ALBERT

Description: Geochronological studies in northern Wedel Jarlsberg Land, southwestern Svalbard (Norway), showed that the Tonian (c. 950 Ma) igneous rocks were subjected to metamorphism during the Torellian (c. 640 Ma) and early Caledonian (470–460 Ma) events. Predominant augen gneisses, derived from a Tonian protolith, are intercalated in that area, with schists comprising two distinct metamorphic mineral assemblages. The M1 (Torellian) assemblage containing garnet-I + quartz + plagioclase-I + biotite-I + muscovite-I was formed under amphibolite-facies conditions at c. 550–600 °C and 5–8 kbar (1 kbar = 100 MPa). The M2 (Caledonian) assemblage comprising garnet-II + quartz + plagioclase-II + biotite-II + muscovite-II + zoisite + chlorite crystallized at c. 500–550 °C and 9–12 kbar, corresponding to epidote–amphibolite facies conditions. The M2 mineral assemblage constitutes the pervasive Caledonian fabric of the schists that was subsequently reactivated in a left-lateral strike-slip shear regime. The subsequent c. 70° clockwise rotation of the original structure to its present position was caused by a large-scale passive rotation during the Paleogene Eurekan orogeny. The new pressure–temperature estimates suggest that metamorphic basement in the study area was consolidated during the Torellian middle-grade event and then overprinted by Caledonian moderate- to high-pressure subduction-related metamorphism. A following sinistral shear zone assembled the present structure of basement units. Our results pose a question about the possible extent of Torellian precursor to the Caledonian basement across the High Arctic and the scale of its subsequent involvement in early Caledonian subduction. In conjunction with previous studies, the results suggest a possible correlation between southwestern Spitsbergen and the Pearya Terrane in Ellesmere Island.

Description: Ion microprobe dating in Wedel Jarlsberg Land, southwestern Spitsbergen, provides new evidence of early Neoproterozoic ( c . 950 Ma) meta-igneous rocks, the Berzeliuseggene Igneous Suite, and late Neoproterozoic ( c . 640 Ma) amphibolite-facies metamorphism. The older ages are similar to those obtained previously in northwestern Spitsbergen and Nordaustlandet where they are related to the Tonian age Nordaustlandet Orogeny. The younger ages complement those obtained recently from elsewhere in Wedel Jarlsberg Land of Torellian deformation and metamorphism at 640 Ma. The Berzeliuseggene Igneous Suite occurs in gently N-dipping, top-to-the-S-directed thrust sheets on the eastern and western sides of Antoniabreen where it is tectonically intercalated with younger Neoproterozoic sedimentary formations, suggesting that it provided a lower Tonian basement on which upper Tonian to Cryogenian sediments (Deilegga Group) were deposited. They were deformed together during the Torellian Orogeny, prior to deposition of Ediacaran successions (Sofiebogen Group) and overlying Cambro-Ordovician shelf carbonates, and subsequent Caledonian and Cenozoic deformation. The regional importance of the late Neoproterozoic Torellian Orogeny in Svalbard's Southwestern Province and its correlation in time with the Timanian Orogeny in the northern Urals as well as tectonostratigraphic similarities between the Timanides and Pearya (northwestern Ellesmere Island) favour connection of these terranes prior to the opening of the Iapetus Ocean and Caledonian Orogeny.

Description: Nitrogen fixation by filamentous cyanobacteria supplies significant amounts of new nitrogen (N) to the Baltic Sea. This balances N loss processes such as denitrification and anammox and forms an important N source supporting primary and secondary production in N-limited post-spring bloom plankton communities. Laboratory studies suggest that filamentous diazotrophic cyanobacteria growth and N2-fixation rates are sensitive to ocean acidification with potential implications for new N supply to the Baltic Sea. In this study, our aim was to assess the effect of ocean acidification on diazotroph growth and activity as well as the contribution of diazotrophically-fixed N to N supply in a natural plankton assemblage. We enclosed a natural plankton community in a summer season in the Baltic Sea near the entrance to the Gulf of Finland in six large-scale mesocosms (volume ~ 55 m3) and manipulated fCO2 over a range relevant for projected ocean acidification by the end of this century (average treatment fCO2: 365–1231 μatm). The direct response of diazotroph growth and activity was followed in the mesocosms over a 47 day study period during N-limited growth in the summer plankton community. Diazotrophic filamentous cyanobacteria abundance throughout the study period and N2-fixation rates (determined only until day 21 due to subsequent use of contaminated commercial 15N-N2 gas stocks) remained low. Thus estimated new N inputs from diazotrophy were too low to relieve N limitation and stimulate a summer phytoplankton bloom. Instead regeneration of organic N sources likely sustained growth in the plankton community. We could not detect significant CO2-related differences in inorganic or organic N pools sizes, or particulate matter N : P stoichiometry. Additionally, no significant effect of elevated CO2 on diazotroph activity was observed. Therefore, ocean acidification had no observable impact on N cycling or biogeochemistry in this N-limited, post-spring bloom plankton assemblage in the Baltic Sea.

Description: Two Proterozoic terranes with different metamorphic histories are distinguished from geological mapping in southwestern Wedel Jarlsberg Land: a northern greenschist facies terrane and a southern amphibolite facies terrane which has been overprinted by greenschist facies metamorphism. To better characterize the tectonothermal history of these terranes we have obtained new 40Ar/39Ar mineral dates from this area. A muscovite separate from the northern terrane yielded a Caledonian plateau age of 432±7 Ma. The southern terrane yielded significantly older 40Ar/39Ar ages with three muscovite plateau dates of 584±14 Ma, 575±15 Ma, and 459±9 Ma, a 484±5 Ma biotite plateau date, and a 616±17 Ma hornblende plateau date. The oldest thermochronological dates are over 300 Ma younger than the age of amphibolite facies metamorphism and therefore probably do not represent uplift-related cooling. Instead, the Vendian dates correlate well with a regionally widespread magmatic and metamorphic/thermal resetting event recognized within Caledonian complexes of northwestern Spitsbergen and Nordaustlandet. The apparent Ordovician dates are interpreted to represent partial resetting, suggesting that late Caledonian greenschist facies overprinting of the southern terrane was of variable intensity.

Description: A major, potential stressor of marine systems is the changing water chemistry following increasing seawater carbon dioxide concentration (CO2), commonly termed ocean acidification. In order to understand how an Arctic pelagic ecosystem may respond to future CO2, a deliberate ocean acidification and nutrient perturbation study was undertaken in an Arctic fjord. The initial setting and evolution of seawater carbonate chemistry were investigated. Additions of carbon dioxide resulted in a wide range of ocean acidification scenarios. This study documents the changes to the CO2 system throughout the study following net biological consumption and gas exchange with the atmosphere. In light of the common practice of extrapolating results to cover regions away from experimental conditions, a modelling study was also performed to assess the representativeness, in the context of the simulated present and future carbonate system, of the experimental study region to both the near and wider Arctic region. The mesocosm experiment represented the range of simulated marine carbonate system for the coming century and beyond (pCO2 to 1420 μatm) and thus extrapolations may be appropriate to ecosystems exhibiting similar levels of CO2 system drivers. However, as the regional ocean acidification was very heterogenous and did not follow changes in atmospheric CO2, care should be taken in extrapolating the mesocosm response to other regions based on atmospheric CO2 scenarios.

Description: Net community production (NCP) and ratios of carbon to nutrient consumption were studied during a large-scale mesocosm experiment on ocean acidification in Kongsfjorden, West Spitsbergen, during June–July 2010. Nutrient-deplete fjord water with natural phyto- and bacteriaplankton assemblages, enclosed in nine mesocosms of ~ 50 m3 volume, was exposed to pCO2 levels ranging from 185 to 1420 μatm on initial state. Mean values of pCO2 levels during experiment ranged from 175 to 1085 μatm in different mesocosms. Phytoplankton growth was stimulated by nutrient addition. In this study NCP is estimated as a cumulative change in dissolved inorganic carbon concentrations. Stoichiometric couping between inorganic carbon and nutrient is shown as a ratio of a cumulative NCP to a cumulative change in inorganic nutrients. Three peaks of chlorophyll a concentration occurred during the experiment. Accordingly the experiment was divided in three phases. Overall cumulative NCP was similar in all mesocosms by the final day of experiment. However, NCP varied among phases, showing variable response to CO2 perturbation. Carbon to nitrogen (C : N) and carbon to phosphorus (C : P) uptake ratios were estimated only for the period after nutrient addition (post-nutrient period). For the total post-nutrient period ratios were close to Redfield proportions, however varied from it in different phases. The response of C : N and C : P uptake ratios to CO2 perturbation was different for three phases of the experiment, reflecting variable NCP and dependence on changing microbial community. Through the variable NCP, C : N and C : P uptake ratios for 31 days of the experiment we show a flexibility of biogeochemical response establishing a strong microbial loop in Kongsfjorden under different CO2 scenarios.

Description: Ocean acidification and carbonation, driven by anthropogenic emissions of carbon dioxide (CO2), have been shown to affect a variety of marine organisms and are likely to change ecosystem functioning. High latitudes, especially the Arctic, will be the first to encounter profound changes in carbonate chemistry speciation at a large scale, namely the under-saturation of surface waters with respect to aragonite, a calcium carbonate polymorph produced by several organisms in this region. During a CO2 perturbation study in 2010, in the framework of the EU-funded project EPOCA, the temporal dynamics of a plankton bloom was followed in nine mesocosms, manipulated for CO2 levels ranging initially from about 185 to 1420 μatm. Dissolved inorganic nutrients were added halfway through the experiment. Autotrophic biomass, as identified by chlorophyll a standing stocks (Chl a), peaked three times in all mesocosms. However, while absolute Chl a concentrations were similar in all mesocosms during the first phase of the experiment, higher autotrophic biomass was measured at high in comparison to low CO2 during the second phase, right after dissolved inorganic nutrient addition. This trend then reversed in the third phase. There were several statistically significant CO2 effects on a variety of parameters measured in certain phases, such as nutrient utilization, standing stocks of particulate organic matter, and phytoplankton species composition. Interestingly, CO2 effects developed slowly but steadily, becoming more and more statistically significant with time. The observed CO2 related shifts in nutrient flow into different phytoplankton groups (mainly diatoms, dinoflagellates, prasinophytes and haptophytes) could have consequences for future organic matter flow to higher trophic levels and export production, with consequences for ecosystem productivity and atmospheric CO2.

Description: Recent studies on the impacts of ocean acidification on pelagic communities have identified changes in carbon to nutrient dynamics with related shifts in elemental stoichiometry. In principle, mesocosm experiments provide the opportunity of determining the temporal dynamics of all relevant carbon and nutrient pools and, thus, calculating elemental budgets. In practice, attempts to budget mesocosm enclosures are often hampered by uncertainties in some of the measured pools and fluxes, in particular due to uncertainties in constraining air/sea gas exchange, particle sinking, and wall growth. In an Arctic mesocosm study on ocean acidification using KOSMOS (Kiel Off-Shore Mesocosms for future Ocean Simulation) all relevant element pools and fluxes of carbon, nitrogen and phosphorus were measured, using an improved experimental design intended to narrow down some of the mentioned uncertainties. Water column concentrations of particulate and dissolved organic and inorganic constituents were determined daily. New approaches for quantitative estimates of material sinking to the bottom of the mesocosms and gas exchange in 48 h temporal resolution, as well as estimates of wall growth were developed to close the gaps in element budgets. Future elevated pCO2 was found to enhance net autotrophic community carbon uptake in 2 of the 3 experimental phases but did not significantly affect particle elemental composition. Enhanced carbon consumption appears to result in accumulation of dissolved organic compounds under nutrient recycling summer conditions. This carbon over-consumption effect becomes evident from budget calculations, but was too small to be resolved by direct measurements of dissolved organics. The out-competing of large diatoms by comparatively small algae in nutrient uptake caused reduced production rates under future ocean CO2 conditions in the end of the experiment. This CO2 induced shift away from diatoms towards smaller phytoplankton and enhanced cycling of dissolved organics was pushing the system towards a retention type food chain with overall negative effects on export potential.