ALBERT

Description: We examined the physiological responses of steady-state iron (Fe)-replete and Fe-limited cultures of the biogeochemically critical marine unicellular diazotrophic cyanobacterium Crocosphaera at glacial (19 Pa; 190 ppm), current (39 Pa; 380 ppm), and projected year 2100 (76 Pa; 750 ppm) CO2 levels. Rates of N2 and CO2 fixation and growth increased in step with increasing partial pressure of CO2 (pCO2), but only under Fe-replete conditions. N2 and carbon fixation rates at 75 Pa CO2 were 1.4-1.8-fold and 1.2-2.0-fold higher, respectively, relative to those at present day and glacial pCO2 levels. In Fe-replete cultures, cellular Fe and molybdenum quotas varied threefold and were linearly related to N2 fixation rates and to external pCO2. However, N2 fixation and trace metal quotas were decoupled from pCO2 in Fe-limited Crocosphaera. Higher CO2 and Fe concentrations both resulted in increased cellular pigment contents and affected photosynthesis vs. irradiance parameters. If these results also apply to natural Crocosphaera populations, anthropogenic CO2 enrichment could substantially increase global oceanic N2 and CO2 fixation, but this effect may be tempered by Fe availability. Possible biogeochemical consequences may include elevated inputs of new nitrogen to the ocean and increased potential for Fe and/or phosphorus limitation in the future high-CO2 ocean, and feedbacks to atmospheric pCO2 in both the near future and over glacial to interglacial timescales.

Description: Der 3. Fahrtabschnitt der 1. Reise des neuesten deutschen Forschungsschiffes Maria S. Merian führt in die Schlammvulkanprovinz des Golf von Cadiz. Hier sollen Untersuchungen von biogeochemischen Stoffumsätzen, Fluid- und Gas-Flüssen an spezifischen Ökosystemen wie anoxischen Lebensgemeinschaften und azooxanthellaten Steinkorallen durchgeführt werden. Die Fahrt, die in 2 Unterabschnitte geteilt ist, beginnt in Kiel gefolgt von einem Zwischenstopp in Cadiz (Spanien) und endet in Lissabon (Portugal). MSM- 1/3 ist eine multidisziplinäre Expedition mit biologischen, geologischen und hydrographischen Fragestellungen. Ein Teil der Untersuchungen wird im Rahmen des „Geotechnologien” Programms des BMBF und der DFG für den Schwerpunkt „Methan im Geo-/Biosystem” durch das am IFM-GEOMAR koordinierte und für das ebenfalls hier schwerpunktmäßig angesiedelte Programm COMET (Controls on methane fluxes and their climatic relevance in marine gas hydrate-bearing environments) durchgeführt. Ein weiterer Teil der Ausfahrt dient den Untersuchungen im Rahmen des FP-6 Programms der EU HERMES (Hotspot Ecosystem Research on the Margins of European Seas). Aus dem HERMES-Programm nehmen 6 Partner teil. Beide Forschungsvorhaben sind sehr umfangreich und in ihrer Thematik komplex. Es gibt neben der geographischen Orientierung auf das Gebiet des Golf von Cadiz eine Vielzahl von inhaltlichen, personellen und logistischen Verbindungen zwischen beiden Programmen. Golf von Cadiz: Geologischer Hintergrund Die Region des Golf von Cadiz hat eine sehr komplexe geologische Geschichte. Sie ist seit der Trias durch mehrere tektonische Phasen mit Extension, Kompression und Lateralverschiebungen gekennzeichnet. Während des Mesozoikums und frühen Känozoikums bildeten sich in diesem Gebiet Bruchzonen mit Halbgraben-Strukturen und Karbonatplattformen. Im Torton verlagerte sich der Gibraltar-Bogen nach Westen. Dadurch wurde der Golf von Cadiz zu einem Forearc-Becken, in das Olistostrome (Rutschmassen) hineinglitten. In diesem Ablagerungsmilieu, das sonst für Akkretionskeile charakteristisch ist, wurden die Sedimente des südiberischen und nordafrikanischen Kontinentalrandes der damaligen Tethys stark deformiert. Die Olistostrom-Bildung war im oberen Miozän beendet. Gleichzeitig nahm die Subsidenz des Gebietes zu, und es kam zur Ausbildung von mächtigen Abfolgen progradierender und aggradierender Vorschüttfächer. Die geodynamische Interpretation dieser tektonisch sehr komplexen Region ist bis heute kontrovers. Der Gibraltarbogen liegt am östlichen Ausläufer der Azoren-Gibraltar Transformstörung, die als transpressionelle Grenze der iberischen und afrikanischen Platte gesehen wird. Die NW-SE gerichtete Konvergenz dieser beiden Platten zeigt sehr langsame Relativbewegungen von nur 4 mm pro Jahr. Die Ergebnisse neuester geophysikalischer Untersuchungen weisen jedoch darauf hin, dass auch eine ostwärtige Subduktion unter den Gibraltar-Bogen die gegensätzlichen Beobachtungen tektonischer Phänomene aus dem Riffgebirge und der Bethischen Kordillere erklären kann. Eine westwärts gerichtete Gegenrotation erzeugt Krustendehnung und damit Subsidenz in der Alboran See, während die damit verbundene westwärtige Verlagerung des Gibraltar-Bogens eine kompressionelle Deformation des Atlantis-Akkretionskeiles bewirkt. Es ist zu erwarten, dass die aktive Subduktion im Golf von Cadiz einen starken Einfluss auf das natürliche Gefahrenpotential dieser Region ausübt. Sie muss beispielsweise als Ursache für das große Erdbeben von 1755 gesehen werden (Stärke 8.5), durch das und den nachfolgenden Tsunami schwere Schäden in Lissabon und im angrenzenden Küstengebiet des Golf von Cadiz verursacht wurden. Diese historischen Ereignisse sind ein gewichtiger Grund dafür, dass der Golf von Cadiz eine Schlüsselregion für Europäische Forschungsaktivitäten und instrumenteller Langzeitbeobachtungen im Rahmen der EU-Programme ESONET, HERMES und EuroSEIZE bildet. Aus den Ergebnissen verschiedener Expeditionen ergeben sich viele Hinweise auf weit verbreitete Fluidaustritte, Karbonatmounds mit Tiefwasserkorallen (Lophelia-Skelette), Kohlenwasserstoff-Gasaustritte und Schlammdiapirismus am portugiesischen, spanischen und marokkanischen Kontinentalrand des Golf von Cadiz. Diese Phänomene wurden als Indikatoren für die weit verbreitete Existenz von gasübersättigten Sedimenten und der Migration von Fluiden diffusiv durch die Sedimente oder advektiv entlang von tektonischen Störungen interpretiert.

Description: To date no study exists that directly addresses changes in dynamics of heterotrophic bacteria in surface waters in relation to partial pressure of CO2 (pCO2). Therefore, we studied the effect of changes in pCO2 on bacterial abundance and activities by using mesocosms with different pCO2 levels (~190, ~370, and ~700 ppmV, representing past, present-day, and future atmospheric pCO2, respectively). Abundance of total bacteria did not differ with increasing pCO2 throughout the whole study period, whereas bacterial protein production (BPP) was highest at highest pCO2. This effect was even more pronounced for cell-specific production rates, especially those of attached bacteria, which were up to 25 times higher than those of free bacteria. During the breakdown of the bloom, however, the abundance of both free and attached bacteria was significantly increased with pCO2. Differences in bacterial growth rate (µ) were smaller than those of BPP, but both µ and BPP of attached bacteria were elevated under high pCO2. Averages of total protease as well as α- and α -glucosidase activities were highest at elevated pCO2 levels, but a statistically significant dependence on pCO2 was only evident for protease activity. There is a measurable but indirect effect of changes in pCO2 on bacterial activities that are mainly linked to phytoplankton and presumably particle dynamics

Description: Nutrient addition bioassay experiments were performed in the low-nutrient, low-chlorophyll oligotrophic subtropical North Atlantic Ocean to investigate the influence of nitrogen (N), phosphorus (P), and/or iron (Fe) on phytoplankton physiology and the limitation of primary productivity or picophytoplankton biomass. Additions of N alone resulted in 1.5-2 fold increases in primary productivity and chlorophyll after 48 h, with larger (~threefold) increases observed for the addition of P in combination with N (NP). Measurements of cellular chlorophyll contents permitted evaluation of the physiological response of the photosynthetic apparatus to N and P additions in three picophytoplankton groups. In both Prochlorococcus and the picoeukaryotes, cellular chlorophyll increased by similar amounts in N and NP treatments relative to all other treatments, suggesting that pigment synthesis was N limited. In contrast, the increase of cellular chlorophyll was greater in NP than in N treatments in Synechococcus, suggestive of NP co-limitation. Relative increases in cellular nucleic acid were also only observed in Synechococcus for NP treatments, indicating co-limitation of net nucleic acid synthesis. A lack of response to relief of nutrient stress for the efficiency of photosystem II photochemistry, Fv :Fm, suggests that the low nutrient supply to this region resulted in a condition of balanced nutrient limited growth, rather than starvation. N thus appears to be the proximal (i.e. direct physiological) limiting nutrient in the oligotrophic sub-tropical North Atlantic. In addition, some major picophytoplankton groups, as well as overall autotrophic community biomass, appears to be co-limited by N and P.

Description: While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.

Description: During the European Iron Fertilisation Experiment (EIFEX), performed in the Southern Ocean, we investigated the reactions of different phytoplankton size classes to iron fertilization, applying measurements of size fractionated pigments, particulate organic matter, microscopy, and flow cytometry. Chlorophyll a (Chl a) concentrations at 20-m depth increased more than fivefold following fertilization through day 26, while concentrations of particulate organic carbon (POC), nitrogen (PON), and phosphorus (POP) roughly doubled through day 29. Concentrations of Chl a and particulate organic matter decreased toward the end of the experiment, indicating the demise of the iron-induced phytoplankton bloom. Despite a decrease in total diatom biomass at the end of the experiment, biogenic particulate silicate (bPSi) concentrations increased steadily due to a relative increase of heavily silicified diatoms. Although diatoms 〉 20 mu m were the main beneficiaries of iron fertilization, the growth of small diatoms (2-8 mu m) was also enhanced, leading to a shift from a haptophyte- to a diatom-dominated community in this size fraction. The total biomass had lower than Redfield C : N, N : P, and C : P ratios but did not show significant trends after iron fertilization. This concealed various alterations in the elemental composition of the different size fractions. The microplankton 20 mu m) showed decreasing C : N and increasing N : P and C : P ratios, possibly caused by increased N uptake and the consumption of cellular P pools. The nanoplankton (2-20 mu m) showed almost constant C : N and decreasing N : P and C : P ratios. Our results suggest that the latter is caused by a shift in composition of taxonomic groups.