Deep-sea research. Part A, Oceanographic research papers最新文献

Procedures have been developed for the analyses of dissolved and particulate ²³⁴Th, ²²⁸Th, ²³⁰Th and ²³²Th in seawater. Large volume samples (>1000 1) are collected using in situ pumps. Seawater is pumped sequentially through a filter cartridge and two MnO₂ adsorbers for the collection of particulate and dissolved Th, respectively. Both filters adsorbers are analysed for ²³⁴Th using a simple gamma counting technique. This newly developed ²³⁴Th procedure can be conducted at sea, and thus provides an easy and efficient method for ²³⁴Th analyses on large volume samples. Subsequent radiochemical purification procedures and low-level alpha counting techniques are used in the laboratory for the analyses of ²²⁸Th, ²³⁰Th and ²³²Th on these same samples.

Giant appendicularians (Bathochordaeus sp., Urochordata, Appendicularia) were observed in midwater in Monterey Canyon, Monterey Bay, California, from manned submersibles, Deep Rover, Alvin and MIR I, and with video from a ROV. Bathochordaeus utilizes secreted mucus structures to feed, but these structures and the orientation of the animal to the feeding-filter differ significantly from those of other genera in the Family Oikopleuridae. A continuously secreted sheet of mucus (unlike the episodically produced structured houses of other appendicularians) envelops both the body and the feeding-filter, protecting the animal from predators and scavenging large particles from the water feeding-filter, protecting the animal from sheet is occasionally up to 2 m in diameter, and large amounts of particulate material accumulate on this surface over time. We calculate that an individual can maintain the mucus sheet at specific depth horizons for as long as 30 days, collecting and impeding the downward flux of particulates. Eventually the sheet is disturbed or separates from the animal and feeding-filter due to its sediment burden, and collapses into a compacted mass which sinks rapidly (±800 m day⁻ to the sea bed to depths of at least 3500 m. The obvious importance of these often common, large, filter-feeding appendicularians in water column ecology and vertical flux will require further investigation.

The burrowing enteropneust Stereobalanus canadensis from the deep-sea benthos in the Norwegian Sea was investigated for halogenated metabolites in its body tissues and in its burrow wall lining; the latter was also searched for meiofauna organisms and bacteria. Homogenates of the enteropneust revealed the presence of three brominated metabolites, one of which was identified as 2,4,6-tribromophenol, varying in concentrations from 0.5 to 7 μg g⁻¹ WW. The two other metabolites were tentatively identified as a mono- and dibromo-derivative of a n-hexylhydroquinonemonomethylether and found in concentrations varying from 10 to 50 μg g⁻¹ WW. The bromohydroquinones were also found in burrow wall sediment at a concentration 10³−10⁴ times lower than in animal tissues, but not in adjacent sediment layers. No benthic metazoans were found in the burrow wall lining made by S. canadensis; only a slightly higherabundance of bacteria and a small foraminifer Lagena sp. was evident. These biotic results are in contrast to those obtained from the burrow wall lining made by a co-occurring echiuran. The depletion of a benthic metazoan fauna in the burrow wall lining from S. canadensis is possibly caused by the presence of toxic brominated metabolites excreted by the enteropneust.

Direct velocity observations from four locations in the Gulf Stream between Cape Hatteras and the Grand Banks are analysed to determine the baroclinic and barotropic transport of the Stream. Three of the sites are moored arrays where a method similar to that proposed by Hall and Bryden (1985, Geophysical Research Letters, 12, 203–206) and Hall (1986, Journal of Physical Oceanography, 16, 1814–1818) is used; the fourth is the Pegasus site of Halkin and Rossby (1985, Journal of Physical Oceanography, 15, 1439–1452). The baroclinic transport is found to change little from site to site while the barotropic changes substantially. Total transport reaches 150 Sv at 60°W and remains at that strength to 55°W, the farthest east that moored information is available. These results, augmented by additional information, are used to deduce a scheme for the total transport steamfunction in the western North Atlantic.

The relationship between primary production and sediment trap-derived downward flux of particulate organic matter was characterized over a 2 year period at the U.S. JGOFS Bermuda Atlantic Time-series Study (BATS) site to evaluate the importance of temporal variations in upper ocean biogeochemical processes. Water column-integrated primary production (∫PP), determined once each cruise using ¹⁴C incubations (in situ dawn-to-dusk), peaked in late winter/early spring of both 1989 and 1990. Smaller increases in ∫PP also occured in July 1989 and October–December 1990. Annual ∫PP was 9.2 mol C m⁻² y⁻¹ in 1989 and 12 mol C m⁻² y⁻¹ in 1990. This was higher than the 1959–1963 annual average (6.8 mol C m⁻² y⁻¹) determined at Station “S” located approximately 50 km northwest of the BATS site.

Fluxes associated with sinking of total particulate mass, particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured at 150, 200, 300 and 400 m using a free-floating sediment trap array generally deployed once each cruise for 72 h. Fluxes varied seasonally, and within our ability to resolve differences (i.e. monthly sampling), there was no distinguishable time offset between peaks in ∫PP and corresponding peaks in elemental flux. Fluxes generally decreased with increasing depth, and fluxes of POC and PON were positively correlated with particulate mass flux at all depths. POC/PON (C/N) ratios at 150 m during periods of high ∫PP were generally characteristics of live planktonic biomass. Higher C/N ratios in material collected by the deeper traps were consistent with more rapid losses of PON than POC from sinking particles. POC and PON fluxes at 150 m, nominally the base of the euphotic zone, were positively correlated with ∫PP. The fraction of ∫PP leaving the euphotic zone in the form of sinking particles (i.e. collected in traps) varied seasonally and was inversely proportionato ∫PP. Surface export of organic matter estimated by sediment traps at 150m was 0.78 mol C m⁻²y⁻¹ (0.10 mol N m⁻²y⁻¹) in 1989 and 0.77 mol C m⁻²y⁻¹ (0.11 mol N m⁻²y⁻¹) in 1990.

We report results of a CTD and chlorphyll $\text{a}$ survey from Cobb Seamount, a shallow seamount in the northeast Pacific. Our results show a several-fold increasein the standing crop of chlorophyll $\text{a}$ is centred over the seamount. Current meter and drifter data indicate an anticyclonic deflection of deep currents around consistent with a theoretical stratified Tylor cone. Cobb differs from other seamounts where similar phenomena have been reported (Owens and Hogg; 1980, Deep-Sea Research, 27, 1029–1045; Gouldet al., 1981, Deep-Sea Research, 28, 409–440; Genin and Boehlert, 1985, Journal of Marine Research, 43, 907–924) in that its summit penetrates well into the euphotic zone. A Taylor column existing at such shallow depths could locally enhance primary production, providing a significant source of energy for higher trophic levels on the seamount. Indirect evidence for such a scenario comes from observations of a high biomass benthic community on Cobb Seamount.

The convective/advective balance at the northern end of the Gulf of Elat was investigated by comparing observed data to a numerical model's predictions. The data, monthly temperature and salinity profiles collected from July 1988 to August 1989, indicate a continuously developing annual cycle, with the water column reaching vertical homogeneity in February and the new thermocline beginning to develop in March. In the summer, an upper 200 m thermally stratified layer (surface temperatures reaching 26°C) overlies a thermally homogeneous layer of 21°C. Salinity is close to 40.5% and varies by less than 0.5% throughout the year, although a salinity minimum develops in the upper layer in late spring and erodes and deepens in the fall and winter as the water column becomes mixed.

The strictly one-dimensional convective model successfully reproduces the thermal structure, with a slight lag in summer thermocline development, but is unable to predict the observed salinity minimum. The addition of some advected Red Sea water (40.3%) to the model enables the reproduction of the salinity minimum. This inflow of warmer water also may account for the relatively early thermocline development.

Observations with a shipborne Acoustic Doppler Current Profiler (ADCP) were made in the Faeroe Bank Channel. When underway in strong winds and rough seas, spurious currents (>50 cm s⁻¹) were observed which vanished when the ship was hove to. On the station strong tidal/inertial currents were detected (ca 20 cm s⁻¹) at two locations, over periods of 12 and 27 h. Transient current estimates were extracted by a least-squares model fit and the residuals filtered by optimum interpolation. The resulting non-divergent currents were combined with geostrophic shear derived from simultaneous CTD and XBT observations. Transport of, and mixing within, the Norwegian Sea overflow confirm previous determinations. The implication of this research for the conduct of WOCE transoceanic sections is described.

Megafaunally produced sediment mounds can be sites of rapid biodeposition and may be important sources of infaunal disturbance aat the deep-sea floor. We conducted experiments in the Santa Catalina Basin (1240 m depth) using artificial mounds (≈9 cm high by 35 cm wide) to assess macrobenthic disturbance from mound formation and to evaluate modes and patterns of recolonization. To differentiate colonization modes, we created two types of mounds: unfloored (allowing all potential colonists) and floored (excluding burrowing immigrants).

Burial beneath an average of 5–6 cm of artificial-mound sediments yielded a 32% reduction in macrofaunal abundance over time scales of ≤1 month. All functional groups were disturbed by burial, although subsurface deposit feeders appearedd to be the least susceptible. In addition, eight of the 14 dominant background species showed significant population reduction on mound treatments. Macrobenthos in unfloored treatments reached background levels of abundance after 11 months, suggesting colonization rates 3 × higher than estimated by previous deep-sea studies using colonization trays. Comparisons between floored and unfloored treatments suggest that burrowing was a significant dispersal mode for colonists. Intermediate peaks in the abundance of two infaunal species on unfloored artificial mounds, as well as changes in trophic-group composition, indicate that community succession proceeded for at least 23 months, these treatments also exhibited enhanced species diversity, providing the first direct evidence that the intermediate disturbance hypothesis helps to explain high macrobenthic diversity in the deep sea.

A deep nephelometer has been developed to obtain vertical profiles of scattered light in the oceans. It was designed to study Bottom and Intermediate Nepheloid layers encountered in deep ocean. It is an adaptation of a shallow water device previously built for euphotic layer studies. The instrument and its calibration are described; results from different applications are given.