EGU General Assembly Conference Abstracts, Apr 1, 2015
Knowledge on the variability in quantity and compositions of various size groups of aerosols is i... more Knowledge on the variability in quantity and compositions of various size groups of aerosols is important to understand their sources and their role in biogeochemical and climate processes. Here, we studied total suspended particles (TSP), PM 10 and PM 2.5 for their quantitative and water soluble compositional (F -, Cl -, SO 4 2-, NO 3 -, NH 4 + , Na + , K + , Ca 2+ , and Mg 2+ ) distributions, and to understand their nature and potential sources at Goa and Visakhapatnam on the west and east coasts, respectively, of India. While the mean concentrations of TSP were found to be 117 ± 44 and 85 ± 51 μg/m 3 its maximal levels occurred in spring intermonsoon (SIM; 141 ± 52) and winter monsoon (WM; 155 ± 145 μg/m 3 ) seasons at Goa and Visakhapatnam, respectively. PM 10 and PM 2.5 exhibited higher ranges at Visakhapatnam than Goa. The increase in PM 2.5 abundance from WM to SIM at Visakhapatnam seems to occur in coincidence with decrease in TSP favored by topography and ambient meteorological conditions. Locally released and seasonally transported (from land and sea) constituents contributed to the observed variability in aerosol compositions. Sulphate dominated the aerosol composition at both Goa (57-64%) and Visakhapatnam (43-55%) followed by NO 3 -(5-16% and 6-18%, respectively) where the former component was higher in PM 10 and PM 2.5 . The NO 3 -was more in TSP. Relations between SO 4 2-and NH 4 + suggested possible presence of NH 4 HSO 4 . Examination of ionic ratios and balance suggested near neutrality in PM 10 and PM 2.5 while TSP was acidic at the both locations. Notable relations between Ca 2+ and NO 3 -, particularly in PM 10 at Goa, indicated their release from mining related activities.
Data on organic and inorganic nutrients in unfiltered seawater that was sampled at and around Sta... more Data on organic and inorganic nutrients in unfiltered seawater that was sampled at and around Station ALOHA, north of Oahu, Hawaii, in the North Pacific Subtropical Gyre. Seawater was collected into HDPE or polypropylene bottles and immediately frozen. Silicate, phosphate and nitrate+nitrite are determined colormetrically on a SEAL Analytical Autoanalyzer (AA3 with HR detectors), with the exception of nitrate+nitrite that is <0.5umol/L, which is analyzed by high-sensitivity chemiluminescence. Total phosphorus (TP) and total nitrogen (TN) are determined by analysis of phosphate and nitrate, respectively, after oxidation by high-intensity ultraviolet light. Total organic phosphorus and total organic nitrogen are determined by subtracting background PO4 and NO3+NO2 from TP and TN, respectively. Total organic carbon is determined by combustion on a Shimadzu TOC-V analyzer. This dataset was originally published in the following article, in which additional details and interpretations ...
In stratified oligotrophic waters, phytoplankton communities forming the deep chlorophyll maximum... more In stratified oligotrophic waters, phytoplankton communities forming the deep chlorophyll maximum (DCM) are isolated from atmospheric iron sources above and remineralized iron sources below. Reduced supply leads to a minimum in dissolved iron (dFe) near 100 m, but it is unclear if iron limits growth at the DCM. Here, we propose that natural iron addition events occur regularly with the passage of mesoscale eddies, which alter the supply of dFe and other nutrients relative to the availability of light, and can be used to test for iron limitation at the DCM. This framework is applied to two eddies sampled in the North Pacific Subtropical Gyre. Observations in an anticyclonic eddy center indicated downwelling of iron‐rich surface waters, leading to increased dFe at the DCM but no increase in productivity. In contrast, uplift of isopycnals within a cyclonic eddy center increased supply of both nitrate and dFe to the DCM, and led to dominance of picoeukaryotic phytoplankton. Iron addition experiments did not increase productivity in either eddy, but significant enhancement of leucine incorporation in the light was observed in the cyclonic eddy, a potential indicator of iron stress among Prochlorococcus. Rapid cycling of siderophores and low dFe:nitrate uptake ratios also indicate that a portion of the microbial community was stressed by low iron. However, near‐complete nitrate drawdown in this eddy, which represents an extreme case in nutrient supply compared to nearby Hawaii Ocean Time‐series observations, suggests that recycling of dFe in oligotrophic ecosystems is sufficient to avoid iron limitation in the DCM under typical conditions.
Photolysis of dissolved organic matter using high‐intensity, ultraviolet (UV) light has been util... more Photolysis of dissolved organic matter using high‐intensity, ultraviolet (UV) light has been utilized since the 1960s as a method for the oxidation and subsequent quantification of dissolved organic nitrogen and phosphorus (DON and DOP) in both freshwater and marine water. However, conventional UV systems yielded variable and sometimes unreliable results; consequently, the method fell out of favor throughout much of the oceanographic community. Researchers turned to other oxidation methods such as persulfate oxidation or high‐temperature combustion, even though they have difficulty when DON and DOP are <10% of the total dissolved N and P (for example, in the deep sea and in surface waters at high latitudes). Here, we revive the UV oxidation method using modernized light‐generating equipment and high‐precision colorimetric analysis of the oxidation products, resulting in the most well‐constrained full ocean depth profiles of DON and DOP that are available to date. At Station ALOHA...
Cell size is broadly applied as a convenient parameterization of ecosystem models and is widely a... more Cell size is broadly applied as a convenient parameterization of ecosystem models and is widely applicable to constrain the activities of organisms spanning large size ranges. However, the size structure of the majority of the marine picoplankton assemblage is narrow and beneath the lower size limit of the empirical allometric relationships established so far (typically >1 μm). We applied a fine‐resolution (0.05 μm increments) size fractionation method to estimate the size dependence of metabolic activities of picoplankton populations in the 0.10–1.00 μm size interval within the surface North Pacific Subtropical Gyre microbial assemblage. Group‐specific carbon retained on each filter was quantified by flow cytometric conversion of light scatter to cellular carbon quotas. Median carbon quotas were 25.7, 22.6, and 5.9 fg C cell−1 for populations of the picocyanobacterium Prochlorococcus, high‐scatter heterotrophs, and low‐scatter heterotrophs, respectively. Carbon‐specific rates of...
The southeast subtropical Pacific Ocean was sampled along a zonal transect between the coasts of ... more The southeast subtropical Pacific Ocean was sampled along a zonal transect between the coasts of Chile and Easter Island. This remote area of the world's ocean presents strong gradients in physical (e.g., temperature, density and light), chemical (e.g., salinity and nutrient concentrations) and microbiological (e.g., cell abundances, biomass and specific growth rates) properties. The goal of this study was to describe the phosphorus (P) dynamics in three main ecosystems along this transect: the upwelling regime off the northern Chilean coast, the oligotrophic area associated with the southeast subtropical Pacific gyre and the transitional area in between these two biomes. We found that inorganic phosphate (Pi) concentrations were high and turnover times were long (>210 nmol l À1 and >31 d, respectively) in the upper water column, along the entire transect. Pi uptake rates in the gyre were low (euphotic layer integrated rates were 0.26 mmol m À2 d À1 in the gyre and 1.28 mmol m À2 d À1 in the upwelling region), yet not only driven by decreases in particle mass or cell abundance (particulate P-and cell-normalized Pi uptake rates in the euphotic layer were $1-4 times and $3-15 times lower in the gyre than in the upwelling, respectively). However these Pi uptake rates were at or near the maximum Pi uptake velocity (i.e., uptake rates in Pi amended samples were not significantly different from those at ambient concentration: 1.5 and 23.7 nmol l À1 d À1 at 50% PAR in the gyre and upwelling, respectively). Despite the apparent Pi replete conditions, selected dissolved organic P (DOP) compounds were readily hydrolyzed. Nucleotides were the most bioavailable of the DOP substrates tested. Microbes actively assimilated adenosine-5 0triphosphate (ATP) leading to Pi and adenosine incorporation as well as Pi release to the environment. The southeast subtropical Pacific Ocean is a Pi-sufficient environment, yet DOP hydrolytic processes are maintained and contribute to P-cycling across the wide range of environmental conditions present in this ecosystem.
Nitrogen (N) is the major limiting nutrient for phytoplankton growth and productivity in large pa... more Nitrogen (N) is the major limiting nutrient for phytoplankton growth and productivity in large parts of the world's oceans. Differential preferences for specific N substrates may be important in controlling phytoplankton community composition. To date, there is limited information on how specific N substrates influence the composition of naturally occurring microbial communities. We investigated the effect of nitrate ( ), ammonium ( ), and urea on microbial and phytoplankton community composition (cell abundances and 16S rRNA gene profiling) and functioning (photosynthetic activity, carbon fixation rates) in the oligotrophic waters of the North Pacific Ocean. All N substrates tested significantly stimulated phytoplankton growth and productivity. Urea resulted in the greatest (>300%) increases in chlorophyll a (<0.06 μg L−1 and ∼0.19 μg L−1 in the control and urea addition, respectively) and productivity (<0.4 μmol C L−1 d−1 and ∼1.4 μmol C L−1 d−1 in the control and ure...
Light and dark phosphate (PO 4 3-) uptake rates were investigated in the North Pacific Subtropica... more Light and dark phosphate (PO 4 3-) uptake rates were investigated in the North Pacific Subtropical Gyre (NPSG) and along a coastal to open ocean transect in the South Pacific Ocean. PO 4 3-uptake rates were consistently higher when incubated in the light, but the ratio of uptake in the light and dark (L:D) decreased with depth. In the NPSG, the L:D ratio of euphotic-layer integrated PO 4 3-uptake was 1.58 ± 0.08 (± SE, n = 15 profiles), and the average L:D ratio was 1.60 ± 0.45 (± SD, n = 42) between 5 and 45 m and 1.25 ± 0.70 (± SD, n = 28) between 150 and 175 m. The L:D ratio was higher for the pigmented plankton-enriched size fractions (0.6 to 2 µm and > 2 µm), but results were difficult to interpret at the oligotrophic stations where non-pigmented and pigmented plankton cell sizes overlapped. Group-specific measurements obtained using flow cytometric cell sorting demonstrated that Prochlorococcus PO 4 3-uptake rates were higher when the samples were incubated under ambient light. Adenosine-5′-triphosphate (ATP) uptake by Prochlorococcus was also higher in the light for the uptake of both the terminal PO 4 3-group ([γ-33 P]ATP) and adenine moiety ([2, 8-3 H]ATP). This could be the result of secondary uptake of PO 4 3-and/or adenine after ATP cleavage by non-pigmented picoplankton. There was no significant difference in P-assimilation by non-pigmented picoplankton between light and dark incubated samples. Light dependence of phytoplankton PO 4 3-uptake could thus influence the functioning of the microbial loop and the flows of matter and energy in marine environments by creating temporal patterns of resource utilization.
In 1976, John D. Isaacs proposed to use wave energy to pump cold and nutrient-rich deep water int... more In 1976, John D. Isaacs proposed to use wave energy to pump cold and nutrient-rich deep water into the sunlit surface layers. The motivation for this endeavor has taken many forms over the years, from energy production to fueling aquaculture to the more recent suggestion that artificial upwelling could be used to stimulate primary productivity and anthropogenic carbon sequestration in oligotrophic regions of the ocean. However, the potential for biological carbon sequestration in response to upwelling will depend on the ...
Several studies have demonstrated that Prochlorococcus , the most abundant photosynthetic organis... more Several studies have demonstrated that Prochlorococcus , the most abundant photosynthetic organism on Earth, can assimilate organic molecules, such as amino acids, amino sugars, ATP, phosphonates, and dimethylsulfoniopropionate. This autotroph can also assimilate small amounts of glucose, supporting the hypothesis that Prochlorococcus is mixotrophic.
A large-volume mesocosm-based nutrient perturbation experiment was conducted off the island of Ha... more A large-volume mesocosm-based nutrient perturbation experiment was conducted off the island of Hawai‘i, USA, to investigate the response of surface ocean phytoplankton communities to the addition of macronutrients, trace metals, and vitamins and to assess the feasibility of using mesocosms in the open ocean. Three free-drifting mesocosms (~60 m3) were deployed: one mesocosm served as a control (no nutrient amendments); a second (termed +P) was amended with nitrate (N), silicate (Si), phosphate (P), and a trace metal + vitamin mixture; and a third (termed -P) was amended with N, Si, and a trace metal + vitamin mixture but no P. These mesocosms were unreplicated due to logistical constraints and hence differences between treatments are qualitative. After 6 d, the largest response of the phytoplankton community was observed in the +P mesocosm, where chlorophyll a and 14C-based primary production were 2-3× greater than in the -P mesocosm and 4-6× greater than in the control. Comparison ...
A method is presented for the online measurement of methane in aquatic environments by applicatio... more A method is presented for the online measurement of methane in aquatic environments by application of membrane inlet mass spectrometry (MIMS). For this purpose, the underwater mass spectrometer Inspectr200-200 was applied. A simple and reliable volumetric calibration technique, based on the mixing of two end member concentrations, was used for the analysis of CH 4 by MIMS. To minimize interferences caused by the high water vapor content, permeating through the membrane inlet system into the vacuum section of the mass spectrometer, a cool-trap was designed. With the application of the cool-trap, the detection limit was lowered from 100 to 16 nmol/L CH 4. This allows for measurements of methane concentrations in surface and bottom waters of coastal areas and lakes. Furthermore, in case of membrane rupture, the cool-trap acts as a security system, avoiding total damage of the mass spectrometer by flushing it with water. The Inspectr200-200 was applied for studies of methane and carbon dioxide concentrations in coastal areas of the Baltic Sea and Lake Constance. The low detection limit and fast response time of the MIMS allowed a detailed investigation of methane concentrations in the vicinity of gas seepages. aAm Soc Mass
In the contemporary North Pacific subtropical gyre (NPSG) the extant microbial community is based... more In the contemporary North Pacific subtropical gyre (NPSG) the extant microbial community is based on prokaryotic cells with the cyanobacterium Prochlorococcus dominating the phototrophic component. ...
EGU General Assembly Conference Abstracts, Apr 1, 2015
Knowledge on the variability in quantity and compositions of various size groups of aerosols is i... more Knowledge on the variability in quantity and compositions of various size groups of aerosols is important to understand their sources and their role in biogeochemical and climate processes. Here, we studied total suspended particles (TSP), PM 10 and PM 2.5 for their quantitative and water soluble compositional (F -, Cl -, SO 4 2-, NO 3 -, NH 4 + , Na + , K + , Ca 2+ , and Mg 2+ ) distributions, and to understand their nature and potential sources at Goa and Visakhapatnam on the west and east coasts, respectively, of India. While the mean concentrations of TSP were found to be 117 ± 44 and 85 ± 51 μg/m 3 its maximal levels occurred in spring intermonsoon (SIM; 141 ± 52) and winter monsoon (WM; 155 ± 145 μg/m 3 ) seasons at Goa and Visakhapatnam, respectively. PM 10 and PM 2.5 exhibited higher ranges at Visakhapatnam than Goa. The increase in PM 2.5 abundance from WM to SIM at Visakhapatnam seems to occur in coincidence with decrease in TSP favored by topography and ambient meteorological conditions. Locally released and seasonally transported (from land and sea) constituents contributed to the observed variability in aerosol compositions. Sulphate dominated the aerosol composition at both Goa (57-64%) and Visakhapatnam (43-55%) followed by NO 3 -(5-16% and 6-18%, respectively) where the former component was higher in PM 10 and PM 2.5 . The NO 3 -was more in TSP. Relations between SO 4 2-and NH 4 + suggested possible presence of NH 4 HSO 4 . Examination of ionic ratios and balance suggested near neutrality in PM 10 and PM 2.5 while TSP was acidic at the both locations. Notable relations between Ca 2+ and NO 3 -, particularly in PM 10 at Goa, indicated their release from mining related activities.
Data on organic and inorganic nutrients in unfiltered seawater that was sampled at and around Sta... more Data on organic and inorganic nutrients in unfiltered seawater that was sampled at and around Station ALOHA, north of Oahu, Hawaii, in the North Pacific Subtropical Gyre. Seawater was collected into HDPE or polypropylene bottles and immediately frozen. Silicate, phosphate and nitrate+nitrite are determined colormetrically on a SEAL Analytical Autoanalyzer (AA3 with HR detectors), with the exception of nitrate+nitrite that is <0.5umol/L, which is analyzed by high-sensitivity chemiluminescence. Total phosphorus (TP) and total nitrogen (TN) are determined by analysis of phosphate and nitrate, respectively, after oxidation by high-intensity ultraviolet light. Total organic phosphorus and total organic nitrogen are determined by subtracting background PO4 and NO3+NO2 from TP and TN, respectively. Total organic carbon is determined by combustion on a Shimadzu TOC-V analyzer. This dataset was originally published in the following article, in which additional details and interpretations ...
In stratified oligotrophic waters, phytoplankton communities forming the deep chlorophyll maximum... more In stratified oligotrophic waters, phytoplankton communities forming the deep chlorophyll maximum (DCM) are isolated from atmospheric iron sources above and remineralized iron sources below. Reduced supply leads to a minimum in dissolved iron (dFe) near 100 m, but it is unclear if iron limits growth at the DCM. Here, we propose that natural iron addition events occur regularly with the passage of mesoscale eddies, which alter the supply of dFe and other nutrients relative to the availability of light, and can be used to test for iron limitation at the DCM. This framework is applied to two eddies sampled in the North Pacific Subtropical Gyre. Observations in an anticyclonic eddy center indicated downwelling of iron‐rich surface waters, leading to increased dFe at the DCM but no increase in productivity. In contrast, uplift of isopycnals within a cyclonic eddy center increased supply of both nitrate and dFe to the DCM, and led to dominance of picoeukaryotic phytoplankton. Iron addition experiments did not increase productivity in either eddy, but significant enhancement of leucine incorporation in the light was observed in the cyclonic eddy, a potential indicator of iron stress among Prochlorococcus. Rapid cycling of siderophores and low dFe:nitrate uptake ratios also indicate that a portion of the microbial community was stressed by low iron. However, near‐complete nitrate drawdown in this eddy, which represents an extreme case in nutrient supply compared to nearby Hawaii Ocean Time‐series observations, suggests that recycling of dFe in oligotrophic ecosystems is sufficient to avoid iron limitation in the DCM under typical conditions.
Photolysis of dissolved organic matter using high‐intensity, ultraviolet (UV) light has been util... more Photolysis of dissolved organic matter using high‐intensity, ultraviolet (UV) light has been utilized since the 1960s as a method for the oxidation and subsequent quantification of dissolved organic nitrogen and phosphorus (DON and DOP) in both freshwater and marine water. However, conventional UV systems yielded variable and sometimes unreliable results; consequently, the method fell out of favor throughout much of the oceanographic community. Researchers turned to other oxidation methods such as persulfate oxidation or high‐temperature combustion, even though they have difficulty when DON and DOP are <10% of the total dissolved N and P (for example, in the deep sea and in surface waters at high latitudes). Here, we revive the UV oxidation method using modernized light‐generating equipment and high‐precision colorimetric analysis of the oxidation products, resulting in the most well‐constrained full ocean depth profiles of DON and DOP that are available to date. At Station ALOHA...
Cell size is broadly applied as a convenient parameterization of ecosystem models and is widely a... more Cell size is broadly applied as a convenient parameterization of ecosystem models and is widely applicable to constrain the activities of organisms spanning large size ranges. However, the size structure of the majority of the marine picoplankton assemblage is narrow and beneath the lower size limit of the empirical allometric relationships established so far (typically >1 μm). We applied a fine‐resolution (0.05 μm increments) size fractionation method to estimate the size dependence of metabolic activities of picoplankton populations in the 0.10–1.00 μm size interval within the surface North Pacific Subtropical Gyre microbial assemblage. Group‐specific carbon retained on each filter was quantified by flow cytometric conversion of light scatter to cellular carbon quotas. Median carbon quotas were 25.7, 22.6, and 5.9 fg C cell−1 for populations of the picocyanobacterium Prochlorococcus, high‐scatter heterotrophs, and low‐scatter heterotrophs, respectively. Carbon‐specific rates of...
The southeast subtropical Pacific Ocean was sampled along a zonal transect between the coasts of ... more The southeast subtropical Pacific Ocean was sampled along a zonal transect between the coasts of Chile and Easter Island. This remote area of the world's ocean presents strong gradients in physical (e.g., temperature, density and light), chemical (e.g., salinity and nutrient concentrations) and microbiological (e.g., cell abundances, biomass and specific growth rates) properties. The goal of this study was to describe the phosphorus (P) dynamics in three main ecosystems along this transect: the upwelling regime off the northern Chilean coast, the oligotrophic area associated with the southeast subtropical Pacific gyre and the transitional area in between these two biomes. We found that inorganic phosphate (Pi) concentrations were high and turnover times were long (>210 nmol l À1 and >31 d, respectively) in the upper water column, along the entire transect. Pi uptake rates in the gyre were low (euphotic layer integrated rates were 0.26 mmol m À2 d À1 in the gyre and 1.28 mmol m À2 d À1 in the upwelling region), yet not only driven by decreases in particle mass or cell abundance (particulate P-and cell-normalized Pi uptake rates in the euphotic layer were $1-4 times and $3-15 times lower in the gyre than in the upwelling, respectively). However these Pi uptake rates were at or near the maximum Pi uptake velocity (i.e., uptake rates in Pi amended samples were not significantly different from those at ambient concentration: 1.5 and 23.7 nmol l À1 d À1 at 50% PAR in the gyre and upwelling, respectively). Despite the apparent Pi replete conditions, selected dissolved organic P (DOP) compounds were readily hydrolyzed. Nucleotides were the most bioavailable of the DOP substrates tested. Microbes actively assimilated adenosine-5 0triphosphate (ATP) leading to Pi and adenosine incorporation as well as Pi release to the environment. The southeast subtropical Pacific Ocean is a Pi-sufficient environment, yet DOP hydrolytic processes are maintained and contribute to P-cycling across the wide range of environmental conditions present in this ecosystem.
Nitrogen (N) is the major limiting nutrient for phytoplankton growth and productivity in large pa... more Nitrogen (N) is the major limiting nutrient for phytoplankton growth and productivity in large parts of the world's oceans. Differential preferences for specific N substrates may be important in controlling phytoplankton community composition. To date, there is limited information on how specific N substrates influence the composition of naturally occurring microbial communities. We investigated the effect of nitrate ( ), ammonium ( ), and urea on microbial and phytoplankton community composition (cell abundances and 16S rRNA gene profiling) and functioning (photosynthetic activity, carbon fixation rates) in the oligotrophic waters of the North Pacific Ocean. All N substrates tested significantly stimulated phytoplankton growth and productivity. Urea resulted in the greatest (>300%) increases in chlorophyll a (<0.06 μg L−1 and ∼0.19 μg L−1 in the control and urea addition, respectively) and productivity (<0.4 μmol C L−1 d−1 and ∼1.4 μmol C L−1 d−1 in the control and ure...
Light and dark phosphate (PO 4 3-) uptake rates were investigated in the North Pacific Subtropica... more Light and dark phosphate (PO 4 3-) uptake rates were investigated in the North Pacific Subtropical Gyre (NPSG) and along a coastal to open ocean transect in the South Pacific Ocean. PO 4 3-uptake rates were consistently higher when incubated in the light, but the ratio of uptake in the light and dark (L:D) decreased with depth. In the NPSG, the L:D ratio of euphotic-layer integrated PO 4 3-uptake was 1.58 ± 0.08 (± SE, n = 15 profiles), and the average L:D ratio was 1.60 ± 0.45 (± SD, n = 42) between 5 and 45 m and 1.25 ± 0.70 (± SD, n = 28) between 150 and 175 m. The L:D ratio was higher for the pigmented plankton-enriched size fractions (0.6 to 2 µm and > 2 µm), but results were difficult to interpret at the oligotrophic stations where non-pigmented and pigmented plankton cell sizes overlapped. Group-specific measurements obtained using flow cytometric cell sorting demonstrated that Prochlorococcus PO 4 3-uptake rates were higher when the samples were incubated under ambient light. Adenosine-5′-triphosphate (ATP) uptake by Prochlorococcus was also higher in the light for the uptake of both the terminal PO 4 3-group ([γ-33 P]ATP) and adenine moiety ([2, 8-3 H]ATP). This could be the result of secondary uptake of PO 4 3-and/or adenine after ATP cleavage by non-pigmented picoplankton. There was no significant difference in P-assimilation by non-pigmented picoplankton between light and dark incubated samples. Light dependence of phytoplankton PO 4 3-uptake could thus influence the functioning of the microbial loop and the flows of matter and energy in marine environments by creating temporal patterns of resource utilization.
In 1976, John D. Isaacs proposed to use wave energy to pump cold and nutrient-rich deep water int... more In 1976, John D. Isaacs proposed to use wave energy to pump cold and nutrient-rich deep water into the sunlit surface layers. The motivation for this endeavor has taken many forms over the years, from energy production to fueling aquaculture to the more recent suggestion that artificial upwelling could be used to stimulate primary productivity and anthropogenic carbon sequestration in oligotrophic regions of the ocean. However, the potential for biological carbon sequestration in response to upwelling will depend on the ...
Several studies have demonstrated that Prochlorococcus , the most abundant photosynthetic organis... more Several studies have demonstrated that Prochlorococcus , the most abundant photosynthetic organism on Earth, can assimilate organic molecules, such as amino acids, amino sugars, ATP, phosphonates, and dimethylsulfoniopropionate. This autotroph can also assimilate small amounts of glucose, supporting the hypothesis that Prochlorococcus is mixotrophic.
A large-volume mesocosm-based nutrient perturbation experiment was conducted off the island of Ha... more A large-volume mesocosm-based nutrient perturbation experiment was conducted off the island of Hawai‘i, USA, to investigate the response of surface ocean phytoplankton communities to the addition of macronutrients, trace metals, and vitamins and to assess the feasibility of using mesocosms in the open ocean. Three free-drifting mesocosms (~60 m3) were deployed: one mesocosm served as a control (no nutrient amendments); a second (termed +P) was amended with nitrate (N), silicate (Si), phosphate (P), and a trace metal + vitamin mixture; and a third (termed -P) was amended with N, Si, and a trace metal + vitamin mixture but no P. These mesocosms were unreplicated due to logistical constraints and hence differences between treatments are qualitative. After 6 d, the largest response of the phytoplankton community was observed in the +P mesocosm, where chlorophyll a and 14C-based primary production were 2-3× greater than in the -P mesocosm and 4-6× greater than in the control. Comparison ...
A method is presented for the online measurement of methane in aquatic environments by applicatio... more A method is presented for the online measurement of methane in aquatic environments by application of membrane inlet mass spectrometry (MIMS). For this purpose, the underwater mass spectrometer Inspectr200-200 was applied. A simple and reliable volumetric calibration technique, based on the mixing of two end member concentrations, was used for the analysis of CH 4 by MIMS. To minimize interferences caused by the high water vapor content, permeating through the membrane inlet system into the vacuum section of the mass spectrometer, a cool-trap was designed. With the application of the cool-trap, the detection limit was lowered from 100 to 16 nmol/L CH 4. This allows for measurements of methane concentrations in surface and bottom waters of coastal areas and lakes. Furthermore, in case of membrane rupture, the cool-trap acts as a security system, avoiding total damage of the mass spectrometer by flushing it with water. The Inspectr200-200 was applied for studies of methane and carbon dioxide concentrations in coastal areas of the Baltic Sea and Lake Constance. The low detection limit and fast response time of the MIMS allowed a detailed investigation of methane concentrations in the vicinity of gas seepages. aAm Soc Mass
In the contemporary North Pacific subtropical gyre (NPSG) the extant microbial community is based... more In the contemporary North Pacific subtropical gyre (NPSG) the extant microbial community is based on prokaryotic cells with the cyanobacterium Prochlorococcus dominating the phototrophic component. ...
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Papers by Karin Björkman