Carbon cycling in a high-arctic marine ecosystem – Young Sound, NE Greenland

Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m⁻²) is similar to phytoplankton production (6–10 g C m⁻²). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m⁻² yr⁻¹. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m⁻² yr⁻¹ is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m⁻² yr⁻¹ of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m⁻² yr⁻¹ was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.     

Production of <Emphasis Type="Italic">Acartia steueri</Emphasis> (Copepoda: Calanoida) in Ilkwang Bay,Southeastern Coast of Korea

Production of the marine calanoid copepod Acartia steueri was measured from 2 October 1991 to 8 October 1992 at a station in Ilkwang Bay, on the southeastern coast of Korea. Phytoplankton standing stock ranged over 1.0 to 9.3 mg chl.a m⁻³, and annual primary productivity (by the C-14 method) at three stations was estimated at 200 gC m⁻² yr⁻¹. Acartia steueri (nauplii + copepodids + adults) were present in the plankton throughout the year, with seasonal variation in abundance. Biomass of A. steueri, excluding the NI stage, was 0.01–4.55 mgC m⁻³ (mean: 0.68 mgC m⁻³) with peaks in November, February, May and July-early August, and relatively low biomass in September– January. Instantaneous growth rates of the nauplius stages were higher than the copepodid stages. Annual production of A. steueri was 25.1 mgC m⁻³ yr⁻¹ (or 166 mgC m⁻² yr⁻¹), showing peaks in November, May and July–August with a small peak in February, and low production in December–April and September–October. There were no significant relationships between the daily production rate of A. steueri and temperature or chlorophyll a concentration, indicating that unknown other factors might be related to the variation of the production rate.     

Primary productivity in the offshore Oyashio in the spring and summer 1990

Primary productivity was measured byin situ method using¹³C in the offshore Oyashio region in the spring (May) and summer (September) of 1990. Most of the values were within the range of 0.1 to 4 gC 1^–1 h^–1 although a very large value, 7.96 gC l^–1 h^–1, was observed in summer. Most daily primary production fell within the range of 372 to 633 mgC m^–2 d^–1 although a very large value, 2,109 mgC m^–2 d^–1, was observed around the frontal area in summer. Chlorophylla (Chl.a) exceeded 1 g l^–1 in many cases, and the maximum was 4.61 g l^–1 in spring and 7.53 g l^–1 in summer. Most primary productivity per unit Chl.a (photosynthetic assimilation ratio) was within the range of 0.1 to 3 gC gChl.a ^–1 h^–1 although higher values, 3–6 gC gChl.a ^–1 h^–1, were observed where small-size phytoplanktons (<2 m) were dominant. These results were compared with results obtained until now in the Oyashio region. The values beyond the range obtained so far in the offshore region were also observed in this study. Furthermore, it was pointed out that the size composition of phytoplankton community has significant influence on the results of Chl.a and photosynthetic assimilation ratio in the Oyashio region.     

Microzooplankton and mesozooplankton in an upwelling filament off Galicia: modelling and sensitivity analysis of the linkages and their impact on the carbon dynamics

This paper reports estimates of trophic flows of carbon off the Galician coast from a 1D ecological model, which are compared with field data from a two week Lagrangian drift experiment. The model consists of 9 biological components: nitrate, ammonium, >5μm phytoplankton, <5μm phytoplankton, heterotrophic nanoflagellates/dinoflagellates (5–20 μm), heterotrophic dinoflagellates (>20 μm), ciliates, fast sinking detritus and slow sinking detritus. Calculations were made for the fluxes of carbon between biological components within the upper 45m of the water column. The temporal development of primary production during the simulation period of two weeks was in good agreement with field estimates, which varied between 248 and 436mgC.m⁻².d⁻¹. Heterotrophic nanoflagellates had the greatest impact on carbon flux, with a grazing rate of 168mgC.m⁻².d⁻¹. Herbivorous grazing by microzooplankton amounted to 215mgC.m⁻².d⁻¹, whereas grazing by copepods on phytoplankton was 35mgC.m⁻² d⁻¹. Copepods grazing on microzooplankton was minor (0.47mgC.m⁻².d⁻¹) and the export flux from the upper 45m was 302mgC.m⁻².d⁻¹. Sensitivity analyses, in which the grazing parameters (i.e the functional relationship between ingestion and food concentration) were changed, were carried out on the heterotrophic dinoflagellate, ciliate and heterotrophic nanoflagellates/dinoflagellate components of the model. These changes did not alter the temporal development of heterotrophic nanoflagellates/dinoflagellates biomass significantly, but ciliates and heterotrophic dinoflagellates were more sensitive to variations in the grazing parameters. The overall conclusion from this modelling study is that the coupling between small phytoplankton and heterotrophic nanoflagellates was the quantitatively most important process controlling carbon flow in this region.     

The herbivorous impact of microzooplankton during two short-term Lagrangian experiments off the NW coast of Galicia in summer 1998

Microzooplankton (heterotrophic microplankton and heterotrophic nanoflagellates) and their herbivorous activity were estimated from dilution experiments in August 1998 during two Lagrangian drift experiments that sampled contrasting conditions—an upwelling/relaxation event along the shelf edge and an oligotrophic offshore filament. During upwelling/relaxation, heterotrophic microplankton were present at mean surface concentrations between 15,000 and 48,000 cells l⁻¹. Heterotrophic nanoflagellate concentrations were between 200 and 700 cells ml⁻¹ and the most abundant component of the heterotrophic microplankton was the aloricate choreotrich ciliates which increased dramatically in concentration from 6,000 to 24,000 cells l⁻¹ during the first 4 days of the study. Total microzooplankton biomass reached a maximum of 39mgC.m⁻³. In the filament, which developed from the upwelling, cell concentrations were lower and averaged 4,500 cells l⁻¹ for heterotrophic microplankton and 250 cells ml⁻¹ for heterotrophic nanoflagellates. Total microzooplankton biomass was about 10–12mgC.m⁻³. Microzooplankton turned over between 40 and 85% of the phytoplankton standing stock, thereby consuming between 5 and 78mg phytoplankton carbon.m⁻³.d⁻¹. The magnitude of this activity was highest during upwelling/relaxation and was positively correlated to heterotrophic nanoflagellate biomass and chlorophyll-a concentration but not heterotrophic microplankton biomass. The proportion of primary production grazed decreased from 160 to 59% d⁻¹ during upwelling/relaxation and ranged between 60 and 90% d⁻¹ in the filament. Microzooplankton herbivory within the euphotic zone increased from 684 to >2000mgC.m⁻².d⁻¹ during upwelling/relaxation and was between 327 and 802mgC.m⁻².d⁻¹ in the filament. Although microzooplankton herbivory was lower and less variable during the filament study, microzooplankton consumed on average 60% of the phytoplankton standing stocks which was higher than found during upwelling/relaxation. Microzooplankton assimilation efficiency ranged between 3 and 33% during upwelling/relaxation and between 0 and 13% in the filament. Our data demonstrate a close coupling between phytoplankton growth and microzooplankton herbivory in surface waters off the Galician Coast and suggest that microzooplankton may have been a significant sink for phytogenic carbon during August 1998.     

Primary production and chlorophyll distributions in the subtropical and tropical waters of the Atlantic Ocean in the autumn of 2002

In October and November 2002, high and relatively high values of the chlorophyll a concentration at the sea surface (C _chl) were observed in the English Channel (0.47 mg/m³), in the waters of the North Atlantic Current (0.25 mg/m³), in the tropical and subtropical anticyclonic gyres (0.07–0.42 mg/m³), and also in the southwestern region of the southern subtropical anticyclonic gyre (usually 0.11–0.23 mg/m³). The central regions of the southern subtropical anticyclonic gyre (SATG) and the North Atlantic tropical gyre (NATR) were characterized by lower values of C _chl (0.02–0.08 mg/m³ for the SATG and 0.07–0.14 mg/m³ for the NATR). At most of the SATG stations, the values of the surface primary production (C _phs) varied from 2.5 to 5.5 mg C/m³ per day and were mainly defined by the fluctuations of C _chl (r = +0.78) rather than by those of the assimilation number (r = +0.54). The low assimilation activity of phytoplankton in these waters (1.3–4.6 mg chl a per hour) pointed to a lack of nutrients. An analysis of the variability of their concentration and the composition of photosynthetic pigments showed that, in the waters north of 30° N, the growth of phytoplankton was mostly restricted by the deficiency of nitrogen, while, in more southern areas, at the majority of stations (about 60%), the phosphorus concentrations were the minimum. At the low concentrations of nitrates and nitrites, ammonium represented itself as a buffer that prevented planktonic algae from extreme degrees of nitric starvation. In the tropical waters and in the waters of the SATG, the primary production throughout the water column varied from 240 to 380 mg C/m² 30° per day. This level of productivity at stations with low values of C _chl (<0.08 mg/m³) was provided by a well-developed deep chlorophyll maximum and a high transparency of the water. The light curves of photosynthesis based on in situ measurements point to the high efficiency of utilizing the penetrating solar radiation by phytoplankton on cloudy days.     

Contrasts in sedimentation flux below the southern California Current in late 1996 and during the El Niño event of 1997–1998

The vertical flux of particulate matter at 330 m depth in San Lázaro Basin off southern Baja California ranged from 63 to 587 mg m⁻² d⁻¹ between August and November 1996. Organic carbon contents were between 5.6 and 14.8%, yielding flux rates of 9–40 mgC m⁻² d⁻¹. In December 1997 and January 1998, at the height of the strong El Niño event, the respective fluxes (47–202 mg m⁻² d⁻¹ and 3–8 mgC m⁻² d⁻¹) were comparable. The February–June 1998 records, however, revealed sharply reduced mass (1–6 mg m⁻² d⁻¹) and organic carbon (0.2–0.8 mgC m⁻² d⁻¹) fluxes. The organics collected in 1996 were predominantly autochthonous (δ¹³C=−22‰; C/N=8). The variations in δ¹⁵N (8.3–11.0‰) suggest an alternation of new and regenerated production, possibly associated with fluctuations in the intensity of deep mixing during that autumn. The relatively high organic matter fluxes in December 1997 appear to be associated with regenerated production. The average composition from February to June 1998 (δ¹³C=−23.6‰; ¹⁵N=11.7‰; C/N=10.5) indicates degraded material of marine origin. The maximum δ¹⁵N value found (14‰) suggests that deeper, denitrified waters were brought to the surface and possibly advected laterally. Regime changes in the waters of the basin occur at 6–10 week intervals, evidenced by concurrent shifts in most of the measured parameters, including fecal pellet types and metal chemistry. The marine snow-dominated detritus collected showed a shift from a mixed diatom-rich-radiolarian-coccolith assemblage in late 1996 to a coccolith-dominated assemblage, including the contents of fecal pellets, during the 1997–1998 El-Niño period. T–S profiles, plankton analysis and chlorophyll contents of the upper water column indicated that the strong phytoplankton bloom, normally associated with seasonal upwelling along the Pacific coast of Baja, did not occur during the spring of 1998. The persistence of oligotrophic conditions during the 1997–1998 El Niño event favored the dominance of nanoplankton and reduced the vertical flux of particles.     

Primary production and nutrient assimilation in the Iberian upwelling in August 1998

Primary production was measured during two Lagrangian experiments in the Iberian upwelling. The first experiment, in a body of upwelled water, measured day-to-day changes in phytoplankton activity as the water mass moved south along the shelf break. Nutrient concentrations decreased over a five day period, with concomitant increases in phytoplankton biomass. Initially the maximum phytoplankton biomass was in the upper 10m but after four days, a sub-surface chlorophyll maximum was present at 30m. Depth-integrated primary production at the beginning of the experiment was 70mmolC.m⁻².d⁻¹ (838mgC.m⁻².d⁻¹) and reached a maximum of 88mmolC.m⁻².d⁻¹ (1053mgC.m⁻².d⁻¹) on day 3. On day 1, the picoplankton fraction (<2μm) was slightly more productive than larger (>5μm) phytoplankton, but the increase in overall production during the drift experiment was by these larger cells. Nitrate was the dominant nitrogen source. As nutrient concentrations declined, ammonium became increasingly more important as a nitrogen source and the f-ratio decreased from 0.7 to 0.5. Picoplankton cells (<2μm) were responsible for most (65–80%) of the ammonium uptake. The C:N:P uptake ratios were very close to the Redfield ratio for the first four days but as nutrients became depleted high C:N uptake ratios (11 to 43) were measured. Over the period of the experiment, nitrate concentration within the upper 40m decreased by 47.91mmolN.m⁻². In vitro estimates, based on ¹⁵N nitrate uptake, accounted for 56% of the decrease in nitrate concentration observed in the drifting water mass. Ammonium uptake over the same four day period was 16.28mmolN.m⁻², giving a total nitrogen uptake of 43.18mmolN.m⁻².In the second experiment, an offshore filament was the focus and a water mass was sampled as it moved offshore. Nutrient concentrations were very low (nitrate was <10nmol l⁻¹ and ammonium was 20–40nmol l⁻¹). Primary production rate varied between 36mmolC.m⁻².d⁻¹ (436mgC.m⁻².d⁻¹) and 21mmolC.m⁻².d⁻¹ (249mgC.m⁻².d⁻¹). Picophytoplankton was the most productive fraction and was responsible for a constant proportion (ca 0.65) of the total carbon fixation. Uptake rates of both nitrate and ammonium were between 10 and 20% of those measured in the upwelling region. Urea could be a very significant nitrogen source in these waters with much higher uptake rates than nitrate or ammonium; urea turnover times were ca. one day but the source of the urea remains unknown. Urea uptake had a profound effect on calculated f ratios. If only nitrate and ammonium uptake was considered, f ratios were calculated to be 0.42–0.46 but inclusion of urea uptake reduced the f ratio to <0.1. The primary production of this oligotrophic off-shore filament was driven by regenerated nitrogen.     

Abundance and size composition of the summer phytoplankton communities in the western North Pacific Ocean,the Bering Sea,and the Gulf of Alaska

Chlorophylla concentrations (Chla) of size-fractionated phytoplankton samples were measured in the western North Pacific Ocean, the Bering Sea, and the Gulf of Alaska during the summer of 1986. Among samples collected in the upper 100 m (total of 210 samples), 207 samples were dominated by micro- (>10 m) or picoplankton (<2 m) and only three samples were represented by nanoplankton (2–10 m). These 207 samples were classified based on the total Chla content into three types: Type H (>1.0 g l^–1), Type M (0.5–1.0 g l^–1), and Type L (<0.5 g l^–1). These types further divided into two subtypes (-p and-m), depending upon dominancy of pico (-p) and microplankton (-m). The phytoplankton community was represented by Type L-p in the Gulf of Alaska, where 80% of the samples fell into this type. It was represented by Type M-p in the western North Pacific and the Oceanic Domain in the Bering Sea, where 53 and 41% of samples were identified as this type, respectively. In the Middle Domain of the Bering Sea, 68% of samples collected below the nitracline was Type H-m, which indicates blooms of microplanton. This type was also observed in the neritic waters near the Aleutian Islands. These types described above are consistent with a general trend that an increase in phytoplankton abundance is attributed to the growth of microplankton. An unusual type occurred above the nitracline of the Middle Domain, where microplankton prevailed, although the total Chla was less (Type L-m). This type represents a feature of late phase of an ice edge bloom. Another unusual type was found mainly in the Outer Domain of the Bering Sea, where the total Chla was high and picoplankton prevailed (Type H-p). The predominance of picoplankton seems to result from the heavy grazing intensity of large calanoid copepods upon microplankton but not upon picoplankton     

Abundance, Biomass, Production and Trophic Roles of Micro- and Net-Zooplankton in Ise Bay, Central Japan, in Winter

We investigated the geographical variations in abundance and biomass of the major taxonomic groups of micro- and net-zooplankton along a transect through Ise Bay, central Japan, and neighboring Pacific Ocean in February 1995. The results were used to estimate their secondary and tertiary production rates and assess their trophic roles in this eutrophic embayment in winter. Ise Bay nourished a much higher biomass of both micro- and net-zooplankton (mean: 3.79 and 13.9 mg C m^–3, respectively) than the offshore area (mean: 0.76 and 4.47 mg C m^–3, respectively). In the bay, tintinnid ciliates, naked ciliates and copepod nauplii accounted for, on average, 69, 18 and 13% of the microzooplankton biomass, respectively. Of net-zooplankton biomass, copepods (i.e. Acartia, Calanus, Centropages, Microsetella and Paracalanus) formed the majority (mean: 63%). Average secondary production rates of micro- and net-zooplankton in the bay were 1.19 and 1.87 mg C m^–3d^–1 (or 23.1 and 36.4 mg C m^–2d^–1), respectively, and average tertiary production rate of net-zooplankton was 0.75 mg C m^–3d^–1 (or 14.6 mg C m^–2d^–1). Available data approximated average phytoplankton primary production rate as 1000 mg C m^–2d^–1 during our study period. The transfer efficiency from primary production to zooplankton secondary production was 6.0%, and the efficiency from secondary production to tertiary production was 25%. The amount of food required to support the zooplankton secondary production corresponded to 18% of the phytoplankton primary production or only 1.7% of the phytoplankton biomass, demonstrating that the grazing impact of herbivorous zooplankton was minor in Ise Bay in winter.     

Phytoplankton production characteristics in the southern Atlantic and the Atlantic sector of the Southern Ocean in the austral summer of 2009–2010

In December–January of 2010 the spatial distribution of the phytoplankton production characteristics was studied along transects in the vicinity of the Greenwich meridian (I) and in the Drake Passage (II). On transect I, the surface chlorophyll a concentration and primary production varied from 0.11 up to 3.57 mg/m³ and from 4.38 up to 37.47 mgC/m³ per day, respectively. The chlorophyll a in the photosynthetic layer and the integrated primary production varied from 10.7 up to 66.1 mg/m² and from 83 to 646 mgC/m² per day, respectively. On transect II in the surface layer, the chlorophyll a concentration changed within the range of 0.09–1.02 mg/m³ and the primary production ranged from 2.08 to 9.49 mgC/m³. The integrated values ranged from 6.32 to 38.29 mg/m² and from 41 to 221 mgC/m² per day, respectively. The moderate means of themaximum quantum yield (F _v/F _m) on transects I and II (0.41 and 0.35, respectively) testify to the low activity of the phytoplankton’s photosynthetic apparatus. The studied water areas in the Southern Ocean differed both in the phytoplankton biomass expressed in the chlorophyll a concentration values and in the conditions of the primary production formation.     

Seasonal phytoplankton composition, productivity and biomass in the Neuse River estuary, North Carolina

Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated (r = 0·82) with nitrate concentration and inversely correlated (r = −0·73) with salinity, while nitrate and salinity were inversely correlated (r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m⁻², mean chlorophyll a was 11·8 mg m⁻³, and mean phytoplankton density was 1·56 × 10³ cells ml⁻¹. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m⁻².     

Environmental controls on phytoplankton community composition in the Thames plume, U.K.

The aim of this study was to investigate controls on the phytoplankton community composition and biogeochemistry of the estuarine plume zone of the River Thames, U.K. using an instrumented moored buoy for in situ measurements and preserved sample collection, and laboratory-based measurements from samples collected at the same site. Instrumentation on the moored buoy enabled high frequency measurements of a suite of environmental variables including in situ chlorophyll, water-column integrated irradiance, macronutrients throughout an annual cycle for 2001 e.g. nitrate and silicate, and phytoplankton biomass and species composition. The Thames plume region acts as a conduit for fluvial nutrients into the wider southern North Sea with typical winter concentrations of 45 μM nitrate, 17 μM silicate and 2 μM phosphate measured. The spring bloom resulted from water-column integrated irradiance increasing above 60 W h m^− 2 d^− 1 and was initially dominated by a diatom bloom mainly composed of Nitzschia sp. and Odontella sinesis. The spring bloom then switched after  30 days to become dominated by the flagellate Phaeocystis reaching a maximum chlorophyll concentration of 37.8 μg L^− 1. During the spring bloom there were high numbers of the heterotrophic dinoflagellates Gyrodinium spirale and Katodinium glaucum that potentially grazed the phytoplankton bloom. This diatom–flagellate switch was predicted to be due to a combination of further increasing water-column integrated irradiance > 100 W h m^− 2 d^− 1 and/or silicate reaching potentially limiting concentrations (< 1 μM). Post spring bloom, diatom dominance of the lower continuous summer phytoplankton biomass occurred despite the low silicate concentrations (Av. 0.7 μM from June–August). Summer diatom dominance, generally due to Guinardia delicatula, was expected to be as a result of microzooplankton grazing, dominated by the heterotrophic dinoflagellate Noctiluca scintillans, controlling 0.7–5.0 μm ‘flagellate’ fraction of the phytoplankton community with grazing rates up to 178% of ‘flagellate’ growth rate. The Thames plume region was therefore shown to be an active region of nutrient and phytoplankton processing and transport to the southern North Sea. The use of a combination of moorings and ship-based sampling was essential in understanding the factors influencing nutrient transport, phytoplankton biomass and species composition in this shelf sea plume region.     

Primary productivity and solar radiation off Sanriku in May 1997

We measured the in situ primary production at four stations from the surface to 80 m off Sanriku in late May 1997. The depth-integrated daily primary production in the upper 80 m was estimated to be 391, 468, and 855 mgC m⁻²d⁻¹ in water from the Oyashio, and 336 mgC m⁻²d⁻¹ in the warm-core ring. The variation in the primary production was primarily due to the variation in phytoplankton activity (chlorophyll α-specific primary production). A combination of previous and present studies in water from the Oyashio and the warm-core ring suggested that phytoplankton activity is proportional to light intensity between 12 and 50 Ein m⁻²d⁻¹ which is close to the usual light condition (61–75 Ein m⁻²d⁻¹) off Sanriku in May and June. Light may be a limiting factor for phytoplankton off Sanriku in late spring and early summer.     

Biological and physical controls on dissolved dimethylsulfide over the north-eastern continental shelf of New Zealand

Data presented in this paper are part of an extensive investigation of the physics of cross-shelf water mass exchange in the north-east of New Zealand and its effect on biological processes. Levels of dissolved dimethylsulfide (DMS) were quantified in relation to physical processes and phytoplankton biomass. Measurements were made at three main sites over the north-east continental shelf of New Zealand's North Island during a current-driven upwelling event in late spring 1996 (October) and an oceanic surface water intrusion event in summer 1997 (January). DMS concentrations in the euphotic zone ranged between 0.4 and 12.9 nmol dm⁻³. Integrated water column DMS concentrations ranged from 33 to 173 μmol m⁻² in late spring during the higher biomass (15–62 Chl-a mg m⁻²) month of October, and from 25 to 38 μmol m⁻² in summer during the generally lower biomass (16–42 Chl-a mg m⁻²) month of January. We observed high levels of DMS in the surface waters at an Inner Shelf site in association with a Noctiluca scintillans bloom which is likely to have enhanced lysis of DMSP-producing algal cells during phagotrophy. Integrated DMS concentrations increased three-fold at a Mid Shelf site over a period of a week in conjunction with a doubling of algal biomass. A high correlation (r²=0.911, significant <0.001) of integrated DMS and chlorophyll-a concentrations for compiled data from all stations indicated that chlorophyll-a biomass may be a reasonable predictor of DMS in this region, even under highly variable hydrographic conditions. Integrated bacterial production was inversely correlated to DMS production, indicating active bacterial consumption of DMS and/or its precursor.     

Abundance, variability, and potential grazing impact of planktonic ciliates in the open subaratic Pacific Ocean

The abundance and variability of planktonic ciliates in the open subarctic Pacific were determined during four month-long cruises in 1987 and 1988. The ciliate community, numerically dominated by relatively small aloricate choreotrichs, was comparable in abundance to communities in a range of oceanic and neritic environments, including waters with much higher average chlorophyll concentrations. Integrated (0–80m) ciliate biomass was typically 100–200mgC m⁻², although 3- to 4-fold higher levels were observed on two occasions in spring. Ciliate community biomass, in general, was dominated by large (>20μm width) individuals, although in August 1988 the biomass of smaller cells was as great or greater. The estimated grazing impact of the ciliate community averaged 20% of the primary production. On one instance in May 1988, however, a large biomass of ciliates led to an estimated grazing impact equivalent to 55% of phytoplankton production. While ciliates may be major phytoplankton grazers during sporadic ciliate “blooms”, dino- and other heterotrophic flagellates, which make up the bulk of microheterotroph biomass, must normally be of equal or greater importance as herbivores in this ocean region.     

Photosynthate allocation in a temperate sea over an annual cycle: the relationship between protein synthesis and phytoplankton physiological state

The seasonal and vertical variations in the patterns of photosynthate allocation into biomolecules by natural phytoplankton assemblages were determined, together with their species composition, in a coastal station of the central Cantabrian Sea (southern Bay of Biscay). Chlorophyll-a concentration ranged from values below 20 mg m⁻² in winter to values above 80 mg m⁻² during spring and during an upwelling event in summer. Low primary production rates (<300 mgC m⁻² d^-1) were measured during winter and during summer stratification periods. The rate of C fixation during summer upwelling conditions exceeded 3500 mgC m⁻² d⁻¹. In terms of photosynthate partitioning, proteins were the dominant fraction, as they typically accounted for >30% of total photo-assimilated C, with polysaccharides and low molecular weight metabolites showing incorporation percentages around 10–30%. Relative C incorporation into lipids was generally <15%. Recurrent patterns of vertical variability in photosynthate partitioning were observed: the relative synthesis of proteins increased toward the bottom of the euphotic zone, whereas the relative C incorporation into polysaccharides and lipids tended to be higher near the surface. When primary production decreased, the synthesis of proteins was maintained more than that of other molecules. Throughout the year, the relative synthesis of proteins was inversely correlated with phytoplankton biomass, production and growth rate. The conservation of protein synthesis under growth-limiting conditions and the enhancement of lipid and polysaccharide synthesis when irradiance is high seem to constitute general patterns of photosynthate partitioning in marine phytoplankton. In our study, these patterns represented metabolic strategies of phytoplankton in response to changing environmental factors, rather than the effect of variations in the species composition of the community.     

Particulate organic carbon supply to the sea bottom: stable carbon isotope ratio analysis of the sediment trap samples at the mouth of otsuchi bay,Northeastern Japan

An array of sediment traps was deployed for the analysis of the pattern of particulate organic carbon (POC) supply to the sea bottom in April, May and July 1988 at the mouth of Otsuchi Bay (about 80 m depth), Northeastern Japan.On the basis of a simple two-component mixing model using stable carbon isotope ratios, the POC flux was separated into marine planktonic and terrestrial components. Both the planktonic and terrestrial POC fluxes had maximum values at 30 m above the sea bottom throughout the three experiments. The planktonic POC flux showed a significant decrease with depth between 30 m and 10 m or 5 m above the bottom. Vertical supply of the planktonic POC and supply of the resuspended planktonic POC were estimated on the basis of regression lines between water depth and the planktonic POC flux in the depth range where the flux decreases with depth.Vertical supply of the planktonic POC and supply of the resuspended planktonic POC to the sea bottom were largest in May (52.1 mgC m^–2 d^–1 and 19.5 mgC m^–2 d^–1 at 5 m above the sea bottom), and horizontal supplies of the terrestrial POC were almost constant (31.9±3.5 mgC m^–2 d^–1 at 5 m above the bottom) throughout the three experiments.     

Vertical flux of biogenic matter during a Lagrangian study off the NW Spanish continental margin

Lagrangian experiments with short-term, drifting sediment traps were conducted during a cruise on RRS Charles Darwin to the NW coast of Spain to study the vertical flux and composition of settling biogenic matter. The cruise was split into two legs corresponding to (i) a period of increased production following an upwelling event on the continental shelf (3–10 August 1998) and (ii) an evolution of a cold water filament originating from the upwelled water off the shelf (14–19 August). The export of particulate organic carbon (POC) from the upper layer (0–60m) on the shelf was 90–240mgC.m⁻².d⁻¹ and off the shelf was 60–180mgC.m⁻².d⁻¹. Off shelf the POC flux at 200m was 50–60mg.m⁻².d⁻¹. A modest sedimentation of diatoms (15–30mgC.m⁻².d⁻¹) after the upwelling was associated with increased vertical flux of chlorophyll a (1.8–2.1mg.m⁻².d⁻¹) and a decrease of the POC:PON molar ratio of the settled material from 9 to 6.4. Most of the pico-, nano-, and microplankton in the settled material were flagellates; diatoms were significant during the on shelf and dinoflagellates during the off shelf leg. Off shelf, the exponential attenuation of POC flux indicated a strong retention capacity of the plankton community between 40 and 75m. POC:PON ratio of the settled particulate matter decreased with depth and the relative portion of flagellates increased, suggesting a novel, flagellate and aggregate mediated particulate flux in these waters. Export of POC from the euphotic layer comprised 14–26% of the integrated primary production per day during the on shelf leg and 25–42% during the off shelf leg, which characterises the importance of sedimentation in the organic carbon budget of these waters.     

Depth profiles of volatile iodine and bromine-containing halocarbons in coastal Antarctic waters

Measurements of bromoform (CHBr₃), diiodomethane (CH₂I₂), chloroiodomethane (CH₂ICl) and bromoiodomethane (CH₂IBr) were made in the water column (5–100 m depth) of the Southern Ocean within 0–40 km of the Antarctic sea ice during the ANTXX1/2 transect of the German R/V Polarstern, at five locations between 70–72°S and 9–11°W in the Antarctic spring/summer of 2003–2004. Some of the profiles exhibited a very pronounced layer of surface sea-ice meltwater, as evidenced by salinity minima and temperature maxima, along with surface maxima in concentrations of CHBr₃, CH₂I₂, CH₂ICl and CH₂IBr. These results are consistent with in situ surface halocarbon production by ice algae liberated from the sea ice, although production within the sea ice followed by transport cannot be entirely ruled out. Additional sub-surface maxima in halocarbons occurred between 20 and 80 m. At a station further from shore and not affected by surface sea-ice meltwater, surface concentrations of CH₂I₂ were decreased whereas CH₂ICl concentrations were increased compared to the stations influenced by meltwater, consistent with photochemical conversion of CH₂I₂ to CH₂ICl, perhaps during upward mixing from a layer at  70 m enhanced in iodocarbons. Mean surface (5–10 m) water concentrations of halocarbons in these coastal Antarctic waters were 57 pmol l^− 1 CHBr₃ (range 44–78 pmol l^− 1), 4.2 pmol l^− 1 CH₂I₂ (range 1.7–8.2 pmol l^− 1), 0.8 pmol l^− 1 CH₂IBr (range 0.2–1.4 pmol l^− 1), and 0.7 pmol l^− 1 CH₂ICl (range 0.2–2.4 pmol l^− 1). Concurrent measurements in air suggested a sea-air flux of bromoform near the Antarctic coast of between 1 and 100 (mean 32.3, median 10.4) nmol m^− 2 day^− 1 and saturation anomalies of 557–1082% (mean 783%, median 733%), similar in magnitude to global shelf values. In surface samples affected by meltwater, CH₂I₂ fluxes ranged from 0.02 to 6.1 nmol m^− 2 day^− 1, with mean and median values of 1.9 and 1.1 nmol m^− 2 day^− 1, respectively.