Volume 5 Issue 8, August 2012

The southeastern US coastline is under threat as land subsides and sea level rises. Measurements of the 2011 Mississippi River flood suggest that the river carries enough sandy sediment to offset some of this coastal drowning.

Earth's magnetic field is characterized by a puzzling hemispheric asymmetry. Calculations of core dynamo processes suggest that lopsided growth of the planet's inner core may be part of the cause.

Enigmatically, some landslides flow farther than normal frictional resistance allows. Cassini images of Saturn's icy moon Iapetus reveal a multitude of long-runout landslides that may have been enabled by flash heating along the sliding surface.

The geomagnetic field varies on a wide range of timescales. A review of emerging research suggests that field variations on the order of tens of millions of years may be linked to changes in heat flow across the core–mantle boundary.

The Bonnet Carré Spillway diverts floodwaters from the Mississippi River to Lake Pontchartrain, and was opened for 42 days during the 2011 flood. According to measurements of the newly deposited sediments, at least 31–46% of the river’s sand load was diverted into the spillway at this time, suggesting that such diversions can help mitigate coastal wetland loss.

In marine and freshwater ecosystems, anaerobic ammonium oxidation is coupled to nitrite reduction, and accounts for a significant fraction of ecosystem nitrogen loss. Laboratory incubations suggest that ammonium oxidation coupled to iron reduction contributes to nitrogen loss in anaerobic slurries of tropical forest soils.

The exchange of water between subtropical North Atlantic Deep Water and the Antarctic Circumpolar Current is important, but poorly constrained. A subsurface acoustic image taken in the confluence region shows a prominent swirling structure, 500 m high and 10 km wide, that could be either a thermohaline intrusion or a localized and intermittent overturning event.

Biologically available nitrogen limits phytoplankton growth over much of the ocean. Data-constrained model simulations suggest that bioavailable nitrogen losses match gains in the global ocean, indicative of a balanced budget.

The severity and incidence of climatic extremes, including drought, have increased as a result of climate warming. Analyses of observational and reanalysis data suggest that the strength of the western North American carbon sink declined by 30–298 Tg carbon per year during the drought at the turn of the century.

Global warmth 20–15 million years ago allowed vegetation to grow on formerly ice-covered areas of Antarctica. Leaf wax and pollen data show that this growth was supported by increased hydrologic activity over the Antarctic coast, derived from a local moisture source.

Volcanic eruptions can inject hazardous ash clouds into the atmosphere. Numerical simulations and experiments on volcanic rock samples show that clasts initially formed deep in the volcanic conduit break-up during collisions in the conduit, thus generating fine-grained clouds of ash.

The axis of the geomagnetic field is offset eastwards from Earth’s centre by more than 500 km. Simulations of Earth’s geomagnetic field using a numerical dynamo model show that lopsided growth of the inner core, with faster solidification occurring in one hemisphere, could cause the offset.

The mantle and continental crust contain excessive amounts of radiogenic lead, implying that a complementary reservoir of unradiogenic lead should exist somewhere on Earth. Isotopic analyses of mantle rocks exposed on the Atlantic Ocean floor reveal that sulphide inclusions can have extremely unradiogenic lead compositions, suggesting that the reservoir could exist within the mantle itself.

The great distance travelled by long-runout landslides, observed previously on the Earth and Mars, requires a mechanism of friction reduction. Identification and analysis of long-runout landslides on Saturn’s moon Iapetus suggests that the Iapetian landslides are enabled by flash heating of the icy sliding surface.

The Southern Ocean makes a substantial contribution to the oceanic carbon sink. Observationally based estimates of carbon subduction suggest that carbon sequestration depends on physical properties, such as mixed layer depth, ocean currents, wind and eddies, that are potentially sensitive to climate variability and change.