Letters in 2012

In spring 2011, a record-breaking flood necessitated diversion of water from the lower Mississippi River to the Atchafalaya River Basin. A comparison between the dynamics in the two basins based on field-calibrated satellite observations and in situ data suggests that river-mouth dynamics and wetland sedimentation are directly linked.

Earthquake rupture is influenced by stress conditions in the crust before the quake. Analysis and modelling of surface deformation caused by the May 2011 earthquake in Lorca, Spain, indicate that groundwater extraction influenced the pattern of fault rupture.

Over the past decade, Kīlauea and Mauna Loa—adjacent volcanoes in Hawai‘i—have inflated and deflated in tandem, yet their shallow volcanic plumbing systems are separate. Numerical modelling of the volcanoes shows that dynamic stress transfer by asthenospheric pore pressure is a viable mechanism for volcano coupling in Hawai‘i.

Marine ice streams whose beds deepen inland are thought to be inherently unstable. Numerical modelling of the Maguerite Bay ice-stream retreat in West Antarctica since the Last Glacial Maximum suggests that an ice stream can stabilize on an inland-sloping bed owing to increased lateral drag where the ice stream narrows.

During the Last Glacial Maximum, the pattern of Atlantic Meridional Overturning Circulation was different from today. A combination of sediment chemistry and a scavenging model suggests that the glacial circulation was shallower and at least as vigorous as today.

Over the past few years, it has become clear that the Moon’s surface is not entirely dry. The direct identification of hydroxyl in glasses produced in lunar soils by the impact of micrometeorites supports the idea that water was delivered to the lunar surface by the solar wind.

The Atlantic Ocean has been suggested as an important driver of variability in European climate on decadal timescales. Analyses of ocean and atmosphere temperature data from observations suggest that the shift in European climate during the 1990s was a result of warming in the North Atlantic Ocean.

The last glacial period was marked by rapid reorganizations of oceanic and atmospheric circulation. Speleothem records from the Amazon Basin suggest that precipitation variability was linked to these events.

Life on land dates back at least 2.7 billion years, but the effects of this early terrestrial biosphere on biogeochemical cycling are poorly constrained. Marine sulphur data and geochemical modelling suggest that microbial pyrite weathering has transferred a substantial amount of sulphur to the oceans for at least 2.5 billion years.

The North Atlantic Oscillation influences climate in the Arctic region and northern Europe. Reconstructions of circulation patterns associated with the North Atlantic Oscillation from a 5,200-year-long lake sediment record suggest that the atmospheric circulation responded to significant transitions in Northern Hemisphere climate.

Stratospheric circulation is known to affect weather in the troposphere. Climate modelling reveals a connection between variations in the stratospheric and North Atlantic ocean circulation over the past 30 years, and demonstrates that the stratosphere is an important component of climate over multidecadal timescales.

Glaciers store and transform organic carbon, which, on release, could support downstream microbial life. An analysis of 26 glaciers in the European Alps suggests that a significant fraction of glacier organic matter is available for microbial consumption.

Seamount chains in the southeast Atlantic Ocean are thought to have formed above plumes sourced from the deep mantle. Dating of lavas erupted along the trails show that the formation and distribution of the seamount chains is also controlled by the motion and structure of the African Plate.

Precipitation extremes increase in intensity over many regions of the globe in simulations of a warming climate, but not always consistently. Observational constraints, together with a close relationship between model responses to interannual variability and climate change, suggest a high sensitivity of tropical extreme precipitation to warming.

Permafrost soils contain almost twice as much carbon as the current atmospheric carbon pool. Climate model simulations suggest that the feedback generated by future permafrost carbon release could lead to a further warming of 0.13–1.69 °C by 2300.

Increased temperatures and declines in water availability have influenced the productivity of mountain forests over the past half century. An analysis of 25 years of observational and satellite data suggests that mid-elevation forest greenness is strongly regulated by snow accumulation.

Boundary-layer clouds modify the near-surface climate and interact with the water and carbon cycles. Biophysical modelling suggests that rising atmospheric CO₂ levels and the associated closing of plant stomata may suppress boundary-layer cloud formation in the mid-latitudes, and demonstrates how biological and physical aspects of the climate system are intertwined.

Slow earthquakes in subduction zones have been linked to high pore-fluid pressures. Laboratory measurements reveal a high permeability contrast between crust and mantle rocks, implying that water released from the subducting slab could accumulate at the crust–mantle boundary of the overlying plate, raising pore-fluid pressures and generating slow earthquakes.

Nitrous oxide is a potent greenhouse gas that destroys stratospheric ozone. Measurements of nitrous oxide emissions from a Canadian river suggest that future increases in nitrate export to rivers will not necessarily lead to higher nitrous oxide emissions, but more widespread hypoxia most likely will.

In the Arctic Ocean, a salinity gradient separates a shallow layer of cold, relatively fresh water from the warmer, saltier Atlantic water below. A reconstruction of intermediate water temperatures in the Arctic during the last glacial period shows the presence of relatively warm water that may reflect a deepening of the halocline.