Lamont Weekly Report, August 8, 2014

     It was the week of the abstract submission deadline for the American Geophysical Union’s Fall Meeting, and those who waited until Wednesday to submit their contribution learned that AGU’s servers and new abstract management software were not up to the challenge of handling as many as 10,000 submissions in the final 24 hours before the cutoff. A one-day extension may not have recovered all of the good will lost, but everyone who wanted to submit an abstract was finally given an opportunity to do so.
     On Monday, the Geochemistry Division welcomed Kelsey Dyez as a new Postdoctoral Research Fellow and NSF Earth Sciences Postdoctoral Fellow. A paleoceanographer and paleoclimatologist, Kelsey obtained his Ph.D. in 2012 at the University of California, Santa Cruz, under the supervision of Christina Ravelo and Paul Koch. After serving as a postdoctoral fellow at the Universitat Autònoma de Barcelona, he held a visiting faculty position at San Francisco State University. Kelsey’s research focuses on reconstructing climate variability from the geochemistry of foraminifera and organic biomarkers in marine sediments. At Lamont he will work with Bärbel Hönisch and Pratigya Polissar on the analysis of boron isotopes and alkenones in sediments to reconstruct atmospheric pCO2 in the early Pleistocene.
     On Tuesday, a toaster oven caught fire in an unattended laboratory in the Comer Building. The device was on a wooden shelf, and there were stacks of paper towels on the shelf above. Smoke from the combustion spread into the hallway and adjacent labs, and alert individuals in a nearby lab responded with fire extinguishers and put out the fire. Although repairs now needed to the laboratory wall and shelving are reported to be modest, considerable clean up of soot is necessary. The incident revealed a flaw in the building’s smoke detection and alarm system that is currently being addressed. Lamont’s Safety Office has offered to provide advice to all managers and users of laboratories in which appliances or laboratory procedures might pose fire hazards, and I hope that all of you in that situation will accept their offer.
      Also on Tuesday, Jennifer Nakamura, a full-time Senior Staff Associate in OCP's climate group, successfully defended her Ph.D. thesis in Columbia’s Department of Earth and Environmental Engineering. Completed in her “spare time,” Jennie's thesis was on the “Hydroclimatology of extreme precipitation and floods originating from the North Atlantic Ocean” and was supervised by Yochanan Kushnir and Manu Lall in DEEE.  Jennie devoted 13 years to the completion of her Ph.D., and congratulations by all are in order.
     OCP also reports that a Lamont weather station has been set up on the roof of the Oceanography Building, the result of efforts by graduate students Sophia Brummer, John Dwyer, and their cohorts on the weather station committee. Weather conditions specific to the Lamont Campus may now be found at
     One of the benefits of the first half of August for me is that there are fewer meetings than during the rest of the year, and I can spend more time reading the contributions to the scientific literature by my colleagues. Several papers caught my eye this week.
     In this month’s issue of the Bulletin of the Seismological Society of America, Chris Scholz offers a simple mechanical model for great earthquakes along the Cascadia subduction zone. He begins with a published paleoseismological study of such earthquakes over the past 10,000 years derived from turbidite deposits in submarine canyons, onshore tsunami deposits, and the geological record of raised beaches and other measures of vertical coastal movements. The paleoseismological study indicated that the plate boundary ruptures in four characteristic segment types of different but overlapping extents and different recurrence rates. Chris applied an empirical relation between slip area and seismic moment and an assumption of constant stress drop to derive an estimate for the along-strike distribution of slip for each earthquake type. A sum of the slip over all documented earthquakes in the geological record gives a plate convergence rate that agrees with independent geological and more recent geodetic estimates and indicates that the seismogenic zone of the plate interface along the subduction zone is fully coupled. The most recent great earthquake in Cascadia was in 1700 and had an estimated moment magnitude of about 9. Chris’s paper stops short of the situation, central to his novel Stick-Slip, in which a famous seismologist discovers that another magnitude 9 earthquake is expected along the Cascadia subduction zone within a year (
     In the latest issue of Geophysical Research Letters, Clément Hibert, Göran Ekström, and Colin Stark report that seismic records of two large landslides that occurred last year in a large, open-pit copper mine in Bingham Canyon, Utah, have yielded considerable information on the dynamics of the events. From long-period seismograms the group deduced runout trajectories consistent with the distribution of slide deposits, and from short-period seismograms the team inferred changes in momentum associated with acceleration and deceleration of slide material. The paper is part of a broader study by the group of remote seismological characterization of large landslides in near real time.
     In the August issue of Geology, a paper by a team that includes Suzanne Carbotte and was led by Adrien Arnulf of the Scripps Institution of Oceanography presents a reanalysis of multichannel seismic lines acquired 12 years ago by the R/V Ewing over Axial Seamount on the Juan de Fuca Ridge. The group imaged the axial magma chamber with a new methodology that included full waveform inversion of the refracted energy that arrives ahead of the seafloor reflection. The results indicate the thickest (~1 km) melt lens documented beneath any spreading center to date, a result attributed to the fact that Axial Seamount overlies the Cobb hotspot, at the ridge-axis end of the Cobb-Eickelberg seamount chain.
     And in the August issue of Nature Geoscience, the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) team, including Andreas Thurnherr, documents hydrographic evidence that abyssal mixing is linked to the variability of ocean mesoscale eddies on timescales of months to decades. The Southern Ocean limb of the global ocean circulation pattern consists of two cells. The upper cell involves the southward flow and upwelling of mid-depth waters from the North Atlantic, their transformation to lighter waters within the upper reaches of the Antarctic Circumpolar Current (ACC), and their subsequent return northward. The lower cell involves southward shoaling of mid-depth waters and the formation by cooling along the Antarctic margin of dense water that sinks to abyssal depths, moves northward across the ACC, and there is rendered less dense by small-scale mixing. It is this last mixing phase that was the focus of repeated DIMES cruises to the Drake Passage. The sensitivity of abyssal mixing and thereby the overall rate of abyssal ocean overturn to the intensity of the regional eddy field, which is regulated by the westerly winds of the southern hemisphere, indicates that such mixing is sensitive to changes in wind forcing induced by changes in climate.
     In the aftermath of the flurry of AGU abstract submission, may you avoid major earthquakes, landslides, hotspot magmatism, and turbulent mixing and instead enjoy the relaxing pace of a weekend in early August.