Posts Tagged 'Arctic'

Simulation of factors affecting Emiliania huxleyi blooms in Arctic and sub-Arctic seas by CMIP5 climate models: model validation and selection

The observed warming in the Arctic is more than double the global average, and this enhanced Arctic warming is projected to continue throughout the 21st century. This rapid warming has a wide range of impacts on polar and sub-polar marine ecosystems. One of the examples of such an impact on ecosystems is that of coccolithophores, particularly Emiliania huxleyi, which have expanded their range poleward during recent decades. The coccolithophore E. huxleyi plays an essential role in the global carbon cycle. Therefore, the assessment of future changes in coccolithophore blooms is very important.

Currently, there are a large number of climate models that give projections for various oceanographic, meteorological, and biochemical variables in the Arctic. However, individual climate models can have large biases when compared to historical observations. The main goal of this research was to select an ensemble of climate models that most accurately reproduces the state of environmental variables that influence the coccolithophore E. huxleyi bloom over the historical period when compared to reanalysis data. We developed a novel approach for model selection to include a diverse set of measures of model skill including the spatial pattern of some variables, which had not previously been included in a model selection procedure. We applied this method to each of the Arctic and sub-Arctic seas in which E. huxleyi blooms have been observed. Once we have selected an optimal combination of climate models that most skilfully reproduce the factors which affect E. huxleyi, the projections of the future conditions in the Arctic from these models can be used to predict how E. huxleyi blooms will change in the future.

Here, we present the validation of 34 CMIP5 (fifth phase of the Coupled Model Intercomparison Project) atmosphere–ocean general circulation models (GCMs) over the historical period 1979–2005. Furthermore, we propose a procedure of ranking and selecting these models based on the model’s skill in reproducing 10 important oceanographic, meteorological, and biochemical variables in the Arctic and sub-Arctic seas. These factors include the concentration of nutrients (NO3, PO4, and SI), dissolved CO2 partial pressure (pCO2), pH, sea surface temperature (SST), salinity averaged over the top 30 m (SS30 m), 10 m wind speed (WS), ocean surface current speed (OCS), and surface downwelling shortwave radiation (SDSR). The validation of the GCMs’ outputs against reanalysis data includes analysis of the interannual variability, seasonal cycle, spatial biases, and temporal trends of the simulated variables. In total, 60 combinations of models were selected for 10 variables over six study regions using the selection procedure we present here. The results show that there is neither a combination of models nor one model that has high skill in reproducing the regional climatic-relevant features of all combinations of the considered variables in target seas. Thereby, an individual subset of models was selected according to our model selection procedure for each combination of variable and Arctic or sub-Arctic sea. Following our selection procedure, the number of selected models in the individual subsets varied from 3 to 11.

The paper presents a comparison of the selected model subsets and the full-model ensemble of all available CMIP5 models to reanalysis data. The selected subsets of models generally show a better performance than the full-model ensemble. Therefore, we conclude that within the task addressed in this study it is preferable to employ the model subsets determined through application of our procedure than the full-model ensemble.

Continue reading ‘Simulation of factors affecting Emiliania huxleyi blooms in Arctic and sub-Arctic seas by CMIP5 climate models: model validation and selection’

Higher sensitivity towards light stress and ocean acidification in an Arctic sea‐ice associated diatom compared to a pelagic diatom

Thalassiosira hyalina and Nitzschia frigida are important members of Arctic pelagic and sympagic (sea‐ice associated) diatom communities. We investigated the effects of light stress (shift from 20 to 380 µmol photons m‐2 s‐1, resembling upwelling or ice break‐up) under contemporary and future pCO2 (400 vs. 1000 µatm).

The responses in growth, elemental composition, pigmentation and photophysiology were followed over 120 h and are discussed together with underlying gene expression patterns.

Stress response and subsequent re‐acclimation were efficiently facilitated by T. hyalina, which showed only moderate changes in photophysiology and elemental composition, and thrived under high‐light after 120 h. In N. frigida, photochemical damage and oxidative stress appeared to outweigh cellular defenses, causing dysfunctional photophysiology and reduced growth. pCO2 alone did not specifically influence gene expression, but amplified the transcriptomic reactions to light stress, indicating that pCO2 affects metabolic equilibria rather than sensitive genes.

Large differences in acclimation capacities towards high‐light and high pCO2 between T. hyalina and N. frigida indicate species‐specific mechanisms in coping with the two stressors, which may reflect their respective ecological niches. This could potentially alter the balance between sympagic vs. pelagic primary production in a future Arctic.

Continue reading ‘Higher sensitivity towards light stress and ocean acidification in an Arctic sea‐ice associated diatom compared to a pelagic diatom’

Freshening of the western Arctic negates anthropogenic carbon uptake potential

As human activities increase the atmospheric concentration of carbon dioxide (CO2), the oceans are known to absorb a significant portion. The Arctic Ocean has long been considered to have enormous potential to sequester anthropogenic CO2, and mitigate emissions. The frigid waters make CO2 more soluble, and as sea ice melts, greater surface area is exposed to absorb CO2. However, sparse data have made quantifying the amount of anthropogenic CO2 in the Arctic difficult, stimulating much debate over the basin’s contribution to CO2 sequestration from the atmosphere. Using three separate cruises in 1994, 2005, and 2015 in the Canada and Makarov basins, we analyze the decadal variability in anthropogenic CO2 uptake in the central western Arctic. Here we show, from direct carbon system measurements spanning two decades, that despite increased atmospheric CO2, total dissolved inorganic carbon has actually decreased, with minimal anthropogenic CO2 uptake. The reduction in dissolved CO2 results from a dilution of total alkalinity by increased freshwater supply, particularly river water. Changes in the freshwater budget of the western Arctic override its uptake potential, resulting in a weak sink, or possibly source of CO2.

Continue reading ‘Freshening of the western Arctic negates anthropogenic carbon uptake potential’

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

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 due to its relatively low buffering capacity 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. Nonetheless, few of these observations were made in the last five years and the spatial coverage in the latter region is poor. Additionally, the strong variability inherent to this dynamic shelf environment renders the temporal imprint of ocean acidification on carbonate system parameters (pH, pCO2, DIC, Ω) virtually indistinguishable on decadal timescales. We use a dataset of carbonate system parameters measured in Canadian Arctic Archipelago (CAA) and its adjacent basins to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability. Our findings reveal that, in addition to the surface of the Canada Basin, the entire water column of the Queen Maud Gulf was undersaturated with respect to aragonite in 2015 and 2016. We also estimate that approximately a third of the interannual variability in surface DIC in the CAA results from fluctuations in biological activity.

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

Origin and accumulation of an anthropogenic CO2 and 13C Suess effect in the Arctic Ocean

We determined the impact of anthropogenic CO2 (Cant) accumulation on the δ13C of dissolved inorganic carbon (DIC) in the Arctic Ocean (i.e., the 13C Suess effect) based on δ13C measurements during a GEOTRACES cruise in 2015. The δ13C decrease was estimated from the amount of Cant change derived by the transit time distribution (TTD) approach and the ratio of the anthropogenic δ13C/DIC change (RC). A significant Cant increase (up to 45 μmol kg−1) and δ13C decrease (up to −0.9‰) extends to ~2000 m in the Canada and Makarov Basin. We find distinctly different RC values for the intermediate water (300–2000 m) and upper halocline water (<200 m) of −0.020 and −0.012‰ (μmol kg−1)−1, respectively, which identifies two sources of Cant accumulation from North Atlantic and North Pacific. Furthermore, estimated RC for intermediate waters is the same as the RC observed in the Greenland Sea and the rate of anthropogenic DIC increase estimated for intermediate waters at 0.9 μmol kg−1 yr−1 is identical to the estimated rate in the Iceland Sea. These observations indicate that the high rate of Cant accumulation and δ13C decrease in the Arctic Ocean is primarily a result of the input of Cant, via ventilation of intermediate waters, from the Nordic Sea rather than local anthropogenic CO2 uptake within the Arctic Basin. We determine the preindustrial δ13C (δ13CPI) distributions and find distinct δ13CPI signatures of the intermediate and upper halocline waters that reflect the difference in δ13CPI–PO4 relationship of Atlantic and Pacific source water.

Continue reading ‘Origin and accumulation of an anthropogenic CO2 and 13C Suess effect in the Arctic Ocean’

Impact of climate change and ocean acidification on ocean-based industries and society in Norway

This report presents a review of the scientific literature on how key ecosystems, ecosystem services and ocean-based industries in Norway are affected by climate change and ocean acidification today and under future scenarios. The project has also compiled knowledge on how ocean-based actions can help mitigate and reduce the magnitude of climate change, ocean acidification and environmental problems. Further possible trade-off related to ocean-based action were identified as well as how climate change and ocean acidification may potentially affect these ocean-based opportunities. Finally, the report presents published findings on possible future impacts on society and implications for policy and management.

Continue reading ‘Impact of climate change and ocean acidification on ocean-based industries and society in Norway’

The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)

Compared to the rest of the globe, the Arctic Ocean is affected disproportionately by climate change. Despite these fast environmental changes, we currently know little about the effects of ocean acidification (OA) on marine key species in this area. Moreover, the existing studies typically test the effects of OA under constant, hence artificial, light fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to current (400 µatm) and future (1000 µatm) pCO2 levels under a constant as well as a dynamic light, simulating more realistic light fields as experienced in the upper mixed layer. To describe and understand the responses to these drivers, growth, particulate organic carbon (POC) production, elemental composition, photophysiology and reactive oxygen species (ROS) production were analysed. M. pusilla was able to benefit from OA on various scales, ranging from an increase in growth rates to enhanced photosynthetic capacity, irrespective of the light regime. These beneficial effects were, however, not reflected in the POC production rates, which can be explained by energy partitioning towards cell division rather than biomass build-up. In the dynamic light regime, M. pusilla was able to optimize its photophysiology for effective light usage during both low- and high-light periods. This photoacclimative response, which was achieved by modifications to photosystem II (PSII), imposed high metabolic costs leading to a reduction in growth and POC production rates when compared to constant light. There were no significant interactions observed between dynamic light and OA, indicating that M. pusilla is able to maintain effective photoacclimation without increased photoinactivation under high pCO2. Based on these findings, M. pusilla is likely to cope well with future conditions in the Arctic Ocean.

Continue reading ‘The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)’

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Ocean acidification in the IPCC AR5 WG II

OUP book