摘要:

Short‐term free‐drifting particle interceptor traps were deployed at 28 stations from April to July 1998 in the North Water Polynya (northern Baffin Bay). The amount, composition, and vertical transformation of the organic material sinking out of the euphotic zone were assessed. Clear seasonal sedimentation patterns were apparent throughout the Polynya. Maximum sedimentation occurred during the month of June, at which time high sedimentation of intact diatom cells and empty frustules was observed. In July, abundant resting spores and zooplankton feces were sinking out of the euphotic zone. Vertical transformation of the sinking material, between 50 m and 100 m, revealed a consistent loss of ∼30–35% for particulate organic carbon and nitrogen and a loss of ∼10% for biogenic silica. A temperature model of silica dissolution was used to assess the role of temperature in controlling the low loss of biogenic silica observed in the upper water column. Model results show divergence of modeled rates from in situ loss rates at times when the biosiliceous fraction of the sinking material was high. This indicates that biological factors played a key role in reducing biogenic silica dissolution in the North Water Polynya. Sedimentation of intact cells, abundant resting spores, and feces all contributed to enhance preservation of silica in the sinking material. These results suggest that the North Water Polynya is a sink for biogenic silica and emphasize the significance of biological processes in controlling the silica pump in the marine en

ISSN:0148-0227    

DOI:10.1029/2000JC000408

年代:2002

数据来源: WILEY

摘要:

Using acoustic Doppler current profiler (ADCP) and conductivity‐temperature‐depth (CTD) data sets obtained from 1991 to 1993, volume, freshwater, and temperature transports through the Tsushima‐Korea Straits are estimated. To remove tidal currents contained in raw ADCP data, tidal currents are calculated using harmonic constants obtained by ADCP surveys from 1998 to 1999. The annual mean and range of the volume transport through the straits are 2.4 Sv (1 Sv = 106m3/s) and 0.8 Sv, respectively. These values are consistent with those of previous studies. The annually averaged freshwater transport is 33 × 106kg/s, which is the same as the total river discharge around the Yellow and East China Seas. This suggests that the total river discharge and freshwater transport through the Tsushima‐Korea Straits are the prominent two components in the freshwater budget, averaged annually in the Yellow and East China Seas. The annually averaged temperature transport through the Tsushima‐Korea Straits

ISSN:0148-0227    

DOI:10.1029/2000JC000702

年代:2002

数据来源: WILEY

摘要:

The response of the buoyant plume from the Chesapeake Bay to upwelling favorable winds and during conditions of low freshwater discharge is examined using an offshore array of bottom‐deployed acoustic Doppler current profilers (ADCPs) as well as ancillary data. During periods of northward (upwelling favorable) winds the observed response is strong offshore flow (U>0.2 m/s) in a shallow layer of plume water and a rapid reversal of the near‐surface flow from the usual southward flow associated with inertial turning of the plume. The offshore migration of the plume front is deduced from sequential arrivals at the various mooring locations. The orientation of the plume front is approximately alongshore (north‐south), suggesting that the upwelling response is two‐dimensional. A plume thickness calculated from the ADCP data is relatively constant at about 4 m as the plume moves across the moorings. The offshore propagation speed of the plume front of about 0.20 m/s matched the advection speed predicted by Ekman theory using the calculated plume layer thickness. The mooring velocity profiles provide a view of the across‐plume structure in a reference frame fixed to the front. This reveals a pattern of circulatory motion with sinking of plume and ambient water at the front and an ascending motion occurring inshore, suggesting a recirculation between the seaward and inshore portions of the plume. These results are consistent with recent model simulations of the response of a river plume during upwelling favora

ISSN:0148-0227    

DOI:10.1029/2000JC000698

年代:2002

数据来源: WILEY

摘要:

In this paper we study the energy dissipation due to current‐limited wave breaking in monochromatic and random waves with the help of experimental tests. The opposing currents are strong enough for wave blocking to occur. A modified bore model is used to simulate the dissipation rate in the monochromatic waves, and an empirical bulk dissipation formula for wave breaking in random waves is proposed. The effects of wave blocking on the dynamics of the wave field are also discusse

ISSN:0148-0227    

DOI:10.1029/2001JC001042

年代:2002

数据来源: WILEY

摘要:

In August 1997, RRSDiscoverycruise 230 (World Ocean Circulation Experiment (WOCE) section A25) ran a hydrographic section into Cape Farewell on the southern tip of Greenland. The closest approach to the shore was 2 nm in a water depth of 160 m over the east Greenland shelf. Analysis of the hydrographic data (conductivity‐temperature‐depth (CTD), vessel‐mounted acoustic Doppler current profiler, and thermosalinograph) has revealed a current flowing southwestward, ∼15 km wide, 100 m deep, and centered ∼10 km offshore. We believe it to be driven by meltwater runoff from Greenland. This feature, which we call the East Greenland Coastal Current (EGCC), carries a little less than 1 Sv (106m3s−1) with peak current speeds of ∼1 m s−1at the surface. The center of the EGCC lies on a salinity front with maximum salinity contrast ∼4 practical salinity units (psu) between coast and shelf break and between surface and bottom. A spot value of freshwater transport is 0.06 Sv (1800 km3yr−1), which is equivalent to ∼30% of the Arctic freshwater gain. The presence of the EGCC and its continuity up the east Greenland coast as far as Denmark Strait is confirmed in satellite sea surface temperature images and surface drifter tracks. We estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperat

ISSN:0148-0227    

DOI:10.1029/2001JC000935

年代:2002

数据来源: WILEY

摘要:

Two large, mesoscale, anticyclonic eddies formed along the west coast of the Queen Charlotte Islands of western Canada in early 1998. Altimetry measurements from TOPEX/Poseidon and ERS‐2 satellites suggest that these eddies first appeared near Cape St. James at the southern tip of the islands. The eddies merged in June to form “Haida‐1998,” the highest eddy ever observed in the region. Currents near Cape St. James in winter follow complicated patterns attributed to tidal rectification and pressure‐driven outflow from Hecate Strait. The adjustment of these flows to the bathymetric features likely contributes to the formation of Haida Eddies. Eddies that first appear farther north along the west coast of the Queen Charlotte Islands are set up by other processes, such as baroclinic in

ISSN:0148-0227    

DOI:10.1029/2001JC000876

年代:2002

数据来源: WILEY

摘要:

More than 400 profiles of (salinity) density and velocity microstructure with 923 turbulent patches were collected over 4 days from an anchored boat with the Portable Flux Profiler (PFP) in the Swan River estuary during the wet season. By using the PFP the buoyancy flux was measured directly and estimated indirectly for this flow. Overturns were suppressed by the strong stratification, and large‐scale anisotropy was correlated with turbulent Froude number. The direct measurements of the buoyancy flux exhibited both positive (downgradient) and negative (upgradient) values within the turbulent patches. The net average mixing efficiency was 0.04, less than the commonly used value of 0.17. Therefore the rate of vertical transport was small even though the dissipation levels within the turbulent patches were relatively high. The magnitude of the above mentioned competing fluxes increased with decreasing turbulent Froude numbers even though the net flux when bin‐averaged with respect to turbulent Froude number remained close to z

ISSN:0148-0227    

DOI:10.1029/2001JC000977

年代:2002

数据来源: WILEY

摘要:

The circulation driven by buoyancy and mesoscale eddy effects in the Atlantic layer of the Canada Basin is obtained diagnostically from a climatological density field. The buoyancy forcing is caused by the divergence of diapycnal flow. The diapycnal flow is estimated from a density balance between the diapycnal advection and diffusion based on the density field. On the other hand, the eddy forcing is formulated as the curl of vertical friction. The vertical friction is estimated from geostrophic shear, which is obtained from the density field. Both the flow fields caused by the buoyancy forcing and by the eddy forcing similarly suggest a new flow structure characterized by a transbasin westward flow, which appears from the eastern central basin to the southwestern basin. The transbasin westward flow is also shown in geostrophic circulation at 500 m relative to reference levels in a wide range (1000–3000 m). The significant part of the flow is consistent with a temperature distribution at 500

ISSN:0148-0227    

DOI:10.1029/2000JC000286

年代:2002

数据来源: WILEY

摘要:

The measurement of mean water levels, roller geometries, and phase ensemble‐averaged velocity and turbulence intensity fields under spilling and plunging waves breaking in a two‐dimensional laboratory surf zone is presented. The velocities were measured using digital correlation image velocimetry, while water levels and roller geometries were determined through gray scale filtering of video images. The phase ensemble‐averaged horizontal and vertical components of velocity and turbulence intensities are measured throughout the entire flow domain, including the wave roller area, by utilizing the aerated areas as part of the flow structure. The time‐averaged horizontal velocities (undertow), turbulence intensities, and turbulent kinetic energies are determined by averaging across the wave phase. Turbulence magnitudes are found to compare favorably with existing laser Doppler anemometry measurements below the wave trough level, where such measurements have generally been confined because of aeration contamination effects. The significantly higher velocity and turbulence intensity magnitudes measured above the trough level in the present experiments highlight the novel nature of the present investigation for describing flow regimes in the su

ISSN:0148-0227    

DOI:10.1029/2000JC000755

年代:2002

数据来源: WILEY

摘要:

Using the World Ocean Atlas data set, we examine the origins and flow paths of subducted waters observed along the 137°E section in the western North Pacific. The waters studied consist mainly of the water mass known as North Pacific Tropical Water, but includes much of the water midlatitude thermocline. A method is developed to trace these waters from 137°E back through the subtropical gyre to their outcrops. Subducted waters are aged using this technique and found to be between 0.5 and 35 years old by the time they reach 137°E. For this subducted regime, waters on a given isopycnal observed along 137°E increase in age with decreasing latitude, with waters at the southern end of the section being 2–3 times older than waters at the northern end. This estimate of age is consistent with previous estimates calculated from chlorofluorocarbon measurements. It is found that subducted water masses are strongly homogenized by the time they reach 137°E. That is, the originally subducted waters have a wide variation in θ‐Scharacteristics, but by the time they reach 137°E, they form a coherent water mass with a tight θ‐Srelation. It is shown that isopycnal mixing is not a plausible mechanism for this homogenization but that diapycnal mixing is a more l

ISSN:0148-0227    

DOI:10.1029/2000JC000722

年代:2002

数据来源: WILEY