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• 1. [Article] Iron, nutrient, and phytoplankton distributions in Oregon coastal waters

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Iron, nutrient, and phytoplankton distributions in Oregon coastal waters Author: Wheeler, Patricia A., Chase, Zanna, Marra, John, van Geen, Alexander, Kosro, P. Michael, 1951- Copyrighted by American Geophysical Union. Title: Iron, nutrient, and phytoplankton distributions in Oregon coastal waters Author: Wheeler, Patricia A., Chase, Zanna, Marra, John, van Geen, Alexander, Kosro, P. Michael, 1951- Copyrighted by American Geophysical Union. Close

• 2. [Article] Anthropogenic CO₂ invasion into the northeast Pacific based on concurrent δ¹³CDIC and nutrient profiles from the California Current

  The stable isotopic signature of dissolved inorganic carbon (δ¹³CDIC) in the northeast Pacific Ocean is lower in near-surface waters by 1.1‰ relative to values predicted from global oceanic trends of ...

  Citation × Citation Citation Abstract Copy Title: Anthropogenic CO₂ invasion into the northeast Pacific based on concurrent δ¹³CDIC and nutrient profiles from the California Current Author: Wheeler, Patricia A., Key, R. M., Mix, Alan C., Ortiz, Joseph D. The stable isotopic signature of dissolved inorganic carbon (δ¹³CDIC) in the northeast Pacific Ocean is lower in near-surface waters by 1.1‰ relative to values predicted from global oceanic trends of δ¹³CDIC versus nutrients. A combination of anthropogenic carbon uptake from the atmosphere and thermodynamic, air-sea gas exchange processes in different water mass source areas account for the isotopic depletion. Here we evaluate the efficacy of using a concurrent nutrient-δ¹³C strategy to separate these two effects, with the goal of improving estimates of anthropogenic carbon uptake over the course of the Industrial Revolution. In depth profiles from the sea surface to 2500 m at four stations across the California Current (42ºN), nitrate, rather than phosphate, is best correlated to δ¹³CDIC providing the best choice for this experiment. On the basis of an assumption of no anthropogenic carbon in North Pacific Deep Waters between 1000–2500 m depth (potential densities, σθ ~ 27.3–27.7), the “anthropogenic – preanthropogenic” carbon isotope shift (∆δ¹³Ca–p) in near-surface waters of the northeast Pacific is inferred to be -0.62 ± 0.17‰, while the thermodynamic air-sea gas exchange signature is estimated at -0.48 ± 0.17‰. Values of ∆δ¹³Ca–p (similar to the regional patterns of ∆¹4C and Tritium penetration) approach zero for σθ > 26.8, indicating little penetration of anthropogenic carbon into the North pacific Intermediate Water or the upper North pacific Deep Water. Our results suggest an upper North Pacific sink of anthropogenic carbon over the past ~200 years that is ~40% greater than that estimated for the interval between ~1970 and ~1990 by Quay et al. [1992]. Our estimate of the North Pacific inventory of anthropogenic carbon, added to published estimates from the North Atlantic and Indian Ocean, is smaller than model predictions of the total carbon sink, suggesting that a significant portion of anthropogenic carbon enters the deep sea via the Southern Ocean. Title: Anthropogenic CO₂ invasion into the northeast Pacific based on concurrent δ¹³CDIC and nutrient profiles from the California Current Author: Wheeler, Patricia A., Key, R. M., Mix, Alan C., Ortiz, Joseph D. The stable isotopic signature of dissolved inorganic carbon (δ¹³CDIC) in the northeast Pacific Ocean is lower in near-surface waters by 1.1‰ relative to values predicted from global oceanic trends of δ¹³CDIC versus nutrients. A combination of anthropogenic carbon uptake from the atmosphere and thermodynamic, air-sea gas exchange processes in different water mass source areas account for the isotopic depletion. Here we evaluate the efficacy of using a concurrent nutrient-δ¹³C strategy to separate these two effects, with the goal of improving estimates of anthropogenic carbon uptake over the course of the Industrial Revolution. In depth profiles from the sea surface to 2500 m at four stations across the California Current (42ºN), nitrate, rather than phosphate, is best correlated to δ¹³CDIC providing the best choice for this experiment. On the basis of an assumption of no anthropogenic carbon in North Pacific Deep Waters between 1000–2500 m depth (potential densities, σθ ~ 27.3–27.7), the “anthropogenic – preanthropogenic” carbon isotope shift (∆δ¹³Ca–p) in near-surface waters of the northeast Pacific is inferred to be -0.62 ± 0.17‰, while the thermodynamic air-sea gas exchange signature is estimated at -0.48 ± 0.17‰. Values of ∆δ¹³Ca–p (similar to the regional patterns of ∆¹4C and Tritium penetration) approach zero for σθ > 26.8, indicating little penetration of anthropogenic carbon into the North pacific Intermediate Water or the upper North pacific Deep Water. Our results suggest an upper North Pacific sink of anthropogenic carbon over the past ~200 years that is ~40% greater than that estimated for the interval between ~1970 and ~1990 by Quay et al. [1992]. Our estimate of the North Pacific inventory of anthropogenic carbon, added to published estimates from the North Atlantic and Indian Ocean, is smaller than model predictions of the total carbon sink, suggesting that a significant portion of anthropogenic carbon enters the deep sea via the Southern Ocean. Close

• 3. [Article] Cold halocline, increased nutrients and higher chlorophyll off Oregon in 2002

  Observed changes in the nutrient levels in the halocline of the California Current during 2002 indicated a natural eutrophication that was accompanied by increased chlorophyll and oxygen in surface water. ...

  Citation × Citation Citation Abstract Copy Title: Cold halocline, increased nutrients and higher chlorophyll off Oregon in 2002 Author: Wheeler, Patricia A., Huyer, Adriana, 1945-, Fleischbein, Jane Observed changes in the nutrient levels in the halocline of the California Current during 2002 indicated a natural eutrophication that was accompanied by increased chlorophyll and oxygen in surface water. Decreased oxygen in the lower water column over the shelf indicated that much of the phytoplankton production was respired rather than passed on to higher trophic levels. In 2002 the halocline water was >1ºC colder than usual and 0.5ºC colder than any previous observation. Four transect lines off the coast of Oregon show a 50% increase in nitrate, phosphate and silicate at 33 psu in 2002 compared to 1998–2001. The increase in nutrients resulted in a 2-fold increase in chlorophyll standing stocks during the summer of 2002 compared with the preceding four years. A significant portion of the increased production was subsequently respired resulting in low oxygen water over the shelf. Title: Cold halocline, increased nutrients and higher chlorophyll off Oregon in 2002 Author: Wheeler, Patricia A., Huyer, Adriana, 1945-, Fleischbein, Jane Observed changes in the nutrient levels in the halocline of the California Current during 2002 indicated a natural eutrophication that was accompanied by increased chlorophyll and oxygen in surface water. Decreased oxygen in the lower water column over the shelf indicated that much of the phytoplankton production was respired rather than passed on to higher trophic levels. In 2002 the halocline water was >1ºC colder than usual and 0.5ºC colder than any previous observation. Four transect lines off the coast of Oregon show a 50% increase in nitrate, phosphate and silicate at 33 psu in 2002 compared to 1998–2001. The increase in nutrients resulted in a 2-fold increase in chlorophyll standing stocks during the summer of 2002 compared with the preceding four years. A significant portion of the increased production was subsequently respired resulting in low oxygen water over the shelf. Close

• 4. [Article] Diel periodicity in ammonium uptake and regeneration in the oceanic subarctic Pacific: Implications for interactions in microbial food webs

  Diel periodicity in NH4+ uptake and regeneration in the nutrient-rich environment of the oceanic subarctic Pacific was examined. Surface water was incubated in large shipboard microcosms that allowed repeated ...

  Citation × Citation Citation Abstract Copy Title: Diel periodicity in ammonium uptake and regeneration in the oceanic subarctic Pacific: Implications for interactions in microbial food webs Author: Kokkinakis, Steven A., Wheeler, Patricia A., Kirchman, David L., Landry, Michael R. Diel periodicity in NH4+ uptake and regeneration in the nutrient-rich environment of the oceanic subarctic Pacific was examined. Surface water was incubated in large shipboard microcosms that allowed repeated sampling of the planktonic community for NH4+ cycling rates, bacterial production rates, and population densities of the dominant autotrophs and heterotrophs. Changes in NH4+ concentrations and isotopic enrichments indicated that regeneration took place exclusively at night. Nitrogen uptake rates and bacterial production were maximal during the day. Abundance of <2 μm autotrophic flagellates reached a maximum at the end of day or beginning of night, whereas abundance of zooflagellates in the <2 μm and 1–10 μm size classes showed a twofold variation with maximal abundances occurring at the beginning of day. These contrasting diel patterns suggest short-term, cyclic disequilibrium in production and grazing within the microbial food web. Hence, analysis of relationships among the various components of microbial populations in this type of environment will require sampling on much shorter time scales than has been attempted in past studies. Title: Diel periodicity in ammonium uptake and regeneration in the oceanic subarctic Pacific: Implications for interactions in microbial food webs Author: Kokkinakis, Steven A., Wheeler, Patricia A., Kirchman, David L., Landry, Michael R. Diel periodicity in NH4+ uptake and regeneration in the nutrient-rich environment of the oceanic subarctic Pacific was examined. Surface water was incubated in large shipboard microcosms that allowed repeated sampling of the planktonic community for NH4+ cycling rates, bacterial production rates, and population densities of the dominant autotrophs and heterotrophs. Changes in NH4+ concentrations and isotopic enrichments indicated that regeneration took place exclusively at night. Nitrogen uptake rates and bacterial production were maximal during the day. Abundance of <2 μm autotrophic flagellates reached a maximum at the end of day or beginning of night, whereas abundance of zooflagellates in the <2 μm and 1–10 μm size classes showed a twofold variation with maximal abundances occurring at the beginning of day. These contrasting diel patterns suggest short-term, cyclic disequilibrium in production and grazing within the microbial food web. Hence, analysis of relationships among the various components of microbial populations in this type of environment will require sampling on much shorter time scales than has been attempted in past studies. Close

• 5. [Article] Ammonium recycling limits nitrate use in the oceanic subarctic Pacific

  Seasonal and diel changes in nutrient concentrations and nitrogen assimilation rates were used to assess the effects of NH4+ on NO3- assimilation. Surface-water NO3- concentrations ranged from 6 to 17 ...

  Citation × Citation Citation Abstract Copy Title: Ammonium recycling limits nitrate use in the oceanic subarctic Pacific Author: Kokkinakis, Steven A., Wheeler, Patricia A. Seasonal and diel changes in nutrient concentrations and nitrogen assimilation rates were used to assess the effects of NH4+ on NO3- assimilation. Surface-water NO3- concentrations ranged from 6 to 17 μM while NH4+ concentrations ranged from 0 to 0.4 μM. Total N assimilation ranged from 84 to 732 nM d–1 but showed no seasonal trend. NH4+ and urea concentrations were < 1% of total dissolved inorganic N, but use of this “regenerated” N still accounted for 44–89% of total N assimilation. Rates of NO3- assimilation were negatively correlated with ambient NH4+ concentrations, and concentrations of NH4+ between 0.1 and 0.3 μM caused complete inhibition of NO3- assimilation. NO3- was more important as a source of N in spring than in summer. We attribute this pattern to a summer increase in turnover rates for NH4+. Turnover times for the dissolved NH4+ pool were half as long in August as in May. Grazing and recycling in the euphotic zone apparently both play significant roles in preventing depletion of NO3- in the oceanic subarctic Pacific. Title: Ammonium recycling limits nitrate use in the oceanic subarctic Pacific Author: Kokkinakis, Steven A., Wheeler, Patricia A. Seasonal and diel changes in nutrient concentrations and nitrogen assimilation rates were used to assess the effects of NH4+ on NO3- assimilation. Surface-water NO3- concentrations ranged from 6 to 17 μM while NH4+ concentrations ranged from 0 to 0.4 μM. Total N assimilation ranged from 84 to 732 nM d–1 but showed no seasonal trend. NH4+ and urea concentrations were < 1% of total dissolved inorganic N, but use of this “regenerated” N still accounted for 44–89% of total N assimilation. Rates of NO3- assimilation were negatively correlated with ambient NH4+ concentrations, and concentrations of NH4+ between 0.1 and 0.3 μM caused complete inhibition of NO3- assimilation. NO3- was more important as a source of N in spring than in summer. We attribute this pattern to a summer increase in turnover rates for NH4+. Turnover times for the dissolved NH4+ pool were half as long in August as in May. Grazing and recycling in the euphotic zone apparently both play significant roles in preventing depletion of NO3- in the oceanic subarctic Pacific. Close

• 6. [Article] Light-induced growth of phytoplankton collected during the winter from the benthic boundary layer off Oregon, USA

  Despite the importance of the spring phytoplankton bloom off Oregon as a food source for zooplankton, little is known about the sources of phytoplankton seed stock for the bloom or its timing. Experiments ...

  Citation × Citation Citation Abstract Copy Title: Light-induced growth of phytoplankton collected during the winter from the benthic boundary layer off Oregon, USA Author: Wheeler, Patricia A., Letelier, Ricardo M., Wetz, Michael S. Despite the importance of the spring phytoplankton bloom off Oregon as a food source for zooplankton, little is known about the sources of phytoplankton seed stock for the bloom or its timing. Experiments were conducted in the late winter to determine if the benthic boundary layer (BBL) could be a source of viable phytoplankton and to determine to what extent their growth was limited by light. Water collected on 3 dates from the BBL over the inner-shelf and mid-shelf in January 2003 was used for growth experiments run in shipboard incubators held at 10°C. The water was exposed to in situ nutrient concentrations and to 4 light levels and 2 daylengths (9 and 12 h), representative of winter and spring daylengths. Significant increases in chl a and particulate organic matter (POM) were observed in high light and medium light treatments at both daylengths. Chl a increased minimally (≤0.3 μg l–1) in the low light treatments, while no significant increase in POM occurred. Chl a decreased in the control (no light) treatment throughout the experiments. Blooms that developed during these incubations were dominated by Thalassiosira spp., Actinopytchus sp., Asterionellopsis glacialis and other diatoms, consistent with in situ phytoplankton community composition during the spring. Growth occurred at light levels that were generally 40 to 50% of that measured in surface waters in January, suggesting that light levels at the surface are conducive to growth, but that mixing prevents significant growth during the winter. Title: Light-induced growth of phytoplankton collected during the winter from the benthic boundary layer off Oregon, USA Author: Wheeler, Patricia A., Letelier, Ricardo M., Wetz, Michael S. Despite the importance of the spring phytoplankton bloom off Oregon as a food source for zooplankton, little is known about the sources of phytoplankton seed stock for the bloom or its timing. Experiments were conducted in the late winter to determine if the benthic boundary layer (BBL) could be a source of viable phytoplankton and to determine to what extent their growth was limited by light. Water collected on 3 dates from the BBL over the inner-shelf and mid-shelf in January 2003 was used for growth experiments run in shipboard incubators held at 10°C. The water was exposed to in situ nutrient concentrations and to 4 light levels and 2 daylengths (9 and 12 h), representative of winter and spring daylengths. Significant increases in chl a and particulate organic matter (POM) were observed in high light and medium light treatments at both daylengths. Chl a increased minimally (≤0.3 μg l–1) in the low light treatments, while no significant increase in POM occurred. Chl a decreased in the control (no light) treatment throughout the experiments. Blooms that developed during these incubations were dominated by Thalassiosira spp., Actinopytchus sp., Asterionellopsis glacialis and other diatoms, consistent with in situ phytoplankton community composition during the spring. Growth occurred at light levels that were generally 40 to 50% of that measured in surface waters in January, suggesting that light levels at the surface are conducive to growth, but that mixing prevents significant growth during the winter. Close

• 7. [Article] Uptake of ammonium and urea in the northeast Pacific: comparison between netplankton and nanoplankton

  The stable isotope 15N was used to measure nitrogen uptake in the coastal upwelling region off Oregon and Washington, USA, where nitrate concentrations in the surface water ranged from 0.7 to 49.1 μM. ...

  Citation × Citation Citation Abstract Copy Title: Uptake of ammonium and urea in the northeast Pacific: comparison between netplankton and nanoplankton Author: Kokkinakis, Steven A., Wheeler, Patricia A. The stable isotope 15N was used to measure nitrogen uptake in the coastal upwelling region off Oregon and Washington, USA, where nitrate concentrations in the surface water ranged from 0.7 to 49.1 μM. Nanoplankton biomass (1 to 10 pm) was relatively more abundant at low-nitrate stations, while netplankton biomass (10 to 200 μm) was dominant at high-nitrate stations. Ammonium was more important than urea as a regenerated nitrogen source for both size classes of plankton, and ambient ammonium concentrations appeared to inhibit urea assimilation. Nanoplankton and netplankton were equally important in use of regenerated nitrogen in low-nitrate waters, while netplankton dominated nitrogen use in high-nitrate waters. In high-nitrate waters, the percent uptake in each size fraction was proportional to the percent particulate nitrogen (PN) and chlorophyll a (chl a) in that fraction. At low-nitrate stations, uptake in each fraction was proportional to PN but not to chl a. Nitrogen-specific (mass N taken up/mass particulate N) uptake rates ranged from 0.2 to 2.6 d-l, and were generally higher for the netplankton than for the nanoplankton fraction. However, these rates are not directly proportional to phytoplankton use as a result of varying amounts of non-phytoplankton N. Phytoplankton N was estimated by assuming a constant chl a/PN ratio for each size class, and used to calculate phytoplankton-specific uptake rates. Phytoplankton growth rates were estimated by extrapolating the short-term uptake rates to daily rates. Since calculated growth rates exceeded the expected maxima for phytoplankton In the low-nitrate coastal water, we postulate heterotrophic utilization of nitrogen. Title: Uptake of ammonium and urea in the northeast Pacific: comparison between netplankton and nanoplankton Author: Kokkinakis, Steven A., Wheeler, Patricia A. The stable isotope 15N was used to measure nitrogen uptake in the coastal upwelling region off Oregon and Washington, USA, where nitrate concentrations in the surface water ranged from 0.7 to 49.1 μM. Nanoplankton biomass (1 to 10 pm) was relatively more abundant at low-nitrate stations, while netplankton biomass (10 to 200 μm) was dominant at high-nitrate stations. Ammonium was more important than urea as a regenerated nitrogen source for both size classes of plankton, and ambient ammonium concentrations appeared to inhibit urea assimilation. Nanoplankton and netplankton were equally important in use of regenerated nitrogen in low-nitrate waters, while netplankton dominated nitrogen use in high-nitrate waters. In high-nitrate waters, the percent uptake in each size fraction was proportional to the percent particulate nitrogen (PN) and chlorophyll a (chl a) in that fraction. At low-nitrate stations, uptake in each fraction was proportional to PN but not to chl a. Nitrogen-specific (mass N taken up/mass particulate N) uptake rates ranged from 0.2 to 2.6 d-l, and were generally higher for the netplankton than for the nanoplankton fraction. However, these rates are not directly proportional to phytoplankton use as a result of varying amounts of non-phytoplankton N. Phytoplankton N was estimated by assuming a constant chl a/PN ratio for each size class, and used to calculate phytoplankton-specific uptake rates. Phytoplankton growth rates were estimated by extrapolating the short-term uptake rates to daily rates. Since calculated growth rates exceeded the expected maxima for phytoplankton In the low-nitrate coastal water, we postulate heterotrophic utilization of nitrogen. Close

• 8. [Article] Oxygen production and carbon sequestration in an upwelling coastal margin

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Oxygen production and carbon sequestration in an upwelling coastal margin Author: Wheeler, Patricia A., Perlin, Alexander, Hales, Burke, Karp-Boss, Lee Copyrighted by American Geophysical Union. Title: Oxygen production and carbon sequestration in an upwelling coastal margin Author: Wheeler, Patricia A., Perlin, Alexander, Hales, Burke, Karp-Boss, Lee Copyrighted by American Geophysical Union. Close

• 9. [Article] Ecological dynamics in the subarctic Pacific, a possibly iron-limited ecosystem

  It has been suggested that production in offshore waters of the subarctic Pacific is limited by availability of dissolved Fe. Although that is not yet adequately established, the functional consequences ...

  Citation × Citation Citation Abstract Copy Title: Ecological dynamics in the subarctic Pacific, a possibly iron-limited ecosystem Author: Wheeler, Patricia A., Powell, Thomas M., Welschmeyer, Nicholas, Landry, Michael R., Miller, Charles B., Frost, Bruce W. It has been suggested that production in offshore waters of the subarctic Pacific is limited by availability of dissolved Fe. Although that is not yet adequately established, the functional consequences of the limitation (if it exists) can be characterized from the results of the Subarctic Pacific Ecosystem Research (SUPER) program. Fe limitation, or something like it, establishes a phytoplankton community dominated by very small cells. These plants are not limited by Fe availability. Rather, their production is limited by their stock and available illumination. Stock is set by microzooplankton grazers with rapid population growth rates and, thus, rapid response to increases in phytoplankton abundance. Micrograzers provide efficient recycling of nitrogen as NH4, and the ready availability of NH4 sharply limits the annual utilization of NO3. Persistently high NO3 concentrations result. Other possibly Fe-limited, oceanic ecosystems with persistently high, near surface nutrients require similar, detailed analysis of ecosystem function. Title: Ecological dynamics in the subarctic Pacific, a possibly iron-limited ecosystem Author: Wheeler, Patricia A., Powell, Thomas M., Welschmeyer, Nicholas, Landry, Michael R., Miller, Charles B., Frost, Bruce W. It has been suggested that production in offshore waters of the subarctic Pacific is limited by availability of dissolved Fe. Although that is not yet adequately established, the functional consequences of the limitation (if it exists) can be characterized from the results of the Subarctic Pacific Ecosystem Research (SUPER) program. Fe limitation, or something like it, establishes a phytoplankton community dominated by very small cells. These plants are not limited by Fe availability. Rather, their production is limited by their stock and available illumination. Stock is set by microzooplankton grazers with rapid population growth rates and, thus, rapid response to increases in phytoplankton abundance. Micrograzers provide efficient recycling of nitrogen as NH4, and the ready availability of NH4 sharply limits the annual utilization of NO3. Persistently high NO3 concentrations result. Other possibly Fe-limited, oceanic ecosystems with persistently high, near surface nutrients require similar, detailed analysis of ecosystem function. Close

• 10. [Article] Riverine input of macronutrients, iron, and organic matter to the coastal ocean off Oregon, U.S.A., during the winter

  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 ...

  Citation × Citation Citation Abstract Copy Title: Riverine input of macronutrients, iron, and organic matter to the coastal ocean off Oregon, U.S.A., during the winter Author: Wheeler, Patricia A., Hales, Burke, Whitney, Michael M., Chase, Zanna, Wetz, Michael S. 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. Title: Riverine input of macronutrients, iron, and organic matter to the coastal ocean off Oregon, U.S.A., during the winter Author: Wheeler, Patricia A., Hales, Burke, Whitney, Michael M., Chase, Zanna, Wetz, Michael S. 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. Close