AGU journal highlights — March 7

1. California rapidly depleting Central Valley groundwater

Groundwater is being depleted in California’s Central Valley at a rapid rate, according to data from the Gravity Recovery and Climate Experiment (GRACE) satellite. Famiglietti et al. analyze 78 months of GRACE data covering October 2003 to March 2010 to estimate water storage changes in California’s Sacramento and San Joaquin River basins. They find that the basins are losing water at a rate of about 30 millimeters (1.2 inches) per year equivalent water height, or a total of about 30 cubic kilometers (7.2 cubic miles) over the 78-month period. Furthermore, they find that two thirds of this loss, or a total of 20 cubic km (4.8 cubic mi) for the study period, came from groundwater depletion in the Central Valley. Quantifying groundwater depletion can be challenging in many areas because of a lack of monitoring infrastructure and reporting requirements; the study shows that satellite-based monitoring can be a useful way to track groundwater volumes. The authors warn that the current rate of groundwater depletion in the Central Valley may be unsustainable and could have “potentially dire consequences for the economic and food security of the United States.”

Geophysical Research Letters, doi:10.1029/2010GL046442, 2011


Satellites measure recent rates of groundwater depletion in California’s Central Valley

J. S. Famiglietti and M. Lo: UC Center for Hydrologic Modeling, University of California, Irvine, California, USA; and Department of Earth System Science, University of California, Irvine, California, USA;

S. L. Ho: Department of Earth System Science, University of California,
Irvine, California, USA; and Marine Environmental Biology, Department of Biological Sciences, University of Southern California, Los Angeles, California, USA;

J. Bethune: Department of Geology, Carleton College, Northfield, Minnesota, USA;

K. J. Anderson: Department of Earth System Science, University of California, Irvine, California, USA;

T. H. Syed: Department of Earth System Science, University of California,
Irvine, California, USA; and Department of Applied Geology, Indian School of Mines, Dhanbad, India;

S. C. Swenson: Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA;

C. R. de Linage: Department of Earth System Science, University of California,
Irvine, California, USA;

M. Rodell: Hydrological Sciences Branch, NASA Goddard Space Flight Center,
Greenbelt, Maryland, USA.

2. Corals expand poleward as seas warm

Corals are important organisms for ecosystems and are sensitive indicators of the effects of climate warming. While corals are bleaching and dying in tropical areas due to climate warming, in temperate areas they are expanding their range poleward as water temperatures increase, a new study shows. Yamano et al. use 80 years of records to study the range of corals around Japan. Sea surface temperatures have risen in these temperate areas during that time. They find that four of the nine species of coral they studied expanded their range northward since the 1930s, while none had its range shrink southward. The corals expanded northward as quickly as 14 kilometers (8.7 miles) per year. The study suggests that rapid modifications of temperate coastal ecosystems could be taking place.

Geophysical Research Letters, doi:10.1029/2010GL046474, 2011


Rapid poleward range expansion of tropical reef corals in response to rising sea surface temperatures

Hiroya Yamano and Kaoru Sugihara: Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan;

Keiichi Nomura: Kushimoto Marine Park Center, Kushimoto, Japan.

3. Sediments suggest El Niño variability persists with warming

There has been some debate as to whether global warming could lead to a permanent El Niño state rather than a periodically varying El Niño — Southern Oscillation (ENSO), which occurs now. It has also been suggested that ice-free Arctic summers could affect high-latitude and midlatitude circulation patterns and climate variability.

Now sediment records from the Arctic suggest that even as climate warms, the variability of ENSO will continue. Davies et al. analyze the first annually resolved sediment core spanning 1000 years about 70 million years ago during the Late Cretaceous.

The Cretaceous was significantly warmer than present conditions, and the Arctic Ocean was free of ice in the summer. The warmer state during the Cretaceous could be similar to what Earth might look like in the coming decades if climate continues to warm. The sediment record indicates that the ENSO oscillation did occur during that time period, adding to evidence that ENSO is a robust phenomenon likely to continue even as climate warms.

Geophysical Research Letters, doi:10.1029/2010GL046151, 2011


Tropical ocean-atmosphere controls on inter-annual climate variability in the Cretaceous Arctic

Andrew Davies: National Oceanography Centre Southampton, School of Ocean and Earth Science, University of Southampton, Southampton, UK; Now at Neftex Petroleum Consultants Ltd., Abingdon, UK;

Alan E. S. Kemp and Heiko Pälike: National Oceanography Centre Southampton, School of Ocean and Earth Science, University of Southampton, Southampton, UK.

4. Assessing coral reef health

Coral reefs around the world are becoming stressed due to rising temperatures, ocean acidification, overfishing, and other factors. Measuring community level rates of photosynthesis, respiration, and biogenic calcification is essential to assessing the health of coral reef ecosystems, because the balance between these processes determines the potential for reef growth and the export of carbon. Measurements of biological productivity have typically been made by tracing changes in dissolved oxygen in seawater as it passes over a reef. However, this is a labor-intensive and difficult method, requiring repeated measurements.

McGillis et al. study the use of two in situ methods of monitoring productivity on Cayo Enrique Reef, Puerto Rico, in March 2009. They compare a technique that measures changes in dissolved oxygen using a chamber that encloses an area of water above the reef with a technique for measuring the flux of dissolved oxygen in the benthic boundary layer at the seafloor. They show that the boundary layer technique agrees well with the enclosure technique. Both methods can make measurements with high spatial and temporal resolution. The boundary layer technique can be used to monitor metabolic activity of reefs in remote locations, at any depth, and over long time periods. It could also be used for any property for which a gradient can be measured by in situ sensing or discrete sampling. The enclosure method can be used for in situ environmental perturbation experiments. A combination of these methods could be a valuable tool for assessing and studying the effects of climate change on coral reef health.

Geophysical Research Letters, doi:10.1029/2010GL046179, 2011


Productivity of a coral reef using boundary layer and enclosure methods

W. R. McGillis: Lamont Doherty Earth Observatory, Earth Institute at Columbia University, Palisades, New York, USA;

C. Langdon: Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA;

B. Loose: Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA;

K. K. Yates: U.S. Geological Survey, St. Petersburg, Florida, USA;

Jorge Corredor: Department of Marine Sciences, University of Puerto Rico, Mayaguez, Puerto Rico.

5. New way to forecast hurricane surge

In recent years, hurricanes in the Gulf of Mexico, including Katrina and Ike, caused some of the highest surges on record and significant flooding, highlighting the need for good surge forecasts that can be used for early warning and evacuation. However, current approaches for surge forecasting use models that take too much computational time or that have spatial resolution too low to provide adequate forecast accuracy.

Irish et al. propose a new method for determining probabilistic maximum hurricane surge forecasts. Their approach is based on calculations of surge response functions, which are derived from numerical simulations, along with analysis of meteorological forecasts. They apply the method to data from Hurricane Ike and find that they can accurately compute surge forecast probabilities within seconds, given publicly available meteorological forecast data. The method can provide a forecast of how surge would vary along the coast and identify areas most vulnerable to high surges.

Geophysical Research Letters, doi:10.1029/2010GL046347, 2011


Probabilistic hurricane surge forecasting using parameterized surge response functions

Jennifer L. Irish, Youn Kyung Song, and Kuang-An Chang: Zachry Department of Civil Engineering, Texas A&M University, College Station, Texas, USA.

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