Woods Hole Oceanographic Institution

About: Woods Hole Oceanographic Institution is a nonprofit organization based out in Falmouth, Massachusetts, United States. It is known for research contribution in the topics: Population & Mantle (geology). The organization has 5685 authors who have published 18396 publications receiving 1202050 citations. The organization is also known as: WHOI.

Rapid circulation of warm subtropical waters in a major glacial fjord in East Greenland

Abstract: The recent rapid increase in mass loss from the Greenland ice sheet is primarily attributed to an acceleration of outlet glaciers. Oceanographic data obtained in summer 2008 show that subtropical waters that reside year-round in the shelf ocean off Greenland continuously enter a large glacial fjord in East Greenland and contribute to melting at the glacier terminus. The recent rapid increase in mass loss from the Greenland ice sheet1,2 is primarily attributed to an acceleration of outlet glaciers3,4,5. One possible cause of this acceleration is increased melting at the ice–ocean interface6,7, driven by the synchronous warming8,9,10 of subtropical waters offshore of Greenland. However, because of the lack of observations from Greenland’s glacial fjords and our limited understanding of their dynamics, this hypothesis is largely untested. Here we present oceanographic data collected in Sermilik Fjord, East Greenland, by ship in summer 2008 and from moorings. Our data reveal the presence of subtropical waters throughout the fjord. These waters are continuously replenished through a wind-driven exchange with the shelf, where they are present all year. The temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus. Key controls on the melting rate are the volume and properties of the subtropical waters on the shelf, and the patterns of along-shore winds, suggesting that the glaciers’ acceleration has been triggered by a combination of atmospheric and oceanic changes. Our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice-sheet margins.

A Novel Lineage of Proteobacteria Involved in Formation of Marine Fe-Oxidizing Microbial Mat Communities

Abstract: Background. For decades it has been recognized that neutrophilic Fe-oxidizing bacteria (FeOB) are associated with hydrothermal venting of Fe(II)-rich fluids associated with seamounts in the world’s oceans. The evidence was based almost entirely on the mineralogical remains of the microbes, which themselves had neither been brought into culture or been assigned to a specific phylogenetic clade. We have used both cultivation and cultivation-independent techniques to study Ferich microbial mats associated with hydrothermal venting at Loihi Seamount, a submarine volcano. Methodology/Principle Findings. Using gradient enrichment techniques, two iron-oxidizing bacteria, strains PV-1 and JV-1, were isolated. Chemolithotrophic growth was observed under microaerobic conditions; Fe(II) and Fe 0 were the only energy sources that supported growth. Both strains produced filamentous stalk-like structures composed of multiple nanometer sized fibrils of Feoxyhydroxide. These were consistent with mineralogical structures found in the iron mats. Phylogenetic analysis of the small subunit (SSU) rRNA gene demonstrated that strains PV-1 and JV-1 were identical and formed a monophyletic group deeply rooted within the Proteobacteria. The most similar sequence (85.3% similarity) from a cultivated isolate came from Methylophaga marina. Phylogenetic analysis of the RecA and GyrB protein sequences confirmed that these strains are distantly related to other members of the Proteobacteria. A cultivation-independent analysis of the SSU rRNA gene by terminalrestriction fragment (T-RF) profiling showed that this phylotype was most common in a variety of microbial mats collected at different times and locations at Loihi. Conclusions. On the basis of phylogenetic and physiological data, it is proposed that isolate PV-1 T (=ATCC BAA-1019: JCM 14766) represents the type strain of a novel species in a new genus, Mariprofundus ferrooxydans gen. nov., sp. nov. Furthermore, the strain is the first cultured representative of a new candidatus class of the Proteobacteria that is widely distributed in deep-sea environments, Candidatus f (zeta)-Proteobacteria cl. nov.

On the Dynamics and Energy Transformations in Steady‐State Hurricanes

Abstract: A dynamic model of the inflow layer in a steady mature hurricane is evolved, relating wind speed, pressure gradient, surface shearing stress, mass flow, and convergence. The low-level air trajectories are assumed to be logarithmic spirals. With this hypothesis, properties such as maximum wind and central pressure are determined through choice of a parameter depending on the inflow angle: a moderate hurricane arises with inflow angles of about 20°, while 25° gives an intense or extreme storm. Most of this study treats the moderate storm. In order to maintain its core pressure gradients, an oceanic source of sensible and latent heat is required. As a result, latent heat release in the inner hurricane area occurs at higher heat content (warmer moist adiabats) than mean tropical subcloud air. The heat transfer from the ocean and the release of latent heat in the core determine the pressure gradient along the trajectory, and this prescribes the particular trajectory selected by the air among an infinite number available from the logarithmic spiral family. This selection principle is evolved using recent work on “relative stability” of finite amplitude thermal circulations. Of an infinite number of dynamically possible spirals, the one is realized which maximizes the rate of kinetic energy production under the thermodynamic constraints, here formulated in terms of the relation between heat release and pressure gradient. Finally, rainfall, efficiency of work done by the storm, and kinetic energy budgets are examined in an attempt to understand the difference between the hurricane—a rare phenomenon—and the common sub-hurricane tropical storm. DOI: 10.1111/j.2153-3490.1960.tb01279.x

How rapidly is a passive scalar mixed within closed streamlines

Abstract: The homogenization of a passive ‘tracer’ in a flow with closed mean streamlines occurs in two stages: first, a rapid phase dominated by shear-augmented diffusion over a time ≈P1/3(L/U), where the Peclet number P=LU/κ (L,U and κ are lengthscale, velocity scale and diffusivity), in which initial values of the tracer are replaced by their (generalized) average about a streamline; second, a slow phase requiring the full diffusion time ≈ L2/κ. The diffusion problem for the second phase, where tracer isopleths are held to streamlines by shear diffusion, involves a generalized diffusivity which is proportional to κ, but exceeds it if the streamlines are not circular. Expressions are also given for flow fields that are oscillatory rather than steady.

Unexpected changes in the oxic/anoxic interface in the Black Sea

Abstract: THE Black Sea is the largest anoxic marine basin in the world today1. Below the layer of oxygenated surface water, hydrogen sulphide builds up to concentrations as high as 425 μM in the deep water down to a maximum depth of 2,200 m (ref. 2). The hydrographic regime is characterized by low-salinity surface water of river origin overlying high-salinity deep water of Mediterranean origin1,3. A steep pycnocline, centred at about 50 m is the primary physical barrier to mixing and is the origin of the stability of the anoxic (oxygen/hydrogen sulphide) interface. Here we report new observations, however, that indicate dramatic changes in the oceanographic characteristics of the anoxic interface of the Black Sea over decadal or shorter timescales. The anoxic, sulphide-containing interface has moved up in the water column since the last US cruises in 1969 and 1975. In addition, a suboxic zone overlays the sulphide-containing deep water. The expected overlap of oxygen and sulphide was not present. We believe that these observations result from horizontal mixing or flushing events that inject denser, saltier water into the relevant part of the water column. It is possible that man-made reduction in freshwater inflow into the Black Sea could cause these changes, although natural variability cannot be discounted.