Effects of CO2 and long day length on primary productivity in the Arctic Ocean: a perspective on climate change = Efectos del CO2 y largos fotoperiodos en la productividad primaria del Océano Ártico: una perspectiva sobre el cambio climático
Climate change, caused by anthropogenic emissions of carbon dioxide (CO2) and other greenhouse gasses into the atmosphere, is producing profound impacts on ecosystems. The Arctic Ocean is one of the most vulnerable regions of the world and is experiencing the most substantial effects of climate chan...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2018 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/563077 |
| Acceso en línea: | http://hdl.handle.net/10803/563077 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrtic, Oceà Artico, Océano Arctic Ocean Productivitat primària (Biologia) Productividad primaria (Biología) Primary productivity (Biology) Plàncton Plancton Plankton Diòxid de carboni Dióxido de carbono Carbon dioxide Algues marines Algas marinas Marine algae Ciències Experimentals i Matemàtiques 502 |
| Sumario: | Climate change, caused by anthropogenic emissions of carbon dioxide (CO2) and other greenhouse gasses into the atmosphere, is producing profound impacts on ecosystems. The Arctic Ocean is one of the most vulnerable regions of the world and is experiencing the most substantial effects of climate change. This region is characterized by strong seasonality with highly productive episodes, called phytoplankton blooms, that together with the entrance of ice-melt, reduce the CO2 concentration in seawater (from about 370 to 130 μatm). During spring and summer, the low CO2 concentrations might limit the photosynthesis of marine plants and algae. However, during these periods the increase of atmospheric and oceanic CO2 may stimulate the primary productivity in the Arctic Ocean. Increased atmospheric CO2 is directly related with Arctic warming and the consequent acceleration of glaciers and sea-ice melting. During spring and summer, the ice cover retreat increases the light irradiance in submersed areas and ice-free areas become more frequent. An increase of ice-free waters may probably favour the expansion of marine vegetation into the Arctic and the migration of subarctic species to northern regions, characterized by long day length in summer. Since pelagic and benthic ecosystems contribute largely to the primary productivity of the Arctic Ocean, in this thesis I investigate the experimental effects of two abiotic factors: increased CO2 and long day length. These effects have been tested on planktonic communities in surface waters and benthic macrophytes in subarctic and Arctic ecosystems. In parallel, I investigate the relationship between planktonic primary production rates estimated with three different methods: the O2 mass balance, the 18O method and the 14C method. This comparison of methods has been carried out for the first time in the Arctic Ocean, specifically in the north and northwest of the Svalbard shelf, and we conclude that the 14C method, with incubations of 24 h, underestimate the gross primary productivity measured with the O2-based methods, although the relationships change seasonally. In spring, the O2-based methods are the most appropriate methods to estimate the gross primary productivity while in summer both C and O2-based method are adequate. Therefore, the O2-based methods were applied to investigate the possible limitation of CO2 in planktonic communities in two regions of the Arctic Ocean. With this aim, we carried out experiments of CO2 additions in spring and summer in the west and northwest of the Svalbard shelf and observed that the stimulation was restricted to highly productive episodes, when CO2 concentrations were already low and nutrients concentrations were low but still present in seawater. To determine the periods of CO2 limitation, I carried out weekly experiments of increased CO2 during the development of a phytoplankton bloom, from March to late May in 2016 in Godthåbsfjord, southwestern of Greenland. We observed that during approximately two weeks after the bloom reached its maximum production, called the peak bloom stage, the phytoplankton community was limited by the low CO2 concentrations. During this window of time the net primary production rates increased with increasing CO2 concentrations in presence of dissolved inorganic nutrients. Additionally, we experimentally evaluated the effects of long day length, characteristic of Arctic summers, and the effect of increased CO2. on three subarctic macrophytes species: Ascophyllum nodosum, Fucus vesiculosus and Zostera marina. We observed that their photosynthetic activity, measured as the electron transport rate, were highest at long day length. Increased CO2 also had a positive, though non-significant effect on the macroalgae species A. nodosum and on the seagrass Z. marina. Therefore, these species will benefit from increased day length as they expand in the Arctic and migrate poleward with decreasing ice cover. The results of the present thesis suggest that present and future increases of CO2 concentrations are likely to enhance the contribution of the spring bloom to the annual primary production budget in Arctic and subarctic waters. Moreover, long day length will benefit the expansion and poleward migration of the subarctic species investigated. In this thesis, I present experimental evidence of the effects of climate change in pelagic and benthic ecosystems in two regions of the Arctic Ocean, contributing to the field of climate change ecology in the marine environment. Besides, the comparative study of primary production methodologies contributes to the field of Arctic oceanography by which aids in developing further investigation and expectations conducive to forming conclusions on how climate change will affect the Arctic Ocean in the future. |
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