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.

Modeling δ18O in precipitation over the tropical Americas: 1. Interannual variability and climatic controls

Abstract: [1] We use two atmospheric general circulation models (AGCMs), the ECHAM-4 and the GISS II models, to analyze the interannual variability of δ18O in precipitation over the tropical Americas. Several different simulations with isotopic tracers forced with observed global sea surface temperatures (SST) between 1950 and 1998 reveal the influence of varying temperature, precipitation amount, and moisture source contributions on the predicted δ18O distribution. Observational evidence from climatic (NCEP-NCAR) and sparse stable isotope (IAEA-GNIP) data is used to evaluate model performance. The models capture the essential features of surface climate over the tropical Americas in terms of both their spatial and temporal characteristics. Using a low-resolution model (GISS II), adjusted to provide a more realistic Andean topography, or a higher-resolution model (ECHAM-4 T106) leads to an improved δ18O distribution over the tropical Americas with an altitude effect comparable to observations. Water vapor transport and gradual rainout and increasingly depleted composition of water vapor along its trajectory are correctly simulated in both models, although the ECHAM model appears to underestimate the continentality effect over the Amazon basin. A significant dependence of δ18O on the precipitation amount is apparent in both models, in accordance with observations, while the influence of temperature seems to be less significant in most regions and is accurately reproduced by the ECHAM model only. Over most regions, however, the δ18O signal in precipitation is influenced by a combination of factors, such as precipitation amount, temperature, moisture source variability, and atmospheric circulation changes. Over parts of the tropical Americas, the δ18O signal is therefore also significantly correlated with ENSO because ENSO is an integrator of many factors affecting the δ18O composition of precipitation.

Seasonality in the flux of natural radionuclides and plutonium in the deep Sargasso Sea

Abstract: A record of radionuclide fluxes at a deep-ocean station near Bermuda (32°05′N, 64°15′W) was obtained from analysis of a 3-year collection of sediment-trap samples. The trap was placed at a depth of 3200 m, 1000 m above the sea floor, and the samples were recovered at 2-month intervals. Concentrations of 238U, 234U, 232Th, 230Th, 228Th, 231Pa, 210Po, and 239, 240Pu were measured in the trapped material. Most of the radionuclide activity was found in the <37-gmgm sieved fraction. All of the radionuclide fluxes showed seasonal variations that were in phase with the variations in total sediment flux, which were shown in earlier work to be closely tied to the annual cycle of primary production in the overlying surface water. The seasonal variations are especially noteworthy for 230Th and 231Pa, considering that most of their production occurs in the water column below the euphotic zone. Evidently the seasonal influence is transmitted downward by the varying particle flux so that radionuclide scavenging rates at depth, as well as at the surface, are affected. It is suggested that this could be brought about by seasonal variations in the flux of marine snow or in the rate of fecal-matter production in the deep-water column. Fluxes of 230Th and 231Pa integrated over the annual cycle yielded a trapping efficiency of 105 ± 17% for the PARFLUX sediment trap used in this investigation.

A hydrographic section across the subtropical South Indian Ocean

Abstract: Features of the water-property and circulation fields at the southern limit of the continentally bounded Indian Ocean are described on the basis of a transoceanic hydrographic section occupied along roughly Lat. 32°S by the R.R.S. Charles Darwin in November-December 1987. Primary observations consisted of 106 full-depth CTD/O2 stations with discrete measurements of the concentrations of dissolved silica, phosphate and nitrate. The section lies in the southern part of the South Indian subtropical gyre; water-property features in the upper kilometer indicate that the northward interior flow is predominantly in the eastern half of the ocean there, consistent with the forcing pattern of wind-stress curl. The southward return flow is the Agulhas Current, whose transport at Lats 31–32°S is estimated as 85 × 106 m3 s−1. Circumpolar Deep Water flows northward to fill the greater deep Indian Ocean by means of western-boundary currents in the Crozet Basin, Central Indian Basin and Perth Basin. North Atlantic Deep Water entering directly from the mid-latitude South Atlantic is almost entirely confined to the south-western Indian Ocean (Mozambique Basin, Natal Valley) by the topography of the Madagascar Ridge and Mozambique Channel. Geostrophic transport figures are presented based on a zero-velocity surface constructed along the section from the tracer-property evidence of where deep water was moving northward and where southward. Ekman transport, deduced from shipboard acoustic-Doppler profiler measurements, as well as synoptic and historical wind stress data, is found to be small (about 1 × 106 m3 s−1 northward). Net transport (geostrophic and Ekman) across the section is estimated to be 7 × 106 m3 s−1 southward, which implies a similarly sized Indonesia throughflow. Ambiquity in the geostrophic referencing scheme, and the magnitude of baroclinic eddy noise on the section, suggest this figure in uncertain by at least ±10 × 106mm3 s−1. The calculations obtain a figure for net transport of water below 2000 dbars of 27 × 106 m3 s−1 northward, which specifies an average upwelling speed at the 2-km level north of 30°S of 6.9 × 10−5 cm s−1. This estimate, perhaps uncertain by 20–30%, nonetheless contributes to growing evidence for an anomalously vigorous meridional circulation in the Indian Ocean. The associated calculations of heat and fresh water flux divergences demonstrate that the Indian Ocean thermohaline circulation essentially expresses a conversion of bottom and deep water to mid-depth thermocline, and near-surface water.

Large aperture time-series sediment traps; design objectives, construction and application

Abstract: Sediment traps with 0.5 and 1.15 m2 apertures which are capable of collecting 12–25 samples at programmed intervals, typically weekly or bi-monthly, during one continuous semi- to interannual deployment have been developed. They utilize a number of new synthetic materials and stable metallic components which ensure reliable, long-lasting performance at any oceanic depth. The key component of the trap is a set of sequentially rotating samplers which is driven by a microprocessor-controlled electronic stepping motor. The electronic power controller controls sampler exchange with a high degree of flexibility and precision, as well as independently recording the executed sampling events. Each sampling bottle is sealed from ambient water during the time samples are stored before recovery. After continuous improvement and modification during 29.5 deployment-years of application in deep ocean experiments since 1982, we are convinced that these sediment traps can provide a relatively large quantity of settling particles in time-series with high experimental reliability.