Posts Tagged 'Arctic'

Spatial and temporal controls on the inorganic carbon system of the Western Arctic Ocean

The Arctic Ocean plays a critical role in the global carbon cycle. It is believed to be particularly sensitive to the effects of climate change, is already undergoing dramatic changes, and is therefore important to study in that context. Most studies of the inorganic carbon system in the Western Arctic focus on hydrographic datasets from summer and/or fall (July-October), and do not consider the full response of the system to the timing of ice retreat, organic matter production and remineralization, and ice advance. Here we present the first dataset to investigate the spatial and temporal controls on the inorganic carbon system from early spring (pre-phytoplankton), late spring (initial phytoplankton bloom), summer (post-bloom), and fall in 2014. Our results suggest that the timing of ice retreat has important implications for the length of the phytoplankton growing season, and thus influences the magnitude of biological carbon cycling. We extend our analysis to include high-resolution temporal estimates of air-sea CO2 flux, and estimate a total annual CO2 uptake in the Chukchi Sea of ~7.7 Tg C. This is the first dataset to evaluate the importance of different seasonal observations within one year on the annual uptake of CO2 in the western Arctic Ocean. Our results show that extrapolations from one observational dataset result in large over- or underestimations of annual CO2 flux.

Continue reading ‘Spatial and temporal controls on the inorganic carbon system of the Western Arctic Ocean’

Future harvest of living resources in the Arctic Ocean north of the Nordic and Barents Seas: A review of possibilities and constraints

Global warming drives changes in oceanographic conditions in the Arctic Ocean and the adjacent continental slopes. This may result in favourable conditions for increased biological production in waters at the northern continental shelves. However, production in the central Arctic Ocean will continue to be limited by the amount of light and by vertical stratification reducing nutrient availability. Upwelling conditions due to topography and inflowing warm and nutrient rich Atlantic Water may result in high production in areas along the shelf breaks. This may particularly influence distribution and abundance of sea mammals, as can be seen from analysis of historical records of hunting. The species composition and biomass of plankton, fish and shellfish may be influenced by acidification due to increased carbon dioxide uptake in the water, thereby reducing the survival of some species. Northwards shift in the distribution of commercial species of fish and shellfish is observed in the Barents Sea, especially in the summer period, and is related to increased inflow of Atlantic Water and reduced ice cover. This implies a northward extension of boreal species and potential displacement of lipid-rich Arctic zooplankton, altering the distribution of organisms that depend on such prey. However, euphausiid stocks expanding northward into the Arctic Ocean may be a valuable food resource as they may benefit from increases in Arctic phytoplankton production and rising water temperatures. Even though no scenario modelling or other prediction analyses have been made, both scientific ecosystem surveys in the northern areas, as well as the fisheries show indications of a recent northern expansion of mackerel (Scomber scombrus), cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and capelin (Mallotus villosus). These stocks are found as far north as the shelf-break north of Svalbard. Greenland halibut (Reinhardtius hippoglossoides), redfish (Sebastes spp.) and shrimp (Pandalus borealis) are also present in the slope waters between the Barents Sea and the Arctic Ocean. It is assumed that cod and haddock have reached their northernmost limit, whereas capelin and redfish have potential to expand their distribution further into the Arctic Ocean. Common minke whales (Balaenoptera acutorostrata) and harp seals (Pagophilus groenlandicus) may also be able to expand their distribution into the Arctic Ocean. The abundance and distribution of other species may change as well – to what degree is unknown.

Continue reading ‘Future harvest of living resources in the Arctic Ocean north of the Nordic and Barents Seas: A review of possibilities and constraints’

Metabolic response of Arctic pteropods to ocean acidification and warming during the polar night/twilight phase in Kongsfjord (Spitsbergen)

Thecosome pteropods are considered highly sensitive to ocean acidification. During the Arctic winter, increased solubility of CO2 in cold waters intensifies ocean acidification and food sources are limited. Ocean warming is also particularly pronounced in the Arctic. Here, we present the first data on metabolic rates of two pteropod species (Limacina helicina, Limacina retroversa) during the Arctic winter at 79°N (polar night/twilight phase). Routine oxygen consumption rates and the metabolic response [oxygen consumption (MO2), ammonia excretion (NH3), overall metabolic balance (O:N)] to elevated levels of pCO2 and temperature were examined. Our results suggest lower routine MO2 rates for both Limacina species in winter than in summer. In an 18-h experiment, both pCO2 and temperature affected MO2 of L. helicina and L. retroversa. After a 9-day experiment with L. helicina all three metabolic response variables were affected by the two factors with interactive effects in case of NH3 and O:N. The response resembled a “hormesis-type” pattern with up-regulation at intermediate pCO2 and the highest temperature level. For L. retroversa, NH3 excretion was affected by both factors and O:N only by temperature. No significant effects of pCO2 or temperature on MO2 were detected. Metabolic up-regulation will entail higher energetic costs that may not be covered during periods of food limitation such as the Arctic winter and compel pteropods to utilize storage compounds to a greater extent than usual. This may reduce the fitness and survival of overwintering pteropods and negatively impact their reproductive success in the following summer.

Continue reading ‘Metabolic response of Arctic pteropods to ocean acidification and warming during the polar night/twilight phase in Kongsfjord (Spitsbergen)’

Increased pCO2 and temperature reveal ecotypic differences in growth and photosynthetic performance of temperate and Arctic populations of Saccharina latissima

The Arctic population of the kelp Saccharina latissima differs from the Helgoland population in its sensitivity to changing temperature and CO2 levels. The Arctic population does more likely benefit from the upcoming environmental scenario than its Atlantic counterpart.

The previous research demonstrated that warming and ocean acidification (OA) affect the biochemical composition of Arctic (Spitsbergen; SP) and cold-temperate (Helgoland; HL) Saccharina latissima differently, suggesting ecotypic differentiation. This study analyses the responses to different partial pressures of CO2 (380, 800, and 1500 µatm pCO2) and temperature levels (SP population: 4, 10 °C; HL population: 10, 17 °C) on the photophysiology (O2 production, pigment composition, D1-protein content) and carbon assimilation [Rubisco content, carbon concentrating mechanisms (CCMs), growth rate] of both ecotypes. Elevated temperatures stimulated O2 production in both populations, and also led to an increase in pigment content and a deactivation of CCMs, as indicated by 13C isotopic discrimination of algal biomass (εp) in the HL population, which was not observed in SP thalli. In general, pCO2 effects were less pronounced than temperature effects. High pCO2 deactivated CCMs in both populations and produced a decrease in the Rubisco content of HL thalli, while it was unaltered in SP population. As a result, the growth rate of the Arctic ecotype increased at elevated pCO2 and higher temperatures and it remained unchanged in the HL population. Ecotypic differentiation was revealed by a significantly higher O2 production rate and an increase in Chl a, Rubisco, and D1 protein content in SP thalli, but a lower growth rate, in comparison to the HL population. We conclude that both populations differ in their sensitivity to changing temperatures and OA and that the Arctic population is more likely to benefit from the upcoming environmental scenario than its Atlantic counterpart.

Continue reading ‘Increased pCO2 and temperature reveal ecotypic differences in growth and photosynthetic performance of temperate and Arctic populations of Saccharina latissima’

Sea surface pCO2 and O2 dynamics in the partially ice-covered Arctic Ocean

Understanding the physical and biogeochemical processes that control CO2 and dissolved oxygen (DO) dynamics in the Arctic Ocean (AO) is crucial for predicting future air-sea CO2 fluxes and ocean acidification. Past studies have primarily been conducted on the AO continental shelves during low-ice periods and we lack information on gas dynamics in the deep AO basins where ice typically inhibits contact with the atmosphere. To study these gas dynamics, in situ time-series data have been collected in the Canada Basin during late summer to autumn of 2012. Partial pressure of CO2 (pCO2), DO concentration, temperature, salinity, and chlorophyll-a fluorescence (Chl-a) were measured in the upper ocean in a range of sea ice states by two drifting instrument systems. Although the two systems were on average only 222 km apart, they experienced considerably different ice cover and external forcings during the 40-50 d periods when data were collected. The pCO2 levels at both locations were well below atmospheric saturation whereas DO was almost always slightly supersaturated. Modeling results suggest that air-sea gas exchange, net community production (NCP) and horizontal gradients were the main sources of pCO2 and DO variability in the sparsely ice-covered AO. In areas more densely covered by sea ice, horizontal gradients were the dominant source of variability, with no significant NCP in the surface mixed layer. If the AO reaches equilibrium with atmospheric CO2 as ice cover continues to decrease, aragonite saturation will drop from a present mean of 1.00 ± 0.02 to 0.86 ± 0.01.

Continue reading ‘Sea surface pCO2 and O2 dynamics in the partially ice-covered Arctic Ocean’

Seawater pH predicted for the year 2100 affects the metabolic response to feeding in copepodites of the Arctic copepod Calanus glacialis

Widespread ocean acidification (OA) is transforming the chemistry of the global ocean, and the Arctic is recognised as a region where the earliest and strongest impacts of OA are expected. In the present study, metabolic effects of OA and its interaction with food availability was investigated in Calanus glacialis from the Kongsfjord, West Spitsbergen. We measured metabolic rates and RNA/DNA ratios (an indicator of biosynthesis) concurrently in fed and unfed individuals of copepodite stages CII-CIII and CV subjected to two different pH levels representative of present day and the “business as usual” IPCC scenario (RCP8.5) prediction for the year 2100. The copepods responded more strongly to changes in food level than to decreasing pH, both with respect to metabolic rate and RNA/DNA ratio. However, significant interactions between effects of pH and food level showed that effects of pH and food level act in synergy in copepodites of C. glacialis. While metabolic rates in copepodites stage CII-CIII increased by 78% as a response to food under present day conditions (high pH), the increase was 195% in CII-CIIIs kept at low pH—a 2.5 times greater increase. This interaction was absent for RNA/DNA, so the increase in metabolic rates were clearly not a reaction to changing biosynthesis at low pH per se but rather a reaction to increased metabolic costs per unit of biosynthesis. Interestingly, we did not observe this difference in costs of growth in stage CV. A 2.5 times increase in metabolic costs of growth will leave the copepodites with much less energy for growth. This may infer significant changes to the C. glacialis population during future OA.

Continue reading ‘Seawater pH predicted for the year 2100 affects the metabolic response to feeding in copepodites of the Arctic copepod Calanus glacialis’

Long photoperiods sustain high pH in Arctic kelp forests

Concern on the impacts of ocean acidification on calcifiers, such as bivalves, sea urchins, and foraminifers, has led to efforts to understand the controls on pH in their habitats, which include kelp forests and seagrass meadows. The metabolism of these habitats can lead to diel fluctuation in pH with increases during the day and declines at night, suggesting no net effect on pH at time scales longer than daily. We examined the capacity of subarctic and Arctic kelps to up-regulate pH in situ and experimentally tested the role of photoperiod in determining the capacity of Arctic macrophytes to up-regulate pH. Field observations at photoperiods of 15 and 24 hours in Greenland combined with experimental manipulations of photoperiod show that photoperiods longer than 21 hours, characteristic of Arctic summers, are conducive to sustained up-regulation of pH by kelp photosynthesis. We report a gradual increase in pH of 0.15 units and a parallel decline in pCO2 of 100 parts per million over a 10-day period in an Arctic kelp forest over midsummer, with ample scope for continued pH increase during the months of continuous daylight. Experimental increase in CO2 concentration further stimulated the capacity of macrophytes to deplete CO2 and increase pH. We conclude that long photoperiods in Arctic summers support sustained up-regulation of pH in kelp forests, with potential benefits for calcifiers, and propose that this mechanism may increase with the projected expansion of Arctic vegetation in response to warming and loss of sea ice.

Continue reading ‘Long photoperiods sustain high pH in Arctic kelp forests’

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Ocean acidification in the IPCC AR5 WG II

OUP book