The following highlights summarize research papers that have recently been published in Geophysical Research Letters (GRL).
In this release:
- Lack of arches doubled Arctic strait’s sea-ice loss
- Solar wind pulses help blow away Martian atmosphere
- Patterns of colored organic matter reveal ocean features
- Accurately estimating climate feedbacks
- Ocean acidification: Simply predicting key depths
- Deep-ocean billows observed
1. Lack of arches doubled Arctic strait’s sea-ice loss
In most years during the winter, “arches” of ice form across the Nares Strait, a narrow channel between Greenland and Ellesmere Island. These arches block the flow of sea ice, keeping ice contained in the Arctic Ocean. But in 2007, no such arches formed. Kwok et al. use satellite images to determine how much ice had flowed out of the Arctic Ocean through the Nares Strait in each year from 1997 to 2009. The authors find that the volume of ice lost in 2007 was more than twice the average ice loss during those 13 years. Furthermore, although the Nares Strait is quite narrow, ice flowing through it in 2007 accounted for a significant percentage of the total Arctic ice lost — the 2007 ice flow through the Nares Strait was about 10 percent of the average annual ice flow through the much wider Fram Strait. The ice flow in 2007 depleted the thick ice that had built up in the Arctic over multiple years. This multiyear ice could take years to replace, affecting summer ice cover for years. The study shows that ice arches are an important factor in controlling Arctic ice outflow through the Nares Strait. The authors note that as the climate warms, arches could stop forming, leading to increased loss of Arctic sea ice.
Title:
Large sea ice outflow into the Nares Strait in 2007
Authors:
R. Kwok and S. S. Pang: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
L. Toudal Pedersen: Danish Meteorological Institute, Copenhagen, Denmark;
P. Gudmandsen: Danish National Space Center, Technical University of Denmark, Lynby, Denmark.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041872, 2010
http://dx.doi.org/10.1029/2009GL041872
2. Solar wind pulses help blow away Martian atmosphere
Mars is constantly losing parts of its atmosphere to space. The processes driving that loss of atmosphere are not completely understood. A new study shows that pressure from solar wind pulses is a significant contributor to Mars’s atmospheric escape. Edberg et al. analyze solar wind data and satellite observations that track the flux of heavy ions leaving Mars’s atmosphere. The authors find that Mars’s atmosphere does not drift away at a steady pace; instead, atmospheric escape occurs in bursts. The researchers relate those bursts of atmospheric loss to solar events known as corotating interaction regions (CIRs). CIRs form when regions of fast solar wind encounter slower solar wind, creating a high-pressure pulse. When these CIR pulses pass by Mars, they can drive away particles from Mars’s atmosphere. The authors find that during times when these CIRs occurred, the outflow of atmospheric particles from Mars was about 2.5 times the outflow when these events were not occurring. Furthermore, about one third of the material lost from Mars into space is lost during CIRs. The study should help scientists better understand the evolution of Mars’s atmosphere.
Title:
Pumping out the atmosphere of Mars through solar wind pressure pulses
Authors:
N. J. T. Edberg: Department of Physics and Astronomy, University of Leicester, Leicester, UK and Swedish Institute of Space Physics, Uppsala, Sweden;
H. Nilsson, S. Barabash and Y. Futaana: Swedish Institute of Space Physics, Kiruna, Sweden;
A. O. Williams, M. Lester, S. E. Milan, and S. W. H. Cowley: Department of Physics and Astronomy, University of Leicester, Leicester, UK;
M. Fränz: Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041814, 2010
http://dx.doi.org/10.1029/2009GL041814
3. Patterns of colored organic matter reveal ocean features
Chromophoric dissolved organic matter (CDOM) is dissolved organic material in the oceans that is optically measurable. It affects the color of the ocean, light penetration, photochemical reactions, and biological activity in the oceans. Nelson et al. make the first large-scale observations of the distribution and dynamics of CDOM in three major ocean basins. The authors find that field observations of CDOM in the surface are consistent with satellite observations of CDOM. They also consider the sources and sinks of CDOM and the ways in which ocean circulation affects the distribution of CDOM, which is produced by decaying organisms in the ocean, transported by ocean circulation, and bleached by the Sun. In addition, the researchers relate CDOM to apparent oxygen utilization, a measure of biological activity. They find that CDOM distributions are strongly related to apparent oxygen distributions in the Pacific and Indian oceans, though not in the Atlantic. They explain this through a variety of factors relating to circulation and CDOM production. Overall, the authors determine that CDOM, which can be measured through satellite observations, is a useful tracer of changes in biogeochemistry and ocean circulation.
Title:
Tracing global biogeochemical cycles and meridional overturning circulation using chromophoric dissolved organic matter
Authors:
Norman B. Nelson and Chantal M. Swan: Institute for Computational Earth System Science, University of California, Santa Barbara, California, USA;
David A. Siegel: Institute for Computational Earth System Science, University of California, Santa Barbara, California, USA, also at Department of Geography, University of California, Santa Barbara, California, USA;
Craig A. Carlson: Institute for Computational Earth System Science, University of California, Santa Barbara, California, USA, also at Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California, USA.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL042325, 2010
http://dx.doi.org/10.1029/2009GL042325
4. Accurately estimating climate feedbacks
As scientists and policy makers consider global climate change, it is important to accurately determine climate feedbacks and the amount by which the Earth’s surface temperature would change in response to an external forcing (such as by increasing atmospheric carbon dioxide levels). One approach is to estimate the feedbacks from sea surface temperature data and measurements of radiation at the top of the atmosphere. The success of such an approach depends on the details of methods used. Trenberth et al. analyze the methods of one recent study that used data from tropical regions to estimate climate feedbacks. The authors find that the previous study’s method both was defective and did not account for some important factors, such as the eruption of Mount Pinatubo in 1991. Furthermore, the researchers find that climate feedback analysis needs to include changes in ocean heat storage and atmospheric energy transport into and out of the tropics; the use of a limited tropical domain in analyzing climate feedbacks will lead to incorrect results. The authors conclude that although the tropics are important in climate feedbacks, studies that include only the tropics can be misleading.
Title:
Relationships between tropical sea surface temperature and top-of-atmosphere radiation
Authors:
Kevin E. Trenberth and John T. Fasullo: National Center for Atmospheric Research, Boulder, Colorado, USA
Chris O’Dell: Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA;
Takmeng Wong: NASA Langley Research Center, Hampton, Virginia, USA.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL042314, 2010
http://dx.doi.org/10.1029/2009GL042314
5. Ocean acidification: Simply predicting key depths
The buildup of carbon dioxide in the atmosphere is making seawater more acidic, which over time will have profound effects on marine biota and cycling of elements. Over the next few thousand years, this acidification will be counteracted by dissolving calcium carbonate shells of dead organisms in sediments of the deep sea, a process known as carbonate compensation.
Two factors, the carbonate saturation depth and the carbonate compensation depth, are used in studying carbonate dynamics. The carbonate saturation depth is the depth below which the oceans become undersaturated with respect to calcium carbonate. Above this depth, water is saturated with carbonate ions, and calcifying organisms can form and retain calcium carbonate shells. Below this depth, calcium carbonate shells arriving at the sediment surface will dissolve. However, calcium carbonates may be produced or accumulate more rapidly than they dissolve, so some calcium carbonates can remain in sediments below the saturation depth. The carbonate compensation depth is the depth at which calcium carbonates are dissolving at the same rate that they are accumulating; that is, below this depth, calcium carbonates are no longer found in sediments.
Previous methods of predicting carbonate saturation and carbonate compensation depths relied on complex models that were difficult to solve. Boudreau et al. develop a simple formula to predict these depths. The authors use the formula to show that the distance between the two depths is not fixed but depends on carbonate ion concentration, input of calcite, and the dissolution rate. They note that ocean acidification, which increases with rising atmospheric CO2 levels, increases the distance between the two depths.
Title:
Carbonate compensation dynamics
Authors:
Bernard P. Boudreau: Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada;
Jack J. Middelburg: Centre for Estuarine and Marine Ecology, NIOO-KNAW, Yerseke, Netherlands and Geochemistry, Faculty of Geosciences, University of Utrecht, Utrecht, Netherlands;
Filip J. R. Meysman: Centre for Estuarine and Marine Ecology, NIOO-KNAW, Yerseke, Netherlands and Department of Analytical and Environmental Chemistry, Vrije Universiteit,
Brussels, Belgium.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041847, 2010
http://dx.doi.org/10.1029/2009GL041847
6. Deep-ocean billows observed
Ocean wave mixing in the deep ocean is important to ocean circulation, but detailed observations are rare of turbulent mixing at the ocean floor. To take a more detailed look at deep-ocean wave patterns, van Haren and Gostiaux design moored temperature sensors to observe overturning above the sloping side of the Great Meteor seamount, an underwater tablemount in the Canary basin. The authors observe a turbulent mixing pattern with puffy, billowing structures called a Kelvin-Helmholtz billow train. Kelvin-Helmholtz instabilities have been previously observed in the laboratory, in the atmosphere, and near the surface of the ocean; this is the first reported detailed observation of these structures in the deep ocean. The researchers observe patterns with as many as 10 billows forming a train. The observations show how internal ocean waves break above the slopes of the ocean bottom, creating turbulent mixing in the deep ocean. The authors note that this kind of turbulent mixing is important in stirring up sediments and returning nutrients to the water column and could be significant for ocean circulation.
Title:
A deep-ocean Kelvin-Helmholtz billow train
Authors:
Hans van Haren: Royal Netherlands Institute for Sea Research, Den Burg, Netherlands;
Louis Gostiaux: Coriolis, Laboratoire des Ecoulements Geophysiques et Industriels (LEGI), CNRS, Université de Grenoble, France.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041890, 2010
http://dx.doi.org/10.1029/2009GL041890
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