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The article reports on the impact of the 2011 Tohoku-oki earthquake on seafloor displacements. It presents the first results of sea-floor Global Positioning System and acoustic ranging (GPS-A) observations. The observed postseismic displacement rates (DRs) show distinct landward DRs in the large coseismic slip area and slight trenchward DRs in the north of the primary rupture area.

Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of ice contact with the bed at this site about 12,000 years ago. Previous studies and morphologic mapping of the fjord suggest that the Crane Glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the ice shelf collapse. This implies that the 2002 Larsen-B Ice Shelf collapse likely was a response to surface warming rather than to grounding zone instability, strengthening the idea that surface processes controlled the disintegration of the Larsen Ice Shelf. [ABSTRACT FROM AUTHOR]

We reconstructed the radiocarbon activity of intermediate waters in the eastern North Pacific over the past 38,000 years. Radiocarbon activity paralleled that of the atmosphere, except during deglaciation, when intermediate-water values fell by more than 300 per mil. Such a large decrease requires a deglacial injection of very old waters from a deep-ocean carbon reservoir that was previously well isolated from the atmosphere. The timing of intermediate-water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation. [ABSTRACT FROM AUTHOR]

Gravity models are powerful tools for mapping tectonic structures, especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment. We combined new radar altimeter measurements from satellites CryoSat-2 and Jason-1 with existing data to construct a global marine gravity model that is two times more accurate than previous models. We found an extinct spreading ridge in the Gulf of Mexico, a major propagating rift in the South Atlantic Ocean, abyssal hill fabric on slow-spreading ridges, and thousands of previously uncharted seamounts. These discoveries allow us to understand regional tectonic processes and highlight the importance of satellite-derived gravity models as one of the primary tools for the investigation of remote ocean basins. [ABSTRACT FROM AUTHOR]

Oceanic transports of heat, salt, fresh water, dissolved CO2, and other tracers regulate global climate change and the distribution of natural marine resources. The time-mean ocean circulation transports fluid as a conveyor belt, but fluid parcels can also be trapped and transported discretely by migrating mesoscale eddies. By combining available satellite altimetry and Argo profiling float data, we showed that the eddy-induced zonal mass transport can reach a total meridionally integrated value of up to 30 to 40 sverdrups (Sv) (1 Sv = 106 cubic meters per second), and it occurs mainly in subtropical regions, where the background flows are weak. This transport is comparable in magnitude to that of the large-scale wind- and thermohaline-driven circulation. [ABSTRACT FROM AUTHOR]

The subsidence of the sea floor is generally considered a consequence of its passive cooling and densifying since its formation at the ridge and is therefore regarded as a function of lithospheric age only. However, the lithosphere is defined as the thermal boundary layer of mantle convection, which should thus determine its structure. We examined the evolution of the lithosphere structure and depth along trajectories representative of the underlying mantle flow. We show that along these flow lines, the sea-floor depth varies as the square root of the distance from the ridge (as given by the boundary-layer equation) along the entire plate, without any flattening. Contrary to previous models, no additional heat supply is required at the base of the lithosphere. [ABSTRACT FROM AUTHOR]

The article discusses a report within the issue regarding research by Walter and colleagues analyzing superdeep diamonds originating from kimberlite volcanoes in Juina, Brazil. According to researchers, these superdeep diamonds are notable because they host inclusions with compositions comprising the complete phase assemblage expected to crystallize from basalt under lower-mantle conditions. Topics include one of the primary consequences of plate tectonics, which is the subduction of the basaltic oceanic crust with lithospheric slabs into the mantle, the extension of this process into the lower mantle, and evidence from diamonds and their mineral inclusions that show deep mantle cycling of the oceanic crust.

This article focuses on efforts of a marine geologist John Delaney to build a network of observatories on the ocean floor. Delaney actually took one along for a voyage to the bottom of the sea. Dubbed NEPTUNE — for North-East Pacific Time-series Undersea Networked Experiments — the project is jockeying to become part of a broader National Science Foundation plan to build a trio of ocean observatories that would enable scientists to keep a constant watch on the sea. Using samples donated by another researcher, Delaney wrote a thesis that examined how the volatile gases in sea-floor basalt — a volcanic rock — behave when bottled up by the sea's crushing pressure. INSET: A Cautionary Tale From Bermuda.

An introduction is presented in which the editor discusses an article focusing on an analysis of high-resolution ocean depth data across the Australian-Antarctic ocean ridge finding periodicity similar to the Milankovitch cycles associated with ice ages.

The article discusses a report within the issue on a marine gravity model that improves the resolution of global maps constructed using satellite-derived gravity data developed by Sandwell et al., which revealed several previously unknown tectonic features of the ocean floor.