Der Einfluss von Phytoplankton auf den Jodkreislauf im tropischen und südlichen Atlantik

The role of halogene species like iodine in the ocean and how their speciation is affected by marine organisms is not well known. This lack of knowledge demands for more detailed field as well as experimental studies in order to unravel the role of iodine in marine ecosystems. My thesis comprises field work on the iodine speciation in polar and tropical marine environments complemented by a set of laboratory experiments on the role of phytoplankton species from the two regions studied for the iodine biogeochemical cycle. A large scale survey across the Atlantic sector of the Southern Ocean and three cruises to the Mauritanian upwelling region during both strong and weak upwelling seasons provide valuable information on iodine speciation over large spatial scales in case of the former survey, and on seasonal variability in case of the latter cruises. Furthermore, comparison of these two oceanic provinces will allow to decipher differences and conformities in iodine speciation between areas as far apart as the Southern Ocean and the Mauritanian upwelling region. In both provinces the total iodine (iodate + iodide) concentrations were in the same range between 450-480nmol L-1, while surface iodide values in the euphotic zone varied considerably and showed a steep vertical concentration gradient of less than 20nmol L-1 for antarctic and over 200nmol L-1 for tropical waters. In seawater the interconversion of the two inorganic forms of iodine, iodate and iodide, can be mediated by abiotic and/or biotic processes. The accumulation of iodide in the euphotic zone in both regions is suggested to be a more biologically mediated process and as observed in the experimental studies phytoplankton cells do influence the iodate reduction to iodide. However, highest iodide concentrations were not coupled to highest biological productivity instead we observed highest iodide values during post bloom periods in the respective regions indicating a strong relationship between iodide production and phytoplankton senescence during bloom collapse. Interestingly, productive regions with high phytoplankton biomass measured as chlorophyll-a show a decline in surface iodide and also the experimental study revealed an iodide decline in cultures with viable cells suggesting that an iodide oxidation or uptake mechanism is present when cells are in the exponential growth phase. Upwelled water was lower in surface iodide compared to water from a weak-upwelling scenario, and could on one hand be traced by its lower iodide concentrations while in the Weddell Sea Basin we observed elevated iodide in the deep Weddell Sea Bottom Water (WSBW) which could be traced on the other hand by its elevated iodide concentrations. From these results it appears that iodide can be used as a tracer for upwelled water on continental shelves and for newly formed WSBW. From the results gained in the laboratory we can say that iodide formation and senescence in phytoplankton cells are coupled. Iodide production was found to be species specific and not related to chlorophyll-a, cell size or cell numbers. Moreover iodide concentrations peaked in the stationary and/or senescence growth phase. A shift from senescence back to the exponential growth phase resulted in a decline in iodide concentrations indicating that phytoplankton mediated oxidation of iodide to iodate was triggering this shift. In summary, the results of my thesis show that the combined effects of abiotic and biotic processes resulting in iodate reduction are coupled via phytoplankton senescence. These findings challenge the conventional view, as described in other studies, that iodate reduction in the ocean is directly coupled to nutrient uptake and biological production.Die Bedeutung von Halogen-Verbindungen wie Jod im Stoffkreislauf der Ozeane und die Rolle mariner Organismen für die Steuerung dieser Kreisläufe ist noch weit gehend unerforscht. Diese Arbeit leistet einen wichtigen Beitrag zum besseren Verständnis der Bedeutung von Jod in marinen Ökosystemen durch eingehende Feld- und Laborstudien. Meine Arbeit enthält Felddaten von jodhaltigen Verbindungen aus polaren und tropischen Meeresgebieten die durch Laborexperimente mit verschiedenen Phytoplankton-Arten aus den jeweiligen Meeresgebieten vervollständigt wurden. Die Laborexperimente haben gezeigt, dass alle untersuchten Phytoplankton-Arten an der Umwandlung von Jodat zu Jodid beteiligt sind und somit Phytoplankton-Blüten eine maßgebliche Bedeutung für den Jodkreislauf im Ozean haben. Die großflächigen Messungen im atlantischen Sektor des Südpolarmeeres erlaubten einen umfassenden Überblick über die Verteilung von Jod-Verbindungen in diesem Gebiet wohingegen drei Expeditionen ins Mauretanische Auftriebsgebiet wichtige Erkenntnisse über die saisonale Variabilität von Jod lieferten. Durch den Vergleich dieser beiden Meeresgebiete konnten sowohl die Gemeinsamkeiten als auch die Unterschiede in der Verteilung und relativen Zusammensetzung der Jod Verbindungen aufgezeigt werden. Die gegenseitige Umwandlung der beiden inorganischen Formen von Jod im Seewasser, Jodat und Jodid, kann über biotische oder abiotische Prozesse erfolgen. Eine Gemeinsamkeit der beiden oben genannten Meeresgebiete ist die Jod-Gesamtkonzentration (Jodat + Jodid) von 450-480nmol L-1, wohingegen große Unterschiede in der Oberflächenkonzentration von Jodid von weniger als 20nmol L-1 im Südpolarmeer und mehr als 200nmol L-1 in tropischen Gewässern bestehen. Die Akkumulation von Jodid in der euphotischen Zone wird in erster Linie durch biologische Prozesse angetrieben. Wir können dieses anhand unserer Laborexperimente bestätigen in denen ersichtlich wird, dass Phytoplankton die Umwandlung von Jodat zu Jodid stark begünstigt. Allerdings, konnten wir nicht feststellen, dass erhöhte Jodid-Werte an hohe Primärproduktionsraten gekoppelt sind. Vielmehr wurden die höchsten Jodid-Konzentrationen in beiden Meeresgebieten gegen Ende der Blüte gemessen. Diese Beobachtung deutet auf einen Zusammenhang zwischen der Jodid-Produktion und absterbenden Phytoplanktonzellen während des Zusammenbruchs einer Blüte hin. Interessanterweise zeigen Regionen in denen die höchste biologische Produktion stattfindet einen Rückgang in der Konzentration von Jodid-Ionen an der Meeresoberfläche. Diese Feldbeobachtungen konnten durch Laborexperimente bestätigt werden, bei denen die Jodid-Konzentration in wachsenden und gesunden Zellkulturen abnahm. Dies legt die Vermutung nahe, dass Zellen die sich in der exponentiellen Wachstumsphase befinden Jodid oxidieren können. Während Auftriebsereignissen vor Mauretanien wird mit Jodid angereichertes Wasser aus der Tiefe an die Oberfläche transportiert. Außerhalb der Auftriebssaison sind die Jodid-Konzentrationen im Oberflächenwasser hingegen angereichert. Die niedrigeren Jodid-Konzentrationen während Auftriebsereignissen können daher als „Tracer“ bestimmter Wassermassen verwendet werden. Das gleiche gilt für die erhöhten Jodid-Konzentrationen im Tiefenwasser des Weddellmeeres, wobei Jodid hier anhand seiner erhöhten Konzentrationen verfolgt werden kann. Aufgrund dieser Beobachtungen liegt die Vermutung nahe, dass Jodid als „Tracer“ für Auftriebsereignisse aber auch für die Entstehung von Bodenwasser im Weddellmeer verwendet werden kann. Die Laborexperimente haben gezeigt, dass die Entstehung von Jodid an den Zelltod von Phytoplankton gekoppelt ist, wobei die Entstehung abhängig von der Art ist und nicht in Zusammenhang mit Chlorophyll-a-Gehalt, Zellzahlen oder Zellgröße steht. Die höchsten Jodid-Werte wurden immer in der stationären Wachstumsphase bzw. während des Absterbens der Zellen beobachtet. Versetzt man Zellen aus der absterbenden Phase zurück in die exponentielle Phase kann man einen Rückgang in den Jodid-Konzentrationen feststellen, was auf einen Jodid-Oxidationsprozess hindeutet. Zusammenfassend deuten die Ergebnisse alle darauf hin, dass die biotischen und abiotischen Prozesse der Jodat-Reduktion miteinander über den Zusammenbruch von Phytoplankton-Blüten verknüpft sind. Bisher hat man angenommen, dass die Jodat-Reduktion direkt mit der Nährstoffaufnahme und der biologischen Produktion gekoppelt ist, welches durch unsere Entdeckungen nun in Frage gestellt ist

Developing an observational design for epibenthos and fish assemblages in the Chukchi Sea

Accepted manuscript version, licensed CC BY-NC-ND 4.0. Published version available at https://doi.org/10.1016/j.dsr2.2018.11.005.In light of ongoing, and accelerating, environmental changes in the Pacific sector of the Arctic Ocean, the ability to track subsequent changes over time in various marine ecosystem components has become a major research goal. The high logistical efforts and costs associated with arctic work demand the prudent use of existing resources for the most comprehensive information gain. Here, we compare the information that can be gained for epibenthic invertebrate and for demersal fish assemblages reflecting coverage on two different spatial scales: a broader spatial coverage from the Arctic Marine Biodiversity Observing Network (AMBON, 67 stations total), and the spatial coverage from a subset of these stations (14 stations) that reflect two standard transect lines of the Distributed Biological Observatory (DBO). Multivariate cluster analysis was used to discern community similarity patterns in epibenthic invertebrate and fish communities. The 14 stations reflecting the two DBO lines captured about 57% of the epibenthic species richness that was observed through the larger-scale AMBON coverage, with a higher percentage on the more southern DBO3 than the northern DBO4 line. For demersal fishes, both DBO lines captured 88% of the richness from the larger AMBON spatial coverage. The epifaunal assemblage clustered along the south-north and the inshore-offshore axes of the overall study region. Of these, the southern DBO3 line well represented the regional (southern) epifaunal assemblage structure, while the northern DBO4 line only captured a small number of the distinct assemblage clusters. The demersal fish assemblage displayed little spatial structure with only one coastal and one offshore cluster. Again, this structure was well represented by the southern DBO3 line but less by the northern DBO4 line. We propose that extending the coverage of the DBO4 line in the northern Chukchi Sea farther inshore and offshore would result in better representation of the overall northern Chukchi epifaunal and fish assemblages. In addition, the multi-annual stability of epifaunal and, to a lesser extent also fish assemblages, suggests that these components may not need to be sampled on an annual basis and sampling every 2–3 years could still provide sufficient understanding of long-term changes. Sampling these assemblages every few years from a larger region such as covered by the AMBON project would create the larger-scale context that is important in spatial planning of long-term observing

Benthos

Currently, > 4,000 Arctic macro- and megabenthic species are known, representing the majority of Arctic marine faunal diversity. This estimate is expected to increase. • Benthic invertebrates are food to shes, marine mammals, seabirds and humans, and are commercially harvested. • Traditional Knowledge (TK) emphasizes the link between the benthic species and their predators, such as walrus, and their signi cance to culture. • Decadal changes in benthos biodiversity are observed in some well-studied regions, such as the Barents Sea and Chukchi Sea. • Drivers related to climate-change such as warming, ice decline and acidification are affecting the benthic community on a pan-Arctic scale, while drivers such as trawling, river/glacier discharge and invasive species have signficant impact on regional or local scales. • Increasing numbers of species are moving into, or shifting, their distributions in Arctic waters. These species will outcompete, prey on or offer less nutritious value as prey for Arctic species. • Current monitoring efforts have focused on macro- and megabenthic species, but have been confined to the Chukchi Sea and the Barents Sea. Efforts are increasing in waters of Greenland, Iceland, the Canadian Arctic, and in the Norwegian Sea. All other Arctic Marine Areas are lacking long-term benthic monitoring. • As a first step towards an international collaborative monitoring framework, we recommend to develop a time- and cost-effective, long-term and standardized monitoring of megabenthic communities in all Arctic regions with regular annual groundfish assessment surveys. Expanding monitoring on micro-, meio- and macrobenthic groups is encouraged

Floating Ice-Algal Aggregates below Melting Arctic Sea Ice

During two consecutive cruises to the Eastern Central Arctic in late summer 2012, we observed floating algal aggregates in the melt-water layer below and between melting ice floes of first-year pack ice. The macroscopic (1-15 cm in diameter) aggregates had a mucous consistency and were dominated by typical ice-associated pennate diatoms embedded within the mucous matrix. Aggregates maintained buoyancy and accumulated just above a strong pycnocline that separated meltwater and seawater layers. We were able, for the first time, to obtain quantitative abundance and biomass estimates of these aggregates. Although their biomass and production on a square metre basis was small compared to ice-algal blooms, the floating ice-algal aggregates supported high levels of biological activity on the scale of the individual aggregate. In addition they constituted a food source for the ice-associated fauna as revealed by pigments indicative of zooplankton grazing, high abundance of naked ciliates, and ice amphipods associated with them. During the Arctic melt season, these floating aggregates likely play an important ecological role in an otherwise impoverished near-surface sea ice environment. Our findings provide important observations and measurements of a unique aggregate-based habitat during the 2012 record sea ice minimum yea

The GEOTRACES Intermediate Data Product 2014

The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-? data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes

Reduced efficiency of pelagic–benthic coupling in the Arctic deep sea during lower ice cover

Pelagic–benthic coupling describes the connection between surface-water production and seafloor habitats via energy, nutrient and mass exchange. Massive ice loss and warming in the poorly studied Arctic Chukchi Borderland are hypothesized to affect this coupling. The strength of pelagic–benthic coupling was compared between 2 years varying in climate settings, 2005 and 2016, based on δ13C and δ15N stable isotopes of food-web end-members and pelagic and deep-sea benthic consumers. Considerably higher isotopic niche overlap and generally shorter isotopic distance were found between pelagic and benthic food web components in 2005 than in 2016, suggesting weaker coupling in the latter, low-ice year. δ15N values indicated more refractory food consumed by benthos in 2016 and fresher food reaching the seafloor in 2005. Higher δ13C values of zooplankton indirectly suggested a higher contribution of ice algae in 2005 than 2016. The difference in pelagic–benthic coupling between these years is consistent with higher energy retention within the pelagic system, perhaps due to strong stratification in the Amerasian Basin in the recent decade. Weaker coupling to the benthos can be expected to continue with ice loss in the study area, perhaps reducing benthic biomass and remineralization capacity; monitoring of the area is needed to confirm this prediction