Plankton ecology in an ice-covered bay of Lake Michigan: utilization of a winter phytoplankton bloom by reproducing copepods

Plankton ecology was examined during the 1986 winter in Grand Traverse Bay, a 190 m deep, fjordlike bay on Lake Michigan. Before ice cover, algal concentration was low and uniformly distributed with depth, as it is in open Lake Michigan. During ice cover (February and March), a bloom of a typical winter-spring phytoplankton community developed in the upper 40 m, resulting in a 4 to 7-fold increase in feeding rate of adult Diaptomus spp. High algal concentration and zooplankton feeding persisted after ice melt (April). During and after ice cover, lipid concentrations of Diaptomus dropped rapidly from 34% of dry weight to 17 % because of egg production. High incident photosynthetically active radiation (PAR), high (45–50%) PAR transmittance of the ice due to little snow on the ice, and water column stability were probably responsible for the bloom. High ice transparency may be a common feature of large lakes and bays, where strong winds blow snow cover off the ice, or at low latitudes where snowmelt due to occasional rains and warm temperature is common. Winter reproducing calanoid copepods use these blooms to increase their reproductive output.     

Ecological Factors of Hydrolytic Enzyme Activities in the Ob–Yenisey Estuarine Coastal Waters in Winter and Their Modelling

The ice conditions at the Ob–Yenisey estuarine coastal waters with relatively diffuse ice cover have been described using the data obtained in the Kara Sea survey aboard the nuclear icebreaker Yamal in January 22–March 6, 2003. The data on the capacity and rate of enzymatic degradation of various forms of organic matter and on the associated ecological factors in the region of active sea water/continental water interaction are given. We analyzed spatial distribution of the main types of water bodies as well as the cascade structure formed by some biogeochemical barriers near the Ob–Yenisey flaw polynya. We also analyzed the correlations between the indices of extracellular biochemical activity in water and the main abiotic and biotic factors during the organotrophic phase. The processes determining the level of biochemical activity in winter water and the rates of potential degradation of various organic compounds are considered.     

Distribution and diving behaviour of crabeater seals (Lobodon carcinophagus) off Queen Maud Land

Eight crabeater seals (Lobodon carcinophagus) (three females, five males), ranging in body mass between 125 and 220 kg, were captured off Queen Maud Land (70–72°S, 7–16°W) during the last week of February, just after moulting, and tagged with Argos satellite-linked dive recorders to provide data on location and diving depth and duration. During the first few weeks of March the seals were moving in the pack ice along the continental shelf edge, close to the coast of Queen Maud Land. In April and May, when the pack ice extended northwards, most of the seals moved north, one reaching 63°S in late May. In the first half of June the two remaining seals turned south and moved back deep into the pack ice. The seals made about 150 dives per day each throughout the study period. Ninety percent of these were made to depths of less than 52 m. Individual maximum diving depths varied between 288 and 528 m. In March the seals were most active at night, when the dive depth was shallower than during the day. In April and May the seals were more active during day-time, with an absence of any diurnal change in divng depth. These results support the notion that crabeater seals predominantly feed on krill in Antarctic pack ice, even when winter returns to the waters off Queen Maud Land.Publication no. 134 of the Norwegian Antarctic Research Expedtion 1992/1993     

Winter microbial activity in Lake Tuusulanjärvi

Microbial heterotrophic activity, dark CO₂ assimilation, primary productivity and microbial ATP were measured monthly in the extremely eutrophic Lake Tuusulanjärvi during the winter of 1979–1980. Because of continuous water circulation caused by low temperature and artificial aeration of the lake, no winter stratification developed. Very low summertime ³H-glucose turnover times of 5 h increased to a level of 10–20 h from August to January. Winter maximum of 110 h was measured in March, and turnover times returned to 10–20 h in April, before the vernal bloom of algae occured. Oxygen saturation remained over 46% during the winter.High primary productivity was observed in November (400–500 mg C m^–3 day^–1), and measurable productivity was detected under ice in January (80 mg C m^–3 day^–1). Dark CO₂ assimilation increased to 14% of primary productivity in March. No correlation was found between ³H-glucose turnover rate and dark CO₂ assimilation. ATP correlated slightly better with primary productivity than with turnover rate. The single concentration method proved to be sensitive for winter heterotrophic activity measurement.     

Distribution patterns of benthic microalgal standing stock at McMurdo Sound,Antarctica

Summary During the austral summer of 1975–76 and winter of 1977 benthic and water column chlorophyll a and phaeopigments were measured at several sites along the east and west sides of McMurdo Sound, Antarctica. Estimates of in situ primary productivity were made at some McMurdo Sound locations. Additionally, water column samples were collected at 5 stations in the Ross Sea during January, 1976. Standing stock data are analyzed to identify seasonal and spatial patterns. Variability in algal standing stock was related to ambient light levels and appeared to be mediated by ice and snow cover whereby the highest algal standing stock was present under high light conditions (low ice and snow cover, shallow water, summer). Differences in published benthic invertebrate densities appear to be closely allied to differences in benthic primary production, and less so to in situ planktonic ice microalgal production.     

Response of deep-sea benthic foraminifera to Miocene paleoclimatic events, DSDP Site 289

Changes in the Miocene deep-sea benthic foraminifera at DSDP Site 289 closely correlate to the climatically induced variations in deep and bottom waters in the Pacific Ocean. In early Miocene time, oxygen and carbon isotopes indicate that bottom waters were relatively warm and poorly oxygenated. Benthic foraminiferal assemblages are characterized by various species inherited from the Oligocene. Expansion of the Antarctic icecap in the early middle Miocene, 14–16 m.y. ago, increased oxygen isotope values, produced cold, more oxygenated bottom waters and lead to a turnover in the benthic foraminifera. An Oligocene—early Miocene assemblage was replaced by a cibicidoid-dominated assemblage. Some species became extinct and benthic faunas became more bathymetrically restricted with the increased stratification of deep waters in the ocean. In mid-Miocene time, Epistominella exigua and E. umbonifera, indicative of young, oxygenated bottom waters, are relatively common at DSDP Site 289. Further glacial expansion 5–9 m.y. ago lowered sealevel, increased oceanic upwelling and associated biological productivity and intensified the oxygen minima. Abundant hispid and costate uvigerines become a dominant faunal element at shallow depths above 2500 m as E. umbonifera becomes common to abundant below 2500 m. By late Miocene time, benthic faunas similar in species composition and proportion to modern faunas on the Ontong-Java plateau, had become established.     

Depleted methane-derived carbon in waters of Lake Baikal,Siberia

Results of hydrochemical and stable isotope measurements during the ice-breaking period on Lake Baikal indicate an apparent lack of relationship between measured δ¹³C of dissolved inorganic carbon (DIC) and phytoplankton below the trophogenic layer. While planktonic values of −31.7 to −33.5‰ are within a typical lacustrine range, the δ¹³C values of DIC turned out to be very negative, from −28.9 to −35.6‰. These isotopic values of DIC appear to be associated with oxidation of methane that accumulated during winter ice cover period. At the time of sampling, however, the observed depletion did not affect the phytoplankton/DIC fractionation relationship, because the difference between phytoplankton and DIC (−20 to −22‰ in surface waters) lies within the expected range of the fractionation coefficient. By analogy with small lakes, we explain this lack of relationship by the time lag between peak productivity and peak methane oxidation. Our interpretation of the Baikal DIC isotopic signature is consistent with methanogenesis in bottom sediments and with the known presence of widespread unstable gas hydrates and active methane seeps on the lake floor. Our findings suggest that methane is an important component of the Baikal carbon cycle, that late winter concentrations of methane in Baikal under ice may be 3–4 orders of magnitude higher than previously reported values for summer, and that the lake may be emitting a significant amount of methane to the atmosphere.     

Hydrography and characteristics of the phytoplankton in shelf and oceanic waters off southeastern Brazil during winter (July/August 1982) and summer (February/March 1984)

The physical and chemical environment, and the phytoplankton primary production of southeastern Brazil were studied in relation to the general oceanographic structure during two research cruises (winter and summer). In each cruise, a total of 91 stations were occupied. Data were collected on the spatial distribution of nutrients, phytoplankton biomass and photosynthetic capacity over the coastal, shelf and oceanic areas off São Paulo, Paraná and Santa Catarina States.During wintertime, the mixing processes between tropical warm waters of the Brazil Current and subantarctic waters of the Malvinas Current formed strong environmental gradients. The drainings of Rio de La Plata and Lagoa dos Patos are transported northwards by coastal currents, enriching the shelf waters off Santa Catarina State with inorganic nutrients and consequently increasing the chlorophyll a to the highest concentrations (> 3.5 mg m ^–3) measured during the two cruises. In slope waters chlorophyll values were always low (0.05–0.45 mg m ^–3). The chlorophyll within the euphotic layer varied from 8.8–36.7 and 1.2–18.5 mg m^–2 during winter and summer, respectively.The surface photosynthetic rates during winter and summer cruises ranged respectively from 0.21–9.17 and 0.66–19.60 mgC/mgChl.a/h. The mean rates were higher in nearshore waters and decreased seaward.The thermal structure of the water column affected the vertical distribution of chlorophyll a and photosynthesis within the euphotic zone; During unstratified periods (winter) they were uniformly distributed but the occurrence of subsurface peaks of chlorophyll and strong photosynthetic inhibition of low light adapted cells in deeper layers are associated to the seasonal thermocline. Occasionally, upwelling of deep waters from shelf break enriched the deeper euphotic layers in offshore areas. Intensive upwelling was observed off Paranagua Bay (Parana State) and the mechanisms of its formation are discussed.     

Outdoor cultivation ofArthrospira platensis during autumn and winter in temperate climates

Arthrospira (Spirulina) platensis M2 was grown outdoors in 50-mm diameter tubular reactors under the climatic conditions of central Italy (Florence) from September to December 1995 and in March 1996. Except for September, the cultures temperature was regulated. Mean productivities of 0.83, 0.44 and 0.61 g dry wt L^–1 d^–1 were achieved in autumn (September–October), winter (November–December) and March, respectively. In autumn and winter, the photosynthetic efficiency of the cultures and the degree of correlation between productivity and solar irradiance were significantly greater than in summer. The effect of cell density and aeration rate on productivity was evaluated in September. The productivity of cultures operated at high supra-optimal population density was about 30% less at high aeration rate (1.0 LL^–1 min^–1), and 50% less at standard aeration rate (0.17 LL^–1 min^–1), than that of control cultures kept at optimal population density and standard aeration rate. The reduction of productivity in high-density cultures was due to lower daylight output rates and higher night biomass losses (the latter were particularly relevant under standard aeration conditions). The main factor limiting productivity in closed reactors during autumn was the night temperature. Heating the cultures during daylight hours on sunny days did not cause any significant increase of the yields, since under sunlight the unheated cultures also reached the optimal temperature for growth early in the morning. On cloudy days, the day-time temperature of the unheated cultures remained well below the optimum, however this had only a limited effect on productivity since algal growth was mainly light-limited.     

Distribution and abundance of spotted seals Phoca largha and ribbon seals Phoca fasciata in the southern Sea of Okhotsk

The distribution and abundance of spotted seals (Phoca largha) and ribbon seals (Phoca fasciata) were assessed in March and April, 2000, by aerial line-transect surveys along the southern edge of the pack ice off the coast of Hokkaido (southern Sea of Okhotsk), Japan. Five hundred and seventeen spotted seals and 107 ribbon seals were found on the total 2944 km survey line. Total abundance was estimated to be 13 653 spotted (95% CI = 6167–30 252) and 2260 ribbon seals (95% CI = 783–6607) in March, and 6545 spotted (95% CI = 3284–815 644) and 3134 ribbon seals (95% CI = 1247–17 802 512) in April. The pack ice area off Hokkaido had higher densities (0.54 seals km^–2 and 0.58 seals km^–2 in March and April, respectively) of spotted seals than those reported in eastern Sakhalin, whereas densities (0.09 seals km^–2 in March and 0.28 seals km^–2 in April) of ribbon seals were lower than those in eastern Sakhalin. The large number of spotted seal pups suggests that the study area is an important breeding center. A greater number of female spotted seals with pups tended to be found in the center of larger and rougher floes than in other categories, and they were more abundant in stable pack ice areas. Observations of ribbon seals were limited because the survey period preceded the peak of pupping season. Ribbon seal surveys were also hampered by the inability to fly over the main breeding area between the Shiretoko Peninsula and Kunashiri Island.     

Experimental Evidence on Nutrient and Substrate Limitation of Baltic Sea sea-ice Algae and Bacteria

The effect of nutrient limitation on Baltic Sea ice algae, and substrate and nutrient limitation on ice bacteria, was studied in a series of in situ -experiments conducted during the winter of 2002 in northern Baltic Sea. Community level changes in algal biomass (chlorophyll a) and productivity, and bacterial thymidine and leucine incorporation were followed for one week after the addition of nutrient and/or organic carbon rich filtered seawater to the experimental units. The results showed the major contribution of snow cover to the algal responses during the beginning of the ice-covered season. Algal communities were able to grow even in January if no snow was present. Nutrient addition did occasionally have an effect on algal biomass and productivity in the ice. Surprisingly, seeding effect from the ice to the underlying water was negatively affected by the nutrient availability in March. Bacterial limitation varied between nutrient (phosphorus) and substrate limitations. The results showed, that limitation in both algal and bacterial communities changed periodically in the northern Baltic Sea ice.     

Current patterns in McMurdo Sound,Antarctica and their relationship to local biotic communities

Summary Current speed and direction measurements collected during summer (January–February) and sping (November–December) of 1984 indicated that currents in McMurdo Sound, Antarctica were dominated by oscillatory flow associated with diurnal tidal components (O1, K1, P1). Net flow was southward in the eastern Sound, mixed in the central Sound, and northward in the western Sound. Short term observations (<5 days) from nearshore stations indicated a similar but more sluggish pattern of tidal and mean flow. Hydrographic data collected during the same period indicated a similar pattern of cold water with low chlorophyll a content flowing northward from under the Ross Ice Shelf in the western Sound and denser, slightly warmer water with higher chlorophyll a content flowing southward in the eastern Sound. Previous studies have shown that productivity is higher in the eastern Sound than in the west, apparently due to the circulation pattern. The western Sound consists of waters from beneath the Ross Ice Shelf which have a lower phytoplankton standing stock than eastern Sound waters which enter from the north. More sluggish current speeds in the western Sound result in even lower particle fluxes past benthic consumers. Finally, more persistent ice cover in the west further inhibits in situ primary productivity.     

Seasonal variation in abundance and species composition of choanoflagellates (Acanthoecideae) at Antarctic coastal sites

Summary The abundance of loricate choanoflagellates at three shallow inshore sites (< 30 m) near Davis, Antarctica from March 1982 to February 1983 showed marked variation which followed the seasonal cycle of chlorophyll a concentration. In summer the concentration of choanoflagellates ranged from 10⁴–10⁶ cells 1^–1 while in winter they were in the order of 10² cells 1^–1. Species seasonal succession was observed with Bicosta spinifera, Crinolina aperta and Parvicorbicula socialis, organisms which dominated the summer population, being absent in winter whereas Cosmoeca ventricosa and Saepicula leadbeateri were found only in winter. Acanthocorbis unguiculata, Calliacantha simplex and Diaphanoeca grandis were present throughout the year.     

Vertical distributions of a planktonic harpacticoid and a calanoid (Copepoda) in a meromictic Antarctic lake

Lake Abraxas (68° 29 S., 78° 17 E.) has been cut off from the sea for c. 6000 yr. In December, 1985, it had an ice cover 1.38 m thick, a thermocline at 5.2 m, and zero oxygen at 17.7 m and below. The salinity of the oxylimnion was in the range 14–19 g 1^–1. The calanoid, Paralabidocera antarctica (I. C. Thompson), had a maximum density just above a thermocline at 5.0 m, at which depth adult males outnumbered females almost 3 : 1. Immediately beneath the ice adult females outnumbered males 4 : 1. Immature copepodite stages were more abundant relative to adults near the oxycline than at higher levels. The planktonic harpacticoid, Amphiascoides sp., had a maximum density close to the oxycline at 17.2 m.     

Uvigerina proboscidea abundances and paleoceanography of the northern Indian Ocean DSDP Site 214 during the Late Neogene

This study attempts to understand the significance of Uvigerina proboscidea in paleoceanographic reconstructions at the northern (tropical) Indian Ocean DSDP Site 214 from the Late Miocene through the Pleistocene. In this interval at this site, U. proboscidea is the most abundant species of the benthic assemblage and shows abrupt frequency changes (about 1–74%). Based on relative percentages of U. proboscidea calibrated with oxygen and carbon isotope record and the sediment accumulation rates, the modern distribution of the species in the Indian Ocean, and other evidence, the peaks of abundance of U. proboscidea are inferred to represent times of high-surface productivity. This productivity is related to intensified trade winds during strong southwest (SW) Indian monsoons, causing widespread upwelling along equatorial divergence in the Indian Ocean. The sudden increase of U. proboscidea abundance at approximately 8.5–7.5 Ma reflects significant upwelling at the equatorial divergence. This event corresponds to the permanent build-up of West Antarctic ice sheets, and a major increase in SW Indian monsoons related upwelling in the northwestern Indian Ocean. The Chron-6 carbon shift at approximately 6.2 Ma is marked by another peak of abundance, reflecting widespread ocean fertility. The highest abundances of U. proboscidea and highest sediment accumulation rates occur between 5.8 and 5.1 Ma, which coincides with the greatest development of Antarctic ice sheets and strong southwest monsoons. The higher percentages at 3.2–3.1 Ma, approximately 2.4 Ma, and 1.6 Ma all represent phases of high productivity at the equatorial divergence.     

UV radiation and potential biological effects beneath the perennial ice cover of an antarctic lake

High-resolution spectral scans of solar ultraviolet radiation (UVR) were obtained directly beneath the 4.0–5.0 m thick, perennial ice cover of Lake Hoare, South Victoria Land, Antarctica. Both UVA (320–400 nm) and UVB (280–320 nm) radiation were detectable beneath the ice using a diver-deployed, underwater scanning spectroradiometer which permitted accurate measurement in the 280–340 nm range, while avoiding effects of surface shading and/or hole effects. UVR at wavelengths <310 nm was not detectable below the ice. This lower wavelength UVB appears to penetrate the Lake Hoare ice to depths of no more than 1.5 m during relatively cloud-free austral summer days. Based upon estimated biologically effective UVR dosages and DNA dosimeter data, exposure of benthic and planktonic microbes to the UVR encountered immediately beneath the ice is unlikely to inhibit microbial metabolism. Although waters of oligotrophic antarctic lakes are highly transparent to UVR, the thick, high scattering and optically dense ice covers on many of these lakes offers organisms a degree of protection largely unavailable in temperate and tropical systems. Thinning or complete loss of these overlying ice covers is likely to have major consequences for the structure of antarctic lake microbial communities.     

The zooplankton community in the vicinity of the ice edge,western Weddell Sea,March 1986

Summary The zooplankton community in the vicinity of the ice edge in the west central Weddell Sea was investigated in the late austral summer (March 1986). Sampling was done with two ships operating concurrently, one in the pack ice and the other in the adjcent open sea. Metazoan microzooplankton (<1 mm) was most abundant in the epipelagic zone. It consisted mostly of copepod nauplii and copepods of the genera Oithona, Oncaea, Ctenocalanus and Microcalanus. While species composition was similar in both areas, vertical patterns differed in that the microzooplankton had sparse populations in the upper 50 m under the ice. This may have been related to water temperature which in the upper 50 m under the ice was more than 1°C cooler than in the open sea. Zooplankton in the 1–20 mm size range was dominated by the calanoid copepods Metridia gerlachei, Calanus propinquus and Calanoides acutus which constituted half the biomass in the upper 1000 m. Their populations had highest densities in the upper 150 m, though much of the C. acutus population resided below 300 m. Metridia gerlachei and C. propinquus underwent diel vertical migrations in both areas whereas C. acutus did not migrate. Species diversity in the epipelagic zone was moderate and the fauna was characterized by species typical of the oceanic east wind drift. Diversity increased with depth and was due primarily to the appearance of circumpolar mesopelagic copepods in Weddell Warm Deep Water. Biomass of 1–20 mm zooplankton in the 0–1000 m zone was low (1.1–1.3 gDWm^-2) compared to other Southern Ocean areas investigated with comparable methods. It is suggested that this is related to Weddell circulation patterns and the resulting low annual primary production in the central Weddell Sea.     

Primary production of ice algae on a seasonally-ice-covered,continental shelf

Summary Ice algae samples were collected from the winter pack ice off Labrador during March 1984. The population was dominated by centric diatoms. Chlorophyll concentrations ranged from 40 to 190 mg m^–3, and particulate organic carbon from 2 to 10 g m^–3. Assimilation numbers for the ice algae ranged from 1.4 to 2.8 mg C (mg chl)^–1 h^–1 with a mean of 2.3, and were not significantly different from the assimilation numbers of the pelagic community beneath the ice. The ice algae were not photoinhibited at light intensities approaching surface light intensities. It is postulated that the dynamic nature of the ice field permits near-surface light intensities to reach the ice algae community at irregular intervals thereby suppressing photoinhibition.     

Observations on the relationship between the Antarctic coastal diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen and sea ice concentrations during the late Quaternary

The available ecological and palaeoecological information for two sea ice-related marine diatoms (Bacillariophyceae), Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen, suggests that these two species have similar sea surface temperature (SST), sea surface salinity (SSS) and sea ice proximity preferences. From phytoplankton observations, both are described as summer or autumn bloom species, commonly found in low SST waters associated with sea ice, although rarely within the ice. Both species form resting spores (RS) as irradiance decreases, SST falls and SSS increases in response to freezing ice in autumn. Recent work analysing late Quaternary seasonally laminated diatom ooze from coastal Antarctic sites has revealed that sub-laminae dominated either by T. antarctica RS, or by P. glacialis RS, are nearly always deposited as the last sediment increment of the year, interpreted as representing autumn flux. In this study, we focus on sites from the East Antarctic margin and show that there is a spatial and temporal separation in whether T. antarctica RS or P. glacialis RS form the autumnal sub-laminae. For instance, in deglacial sediments from the Mertz Ninnis Trough (George V Coast) P. glacialis RS form the sub-laminae whereas in similar age sediments from Iceberg Alley (Mac.Robertson Shelf) T. antarctica RS dominate the autumn sub-lamina. In the Dumont d'Urville Trough (Adélie Land), mid-Holocene (Hypsithermal warm period) autumnal sub-laminae are dominated by T. antarctica RS whereas late Holocene (Neoglacial cool period) sub-laminae are dominated by P. glacialis RS. These observations from late Quaternary seasonally laminated sediments would appear to indicate that P. glacialis prefers slightly cooler ocean–climate conditions than T. antarctica. We test this relationship against two down-core Holocene quantitative diatom abundance records from Dumont d'Urville Trough and Svenner Channel (Princess Elizabeth Land) and compare the results with SST and sea ice concentration results of an Antarctic and Southern Ocean Holocene climate simulation that used a coupled atmosphere–sea ice–vegation model forced with orbital parameters and greenhouse gas concentrations. We find that abundance of P. glacialis RS is favoured by higher winter and spring sea ice concentrations and that a climatically-sensitive threshold exists between the abundance of P. glacialis RS and T. antarctica RS in the sediments. An increase to > 0.1 for the ratio of P. glacialis RS:T. antarctica RS indicates a change to increased winter sea ice concentration (to >80% concentration), cooler spring seasons with increased sea ice, slightly warmer autumn seasons with less sea ice and a change from ~ 7.5 months annual sea ice cover at a site to much greater than 7.5 months. In the East Antarctic sediment record, an increase in the ratio from <0.1 to above 0.1 occurs at the transition from the warmer Hypsithermal climate into the cooler Neoglacial climate (~ 4 cal kyr) indicating that the ratio between these two diatoms has the potential to be used as a semi-quantitative climate proxy.     

A metagenomic assessment of winter and summer bacterioplankton from Antarctica Peninsula coastal surface waters

Antarctic surface oceans are well-studied during summer when irradiance levels are high, sea ice is melting and primary productivity is at a maximum. Coincident with this timing, the bacterioplankton respond with significant increases in secondary productivity. Little is known about bacterioplankton in winter when darkness and sea-ice cover inhibit photoautotrophic primary production. We report here an environmental genomic and small subunit ribosomal RNA (SSU rRNA) analysis of winter and summer Antarctic Peninsula coastal seawater bacterioplankton. Intense inter-seasonal differences were reflected through shifts in community composition and functional capacities encoded in winter and summer environmental genomes with significantly higher phylogenetic and functional diversity in winter. In general, inferred metabolisms of summer bacterioplankton were characterized by chemoheterotrophy, photoheterotrophy and aerobic anoxygenic photosynthesis while the winter community included the capacity for bacterial and archaeal chemolithoautotrophy. Chemolithoautotrophic pathways were dominant in winter and were similar to those recently reported in global ‘dark ocean'' mesopelagic waters. If chemolithoautotrophy is widespread in the Southern Ocean in winter, this process may be a previously unaccounted carbon sink and may help account for the unexplained anomalies in surface inorganic nitrogen content.