Bishop James K. B.

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James K. B.

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  • Article
    Wintertime phytoplankton bloom in the subarctic Pacific supported by continental margin iron
    (American Geophysical Union, 2006-02-01) Lam, Phoebe J. ; Bishop, James K. B. ; Henning, Cara C. ; Marcus, Matthew A. ; Waychunas, Glenn A. ; Fung, Inez Y.
    Heightened biological activity was observed in February 1996 in the high-nutrient low-chlorophyll (HNLC) subarctic North Pacific Ocean, a region that is thought to be iron-limited. Here we provide evidence supporting the hypothesis that Ocean Station Papa (OSP) in the subarctic Pacific received a lateral supply of particulate iron from the continental margin off the Aleutian Islands in the winter, coincident with the observed biological bloom. Synchrotron X-ray analysis was used to describe the physical form, chemistry, and depth distributions of iron in size fractionated particulate matter samples. The analysis reveals that discrete micron-sized iron-rich hot spots are ubiquitous in the upper 200 m at OSP, more than 900 km from the closest coast. The specifics of the chemistry and depth profiles of the Fe hot spots trace them to the continental margins. We thus hypothesize that iron hot spots are a marker for the delivery of iron from the continental margin. We confirm the delivery of continental margin iron to the open ocean using an ocean general circulation model with an iron-like tracer source at the continental margin. We suggest that iron from the continental margin stimulated a wintertime phytoplankton bloom, partially relieving the HNLC condition.
  • Preprint
    High biomass, low export regimes in the Southern Ocean
    ( 2006-06-28) Lam, Phoebe J. ; Bishop, James K. B.
    This paper investigates ballasting and remineralization controls of carbon sedimentation in the twilight zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 μm, 1-51 μm, >51 μm) suspended particulate matter was collected by large volume in-situ filtration from the upper 1000 m in the Subantarctic (55°S, 172°W) and Antarctic (66°S, 172°W) zones of the Southern Ocean during the Southern Ocean Iron Experiment (SOFeX) in January-February 2002. Particles were analyzed for major chemical constituents (POC, P, biogenic Si, CaCO3), and digital and SEM image analyses of particles were used to aid in the interpretation of the chemical profiles. Twilight zone waters at 66°S in the Antarctic had a steeper decrease in POC with depth than at 55°S in the Subantarctic, with lower POC concentrations in all size fractions at 66°S than at 55°S, despite up to an order of magnitude higher POC in surface waters at 66°S. The decay length scale of >51 μm POC was significantly shorter in the upper twilight zone at 66°S (δe=26 m) compared to 55°S (δe=81 m). Particles in the carbonate-producing 55°S did not have higher excess densities than particles from the diatom-dominated 66°S, indicating that there was no direct ballast effect that accounted for deeper POC penetration at 55°S. An indirect ballast effect due to differences in particle packaging and porosities cannot be ruled out, however, as aggregate porosities were high (~97%) and variable. Image analyses point to the importance of particle loss rates from zooplankton grazing and remineralization as determining factors for the difference in twilight zone POC concentrations at 55°S and 66°S, with stronger and more focused shallow remineralization at 66°S. At 66°S, an abundance of large (several mm long) fecal pellets from the surface to 150 m, and almost total removal of large aggregates by 200 m, reflected the actions of a single or few zooplankton species capable of grazing diatoms in the euphotic zone, coupled with a more diverse particle feeding zooplankton community immediately below. Surface waters with high biomass levels and high proportion of biomass in the large size fraction were associated with low particle loading at depth, with all indications implying conditions of low export. The 66°S region exhibits this “High Biomass, Low Export” (HBLE) condition, with very high >51 μm POC concentrations at the surface (~2.1 μM POC), but low concentrations below 200 m (<0.07 μM POC). The 66°S region remained HBLE after iron fertilization. Iron addition at 55°S caused a ten fold increase in >51 μm biomass concentrations in the euphotic zone, bringing surface POC concentrations to levels found at 66°S (~3.8 μM), and a concurrent decrease in POC concentrations below 200 m. The 55°S region, which began with moderate levels of biomass and stronger particle export, transitioned to being HBLE after iron fertilization. We propose that iron addition to already HBLE waters will not cause mass sedimentation events. The stability of an iron-induced HBLE condition is unknown. Better understanding of biological pump processes in non-HBLE Subantarctic waters is needed.
  • Preprint
    VERTIGO (VERtical Transport In the Global Ocean) : a study of particle sources and flux attenuation in the North Pacific
    ( 2008-03-21) Buesseler, Ken O. ; Trull, Thomas W. ; Steinberg, Deborah K. ; Silver, Mary W. ; Siegel, David A. ; Saitoh, S.-I. ; Lamborg, Carl H. ; Lam, Phoebe J. ; Karl, David M. ; Jiao, N. Z. ; Honda, Makio C. ; Elskens, Marc ; Dehairs, Frank ; Brown, S. I. ; Boyd, Philip W. ; Bishop, James K. B. ; Bidigare, Robert R.
    The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and fluxes through the ocean’s “twilight zone” (defined here as depths below the euphotic zone to 1000 m). Interdisciplinary process studies were conducted at contrasting sites off Hawaii (ALOHA) and in the NW Pacific (K2) during 3 week occupations in 2004 and 2005, respectively. We examine in this overview paper the contrasting physical, chemical and biological settings and how these conditions impact the source characteristics of the sinking material and the transport efficiency through the twilight zone. A major finding in VERTIGO is the considerably lower transfer efficiency (Teff) of particulate organic carbon (POC), POC flux 500 / 150 m, at ALOHA (20%) vs. K2 (50%). This efficiency is higher in the diatom-dominated setting at K2 where silica-rich particles dominate the flux at the end of a diatom bloom, and where zooplankton and their pellets are larger. At K2, the drawdown of macronutrients is used to assess export and suggests that shallow remineralization above our 150 m trap is significant, especially for N relative to Si. We explore here also surface export ratios (POC flux/primary production) and possible reasons why this ratio is higher at K2, especially during the first trap deployment. When we compare the 500 m fluxes to deep moored traps, both sites lose about half of the sinking POC by >4000 m, but this comparison is limited in that fluxes at depth may have both a local and distant component. Certainly, the greatest difference in particle flux attenuation is in the mesopelagic, and we highlight other VERTIGO papers that provide a more detailed examination of the particle sources, flux and processes that attenuate the flux of sinking particles. Ultimately, we contend that at least three types of processes need to be considered: heterotrophic degradation of sinking particles, zooplankton migration and surface feeding, and lateral sources of suspended and sinking materials. We have evidence that all of these processes impacted the net attenuation of particle flux vs. depth measured in VERTIGO and would therefore need to be considered and quantified in order to understand the magnitude and efficiency of the ocean’s biological pump.
  • Article
    Revisiting carbon flux through the ocean's twilight zone
    (American Association for the Advancement of Science, 2007-04-27) Buesseler, Ken O. ; Lamborg, Carl H. ; Boyd, Philip W. ; Lam, Phoebe J. ; Trull, Thomas W. ; Bidigare, Robert R. ; Bishop, James K. B. ; Casciotti, Karen L. ; Dehairs, Frank ; Elskens, Marc ; Honda, Makio C. ; Karl, David M. ; Siegel, David A. ; Silver, Mary W. ; Steinberg, Deborah K. ; Valdes, James R. ; Van Mooy, Benjamin A. S. ; Wilson, Stephanie E.
  • Article
    Multiple sulfur isotope constraints on the modern sulfur cycle
    (Elsevier, 2014-04-16) Tostevin, Rosalie ; Turchyn, Alexandra V. ; Farquhar, James ; Johnston, David T. ; Eldridge, Daniel L. ; Bishop, James K. B. ; McIlvin, Matthew R.
    We present 28 multiple sulfur isotope measurements of seawater sulfate (δ34SSO4δ34SSO4 and Δ33SSO4Δ33SSO4) from the modern ocean over a range of water depths and sites along the eastern margin of the Pacific Ocean. The average measured δ34SSO4δ34SSO4 is 21.24‰ (±0.88‰,2σ±0.88‰,2σ) with a calculated Δ33SSO4Δ33SSO4 of +0.050‰+0.050‰ (±0.014‰,2σ±0.014‰,2σ). With these values, we use a box-model to place constraints on the gross fraction of pyrite burial in modern sediments. This model presents an improvement on previous estimates of the global pyrite burial flux because it does not rely on the assumed value of δ34Spyriteδ34Spyrite, which is poorly constrained, but instead uses new information about the relationship between δ34Sδ34S and δ33Sδ33S in global marine sulfate. Our calculations indicate that the pyrite burial flux from the modern ocean is between 10% and 45% of the total sulfur lost from the oceans, with a more probable range between 20% and 35%.
  • Article
    The continental margin is a key source of iron to the HNLC North Pacific Ocean
    (American Geophysical Union, 2008-04-09) Lam, Phoebe J. ; Bishop, James K. B.
    Here we show that labile particulate iron and manganese concentrations in the upper 500 m of the Western Subarctic Pacific, an iron-limited High Nutrient Low Chlorophyll (HNLC) region, have prominent subsurface maxima between 100–200 m, reaching 3 nM and 600 pM, respectively. The subsurface concentration maxima in particulate Fe are characterized by a more reduced oxidation state, suggesting a source from primary volcagenic minerals such as from the Kuril/Kamchatka margin. The systematics of these profiles suggest a consistently strong lateral advection of labile Mn and Fe from redox-mobilized labile sources at the continental shelf supplemented by a more variable source of Fe from the upper continental slope. This subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing, and is likely a key source of bioavailable Fe to the HNLC North Pacific.
  • Preprint
    Barium in twilight zone suspended matter as a potential proxy for particulate organic carbon remineralization : results for the North Pacific
    ( 2008-01-22) Dehairs, Frank ; Jacquet, Stéphanie H. M. ; Savoye, Nicolas ; Van Mooy, Benjamin A. S. ; Buesseler, Ken O. ; Bishop, James K. B. ; Lamborg, Carl H. ; Elskens, Marc ; Baeyens, W. ; Boyd, Philip W. ; Casciotti, Karen L. ; Monnin, Christophe
    This study focuses on the fate of exported organic carbon in the twilight zone at two contrasting environments in the North Pacific: the oligotrophic ALOHA site (22°45' N 158°W; Hawaii; studied during June–July 2004) and the mesotrophic Subarctic Pacific K2 site (47°N, 161°W; studied during July-August 2005). Earlier work has shown that non-lithogenic, excess particulate Ba (Baxs) in the mesopelagic water column is a potential proxy of organic carbon remineralization. In general Baxs contents were significantly larger at K2 than at ALOHA. At ALOHA the Baxs profiles from repeated sampling (5 casts) showed remarkable consistency over a period of three weeks, suggesting that the system was close to being at steady state. In contrast, more variability was observed at K2 (6 casts sampled) reflecting the more dynamic physical and biological conditions prevailing in this environment. While for both sites Baxs concentrations increased with depth, at K2 a clear maximum was present between the base of the mixed layer at around 50m and 500m, reflecting production and release of Baxs. Larger mesopelagic Baxs contents and larger bacterial production in the twilight zone at the K2 site indicate that more material was exported from the upper mixed layer for bacterial degradation deeper, compared to the ALOHA site. Furthermore, application of a published transfer function (Dehairs et al., 1997) relating oxygen consumption to the observed Baxs data indicated that the latter were in good agreement with bacterial respiration, calculated from bacterial production. These results corroborate earlier findings highlighting the potential of Baxs as a proxy for organic carbon remineralization. The range of POC remineralization rates calculated from twilight zone excess particulate Ba contents did also compare well with the depth dependent POC flux decrease as recorded by neutrally buoyant sediment traps, except in 1 case (out of 4). This discrepancy could indicate that differences in sinking velocities cause an 3 uncoupling of the processes occurring in the fine suspended particle pool from those affecting the larger particle pool which sustains the vertical flux, thus rendering comparison between both approaches risky.
  • Thesis
    The chemistry, biology, and vertical flux of oceanic particulate matter
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1977-01) Bishop, James K. B.
    Particulate matter samples, split into 53 μm size fractions have been obtained using a Large Volume in situ Filtration System (LVFS) during the SOUTHLANT expedition, R/V CHAIN 115. Profiles to 400 m are reported for LVFS Stns. 2 and 4-8. Stns. 4, 5, and 8 (S. E. Atlantic, coastal waters near Walvis Bay and Cape Town, high biological productivity); Stns. 6 and 2 (S.E. Atlantic, Walvis Bay region and equatorial Atlantic, moderate productivity); and Sta. 7 (S.E. Atlantic, edge of central gyre, low productivity) formed a suite of samples for the study of the chemical, biological, morpholigical distributions and of the vertical mass flux of particulate matter as a function of biological productivity. All samples were analysed for Na, K, Mg, Ca, carbonate, opal, Sr, C and N and those from Sta. 2 were further analysed for P, Fe, δ13C, 7Be, 214Bi, 214Pb, (226Ra), 210Po, and 210Pb. Biological distributions of Acantharia, dinoflagellates, coccolithophorids, Foraminifera, diatoms, silicoflagellates, Radiolaria, and tintinnids were made by light microscopy (LM) and augmented by scanning electron microscopy (SEM). Size and morphological distributions of the >53 μm particles, especially Foraminifera, Acantharia, fecal pellets, and fecal matter have been determined by LM and SEM. The particle distributions were controlled at all stations by processes of production, consumption, fragmentation, and aggregation. Maxima in organism abundance and particulate mass were generally coincident. They were found nearest the surface when the mixed layer was absent or poorly developed, and at the base of the mixed layer at the other stations. Organism vertical distributions showed consistent features: Acantharia, and dinoflagellates were always nearest the surface; Foraminifera and diatoms were shallower than or at the base of the mixed layer; Radiolaria and tintinnids were found in the upper thermocline. Coccolithophorids and diatoms were the dominant sources of particulate carbonate and opal in the near surface waters, coccoliths and diatom fragments, deeper. Features of the distributions of particulate matter attributed to the feeding activities of zooplankton were: strong concentration gradients in organisms, mass, and organic matter; enrichment of the >53 μm fraction with coccoliths causing the steady decrease in >53 μm Si/carbonate ratio with depth from values as high as 45 to values near 1.0 at 400 m; the decrease in organic content with depth from values near 100 % near the surface to 50 and 60% at 400 m for the <53 and >53 μm size fractions; the fragmentation of most material below 100 m; and the production of fecal pellets and fecal matter which are carriers of fine material to the sea floor. Other features were: the nearly constant organic C/N ratios (7.3±0.5 δ) found for the 1-53 μm fractions at Stns. 4, 5, 6, and 8 compared with the steady increase observed at Stns. 2 and 7 with depth; particulate carbon was rather uniformy distributed below 200 m with concentrations showing a mild reflection of surface productivity; the <1 μC/N and δ13C values are lower and lighter than the 1-53 μm fraction, perhaps indicative of the presence of marine bacteria; the Ca/carbonate ratios in most samples significantly exceeded 1.0, values as high as 2.5 were observed at Sta. 8; the xs Ca and K have shallow regenerative cycles and contrast with Mg which is bound to a refractory component of organic matter; based on a organic C/ xs Ca ratio of 100-200:1 for surfàce samples, the cycling of xs Ca was calculated to be 1-2 x 1013mol/cm2/y compared with the production of carbonate, 7±2 x 1013 mol/cm2/y. Chemical effects noted were: organic matter had both binding capabilities and ion-exchange capacity for major and minor ions present in seawater. Acantharia (SrS04) dissolve most significantly below 200 m at Sta.2. The vertical mass fluxes through 400 m at Stas. 2, 5, 6, and 7 were calculated from size distributions measured in 1 m3 in seawater for Foramifera, fecal pellets, and fecal matter. Two flux models were used together with Junge distributions for these calculations. Fecal matter and Forainifera transported most mass at Stns. 2 and 5 where the fluxes were between 2 and 3, and 5 and 6 gm/cm2/1000y respectively; fècal matter, Foramnifera, and fecal pellets contributed equally to the .9-1.3gm/cm2/1000y flux at Sta. 6; and fecal pellets and Foraminifera were the carriers of 0.1-0.3 gm/cm2/1000y to the sea floor. Corresponding chemical fluxes of organic carbon, carbonate, and opal were: 80-90, 11-24, and ~10 mmol/cm2/1000y at Sta. 5; 15-20, 2.7-5.0 and 1.7-2.5 mmol/cm2/1000y at Sta. 6; 1-4, 0.6-1.5, and 0.1-0.3 mmol/cm2/1000y at Sta. 7, and 40-65, 4.6-7.4, and 4.9-7.9 mmol/cm2/1000y at station 2. Over 90% of the organic matter produced in the euphotic zone is recycled in the upper 400 m. The efficiency is nearly 99% in areas of low productivity; the organic to carbonate carbon ratios are highest at locations where the flux is greatest as are the Si/carbonate ratios. Besides carbonate, opal, celestite, and other mineral phases, organic matter may be a significant carrier of minor and trace elements to the deep ocean.