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Title Vertical nitrate fluxes in the Arctic Ocean
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Publication Date
Degree Level doctoral
University/Publisher Universitetet i Tromsø
Abstract Upward mixing of remineralized nutrients is essential for photosynthesis in the upper ocean. Weak vertical mixing, which restricts nutrient supply, and sea ice, which leads to low light levels, conspire to severely inhibit marine primary productivity in the Arctic Ocean. However, little has been known about their relative contributions. No large-scale quantitative estimates of the vertical nutrient supply had previously been presented, which has impeded an understanding of its role in shaping the ecology and carbon cycle of the Arctic Ocean. In order to estimate the vertical flux of nitrate into the surface layer in contrasting hydrographic and dynamic regimes, profiles of turbulent microstructure and nitrate concentrations were measured as part of a number of cruises and ice camps in the area extending from eastern Fram Strait into the Nansen Basin. These have been supplemented with obervations of the seasonal nutrient cycle at a mooring in the same area, and a reanalysis of available data on nitrate concentrations and turbulent mixing in other parts of the central Arctic Ocean. Hydrography was found to be the biggest driver of variability in nitrate fluxes. Strong stratification, wherever encountered, restricted nitrate supply, often in concert with concurrently weak turbulent mixing, both in the seasonal nitracline (0.3–0.7 mmol N m-2 d-1) and the deep basin (0.01–0.2 mmol N m-2 d-1). Thus deep winter mixing supplies the bulk of the nitrate pool on the relatively productive shelves (e.g. 2.5 mmol N m-2 d-1 in the inflow of Atlantic Water during winter), but in the strongly stratified Canadian Basin, fluxes are low year-round (on the order of 0.01 mmol N m-2 d-1) and place a tight limit on new production. Only the weakly stratified Atlantic derived water in the Nansen Basin close to Fram Strait seems to have a certain potential to support future increases in new production under a seasonal ice cover.
Subjects/Keywords VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452; VDP::Matematikk og Naturvitenskap: 400::Geofag: 450::Oseanografi: 452; VDP::Mathematics and natural science: 400::Zoology and botany: 480::Marine biology: 497; VDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Marinbiologi: 497
Contributors Reigstad, Marit (advisor)
Language en
Country of Publication no
Record ID handle:10037/10948
Repository tromso
Date Indexed 2019-10-07
Issued Date 2017-03-16 00:00:00

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…framework 4 Perspectives ———————————————————— 19 Vertical nitrate fluxes as a framework for studying primary production — The future of Arctic marine primary production — Outlook Thanks ————————————————————————— 24 Bibliography…

…27 iii 1 Introduction and Background 1.1 Vertical fluxes and primary production The growth of marine phytoplankton is confined to the uppermost layer of the ocean called the euphotic zone. Organic matter has a tendency to sink and thus exports…

…which represents the oceanic buffering capacity of atmospheric levels of carbon dioxide. The present and future of the nutrient supply to the photic zone in the world ocean has also received considerable attention regarding the future of marine

…ecosystems, since changes in the nutrient loading will have the ability to drive marked changes in the marine community structure (e.g. Li et al., 2009; Peter and Sommer, 2013; Sommer et al., 2016). The upward flux can be both advective (like…

…primary production because organic matter is often found to follow a fixed stoichiometry, the so-called “Redfield ratio” (see the seminal paper by Redfield et al., 1963). While the importance of the vertical nitrate flux for Arctic marine ecology…

…in the seasonally stratified upper Arctic Ocean will be of particular importance to understand the physical environment in which marine primary producers grow. Along the way, I describe both large-scale patterns and the seasonal distribution of NO− 3…

…time and space (e.g. Mackas et al., 1985; Abbott, 1993). However, general circulationbiogeochemical coupled models fundamentally disagree about the future of Arctic marine primary production, largely due to different representations of…

…temperature, salinity, mortality, grazing, and heterotrophic respiration, that sets the community structure of marine ecosystems. 4.2 The future of Arctic marine primary production The work presented in this thesis demonstrates a clear need to distinguish…

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