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Zeitliche Variabilität von internen Wellen und vertikaler Vermischung im Nordatlantik

Das Ziel dieses Projektes ist die Untersuchung der zeitlichen Variabilität in der Energie von internen Wellen und der Stärke von vertikaler Vermischung in Abhängigkeit des Nordatlantikstroms und dem damit verbundenen Wirbelfeld. Hierfür werden 5-6 Jahre von Strömungsmesserdaten und Temperatur/Leitfähigkeitsmessungen von drei Verankerungen entlang eines Schnittes westlich des Mittelatlantischen Rückens (MAR) sowie LADCP/CTD Daten von fünf Schifffahrten genutzt. Konkrete wissenschaftliche Ziele dabei sind:- Erstellung von Zeitserien der Energie in internen Wellen unter Benutzung der Verankerungszeitreihen von Strömung und Schichtung- Untersuchung der Zeitskalen auf denen Veränderungen in der Energie interner Wellen stattfinden. Mögliche Ursachen für Variabilität sind der Windeintrag, Position des Nordatlantikstroms und Wirbel- Identifizierung von Prozessen, welche die beobachteten internen Wellen generieren, wie z.B. Gezeiten, Stürme, Jahresgang, Wirbel, die Arme des Nordatlanikstroms (Verhältnis von lokalen zu großräumigen Erzeugungsmechanismen)- Bestimmung der Vermischungsraten (Temperaturinversionen, Thorpe Skalen, Feinstrukturparameterisierung) in Abhängigkeit der variablen Hintergrundbedingungen Hierfür werden zunächst Spektren potentieller und kinetischer Energy der internen Wellen auf ihre Abhängigkeit von veränderlichen Hintergrundbedingungen wie z.B. Wind, Gezeiten, Wirbel, Schichtung und Variabilität im Nordatlantikstrom sowieso des Einflusses der Topographie untersucht. Die instrumentelle Ausstattung der Verankerungen seit Sommer 2012 erlaubt zusätzlich die Approximation der internen Wellen durch vertikale Moden und damit verbunden die Berechnung von Energieflüssen, welche wichtige Informationen über die Menge und die Variabilität in der Energie, die in internen Wellen im Nordatlantik transportiert wird, liefern. Außerdem geben diese so gewonnenen Energieflüsse in Kombination mit der Berechnung von Ausbreitungspfaden von internen Wellen, welche am mittelatlantischen Rücken erzeugt wurden, Aufschluss über die relative Bedeutung der Topographie des MAR für die Erzeugung von internen Wellen. Beginnend vom Sommer 2015 werden die Analysen erweitert, indem Temperatur- und Druckdaten mit hoher Tiefenauflösung für die Berechnung von Thorpe Skalen und Dissipationsraten und deren zeitlichen Variabilität genutzt werden. Weitere Informationen über die zeitliche und räumliche Variabilität der Vermischungsraten im Nordatlantik werden durch die Analyse von Diffusionsraten, die anhand von LADCP/CTD Daten und einer Feinstrukturparameterisierung berechnet werden, erlangt. Dies liefert weitere Aufschlüsse über die dominanten Prozesse in der Erzeugung von internen Wellen und vertikaler Vermischung im Nordatlantik, sowie deren zeitlicher und räumlicher Variabilität.

Seawater carbonate chemistry and benthic foraminifera Ammonia sp. uranium incorporation during experiments, 2013

The chemical and isotopic composition of foraminiferal shells (so-called proxies) reflects the physico-chemical properties of the seawater. In current day paleoclimate research, the reconstruction of past seawater carbonate system to infer atmospheric CO2 concentrations is one of the most pressing challenges and a variety of proxies have been investigated, such as foraminiferal U/Ca. Since in natural seawater and traditional CO2 perturbation experiments, the carbonate system parameters co-vary, it is not possible to determine the parameter of the carbonate system causing e.g. changes in U/Ca, complicating the use of the latter as a carbonate system proxy. We overcome this problem, by culturing the benthic foraminifer Ammonia sp. at a range of carbonate chemistry manipulation treatments. Shell U/Ca values were determined to test sensitivity of U incorporation to various parameters of the carbonate system. We argue that CO3 is the parameter affecting the U/Ca ratio and consequently, the partitioning coefficient for U in Ammonia sp DU. We can confirm the strong potential of foraminiferal U/Ca as a CO3 proxy.

Seawater carbonate chemistry and maximum growth rates of Skeletonema marinoi and Alexandrium ostenfeldii, toxin composition of Alexandrium ostenfeldii in a laboratory experiment

Phytoplankton populations can display high levels of genetic diversity that, when reflected by phenotypic variability, may stabilize a species response to environmental changes. We studied the effects of increased temperature and CO2 availability as predicted consequences of global change, on 16 genetically different isolates of the diatom Skeletonema marinoi from the Adriatic Sea and the Skagerrak (North Sea), and on eight strains of the PST (paralytic shellfish toxin)-producing dinoflagellate Alexandrium ostenfeldii from the Baltic Sea. Maximum growth rates were estimated in batch cultures of acclimated isolates grown for five to 10 generations in a factorial design at 20 and 24 °C, and present day and next century applied atmospheric pCO2, respectively. In both species, individual strains were affected in different ways by increased temperature and pCO2. The strongest response variability, buffering overall effects, was detected among Adriatic S. marinoi strains. Skagerrak strains showed a more uniform response, particularly to increased temperature, with an overall positive effect on growth. Increased temperature also caused a general growth stimulation in A. ostenfeldii, despite notable variability in strain-specific response patterns. Our data revealed a significant relationship between strain-specific growth rates and the impact of pCO2 on growth-slow growing cultures were generally positively affected, while fast growing cultures showed no or negative responses to increased pCO2. Toxin composition of A. ostenfeldii was consistently altered by elevated temperature and increased CO2 supply in the tested strains, resulting in overall promotion of saxitoxin production by both treatments. Our findings suggest that phenotypic variability within populations plays an important role in the adaptation of phytoplankton to changing environments, potentially attenuating short-term effects and forming the basis for selection. In particular, A. ostenfeldii blooms may expand and increase in toxicity under increased water temperature and atmospheric pCO2 conditions, with potentially severe consequences for the coastal ecosystem.

Seawater carbonate chemistry and hatching success and size of the marine clam Limecola balthica

Anthropogenic CO2 emissions are rapidly changing seawater temperature, pH and carbonate chemistry. This study compares the embryonic development under high pCO2conditions across the south-north distribution range of the marine clam Limecola balthicain NW Europe. The combined effects of elevated temperature and reduced pH on hatching success and size varied strongly between the three studied populations, with the Gulf of Finland population appearing most endangered under the conditions predicted to occur by 2100. These results demonstrate that the assessment of marine faunal population persistence to future climatic conditions needs to consider the interactive effects of co-occurring physico-chemical alterations in seawater within the local context that determines population fitness, adaptation potential and the system resilience to environmental change.

oWLK-GCM objective weather types derived from General Circulation Models (Reanalysis data and Global Climate Model Simulations)

Objective weather types of Deutscher Wetterdienst derived from different Reanalysis and Global Climate Model simulations for the control run (1951-2000) and the projection period (2000-2100). Furthermore, the NAO-index is also provided. On the one hand, the dataset is useful for evaluation of representative circulation statistics in Central Europe, on the other hand, for the analysis of future weather types due to climate change. Added temperature and precipitation data allow to study the weather type effectiveness for these important climate parameters.

Seawater carbonate chemistry and benthic foraminifera Ammonia sp. mass, size, and growth rate during experiments, 2013

About 30% of the anthropogenically released CO2 is taken up by the oceans; such uptake causes surface ocean pH to decrease and is commonly referred to as ocean acidification (OA). Foraminifera are one of the most abundant groups of marine calcifiers, estimated to precipitate ca. 50 % of biogenic calcium carbonate in the open oceans. We have compiled the state of the art literature on OA effects on foraminifera, because the majority of OA research on this group was published within the last three years. Disparate responses of this important group of marine calcifiers to OA were reported, highlighting the importance of a process-based understanding of OA effects on foraminifera. We cultured the benthic foraminifer Ammonia sp. under a range of carbonate chemistry manipulation treatments to identify the parameter of the carbonate system causing the observed effects. This parameter identification is the first step towards a process-based understanding. We argue that CO3 is the parameter affecting foraminiferal size-normalized weights (SNWs) and growth rates. Based on the presented data, we can confirm the strong potential of Ammonia sp. foraminiferal SNW as a CO3 proxy.

Seawater carbonate chemistry and seasonal variations of Fucus vesiculosus fertility in the western Baltic Sea

Ocean warming and acidification may substantially affect the reproduction of keystone species such as Fucus vesiculosus (Phaeophyceae). In four consecutive benthic mesocosm experiments, we compared the reproductive biology and quantified the temporal development of Baltic Sea Fucus fertility under the single and combined impact of elevated seawater temperature and pCO2 (1100 ppm). In an additional experiment, we investigated the impact of temperature (0–25°C) on the maturation of North Sea F. vesiculosus receptacles. A marked seasonal reproductive cycle of F. vesiculosus became apparent in the course of 1 year. The first appearance of receptacles on vegetative apices and the further development of immature receptacles of F. vesiculosus in autumn were unaffected by warming or elevated pCO2. During winter, elevated pCO2 in both ambient and warmed temperatures increased the proportion of mature receptacles significantly. In spring, warming and, to a lesser extent, elevated pCO2 accelerated the maturation of receptacles and advanced the release of gametes by up to 2 weeks. Likewise, in the laboratory, maturation and gamete release were accelerated at 15–25°C relative to colder temperatures. In summary, elevated pCO2 and/or warming do not influence receptacle appearance in autumn, but do accelerate the maturation process during spring, resulting in earlier gamete release. Temperature and, to a much lesser extent, pCO2 affect the temporal development of Fucus fertility. Thus, rising temperatures will mainly shift or disturb the phenology of F. vesiculosus in spring and summer, which may alter and/or hamper its ecological functions in shallow coastal ecosystems of the Baltic Sea.

Seawater carbonate chemistry and growth of calcifying tubeworm shells (Spirorbis spirorbis)

The calcareous tubeworm Spirorbis spirorbis is a widespread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus Fucus). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO2 increase. However, Spirorbis tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO2 may influence S. spirorbisshell growth we carried out four seasonal experiments in the Kiel Outdoor Benthocosms at elevated pCO2 and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of S. spirorbis are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO2 conditions. No influence of daily average CaCO3 saturation state on the growth rates of S. spirorbis was observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favoured selective shell surface dissolution. The results suggest an overall resistance of S. spirorbis growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, S. spirorbis did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO2, the growth rates of juvenile S. spirorbis were higher under elevated temperature conditions. The results reveal that S. spirorbis may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification.

Seawater carbonate chemistry and PI-curve parameters, non-photochemical quenching, maximum quantum yield, gross oxygen production and chlorophyll concentrations of Fucus vesiculosus in the Kiel Outdoor Benthocosms

Shallow coastal marine ecosystems are exposed to intensive warming events in the last decade, threatening keystone macroalgal species such as the bladder wrack (Fucus vesiculosus, Phaeophyceae) in the Baltic Sea. Herein, we experimentally tested in four consecutive benthic mesocosm experiments, if the single and combined impact of elevated seawater temperature (+ 5◦C) and pCO2 (1100 ppm) under natural irradiance conditions seasonally affected the photophysiological performance (i.e., oxygen production, in vivo chlorophyll a fluorescence, energy dissipation pathways and chlorophyll concentration) of Baltic Sea Fucus. Photosynthesis was highest in spring/early summer when water temperature and solar irradiance increases naturally, and was lowest in winter (December to January/February). Temperature had a stronger effect than pCO2 on photosynthetic performance of Fucus in all seasons. In contrast to the expectation that warmer winter conditions might be beneficial, elevated temperature conditions and sub-optimal low winter light conditions decreased photophysiological performance of Fucus. In summer, western Baltic Sea Fucus already lives close to its upper thermal tolerance limit and future warming of the Baltic Sea during summer may probably become deleterious for this species. However, our results indicate that over most of the year a combination of future ocean warming and increased pCO2 will have slightly positive effects for Fucus photophysiological performance.

Surface seawater carbonate chemistry, nutrients and phytoplankton community composition on a transect between North Sea and Arctic Ocean, 2008

This data was collected during the 'ICE CHASER' cruise from the southern North Sea to the Arctic (Svalbard) in July-Aug 2008. This data consists of coccolithophore abundance, calcification and primary production rates, carbonate chemistry parameters and ancillary data of macronutrients, chlorophyll-a, average mixed layer irradiance, daily irradiance above the sea surface, euphotic and mixed layer depth, temperature and salinity.

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