Posts Tagged 'Arctic'



Effects of river delivery of nutrients and carbon on the biogeochemistry of the Arctic Ocean

Coastal oceans play an important role in the carbon cycle and are hotspots of ocean primary production and ocean acidification. These coastal regions are strongly influenced by rives, especially in the Arctic. Despite the importance of the riverine delivery of carbon and nutrients, their effect on the Arctic Ocean is still poorly understood due to hostile conditions and the consequently low number of observations. This thesis aims at improving our understanding of the influence of Arctic riverine delivery of carbon and nutrients by using ocean biogeochemical models. The first part of the thesis evaluated the model skills of the ocean biogeochemical model NEMO-PISCES in the Arctic Ocean. By analyzing model results at different horizontal resolutions, the importance of lateral influx from the adjacent oceans for anthropogenic carbon cycle in the Arctic Ocean was  demonstrated. These results were then used to adjust a previously published data-based estimate of anthropogenic carbon storage in the Arctic Ocean and the corresponding ocean acidification. In the second part, a pan-Arctic observation-based dataset of riverine carbon and nutrient fluxes was created. This dataset was then used to force the ocean biogeochemical model and the river fluxes were quantified. River fluxes have been shown to sustain up to 24% of Arctic Ocean primary production, to reduce the air-sea CO2 uptake by 20%, and to reduce surface ocean acidification seasonally. Eventually, idealized simulations were made to quantify the sensitivity of the Arctic Ocean biogeochemistry to future changes in riverine delivery of carbon and nutrients. Sensitivities are of small magnitude on a pan-Arctic scale, importance in the coastal areas, and the dominant factor close to river mouths.

Continue reading ‘Effects of river delivery of nutrients and carbon on the biogeochemistry of the Arctic Ocean’

Model constraints on the anthropogenic carbon budget of the Arctic Ocean (update)

The Arctic Ocean is projected to experience not only amplified climate change but also amplified ocean acidification. Modeling future acidification depends on our ability to simulate baseline conditions and changes over the industrial era. Such centennial-scale changes require a global model to account for exchange between the Arctic and surrounding regions. Yet the coarse resolution of typical global models may poorly resolve that exchange as well as critical features of Arctic Ocean circulation. Here we assess how simulations of Arctic Ocean storage of anthropogenic carbon (Cant), the main driver of open-ocean acidification, differ when moving from coarse to eddy-admitting resolution in a global ocean-circulation–biogeochemistry model (Nucleus for European Modeling of the Ocean, NEMO; Pelagic Interactions Scheme for Carbon and Ecosystem Studies, PISCES). The Arctic’s regional storage of Cant is enhanced as model resolution increases. While the coarse-resolution model configuration ORCA2 (2) stores 2.0 Pg C in the Arctic Ocean between 1765 and 2005, the eddy-admitting versions ORCA05 and ORCA025 (1∕2 and 1∕4) store 2.4 and 2.6 Pg C. The difference in inventory between model resolutions that is accounted for is only from their divergence after 1958, when ORCA2 and ORCA025 were initialized with output from the intermediate-resolution configuration (ORCA05). The difference would have been larger had all model resolutions been initialized in 1765 as was ORCA05. The ORCA025 Arctic Cant storage estimate of 2.6 Pg C should be considered a lower limit because that model generally underestimates observed CFC-12 concentrations. It reinforces the lower limit from a previous data-based approach (2.5 to 3.3 Pg C). Independent of model resolution, there was roughly 3 times as much Cant that entered the Arctic Ocean through lateral transport than via the flux of CO2 across the air–sea interface. Wider comparison to nine earth system models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) reveals much larger diversity of stored Cant and lateral transport. Only the CMIP5 models with higher lateral transport obtain Cant inventories that are close to the data-based estimates. Increasing resolution also enhances acidification, e.g., with greater shoaling of the Arctic’s average depth of the aragonite saturation horizon during 1960–2012, from 50 m in ORCA2 to 210 m in ORCA025. Even higher model resolution would likely further improve such estimates, but its prohibitive costs also call for other more practical avenues for improvement, e.g., through model nesting, addition of coastal processes, and refinement of subgrid-scale parameterizations.

Continue reading ‘Model constraints on the anthropogenic carbon budget of the Arctic Ocean (update)’

Impacts of the changing ocean-sea ice system on the key forage fish Arctic cod (Boreogadus saida) and subsistence fisheries in the Western Canadian Arctic—evaluating linked Climate, Ecosystem and Economic (CEE) models

This study synthesizes results from observations, laboratory experiments and models to showcase how the integration of scientific methods and indigenous knowledge can improve our understanding of (a) past and projected changes in environmental conditions and marine species; (b) their effects on social and ecological systems in the respective communities; and (c) support management and planning tools for climate change adaptation and mitigation. The study links climate-ecosystem-economic (CEE) models and discusses uncertainties within those tools. The example focuses on the key forage species in the Inuvialuit Settlement Region (Western Canadian Arctic), i.e., Arctic cod (Boreogadus saida). Arctic cod can be trophically linked to sea-ice algae and pelagic primary producers and are key vectors for energy transfers from plankton to higher trophic levels (e.g., ringed seals, beluga), which are harvested by Inuit peoples. Fundamental changes in ice and ocean conditions in the region affect the marine ecosystem and fish habitat. Model simulations suggest increasing trends in oceanic phytoplankton and sea-ice algae with high interannual variability. The latter might be linked to interannual variations in Arctic cod abundance and mask trends in observations. CEE simulations incorporating physiological temperature limits data for the distribution of Arctic cod, result in an estimated 17% decrease in Arctic cod populations by the end of the century (high emission scenario), but suggest increases in abundance for other Arctic and sub-Arctic species. The Arctic cod decrease is largely caused by increased temperatures and constraints in northward migration, and could directly impact key subsistence species. Responses to acidification are still highly uncertain, but sensitivity simulations suggests an additional 1% decrease in Arctic cod populations due to pH impacts on growth and survival. Uncertainties remain with respect to detailed future changes, but general results are likely correct and in line with results from other approaches. To reduce uncertainties, higher resolution models with improved parameterizations and better understanding of the species’ physiological limits are required. Arctic communities should be directly involved, receive tools and training to conduct local, unified research and food chain monitoring while decisions regarding commercial fisheries will need to be precautionary and adaptive in light of the existing uncertainties.

Continue reading ‘Impacts of the changing ocean-sea ice system on the key forage fish Arctic cod (Boreogadus saida) and subsistence fisheries in the Western Canadian Arctic—evaluating linked Climate, Ecosystem and Economic (CEE) models’

Arctic ocean acidification assessment 2018: summary for policy-makers

Some of the fastest rates of acidification are occurring in the Arctic, due mainly to the higher capacity of colder water to absorb CO2, but also due to dilution by river run-off and ice melt, and the inflow of naturally low pH waters from the Pacific. Changes are already evident in the Arctic Ocean’s marine carbonate system – which, among other things, has been shown to influence growth, reproduction and ultimately survival in some organisms. These changes may cause significant ecological shifts in the coming decades. These shifts could, in turn, have significant socioeconomic consequences, not only for Arctic communities, but more widely. These concerns were referenced in the Fairbanks Declaration of 11 May 2017, when ministers representing the eight Arctic states, and representatives of the six Permanent Participant organizations, noted “with concern the vulnerability of Arctic marine ecosystems to the impacts of ocean acidification”, and called for continuing study and awareness raising regarding those impacts and their consequences.

Continue reading ‘Arctic ocean acidification assessment 2018: summary for policy-makers’

Describing seasonal marine carbon system processes in Cambridge Bay Nunavut using an innovative sensor platform

The marine carbonate system is a critical component of global biogeochemical cycles. It determines a given marine region’s status as a source or sink for atmospheric CO2, and long-term changes (i.e. ocean acidification) that can affect key ecosystem functions. Carbonate system processes are highly-variable through space and time, which makes it difficult to fully characterize a region without either intensive sampling, or long-term deployment of high-precision instruments. Both of these are difficult in the Arctic, where challenging logistics limit sampling opportunities, and instruments must endure extreme conditions. In this work, we present the first high-resolution marine carbon system dataset covering a full Arctic cycle of sea ice growth and melt. We deployed a Satlantic SeaFET Ocean pH Sensor and a Pro-Oceanus CO2-Pro CV sensor for consecutive nearly year-long deployments onboard the Cambridge Bay Ocean Networks Canada Undersea Community Observatory from September 2015 – June 2018. The sensors measurements were compared to discrete sample references, and determined to require multipoint in situ calibration, but were representative of the greater sea surface mixed layer inside the bay through most of the year. Using a diagnostic box model approach, seasonal influencing processes on the marine carbon system at the platform were quantitatively determined. Air-sea gas exchange and biologic respiration/ remineralization were dominant in the fall, whereas following sea ice freeze-up brine rejection drove pCO2 to seasonal supersaturation with respect to the atmosphere, and the aragonite saturation state to become undersaturated. Shortly after the sun rose under the ice in the late winter, the ecosystem at the platform became net autotrophic at very low light levels, driving pCO2 to undersaturation. As sea ice melted, an under-ice phytoplankton bloom drew down a significant amount of carbon before the open water season, returning the aragonite saturation state to supersaturation at the platform. These observations show a dynamic system, where biological processes occur at times and rates previously unknown to the literature. These processes will need to be included in future biogeochemical modelling efforts, if we are to properly resolve the current, and future, role of the Arctic Ocean basin in global biogeochemical cycles.

Continue reading ‘Describing seasonal marine carbon system processes in Cambridge Bay Nunavut using an innovative sensor platform’

Threats to Arctic ecosystems

Pollution, ocean acidification and global warming are all major threats to Arctic ecosystems and are all inextricably linked. Major global air and ocean currents bring pollutants north to the “Arctic sink” where they accumulate over time, affecting ecosystems and wildlife. Meanwhile, carbon pollution from fossil fuels is causing widespread ocean acidification and global warming, which is happening two to three times faster in the Arctic than other regions. While climate change is having direct effects on Arctic ecosystems, the dynamics of pollutants within Arctic ecosystems are also being affected, enhancing pollutant mobility and effects in some cases.

Continue reading ‘Threats to Arctic ecosystems’

Marine CO2 system variability in a high arctic tidewater-glacier fjord system, Tempelfjorden, Svalbard

Highlights

• The marine CO2 system was investigated in an Arctic fjord between 2015 and 2017.

• Primary production caused the largest changes observed in pCO2 and the saturation state of aragonite.

• Air-sea CO2 uptake and freshwater release governed the surface pCO2 over the melt season.

• At least a freshwater fraction larger than 50% was needed to provide aragonite undersaturated waters.

• An excess in the salinity normalized DIC, corrected for primary production/respiration, was found in the deepest water.

Abstract

The marine CO2 system in Tempelfjorden (Svalbard) was investigated between August 2015 and December 2017 using total alkalinity, pH, temperature, salinity, oxygen isotopic ratio, and nutrient data. Primary production resulted in the largest changes that were observed in the partial pressure of CO2 (pCO2, 140 μatm) and the saturation state of aragonite (ΩAr, 0.9). Over the period of peak freshwater discharge (June to August), the freshwater addition and air-sea CO2 uptake (on average 15.5 mmol m−2 day−1 in 2017) governed the surface pCO2. About one fourth of the uptake was driven by the freshening. The sensitivity of ΩAr to the freshwater addition was investigated using robust regressions. If the effect of air-sea CO2 exchange was removed from ΩAr, a freshwater fraction larger than 50% (lower range of uncertainty) was needed to provide aragonite undersaturated waters. This study shows that ΩAr and freshwater fraction relationships that are derived from regression techniques and the interpretation thereof are sensitive to the effect of air-sea CO2 exchange. Since the freshening in itself only drives a fraction of the air-sea CO2 uptake, studies that do not account for this exchange will overestimate the impact of freshwater on ΩAr. Finally, in the summer an excess in the salinity normalized dissolved inorganic carbon, corrected for aerobic primary production/respiration, of on average 86 μmol kg−1 was found in the deepest water of the fjord. This excess is suggested to be a result of enhanced CO2 uptake and brine release during the period of sea ice growth.

Continue reading ‘Marine CO2 system variability in a high arctic tidewater-glacier fjord system, Tempelfjorden, Svalbard’


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Ocean acidification in the IPCC AR5 WG II

OUP book