phytoplankton and pathways of carbon cycling in surface waters, i.e. recycling within or export out of the Euphotic Zone, were investigated in the Northeast Water (NEW) Polynya (77-81 °N) from 23 May to 17 August 1993. Sampling represented a wide range of ice, hydrographic and nutrient conditions. Phytoplankton and zooplankton abundances, and phytoplankton production rates were determined in the field, whereas potential rates of grazing by copepods, dinoflagellates and appendicularians were calculated from abundances and temperature, using assumptions from the literature. The potential downward and lateral export of phytoplankton was also calculated by resolving a carbon budget for the Euphotic Zone. The present study suggests that, in the NEW, different pathways for the cycling of carbon existed in seasonally ice-free (in the polynya) and continuously ice-covered areas (outside the polynya). Outside the polynya, the fate of large-sized phytoplankton could not be assessed because the heterotrophic community presumably grazed on a variety of food items, including ice algae, microzooplankton and large-sized phytoplankton. In the polynya, the fate of large-sized phytoplankton production was to be mostly recycled at the beginning of sampling and to be mostly exported downward or laterally as the bloom of large-sized phytoplankton developed. Generally, copepods mostly contributed to recycling, but sometimes dinoflagellates or appendicularians alone recycled most of the large-sized phytoplankton production.
Angelicque E. White - One of the best experts on this subject based on the ideXlab platform.
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Particle distributions and dynamics in the Euphotic Zone of the North Pacific Subtropical Gyre
Journal of Geophysical Research: Oceans, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (
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particle distributions and dynamics in the Euphotic Zone of the north pacific subtropical gyre
Journal of Geophysical Research, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (<202 µm) in the upper Euphotic Zone (25–75 m), as estimated using an empirical formula to transform particle volume to carbon concentrations. Over the entire vertical layer considered (20–180 m), the largest contribution to particle volume corresponded to particles between 3 and 10 µm in diameter. Although the exponent of a power law parameterization suggested that larger particles had a lower relative abundance than in other regions of the global ocean, this parameter and hence conclusions about relative particle abundance are sensitive to the shape of the size distribution and to the curve fitting method. Results on the vertical distribution of particles indicate that different size fractions varied independently with depth. Particles between 1.25 and 2 µm reached maximal abundances coincident with the depth of the chlorophyll a maximum (averaging 121 ± 10 m), where eukaryotic phytoplankton abundances increased. In contrast, particles between 2 and 20 µm tended to accumulate just below the base of the mixed layer (41 ± 14 m). Variability in particle size tracked changes in the abundance of specific photoautotrophic organisms (measured with flow cytometry and pigment concentration), suggesting that phytoplankton population dynamics are an important control of the spatiotemporal variability in particle concentration in this ecosystem.
Ricardo M. Letelier - One of the best experts on this subject based on the ideXlab platform.
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Particle distributions and dynamics in the Euphotic Zone of the North Pacific Subtropical Gyre
Journal of Geophysical Research: Oceans, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (
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particle distributions and dynamics in the Euphotic Zone of the north pacific subtropical gyre
Journal of Geophysical Research, 2015Co-Authors: Benedetto Barone, David M. Karl, Robert R. Bidigare, Matthew J. Church, Ricardo M. Letelier, Angelicque E. WhiteAbstract:During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the Euphotic Zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks (<202 µm) in the upper Euphotic Zone (25–75 m), as estimated using an empirical formula to transform particle volume to carbon concentrations. Over the entire vertical layer considered (20–180 m), the largest contribution to particle volume corresponded to particles between 3 and 10 µm in diameter. Although the exponent of a power law parameterization suggested that larger particles had a lower relative abundance than in other regions of the global ocean, this parameter and hence conclusions about relative particle abundance are sensitive to the shape of the size distribution and to the curve fitting method. Results on the vertical distribution of particles indicate that different size fractions varied independently with depth. Particles between 1.25 and 2 µm reached maximal abundances coincident with the depth of the chlorophyll a maximum (averaging 121 ± 10 m), where eukaryotic phytoplankton abundances increased. In contrast, particles between 2 and 20 µm tended to accumulate just below the base of the mixed layer (41 ± 14 m). Variability in particle size tracked changes in the abundance of specific photoautotrophic organisms (measured with flow cytometry and pigment concentration), suggesting that phytoplankton population dynamics are an important control of the spatiotemporal variability in particle concentration in this ecosystem.
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light driven seasonal patterns of chlorophyll and nitrate in the lower Euphotic Zone of the north pacific subtropical gyre
Limnology and Oceanography, 2004Co-Authors: Ricardo M. Letelier, David M. Karl, Mark R Abbott, Robert R. BidigareAbstract:The Euphotic Zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long-term oligotrophic habitat assessment; 228459N, 1588009W) 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 m 22 inorganic nitrogen [NO 1 NO ] in the 90‐200-m depth range, 22 32 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.
