The responses of larger (>50 µm in diameter) protozooplankton groups to a phytoplankton bloom ... more The responses of larger (>50 µm in diameter) protozooplankton groups to a phytoplankton bloom induced by in situ iron fertilization (EisenEx) in the Polar Frontal Zone (PFZ) of the Southern Ocean in austral spring are presented. During the 21 days of the experiment, samples were collected from seven discrete depths in the upper 150 m inside and outside the fertilized patch for the enumeration of acantharia, foraminifera, radiolaria, heliozoa, tintinnid ciliates and aplastidic thecate dinoflagellates. Inside the patch, acantharian numbers increased twofold, but only negligibly in surrounding waters. This finding is of major interest, since acantharia are suggested to be involved in the formation of barite (BaSO_4 ) found in sediments and which is a palaeoindicator of both ancient and modern high productivity regimes. Foraminifera increased significantly in abundance inside and outside the fertilized patch. However the marked increase of juveniles after a full moon event suggests a lunar periodicity in the reproduction cycle of some foraminiferan species rather than a reproductive response to enhanced food availability. In contrast, adult radiolaria showed no clear trend during the experiment, but juveniles increased threefold indicating elevated reproduction. Aplastidic thecate dinoflagellates almost doubled in numbers and biomass, but also increased outside the patch. Tintinnid numbers decreased twofold, although biomass remained constant due to a shift in the size spectrum. Empty tintinnid loricae, however, increased by a factor of two indicating that grazing pressure on this group mainly by copepods intensified during EisenEx. The results show that iron-fertilization experiments can shed light on the biology and the role of these larger protists in pelagic ecosystem which will improve their use as proxies in palaeoceanography.
Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlie... more Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlier and occur further north with retreating and thinning sea ice cover. The current study is the first compilation of phytoplankton bloom development and fate in the seasonally variable sea ice zone north of Svalbard from winter to late summer, using short-term sediment trap deployments. Clear seasonal patterns were discovered, with low winter and pre-bloom phytoplankton standing stocks and export fluxes, a short and intense productive season in May and June, and low Chl a standing stocks but moderate carbon export fluxes in the autumn post-bloom conditions. We observed intense phytoplankton blooms with Chl a standing stocks of >350 mg m−2 below consolidated sea ice cover, dominated by the prymnesiophyte Phaeocystis pouchetii. The largest vertical organic carbon export fluxes to 100 m, of up to 513 mg C m−2 day−1, were recorded at stations dominated by diatoms, while those dominated by ...
ABSTRACT In this study an ice-algal mathematical model is used to resolve the vertical fine struc... more ABSTRACT In this study an ice-algal mathematical model is used to resolve the vertical fine structure of sea ice with ice algae, and results are compared to simulations with ice algae located only at the bottom ice layer and to those where ice algae are distributed homogeneously across part of the ice column. Ice algae are reported to contribute 4-26% of overall Arctic Ocean primary production and are an important food source for the ice-associated ecosystem. Thus, it is important to estimate the future impacts of global warming on the contribution of ice algae to Arctic primary production. Primary production models, describing the relationships between ice-algal physiology and population dynamics, with environmental forcing and trophic interactions involving bacteria and grazers, can be applied to quantify such impacts. One important aspect in these models is how to represent the vertical distribution of ice algae in sea ice. In most models, only the bottom ice layer is considered where most of the algal biomass tends to be concentrated. However, since ice algae are also present along the entire ice column, this may lead to underestimation of ice-algal production. Some empirical data and model results suggest that ice algae located in the surface and interior layers may be kept at lower concentrations, in spite of high growth rates, due to grazing by micro- and meiofauna. Results obtained in this study show the importance of resolving vertically the distribution of ice algae to avoid bias in primary production estimates, well in line with empirical studies.
Peeken, Ilka and Sauter, Eberhard and Sachs, Oliver and Schlüter, Michael and Schwarz, Jill Nicol... more Peeken, Ilka and Sauter, Eberhard and Sachs, Oliver and Schlüter, Michael and Schwarz, Jill Nicola and Assmy, Philipp and Bracher, Astrid and Bathmann, Ulrich (2010): Deep export of organic matter to the seafloor of the Southern Ocean - New insights into spatial variability ...
Ample evidence has now accumulated showing that phytoplankton growth rates in the modern Southern... more Ample evidence has now accumulated showing that phytoplankton growth rates in the modern Southern Ocean are limited by iron availability. A major source of iron to the land-remote ocean is aeolian dust and it is very likely that higher dust input during glacials will have resulted in higher productivity and much greater CO2 drawdown. The phytoplankton blooms characteristic of iron-replete ecosystems tend to be dominated by a few key species (generally diatoms) whose biomass fuels the biological carbon pump. In situ iron fertilization experiments provide a powerful tool to study the ecology and biological characteristics of these key species which determine magnitude and composition of flux. During EisenEx, carried out with RV Polarstern in the Polar Frontal Zone during November 2000, the ecology of dominant phytoplankton species in the iron-fertilized bloom was studied in detail. We show that selective grazing pressure of a large range of protozoo- and metazooplankton was a major fa...
Mechanisms of particle selectivity controlling agglutination within the agglomerated tintinnid ge... more Mechanisms of particle selectivity controlling agglutination within the agglomerated tintinnid genus Stenosemella spp. Jörgensen were studied during two iron fertilisation experiments (EisenEx and EIFEX) conducted in the Southern Ocean in austral spring 2000 and late austral summer to early autumn 2004. Representative SEM pictures of Stenosemella spp. loricae were taken on the day of fertilisation, during the middle and at the end of both experiments. Whereas during EisenEx particles used for agglutination were unambiguously dominated by coccoliths of Emiliania huxleyi (Lohmann) Hay & Mohle, agglutinated particles during EIFEX mainly consisted of broken diatom frustules (BF) of heavily silicified species. This observation is supported by the ratio of E. huxleyi (Eh)/BF abundances in the water column during both experiments. During EisenEx we observed an Eh/BF ratio which was an order-of-magnitude higher compared to the EIFEX experiment. Thus, our results clearly indicated that particle availability seems to be the driving mechanism in the agglutination of Southern Ocean tintinnids. Furthermore, possible implications for the vertical flux of agglutinated biogenic particles to deep ocean waters and sediments are discussed.
Proceedings of the National Academy of Sciences, 2013
Significance Silica-shelled diatoms dominate marine phytoplankton blooms and play a key role in o... more Significance Silica-shelled diatoms dominate marine phytoplankton blooms and play a key role in ocean ecology and the global carbon cycle. We show how differences in ecological traits of dominant Southern Ocean diatom species, observed during the in situ European Iron Fertilization Experiment (EIFEX), can influence ocean carbon and silicon cycles. We argue that the ecology of thick-shelled diatom species, selected for by heavy copepod grazing, sequesters silicon relative to other nutrients in the deep Southern Ocean and underlying sediments to the detriment of diatom growth elsewhere. This evolutionary arms race provides a framework to link ecology with biogeochemistry of the ocean.
The responses of larger (>50 µm in diameter) protozooplankton groups to a phytoplankton bloom ... more The responses of larger (>50 µm in diameter) protozooplankton groups to a phytoplankton bloom induced by in situ iron fertilization (EisenEx) in the Polar Frontal Zone (PFZ) of the Southern Ocean in austral spring are presented. During the 21 days of the experiment, samples were collected from seven discrete depths in the upper 150 m inside and outside the fertilized patch for the enumeration of acantharia, foraminifera, radiolaria, heliozoa, tintinnid ciliates and aplastidic thecate dinoflagellates. Inside the patch, acantharian numbers increased twofold, but only negligibly in surrounding waters. This finding is of major interest, since acantharia are suggested to be involved in the formation of barite (BaSO_4 ) found in sediments and which is a palaeoindicator of both ancient and modern high productivity regimes. Foraminifera increased significantly in abundance inside and outside the fertilized patch. However the marked increase of juveniles after a full moon event suggests a lunar periodicity in the reproduction cycle of some foraminiferan species rather than a reproductive response to enhanced food availability. In contrast, adult radiolaria showed no clear trend during the experiment, but juveniles increased threefold indicating elevated reproduction. Aplastidic thecate dinoflagellates almost doubled in numbers and biomass, but also increased outside the patch. Tintinnid numbers decreased twofold, although biomass remained constant due to a shift in the size spectrum. Empty tintinnid loricae, however, increased by a factor of two indicating that grazing pressure on this group mainly by copepods intensified during EisenEx. The results show that iron-fertilization experiments can shed light on the biology and the role of these larger protists in pelagic ecosystem which will improve their use as proxies in palaeoceanography.
Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlie... more Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlier and occur further north with retreating and thinning sea ice cover. The current study is the first compilation of phytoplankton bloom development and fate in the seasonally variable sea ice zone north of Svalbard from winter to late summer, using short-term sediment trap deployments. Clear seasonal patterns were discovered, with low winter and pre-bloom phytoplankton standing stocks and export fluxes, a short and intense productive season in May and June, and low Chl a standing stocks but moderate carbon export fluxes in the autumn post-bloom conditions. We observed intense phytoplankton blooms with Chl a standing stocks of >350 mg m−2 below consolidated sea ice cover, dominated by the prymnesiophyte Phaeocystis pouchetii. The largest vertical organic carbon export fluxes to 100 m, of up to 513 mg C m−2 day−1, were recorded at stations dominated by diatoms, while those dominated by ...
ABSTRACT In this study an ice-algal mathematical model is used to resolve the vertical fine struc... more ABSTRACT In this study an ice-algal mathematical model is used to resolve the vertical fine structure of sea ice with ice algae, and results are compared to simulations with ice algae located only at the bottom ice layer and to those where ice algae are distributed homogeneously across part of the ice column. Ice algae are reported to contribute 4-26% of overall Arctic Ocean primary production and are an important food source for the ice-associated ecosystem. Thus, it is important to estimate the future impacts of global warming on the contribution of ice algae to Arctic primary production. Primary production models, describing the relationships between ice-algal physiology and population dynamics, with environmental forcing and trophic interactions involving bacteria and grazers, can be applied to quantify such impacts. One important aspect in these models is how to represent the vertical distribution of ice algae in sea ice. In most models, only the bottom ice layer is considered where most of the algal biomass tends to be concentrated. However, since ice algae are also present along the entire ice column, this may lead to underestimation of ice-algal production. Some empirical data and model results suggest that ice algae located in the surface and interior layers may be kept at lower concentrations, in spite of high growth rates, due to grazing by micro- and meiofauna. Results obtained in this study show the importance of resolving vertically the distribution of ice algae to avoid bias in primary production estimates, well in line with empirical studies.
Peeken, Ilka and Sauter, Eberhard and Sachs, Oliver and Schlüter, Michael and Schwarz, Jill Nicol... more Peeken, Ilka and Sauter, Eberhard and Sachs, Oliver and Schlüter, Michael and Schwarz, Jill Nicola and Assmy, Philipp and Bracher, Astrid and Bathmann, Ulrich (2010): Deep export of organic matter to the seafloor of the Southern Ocean - New insights into spatial variability ...
Ample evidence has now accumulated showing that phytoplankton growth rates in the modern Southern... more Ample evidence has now accumulated showing that phytoplankton growth rates in the modern Southern Ocean are limited by iron availability. A major source of iron to the land-remote ocean is aeolian dust and it is very likely that higher dust input during glacials will have resulted in higher productivity and much greater CO2 drawdown. The phytoplankton blooms characteristic of iron-replete ecosystems tend to be dominated by a few key species (generally diatoms) whose biomass fuels the biological carbon pump. In situ iron fertilization experiments provide a powerful tool to study the ecology and biological characteristics of these key species which determine magnitude and composition of flux. During EisenEx, carried out with RV Polarstern in the Polar Frontal Zone during November 2000, the ecology of dominant phytoplankton species in the iron-fertilized bloom was studied in detail. We show that selective grazing pressure of a large range of protozoo- and metazooplankton was a major fa...
Mechanisms of particle selectivity controlling agglutination within the agglomerated tintinnid ge... more Mechanisms of particle selectivity controlling agglutination within the agglomerated tintinnid genus Stenosemella spp. Jörgensen were studied during two iron fertilisation experiments (EisenEx and EIFEX) conducted in the Southern Ocean in austral spring 2000 and late austral summer to early autumn 2004. Representative SEM pictures of Stenosemella spp. loricae were taken on the day of fertilisation, during the middle and at the end of both experiments. Whereas during EisenEx particles used for agglutination were unambiguously dominated by coccoliths of Emiliania huxleyi (Lohmann) Hay & Mohle, agglutinated particles during EIFEX mainly consisted of broken diatom frustules (BF) of heavily silicified species. This observation is supported by the ratio of E. huxleyi (Eh)/BF abundances in the water column during both experiments. During EisenEx we observed an Eh/BF ratio which was an order-of-magnitude higher compared to the EIFEX experiment. Thus, our results clearly indicated that particle availability seems to be the driving mechanism in the agglutination of Southern Ocean tintinnids. Furthermore, possible implications for the vertical flux of agglutinated biogenic particles to deep ocean waters and sediments are discussed.
Proceedings of the National Academy of Sciences, 2013
Significance Silica-shelled diatoms dominate marine phytoplankton blooms and play a key role in o... more Significance Silica-shelled diatoms dominate marine phytoplankton blooms and play a key role in ocean ecology and the global carbon cycle. We show how differences in ecological traits of dominant Southern Ocean diatom species, observed during the in situ European Iron Fertilization Experiment (EIFEX), can influence ocean carbon and silicon cycles. We argue that the ecology of thick-shelled diatom species, selected for by heavy copepod grazing, sequesters silicon relative to other nutrients in the deep Southern Ocean and underlying sediments to the detriment of diatom growth elsewhere. This evolutionary arms race provides a framework to link ecology with biogeochemistry of the ocean.
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