摘要:

Neutrally buoyant SOFAR floats at nominal depths of 800, 1800, and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the Atlantic near 6°N and at several sites near 11°N as well as along the equator. Trajectories at 1800 m show a swift (>50 cm/s), narrow (100 km wide), southward flowing deep western boundary current (DWBC) extending from 7°N to the equator. The average transport per unit depth in the DWBC was estimated to be 13.8 × 103m2/s. Coupling this value with mean velocities measured in the DWBC by current meters gave a volume transport of 15 × 106m3/s between depths of 900 m and 2800 m. Approximately 6 × 106m3/s recirculated northward between the DWBC and the Mid‐Atlantic Ridge, leaving 9 × 106m3/s as cross‐equatorial transport. No obvious DWBC nor swift equatorial current was observed by the 3300‐m floats; a low mean velocity at this depth lay between F‐11 and higher velocity cores above and below. The 1800‐m trajectories also suggest that at times (February‐March 1989) the North Atlantic Deep Water in the DWBC turned eastward and flowed along the equator and at other times (August‐September 1990) the DWBC crossed the equator and continued southward. The velocity near the equator, calculated by grouping floats in a box along the equator, was eastward at 4.1 cm/s from February 1989 to February 1990 and westward at 4.6 cm/s from March 1990 to November 1990. Thus the amount of cross‐equatorial flow in the DWBC appeared to be linked to low‐frequency variability of the structure of the equatorial current system. Floats in Antarctic Intermediate Water at 800 m revealed a northwestward western boundary current, although flow patterns were complicated. Three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm/s. Six 800‐m floats drifted eastward along the equator between 5°S and 6°N at a mean velocity of 11 cm/s; one reached 5°W in the Gulf of Guinea, suggesting that the equatorial currents at this depth extended at least 35°–40° along the equator. Three of these floats reversed direction ne

ISSN:0148-0227    

DOI:10.1029/93JC00051

年代:1993

数据来源: WILEY

摘要:

Geosat Exact Repeat Mission (ERM) altimetry data, collected during 1987–1988 over the Caribbean Sea, are used to detect and track the movement of mesoscale sea surface height anomalies. Along‐track derivatives are used to estimate the mean sea surface height. Contour maps of sea surface height (SSH) anomaly are generated for each 17‐day exact repeat period. Two anticyclonic features are observed during April‐July, one each year, with SSH signatures that reached +30 cm. These features initially are observed near the Beata Ridge and propagate westward with an average speed of 15 cm/s. No mesoscale anomalies associated with the Caribbean Current are apparent during other seasons. The formation of the anticyclones coincides with the seasonal increase to maximum wind stress curl and water transport in the central Caribbean. A quasi‐permanent cyclonic eddy is detected near the southwestern portion of the Colombian Basin, confirming model pr

ISSN:0148-0227    

DOI:10.1029/93JC00125

年代:1993

数据来源: WILEY

摘要:

During May 1990, satellite‐tracked buoy, water property, and ichthyoplankton observations were collected over the Shelikof sea valley in the western Gulf of Alaska. These observations revealed the presence of an anticyclonic mesoscale eddy (radius 10–12 km). Characteristics of the eddy included a relatively warm, low‐salinity core and high concentrations of walleye pollock larvae. The eddy remained nearly stationary for several weeks before moving westward into shoaler waters. During translation, the eddy maintained its characteristics. Speeds from geopotential topography and direct measurements agreed. Current speeds generally increased with distance from the center of the eddy; maximum speeds (>30 cm s−1) existed near the perimeter. Analysis of water properties indicates little or no exchange of mass occurred with adjacent waters. The lack of dispersion permits us to estimate larval mortality (≤4.7% d−1) based only on biological factors. Eddy formation occurred through baroclinic instability upstream within Shelikof St

ISSN:0148-0227    

DOI:10.1029/93JC00573

年代:1993

数据来源: WILEY

摘要:

Hydrographic observations from the Iberian Basin demonstrate the variability of water masses in upper and intermediate layers. The surveyed area embraces the internal front between water masses from higher latitudes and the Mediterranean outflow, exhibits several isolated Mediterranean eddy (meddy) structures at middepth, and displays the virtual source region for the Mediterranean Water (MW) tongue off the Portuguese continental slope. The description is enhanced by additional chlorofluoromethane measurements, which show anomalously high concentrations at middepth, due to mixing of MW with the overlying Atlantic waters in the Gulf of Cadiz. The geostrophic stream function shows several meddylike features that not only are remarkably extended in the depth range of the MW, but are also correlated with surface height anomalies.

ISSN:0148-0227    

DOI:10.1029/93JC00040

年代:1993

数据来源: WILEY

摘要:

We use the method developed by Kirwan et al. and Halide to obtain the differential kinematic properties (DKP) and the position and velocity of a flow field singularity from a single drifter trajectory. This method, hereinafter called the OK method, has been successfully tested using artificial trajectories that were generated from flow fields containing one singularity. The OK method requires fourth‐order time derivatives of data. A new regression method that calculates DKP from a cluster of drifters is presented. This new regression method does not artificially set the flow center to the cluster centroid. It has been successfully tested by application to the trajectories generated from flow fields containing one singularity. Depending upon the spatial distribution of drifters relative to the singularity, the new regression method can be much less sensitive to noise than the OK method. Trajectories generated by flow fields with both saddle and vortex points were analyzed. Both methods worked when trajectories were close to the singularity, but not otherwise. Trajectories measured on the Scotian shelf were not amenable to either method of analysis, presumably because the trajectories did not result from only one singularit

ISSN:0148-0227    

DOI:10.1029/92JC01728

年代:1993

数据来源: WILEY

摘要:

In September‐October 1988 and April 1989 a series of hydrographic transects were completed across the Gulf Stream front in a meander crest and meander trough, respectively. One of the main experimental objectives was to relate the spatial distribution of chlorophyll to the physical fields of Gulf Stream meanders. Chlorophyll distributions are derived from conductivity‐temperature‐depth (CTD)/fluorescence profiles calibrated with discrete pigment samples collected from bottles at several depths at various stations. Objective analysis (OA) maps and vertical sections, in stream coordinates, of chlorophyll on density surfaces show the chlorophyll distribution was strongly related to the structure of the Gulf Stream front. In particular, chlorophyll concentrations greater than 0.4 mg m−3were at, or inshore of, the Gulf Stream north wall. Characteristic length scales of chlorophyll distribution determined from the horizontal and temporal correlation function are the same order (50–100 km) as length scales of the physical variables. The maximum chlorophyll concentrations in the vertical were from the surface to 50‐m depth on the western flank of the meander crest and deepened to 75‐ to 100‐m depth on the eastern flank. This coincides with the deepening of the 24.4–25.7 σθsurfaces from the western to the eastern flank of the meander crest. Although in the spring cruise the maximum chlorophyll concentrations were also found at depths between the surface and 100 m, there were no clear distinctions in pigment distributions between the western and eastern transects of a relatively weak trough. Maximum chlorophyll concentrations, 1.0–1.5 mg m−3, from the 1989 spring bloom in slope waters were about double those observed in the 1988 fall data. The primary physical mechanisms influencing the mesoscale pigment distribution in Gulf Stream meanders observed in this study are (1) outcropping of nutrient‐bearing strata in the spring, (2) meander‐induced upwelling of nutrients along sloping isopycnals, and (3) Gu

ISSN:0148-0227    

DOI:10.1029/92JC02911

年代:1993

数据来源: WILEY

摘要:

The18O/16O of dissolved oxygen was measured in the upper ocean of the subarctic Pacific in 1988. In May and August, at stations Papa (50°N, 145°W) and R (53°N, 145°W), the mean δ18O in the mixed layer was 23.84±0.20 and 24.00±0.24 ‰ (versus standard mean ocean water) consistently more depleted than atmospheric saturation levels by about 0.4 ‰. This relative depletion is caused by input of photosynthetically produced O2. A value for the isotopic fractionation effect during respiration (αT) of 0.978±0.006 was determined from the time rate of change of the concentration and δ18O of O2in the mixed layer measured during August 1988. Below the mixed layer (100–280 m) the O2concentration decreased with a corresponding increase in δ18O. Model derived values for αTover this depth region ranged from 0.980 to 0.988 and depended on the mixing model. The difference between αTdeterminations for the surface layer versus upper thermocline likely results from mixing model inaccuracies or different isotope fractionation effects during plankton and bacterial respiration. If the calculated mixed layer αTvalues apply oceanwide, then photosynthesis and respiration by the marine biota have a similar effect to land plants in maintaining the δ18O of atm

ISSN:0148-0227    

DOI:10.1029/92JC03017

年代:1993

数据来源: WILEY

摘要:

The electron microscope has been used in studies of the nature of methane sulfonic acid (MSA) particles collected from the air of Sakushima Island in Japan, near the Pacific Ocean. Particles were impacted on electron microscope screens for morphological analysis and thin‐film chemical tests. MSA particles could be identified on the basis of their distinctive morphology on the collection surface. In contrast to MSA, sulfuric acid has a similar morphology on a carbon film, but a different morphology on a nitron‐barium chloride film. It was found that MSA‐containing particles were dominant in the coarse‐particle fraction under very humid conditions. The examination also suggested that the MSA particles were present as mixed particles. The number concentration of MSA particles varied from 0 cm−3to 10−1cm−3. Possible mechanisms for the formation of MSA‐containing particles are discussed in light of the fie

ISSN:0148-0227    

DOI:10.1029/93JC00038

年代:1993

数据来源: WILEY

摘要:

The influence of thermal stability at the air‐sea interface on computed values of the transfer velocities of trace gases is examined. The novel “whitecap” model for air‐sea gas exchange of Monahan and Spillane (1984), extended here to include thermal stability effects, is linked with an atmospheric general circulation model to compute global transfer velocity patterns of a climate reactive gas, CO2. The important terms in the model equations such as the whitecap coverage, friction velocity, neutral and local drag coefficients and the stability parameterψm(Z/L) are discussed and analyzed. The atmospheric surface level air temperature, relative humidity, wind speed and sea surface temperature, obtained from the National Center for Atmospheric Research Community Climate Model 1 (CCM1) are used to drive algorithms describing the air‐sea transfer velocity of trace gases. The transfer velocity for CO2(kCO2) is then computed for each 2.8° × 2.8° latitudinal‐longitudinal area every 24 hours for 5 years of the seasonal‐hydro runs of the CCM1. The new model results are compared to previously proposed formulations using the identical CCM1 forcing terms. Air‐sea thermal stability effects on the transfer velocity for CO2are most important at mid‐high wind speeds. Where cold air from continental interiors is transported over relatively warm oceanic waters, the transfer velocities are enhanced over neutral stability values. The depression of computedkCO2values when warm air resides over cold water is especially important, due to asymmetry in the stability dependence of the drag coefficient. The stability influence is 20% to 50% ofkCO2for modest air‐sea temperature differences and up to 100% for extreme cases of stability or instability. The stability dependent “whitecap” model, using the transfer velocity coefficients for whitecap and nonwhitecap areas suggested by Monahan and Spillane (1984), produces CO2transfer velocities that range from 13 to 50 cm h−1for a monthly mean. High‐latitude regions of both hemispheres experience winter season means of 40 to 50 cm h−1. The global area‐weighted mean CO2transfer velocity is 19.2 cm h−1, in reasonable agreement with the14C estimate of Broecker and Peng (1974). Although consistent with global14C estimates, the initial version of the model predicts a factor of 2 to 3 higher CO2transfer velocities over areas with low wind speeds relative to the parameterizations of Liss and Merlivat (1986) and Tans et al. (1990). New transfer velocity coefficients for whitecap and nonwhitecap areas are suggested that bring the low wind speed results into better agreement with observations and other models. The calculations described here suggests that oceanic gas exchange with the atmosphere is sensitive to thermal stability at the air‐sea interface. This specific, turbulence‐related geophysical forcing may account for a portion of the observed scatter in previously obtained experimental data that

ISSN:0148-0227    

DOI:10.1029/93JC00039

年代:1993

数据来源: WILEY

摘要:

A series of experiments were conducted in artificial seawater to study the effects of salinity and surface tension on the bubble‐mediated sea‐to‐air transfer of surfactant materials. The bubble transport of a surfactant tracer (14C‐labeled oleic acid) from seawater to the air‐water interface and, subsequently, to a 10‐cm height above the water surface by bubble bursting was measured. The change in surface tension induced by bubbling was also determined. We have found that the amount of oleic acid transported to the water surface by bubble scavenging increases as the salinity increases. In consequence, so does the quantity of oleic acid ejected into the air. The ratio of the quantity of oleic acid ejected to a height of 10 cm above the water surface to the amount transported to the water surface was constructed. This ratio was found to increase with decreasing surface tension, indicating that the energetics of the bubble bursting process are strongly influenced by the surface tension encountered duri

ISSN:0148-0227    

DOI:10.1029/93JC00251

年代:1993

数据来源: WILEY