Posts Tagged 'Arctic'

Glacial drivers of marine biogeochemistry indicate a future shift to more corrosive conditions in an Arctic fjord

A detailed survey of a high Arctic glacier fjord (Kongsfjorden, Svalbard) was carried out in summer 2016, close to the peak of the meltwater season, in order to identify the effects of glacier runoff on nutrient distributions and the carbonate system. Short‐term weather patterns were found to exert a strong influence on freshwater content within the fjord. Freshwater inputs from glacier runoff and ice meltwater averaged (±SD) low nitrate (1.85±0.47 μM; 0.41±0.99 μM), orthophosphate (0.07±0.27 μM; 0.02 ±0.03 μM), dissolved organic carbon (27 ±14 μM in glacier runoff), total alkalinity (708±251 μmol kg‐1; 173±121 μmol kg‐1) and dissolved inorganic carbon (622±108 μmol kg‐1; 41±88 μmol kg‐1), as well as a modest silicate concentration (3.71±0.02 μM; 3.16±5.41 μM). pCO2 showed a non‐conservative behavior across the estuarine salinity gradient with a pronounced under‐saturation in the inner‐fjord, leading to strong CO2 uptake from the atmosphere. The combined effect of freshwater dilution and atmospheric CO2 absorption was the lowering of aragonite saturation state, to values that are known to negatively affect marine calcifiers (ΩAr, 1.07). Glacier discharge was therefore a strong local amplifier of ocean acidification. Future increases in discharge volume and the loss of marine productivity following the retreat of marine‐terminating glaciers inland are both anticipated to further lower ΩAr within inner‐fjord surface waters. This shift may be partially buffered by an increase in the mean freshwater total alkalinity as the fractional importance of iceberg melt to freshwater fjord inputs declines and runoff increases.

Continue reading ‘Glacial drivers of marine biogeochemistry indicate a future shift to more corrosive conditions in an Arctic fjord’

Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification

Ocean acidification (OA) will affect marine biotas from the organism to the ecosystem level. Yet, the consequences for the biological carbon pump and thereby the oceanic sink for atmospheric CO2 are still unclear. Here we show that OA considerably alters the C/N ratio of organic-matter export (C/Nexport), a key factor determining efficiency of the biological pump. By synthesizing sediment-trap data from in situ mesocosm studies in different marine biomes, we find distinct but highly variable impacts of OA on C/Nexport, reaching up to a 20% increase/decrease under partial pressure of CO2 (pCO2) conditions projected for 2100. These changes are driven by pCO2 effects on a variety of plankton taxa and corresponding shifts in food-web structure. Notably, our findings suggest a pivotal role of heterotrophic processes in controlling the response of C/Nexport to OA, thus contradicting the paradigm of primary producers as the principal driver of biogeochemical responses to ocean change.

Continue reading ‘Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification’

Phytoplankton dynamics in a changing Arctic Ocean

Changes in the Arctic atmosphere, cryosphere and Ocean are drastically altering the dynamics of phytoplankton, the base of marine ecosystems. This Review addresses four major complementary questions of ongoing Arctic Ocean changes and associated impacts on phytoplankton productivity, phenology and assemblage composition. We highlight trends in primary production over the last two decades while considering how multiple environmental drivers shape Arctic biogeography. Further, we consider changes to Arctic phenology by borealization and hidden under-ice blooms, and how the diversity of phytoplankton assemblages might evolve in a novel Arctic ‘biogeochemical landscape’. It is critical to understand these aspects of changing Arctic phytoplankton dynamics as they exert pressure on marine Arctic ecosystems in addition to direct effects from rapid environmental changes.

Continue reading ‘Phytoplankton dynamics in a changing Arctic Ocean’

Response of bacterial communities in Barents Sea sediments in case of a potential CO2 leakage from carbon reservoirs

Highlights

  • Simulation of real conditions of a CCS site are essentials for environmental risk assessments.

  • Marine bacteria may adapt to a new situation in case of acidification event for a short time.

  • Marine bacteria community is altered in case of a CO2 leakage after 3 weeks in long-term simulation.

  • Results did not show a potential recovery of marine bacteria when CO2 was stopped within the monitored period.

Abstract

Carbon capture and storage sites in Barents Sea shelf are currently in progress as part of climate change mitigation activities. However environmental impacts of a possible CO2 seepage on bacterial community are lacking knowledge. This work addressed potential consequences on bacterial communities from Snøvit region in Barents Sea sediments. Long-term experiment (92 days) was carried out mimicking realistic conditions of pressure (∼30 bars) using the unique hyperbaric chamber (Karl Erik TiTank). The experiment was divided in three stages: i) 21 days of no CO2, ii) 50 days of simulation of carbon dioxide leakage (depletion of pH to 7.0) and iii) 14 days emulating a leakage cessation. Results suggested that bacterial communities can adapt to a CO2 leakage in short term. However, bacteria showed negative effects in terms of activity, community structure, and number of cells after long term CO2 exposure. After CO2 leakage cessation, bacterial communities did not show a significant recovery. These findings highlighted that, even though marine bacteria showed adaptation to the new conditions (acidified environment), in case of a small but continuous CO2 leakage marine bacteria might not be recovered upon pre-exposure status.

    Continue reading ‘Response of bacterial communities in Barents Sea sediments in case of a potential CO2 leakage from carbon reservoirs’

    Contrasting responses to salinity and future ocean acidification in arctic populations of the amphipod Gammarus setosus

    Highlights

    • Climate change is leading to changes in salinity and pCO2 in arctic/sub-arctic coastal ecosystems.

    • We examined Gammarus setosus at 3 sites along a salinity gradient in the field and laboratory.

    • Reduced salinity had more of an effect than elevated pCO2 by reducing energy budgets.

    • Lower salinities increased ion transporting capacities in the laboratory but not in the field.

    • G. setosus at lower salinity sites have lower energy budgets suggesting impacts on performance.

    Abstract

    Climate change is leading to alterations in salinity and carbonate chemistry in arctic/sub-arctic marine ecosystems. We examined three nominal populations of the circumpolar arctic/subarctic amphipod, Gammarus setosus, along a salinity gradient in the Kongsfjorden-/Krossfjorden area of Svalbard. Field and laboratory experiments assessed physiological (haemolymph osmolality and gill Na+/K+-ATPase activity, NKA) and energetic responses (metabolic rates, MO2, and Cellular Energy Allocation, CEA). In the field, all populations had similar osmregulatory capacities and MO2, but lower-salinity populations had lower CEA. Reduced salinity (S = 23) and elevated pCO2 (∼1000 μatm) in the laboratory for one month increased gill NKA activities and reduced CEA in all populations, but increased MO2 in the higher-salinity population. Elevated pCO2 did not interact with salinity and had no effect on NKA activities or CEA, but reduced MO2 in all populations. Reduced CEA in lower-rather than higher-salinity populations may have longer term effects on other energy demanding processes (growth and reproduction).

    Continue reading ‘Contrasting responses to salinity and future ocean acidification in arctic populations of the amphipod Gammarus setosus’

    The seasonal phases of an Arctic lagoon reveal non-linear pH extremes

    The western Arctic Ocean, including its shelves and coastal habitats, has become a focus in ocean acidification research over the past decade as the colder waters of the region and the reduction of sea ice appear to promote the uptake of excess atmospheric CO2. Due to seasonal sea ice coverage, high-frequency monitoring of pH or other carbonate chemistry parameters is typically limited to infrequent ship-based transects during ice-free summers. This approach has failed to capture year-round nearshore carbonate chemistry dynamics which is modulated by biological metabolism in response to abundant allochthonous organic matter to the narrow shelf of the Beaufort Sea and adjacent regions. The coastline of the Beaufort Sea comprises a series of lagoons that account for > 50 % of the land-sea interface. The lagoon ecosystems are novel features that cycle between open and closed phases (i.e., ice-free, and ice covered, respectively). In this study, we collected high-frequency pH, salinity, temperature, and PAR measurements in association with the Beaufort Lagoon Ecosystem LTER for an entire calendar year in Kaktovik Lagoon, Alaska, USA, capturing two open water phases and one closed phase. Hourly pH variability during the open water phases are some of the fastest rates reported, exceeding 0.4 units. Baseline pH varied substantially between open phase 2018 and open phase 2019 with a difference of ~ 0.2 units despite similar hourly rates of change. Salinity-pH relationships were mixed during all three phases displaying no correlation in open 2018, a negative correlation in closed 2018–2019, and positive correlation during open 2019. The high-frequency of pH variability could partially be explained by photosynthesis-respiration cycles as correlation coefficients between daily average pH and PAR were 0.46 and 0.64 for open 2018 and open 2019 phases, respectively. The estimated annual daily average CO2 efflux was 5.9 ± 19.3 mmol m−2 d−1, which is converse to the negative influx of CO2 estimated for the coastal Beaufort Sea despite exhibiting extreme variability. Considering the geomorphic differences in Beaufort Sea lagoons, further investigation is needed to assess if there are periods of the open phase in which all lagoons are sources of carbon to the atmosphere, potentially offsetting the predicted sink capacity of the greater Beaufort Sea.

    Continue reading ‘The seasonal phases of an Arctic lagoon reveal non-linear pH extremes’

    Summer and winter MgCO3 levels in the skeletons of Arctic bryozoans

    Highlights

    • Summer and winter MgCO3 levels in skeleton of Arctic bryozoans by Anna Iglikowska, Małgorzata Krzemińska, Paul E. Renaud, Jørgen Berge, Haakon Hop and Piotr Kukliński.
    • Arctic seawater differs in carbonate saturation state during polar night and day.

    • During summer carbonate saturation gradient is expected related to depth.

    • Carbonate saturation state may influence Mg accumulation in biogenic calcite.

    • No differences between summer and winter levels of skeletal MgCO3 were found.

    • Bryozoans are able to regulate their skeletal MgCO3 concentrations biologically.

    Abstract

    In the Arctic, seasonal patterns in seawater biochemical conditions are shaped by physical, chemical, and biological processes related to the alternation of seasons, i.e. winter polar night and summer midnight sun. In summertime, CO2 concentration is driven by photosynthetic activity of autotrophs which raises seawater pH and carbonate saturation state (Ω). In addition, restriction of photosynthetic activity to the euphotic zone and establishment of seasonal stratification often leads to depth gradients in pH and Ω. In winter, however, severely reduced primary production along with respiration processes lead to higher CO2 concentrations which consequently decrease seawater pH and Ω.

    Many calcifying invertebrates incorporate other minerals, in addition to calcium, into their skeletons, with potential consequences for stability of the mineral matrix and vulnerability to abrasion of predators. We tested whether changes in seawater chemistry due to light-driven activities of marine biota can influence the uptake of Mg into calcified skeletons of Arctic Bryozoa, a dominant faunal group in polar hard-bottom habitats. Our results indicate no clear differences between summer and winter levels of skeletal MgCO3 in five bryozoan species despite differences in Ω between these two seasons. Furthermore, we could not detect any depth-related differences in MgCO3 content in skeletons of selected bryozoans. These results may indicate that Arctic bryozoans are able to control MgCO3 skeletal concentrations biologically. Yet recorded spatial variability in MgCO3 content in skeletons from stations exhibiting different seawater parameters suggests that environmental factors can also, to some extent, shape the skeletal chemistry of Arctic bryozoans.

    Continue reading ‘Summer and winter MgCO3 levels in the skeletons of Arctic bryozoans’

    Modeled impacts of sea ice exchange processes on Arctic Ocean carbon uptake and acidification (1980–2015)

    Marine organisms and ecosystems face multiple, temporally variable stressors in a rapidly changing world. Realistic experiments that incorporate these aspects of physiological stress are important for advancing our ability to understand, predict, and manage their ecological impacts. However, the experimental systems needed to conduct such experiments can be costly. Here, we describe a low‐cost, modular control system that can be used with seawater sensors and actuators to dynamically manipulate multiple seawater variables. It enables researchers to run a variety of realistic multiple‐stressor, variable exposure experiments with a range of marine organisms. This tank controller system is based on the open‐source Arduino prototyping platform and features a custom‐made circuit board with a 16‐bit analog‐to‐digital converter, a real‐time clock, a MicroSD memory card reader, a high‐voltage transistor array, and solderless screw terminal connectors for easy connection of sensors, actuators, and power supplies. The assembly and use of this controller system does not require extensive electronics engineering or programming experience, and each module can be assembled for under 80 USD in parts. To demonstrate the system’s capabilities, we present seawater manipulations from experiments involving (1) simultaneous manipulations of dissolved oxygen and pH; (2) fluctuating dissolved oxygen levels; and (3) a controlled stepwise decrease in dissolved oxygen at different temperatures. The low cost and high customizability of this Arduino‐based control system can contribute to expanding capacities for running global change experiments for researchers and students worldwide.

    Continue reading ‘Modeled impacts of sea ice exchange processes on Arctic Ocean carbon uptake and acidification (1980–2015)’

    Seasonal dynamics of carbonate chemistry, nutrients and CO2 uptake in a sub-Arctic fjord

    Environmental change can have a significant impact on biogeochemical cycles at high latitudes and be particularly important in ecologically valuable fjord ecosystems. Seasonality in biogeochemical cycling in a sub-Arctic fjord of northern Norway (Kaldfjorden) was investigated from October 2016 to September 2018. Monthly changes in total inorganic carbon (CT), alkalinity (AT), major nutrients and calcium carbonate saturation (Ω) were driven by freshwater discharge, biological production and mixing with subsurface carbon-rich coastal water. Stable oxygen isotope ratios indicated that meteoric water (snow melt, river runoff, precipitation) had stratified and freshened surface waters, contributing to 81% of the monthly CT deficit in the surface layer. The timing and magnitude of freshwater inputs played an important role in Ω variability, reducing AT and CT by dilution. This dilution effect was strongly counteracted by the opposing effect of primary production that dominated surface water Ω seasonality. The spring phytoplankton bloom rapidly depleted nitrate and CT to drive highest Ω (~2.3) in surface waters. Calcification reduced AT and CT, which accounted for 21% of the monthly decrease in Ω during a coccolithophore bloom. Freshwater runoff contributed CT, AT and silicates of terrestrial origin to the fjord. Lowest surface water Ω (~1.6) resulted from organic matter remineralisation and mixing into subsurface water during winter and spring. Surface waters were undersaturated with respect to atmospheric CO2, resulting in modest uptake of –0.32 ± 0.03 mol C m–2 yr–1. Net community production estimated from carbon drawdown was 14 ± 2 g C m–2 yr–1 during the productive season. Kaldfjorden currently functions as an atmospheric CO2 sink of 3.9 ± 0.3 g C m–2 yr–1. Time-series data are vital to better understand the processes and natural variability affecting biogeochemical cycling in dynamic coastal regions and thus better predict the impact of future changes on important fjord ecosystems.

    Continue reading ‘Seasonal dynamics of carbonate chemistry, nutrients and CO2 uptake in a sub-Arctic fjord’

    The recent state and variability of the carbonate system of the Canadian Arctic in the context of ocean acidification (update)

    Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecosystems around the globe. The Arctic Ocean is particularly vulnerable to acidification and thus is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the carbonate mineral aragonite (ΩA<1), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago (CAA), a dynamic region with an inherently strong variability in biogeochemical processes. Nonetheless, few of these observations were made in the last 5 years and the spatial coverage in the latter region is poor. We use a dataset of carbonate system parameters measured in the CAA and its adjacent basins (Canada Basin and Baffin Bay) from 2003 to 2016 to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability over more than a decade. Our findings reveal that, in the summers of 2014 to 2016, the ocean surface across our study area served as a net CO2 sink and was partly undersaturated with respect to aragonite in the Canada Basin and the Queen Maud Gulf, the latter region exhibiting undersaturation over its entire water column at some locations. We estimate, using measurements made across several years, that approximately a third of the interannual variability in surface dissolved inorganic carbon (DIC) concentrations in the CAA results from fluctuations in biological activity. In consideration of the system's variability resulting from these fluctuations, we derive times of emergence of the anthropogenic ocean acidification signal for carbonate system parameters in the study area.

    Continue reading ‘The recent state and variability of the carbonate system of the Canadian Arctic in the context of ocean acidification (update)’


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