bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnostic patterns of seasonal and interannual temperature variation off the west coast of the United States: Local and remote large‐scale atmospheric forcing
Authors: Norton Jerrold G. , McLain Douglas R.
Published: February 2004

Remote forcing from the equatorial Pacific and local forcing from the North Pacific lead to interannual ocean temperature change along the west coast of the United States. In fall‐winter seasons, coherent temperature changes extending from the surface to 300 m depth indicate remote forcing. Correlations between time series of ocean temperature change and series of equatorial sea level pressure (SLP) at 12.4°S × 130.9°E were as great below 100 m as at the surface. From 1954 to 1986, coherent warming events occurred only during moderate to strong El Niño years. Warming events more closely related to local North Pacific SLP at 45°N × 165°W have correlations which were greatest at the ocean surface. The first three empirical orthogonal functions (EOFs) derived from ocean temperature change series at 0, 100, 200, and 300 m accounted for more than 98% of the variance. The first EOF is most closely correlated with remote forcing, and the second and third EOFs are closely correlated to local forcing. At the sea surface, lags of up to 6 months were found for remote forcing, while lags of less than 3 months were characteristic of local forcing. At 300 m there was an additional oceanic response which appears in phase with remote forcing. The study shows that interannual warming off the west coast has two distinguishable geographical origins and that the remotely generated warming signal arrives as complex dynamic structure having apparent propagation rates from 30 to greater than 200 km/d.
Film drops produced by air bubbles bursting at the surface of seawater
Authors: Wu Jin
Published: February 2004

By taking together various observations on air bubbles bursting at the surface of seawater, the production rate and size spectrum of film drops are deduced. The number of film drops produced is proportional to the square of bubble diameter, and the size spectrum of film drops produced by bubbles of various diameters is universal. These are consistent with the concept that the numerical production of film drops is related physically to the surface area of the bubble film cap. The size spectrum of film drops can be described by a two‐segment power law: d−1/2 and d−2 divided at the droplet diameter d = 90 μm. Many film drops were observed having diameters much greater than the previously suggested diameters, 4–15 μm, separating the dominant contribution of film and jet drops.
A model for microbubble scavenging of surface‐active lipid molecules from seawater
Authors: Skop Richard A. , Viechnicki John T. , Brown John W.
Published: February 2004

We have examined microbubble scavenging of four different types of lipid materials (oleic acid, stearic acid, triolein, and cholesterol) from seawater. These experiments have covered a range of bubble diameters (approximately 200 to 750 μm), bubble Reynolds numbers (approximately 10 to 150), and bubble void fractions (approximately 0.08% to 1.3%). We present here a model which synthesizes the experimental results. The model is based on turbulent diffusion to a single bubble coupled with experimentally determined adsorption kinetics. We have also introduced into the model a factor to account for the dependency of the scavenging observations on bubble void fraction. The introduction of this factor can be anticipated, because the flow hydrodynamics of single bubbles and bubble plumes are quite different. However, these differences are not well enough understood at this time to permit a thorough theoretical explanation of the void fraction factor.
Turbulence closure modeling of estuarine stratification
Authors: Nunes Vaz Richard A. , Simpson John H.
Published: February 2004

Transient stratification in estuaries reflects competition between the stratifying influences of the vertical gravitational circulation and elastic straining of the longitudinal density gradient by vertical shear, set against the mixing influence of, principally, tidally generated turbulence. A one‐dimensional (vertical) numerical model of an estuary, using seven different parameterizations of vertical mass and momentum mixing coefficients from the literature, is used to make general predictions about the nature of the time‐dependent signal of stratification in an estuary. These predictions show good agreement with published predictions from simpler models and they demonstrate that, at higher frequencies (e.g., first and second species tides) stratification is produced primarily from elastic straining but that, at lower frequencies (due to the fortnightly spring‐neap modulation, for example) the estuarine gravitational circulation tends to dominate. The same model, with rotation included, is then used to hindcast a time series of stratification from Spencer Gulf, South Australia, in order to test parameterizations of mixing coefficients against real data. The character of the semidiurnal and diurnal stratification signal is better predicted by some schemes than others. Against qualitative and quantitative criteria, the Mellor and Yamada (1982) and Pacanowski and Philander (1981) schemes perform best. All schemes, however, underpredict the amplitude of the stratification signal at all timescales. At longer timescales, associated with the springs‐neaps cycle, this is believed to be due to a difference in the degree of geostrophic adjustment of the model and the observations, produced by the three‐dimensional topography of the observational site (Spencer Gulf, South Australia).
Calibration of the TOPEX/POSEIDON altimeters at Lampedusa: Additional results at Harvest
Authors: Ménard Y. , Jeansou E. , Vincent P.
Published: February 2004

The Italian Lampedusa island in the Mediterranean Sea was chosen by the Centre National d'Etudes Spatiales (CNES) to support the verification of altimeters on board the TOPEX/POSEIDON satellite. The orbit was phased in such a way that a descending pass overflies a small islet called Lampione, 20 km west of Lampedusa. During the TOPEX/POSEIDON verification phase, until mid‐December 1992, the satellite passed nine times over Lampedusa. The Lampedusa site was equipped with all the required instrumentation to provide independent and accurate knowledge of the altimeter system components: sea level, orbit, and geophysical corrections. In addition, a reprocessing of the altimeter data was performed to better adjust the waveform parameters estimation especially when quasi‐specular echoes due to flat sea conditions have disturbed the on‐board estimation. Three different local orbits computed by expert groups (Centre d'Etudes et de Recherches Geodynamiques et Astronomiques, Delft University of Technology, and Jet Propulsion Laboratory), plus CNES and NASA global orbits were considered. The bias of the CNES altimeter (SSALT) was then calculated, based on six overflights, giving a mean value of 0.7 cm. A SSALT bias also was calculated at Harvest, the NASA calibration site, using six overflights. The deduced bias is 1.3 cm. Integrating both site results gives a mean SSALT bias of 1 cm with an uncertainty of 2.4 cm. The NASA altimeter (ALT) bias computed at Lampedusa is −18.5 cm with an uncertainty of 3.4 cm (the negative sign meaning that the altimeter is measuring short), but this result must be carefully considered because it was obtained with only two overflights. Considering the Lampedusa SSALT calibration results and those derived from statistical repeat track analysis giving an estimation of the relative bias between SSALT and ALT (e.g., Le Traon et al., this issue) a bias of −14.8 cm with an uncertainty of 2.6 cm was found for the ALT altimeter.
The Amazon River Plume during AMASSEDS: Spatial characteristics and salinity variability
Authors: Lentz Steven J. , Limeburner Richard
Published: February 2004

The Amazon River discharge forms a plume of low‐salinity water that extends offshore and northwestward over the north Brazilian shelf. Observations acquired as part of A Multidisciplinary Amazon Shelf SEDiment Study (AMASSEDS) are used to characterize the spatial structure and temporal variability of the Amazon Plume. Four shipboard conductivity‐temperature‐depth (CTD) surveys spanning the shelf from 1°S to 5°N during rising (March 1990), maximum (May 1990), falling (August 1989), and minimum (November 1991) discharge show the Amazon Plume is typically 3 to 10 m thick and 80 to over 200 km wide. Northwest of the river mouth, the plume is often characterized by a wedge of low‐salinity water adjacent to the coast and a separate tongue of low‐salinity water extending offshore over the middle to outer shelf. A bottom front separating the low‐salinity plume water from oceanic water is consistently located between the 10‐ and 20‐m isobaths. A moored array deployed about 300 km northwest of the river mouth from February to June 1990 included inner and midshelf moorings in 18 and 65 m of water on which temperature‐conductivity measurements were made. The moored observations reveal salinity variations within the Amazon Plume of over 10 psu on timescales of days to weeks. This variability includes intermittent events in which plume water pools up in the vicinity of the river mouth and the plume width can exceed 200 km. These accumulation events are apparently due to wind events with a southeastward component which impede or block the normally northwestward freshwater transport. The resulting bulges in the plume are then released northwestward when the wind reverses. Volume budgets indicate the Amazon Plume entrains roughly twice the river discharge between the river mouth at the equator and 3°N. Estimates of gradient Richardson numbers from the moorings suggest entrainment, due to the strong semidiurnal tidal currents, occurs where the plume intersects the bottom and over the outer portion of the plume, where salinities approach oceanic values.
Surface heat flux, horizontal advection, and the seasonal evolution of water temperature on the Scotian Shelf
Authors: Umoh Joseph U. , Thompson Keith R.
Published: February 2004

Seasonal temperature variations on the Scotian Shelf penetrate to a depth of about 75 m. The net surface heat flux (Q) can explain about 85% of the annual cycle in the rate of change of mean temperature over this depth range. The long‐term mean heat budget for a midshelf location shows that horizontal advection (−40 W m−2) is almost exactly balanced by the combined contributions of Q (25 W m−2), horizontal mixing (11 W m−2), and vertical diffusion (6 W m−2). The seasonal evolution of temperature structure on the mid‐Scotian Shelf is modeled with a one‐dimensional vertical diffusion equation, modified to include the effect of horizontal advection. The model features a vertical eddy diffusivity (Kυ) that varies with the background density stratification (N) according to the parameterization Kυ = K0(1 + αNp)−1. The three free parameters (K0, α and p) are estimated by best fitting, in a least squares sense, the predicted temperatures to observations at standard depths between the surface and 100 m. Typical values of Kυ, lie in the range 0.2–20 × 10−4 m2 s−1 with the highest values found in winter and close to the surface, as expected. The root mean square of the differences between observed and predicted monthly temperatures is small and equal to 1.0°C. The root mean square of the errors increases significantly (from 1.0°C to 3.1°C) on fitting with a constant Kυ, highlighting the importance of allowing Kυ, to vary with depth and time. The diffusion model is finally used to examine the role of Q and horizontal advection in the seasonal evolution of the temperature profile on the Scotian Shelf and, in particular, the cold intermediate layer which is a prominent feature of the hydrography on the midshelf.
Oceanic response to the wind forcing associated with the Intertropical Convergence Zone in the northern hemisphere
Authors: Xie Shang‐Ping
Published: February 2004

A zonally oriented band of warm surface water, centered on 10°N and collocated with the atmospheric Intertropical Convergence Zone (ITCZ), is observed in the Atlantic and eastern Pacific Oceans. The annual mean sea surface temperature (SST) in the southern hemisphere, on the other hand, is much lower than that in the warm water band. Such an equatorially asymmetric distribution of SST is considered to be responsible for the persistent stay of the ITCZ in the northern hemisphere. A three‐dimensional ocean general circulation model is used to investigate the maintenance of this high SST band. The model is driven by the wind forcing associated with an idealized zonally symmetric ITCZ in the northern hemisphere. Focusing on the effects of the wind forcing, we assume equatorial symmetry in other atmospheric fields. In such a model the equatorially asymmetric distribution of the wind speed, which affects the ocean through evaporation, is found to be the primary cause of the asymmetric SST distribution. The meridional advection of temperature by the ocean currents affects the latitude of the warm water band. The effects of the eastward advection of the warm western Pacific water by the North Equatorial Countercurrent and of the coastal up welling along the South American coast are also examined.
Eddy kinetic energy of the North Atlantic subpolar gyre from satellite altimetry
Authors: Heywood Karen J. , McDonagh Elaine L. , White Margaret A.
Published: February 2004

The surface eddy kinetic energy field of the North Atlantic subpolar gyre (40–65°N, 5–60°W) is studied using the altimetric satellites Geosat (1987–1988) and ERS‐1 (1992–1993). This is, on the whole, an area of low eddy activity; previous studies of the North Atlantic have usually concentrated on the highly variable Gulf Stream system. We review what is known of the surface circulation of the region. We confirm that there is a close relationship between the eddy kinetic energy and the mean currents and that it is strongly constrained by the topography; the eddy field occurs in deep water and follows the contours, particularly around the Flemish Cap. High eddy kinetic energy is seen on the flanks of topography and is higher where the slope is steeper. This is particularly clear on both east and west flanks of the Rockall Plateau. Interannual changes in the currents are revealed by the differences between the Geosat and ERS‐1 eddy kinetic energy maps. In some years (1988 and 1992–1993) the northern core of the North Atlantic Current (NAC), usually assumed to be tied to the Charlie Gibbs Fracture Zone (52°N), is considerably weaker and may not exist at all, while in 1987 there is a distinct core here. In 1988 and 1992–1993 the main eddy region shifts farther to the south, to about 49°N in 1988 and 50°N in 1992–1993. In 1987 there is also a current core even farther south, centered at about 47°N, implying that in that year the NAC is arranged into two distinct branches.
Sea surface temperature measurements by the along‐track scanning radiometer on the ERS 1 satellite: Early results
Authors: Mutlow C. T. , Závody A. M. , Barton I. J. , Llewellyn‐Jones D. T.
Published: February 2004

The along‐track scanning radiometer (ATSR) was launched in July 1991 on the European Space Agency's first remote sensing satellite, ERS 1. An initial analysis of ATSR data demonstrates that the sea surface temperature (SST) can be measured from space with very high accuracy. Comparison of simultaneous measurements of SST made from ATSR and from a ship‐borne radiometer show that they agree to within 0.3°C. To assess data consistency, a complementary analysis of SST data from ATSR was also carried out. The ATSR global SST field was compared on a daily basis with daily SST analysis of the United Kingdom Meteorological Office (UKMO). The ATSR global field is consistently within 1.0°C of the UKMO analysis. Also, to demonstrate the benefits of along‐track scanning SST determination, the ATSR SST data were compared with high‐quality bulk temperature observations from drifting buoys. The likely causes of the differences between ATSR and the bulk temperature data are briefly discussed. These results provide early confidence in the quantitative benefit of ATSR's two‐angle view of the Earth and its high radiometric performance and show a significant advance on the data obtained from other spaceborne sensors. It should be noted that these measurements were made at a time when the atmosphere was severely contaminated with volcanic aerosol particles, which degrade infrared measurements of the Earth's surface made from space.
The corrections for significant wave height and attitude effects in the TOPEX radar altimeter
Authors: Hayne G. S. , Hancock D. W. , Purdy C. L. , Callahan P. S.
Published: February 2004

The routine ground processing of data from the NASA radar altimeter of TOPEX/POSEIDON includes instrument corrections for the effects of significant wave height and attitude angle changes on the altimeter's estimates of range, backscattered power, and significant wave height. This paper describes how these instrument corrections were generated and how they are applied. Detailed waveform fitting to telemetered waveform samples is used to assess the effectiveness of the corrections. There are several altimeter hardware‐caused small waveform departures from the model waveforms and these departures, designated waveform “features,” are described in detail. A consequence of the waveform features, and their positioning relationship to range rate, is that range data for ground tracks moving toward the equator may differ systematically by about a centimeter compared to range data for ground tracks moving away from the equator. The results and discussion are limited to side A of the redundant altimeter, as only side A has been operated on orbit.
Seasonal and interannual variability of coastal zone color scanner phytoplankton pigments and winds in the eastern tropical Pacific
Authors: Fiedler Paul C.
Published: February 2004

Time series of phytoplankton pigment concentration along coastal and oceanic transects in the eastern tropical Pacific Ocean were derived from coastal zone color scanner monthly composite data for November 1978 through June 1986. Seasonal and interannual variability made up about half the total variance of the time series. Seasonal cycles typically consisted of a spring minimum and fall maximum, although many local variations were observed. Interannual variability was as great as seasonal variability and was dominated by the 1982–1983 El Niño event. The decline in pigment concentration during 1983 was less to the west of the Galapagos than to the east and along the Central American coast. Physical forcing of pigment variability was investigated by testing correlations between pigment concentration and wind variables associated with upwelling and mixing. Seasonal cycles and some interannual changes in pigment concentration were correlated with local wind‐driven processes that cause variation in primary productivity. Correlations between pigments and local winds in oceanic transects were different at seasonal and interannual scales, implying remote forcing at the interannual timescale.
Thorium‐234/uranium‐238 disequilibrium as an indicator of scavenging rates and participate organic carbon fluxes in the Northeast Water Polynya, Greenland
Authors: Cochran J. Kirk , Barnes Christina , Achman Diane , Hirschberg David J.
Published: February 2004

Analyses of particulate and dissolved distributions of the naturally occurring radionuclide 234Th (half‐life=24.1 days) in the water column of the Northeast Water Polynya (Greenland continental shelf) show deficiencies relative to equilibrium with 238U that are related to uptake onto sinking particles. The deficiencies are generally enhanced in the upper 50 m of the water column (Polar Water), a zone of high suspended particle, particulate organic carbon, and pigment concentrations. In July–August 1992, residence times of dissolved Th relative to uptake onto particles ranged from 52 to 293 days and those of particulate Th relative to sinking ranged from 6 to 52 days in the upper 50 m. In contrast, removal was enhanced in July–August 1993, with dissolved and particulate 234Th residence times ranging from 45 to 167 days and 4 to 57 days, respectively. The assumption of steady state used in these calculations is not strictly valid, in that both years showed progressive increases in 234Th removal at stations reoccupied several weeks apart. Spatial variation in 234Th removal from the water column also is evident and may be due, in part, to progressive 234Th removal associated with the inferred anticyclonic circulation within the polynya. Inventories of particulate 234Th in the upper 50 m correlate well with inventories of suspended particulate matter and particulate organic carbon (POC). Using the ratio of POC/234Th on suspended particles and the 234Th fluxes obtained from disequilibrium with respect to 238U to calculate POC fluxes gives values of 12 to 45 (mean = 25±14) mmol C m−2 d−1 in 1992 and 17 to 45 (mean = 35±10) mmol m−2 d−1 in 1993. A direct comparison of the Th‐derived POC fluxes from the 1992 data is possible with those obtained independently based on depletions of dissolved nutrients (29.2±23.5 mmol m−2 d−1 (Wallace et al., this issue)) and dissolved inorganic carbon (14±7.4 mmol m−2 d−1 (Yager et al., this issue)). The good agreement reflects the fact that during the summer, particle cycling and flux in the surface water of the polynya are apparently dominated by biogenic particles. Removal of 234Th from the water column is balanced, within the uncertainties, by inventories of excess 234Th in bottom sediments, with both water column deficiencies and sediment inventories greater in 1993 than 1992. This indicates that on the timescale of several half‐lives of 234Th (∼100 days) the polynya is in balance with respect to 234Th (and probably the particles with which it is associated).
The Northeast Water Polynya as an atmospheric CO2 sink: A seasonal rectification hypothesis
Authors: Yager Patricia L. , Wallace Douglas W. R. , Johnson Kenneth M. , Smith Walker O. , Minnett Peter J. , Deming Jody W.
Published: February 2004

During the multidisciplinary ‘NEW92’ cruise of the United States Coast Guard Cutter (USCGC) Polar Sea to the recurrent Northeast Water (NEW) Polynya (77–81°N, 6–17°W; July–August 1992), total dissolved inorganic carbon and total alkalinity in the water column were measured with high precision to determine the quantitative impact of biological processes on the regional air‐sea flux of carbon. Biological processes depleted the total inorganic carbon of summer surface waters by up to 2 mol C m−2 or about 3%. On a regional basis this depletion correlated with depth‐integrated values of chlorophyll a, particulate organic carbon, and the inorganic nitrogen deficit. Replacement of this carbon through exchange with the atmosphere was stalled owing to the low wind speeds during the month of the cruise, although model calculations indicate that the depletion could be replenished by a few weeks of strong winds before ice forms in the autumn. These measurements and observations allowed formulation of a new hypothesis whereby seasonally ice‐covered regions like the NEW Polynya promote a unique biologically and physically mediated “rectification” of the typical (ice free, low latitude) seasonal cycle of air‐sea CO2 flux. The resulting carbon sink is consistent with other productivity estimates and represents an export of biologically cycled carbon either to local sediments or offshore. If this scenario is representative of seasonally ice‐covered Arctic shelves, then the rectification process could provide a small, negative feedback to excess atmospheric CO2.
Benthic response to water column productivity patterns: Evidence for benthic‐pelagic coupling in the Northeast Water Polynya
Authors: Ambrose William G. , Renaud Paul E.
Published: February 2004

Polynyas, recurring ice‐free areas amid pack or drift ice, are model systems for predicting the potential productivity of pelagic and benthic communities in polar regions. The Northeast Water Polynya on the northeast Greenland continental shelf and surrounding ice‐covered areas were investigated to address the influence of water column processes on the benthos. We measured infaunal density, polychaete biomass, sediment carbon concentration, and benthic pigment concentration from replicate box cores at 16 stations. Benthic pigment concentration is the most important predictor of infaunal density and polychaete biomass, explaining nearly half of the variance in these variables. Benthic pigment concentrations are strongly related to the concentrations of water column pigments, suggesting that the signal of water column productivity is received on the bottom and transmitted to the fauna. The highest densities and biomass are found near the mouth of the Northern Trough and are probably fueled by biogenic material produced by the developing phytoplankton community as it is advected down the trough. Density and biomass are also generally higher under the ice‐free water of the Northern Trough than under the ice‐covered Southern Trough. This pattern may be explained by greater primary productivity in the Northern than Southern Trough and/or by a decoupling of water column and benthic process by Zooplankton grazing in the south. Sediment organic carbon concentration is between 0.5% and 1.5%, indicating that the sediment is probably not an unusually large carbon sink relative to shelf and deep‐sea systems in temperate and polar regions. These results reinforce an emerging pattern of efficient transfer of carbon from water column to benthos in high latitudes. Owing to the abundance of small‐scale and mesoscale areas of enhanced phytoplankton production in the Arctic (e.g., leads, marginal ice zones), benthic biomass in the Arctic Ocean and surrounding seas may be higher than previously anticipated.
Mixed boundary conditions in ocean general circulation models and their influence on the stability of the model's conveyor belt
Authors: Mikolajewicz Uwe , Maier‐Reimer Ernst
Published: February 2004

When driven under “mixed boundary conditions”, coarse resolution ocean general circulation models (OGCMs) generally show a high sensitivity of the present‐day thermohaline circulation against perturbations. We will show that an alternative formulation of the boundary condition for temperature, a mixture of prescribed heat fluxes and additional restoring of the sea surface temperature to a climatological boundary temperature with a longer time constant, drastically alters the stability of the modes of the thermohaline circulation. The results from simulations with the Hamburg large‐scale geostrophic OGCM indicate that the stability of the mode of the thermohaline circulation with formation of North Atlantic deepwater increases, if the damping of sea surface temperature anomalies is reduced, whereas the opposite is true for the mode without North Atlantic deep water formation. It turns out that the formulation of the temperature boundary condition also affects the variability of the model.
Resonant fluidization of silty soil by water waves
Authors: Foda Mostafa A. , Tzang Shiaw‐Yih
Published: February 2004

A new resonant stage is identified in the laboratory during the complex process of soil fluidization by water waves. Massive fluidization failure is consistently observed following internal resonance events inside the silt bed. The weakening effect of this resonance is observed to endure long periods of consolidation. A wave reloading, following such a consolidation period, on a preresonated soil usually results in a recurrence of a similarly massive fluidization failure. Analysis of pore pressure records indicates that the resonance events are localized in space and the associated wave modes are short in wavelengths. It is proposed that these resonant events are a consequence of a strong channeling of the seepage flow within the silt bed.
Influence of the St. Lawrence Island Polynya upon the Bering Sea benthos
Authors: Grebmeier Jacqueline M. , Cooper Lee W.
Published: February 2004

The influence of a polynya, a persistent ice‐free region, on water column production and subsequent transport to the shallow continental shelf benthos of the Bering Sea was evaluated by studying spatial patterns of organic material deposition, benthic biomass, community sediment metabolism, benthic population structure, and other potential indicators of enhanced organic carbon transport to benthic communities underlying the St. Lawrence Island Polynya. Despite suggestions that polynyas may be important localized centers of primary production in polar waters, we found that the St. Lawrence Island Polynya does not obviously enhance the biomass of benthic communities directly below the polynya. However, southward flowing, baroclinic currents generated as a result of brine injection at the polynya edge do appear to have an influence on the biomass and ecological structure of Bering Sea benthic communities south of St. Lawrence Island. These currents appear to affect mean sediment oxygen consumption, surface organic carbon/nitrogen ratios, total organic content, and bottom water ammonia by sweeping phytodetrital matter south and to the west of the island. A particle‐reactive, short‐lived, natural radioisotope, 7Be, used as an indicator of rapid (days to weeks) deposition of particulate material from the water column, was detected only in surface sediments to the southwest of the island, indicating enhancement of particle deposition to the southwest of the island. Finally, the 18O content of tunicate cellulose was highest in the polynya region, consistent with increased filter feeding in the late winter when the polynya is present, and presumably promoting primary production in the open water. The Anadyr Current, consisting of nutrient‐rich, deeper Bering Sea water that is upwelled onto the shelf in the Gulf of Anadyr, flows west to east in the region south of St. Lawrence Island throughout the year and is the major forcing function for high production in the region. The interaction of Anadyr Water with the winter/spring ephemeral polynya and associated baroclinic currents combine to positively influence benthic communities.
Copepod grazing and fine‐scale distribution patterns during the Marine Light‐Mixed Layers experiment
Authors: Cowles Timothy J. , Fessenden Lynne M.
Published: February 2004

The mesozooplankton in the upper 100 m at 59°N, 21°W were dominated by the copepodite stages of Calanus finmarchicus in both May and August 1991. Abundance of C. finmarchicus in the upper 20 m of the water column was 800 m−3 in May and 200 m−3 in August. Although hydrographic conditions changed from well mixed to stratified between May and August, the fine‐scale vertical distribution pattern of C. finmarchicus was essentially the same during these two surveys of the Marine Light‐Mixed Layers site. Copepodite stage five (CV) comprised a larger fraction of the population in August compared to May, however. Gut evacuation experiments with C. finmarchicus indicated that late copepodite and adult female life stages had evacuation rates of approximately 4% h−1 in both May and August. Although these evacuation rates are consistent with others measured for Calanus, the relatively low biomass in the upper 100 m resulted in an estimated daily grazing impact by Calanus of less than 5 % of the phytoplankton standing stock in May, and less than 1% in August. The ingestion rates we measured suggest that the total grazing impact of all mesozooplankton grazers is less than 10% of daily primary production. These relatively low ingestion rates on phytoplankton provide these copepods with less than half of the total daily carbon intake required to balance estimated rates of respiration and growth in the field. In order to balance these metabolic costs, we estimate that the mesozooplankton would need to ingest the equivalent of at least 100% of the estimated microzooplankton/protist daily production.
Currents and transports of the Monsoon Current south of Sri Lanka
Authors: Schott F. , Reppin J. , Fischer J. , Quadfasel D.
Published: February 2004

The zonal monsoon circulation south of India/Sri Lanka is a crucial link for the exchange between the northeastern and the northwestern Indian Ocean. The first direct measurements from moored stations and shipboard profiling on the seasonal and shorter‐period variability of this flow are presented here. Of the three moorings deployed from January 1991 to February 1992 along 80°30′E between 4°11′N and 5°39′N, the outer two were equipped with upward looking acoustic Doppler current profilers (ADCPs) at 260‐m depth. The moored and shipboard ADCP measurements revealed a very shallow structure of the near‐surface flow, which was mostly confined to the top 100 m and required extrapolation of moored current shears toward the surface for transport calculations. During the winter monsoon, the westward flowing Northeast Monsoon Current (NMC) carried a mean transport of about 12 Sv in early 1991 and 10 Sv in early 1992. During the summer monsoon, transports in the eastward Southwest Monsoon Current (SMC) were about 8 Sv for the region north of 3°45′N, but the current might have extended further south, to 2°N, which would increase the total SMC transport to about 15 Sv. The circulation during the summer was sometimes found to be more complicated, with the SMC occasionally being separated from the Sri Lankan coast by a band of westward flowing low‐salinity water originating in the Bay of Bengal. The annual‐mean flow past Sri Lanka was weakly westward with a transport of only 2–3 Sv. Using seasonal‐mean ship drift currents for surface values in the transport calculations yielded rather similar results to upward extrapolation of the moored profiles. The observations are compared with output of recent numerical models of the Indian Ocean circulation, which generally show the origin of the zonal flow past India/Sri Lanka to be at low latitudes and driven by the large‐scale tropical wind field. Superimposed on this zonal circulation is local communication along the coast between the Bay of Bengal and the Arabian Sea.
An improved mixed layer model for geophysical applications
Authors: Kantha Lakshmi H. , Clayson Carol Anne
Published: February 2004

An improved mixed layer model, based on second‐moment closure of turbulence and suitable for application to oceanic and atmospheric mixed layers, is described. The model is tested against observational data from different locations in the global oceans, including high latitudes and tropics. The model belongs to the Mellor‐Yamada hierarchy but incorporates recent findings from research on large eddy simulations and second‐moment closure. The modified expansion of Galperin, Kantha, Hassid and Rosati (1988) that leads to a much simpler and more robust quasi‐equilibrium turbulence model is employed instead of the original Mellor and Yamada (1974) model. Findings from ongoing research at the National Center for Atmospheric Research on large eddy simulations of the atmospheric boundary layer are utilized to improve parameterizations of pressure covariance terms in the second‐moment closure. Shortwave solar radiation penetration is given careful treatment in the model so that the model is applicable to investigations of biological and photochemical processes in the upper ocean. But by far the major improvement is in the inclusion of the shear instability‐induced mixing in the strongly stratified region below the oceanic mixed layer that leads to a more realistic and reliable mixed layer model that is suitable for application to a variety of geophysical mixed layers and circulation problems. The model appears to predict the mixing in the upper ocean well on a variety of time scales, from event scale storm‐induced deepening and diurnal scale variability to seasonal time scales. With proper attention to the heat and salt balances in the upper ocean, it should be possible to use it for simulations of interannual variability as well. While the model validation has been primarily against oceanic mixed layer data sets, it is believed that the improvements can be readily incorporated into a model of the atmospheric boundary layer as well.
A numerical model of Arctic leads
Authors: Kantha Lakshmi H.
Published: February 2004

Arctic leads are thought to play an important role in the air‐sea heat exchange at high latitudes. The evolution of the local ice‐ocean‐atmosphere coupled system, when a lead opens up and immediately begins to refreeze, is of considerable interest in terms of the heat exchanged by the ocean to the atmosphere, as well as the amount of salt extruded into the oceanic mixed layer. Here we will present a coupled model of the ice‐ocean system that provides a quantitative description of a refreezing lead, especially the evolution of the ice cover and the mixed layer below. The model is applied and compared with what has been learned from the Lead Experiment (LEADEX) observations in the April of 1992 in the Beaufort Sea. The results suggest that Arctic leads, especially during winter, are, in general, close to a state of free convection. Strong convection driven by the extruded brine in a refreezing lead drives vigorous mixing in the mixed layer immediately below, irrespective of the advective velocity of ice. Turbulence intensities reach quite high values during the initial phases of refreezing but weaken gradually with a half‐life time of about 2 days. Inertial oscillations are superimposed on the resulting currents and are especially vigorous below the mixed layer. The ice builds up to a thickness of over 12 cm in the first 24 hours in a refreezing lead, in accordance with LEADEX observations, with a significant contribution coming from frazil ice formation in the supercooled water below. Not surprisingly, since the water below is at or close to freezing, advection of water masses past the lead due to ice motion or prevailing currents does not alter the refreezing rate substantially, even though the frazil ice contribution shows a significant increase. Advection does affect the local properties in the mixed layer immediately below and downstream of the lead. For example, the increase in salinity, an indicator of the intensity of the refreezing process in a lead, depends very much on the motion of ice cover relative to the underlying water. For large advective velocities the salinity increase is an order of magnitude smaller than the purely convective situation and the turbulence is dominated by that generated by shear underneath the rough ice, upstream of the lead which tends to mask that generated by convection in the lead itself. For a stationary lead, refreezing gives rise to an inward jet underneath the ice and outward flow at the base of the mixed layer. Vertical motion is in the form of convective cells centered at the lead edges.
The Atlantic Deep Western Boundary Current: Water masses and transports near the equator
Authors: Rhein Monika , Stramma Lothar , Send Uwe
Published: February 2004

The distributions and transports of deepwater masses at the western boundary in the tropical Atlantic off Brazil have been studied on three surveys along 35°W and 5°S and one at 10°S. Transports are obtained from direct measurements of the velocity fields (Pegasus profiling system and lowered acoustic Doppler current profiler) and from geostrophic computations. Using chlorofluoromethane (CFM) and hydrographic distributions, four water masses could be identified forming the North Atlantic Deep Water (NADW) system. Two of these have a high CFM content, the “shallow upper NADW” (SUNADW) and the “overflow lower NADW” (OLNADW). These exhibit the highest velocity signals at 35°W, where distinct flow cores seem to exist; most of the southeastward flow of the SUNADW (centered around 1600 m) occurs 320 km offshore between 3°09′S and 1°50′S (9.7±3.3 Sv); farther north in that section, a highly variable reversing flow is found in a second velocity maximum. The transport of OLNADW (centered around 3800 m) of 4.6±2.6 Sv is guided by the Parnaiba Ridge at 1°45′S, 35°W. The water masses located between the two CFM maxima, the Labrador Sea Water (LSW) and the LNADW old water mass (LNADW‐old), did not show any persistent flow features, however, a rather constant transport of 11.1±2.6 Sv was observed for these two layers. The total southeastward flow of the NADW at 35°W showed a transport of 26.8±7.0 Sv, if one neglects the reversing SUNADW north of 1°50′S. At 5°S the flow of all deepwater masses shows vertically aligned cores; the main southward transport occurred near the coast (19.5±5.3 Sv). The boundary current is limited offshore by a flow reversal, present in all three surveys, but located at different longitudes. At 10°S a southward transport of 4.7 Sv was observed in November 1992. However, the section extended only to 32°30′W, so that probably a significant part of the flow has been missed. An important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35°W, which could lead to large uncertainties in the interpretation of single cruise observations. Despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations.
Influence of mid‐ocean ridges on Rossby waves
Authors: Wang Liping , Koblinsky Chester J.
Published: February 2004

Influence of mid‐ocean ridges on Rossby wave activity is discussed in simple models. Ridges can influence Rossby waves in two ways, topographic scattering and mid‐ocean local generation. It is found that both processes are rather sensitive to model parameters such as frequency, ridge height, and ridge width in both barotropic and baroclinic models. In the barotropic model, for certain model parameters there is perfect transmission of Rossby waves, while for some other model parameters the transmission is rather weak. In a two‐layer model, if the frequency is not low enough, trapping of baroclinic signals around topography will occur. The mid‐ocean ridge is generally not as efficient as the eastern boundary in generating barotropic waves except at high frequencies in a barotropic model. It is much more efficient than the eastern boundary in generating baroclinic waves when wind forcing has a very large zonal scale, while less efficient when wind forcing has a short zonal scale.
Imaging of oceanic features by ERS 1 synthetic aperture radar
Authors: Nilsson Carl S. , Tildesley Paul C.
Published: February 2004

Data from the European Space Agency's ERS 1 satellite synthetic aperture radar (SAR) covering the region of the East Australian Current during late 1991 have been analyzed in conjunction with ship and airborne data and infrared imagery. Apart from wind effects, the largest differences in backscatter seem to be associated with different water masses, these differences probably being caused by wave damping due to natural surfactants. Slicklike features in the Tasman Sea are common, even in the deep ocean, when the winds are light. Ocean currents are often visible but as relatively subtle features. It is unlikely that changes in atmospheric boundary layer stability due to changing sea surface temperature are the dominant mechanism for radar imaging of ocean currents. It is suggested that C band radar backscatter will prove to be more directly correlated with biological activity (and ocean color) than with sea surface temperature, particularly at higher latitudes. Surfactants could cause errors of 20% or more in wind speeds derived from satellite scatterometers.
Lead‐induced atmospheric circulations
Authors: Alam Afshan , Curry Judith
Published: February 2004

Leads provide a significant source of heat and moisture to the Arctic winter atmosphere, and plumes from wide leads have been observed to penetrate the Arctic inversion. We have developed a two‐dimensional, high‐resolution, deep anelastic numerical model to investigate the atmospheric convection from leads with widths ranging from 100 m to 10 km. A second‐order turbulence closure scheme is used to parameterize the atmospheric turbulence in the horizontally inhomogeneous system. This study describes how the lead‐induced circulations can enhance the vertical transport of heat into the atmospheric boundary layer. This model is compared with large‐eddy simulation results and with lidar observations of a lead‐induced ice crystal plume. The model is used to study the effect of varying lead widths and ambient atmospheric conditions on the resultant convection from leads, and some preliminary results are described.
On the origins of deep and bottom waters of the Indian Ocean
Authors: Mantyla Arnold W. , Reid Joseph L.
Published: February 2004

The characteristics of the deep and bottom waters of the Indian Ocean, when illustrated on potential‐density anomaly surfaces, indicate that the waters enter from both the Atlantic and Pacific Oceans. The paths of spreading are constrained by the complex topography, and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments, especially in the northern Indian Ocean. The Weddell Sea contributes to the densest waters found in the western basins and the Ross Sea and Adelie coast to the densest waters found in the eastern basins. Both dense water varieties are altered by and incorporated in the less dense water above; initially, water carried by the circumpolar current, then water from the north Atlantic, and finally by deep water whose characteristics are derived in the northern Indian Ocean. Contact with the sediments increases the silica content of the bottom water in the Southern Ocean. In the northern Indian Ocean the sediments alter the silica of the water at the bottom and, together with enhanced salinity from diffusion of saline overflows from the marginal seas above, imprint unique markers to the deep water that flows back to the south. At middepths the series of ridges between Madagascar and Australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern Indian Ocean characteristics southward. Within the circumpolar current, low‐oxygen deep water from the Pacific is carried across the Atlantic and into the Indian Ocean south of Africa. Part flows around the cyclonic Weddell Sea Gyre, and part extends across the Southern Ocean. Water from another Pacific source can be seen near 2000 m extending westward from the Tasman Sea, south of Australia and across the Indian Ocean, and perhaps to the Aghulas Current region southeast of Africa.