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Phototrophic and heterotrophic nanoplankton (PNAN, HNAN; 2–20mm protists) and microplankton (PMIC, HMIC; 20–200mm protists and micrometazoa) are major taxa involved in partitioning carbon and energy within the pelagic food web. In the Ross Sea, Antarctica, plankton biomass appears to be controlled by the seasonal recession ofthe sea ice and the f ofthe Ross Sea polynya during the short austral spring-summer period. During four cruises in 1996–1997 within the southern Ross Sea as part of the US JGOFS program, we determined the abundances and biomasses ofphototrophic and heterotrophic nanoplankton and microplankton primarily along a transect at 76130 0 S. The colonial prymnesiophyte Phaeocystis antarctica (excluding mucus carbon) contributed significantly to community structure during both non-bloom and bloom periods (B25% and 90%, respectively, ofmicrobial biomass). However, shif ts occurred both seasonally and spatially between a diatom/heterotrophic dinoflagellate and a colonial P. antarctica-dominated assemblage. While nanoplankton biomass varied o50% during any particular cruise, PNAN and HNAN biomass ranged more than three orders ofmagnitude among the f our cruises (0.1–359 and 1.5–268 mmol C m � 2 , respectively). Cruise averages ofPMIC biomass ranged f rom 2.5 to 530 mmol C m � 2 , and a maximum biomass of1530 mmol C m � 2 was observed during the bloom ofcolonial P. antarctica in summer. Average heterotrophic biomass was o30% ofthe total microbial biomass (excluding bacteria) from early austral spring through summer. This value rose to E87% in autumn following the decline and disappearance of P. antarctica. The contribution oftotal nano- and microplankton biomass to POC in the upper 60 m over the three sampled seasons varied from 7% to 52.4% with an overall average of 21.8% for all four cruises which is comparable to contributions of these assemblages in other oceans even with the strong seasonal dominance of P. antarctica. r 2001 Elsevier Science Ltd. All rights reserved.

International audience; Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea-ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This paper reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea-ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms, but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed. This article is protected by copyright. All rights reserved.

The haptophyte Phaeocystis antarctica Karsten is a dominant species within the seasonal bloom in the Ross Sea. One of the unique characteristics of this form is that carbon is partitioned between the cells and the colonial matrix, a relationship that is poorly documented for this region. We combined particulate organic carbon measurements and microscopic analysis of P. antarctica-dominated samples to assess the contribution of single cells, colony-associated cells, and mucilage to the carbon concentrations of waters with P. antarctica. Two cruises to the Ross Sea were completed, one in austral spring 1994 and one in summer 1995–1996. In 1994 the bloom was dominated by colonial P. antarctica that contributed up to 96% of the total autotrophic carbon, whereas in 1995–1996 a mixture of P. antarctica and diatoms occurred. P. antarctica colony volume (V ) was related to colonial cell number (NC) by the relationship V = 417 ×NC1.67. Total colony carbon (CCOL) was calculated as the sum of cell carbon (CCC) and mucus-related carbon (CM). We found the contribution of mucus carbon to be 213 ng C mm−3 of colony volume. For P. antarctica-dominated assemblages sampled at the peak of the bloom, CM represented a minor fraction (14 ± 4%) of colony carbon, and during early summer conditions CM was at most 33% of CCOL. This organism plays a cardinal role in the carbon cycle of many regions. These results constrain the partitioning of carbon between cellular material and the colony matrix, information that is necessary to accurately describe the biogeochemical cycles influenced by this species.

A pelagic food web model was formulated with the goal of developing a quantitative understanding of the relationship between total production, export production, and environmental variables in marine ecosystems. The model assumes that primary production is partitioned through both large and small phytoplankton and that the food web adjusts to changes in the rate of allochthonous nutrient inputs in a way that maximizes stability, i.e., the ability of the system to return to steady state following a perturbation. The results of the modeling exercise indicate that ef ratios, defined as new production/total production = export production/total production, are relatively insensitive to total production rates at temperatures greater than ∼25°C and lie in the range 0.1-0.2. At moderate to high total production rates, ef ratios are insensitive to total production and negatively correlated with temperature. The maximum ef ratios are ∼0.67 at high rates of production and temperatures of 0°−10°C. At temperatures less than ∼20°C, there is a transition from low ef ratios to relatively high ef ratios as total production increases from low to moderate values. This transition accounts for the hyperbolic relationship often presumed to exist between ef ratios and total production. At low rates of production the model predicts a negative correlation between production and ef ratios, a result consistent with data collected at station ALOHA (22°45′N, 158°W) in the North Pacific subtropical gyre. The predictions of the model are in excellent agreement with results reported from the Joint Global Ocean Flux Study (JGOFS) and from other field work. In these studies, there is virtually no correlation between total production and ef ratios, but temperature alone accounts for 86% of the variance in the ef ratios. Model predictions of the absolute and relative abundance of autotrophic and heterotrophic microorganisms are in excellent agreement with data reported from field studies. Combining the ef ratio model with estimates of ocean temperature and photosynthetic rates derived from satellite data indicates that export production on a global scale is ∼20% of net photosynthesis. The results of the model have important implications for the impact of climate change on export production, particularly with respect to temperature effects.

To understand marine biogeochemical cycles, it is critical to quantitatively balance organic matter transformations within the euphotic zone. Such an assessment for nitrogen is difficult because of lateral advection, uncertainties in individual measurements, the complexity of elemental transformations (including nitrification and denitrification), and the difficulty of collecting data on appropriate space and time scales. Two cruises were conducted to the southern Ross Sea, Antarctica, to understand the time-varying fluxes of nitrogen into its various pools. From these data a balanced inventory was constructed. Nitrate removal in the upper 200 m was balanced by particulate and dissolved organic nitrogen production, ammonification, and vertical flux. In austral spring nearly all (92%) of the new production remained as particulate nitrogen, but this percentage decreased markedly (52%) by mid-summer, when nitrogen regeneration, PN flux, and DON production were 23, 13 and 12% of net production, respectively. The organic matter budget in this coastal Antarctic site is dominated by particle transformations.

The standing stock of particulate organic carbon (POC) was determined during five cruises in the Ross Sea in 1996 and 1997 and compared with primary production of carbon measured in short-term 14C-incubations and the flux of organic carbon collected in moored sediment traps. POC concentrations were estimated from transmissometer profiles that were calibrated with discrete POC bottle samples from each cruise. The mean standing stock of POC integrated to a depth of 100 m and averaged along a 330 km transect at 76.5°S in mid-October (early spring) was only 240 mmol C m −2 , but more than doubled to 560 mmol C m −2 10 days later. By mid-January (summer) the standing stock had increased by an order of magnitude to ∼5300 mmol C m −2 , but dropped to 3500 mmol C m −2 one week later. By late April (autumn), the standing stock was only 200 mmol C m −2 . The following spring the standing stock increased from 700 mmol C m −2 in late November to 2200 mmol C m −2 in early December. Despite the high standing stock in the photic zone in summer, 1997, little POC was collected in the moored sediment traps until late summer (February–March) when the traps showed an increase in POC and silica flux. A three-fold increase in POC flux occurred in autumn (March–April) dominated by pteropods, but the standing stock of POC in the photic zone at that time was very low. Light-scattering sensor data suggest that, although present in all seasons, aggregates were most abundant in autumn and were distributed throughout the water column. These aggregates may have temporarily stored POC and provided food support for a pteropod population that died and settled into the traps in March–April. Still, the trap POC flux was only 5% of the peak standing stock. Resuspension and lateral advection of recently settled organic matter from a nearby topographic high may explain the larger flux measured in the deep sediment traps, a flux that continued into winter.

Dissolved and particulate organic matter was measured during six cruises to the southern Ross Sea. The cruises were conducted during late austral winter to autumn from 1994 to 1997 and included coverage of various stages of the seasonal phytoplankton bloom. The data from the various years are compiled into a representative seasonal cycle in order to assess general patterns of dissolved organic matter (DOM) and particulate organic matter (POM) dynamics in the southern Ross Sea. Dissolved organic carbon (DOC) and particulate organic carbon (POC) were at background concentrations of approximately 42 and 3 μM C, respectively, during the late winter conditions in October. As the spring phytoplankton bloom progressed, organic matter increased, and by January DOC and POC reached as high as 30 and 107 μM C, respectively, in excess of initial wintertime conditions. Stocks and concentrations of DOC and POC returned to near background values by autumn (April). Approximately 90% of the accumulated organic matter was partitioned into POM, with modest net accumulation of DOM stocks despite large net organic matter production and the dominance of Phaeocystis antarctica. Changes in NO3 concentration from wintertime values were used to calculate the equivalent biological drawdown of dissolved inorganic carbon (DICequiv). The fraction of DICequiv drawdown resulting in net DOC production was relatively constant (ca. 11%), despite large temporal and spatial variability in DICequiv drawdown. The C : N (molar ratio) of the seasonally produced DOM had a geometric mean of 6.2 and was nitrogen-rich compared to background DOM. The DOM stocks that accumulate in excess of deep refractory background stocks are often referred to as “semi-labile” DOM. The “semi-labile” pool in the Ross Sea turns over on timescales of about 6 months. As a result of the modest net DOM production and its lability, the role DOM plays in export to the deep sea is small in this region.

Dissolved and particulate trace metal concentrations (dissolved Fe, Zn, Cd, Co, Cu and Ni; particulate Fe, Mn and Al) were measured along two transects in the Ross Sea during austral summer of 1990. Total Fe concentrations in southern Ross Sea and inshore waters were elevated >3.5 times that of northern waters. Dissolved Zn, Cd and Co concentrations were lower by factors of 4.5, 3.5 and 1.6 in southern surface waters relative to northern waters. Dissolved Cu and Ni concentrations were similar in both areas. Elevated Fe concentrations coincided with areas of increased productivity, phytoplankton biomass and nutrient drawdown, indicating that Fe is an important factor controlling the location of phytoplankton blooms in the Ross Sea. Particulate concentrations of Fe, Mn and Al indicate two possible sources of iron to the Ross Sea, resuspension of continental shelf sediments and iron incorporated in annual sea ice and released with meltwaters.

Phytoplankton standing stocks and carbon assimilation were measured during four cruises to the southern Ross Sea, Antarctica during 1996 and 1997 in order to assess the details of the seasonal cycle of biomass and productivity. The seasonal composite showed that phytoplankton biomass increased rapidly during the austral spring, and integrated chlorophyll reached a maximum during the summer (January 15) and decreased thereafter. Particulate matter ratios (carbon:nitrogen, carbon:chlorophyll) also showed distinct seasonal trends with summer minima. Carbon assimilation increased rapidly in the spring, and reached a maximum of 231 mmol C m−2 d−1, ca. four weeks earlier than the maximum observed biomass (during early December). It decreased rapidly thereafter, and in austral autumn when ice formed, it approached zero. The time of maximum growth rate coincided with the maximum in C-assimilation, and at 0.66 d−1 equaled predictions based on laboratory cultures. Growth rates over the entire growing season, however, were generally much less. Deck-board incubations suggested that photoinhibition occurred at the greatest photon flux densities, but in situ incubations revealed no such surface inhibition. We suggest that due to the nature of the irradiance field in the Antarctic, assemblages maintained in on-deck incubators received more light than those in situ, which resulted in photoinhibition. This in turn resulted in a 17% underestimate in on-deck productivity relative to in situ determinations. The phytoplankton bloom appeared to be initiated when vertical stability was imparted in austral spring, coincident with greater daily photon flux densities. Conversely, decreased productivity likely resulted from trace metal limitation, whereas biomass declines likely resulted from enhanced loss rates, such as aggregate formation and enhanced vertical flux of larger particles. The seasonal progression of productivity and biomass in the southern Ross Sea was similar to other areas in the ocean that experience blooms, and the cycling of carbon in this region is extensive, despite the fact that the growing season extends no more than five months.

Net community production (NCP) and nutrient deficits (Def( X )) were calculated using decreases in dissolved CO 2 and nutrient concentrations due to biological removal in the upper 200 m of the water column during four cruises in the Ross Sea, Antarctica along 76°30′S in 1996 and 1997. A comparison to excess dissolved and particulate organic carbon showed close agreement between surplus total organic carbon (TOC) and NCP during bloom initiation and productivity maximum; however, when TOC values had returned to low wintertime values NCP was still significantly above zero. This seasonal NCP, 3.9±1 mol C m −2 , must be equivalent to the particle export to depths greater than 200 m over the whole productive season. We estimate that the annual export was 55±22% of the seasonal maximum in NCP. The fraction of the seasonal maximum NCP that is exported through 200 m is significantly higher than that measured by moored sediment traps at a depth of 206 m. The removal of carbon, nitrate and phosphate (based on nutrient disappearance since early spring) and their ratios showed significant differences between regions dominated by diatoms and regions dominated by the haptophyte Phaeocystis antarctica . While the ΔC/ΔN removal ratio was similar (7.8±0.2 for diatoms and 7.2±0.1 for P. antarctica ), the ΔN/ΔP and ΔC/ΔP removal ratios for diatoms (10.1±0.3 and 80.5±2.3) were significantly smaller than those of P. antarctica (18.6±0.4 and 134.0±4.7). The similarity in ΔC/ΔN removal ratios of the two assemblages suggests that preferential uptake of phosphate by diatoms caused the dramatic differences in ΔC/ΔP and ΔN/ΔP removal ratios. In contrast to low ΔC/ΔP and ΔN/ΔP removal ratio in diatom-dominated areas early in the growing season, deficit N/P and C/P ratios in late autumn indicate that the elemental stochiometry of exported organic matter did not deviate significantly from traditional Redfield ratios. Changes in biologically utilized nutrient and carbon ratios over the course of the growing season indicated either a substantial remineralization of phosphate or a decrease in phosphate removal relative to carbon and total inorganic nitrogen over the bloom period. The species dependence in C/P ratios, and the relative constancy in the C/N ratios, makes N a better proxy of biological utilization of CO 2 .

The net community production (NCP) of the Ross Sea, from the early austral spring (mid-October) to the austral summer (mid-February), has been estimated from the seasonal drawdown of CO 2 concentrations integrated over the top 100 m of the water column. The deficits in nutrients and CO 2 indicate three distinct biogeochemical regimes. The regime in the southwestern Ross Sea (Region I) had relatively shallow mixed layers and was dominated by diatom growth, as evidenced by a silicate (Def(Si)) to NCP removal ratio (0.11±0.04) that was similar to the silicate-to-carbon ratio found in diatoms growing in temperate regions. High NCP values (4.9–8.7 mol m −2 ) and low ratios of surplus total organic carbon (Surp(TOC)) to NCP (from 0.27 to 0.67) show high organic carbon export out of the upper 100 m of the water column. The second regime (Region II), located in the center of the southern Ross Sea polynya, also had high NCP's (4.4–10.8 mol m −2 ) but the mixed layers were deeper. The average Def(Si)/NCP ratio was 0.04±0.02, much lower than the southwestern sector and consistent with the observed growth of the haptophyte Phaeocystis antarctica . An increase in Def(Si) and the Def(Si)/NCP ratio during re-occupations of selected stations indicate the presence and persistence of diatom growth late into the summer. The third regime (Region III), in the northeastern Ross Sea, had shallow mixed layers and a wider range of Def(Si)/NCP ratios (0.10–0.31), indicating variations in silicate-to-carbon uptake by diatoms. The low NCP's (1.2–4.2 mol C m −2 ) that distinguished this area also may be due to micro-nutrient deficiencies in addition to prolonged ice coverage. NCP over the continental shelf of the Ross Sea (441,000 km 2 , defined by the 1000-m isopleth) is estimated to be 25±10 Tg of carbon per year, with a mean rate of 4.8±1.9 mol m −2 yr. By mid-February, the productivity peak of the 1997 growing season had passed, and 19±7% of NCP remained in the upper 100 m as DOC, which presumably would not be exported but remineralized prior to the next growing season. During the same time period, 16±25% of NCP had already been removed from the upper 100 m as sinking biogenic particles, leaving 65% present in the POC fraction to be exported later or remineralized. High export of organic carbon (>50% of NCP) was shown in both diatom- and Phaeocystis -dominated regimes.

The development of the seasonal phytoplankton bloom in the Ross Sea was studied during two cruises. The first, conducted in November-December 1994, investigated the initiation and rapid growth of the bloom, whereas the second (December 1995-January 1996) concentrated on the bloom's maximum biomass period and the subsequent decline in biomass. Central to the under- standing of the controls of growth and the summer decline of the bloom is a quantitative assessment of the growth rate of phytoplankton. Growth rates were estimated over two time scales with different methods. The first estimated daily growth rates from isotopic incorporation under simulated in situ conditions, including 14 C, 15 N and 32 Si uptake measurements combined with estimates of standing stocks of particulate organic carbon, nitrogen and biogenic silica. The second method used daily to weekly changes in biomass at selected locations, with net growth rates being estimated from changes in standing stocks of phytoplankton. In addition, growth rates were estimated in large-volume experi- ments under optimal irradiances. Growth rates showed distinct temporal patterns. Early in the growing season, short-term estimates suggested that growth rates of in situ assemblages were less than maximum (relative to the temperature-limited maximum) and were likely reduced due to low irradi- ance regimes encountered under the ice. Growth rates increased thereafter and appeared to reach their maximum as biomass approached the seasonal peak, but decreased markedly in late December. Differences between the two major taxonomic groups present were also noted, especially from the isotopic tracer experiments. The haptophyte Phaeocystis antarctica was dominant in 1994 throughout the growing season, and it exhibited the greatest growth rates (mean 0.41 day-1) during spring. Diatom standing stocks were low early in the growing season, and growth rates averaged 0.10 day-1. In summer, diatoms were more abundant, but their growth rates remained much lower (mean of 0.08 day-1) than the potential maximum. Understanding growth rate controls is essential to the develop- ment of predictive models of the carbon cycle and food webs in Antarctic waters.

The flux of particles from the euphotic zone through 200 m was investigated on the Ross Sea continental shelf during two cruises, the first in November-December 1994 and the second in December 1995 and January 1996. An assessment of surface layer phytoplankton biomass and productivity was made simultaneously. Particle flux was measured using floating sediment traps whose collection efficiency was assessed rigorously. Phytoplankton biomass and productivity increased rapidly in November-December, and biomass was maximal in mid-December. Thereafter productivity appeared to decline substantially. Biomass declined as well, but not as rapidly as productivity. Vertical flux rates were low early in the bloom period, averaging 457 mg m−2 d−1, but increased markedly in late December and January (mean = 1160 mg m−2 d−1). Daily losses due to vertical flux represented only 2.3% of the surface layer particulate organic carbon standing stock. Measured particle fluxes were greater than those observed previously, and this is attributed to the period and depths sampled as well as to the care taken to ensure accuracy of sample collection. As in other regions, vertical flux of biogenic material is coupled with surface layer production and biomass. In our study area, however, a distinct temporal lag is introduced between surface production and flux at depth as a result of the temporal characteristics of the dominant mechanism generating large particles (aggregation) as well as the characteristic species of the region (Phaeocystis antarctica).

The relationship between new production, as assessed by short-term isotopic incubations, and vertical flux, quantified by both short- and long-term deployments of sediment traps, was investigated on the Ross Sea continental shelf in austral summer, 1990 and 1992. Three sites were analyzed, the first in the western Ross Sea where surface waters were dominated by pennate diatoms, the second in the south–central Ross Sea where the prymnesiophyte Phaeocystis antarctica dominated, and the third in the northern region which was dominated by diatoms. We found that the flux at the western site varied by a factor of 3.6 over a 1-month period (from 18.4 to 65.4 mg C m−2 day−1), whereas new production varied over nearly two orders of magnitude. At the Phaeocystis site, flux was much more variable. Although the temporally weighted flux averaged 7.34 mg C m−2 day−1, the flux at 570 m ranged from 0.5 to 74.8 mg C m−2 day−1, and the flux at 50 m in a floating trap reached 92.7 mg C m−2 day−1. New production ranged from 0.30 to 1.23 g C m−2 day−1. Primary production, new production and f-ratios at both sites decreased through time (mean February values of each were 42, 37 and 12% of January averages), but the seasonal decrease in vertical flux exhibited a significant time lag behind the productivity decrease. A carbon budget is constructed which suggests that heterotrophic mineralization within the water column is a significant removal term, and that substantial spatial variability in this term exists. The relationship between new production in the euphotic zone to that of export production is ambiguous in the Ross Sea, in part because isotopic methods quantify the material available for export on time scales that do not necessarily apply to processes which dominate export production. Integration of seasonal time scales, remineralization rates, and vertical flux rates is required to understand the quantitative relationships involved in export from the surface layer.

The effects of irradiance on nitrate uptake and subsequent dissolved organic nitrogen (DON) release were investigated using laboratory cultures of Phaeocystis sp. and phytoplankton assemblages dominated by Phaeocystis antarctica in the Ross Sea during cruises in November–December, 1994 and December 1995–January, 1996. 15N-labeled nitrate was used to determine nitrate uptake rates, and an ion retardation column (IRC) method was used to determine 15N-DON release rates (both the total as well as the low molecular weight (LMW) fraction). Nitrate uptake was strongly dependent on irradiance. The maximum specific nitrate uptake rate achieved by Phaeocystis cultures in short (

In this study we evaluate the partitioning of organic carbon between the particulate and dissolved pools during spring phytoplankton blooms in the Ross Sea, Antarctica, and the Sargasso Sea. As part of a multidisciplinary project in the Ross Sea polynya we investigated the dynamics of the dissolved organic carbon (DOC) pool and the role it played in the carbon cycle during the 1994 spring phytoplankton bloom. Phytoplankton biomass during the bloom was dominated by an Antarctic Phaeocystis sp. We determined primary productivity (PP; via H’CO, incubations), particulate organic carbon (POC), bacterial productivity (BP; via [‘Hlthymidine incorporation), and DOC during two occupations of 76”3O’S from 175”W to 168”E. Results from this bloom are compared to blooms observed in the Sargasso Sea in the vicinity of the Bermuda Atlantic Time-Series Study station (BATS). We present data that demonstrate clear differences in the production, biolability, and accumulation of DOC between the two ocean regions. Despite four- to fivefold greater PP in the Ross Sea, almost an order of magnitude less DOC (mmol m ?) accumulated during the Ross Sea bloom compared to the Sargasso Sea blooms. In the Ross Sea 89% (- 1 mol C m ‘) of the total organic carbon (TOC) that accumulated during the bloom was partitioned as POC, with the remaining 11% (- 0.1 mol C rn’) partitioned as DOC. In contrast, a mean of 86% (0.7.5-1.0 mol m ‘) of TOC accumulated as DOC during the 1992, 1993, and 1995 blooms in the Sargasso Sea, with as little as 14% (0.08-0.29 mol C m-?) accumulating as POC. Although a relatively small portion of the fixed carbon was produced as DOC in the Ross Sea, the bacterial carbon demand indicated that a qualitatively more labile carbon was produced in the Ross Sea compared to the Sargasso Sea. There are fundamental differences in organic carbon partitioning between the two systems that may be controlled by plankton community structure and food-web dynamics.

Coastal zone color scanner (CZCS) imagery of phytoplankton pigments and passive microwave imagery of sea ice distributions in the southwestern Ross Sea are presented for three different seasons (1978–1989, 1979–1980, and 1981–1982) and were analyzed in conjunction with meteorological data obtained from a series of automatic weather stations (AWS). Dynamics of the phytoplankton bloom in Terra Nova Bay differed from those in the Ross Sea owing to spatial differences in katabatic wind fields which determine when the surface waters stratify. Interannual variation in the timing of formation of the Ross Sea polynya appears to be controlled by winter temperatures, which determine sea ice thickness and integrity, rather than variability or intensity in wind stress. Together, CZCS, AWS, and passive microwave data suggest that when the Ross Sea polynya forms early, stronger and more frequent katabatic winds result in increased advective losses of phytoplankton in surface waters and a delay in the phytoplankton bloom. If polynya formation is delayed until after the winds diminish in frequency, the phytoplankton bloom will develop earlier. The observation that diatoms dominate both the marginal ice zone and Terra Nova Bay, which are hydrographically similar, while Phaeocystis antarctica is found in unstable waters north of the Ross Ice Shelf, suggests that stratification plays an important role in determining species composition in the Ross Sea.

The fate of large-sized phytoplankton and pathways of carbon cycling in surface waters, i.e. recycling within or export out of the euphotic zone, were investigated in the Northeast Water (NEW) Polynya (77-81 °N) from 23 May to 17 August 1993. Sampling represented a wide range of ice, hydrographic and nutrient conditions. Phytoplankton and zooplankton abundances, and phytoplankton production rates were determined in the field, whereas potential rates of grazing by copepods, dinoflagellates and appendicularians were calculated from abundances and temperature, using assumptions from the literature. The potential downward and lateral export of phytoplankton was also calculated by resolving a carbon budget for the euphotic zone. The present study suggests that, in the NEW, different pathways for the cycling of carbon existed in seasonally ice-free (in the polynya) and continuously ice-covered areas (outside the polynya). Outside the polynya, the fate of large-sized phytoplankton could not be assessed because the heterotrophic community presumably grazed on a variety of food items, including ice algae, microzooplankton and large-sized phytoplankton. In the polynya, the fate of large-sized phytoplankton production was to be mostly recycled at the beginning of sampling and to be mostly exported downward or laterally as the bloom of large-sized phytoplankton developed. Generally, copepods mostly contributed to recycling, but sometimes dinoflagellates or appendicularians alone recycled most of the large-sized phytoplankton production.

The distribution and production of transparent exopolymer particles (TEPs) were studied quantitatively both in cultures of Phaeocystis antarctica Karsten (Prymnesiophyceae) and in natural phytoplankton assemblages in the Ross Sea, Antarctica. TEP production in culture was a function of growth rate and photosynthetic activity and was strongly influenced by photon flux density. The concentrations of TEP measured during a bloom, dominated by P. antarctica, were higher than those produced by coastal diatom blooms and were correlated with chlorophyll a (Chl a), being low at Chl a levels below 3 μgL−1 but increasing rapidly at greater Chl a concentrations. Because higher chlorophyll hek are dominated 4 larger P. antarctica colonies, this relationship suggests that TEP was produced primarily by sloughing and disintegration of the colonial matrix. TEP concentrations (both absolute and relative to Chl a) increased as the bloom's biomass increased. Vertical distributions of TEP and Chl a showed TEP: chlorophyll maxima at the bottom of the water column at most stations. Because TEP and floc formation are tightly coupled, we suggest that mucous flocs derived from TEP, rather than intact P. antarctica colonies, are the dominant component of aggregates and subsequent organic carbon vertical flux.

Although satellite data of surface layer pigments have suggested that the daily productivity in the Ross Sea is among the largest found in any marine system, no modern oceanographic cruise has entered the Ross Sea polynya to quantitatively assess the austral spring productivity over time scales of days to weeks. We conducted a cruise to the Ross Sea polynya in November–December, 1994 to measure the contribution of phytoplankton during the austral spring to the annual productivity of the region and found markedly enhanced levels of phytoplankton biomass. Chlorophyll concentrations were greater than 3 µg l−1 in mid-November, a time when the polynya was covered by a thin (ca. 20–30 cm) layer of ice. Particulate matter concentrations increased through time, and by early December chlorophyll and particulate carbon concentrations exceeded 10 µg l−1 and 53 µmol l−1, respectively. Primary productivity also increased through time: the mean productivity in early December equaled 3.53 g C m−2 d−1, and maximum measured rates exceeded 6 g C m−2 d−1. Productivity based on nitrate disappearance averaged 1.52 g C m−2 d−1 (with a maximum rate of 2.49 g C m−2 d−1), suggesting that the bloom's new production was also substantial. The Ross Sea polynya is the most southerly location in the Antarctic where phytoplankton growth is initiated this early and which supports such high standing stocks by early December. Inclusion of this production in a carbon budget for the region suggests that this area supports an annual production of 200 g C m−2, the largest of any region in the Southern Ocean, and confirms its hyperproductive nature.

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. Abundance, biomass and distribution of autotrophic flagellates, autotrophic dinoflagellates and diatoms were measured in the Northeast Water (NEWr Polynya during summer, 1993, using epifluorescence microscopy (EFMr and high-pressure liquid chromotography (HPLCr. Numerous discrepancies existed between results from EFM and HPLC. Phytoplankton communities determined microscopically at the depth of the chlorophyll maximum consisted primarily of flagellates in various size classes (average 1.3×10 7 cells l −1 , 8.5 μg C l −1 r and the small diatom Chaetoceros socialis (average 5×10 6 cells l −1 , 52 μg C l −1 r, with subsurface maxima of both groups usually occurring close to the nitricline. A wide variety was observed in the composition of the phytoplankton community with respect to biomass of individual taxa. The biomass of autotrophic flagellates represented on average 23% of the total autotrophic biomass in all regions of the study area as defined by water mass type. Based on carbon units derived from pigment concentrations (HPLCr, prasinophytes and haptophytes each contributed 24% to total flagellate (non-dinoflagellater biomass and chrysophytes contributed 52%. In the northeast quadrant, influenced by the East Greenland Current, haptophyte contribution dropped to 9%. Most of the biomass of autotrophic flagellates was in cells

The distribution of phytoplankton biomass and pigments was determined in the Ross Sea during late austral summer 1992. Large gradients in biomass were noted both in the east-west and north-south direction, with maximum particulate matter concentrations occurring in the southwest portion of the Ross Sea. Two xanthophyll pigments dominated the profiles, fucoxanthin (indicative of diatoms) and 19′ hexanoyloxyfucoxanthin (hex) (indicative of the prymnesiophyte Phaeocystis antarctica). Fucoxanthin concentrations were greatest near the coast of Victoria Land and within the northern transect, whereas hex concentrations were highest offshore in the SE Ross Sea. Particulate carbon:chlorophyll a (POC:chl) ratios in diatom-dominated waters of the western Ross Sea were relatively high (210). The POC:chl ratio for Phaeocystis antarctica populations from the SE Ross Sea was substantially less (92) than the ratios observed in diatom-dominated waters. Pigment 14C labeling indicated that phytoplankton carbon in the diatom-dominated northern Ross Sea accounted for approximately 30% of the POC, with a phytoplankton C:chl ratio of 130. Short-term (24 hour) vertical fluxes of pigments ranged from 3 to 40 μg chl a m−2 d−1. Diatom-dominated regions had greater fluxes of phaeophorbides, suggesting that metazoans were the most important grazers at these locations. In contrast, the phaeophytin/total phaeopigment ratio was highest in waters dominated by Phaeocystis antarctica. The distribution of phytoplankton biomass and pigments revealed a spatially variable distribution of taxa, one which clearly has important consequences to food-web dynamics, biogeochemical cycles, and vertical flux patterns in the Ross Sea.

We examined the cycling of organic carbon and biogenic silica in the water column and upper sediments of the Ross Sea, seeking to understand the processes leading to the formation of opal-rich, organic-poor sediments over much of the Southern Ocean. Between January, 1990 and December, 1994 we conducted three cruises, performing tracer incubation studies (14C, 15N, 30Si, 32Si) to measure rates of primary production, nitrate-based “new” production, biogenic silica production and biogenic silica dissolution in the upper 50 m over most of the Ross Sea shelf in spring, mid summer and late summer. We deployed sediment traps from January, 1990 to early March, 1992 to measure the mid-water (250 m) and near-bottom gravitational fluxes of particulate organic carbon, nitrogen and biogenic silica year-round at three sites, and obtained sediment cores at 15 sites to assess the accumulation rates of organic carbon and biogenic silica in all known sediment regimes on the shelf. At 9 of those sites we also measured nutrient efflux from the sediments, enabling us to calculate benthic recycling fluxes of organic matter and opal. These data permit estimates of the annual production, near-surface recycling, vertical sinking flux, delivery to the seabed, benthic regeneration and long-term burial of both organic and siliceous material, integrated over a 3.3 × 105 km2 area that covers 75–80% of the Ross Sea shelf. The resulting annual budgets for carbon and silica indicate highly selective preservation of biogenic silica over organic carbon between 50 and 250 m in the water column, as well as in the upper seabed. Selective preservation of silica within the upper 50 m is not indicated, and both organic matter and silica are transported from 250 m to the sea floor with virtually 100% efficiency. The SiO2/C mass ratios for surface-layer production, 250-m sinking flux, delivery to the seabed and long-term burial are approximately 0.85, 6.1, 6.2 and 27, respectively. This progressive enrichment in silica results in long-term burial of 5.8% of the biogenic silica and 0.17% of the organic carbon produced by phytoplankton in the surface layer, a factor of 30 greater preservation efficiency for silica than for carbon. Nevertheless, the ratio of opal burial to opal production in the Ross Sea is only about twice the apparent global average of 3% and

The temporal and spatial patterns of phytoplankton biomass, productivity, and particulate matter composition in the Ross Sea were assessed during cruises in January 1990 and February 1992. Biomass and primary productivity in the southern Ross Sea were greatest during mid-January, with surface chlorophyll concentrations, particulate organic carbon levels, and integrated primary productivity averaging 4.9 μg L−1, 0.54 mg L−1 and 2.63 g C m−2 d−1, respectively. Comparable mean concentrations and rates for February were 1.1 μg L−1, 0.29 mg L−1, and 0.78 g C m−2 d−1 (decreases of 76, 46, and 70%, respectively), indicative of the scale of temporal changes. A distinct south-north transition also was observed both in productivity and phytoplankton biomass, with the lowest values occurring in the northern Ross Sea. East-west gradients in phytoplankton biomass and composition occurred within the southern Ross Sea. The areal productivity of the Ross Sea ranged from 0.15 to 2.85 g C m−2 d−1 and is among the highest found in the entire Antarctic. Carbon:chlorophyll ratios were uniformly high but were highest (150) in 1990 in the diatom-dominated western Ross Sea. Surface growth rates were modest, averaging less than 0.2 day−1 during both seasons. We hypothesize that the marked seasonality in the region provides an environment in which net growth rates, although slow, are maximized through low loss rates and which allows biomass to accumulate in the surface layer. Furthermore, the temporal variations are quantitatively similar to the observed spatial variations. Therefore the dominant determinant of phytoplankton biomass and productivity at any one point on the Ross Sea continental shelf is the stage of the seasonal growth cycle.

Phytoplankton biomass and primary productivity were assessed on the continental shelf in the plume of the Amazon River during a series of cruises conducted within periods of minimum, maximum, rising and falling river discharge. Chlorophyll concentrations were greatest (up to 25.5 μg l −1 ) in a zone located outside the turbid, high nutrient, low salinity riverine waters but shoreward of the clear, high salinity, low nutrient waters. Vertical distributions of chlorophyll further delineated the influences of these environmental regimes, with maximum chlorophyll concentrations occurring in the upper 5 m of water columns characterized by reduced salinities and elevated nutrients at the surface and low nutrient, high salinity water below. Fluorescence was elevated in the transition zone as a result of the phytoplankton standing stocks, and was also elevated in low-salinity waters influenced by the Amazon outflow. The residual fluorescence was coupled to salinity but not to chlorophyll, which suggested that it was related to dissolved organic matter which originated in the Amazon. Primary productivity on the continental shelf was greatest in the transition zone and occasionally exceeded 8 g C m −2 d −1 . Productivity in the turbid, nutrient-rich waters and the clear, offshore regions averaged 2.18 and 0.81 g C m −1 d −1 , respectively. Phytoplankton photosynthesis in waters influenced by the Amazon River appeared to be limited by low levels of available irradiance inshore, whereas offshore it was nutrient-limited. The narrow zone of high production was supported by the riverine input of nutrients and the dynamics of sediment flocculation. Removal of the inorganic sediment load was necessary to allow for adequate irradiance penetration to support photosynthesis.

Biogeochemical processes in the Amazon River/ocean mixing zone were examined during four AmasSeds cruises between August 1989 and November 1991. On the Amazon shelf, the distributions of chlorophyll-a, oxygen supersaturation, pH and the biogenic-silica content of suspended matter all showed coherent patterns highlighting areas of high primary productivity. Phytoplankton blooms occurred seaward of the high-turbidity waters (suspended-solid concentration >10 mg 11¯) and the extent of the bloom depended on the supply of nitrate from the Amazon River, as well as the time available to phytoplankton in the “optimal-growth zone” (a region of relatively low turbidity and high nutrients). Of the four AmasSeds field cruises, the largest phytoplankton bloom occurred during March 1990, when the nitrate flux to the shelf was highest and the plume residence time was the longest. The biogenic-silica standing crop in Amazon shelf waters (area of 8.9 × 1010 m2) varied from 29 to 66 × 108 moles during the two-year study period, whereas the depth-integrated silicate anomaly on the shelf (i.e. the difference between the observed nutrient concentration and the salinity-predicted value from the ideal mixing of riverine and oceanic end members) varied from +5 to −170 × 108 moles. Chlorophyll-a inventories on the shelf ranged from 10 to 36 × 108 g. The maximum extent of nutrient removal occurred during the March 1990 cruise, consistent with the maximum standing crops of biogenic silica and chlorophyll-a. Excess silicate and excess inorganic-nitrogen concentrations (relative to the ideal mixing line) commonly occurred in inner-shelf waters (

Sea ice core chlorophyll a data are used to describe the seasonal, regional and vertical distribution of algal biomass in Southern Ocean pack ice. The Antarctic Sea Ice Processes and Climate – Biology (ASPeCt – Bio) circumpolar dataset consists of 1300 ice cores collected during 32 cruises over a period of 25 years. The analyses show that integrated sea ice chlorophyll a peaks in early spring and late austral summer, which is consistent with theories on light and nutrient limitation. The results indicate that on a circum-Antarctic scale, surface, internal and bottom sea ice layers contribute equally to integrated biomass, but vertical distribution shows distinct differences among six regions around the continent. The vertical distribution of sea ice algal biomass depends on sea ice thickness, with surface communities most commonly associatedwith thin ice (

The distribution of phytoplankton biomass in the plume of the Amazon River over the Brazilian continental shelf is analyzed by the use of multiple regression. Previous attempts to assess how different parameters control phytoplankton biomass have used pairwise correlations. A multiple regression approach, however, allows the elucidation of collinearity between these parameters. This approach reveals that phytoplankton biomass may be predicted largely by the following three groups of collinear variables that resemble the “factors” of factor analysis: suspended-sediment concentration and transparency (which generally describe irradiance availability), salinity and temperature (which describe vertical stratification, a measure of water-column stability), and the ambient concentrations of nutrients (phosphate, nitrate, silicic acid, and nitrite). The effects of water clarity and nutrients have been previously described, but the importance of vertical stability has never been separated from the other two. Additional important single variables were oxygen, ammonia, and urea. The strength of the contribution of particular variables to a regression model depends on the season of the cruise and hence on the volume of riverine discharge.

Dimethylsulfide (DMS), particulate dimethylsulfoniopropionate (DMSPp) and phytoplankton pigments were measured on three transects in the Ross Sea, Antarctica during February 1992. Although relatively low chl a levels (mean of 0.7 μg l−1) were encountered, the DMS inventory in the photic zone ranged from 81 to 3484 μol m−2. In comparison, the DMSOp standing stock was very low (range of 13–298μol m−2) and accounted for only 11% of the average integrated DMS concentration. DMS:chl a ratios (58–78 nmol μg−1) were significantly higher in waters dominated by Phaeocystis antarctica compared to diatom-dominated waters (2–12 nmol μg−1). A strong DMS gradient was observed from south to north with the highest DMS concentrations (123 nM) measured in the southern Ross Sea and the lowest (

This is the third and final volume of manuscripts comprising the results from a series of process studies conducted as part of the US Joint Global Ocean Flux Study. The objectives of this study were to provide insights into the quantities and controls of fluxes in the Southern Ocean, to elucidate the processes that control primary production in both space and time, and to use these results to model the processes that were dominant in past environments. The results demonstrate the importance of the Southern Ocean with regard to both the present and past productivity patterns and vertical fluxes from the surface layer.

[1] In austral summer, from December 2008 to January 2009, we investigated the sea-ice carbon dioxide (CO2) system and CO2 controls in the Amundsen and Ross Seas, Antarctica. We sampled seawater, brine and sea ice for the measurements of total alkalinity (AT), total inorganic carbon (DIC), pH, inorganic nutrients, particulate organic carbon (POC) and nitrogen (PON), chlorophyll a, pigments, salinity and temperature. Large variability in all measured parameters was observed in time and space due to the complex sea-ice dynamics. We discuss the controls of the sea-ice CO2 system, such as brine rejection, biological processes, calcium carbonate (CaCO3) precipitation/dissolution and CO2 exchange. Most (80 to 90%) of the DIC loss was due to brine rejection, which suggests that the sea ice acted as an efficient DIC sink from 0.8 and 2.6 mol m−2 yr−1 (9.6–31 g C m−2 yr−1). The remaining change in DIC was to a large extent explained by net biological production. The AT:DIC ratio in the sea ice was higher than in the under-ice water (UIW), with ratios reaching 1.7, which indicated CaCO3 precipitation and concomitant DIC loss in the sea ice. Elevated AT:DIC ratios and carbonate concentrations were also observed in the UIW, which reflect the solid CaCO3 rejected from the ice during melt. The potential for uptake of atmospheric CO2 in the mixed layer increased by approximately 56 μatm due to the combined effect of CaCO3 precipitation during ice formation, and ice melt in summer.

[1] The Ross Sea polynya is among the most productive regions in the Southern Ocean and may constitute a significant oceanic CO2 sink. Based on results from several field studies, this region has been considered seasonally iron limited, whereby a “winter reserve” of dissolved iron (dFe) is progressively depleted during the growing season to low concentrations (∼0.1 nM) that limit phytoplankton growth in the austral summer (December–February). Here we report new iron data for the Ross Sea polynya during austral summer 2005–2006 (27 December–22 January) and the following austral spring 2006 (16 November–3 December). The summer 2005–2006 data show generally low dFe concentrations in polynya surface waters (0.10 ± 0.05 nM in upper 40 m, n = 175), consistent with previous observations. Surprisingly, our spring 2006 data reveal similar low surface dFe concentrations in the polynya (0.06 ± 0.04 nM in upper 40 m, n = 69), in association with relatively high rates of primary production (∼170–260 mmol C m−2 d−1). These results indicate that the winter reserve dFe may be consumed relatively early in the growing season, such that polynya surface waters can become “iron limited” as early as November; i.e., the seasonal depletion of dFe is not necessarily gradual. Satellite observations reveal significant biomass accumulation in the polynya during summer 2006–2007, implying significant sources of “new” dFe to surface waters during this period. Possible sources of this new dFe include episodic vertical exchange, lateral advection, aerosol input, and reductive dissolution of particulate iron.

[1] We calculate net community production (NCP) during summer 2005–2006 and spring 2006 in the Ross Sea using multiple approaches to determine the magnitude and consistency of rates. Water column carbon and nutrient inventories and surface ocean O2/Ar data are compared to satellite-derived primary productivity (PP) estimates and 14C uptake experiments. In spring, NCP was related to stratification proximal to upper ocean fronts. In summer, the most intense C drawdown was in shallow mixed layers affected by ice melt; depth-integrated C drawdown, however, increased with mixing depth. ΔO2/Ar-based methods, relying on gas exchange reconstructions, underestimate NCP due to seasonal variations in surface ΔO2/Ar and NCP rates. Mixed layer ΔO2/Ar requires approximately 60 days to reach steady state, starting from early spring. Additionally, cold temperatures prolong the sensitivity of gas exchange reconstructions to past NCP variability. Complex vertical structure, in addition to the seasonal cycle, affects interpretations of surface-based observations, including those made from satellites. During both spring and summer, substantial fractions of NCP were below the mixed layer. Satellite-derived estimates tended to overestimate PP relative to 14C-based estimates, most severely in locations of stronger upper water column stratification. Biases notwithstanding, NCP-PP comparisons indicated that community respiration was of similar magnitude to NCP. We observed that a substantial portion of NCP remained as suspended particulate matter in the upper water column, demonstrating a lag between production and export. Resolving the dynamic physical processes that structure variance in NCP and its fate will enhance the understanding of the carbon cycling in highly productive Antarctic environments.

Over the last several decades, numerous approaches have been used to observe the rapid development of the annual phytoplankton bloom in the Ross Sea, including ship-based sampling, moored instrumentation, satellite images, and computer modeling efforts. In the Austral Spring of 2010, our group deployed a pair of iRobot Seagliders equipped with fluorometers, oxygen sensors and CTDs in order to obtain data on this phenomenon over the entire duration of the bloom. Data from these deployments will be used, along with samples from the recovery cruise and satellite data, to model and better understand the dynamics of this phytoplankton bloom.

Made available in DSpace on 2013-08-28T14:13:50Z (GMT). No. of bitstreams: 1 WOS000287796800018.pdf: 4189122 bytes, checksum: 57872b9405eca4911ea4efd9756f160c (MD5) Made available in DSpace on 2013-09-30T19:22:54Z (GMT). No. of bitstreams: 2 WOS000287796800018.pdf: 4189122 bytes, checksum: 57872b9405eca4911ea4efd9756f160c (MD5) WOS000287796800018.pdf.txt: 74870 bytes, checksum: b4ae21f33d5d23b3ff5f0482dfbc34ee (MD5) Previous issue date: 2011-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:34:00Z No. of bitstreams: 2 WOS000287796800018.pdf: 4189122 bytes, checksum: 57872b9405eca4911ea4efd9756f160c (MD5) WOS000287796800018.pdf.txt: 74870 bytes, checksum: b4ae21f33d5d23b3ff5f0482dfbc34ee (MD5) Made available in DSpace on 2014-05-20T15:34:00Z (GMT). No. of bitstreams: 2 WOS000287796800018.pdf: 4189122 bytes, checksum: 57872b9405eca4911ea4efd9756f160c (MD5) WOS000287796800018.pdf.txt: 74870 bytes, checksum: b4ae21f33d5d23b3ff5f0482dfbc34ee (MD5) Previous issue date: 2011-01-01 National Aeronautics and Space Agency Nearly half of the earth's photosynthetically fixed carbon derives from the oceans. To determine global and region specific rates, we rely on models that estimate marine net primary productivity (NPP) thus it is essential that these models are evaluated to determine their accuracy. Here we assessed the skill of 21 ocean color models by comparing their estimates of depth-integrated NPP to 1156 in situ C-14 measurements encompassing ten marine regions including the Sargasso Sea, pelagic North Atlantic, coastal Northeast Atlantic, Black Sea, Mediterranean Sea, Arabian Sea, subtropical North Pacific, Ross Sea, West Antarctic Peninsula, and the Antarctic Polar Frontal Zone. Average model skill, as determined by root-mean square difference calculations, was lowest in the Black and Mediterranean Seas, highest in the pelagic North Atlantic and the Antarctic Polar Frontal Zone, and intermediate in the other six regions. The maximum fraction of model skill that may be attributable to uncertainties in both the input variables and in situ NPP measurements was nearly 72%. on average, the simplest depth/wavelength integrated models performed no worse than the more complex depth/wavelength resolved models. Ocean color models were not highly challenged in extreme conditions of surface chlorophyll-a and sea surface temperature, nor in high-nitrate low-chlorophyll waters. Water column depth was the primary influence on ocean color model performance such that average skill was significantly higher at depths greater than 250 m, suggesting that ocean color models are more challenged in Case-2 waters (coastal) than in Case-1 (pelagic) waters. Given that in situ chlorophyll-a data was used as input data, algorithm improvement is required to eliminate the poor performance of ocean color NPP models in Case-2 waters that are close to coastlines. Finally, ocean color chlorophyll-a algorithms are challenged by optically complex Case-2 waters, thus using satellite-derived chlorophyll-a to estimate NPP in coastal areas would likely further reduce the skill of ocean color models. Virginia Inst Marine Sci, Coll William & Mary, Gloucester Point, VA 23062 USA CNRS, LOV, Villefranche Sur Mer, France Univ Paris 06, UMR 7093, Villefranche Sur Mer, France SUNY Stony Brook, Sch Marine & Atmospher Sci, Stony Brook, NY 11794 USA Tokyo Univ Informat Sci, Chiba 2658501, Japan Oregon State Univ, Dept Bot & Plant Pathol, Corvallis, OR 97331 USA Univ Estadual Paulista, BR-11330900 São Paulo, Brazil European Commiss, Joint Res Ctr, I-21027 Ispra, Italy NOAA, NMFS, Narragansett Lab, Narragansett, RI 02882 USA Nagoya Univ, Hydrospher Atmospher Res Ctr, Nagoya, Aichi 4648601, Japan Seikai Natl Fisheries Res Inst, Ishigaki Trop Stn, Okinawa 9070451, Japan CUNY, Brooklyn Coll, Dept Geol, Brooklyn, NY 11210 USA Univ Roma Tor Vergata, Dept Biol, I-00173 Rome, Italy Plymouth Marine Lab, Plymouth PL1 3DH, Devon, England Fisheries & Oceans Canada, Inst Freshwater, Winnipeg, MB R3T 2N6, Canada Univ Calif San Diego, Scripps Inst Oceanog, La Jolla, CA 92093 USA NOAA, Coastal Serv Ctr, Charleston, SC 29405 USA Univ Estadual Paulista, BR-11330900 São Paulo, Brazil NASA: NNG06GA03G

The interaction of physical and biological processes is extremely important in structuring the biological communities in all marine environments, yet the complexity of this interaction at all scales is just beginning to be appreciated. We review the patterns of plankton biomass and the processes that influence plankton production, and in particular emphasize the importance of different processes at different time and space scales (small-scale, mesoscale, and large-scale). Examples of two different systems (the Southern Ocean and the subarctic North Pacific and North Atlantic Oceans) are given to illustrate the complexity and strength of the interactions. We conclude that biological processes may be more important at smaller scales where behavior such as vertical migration and predation may control the plankton production, whereas physical processes may be more important at larger scales in structuring biological communities. An understanding of both, however, is critical to an understanding of the distribution of plankton and the processes governing production in the ocean.

The marginal ice zones of the Arctic are regions of extreme importance to global biogeochemical cycles, in that they are sites of accumulation and transfer of organic matter within the food web and locations of significant fluxes of carbon, both inorganic and organic. Yet a complete seasonal description over the relevant time and space scales has not been conducted. Properly validated numerical models extend our ability to understand these oceanographic features because field studies are limited in their spatial and temporal coverage. Our knowledge of the mosaic of complex air-sea-ice interactions is good enough to relate the forces, through models, which control sea and ice motion, as well as the growth of phytoplankton. We review the use of models in investigations of marginal ice zones in the Arctic and conclude that the primary factor in regulating the initiation, development, and dissipation of ice edge phytoplankton blooms is vertical stratification. Furthermore, the spatial domain of the bloom is controlled by the ice dynamics and the response to local winds. Upwelling does occur at ice edges, but it is generally ineffective in directly stimulating phytoplankton growth. Any stimulation that does occur is via changes in the local ice cover (hence irradiance) field. Other mesoscale features such as eddies, fronts, or current meanders also influence the local biophysical interactions. The use of properly validated models in oceanographic research is a powerful tool for both posing and answering questions dealing with complex interactions that occur in the ocean.

Nitrogen (nitrate and ammonium) uptake was measured in the Greenland Sea during April–May 1989 as part of the Coordinated Eastern Arctic Experiment (CEAREX). The region was dominated by a massive bloom of Phaeocystis pouchetii, and particulate nitrogen concentrations reached 450 mmol m−2 within the bloom. Particulate carbon:nitrogen ratios were similar to other polar assemblages, suggesting that the particulate matter composition was not dominated by carbon-rich extracellular material. Vertically integrated f ratios ranged from 0.09 to 0.90 and generally decreased with time, as did nitrate concentrations. Nitrate uptake rates showed no temporal trend, but ammonium uptake rates were low initially and increased greatly by the end of the study. New production rates were very high, with carbon-based productivities calculated from nitrate uptake rates and observed C:N ratios up to 4.9 g C m−2 d−1. Based on a simple mass balance of organic matter, much (∼60%) of the biogenic material produced in the Phaeocystis bloom apparently was removed from the surface layer. It is hypothesized that the formation of aggregates led to increased fluxes of particulate organic matter from the surface layer. As a result, Phaeocystis blooms may play important roles in the vertical transport of carbon and nitrogen in the Greenland Sea.

[1] Recent investigations into the role of carbon dioxide on phytoplankton growth and composition have clearly shown differential effects among species and assemblages, suggesting that increases in oceanic CO2 may play a critical role in structuring lower trophic levels of marine systems in the future. Furthermore, alarming increases in the occurrence of harmful algal blooms (HABs) in coastal waters have been observed, and while not uniform among systems, appear in some manner to be linked to human impacts (eutrophication) on coastal systems. Models of HABs are in their infancy and do not at present include sophisticated biological effects or their environmental controls. Here we show that subtle biological responses occur in the HAB species Phaeocystis globosa Scherffel as a result of CO2 enrichment induced by gentle bubbling. The alga, which has a polymorphic life history involving the formation of both colonies and solitary cells, exhibited altered growth rates of colonial and solitary forms at [CO2] of 750 ppm, as well as increased colony formation. In addition, substantial modifications of elemental and photosynthetic constituents of the cells (C cell �1 ,Nc ell �1 , potential quantum yield, chl a cell �1 ) occurred under elevated CO2 concentrations compared to those found at present CO2 levels. In contrast, other individual and population variables (e.g., colony diameter, total chlorophyll concentration, carbon/nitrogen ratio) were unaffected by increased CO2. Our results suggest that predictions of the future impacts of Phaeocystis blooms on coastal ecosystems and local biogeochemistry need to carefully examine the subtle biological responses of this alga in addition to community and ecosystem effects. Citation: Wang, Y., W. O. Smith Jr., X. Wang, and S. Li (2010), Subtle biological responses to increased CO2 concentrations by Phaeocystis globosa Scherffel, a harmful algal bloom species, Geophys. Res. Lett., 37, L09604

Phytoplankton assemblages of the Ross Sea are generally dominated by two functional groups: diatoms and haptophytes ( Phaeocystis antarctica ). Within this “normal” pattern of dominance, there is a substantial amount of temporal (over months, seasons and years) and spatial variability. Such variability has a significant impact on several biogeochemical cycles, such as the carbon and sulfur cycles, at the regional and global scales. We compiled all available accessory pigment data for the southern Ross Sea as a means to quantify the prevalence and dominance of each group, and generated a seasonal “climatology” of assemblage composition. The climatological pattern of phytoplankton pigments shows that haptophytes normally grow and accumulate early in the season, and largely in the southern Ross Sea polynya. Diatoms reach a biomass maximum later, and reach most extensive concentrations closer to the coast of Victoria Land. While the pattern of spring growth of P. antarctica followed by an increase in diatom abundance is found frequently, deviations from that pattern were observed. Two periods – November, 2006 and January, 2004 – illustrated that variations of up to one order of magnitude can occur relative to the climatology. These deviations may provide insights into the dominant control mechanisms of the two functional groups.

The colony-forming haptophyte Phaeocystis antarctica is an important primary producer in the Ross Sea, and must survive long periods of darkness and freezing temperature in this extreme environment. We conducted experiments on the responses of P. antarctica -dominated phytoplankton assemblages to prolonged periods of darkness and freezing. Chlorophyll and photosynthetic capacity of the alga declined nonlinearly and independently of each other in the dark, and darkness alone would potentially reduce photosynthetic capacity by only 60 per cent over 150 days (approximately the length of the Antarctic winter in the southern Ross Sea). The estimated reduction of colonial mucous carbon is higher than that of colonial cell carbon, suggesting metabolism of the colonial matrix in the dark. The alga quickly resumed growth upon return to light. Phaeocystis antarctica also survived freezing, although longer freezing durations lengthened the lag before growth resumption. Particulate dimethylsulfoniopropionate relative to chlorophyll increased upon freezing and decreased upon darkness. Taken together, the abilities of P. antarctica to survive freezing and initiate growth quickly after darkness may provide it with the capability to survive in both the ice and the water column, and help explain its repeated dominance in austral spring blooms in the Ross Sea and elsewhere in the Southern Ocean.