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.

Gene expression in the deep biosphere

Abstract: Gene expression of microbes in anaerobic sediment from the Peru Margin at depths up to 159 metres below the sea floor is analysed: anaerobic metabolism of amino acids, carbohydrates and lipids are seen to be the dominant metabolic processes, and genes associated with cell division are found to be correlated with microbial cell concentration, suggesting that ongoing cell division contributes to biomass turnover. Microbial metabolism in the marine subsurface environment is an important factor in various global biogeochemical cycles, yet our understanding of the types of metabolism occurring is limited. This study uses metatranscriptomics to investigate gene expression in sediments up to 159 metres below the seafloor off the coast of Peru. Anaerobic metabolism of amino acids, carbohydrates and lipids are the predominant metabolic processes in this 'deep biosphere' environment, and the distribution of transcripts associated with cell division suggests that microbial cell division is occurring, not just biomass turnover without division. Scientific ocean drilling has revealed a deep biosphere of widespread microbial life in sub-seafloor sediment. Microbial metabolism in the marine subsurface probably has an important role in global biogeochemical cycles1,2,3, but deep biosphere activities are not well understood1. Here we describe and analyse the first sub-seafloor metatranscriptomes from anaerobic Peru Margin sediment up to 159 metres below the sea floor, represented by over 1 billion complementary DNA (cDNA) sequence reads. Anaerobic metabolism of amino acids, carbohydrates and lipids seem to be the dominant metabolic processes, and profiles of dissimilatory sulfite reductase (dsr) transcripts are consistent with pore-water sulphate concentration profiles1. Moreover, transcripts involved in cell division increase as a function of microbial cell concentration, indicating that increases in sub-seafloor microbial abundance are a function of cell division across all three domains of life. These data support calculations1 and models4 of sub-seafloor microbial metabolism and represent the first holistic picture of deep biosphere activities.

Seismic evidence for a lower-mantle origin of the Iceland plume

Abstract: Iceland, one of the most thoroughly investigated hotspots1,2,3, is generally accepted to be the manifestation of an upwelling mantle plume4 Yet whether the plume originates from the lower mantle or from a convective instability at a thermal boundary layer between the upper and lower mantle near 660 km depth5,6 remains unconstrained Tomographic inversions of body-wave delay times show that low seismic velocities extend to at least 400 km depth beneath central Iceland7,8, but cannot resolve structure at greater depth Here we report lateral variations in the depths of compressional-to-shear wave conversions at the two seismic discontinuities marking the top and bottom of the mantle transition zone beneath Iceland We find that the transition zone is 20 km thinner than in the average Earth9 beneath central and southern Iceland, but is of normal thickness beneath surrounding areas, a result indicative of a hot and narrow plume originating from the lower mantle

Spectra of Backscattered Light from the Sea Obtained from Aircraft as a Measure of Chlorophyll Concentration

Abstract: Spectra of sun and skylight backscattered from the sea were obtained from a low-flying aircraft and were compared with measurements of chlorophyll concentration made from shipboard at the same localities and at nearly the same times. Increasing amounts of chlorophyll were found to be associated with a relative decrease in the blue portion of the spectra and an increase in the green. Anomalies in the spectra show that factors other than chlorophyll also affect the water color in some instances; these factors include other biochromes, suspended sediment, surface reflection, polarization, and air light.

The Relation between Decadal Variability of Subtropical Mode Water and the North Atlantic Oscillation

Abstract: The Bermuda station ‘‘S’’ time series has been used to define the variability of subtropical mode water (STMW) from 1954 to 1995. This record, which shows decadal variability at a nominal period of about 12‐14 yr, has been used as a baseline for seeking correlation with large-scale atmospheric forcing and with decadal north‐south excursions of the Gulf Stream position defined by the subsurface temperature at 200-m depth. A common time period of 1954‐89 inclusive, defined by the data sources, shows a high degree of correlation among the STMW potential vorticity (PV), Gulf Stream position, and large-scale atmospheric forcing (buoyancy flux, SST, and sea level pressure). Two pentads with anomalously small and large STMW PV were further studied and composites were made to define a revised North Atlantic Oscillation (NAO) index associated with the decadal forcing. During years of low PV at Bermuda, the NAO index is low, the Gulf Stream is in a southerly position, and the zero wind stress curl latitude is shifted south as are the composite extratropical winter storm tracks, in comparison to the period of high PV at Bermuda. Because the NAO, Gulf Stream separation latitude, and STMW PV variations are in phase with maximum annually averaged correlation at zero year time lag, the authors hypothesize that all must be either coupled with one another or with some other phenomenon that determines the covariability. A mechanism is proposed that could link all of the above together. It relies on the fact that during periods of high STMW PV, associated with a northerly Gulf Stream and a high NAO, one finds enhanced production of mode water in the subpolar gyre and Labrador Sea. Export of the enhanced Labrador Sea Water (LSW) component into the North Atlantic via the Deep Western Boundary Current can influence the separation point of the Gulf Stream in the upper ocean once the signal propagates from the source region to the crossover point with the Gulf Stream. If the SST signal produced by the 100-km shift of the Gulf Stream along a substantial (1000 km) length of its path as it leaves the coast can influence the NAO, a negative feedback oscillation may develop with a timescale proportional to the time delay between the change of phase of the air‐ sea forcing in the Labrador Basin and the LSW transient at the crossover point. Both a simple mechanistic model as well as a three-layer numerical model are used to examine this feedback, which could produce decadal oscillations given a moderately strong coupling.

Trapping of a Coastal Density Front by the Bottom Boundary Layer

Abstract: The dynamics of a surface-to-bottom density front on a uniformly sloping continental shelf and the role of density advection in the bottom boundary layer are examined using a three-dimensional, primitive equation numerical model. The front is formed by prescribing a localized freshwater inflow through the coastal boundary. The resulting freshwater plume turns anticyclonically and moves along the coast, generating offshore transport in the bottom boundary layer, which advects freshwater offshore and creates a sharp surface-to-bottom density front with a surface-intensified alongshelf jet over the front. The offshore buoyancy flux in the bottom boundary layer moves the front offshore until it reaches a depth where the vertical shear within the front leads to a reversal in the cross-shelf velocity at the shoreward edge of the front. Consequently, the offshore buoyancy flux in the bottom boundary layer vanishes shoreward of the front. Within the front, a steady balance is established in the bottom bo...