Plankton copper requirements and uptake in the subarctic Northeast Pacific Ocean

We undertook the first measurements of metabolic Cu requirements (net Cu:C assimilation ratios) and steady-state Cu uptake rates (ρCu_ss) of natural plankton assemblages in the northeast subarctic Pacific using the short-lived radioisotope ⁶⁷Cu. Size-fractionated net Cu:C assimilation ratios varied ～3 fold (1.35–4.21 μmol Cu mol C^?1) among the stations along Line P, from high Fe coastal waters to the Fe-limited open ocean. The variability in Cu:C was comparable to biogenic Fe:C ratios in this region. As previously observed for Fe uptake, the bacterial size class accounted for half of the total particulate ρCu_ss. Interestingly, carbon biomass-normalized rates of Fe uptake from the siderophore desferrioxamine B (DFB) (ρFe_DFB; a physiological proxy for Fe-limitation) by the >20 μm size class were positively correlated with the intracellular net Cu:C assimilation ratios in this size class, suggesting that intracellular Cu requirements for large phytoplankton respond to increased Fe-limitation. At Fe-limited Ocean Station Papa (OSP), we performed short-term Cu uptake (ρCu_L) assays to determine the relative bioavailability of Cu bound to natural and synthetic ligands. Like the volumetric ρCu_ss measured along Line P, the bacterial size class was responsible for at least 50% of the total ρCu_L. Uptake rates of Cu from the various organic complexes suggest that Cu uptake was controlled by the oxidation state of the metal and by the metal:ligand concentration ratio, rather than the concentration of inorganic species of Cu in solution. Collectively, these data suggest that Cu likely plays an important role in the physiology of natural plankton communities beyond the toxicological effects studied previously.     

Distribution of particulate organic carbon and nitrogen in the Bering Sea and northern North Pacific Ocean

Particulate matter was collected in the Bering Sea and the northern North Pacific Ocean during the cruise of R. V. Hakuho-maru, Ocean Research Institute of Tokyo University in summer of 1975. The particulate matter was analyzed for organic carbon and nitrogen, chlorophylla and amino acids.The concentrations of particulate organic carbon and nitrogen were measured with the range of 16–422gC l^–1 and 1–85gN l^–1, 19–186gC l^–1 and 1–26gN l^–1, 46–1,038gC l^–1 and 6–79gN l^–1 and 19–246gC l^–1 and 2–25gN l^–1 in the Oyashio, the Deep Bering Sea, the continental shelf of Bering Sea and the northern North Pacific, respectively. Particulate organic carbon and nitrogen decreased with depth throughout the areas. The average concentrations of organic carbon and nitrogen in the entire water column tended to decrease in the following order; the continental shelf > Oyashio > northern North Pacific > Deep Bering Sea.C/N of particulate matter varied in the range of 3–15 (7 on average) in surface waters throughout the areas and these values tended to increase with depth to 5–20 (11 on average) in deep waters without significant regional variability.Linear regressions between chlorophylla and particulate organic carbon in the euphotic layers indicate that detrital organic carbon accounted for 34.2, 44.9, 49.1 and 25.2 % of particulate organic carbon in the Oyashio, the Deep Bering Sea, the continental shelf and the northern North Pacific, respectively.Particulate amino acid was determined in the range of 10.3–78.0g l^–1, 104–156g l^–1 and 10.4–96.4g l^–1 in the Deep Bering Sea, the continental shelf and the northern North Pacific, respectively. Aspartic acid, glutamic acid, serine, glycine and alanine were found as dominant species of amino acid of particulate matter.     

Silver in the subarctic northeast Pacific Ocean: Explaining the basin scale distribution of silver

Five vertical profiles of silver (Ag) in the subarctic northeast Pacific are presented. Dissolved (< 0.2 μm) Ag concentrations within the surface mixed layer range from 6–25 pM, with the highest observed values at the most coastal site. Elevated Ag concentrations at this station are most likely attributable to the estuarine circulation in the Juan de Fuca Strait. One open-ocean station (P20) exhibited a strong surface Ag maximum. The station was located at the edge of a Haida eddy which raises the possibility that such eddies transport Ag seaward from the coastal zone. Ag concentrations in the deep waters ranged from 60–80 pM. These measurements are consistent with other recent Ag data collected in the Pacific. Ag profiles throughout the Pacific Ocean yield a strong positive correlation between Ag concentration and dissolved silicic acid concentration. However, Ag is depleted relative to silicic acid at intermediate depths where dissolved O₂ concentrations are low, implying a possible removal of Ag from oxygen-depleted waters by scavenging and/or precipitation.     

Cadmium and zinc concentrations in zooplankton in the subarctic region of the North Pacific

Cadmium and zinc concentrations were determined in 10 species of pelagic zooplankton collected in the northern North Pacific, the Bering Sea, the Okhotsk Sea and off Hokkaid?, during the summers of 1974–1976. The mean cadmium contents in euphausiids, copepods, and amphipods were 1.16μg/g dry wt (range: 0.36–2.17μg/g), 6.63μg/g (1.66–14.55μg/g), and 8.28μg/g (2.83–14.50μg/g), respectively. Cadmium in euphausiids was significantly lower in concentration than in the other two crustacean groups. The difference in cadmium levels among the crustacean groups is discussed on the basis of feeding habits and physiological characteristics of the zooplankton. Zinc levels in the crustaceans were similar, with values around 100μg/g (range: 59–195μg/g). Both cadmium and zinc concentrations in euphausiids taken from coastal waters off Hokkaid? were significantly higher than those from the Bering Sea and the northern North Pacific. This trend may reflect coastal pollution rather than characteristics of the species. Contribution No. 117 from the Research Institute of North Pacific Fisheries, Faculty of Fisheries, Hokkaido University     

Metal accumulation in mussels of the Kuril Islands, north-west Pacific Ocean

Concentrations of cadmium, copper, iron, lead, manganese, nickel and zinc were investigated in two species of mussel from the Kuril Islands in the north-western Pacific Ocean: the short-lived mussel Mytilus trossulus and the much larger and longer-lived Crenomytilus grayanus. The concentrations of most elements were low, and these reported levels are believed to reflect background values for pristine locations. However, both iron and zinc concentrations were elevated in some samples taken from areas of hydrothermal vent activity, and these are believed to reflect the enrichment of the two metals in solution at such sites. Furthermore, the concentrations of cadmium were unusually elevated in both species of mussel, especially in the longer-lived C. grayanus. The high accumulation of cadmium in mussels from the Kuril Islands is believed to reflect regional upwelling, but it is also postulated that filtration rates of the mussels are high due to low levels of suspended matter, and this leads to a high assimilation efficiency for cadmium. The distribution of cadmium amongst the tissues of C. grayanus is also reported, and the need for further ecotoxicological studies in the area is proposed.     

Formation rates of subtropical underwater in the Pacific Ocean

Water mass formation rates were calculated for subtropical underwater (STUW) in the North and South Pacific by two partially independent methods. One is based on the World Ocean Circulation Experiment (WOCE)/TOGA drifter array over two periods: 1988–1992, and 1992–1996. Drifter velocities were used to calculate two components of the subduction rate, lateral induction and vertical pumping. The second method used CFC-12 data (1987–1994) from WOCE and Pacific Marine Environmental Laboratory to calculate ages on σ_θ surfaces. Subduction rates were estimated from the inverse age gradient. The two subduction rate methods are independent, but they share a common identification of STUW formation area based on satellite-derived surface temperature maps. Using both methods, one can put bounds on the formation rates: 4–5 Sv in the North and 6–7 Sv in the South Pacific. The drifter calculated STUW subduction rates for 1988–1992 and 1992–1996 are 21 and 13 m/yr in the North Pacific and 25 and 40 m/yr in the South. The CFC-12 calculated STUW subduction rate in the North Pacific is 26 m/yr, and 32 m/yr in the South. The South Pacific rates exceed those in the North Pacific. Consistent differences between the two methods support earlier studies, they conclude that mixing contributes to STUW formation in addition to the larger-scale circulation effects. The drifter and tracer rates agree well quantitatively, within 22%, except for the second period in the North Pacific and there are some differences in spatial patterns. Tracer rates integrate over time, and drifters allow analysis of interannual variability. The decrease in subduction rate between periods in the North Pacific is due to negative lateral induction entraining STUW into the mixed layer. The increase in the South Pacific rate is due to an increase in the vertical pumping. Although Ekman pumping is in phase in the North and South, the subduction rate is out of phase. These results confirm that subduction depends on the large-scale circulation and a combination of the outcrop pattern and air–sea fluxes. Temporal differences in rates and partitioning between the hemispheres are consistent with interannual changes in gyre intensity and current positions.     

Seasonal variability in nitrogenous nutrition of phytoplankton assemblages in the northeastern subarctic Pacific Ocean

Nitrogen uptake rates, and physical, chemical and biological characteristics of the euphotic zone were studied in winter, spring and late summer during the period 1992–1994 along a transect (Line P) extending from the continental slope off the southwest corner of Vancouver Island (British Columbia, Canada; station P4; 49°N, 127°W) to open waters in the NE Pacific (OSP; 50°N, 145°W). Nitrate (NO₃⁻) and silicic acid (Si(OH)₄) concentrations increased offshore during every season. Lowest NO₃⁻ and Si(OH)₄ values were observed during late summer and spring, and highest during winter throughout the euphotic zone. For spring and late summer, surface depletion of NO₃⁻ was observed at the inshore end of the transect, while offshore concentrations were never limiting for phytoplankton growth. Silicic acid was never depleted at any depth or station during the period covered by this study. Ammonium (NH₄⁺) and urea concentrations exhibited a patchy distribution along the transect, with no seasonal variations. Chlorophyll a and particulate nitrogen did not show a consistent longitudinal pattern from year to year. In general, the highest concentrations of chlorophyll a and particulate nitrogen were measured during the late summer cruises, with lower values in spring and lowest in winter. Phytoplankton assemblages were numerically dominated by flagellates <5 μm throughout the water column on each cruise transect. Ammonium, urea and NO₃⁻ uptake rates represented on average 55, 24 and 21% of the depth-integrated total nitrogen uptake, both longitudinally and seasonally; hence, phytoplankton utilized nitrogen in the following order: NH₄⁺>urea>NO₃⁻ along Line P. Ammonium may have inhibited the uptake rates of NO₃⁻ and urea. Urea uptake rates were lower than those of NH₄⁺, but higher values were occasionally observed at a few depths along the transect, particularly during the spring of 1993. Depth-integrated NH₄⁺ uptake rates were generally higher inshore, while NO₃⁻ uptake rates showed higher values offshore during most seasons. In contrast, urea uptake rates did not exhibit a consistent longitudinal trend. The depth-integrated f-ratio ranged from 0.05 to 0.37 with an average of 0.21 for all stations and cruises, and was overestimated on average by 36% when urea was excluded from the calculation. On a yearly basis, primary productivity in the NE subarctic Pacific was based on regenerated nitrogen.     

Distributions of dissolved and particulate biogenic thiols in the subartic Pacific Ocean

Dissolved and particulate concentrations of the biogenic thiols cysteine (Cys), arginine–cysteine (Arg–Cys), glutamine–cysteine (Gln–Cys), γ-glutamate–cysteine (γ-Glu–Cys) and glutathione (GSH) were measured in the subartic Pacific Ocean in the summer of 2003 using high performance liquid chromatography (HPLC) with precolumn derivatization as reported in previous work. In this study, a preconcentration protocol for the derivatized thiols was utilized to extend detection limits of dissolved thiols to picomolar levels. The measured concentrations of particulate and dissolved thiols were uncoupled, with distinctive depth profiles and large differences in the particulate to dissolved ratios between individual compounds. Glutathione was the most abundant particulate thiol whereas the most abundant dissolved thiol was γ-Glu–Cys, with concentrations as high as 15 nM. Given the relatively small pool of intracellular γ-Glu–Cys and the very low dissolved concentrations of GSH, we hypothesize that glutathione released from cells is rapidly converted to the potentially degradation resistant γ-Glu–Cys outside the cell. The relatively high concentrations of other dissolved thiols compared to particulate concentrations implies both biological exudation and slow degradation rates. Some thiols appear to vary with changes in nutrient availability but this effect is difficult to decouple from changes in community structure inferred from pigment analyses. Dissolved thiol concentrations also exceed typical metal concentrations in the subartic Pacific, supporting previous arguments that they may be important in metal speciation.     

High feeding rates on large particles by Neocalanus flemingeri and N. plumchrus,and consequences for phytoplankton community structure in the subarctic Pacific Ocean

The open subarctic Pacific Ocean is a high nitrate low chlorophyll (HNLC) system characterized by low concentrations of phytoplankton, a community dominated by small cells, and iron-limited growth of, especially, the larger phytoplankton. In such systems the main energy and material flow is through the microbial web, with large copepods considered primarily to be grazers on the larger microzooplankton occupying the top of this web. Consistent with this is the recognition that much of the nutrition of the dominant copepods in this system, Neocalanus flemingeri, N. plumchrus and N. cristatus, is derived from microzooplankton. Also, these copepods consume only a small fraction of the total phytoplankton production. In this paper, we show that the contribution made by N. flemingeri and N. plumchrus to establishing and maintaining the community structure of this ecosystem should be re-evaluated. Our experiments indicate these grazers have high clearance rates on large particles, including both large phytoplankton and microzooplankton, and this selective removal contributes to establishment and maintenance of the observed foodweb structure in the Gulf of Alaska. These high feeding rates combined with large populations of these two Neocalanus species concentrated in the upper layer of the ocean, result in population-based feeding rates approximately equal to the growth rates of large phytoplankton under iron-limited conditions. We conclude that N. flemingeri and N. plumchrus populations (a) directly prevent the accumulation of large phytoplankton cells by selectively feeding on them at high rates, and (b) indirectly stimulate the accumulation of the smaller phytoplankton by consumption of their major grazers, the microzooplankton.     

Impact of mesoscale eddies on particulate organic carbon flux in the western subarctic North Pacific

The mechanism that controls particulate organic carbon (POC) flux in the deep sea differs depending on the season and sea. The POC produced in the western subarctic North Pacific are known to be transported to the deep sea efficiently, but the direct relationship between the POC flux and physical processes is still unclear. In this study, we evaluated the effect of mesoscale eddies on POC flux in the western subarctic North Pacific. The seasonal and interannual variabilities of POC flux were investigated using data from a time-series sediment trap deployed at 4810 m at station K2 (47°N, 160°E) from 2005 to 2018. POC flux was high during May–November, appearing to reflect spring and fall blooms at the ocean surface. POC flux also showed interannual variability, with twelve peaks that were mostly affected by enhanced bloom just before the peak. Nine peaks of the twelve peaks were affected by mesoscale eddies, which enhanced bloom around K2 by extending the area with a high chlorophyll-a concentration along the coastal region into the offshore region, suggesting that mesoscale eddies strongly impact the interannual variability of POC flux at K2.

     

Grazing impact of the copepod community in the Oyashio region of the western subarctic Pacific Ocean

The role of copepod grazing on the ecosystem dynamics in the Oyashio region, western subarctic Pacific was investigated during six cruises from June 2001 to June 2002. In situ grazing rates of the copepod community (CGR) were measured by the gut fluorescence method in respect to developmental stages of dominant species. In terms of biomass, more than 80% of the copepod community was dominated by six large calanoid species (Neocalanus cristatus, Neocalanus flemingeri, Neocalanus plumchrus, Eucalanus bungii, Metridia pacifica and Metridia okhotensis) throughout the year. Resulting from the observed pattern of the interzonal migrating copepods, the CGR in the Oyashio region was divided into three phases, i.e. spring (bloom), summer (post-bloom) and autumn-winter phase. During the spring bloom, late copepodites of the interzonal migrating species, N. cristatus, N. flemingeri and E. bungii appeared in the surface layer (0-50 m) to consume the production of the bloom, resulting in a high grazing rate of the copepod community (7.9 mg Chl m⁻² d⁻¹), though its impact on phytoplankton community was low due to the high primary productivity. During the post-bloom period, although the copepod community which was dominated by N. cristatus, N. plumchrus, M. pacifica and newly recruited E. bungii still maintained a high biomass, the CGR was generally lower (1.8-2.6 mg Chl m⁻² d⁻¹ for June and August 2001), probably due to the lower availability of phytoplankton. Nevertheless, the highest CGR was also observed during this period (10.5 mg Chl m⁻² d⁻¹ in June 2002). The high CGR on autotrophic carbon accounted for 69% of the primary production, suggesting that the copepod community in the Oyashio region potentially terminates the phytoplankton bloom. Abundant occurrence of young E. bungii, which is a characteristic phenomenon in the Oyashio region, was largely responsible for the high grazing pressure in June 2002 suggesting that success of reproduction, growth, and survival in E. bungii during the spring bloom is an important factor in controlling phytoplankton abundance during the post-bloom season. During autumn and winter, CGR was the lowest in the year (0.29-0.38 mg Chl. m⁻² d⁻¹) due to the disappearance of the interzonal migrating copepods from the surface layer. Diel migrant M. pacifica was the most important grazer during this period. The annual ingestion of the copepod community is estimated as 37.7 gC m⁻² on autotrophic carbon (converted using C:Chl ratio of 30) or 137.9 gC m⁻² on suspended particles (using C:Chl ratio of in situ value, 58-191), accounting for 13% and 46% of annual primary production, respectively. This study confirms that copepod grazing is an important pathway in carbon flow in the Oyashio region and in particular their role in the phytoplankton dynamics is significant for the termination of the spring bloom.     

Protozoa in the diets of Neocalanus spp. in the oceanic subarctic Pacific Ocean

Copepod species of the genus Neocalanus dominate the zooplankton biomass of the oceanic subarctic Pacific Ocean. Neocalanus spp. populations in the subarctic Pacific environment are successful: they feed, accumulate lipid, and persist from year to year. Prior experimental observations derived from a variety of methods indicated that, although their functional morphology is such that they clear the small phytoplankton cells characteristic of the oceanic subarctic Pacific environment efficiently, Neocalanus spp. do not consume sufficient phytoplankton to meet even basic metabolic requirements in that environment. Hence, their success in the subarctic Pacific must depend on their ability to obtain nutrition from other sources. As part of the SUPER (SUbarctic Pacific Ecosystem Research) program, experiments were performed to test the hypothesis that N. plumchrus and N. cristatus obtain a significant portion of their nutrition from planktonic Protozoa. The experiments demonstrate that Protozoa alone do not provide sufficient nutrition for N. cristatus to meet its basic metabolic needs. Protozoa constitute the major dietary component of N. plumchrus however, in agreement with the predictions of Frost's (1987) model of the subarctic Pacific ecosystem. At a minimum this diet permits N. plumchrus to meet basic metabolic requirements. Copepod grazing activities appear to be sufficient to control protozoan stocks in the oceanic subarctic Pacific during late spring and early summer when Neocalanus spp. inhabit the upper water column.     

Co-limitation of phytoplankton growth by light and Fe during winter in the NE subarctic Pacific Ocean

Phytoplankton acclimate to low irradiance by increasing their cellular demand for Fe, to allow synthesis of additional light-harvesting pigments and Fe-containing redox proteins involved in photosynthesis. In the open NE subarctic Pacific, Fe concentrations limit primary productivity and irradiances may be suboptimal, particularly during winter. Phytoplankton thus may be unable to fulfill their extra Fe requirements for growth under these low-light conditions and become effectively co-limited. We tested this hypothesis by manipulating Fe and light in in vitro experiments at OSP (Ocean Station PAPA, 50°N 145°W) during winter 1997. The results show that metabolic rates, growth, and photosynthetic parameters of phytoplankton are enhanced in winter by increasing either irradiance or Fe. The greatest response occurs when Fe and light are amended concomitantly, confirming that the community is indeed co-limited by both resources. Analysis of environmental conditions (i.e. incident irradiance, mixed layer depth and Fe concentrations) in winter at OSP reveals that they are similar to those observed in the austral spring and fall at three sites in the Southern Ocean. Extrapolating our experimental field results to the Southern Ocean illustrates that co-limitation by light and Fe also may play an important role in regulating phytoplankton growth in this region.     

Phytoplankton growth and microzooplankton grazing in the subarctic Pacific Ocean and the Bering Sea during summer 1999

Phytoplankton growth and microzooplankton grazing rates were measured by the dilution technique in the subarctic North Pacific Ocean along a west–east transect during summer 1999. Average phytoplankton growth rates without added nutrients (μ₀) were 0.33, 0.41, 0.20 and 0.49 d⁻¹ for the four regions sampled: the Western Gyre, the Bering Sea, the Gulf of Alaska gyre and stations along the Aleutian Trench. Average grazing mortality rates (m) were 0.34, 0.27, 0.20 and 0.49 d⁻¹. Limitation of phytoplankton growth by macronutrients, such as NO₃ and SiO₂, was identified only at a few stations, with overall μ₀/μ_n (μ_n is nutrient-enhanced growth rate) averaging 0.9. Phytoplankton growth and microzooplankton grazing were approximately balanced, as indicated by high m/μ₀ ratio, except in the Bering Sea, where the m/μ₀ ratio was 0.65, indicating the relative importance of the diatom-macrozooplankton grazing food chain and possible higher export flux to the deep layer. Flow cytometric analysis revealed that the growth rates of picoplankton (Synechococcus and picoeukaryotes) were usually much lower than the total phytoplankton community growth rates estimated from chlorophyll a, except for stations in the Gulf of Alaska Gyre, where the growth rates for different populations were about the same. Lower than community-average growth rate for picoplankton indicates larger phytoplankters, presumably diatoms, were growing at a much faster rate. Suppressed phytoplankton growth in the Gulf of Alaska was probably a result of iron limitation.     

Chlorophyll a and primary production in the northeastern Pacific Ocean

The primary production and chlorophyll a concentration of picoplankton （0.2 - 2 μm） , nanoplankton （2 - 20μm） and micro- plankton （20 -200 μm） are described in the northeastern Pacific Ocean near the Hawaii Islands during the six survey cruises from 1996 to 2003：DY85-4, DY95-7, DY95-8, DY95-10, DY105-11 and DY105-12.14. The primary production of carbon was in range from 76.8 to 191.9 mg/（m^2 · d） with an average of 116.1 mg/（ m^2 · d） in the east region, and from 73.1 to 222.5 mg/（ m^2 · d） with an average of 127.1 mg/（ m^2 · d） in the west region, similar to the other oligotrophic regions of the Pacific Ocean investigated. The chlorophyll a concentration was about 0.1 mg/m^3 from the surface to the 50 m depth, about 0.2 -0.4 mg/m^3from 50 to 100 m, and gradually decreased below the 100 m depth. The picoplankton accounted for more than 70% of the total chlorophyll a in the upper layer （ surface to 125 m）, but it decreased to less than 50% in depth below 125 m. The nanoplankton and microplankton combined only accounted for less than 30% of the total chlorophyll a in the upper layer, but showed a more even vertical distribution.     

最优插值法及其在热带太平洋海表温度数据同化中的应用

利用M IT gcm模式和最优插值法搭建的同化平台对热带太平洋赤道附近的海表温度SST数据进行了数值同化处理。结果表明,同化处理有效兼顾了模式模拟值和观测值,纠正了模式模拟值出现的误差,数值同化结果更接近于观测值。该同化平台能够更好地反映出SST的分布特征,该同化方法可以有效地对海表数据进行数值预报。