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Submarine groundwater discharge revealed by 228Ra distribution in the upper Atlantic Ocean (2008)

Moore, Willard S. ; Sarmiento, Jorge L. ; Key, Robert M.

Springer Nature

In: Nature Geoscience. 2008; 1(5): 309-311. Published 2008 Apr 20. doi: 10.1038/ngeo183.

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Publikationsdatum: 2008-04-20

Beschreibung: Submarine groundwater discharge is defined as any flow of water at continental margins from the seabed to the coastal ocean, regardless of fluid composition or driving force. The flux of submarine groundwater discharge has been hypothesized to be a pathway for enriching coastal waters in nutrients, carbon and metals. Here, we estimate the submarine groundwater flux from the inventory of 228Ra in the upper Atlantic Ocean, obtained by interpolating measurements at over 150 stations. Only 46% of the loss in 228Ra from radioactive decay is replenished by input from dust, rivers and coastal sediments. We infer that the remainder must come from submarine groundwater discharge. Using estimates of 228Ra concentrations in submarine groundwater discharge, we arrive at a total flux from submarine groundwater discharge of 2-4×1013 m 3yr1, between 80 and 160 of the amount of freshwater entering the Atlantic Ocean from rivers. Submarine groundwater discharge is not a freshwater flux, but a flux of terrestrial and sea water that has penetrated permeable coastal sediments. Our assessment of the volume of submarine groundwater discharge confirms that this flux represents an important vehicle for the delivery of nutrients, carbon and metal to the ocean. © 2008 Nature Publishing Group.

Print ISSN: 1752-0894

Digitale ISSN: 1752-0908

Thema: Geologie und Paläontologie

Publiziert von Springer Nature

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Trends in the sources and sinks of carbon dioxide (2009)

Le Quéré, Corinne ; Raupach, Michael R. ; Canadell, Josep G. ; [weitere]

Springer Nature

In: Nature Geoscience. 2009; 2(12): 831-836. Published 2009 Nov 17. doi: 10.1038/ngeo689.

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Publikationsdatum: 2009-11-17

Beschreibung: Efforts to control climate change require the stabilization of atmospheric CO 2 concentrations. This can only be achieved through a drastic reduction of global CO 2 emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008, in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly constant. Between 1959 and 2008, 43% of each year's CO 2 emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO 2 emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO 2 by the carbon sinks in response to climate change and variability. Changes in the CO 2 sinks are highly uncertain, but they could have a significant influence on future atmospheric CO 2 levels. It is therefore crucial to reduce the uncertainties. © 2009 Macmillan Publishers Limited. All rights reserved.

Print ISSN: 1752-0894

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Thema: Geologie und Paläontologie

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The impact of remineralization depth on the air–sea carbon balance (2009)

Kwon, Eun Young ; Primeau, François ; Sarmiento, Jorge L.

Springer Nature

In: Nature Geoscience. 2009; 2(9): 630-635. Published 2009 Aug 30. doi: 10.1038/ngeo612.

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Publikationsdatum: 2009-08-30

Beschreibung: As particulate organic carbon rains down from the surface ocean it is respired back to carbon dioxide and released into the oceans interior. The depth at which this sinking carbon is converted back to carbon dioxideknown as the remineralization depthdepends on the balance between particle sinking speeds and their rate of decay. A host of climate-sensitive factors can affect this balance, including temperature, oxygen concentration, stratification, community composition and the mineral content of the sinking particles. Here we use a three-dimensional global ocean biogeochemistry model to show that a modest change in remineralization depth can have a substantial impact on atmospheric carbon dioxide concentrations. For example, when the depth at which 63% of sinking carbon is respired increases by 24 m globally, atmospheric carbon dioxide concentrations fall by 10-27 ppm. This reduction in atmospheric carbon dioxide concentration results from the redistribution of remineralized carbon from intermediate waters to bottom waters. As a consequence of the reduced concentration of respired carbon in upper ocean waters, atmospheric carbon dioxide is preferentially stored in newly formed North Atlantic Deep Water. We suggest that atmospheric carbon dioxide concentrations are highly sensitive to the potential changes in remineralization depth that may be caused by climate change. © 2009 Macmillan Publishers Limited. All rights reserved.

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Thema: Geologie und Paläontologie

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Annual boom–bust cycles of polar phytoplankton biomass revealed by space-based lidar (2016)

Behrenfeld, Michael J. ; Hu, Yongxiang ; O’Malley, Robert T. ; [weitere]

Springer Nature

In: Nature Geoscience. 2016; 10(2): 118-122. Published 2016 Dec 19. doi: 10.1038/ngeo2861.

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Publikationsdatum: 2016-12-19

Beschreibung: Polar plankton communities are among the most productive, seasonally dynamic and rapidly changing ecosystems in the global ocean. However, persistent cloud cover, periods of constant night and prevailing low solar elevations in polar regions severely limit traditional passive satellite ocean colour measurements and leave vast areas unobserved for many consecutive months each year. Consequently, our understanding of the annual cycles of polar plankton and their interannual variations is incomplete. Here we use space-borne lidar observations to overcome the limitations of historical passive sensors and report a decade of uninterrupted polar phytoplankton biomass cycles. We find that polar phytoplankton dynamics are categorized by â € boom-bust' cycles resulting from slight imbalances in plankton predator-prey equilibria. The observed seasonal-to-interannual variations in biomass are predicted by mathematically modelled rates of change in phytoplankton division. Furthermore, we find that changes in ice cover dominated variability in Antarctic phytoplankton stocks over the past decade, whereas ecological processes were the predominant drivers of change in the Arctic. We conclude that subtle and environmentally driven imbalances in polar food webs underlie annual phytoplankton boom-bust cycles, which vary interannually at each pole. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

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Thema: Geologie und Paläontologie

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