Traderboersenboard - Einzelnen Beitrag anzeigen

Benjamin · 06-06-2009, 21:47

Ocean stagnation and end-Permian anoxia
Manuscript received May 1, 2000

Roberta M. Hotinski* Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Karen L. Bice Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
02543, USA
Lee R. Kump Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Raymond G. Najjar Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania 16802, USA
Michael A. Arthur Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA

ABSTRACT
Ocean stagnation has been invoked to explain the widespread
occurrence of organic-carbon–rich, laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end-Permian mass extinction. However, to a first approximation, stagnation would severely reduce the upwelling supply of nutrients to the photic zone, reducing productivity. Moreover, it is not obvious that ocean stagnation can be achieved. Numerical experiments performed with a three-dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the Late Permian ocean. We find that polar warming and tropical cooling of sea-surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization. Buildup of quantities of H2S and CO2 in the Late Permian ocean sufficient to directly cause a mass extinction, however, would have required large increases in the oceanic nutrient inventory.

Keywords: Permian, anoxia, ocean circulation, phosphate cycle, oxygen cycle.
http://www.whoi.edu/science/GG/peopl..._etal_2001.pdf
############################

Anoxic event
From Wikipedia, the free encyclopedia
Jump to: navigation, search

As early as 1911, major oceanic currents were well mapped and understood, albeit without today's understanding of how they affect regional and global climatological conditions.
This world perspective on oceanic currents demonstrates the interdependencies of transnational regions on circulating currents.Oceanic anoxic events or anoxic events occur when the Earth's oceans become completely depleted of oxygen (O2) below the surface levels. Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events may have caused mass extinctions. ....

OAE = oceanic anoxic event

... Here is another way of looking at oceanic anoxic events. Assume that the earth releases a huge volume of carbon dioxide during an interval of excessive volcanism; global temperatures rise due to the greenhouse effect; global weathering rates and fluvial (Deutsch: Fluss-) nutrient flux increase; organic productivity in the oceans increases; organic-carbon burial in the oceans increases (OAE begins); carbon dioxide is drawn down (inverse greenhouse effect); global temperatures fall, and the ocean–atmosphere system returns to equilibrium (OAE ends).

In this way, an oceanic anoxic event can be viewed as the Earth’s response to the injection of excess carbon dioxide into the atmosphere and hydrosphere. ...

http://en.wikipedia.org/wiki/Anoxic_event
##################################

Anoxic waters
When oxygen is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water is nitrate. Denitrification occurs, and the nitrate will be consumed rather rapidly. After reducing some other minor elements, the bacteria will turn to reducing sulfate.

06-06-2009, 21:47	#9
Benjamin TBB Family Registriert seit: Mar 2004 Beiträge: 10.374	Ocean stagnation and end-Permian anoxia Manuscript received May 1, 2000 Roberta M. Hotinski* Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Karen L. Bice Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Lee R. Kump Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Raymond G. Najjar Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania 16802, USA Michael A. Arthur Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA ABSTRACT Ocean stagnation has been invoked to explain the widespread occurrence of organic-carbon–rich, laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end-Permian mass extinction. However, to a first approximation, stagnation would severely reduce the upwelling supply of nutrients to the photic zone, reducing productivity. Moreover, it is not obvious that ocean stagnation can be achieved. Numerical experiments performed with a three-dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the Late Permian ocean. We find that polar warming and tropical cooling of sea-surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization. Buildup of quantities of H2S and CO2 in the Late Permian ocean sufficient to directly cause a mass extinction, however, would have required large increases in the oceanic nutrient inventory. Keywords: Permian, anoxia, ocean circulation, phosphate cycle, oxygen cycle. http://www.whoi.edu/science/GG/peopl..._etal_2001.pdf ############################ Anoxic event From Wikipedia, the free encyclopedia Jump to: navigation, search As early as 1911, major oceanic currents were well mapped and understood, albeit without today's understanding of how they affect regional and global climatological conditions. This world perspective on oceanic currents demonstrates the interdependencies of transnational regions on circulating currents.Oceanic anoxic events or anoxic events occur when the Earth's oceans become completely depleted of oxygen (O2) below the surface levels. Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events may have caused mass extinctions. .... OAE = oceanic anoxic event ... Here is another way of looking at oceanic anoxic events. Assume that the earth releases a huge volume of carbon dioxide during an interval of excessive volcanism; global temperatures rise due to the greenhouse effect; global weathering rates and fluvial (Deutsch: Fluss-) nutrient flux increase; organic productivity in the oceans increases; organic-carbon burial in the oceans increases (OAE begins); carbon dioxide is drawn down (inverse greenhouse effect); global temperatures fall, and the ocean–atmosphere system returns to equilibrium (OAE ends). In this way, an oceanic anoxic event can be viewed as the Earth’s response to the injection of excess carbon dioxide into the atmosphere and hydrosphere. ... http://en.wikipedia.org/wiki/Anoxic_event ################################## Anoxic waters When oxygen is depleted in a basin, bacteria first turn to the second-best electron acceptor, which in sea water is nitrate. Denitrification occurs, and the nitrate will be consumed rather rapidly. After reducing some other minor elements, the bacteria will turn to reducing sulfate.