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Indications accumulate that the Arctic Ocean is in transition towards a new, warmer state. With this development, we expect shifts in the composition of Arctic zooplankton communities, as well as adaptations in the life-cycle history of established species. In the Arctic marine food web, carnivorous pelagic amphipods are an important link between herbivorous mesozooplankton and higher trophic levels such as planktivorous fish and seabirds. The present study closely investigates the community patterns of three important epipelagic amphipods Themisto abyssorum, T. libellula and T. compressa, and the deep-water amphipod Cyclocaris guilelmi. The objectives of this work focus on the year-round life-cycle characteristics of pelagic amphipods and on their function in the food web structure at study sites between Greenland and the Svalbard archipelago. In this thesis, three publications address the year-round life-cycle characteristics of Themisto spp. and C. guilelmi sampled by moored sediment traps in the northeastern Fram Strait. The sediment traps are deployed in a long-term observatory, the HAUSGARTEN, which is maintained by the Alfred Wegener Institute for Polar and Marine Research at the boundary between the central Arctic Ocean and the Greenland Sea since 2000. In the epipelagic trap samples hyperiids of the genus Themisto represent the dominant taxa among the collected amphipod community. Length-frequency analyses of year-round samples from 2000 to 2009 indicate a life span of two years for the sub-arctic species T. abyssorum and at least three years for the typical Arctic amphipod T. libellula. From 2004 to 2008, the meso- and bathypelagic amphipod communities in the sediment traps from 800 to 2700 m depth show the prevalent appearance of the deep-water amphipod C. guilelmi. Two other studies focus on the winter feeding strategies of Themisto spp. and C. guilelmi. The results from the gut content analyses indicate for the first time that T. abyssorum and T. libellula are active predators during the Arctic winter, with calanoid copepods as their major prey. In addition, a comparison of summer and winter fatty acid profiles shows a dominance of copepod biomarkers of the genus Calanus in the four investigated amphipod species, indicating that T. abyssorum, T. libellula, T. compressa and C. guilelmi are all part of Calanus-based food web and perform a business-as-usual feeding-mode during the polar night. To conclude, I show that long-term observations and a detailed knowledge of species specific ecology are of high importance for the identification of possible shifts within zooplankton community patterns and to predict their consequences in the food web structure of Arctic ecosystems.

Antifreeze proteins (AFPs) are an important adaptation mechanism for organisms subjected to subzero temperatures. The motivation of this thesis was to elucidate the distribution of AFPs in sea ice diatoms and to study their function. The findings were used to deduce the mechanisms of action and relevance in vivo. Diatom isolates were tested in culture experiments for the presence of recrystallisation inhibition activity, as a measure for AFP activity. Seven Arctic and four Antarctic diatom isolates were subjected to a temperature decrease and salinity shift resembling the inclusion of the diatoms into sea ice. All tested polar diatom species showed AFP activity, ten thereof even without being stressed. In three species, AFP activity was furthermore up-regulated by the temperature and salinity shift. Cell numbers and photosynthetic quantum yield indicated that cellular damage caused by the stress was more severe for water column isolates than for isolates from the ice column. The correlation of recrystallisation to the protein concentration for a Fragilariopsis nana Ant cell extract and a recombinant AFP allowed the calculation of AFP concentrations as AFP equivalents. Intracellular concentrations of 0.3 µM to 68.5 µM AFP equivalents confirmed the function of AFP as recrystallisation inhibitor and even come close to the concentrations required for thermal hysteresis. As AFP equivalents made up 0.1% to 5% of the total cell protein, diatoms invest a large amount of energy to produce AFPs. This indicates that AFPs are an important factor for diatom success in sea ice. Further, two isoforms of AFPs from Fragilariopsis nana were heterologously expressed in Escherichia coli, to study their molecular function. Recombinant proteins were deposited in inclusion bodies, but successfully refolded to functionally active proteins with respect to crystal deformation, recrystallisation inhibition and thermal hysteresis. The two isoforms showed different characteristics. One isoform produced a thermal hysteresis of up to 1.53 °C ± 0.53 °C and modified ice crystal growth to formation of hexagonal bi-pyramidal shapes, whereas the other isoform produced a thermal hysteresis of up to 2.34 °C ± 0.25 °C and ice crystals in the form of hexagonal columns. Thermal hysteresis activity of both proteins was positively correlated with protein concentration. The AFP activity increased with increasing buffer salinity in a linear correlation. High AFP concentrations or buffer salinities caused radial dendritic burst patterns of ice crystals in AFP solution. Thermal hysteresis potentials, crystal deformation habits and burst patterns led to the classification of both AFPs as hyperactive AFPs. In addition, the two isoforms differed with respect to the signal for subcellular localisation. Preceding the antifreeze domain, the gene of the first isoform carries a signal peptide indicating the secretion into the extracellular space, whereas the second isoform has a long N-terminal sequence of unknown function. We thus propose that AFPs have different functions in vivo, with distinct localisations of the proteins inside or outside the cell. To investigate AFP activity in situ, five cDNA libraries of eukaryotic communities from Arctic and Antarctic sea ice were analysed for abundance and phylogenetic relationship of AFP sequences. AFP transcripts were found in all sea ice cDNA libraries from the Arctic (Kongsfjord) and Antarctic (Weddell Sea and Dumont d´Urville Sea). Abundances of AFPs ranged from 115 to 1824 AFP transcripts per 100.000 reads. The different abundances did not correlate with taxonomic distribution or environmental parameters of the respective samples. Phylogenetic placement assigned 90% of the sequences to a clade of AFPs from the diatoms Navicula glacei, Chaetoceros neogracile and the crustacean Stephos longipes. The remaining 10% were placed into a separate clade of Fragilariopsis AFP sequences. In the Arctic sample all AFP sequences were assigned to the Fragilariopsis clade, whereas in only one Antarctic sample were some sequences found in this clade. These findings indicate that AFPs play an important role for eukaryotic sea ice organisms in their natural habitat and that the Navicula/Chaetoceros clade is more prominent than the Fragilariopsis clade under the conditions investigated.

The surface ocean is coupled with the deep ocean via sinking particles that transport carbon to depth: the biological pump. Only a small amount of the organic matter being formed at the surface reaches the seafloor, the remains are recycled. Most of the modification occurs in the mesopelagic. This thesis introduces further developments of a novel technique to examine sinking particle flux. The use of free-floating sediment traps equipped with polyacrylamide gels allows drawing conclusions on export fluxes on the base of intact individual particles. In three field studies, these data were compared to export flux data received with other sampling technologies. The field studies took place in different regions of the Southern Ocean. The focus of all studies was to investigate sinking particles in the mesopelagic and identify export driving processes. Overall, export fluxes were dominated by zooplankton mediated material (faecal pellets or aggregates of faecal matter) during each study.

The impact of food regimes on the feeding dynamics, bioelemental composition and community structure of the two Southern Ocean salps Salpa thompsoni and Ihlea racovitzai are studied. During a mesoscale iron fertilisation experiment (EIFEX) in the Southern Ocean Polar Frontal zone, S. thompsoni showed an enhanced ingestion inside the fast developing bloom but a low degradation efficiency of the diatom rich food. Seasonal feeding dynamics of S. thompsoni and I. racovitzai were investigated during three surveys in the Lazarev Sea in summer, fall, and winter (LAKRIS and IPY 2007/2008). Pigment concentrations in the salp guts of both species showed significant positive correlation to ambient surface chlorophyll concentrations with high feeding activity of Ihlea racovitzai in winter. Ecological impacts of the salps grazing pressure and contribution to the vertical flux by the production of fecal pellets are discussed for both studies. Population structure and demographic development strongly suggest that blooms of both salp species are pulsed events of ephemeral duration in Antarctic waters.

Chaetognaths contribute significantly to the zooplankton abundance and biomass in the world ocean. Stratified sampling between 500 and 2000 m depth with small mesh sizes in the Atlantic Southern Ocean has provided a unique opportunity for a detailed investigation of meso- and bathypelagic chaetognaths. The chaetognath community consisted of ten species with Eukrohnia hamata and Sagitta marri dominating. E. bathypelagica and E. bathyantarctica were characteristic deep-living species. Water depth and season were the determinants of chaetognath abundance and species composition patterns, indicating vertical seasonal migration and vertical segregation of species. Reproduction may be continuous in E. bathypelagica and E. bathyantarctica. These two deep-living species do not store high amounts of lipids and therefore rely on food supply year-round. However, their diet seems to be different because of their varying fatty acid compositions. The impact of meso- and bathypelagic chaetognaths on the copepod community in the Southern Ocean is probably significant and they may hold a central position channelling energy from lower to higher trophic levels.

This thesis provides a detailed insight into genetic diversity among and between Phaeocystis antarctica populations from different regions of the Southern Ocean and the gene flow between them. Genetic, physiological and ecological results are discussed in a broader view giving valuable insights into the ecology of this keystone species in the Southern Ocean. This work is opening a new field of research on P. antarctica, which can be termed 'ecophysiological genetics'. By combining genetic data with results from ecological investigations and physiological experiments, a broader understanding of ecosystem functioning will also direct future studies.

Dinoflagellates of the A. minutum species complex are widely distributed bloomforming, photosynthetic protists typically producing potent neurotoxins which cause paralytic shellfish poisoning (PSP). Human intoxications usually occur via the ingestion of filter-feeding bivalves, but intoxications after consumption of predatory crabs have also been reported. The same group of toxins is produced by certain freshwater cyanobacteria, in which the gene cluster coding for the PSP toxin-producing enzymes has recently been identified. However, the identification of corresponding genes in dinoflagellates is pending, which might be due to their unusual and little understood genomes. The aim of this thesis is to contribute to understanding gene expression and regulation in dinoflagellates by investigating the transcriptome-level gene expression in A. minutum. The gene expression experiments were based on an expressed sequence tag (EST) library, which was generated from pooled samples originating from different treatments to include the highest possible diversity of cDNA sequences. A set of microarray probes based on this library was used for different gene expression experiments, such as the comparison of toxic and non-toxic strains. Three stains were compared at two different times of the light phase, yielding a group of 192 genes differentially expressed between toxic and non-toxic strains at both timepoints. Another experiment was based on the induction of a fivefold increase in toxin levels by the presence of a copepod grazer. In combination with the data obtained from the strain comparison experiment, this resulted in the identification of two sequences potentially correlated to the ability to produce the toxins. Summary 2: Other treatments were designed to represent extreme values of ecologically significant parameters, such as different salinities or nutrient limitation. While the transcriptomic differences between cultures acclimatised to different salinities remained moderate and indicated a high prevalence of differences in post-transcriptional processes, the differences among growth phases and between nutrient-replete and nutrient-limited batch cultures were considerable. By using combinations of comparisons, several genes consistently up-regulated at the transition between exponential growth and stationary phase were identified, as well as 87 genes consistently associated with N- or Plimitation. In the course of this thesis, I identified several A. minutum genes apparently associated with intracellular toxins, as well as patterns of gene expression indicative of culture growth status and of nutrient limitation. These data substantially add to the emerging field of dinoflagellate transcriptomics. Additionally, they provide a starting point for the potential development of new monitoring tools testing the physiological status or toxinproducing potential of A. minutum populations.

This thesis investigates the response of copepods to increased phytoplankton abundance during two mesoscale iron-fertilisation experiments in the Southern Ocean (EisenEx in austral spring 2001 and EIFEX in austral autumn 2004), focussing on the copepods vertical migration behaviour. Their migratory behaviour can be considered as a food finding strategy to cope with the patchy, mostly poor food environment of the Southern Ocean. A large abundance increase of copepods was observed inside the bloom area. Their grazing can significantly alter carbon and nutrient fluxes after iron fertilisation in Southern Ocean.

One microarray, the Phytoplankton Chip was developed . Phytoplankton field samples were taken at the island of Helgoland in the North Sea from 2004 to 2006 at regular intervals. For the phytoplankton community, only the > 20 mikrometer size fraction is identified on a daily basis. For picoplanktonic groups, light microscopy can not differentiate taxa or species. The phyto- and especially picoplanktonic dynamics were successfully analyzed with the Phytoplankton Chip in these three annual cycles. In general, the data showed highly abundant taxa present through all three years and some taxa that were rare. The first group of taxa seemed to be very stable and unaffected by environmental changes.

Antarctic krill (Euphausia superba) is the most abundant of the world's euphausiids and plays a central role in the Southern Ocean pelagic ecosystem. The main focus of this thesis was to evaluate the influence of seasonal light conditions on the physiology of krill, particularly with regard to the over-winter biology and maturity development of krill. The results indicate that, irrespective of food supply, the level of feeding and metabolic activity in krill correlates with the degree of prevailing light conditions. Furthermore, the results indicate that the succession of female and male krill maturity stages is accelerated by light conditions of prolonged photoperiod and enhanced light intensity. Together, the results emphasizes the role of the Southern Ocean light regime as an essential cue governing the seasonal cycle of krill physiology. It is further shown that the photoperiodic response system in krill is not based on melatonin as a transducer of photoperiodic information, although melatonin is assumed to be principally involved in the transduction of photoperiodic information in living organisms.

Based on morphology, the taxonomy of the family Naviculaceae (sensu Krammer&Lange-Bertalot, 1986) has been highly changed (e.g., Round et al., 1990), but little work has been carried out with molecular data for this large and ecologically important group of diatoms. My thesis was aimed at the investigation of evolutionary relationships within the naviculoid pennates using molecular and morphological data. Phylogenies based on sequences of the nuclear-encoded SSU rRNA gene, the LSU rRNA gene, the chloroplast rbcL gene and a combined dataset were compared. This study confirms the assumption that the genus Navicula sensu lato is a very heterogenous group and my results support the monophyly of Navicula sensu stricto. Several 'Navicula' species, which do not belong to the section Lineolatae could be recombined. The monophyly of several genera could be supported. But the actual differentiation of the genera Caloneis and Pinnularia is rejected. The separation of the subgenus Halamphora from the genus Amphora is supported by molecular and morphological data. This study also resolve several relationships between different genera.

Observations on the feeding behaviour of calanoid copepods, microscopical analysis of their faecal pellets and the possible ecological importance of copepod grazing will be addressed in this thesis. Laboratory as well as field studies were applied to investigate the responses of different copepod species to different food environments, covering the three main phytoplankton groups - Diatoms, Dinoflagellates and Coccolithophores. Since many of the species belonging to these groups are surrounded by mineral skeletons, qualitative observations can be revealed by the use of scanning electron microscopy (SEM).The importance of calcifying algae in the marine carbon and calcium cycles is widely known, but the role of copepods for the coccolith calcite dissolution is vague. Dissolution experiments were performed using the calcifying algae Calcidiscus leptoporus. SEM observations of the morphological changes of the coccoliths were used for content interpretation of freshly produced faecal pellets in feeding experiments with the common North Sea copepods Calanus helgolandicus and Temora longicornis. Coccolith calcite dissolution during copepod gut passage was found to be minor and can therefore not contribute significantly to the generally observed calcite dissolution in the upper ocean.Field experiments conducted during a dinoflagellate bloom in the North Sea clearly showed that some copepod species can feed very efficiently on the dinoflagellate species Dinophysis norvegica. SEM observations showed that faecal pellets produced by C. helgolandicus were almost exclusively filled with intact cells of this toxic dinoflagellate species. Faecal pellets, containing intact toxic phytoplankton species may be an important vehicle and new pathway transferring toxins within the pelagic and to the benthic community. The viability of D. norvegica cells within the faecal pellets was not investigated, but lead to the idea to observe the ability of different phytoplankton species to survive the copepod gut passage. Therefore a new staining method was applied. Viable cells of the dinoflagellate Scrippsiella trochoida and the diatom Fragilariopsis kerguelensis were detected within the faecal pellets of different copepod species. F. kerguelensis may protect itself with its stable frustules and also the formation of chains seemed to be advantageous for the survival of single cells when they are grazed. Whereas the long spines of the diatom Chaetoceos dichaeta provided no protection and was reduced to small pieces within the faecal pellets of all copepods investigated. Studies of species specific interactions among copepods and their prey can greatly improve the current understanding of the benefit of certain phytoplankton cell structures. In an additional experiment conducted with the two copepods Acartia clausi and T. longicornis the ability to graze on the largest centric diatom commonly found in the North Sea plankton was under investigation. A. clausi was not able to graze on Coscinodiscus wailesii but T. longicornis showed a very skilful handling of individual cells. The copepod did not ingest the whole cells, but bite a piece off the frustules to reach the protoplasma. After ingestion of the cell content, the empty diatom frustules were rejected. Results showed that traditional methods to determine grazing may sometimes be unsuitable and that new methods need to be developed. The new promising approach of genetical gut content analysis to qualify and quantify the grazing impact of copepods was therefore tested in a study and provided preliminary, but promising results.The general importance of food for copepods can be reflected in their energy requirements for egg production. To observe if and how food concentration is linked to egg production in a common Antarctic copepod species, the reproductive response of Rhincalanus gigas was studied during the build up of a diatom dominated phytoplankton bloom in the Southern Ocean. Results from egg production experiments as well as the maturation of their gonads revealed that R. gigas was able to react directly to enhanced food concentrations.

This thesis aimed at achieving a deeper understanding of the dynamics and structure of microbenthic communities with a focus on protists. The most important discovery concerning protozoa in recent years is the fact that they play a much more important role in for example carbon and energy flow in nature than previously believed. In this thesis several studies were presented which focus on the seasonal dynamics and the spatial distribution of components of the small benthic community in marine and freshwater environments in temperate and arctic climates and which aim at establishing a generalised model of relationships and controlling factors in small benthic food webs. Samples of the upper 3 mm of the surface of soft sediment were collected in coastal freshwater and marine sites in Germany, USA and North East Greenland. The abundance and biomass of bacteria, cyanobacteria, diatoms and nanoflagellates (phototrophic and heterotrophic) were enumerated by means of epifluorescence microscopy. Ciliate species and meiofauna were enumerated with the help of light microscopy after QPS (quantitative protagol staining). Environmental data, such as temperature, salinity, sediment water content, grain size distribution, total and organic carbon- and nitrogen content as well as chlorophyll-a values were determined in order to study their influence on the community structures and total biomass. The investigation of a habitat in a mudflat in Dorum (Germany) revealed that the benthic microbial food web varied with the season with a primacy of bottom-up control during winter and spring, an increasing influence of top-down forces mainly by meiofauna grazing towards summer, decreasing again towards autumn, accompanied by a recovery of microphytobenthos.Investigations of soft sediment communities in different climate and geographic positions of freshwater and marine sites in Germany, North America (USA; Pennsylvania, New Jersey) and in North East Greenland were carried out. The results revealed considerable differences in the biomass of the small benthic components as well as in ciliate species composition and richness. The study of the ciliate species composition also exhibited a high variability of feeding types between the investigated sites, but the herbivorous feeding type seemed to be dominant in all sediments. Differences in total microbenthic biomass, abundance and ciliate species richness could not be attributed to the differences measured in carbon content, salinity or climatic parameters. The amount of chlorophyll-a was the only factor influencing the small benthic biomass. The sources of chlorophyll-a remained unclear. The hypothesis of Manini et al. (2003) stating that the composition of available carbon has a strong influence on the structure and biomass of microbial communities in shallow sediments seemed to hold true for the investigated sites. In a series of laboratory experiments the influence of the absence of all macrograzers as well as the presence of a single common abundant small macrograzer such as Hydrobia ulvae, Corophium sp. as well as Chironomid larvae and polychaets on the components of the microbenthic communities in sediments from all study sites were investigated. The structuring influence of Arenicola marina on components of the small food web was investigated in a long term field experiment on the island of Sylt. The results of the laboratory experiments and those of the field study revealed that the small macrofauna tended to have positive stimulating effects on the microbial community by bioengineering, rather than negative ones by grazing. The exclusion of Arenicola marina in a long term experiment revealed the fact that the role of this grazer was adopted by other grazers.The results of this thesis and literature data led to the conclusion that in small communities of soft sediments the trophic levels are blurred and most species rather feed opportunistically on what is most available. The dominance of the omnivourous feeding type, detritus feeding, stimulating bioengineering effects and feed back mechanisms compose a highly networked food web. The fundamental attributes of microbes such as large absolute population sizes, short generation times and high dispersal capabilities, form a system with rapid changes in species composition.The outcome of this thesis verified the model of Fretwell (1977) for benthic microbial food webs in coastal regions, predicting that top-down forces form the trophic structure, but the bottom-up attributes of the ecosystems, such as nutrients availability, temperature and light, determine the fundament of the community as total biomass, abundance and production.

Comparative molecular genetic and morphometric methods were used to clarify long-standing taxonomic uncertainties in one of the most common freshwater diatom species, Cyclotella meneghiniana Kützing. First a single C. meneghiniana population was sampled by isolating clonal cultures. Frustule ultrastructure of the cultures and of field samples was analysed using two different morphometric methodologies. These analyses contributed significantly to clarifying a problem concerning the delimitation of C. meneghiniana from a closely related species, C. scaldensis Muylaert&Sabbe. Next, patterns of ribosomal DNA sequence variation among fifteen cultures displaying the characteristic C. meneghiniana morphology were explored. The patterns observed indicated the presence of genetic structuring in the population sampled, suggesting that C. meneghiniana was either a complex of multiple, cryptic species, or that of strictly clonally or autogamously reproducing lineages. The following step was surveying sequence variation in the D1/D2 regions of the nuclear ribosomal DNA and in a region of the plastid encoded psaA gene in a collection of strains including C. meneghiniana strains with diverse geographic origins and cultures of some closely related species. Strict covariation was observed in the two genomic regions sequenced, further reinforcing the conclusion that C. meneghiniana is a structured species. The hypothesis that this genetic structuring was caused by the complete lack of allogamous sexual reproduction in this morphospecies was tested by quantifying phylogenetic incompatibility present in AFLP (amplified fragment length polymorphism) genotypes of strains from two populations. The results indicated no significant deviation from panmictic expectations, suggesting that Cyclotella meneghiniana is a complex of several, reproductively isolated species, rather than that of strictly autogamous lineages.

The role of copepod grazing, particularly of :i:Calanus simillimus:/i: and :i:Rhincalanus gigas:/i:, in the biogeochemical cycles of silicon (Si) and carbon (C) in the Antarctic Circumpolar Current (ACC) of the Southern Ocean is investigated. The two grazers show differences in feeding behavior before and in response to a diatom bloom stimulated by :i:in situ:/i: iron fertilization. The continuously high feeding activity of :i:C. simillimus:/i: on diatoms is conducive to enhance the export of primary produced C and Si. The grazing impact of this key species is high enough to influence population dynamics in the microplankton communities of the ACC. In the pre-bloom situation, :i:R. gigas:/i: fulfils most of its carbon requirement through grazing on detritus and thereby effectively reduces the vertical fecal flux produced by :i:C. simillimus:/i:. It is proposed that a Copepod-Retention-System for organic material is put in place by the copepod community under High Nutrient Low Chlorophyll (HNLC) conditions. Prey switching by :i:R. gigas:/i: from detritus to diatoms in the bloom situation lifts the grazing check on the detritus flux and enables loss of particulate C and Si from the surface layer with fast sinking fecal pellets. Results from dissolution experiments indicate that the enclosure of biogenic silica (BSi) in copepod fecal pellets prevents the dissolution of diatom frustules. Diatoms submitted to grazing of copepods and krill (:i:Euphausia superba:/i:) dissolved 4 to 26 times slower than un-grazed controls. :br:Estimates of C ingestion from :i:in vitro:/i: incubations and from gut fluorescence measurements are compared to respiratory carbon needs of copepods. Methods yield generally similar estimates for :i:C. simillimus:/i: whereas methods differ strongly for :i:R. gigas:/i: in the pre-bloom situation, reflecting the above mentioned differences in feeding behavior.

In this work, a coupled biological-physical sea ice model was developed to investigate the influence of transient changes in environmental conditions (e.g. light, temperature and nutrient dynamics) on the sea ice biological communities. To simulate this complex environment, the biological model uses self-adapting physiological schemes and variable cellular N:C and Si:C quotas, including co-limitation, to decouple biomass accumulation and inorganic nutrient availability. Forcing terms (ice temperature, brine salinity, light and nutrients) are controlled by the thermodynamic sea ice model, with emphasis on the light and heat conduction through the sea ice and desalination processes (flux of brine). The model indicates that thermodynamic processes controlling ice formation and growth play a key role in the establishment and vertical distribution of biological sea ice communities. The coupled biological-physical model is described in a Lagrangian manner, where the time-dependent position of simulated ice floes extracted from ice velocity fields are used to compute forcing parameters (e.g. air temperature, oceanic heat flux, solar radiation). A good agreement between model results and field observations was found, indicating that the model well represents the physical and biological processes in sea ice. The model was also used to estimate the total productivity of sea ice in the Weddell Sea, resulting in an annual carbon production of 11 Tg C with a strong seasonal variability. The most productive months are between December and February, when light and temperature conditions in the sea ice are considerably enhanced as compared to the other months. Between May and September, the sea ice productivity ranges from 0.16 to 0.6 Tg C month-1 contributing 17% to the total annual production.