bluuebunny/crossref_metadata_2025 huggingface dataset:
Nutrients and chlorophyll at the shelf break off the southeastern United States during the Genesis of Atlantic Lows Experiment: Winter 1986
Authors: Atkinson L. P. , Miller J. L. , Lee T. N. , Dunstan W. M.
Published: February 2004

The outer shelf and upper slope off Charleston, South Carolina, were the site of oceanographic and meteorological measurements during the winter of 1986. The purpose of the study was to test ideas about front formation, heat transport, and stratification during cold air outbreaks. An ancillary part of the study was the observation of nutrients and chlorophyll concentrations. The observations extended across the shelf and sometimes crossed the Gulf Stream front. The results show slightly elevated nitrate concentrations in outer shelf waters (1–2μM NO3) with chlorophyll concentrations in the 1–1.8μg L−1 range. When effects of Gulf Stream frontal eddies are eliminated, the estimated wintertime wind‐driven transport of nutrients from the deep ocean to the shelf is comparable to that observed during spring and summer. Thus significant onshore nutrient transport can occur throughout the year in this region.
Circulation, mixing, and exchange processes in the vicinity of tidal inlets: A numerical study
Authors: Kapolnai Andras , Werner Francisco E. , Blanton Jackson O.
Published: February 2004

The circulation in the vicinity of an idealized tidal inlet connecting a continental shelf and a coastal sound is examined. The circulation is forced by anM2tide and a weakly buoyant discharge. The buoyant discharge forms a plume in the coastal ocean and induces a distinct anticyclonic circulation at the plume edge that is maintained throughout the tidal cycle. We focus on the plume's onset and its evolution over 5–10 tidal cycles. Over the timescales considered, the plume was roughly circular, slightly skewed in the along‐coast direction. The model solution yielded high vertical Ekman numbersEϵ∼O(5) in the vicinity of the inlet mouth, decreasing seaward from the inlet to an order of magnitude smaller (Eϵ∼ 0.25) at the seaward edge of the plume. Passive particles released in the region seaward of the inlet mouth were used to describe the exchange between the coastal region and the inlet. A marked asymmetry between ebb and flood flows is observed in the vicinity of the inlet, with jet‐like ebbing currents and weaker potential‐flow‐like flooding currents. Over a tidal cycle, net exchanges between the coastal ocean and the inlet are found to be spatially and temporally dependent; that is, particle trajectories depend on the release point and the time of the release in the tidal cycle. The near‐inlet residual circulation shows significant differences in the absence of stratification.
Bottom shear stress in the surf zone
Authors: Cox Daniel T. , Kobayashi Nobuhisa , Okayasu Akio
Published: February 2004

To investigate the bottom shear stress in the surf zone, detailed laboratory measurements were made of the free surface elevations and velocities for the case of regular waves spilling on a rough, impermeable 1:35 slope. The velocity profiles were measured at several vertical lines in the cross‐shore direction to include the shoaling region seaward of breaking, the break point, the transition region, and the inner surf zone. Each vertical line included measuring points at a fraction of the grain height above the rough, fixed bottom. A logarithmic layer was found to exist in the bottom boundary layer for most of the phases over a wave period seaward of the break point and in the surf zone. A regression analysis was used at each phase to estimate the shear velocity and bottom roughness from the phase‐averaged horizontal velocities in the lower portion of the bottom boundary layer. The bottom friction factor was estimated from a quadratic friction equation based on the measured horizontal velocity above the bottom boundary layer together with the estimated shear velocity. The quadratic friction equation with the fitted friction factor was shown to predict the temporal variation of the bottom shear stress within a factor of 2. The bottom roughness estimated from the grain size assuming rough turbulent flow was shown to agree qualitatively with the measured values. The cross‐shore variation of the friction factor estimated from an empirical formula developed for nonbreaking waves was shown to agree within a factor of 2 of the measured values.
Variability of water masses in the western Indian Ocean
Authors: Morales Ruben A. , Barton Eric D. , Heywood Karen J.
Published: February 2004

In 1987, conductivity‐temperature‐depth and current data were collected in two oceanographic surveys carried out around the Indian Ocean coral atolls of Aldabra (46° 20′ E, 9° 25′ S) and Cosmoledo (47° 30′ E, 9° 45′ S) between April and July. During the surveys, significant changes were observed in the temperature and salinity of the upper layers. From temperature‐salinity analysis, the dominant water masses in the upper layers (0–400 m) were categorized and their origin determined. During the first cruise, TS characteristics changed only slightly. Low salinity waters (S = 34.5–34.6 and T = 28°–30°C), brought from the east by the South Equatorial Current, were dominant in the surface layers. During the second cruise, the surface waters were saltier and cooler (S = 35.1 and T = 25°–26°C) and more homogeneous in the upper 200 m as a result of a greater admixture of a southern water mass. Seasonal cooling at this time was responsible for a deeper surface mixed layer. Near the end of the cruise, TS conditions changed suddenly due to an invasion of southern subtropical water masses in the layers above 200 m. Current meter records were dominated by the regional 50‐day oscillation and higher‐frequency variability and did not show the expected increase in strength of the South Equatorial Current to indicate onset of the southwest monsoon. The water mass changes were not correlated with changes in the local currents and were probably caused by advection of patches by the large‐scale flow.
Viewing a cold air outbreak using satellite‐based synthetic aperture radar and advanced very high resolution radiometer imagery
Authors: Mourad Pierre D. , Walter Bernard A.
Published: February 2004

In this phenomenological study we compare nearly simultaneous visible‐wavelength advanced very high resolution radiometer (AVHRR) and synthetic aperture radar (SAR) images of a cold air outbreak that occurred off the ice pack in the Bering Sea. The visible image shows the spatial evolution of the cloud structure from the ice edge to several hundred kilometers offshore. Near the ice edge, the clouds form regular linear features, known as cloud streets. These streets are spaced about 5 km apart, 5 times the depth of the boundary layer. By 200 km offshore, the visible image shows nascent, closed‐cell, mesoscale cellular convection (MCC), with connected disks and smears of white clouds surrounded by arcs and rings of dark, cloud‐free regions. The diameters of the disks range between 10 and 15 km. The SAR image shows the same, broadly defined spatial pattern but with a substantial increase in detail uncorrelated with the AVHRR image. In the area of the cloud streets shown in the AVHRR image are two‐dimensional, elongated regions of enhanced radar backscatter, called SAR streaks, with the same cross‐wind spacing as the cloud streets. This suggests the presence of quasi‐two‐dimensional roll vortices in the atmospheric boundary layer. Downstream, in the area of proto‐MCC, are broadly spaced expanses of enhanced backscatter that form two‐dimensional patterns, such as connected arcs that have structure and scales similar to the spaces between the clouds. The spatial evolution of the streaks and streets broadly conforms to the patterns of downdrafts and updrafts, respectively, exhibited in modeling studies of cold air outbreaks. However, the comparison with modeling studies is more successful for the cloud streets than for the SAR streaks. We suggest that this difference is because the clouds in the AVHRR images give a time‐integrated signal of large‐scale, quasi‐two‐dimensional atmospheric turbulence, whereas mesoscale radar patterns of surface roughness give a relatively instantaneous view of fundamentally three‐dimensional structure within the atmospheric boundary layer.
Subtidal bottom pressure observed at Axial Seamount in the northeastern continental margin of the Pacific Ocean
Authors: Mofjeld H. O. , González F. I. , Eble M. C.
Published: February 2004

Since September 1987, bottom pressure (BP) has been observed at Axial Seamount (45°57.5′N, 130°00.3′W; 1540‐m depth), located 450 km off the Oregon Coast on the Juan de Fuca Ridge. Observations from 1987 to 1992 show that subtidal Axial BP is dominated by barotropic 2‐ to 5‐mbar fluctuations with frequencies ≤ 1/9 cycles per day (cpd). They are slightly smaller than subtidal BP observed 720 km to the west during the Ocean Storms Experiment and a factor of 2–4 smaller than the subtidal fluctuations of adjusted sea level (ASL) at the coast. For the period September 1987 to July 1988, Axial BP and Ocean Storms BP are significantly coherent (coh2 ≥ 0.5), except at intraseasonal frequencies (1/100–1/20 cpd) and in a band (1/8–1/6 cpd) of low Axial BP variance. In the coherent frequency bands, the phase relationships between the two BP series suggest independent atmospheric forcing. On the other hand, Axial BP and coastal ASL are not coherent except at the fortnightly tidal frequency. Looking for possible forcing of Axial BP by the curl of the wind stress (curl) over the NE Pacific, data analyses show that Axial BP and curl (derived from European Centre for Medium‐Range Weather Forecasts winds) are significantly coherent in only two frequency bands: one band narrowly peaked near 1/9.1 cpd for curl in regions south of Axial Seamount and a 1/5–1/3.5 cpd band for curl in a large region NW of the seamount. In the 1/5–1/3.5 band, Axial BP also has a small‐amplitude spectral peak associated with bottom‐trapped (baroclinic) currents near Axial Seamount. Remote Axial BP/curl coherence at some frequencies is qualitatively consistent with the local‐forcing theory of Lippert and Müller [1995] that attributes the coherence to stable phase relationships and the spatial characteristics of the BP/curl transfer function. However, the Axial BP/curl comparison is inhibited by the lack of accurate estimates of curl within 400 km of the coast. Fully understanding the origins and dynamics of subtidal BP at Axial Seamount will require a knowledge of how the complex topography in the region affects the barotropic and baroclinic responses to atmospheric forcing, as well as the propagation of Rossby and other waves.
Mapping tropical Pacific sea level: Data assimilation via a reduced state space Kalman filter
Authors: Cane Mark A. , Kaplan Alexey , Miller Robert N. , Tang Benyang , Hackert Eric C. , Busalacchi Anthony J.
Published: February 2004

The well‐known fact that tropical sea level can be usefully simulated by linear wind driven models recommends it as a realistic test problem for data assimilation schemes. Here we report on an assimilation of monthly data for the period 1975–1992 from 34 tropical Pacific tide gauges into such a model using a Kalman filter. We present an approach to the Kalman filter that uses a reduced state space representation for the required error covariance matrices. This reduction makes the calculation highly feasible. We argue that a more complete representation will be of no value in typical oceanographic practice, that in principle it is unlikely to be helpful, and that it may even be harmful if the data coverage is sparse, the usual case in oceanography. This is in part a consequence of ignorance of the correct error statistics for the data and model, but only in part. The reduced state space is obtained from a truncated set of multivariate empirical orthogonal functions (EOFs) derived from a long model run without assimilation. The reduced state space filter is compared with a full grid point Kalman filter using the same dynamical model for the period 1979–1985, assimilating eight tide gauge stations and using an additional seven for verification [Miller et al., 1995]. Results are not inferior to the full grid point filter, even when the reduced filter retains only nine EOFs. Five sets of reduced space filter assimilations are run with all tide gauge data for the period 1975–1992. In each set a different number of EOFs is retained: 5, 9, 17, 32, and 93, accounting for 60, 70, 80, 90, and 99% of the model variance, respectively. Each set consists of 34 runs, in each of which one station is withheld for verification. Comparing each set to the nonassimilation run, the average rms error at the withheld stations decreases by more than 1 cm. The improvement is generally larger for the stations at lowest latitudes. Increasing the number of EOFs increases agreement with data at locations where data are assimilated; the added structures allow better fits locally. In contrast, results at withheld stations are almost insensitive to the number of EOFs retained. We also compare the Kalman filter theoretical error estimates with the actual errors of the assimilations. Features agree on average, but not in detail, a reminder of the fact that the quality of theoretical estimates is limited by the quality of error models they assume. We briefly discuss the implications of our work for future studies, including the application of the method to full ocean general circulation models and coupled models.
Modeling nutrient and plankton processes in the California coastal transition zone: 1. A time‐ and depth‐dependent model
Authors: Moisan J. R. , Hofmann E. E.
Published: February 2004

A time‐ and depth‐dependent, physical‐bio‐optical model was developed for the California coastal transition zone (CTZ) with the overall objective of understanding and quantifying the processes that contribute to the vertical and temporal development of nutrient and plankton distributions in the CTZ. The model food web components included silicate, nitrate, ammonium, two phytoplankton size fractions, copepods, doliolids, euphausiids, and a detritus pool. The wavelength‐dependent subsurface irradiance field was attenuated by seawater and phytoplankton pigments. The one‐dimensional (1‐D) model adequately simulated the development and maintenance of a subsurface chlorophyll maximum in different regions within the CTZ. An analysis of the individual terms in the model governing equations revealed that phytoplankton in situ growth was primarily responsible for the creation and maintenance of the subsurface chlorophyll maximum at both coastal and oceanic regions in the CTZ. The depth to which the maximum in situ growth occurred was controlled by the combined effect of light and nutrient limitation. Also, the simulated bio‐optical fields demonstrated the effect of nonlinear couplings between food web components and the subsurface irradiance field on vertical biological distributions. In particular, the e‐folding scale of the subsurface photosynthetically available radiation (PAR) was influenced by the level of zooplankton grazing.
Global verification of critical depth theory for phytoplankton bloom with climatological in situ temperature and satellite ocean color data
Authors: Obata Atsushi , Ishizaka Joji , Endoh Masahiro
Published: February 2004

An investigation is made of the global relationship between seasonal variations of the surface mixed‐layer depths derived from monthly climatological hydrographic data and seasonal variations of the surface pigments from monthly satellite ocean color data. At middle and high latitudes of the western North Pacific and the North Atlantic, shallowing of the mixed‐layer depth from winter to spring largely explains basin‐scale features of the spring bloom of phytoplankton in terms of Sverdrup's critical depth theory. In these areas the spring bloom occurs from middle to high latitudes along with the increase of insolation from winter to spring. In the eastern North Pacific and the Southern Ocean the absence of a spring bloom is difficult to explain using the critical depth theory because Sverdrup's parameters are treated as constants, which in nature vary with physiological and ecological conditions. At northern latitudes the termination of fall bloom corresponds to a deepening in the mixed layer beyond the critical depth. Sverdrup's critical depth theory is found useful as a first step in examining the general pattern of phytoplankton seasonality.
Basin‐wide distributions of chlorofluorocarbons CFC‐11 and CFC‐12 in the North Pacific: 1985–1989
Authors: Warner Mark J. , Bullister J. L. , Wisegarver D. P. , Gammon R. H. , Weiss R. F.
Published: February 2004

All of the dissolved chlorofluorocarbon measurements made between 1985 and 1989 along several long zonal and meridional hydrographic sections in the North Pacific are presented in this manuscript. Chlorofluorocarbon (CFC) concentrations are displayed as functions of depth and density along the sections. Over much of the region studied, dissolved CFCs are observed to have penetrated to densities greater than those that outcrop at the surface in the North Pacific (σθ > 26.8). Maxima in CFC concentration are associated with remnant winter mixed layers and with mode waters. When the observed CFC concentrations from these sections are normalized to a common date and mapped onto five density surfaces in the North Pacific, it becomes apparent that the Sea of Okhotsk is an important location for the ventilation of the intermediate waters of the North Pacific. The CFC observations are used together with hydrographic data to study the pathways and timescales of circulation and ventilation processes in the upper and intermediate waters of the North Pacific. Using models of the increases of these compounds as a function of time, CFC “apparent ages” are calculated on these isopycnal surfaces. The CFC apparent ages are used together with observed apparent oxygen utilization to estimate oxygen utilization rates along these sections.
Seasonal variability of particulate organic radiocarbon in the northeast Pacific Ocean
Authors: Druffel Ellen R. M. , Bauer James E. , Williams Peter M. , Griffin Sheila , Wolgast David
Published: February 2004

We present Δ14C measurements of particulate organic carbon (POC) collected on four cruises at our time series site (station M) in the northeast Pacific Ocean. We observe a large gradient with depth in the suspended POC Δ14C values (124–160‰). These profiles display lower Δ14C values (by 20–30‰) in samples between 2500 m and the bottom during June 1992 and July 1993 than those during February and October 1992. Values of Δ14C in sinking POC from deep‐moored sediment trap collections suggest a semiannual trend that displays lower overall Δ14C in material collected during periods of high flux. A limited number of Δ14C measurements of small swimmers picked from the trap 650 m above bottom are similar to surface Δ14C measurements of dissolved inorganic carbon (DIC) and suspended POC, indicating a surface carbon source. Overall, we postulate that the major process causing lower Δ14C values of deep suspended and sinking POC is sorption (or biological incorporation) of “old” DOC onto particulate matter. There appears to be a higher ratio of DOC sorbed to sinking particulate matter at times of high flux (late spring and early fall) that can be thought of as a “stripping out” of DOC from the water column. The DIC Δ14C display a small seasonal variation in the surface waters and is not the sole source of the observed seasonality in the POC Δ14C signals.
Temperature‐nitrate relationships in the central and eastern tropical Pacific
Authors: Chavez Francisco P. , Service Susan K. , Buttrey Samuel E.
Published: February 2004

The relationship between temperature and nitrate in the upper 200 m of the central and eastern tropical Pacific was investigated using regression techniques, and the slope of this relationship was compared along spatial and temporal dimensions. In the open‐ocean waters of the eastern and central Pacific, variation in the slope of the temperature‐nitrate (TN) relationship was primarily north‐south, with the steepness of the slope decreasing to the south. In the more coastal waters of the southeastern Pacific, however, the slope showed strong gradients in the east‐west direction, with the slope steepening from west to east. Seasonal trends in the slope of the TN relationship were examined along the equator. During March–May the relatively flat slope of the TN relationship that is found year‐round in the central Pacific is found to extend further east, associated with the intensification and shoaling of the Equatorial Undercurrent during this same period. Regressions predicting nitrate from temperature were tested on new data and errors of prediction were low for open‐ocean locations (1.4 μM); however, errors increased (to 3.2–4.3 μM) with proximity to coastal waters, reflecting the increasing and variable contribution of nitrate uptake by phytoplankton.
Local ocean response to a multiphase westerly wind burst: 1. Dynamic response
Authors: Smyth W. D. , Hebert D. , Moum J. N.
Published: February 2004

The dynamic response to a westerly wind burst which occurred during the Coupled Ocean Atmosphere Response Experiment in the warm pool of the equatorial Pacific Ocean is described using velocity, hydrography, and microstructure measurements. Turbulent fluxes distributed momentum input from the wind over a near‐surface layer of variable thickness. Coriolis and pressure gradient terms combined to induce a wavelike response whose frequency was close to the local inertial frequency. Wind stress variations on near‐inertial timescales interfered both constructively and destructively with the wave response, exerting considerable influence on the observed currents.
North Pacific Ocean CO2 disequilibrium for spring through summer, 1985–1989
Authors: Landrum Laura L. , Gammon Richard H. , Feely Richard A. , Murphy Paulette P. , Kelly Kimberly C. , Cosca Catherine E. , Weiss Ray F.
Published: February 2004

Extensive measurements of CO2 fugacity in the North Pacific surface ocean and overlying atmosphere during the years 1985–1989 are synthesized and interpreted to yield a basin‐wide estimate of ΔfCO2. The observations, taken from February through early September, suggest that the subtropical and subarctic North Pacific is a small sink for atmospheric CO2 (0.07 to 0.2 Gton C (half year)−1 for the region north of 15°N). Objective analysis techniques are used to estimate uncertainty fields resulting from constructing basin‐wide contours of oceanic fCO2 on the basis of individual cruise transects. The uncertainties are significant and imply that future sampling programs need to recognize that estimating oceanic uptake of anthropogenic CO2 from ship‐transect observations of oceanic fCO2 alone will require very extensive sampling.
Combined analysis of the radar cross‐section modulation due to the long ocean waves around 14° and 34° incidence: Implication for the hydrodynamic modulation
Authors: Hauser Danièle , Caudal Gérard
Published: February 2004

The analysis of synthetic aperture radar observations over the ocean to derive the directional spectra of the waves is based upon a complex transfer function which is the sum of three terms: tilt modulation, hydrodynamic modulation, and velocity bunching effect. Both the hydrodynamic and the velocity bunching terms are still poorly known. Here we focus on the hydrodynamic part of the transfer function, from an experimental point of view. In this paper a new method is proposed to estimate the hydrodynamic modulation. The approach consists in analyzing observations obtained with an airborne real‐aperture radar (called RESSAC). This radar (C band, HH polarized, broad beam of 14° × 3°) was used during the SEMAPHORE experiment, in two different modes. From the first mode (incidence angles from 7° to 21°) the directional spectra of the long waves are deduced under the assumption that the hydrodynamic modulation can be neglected (small incidence angles) and validated against in situ measurements. From the second mode (incidence angle from 27° to 41°) the amplitude and phase of the hydrodynamic modulation are deduced by combining the measured signal modulation spectrum at a mean incidence angle of 34° and the directional wave spectrum obtained from the first mode. The results, obtained in four different wind‐wave cases of the SEMAPHORE experiment, show that the modulus of the hydrodynamic modulation is larger than that of the tilt modulation. Furthermore, we find that the modulus of the hydrodynamic transfer function is several times larger (by a factor 2–12) than the theoretical value proposed in previous works and 1.5–2.5 larger than experimental values reported in recent papers. The phase of the hydrodynamic modulation is found to be close to zero for waves propagating at an angle from the wind direction and between −20° and −40° for waves propagating along the wind direction. This indicates a significant influence of the wind‐wave angle on the phase of the hydrodynamic modulation, in agreement with experimental results reported in recent papers.
Ocean surface features and currents measured with synthetic aperture radar interferometry and HF radar
Authors: Graber Hans C. , Thompson Donald R. , Carande Richard E.
Published: February 2004

This paper describes the results of the first quantitative comparison between high‐resolution ocean surface current fields extracted from interferometric synthetic aperture radar (INSAR) measurements and those from a high‐frequency (HF) ocean surface current radar (OSCR) system. Data from each of these radar systems along with supporting measurements from shipboard and buoy‐mounted sensors were collected during the High‐Resolution Remote Sensing Experiment (High‐Res) on June 20, 1993, on the continental shelf off the coast of Cape Hatteras, North Carolina. Both components of the surface current were obtained from the INSAR system at roughly 10‐m resolution from two orthogonal flight legs over the region separated in time by about 30 min. The OSCR system measured two‐dimensional surface current vectors at about 1‐km resolution over this same region, while the USNS Bartlett was collecting hydrographic samples and near‐surface current measurements. Two‐dimensional wave spectra as well as meteorological and additional current measurements were collected at two buoys within the experimental area. We discuss in the paper two techniques for eliminating the effect of surface wave motion on the INSAR current estimates. One method relies on some knowledge of the local wind and wave field and the use of a microwave scattering model. The other method makes use of a few in situ current measurements spaced at different range locations across the INSAR image. Using either of these techniques, we find that the agreement between the INSAR and OSCR current estimates is generally very good. Furthermore, the INSAR current and magnitude imagery show the presence of undulating surface features where abrupt changes in the current speed and direction occurred. The ship surveys indicate that these features were caused by the collision of water masses of different density. We show for the first time in this paper a high‐resolution, area‐extensive vector surface current map derived from the INSAR of the two‐dimensional flow in the vicinity of these features. Our results demonstrate convincingly that high‐resolution oceanic surface current vectors can be derived from INSAR current measurements and that these measurements may be very beneficial for detailed studies of the dynamics of small‐scale surface features in regions of strong current divergences or shears.
Air‐snow exchange investigations at Summit, Greenland: An overview
Authors: Dibb Jack E. , Jaffrezo Jean‐Luc
Published: February 2004

The Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project (GRIP) deep drilling programs at Summit, Greenland included support (both logistical and scientific) of extensive investigation of atmospheric transport and air‐snow exchange processes of gases and particles relevant to the interpretation of the ice‐core records. Much of the sampling for the air‐snow exchange investigations was conducted at a unique solar‐powered camp 30 km southwest of the GISP2 drill camp (even further from the GRIP camp) and was characterized by a high degree of international collaboration and cooperation. The wide range of expertise and analytical capabilities of the 20‐plus investigators participating in these studies has provided important insight into the meteorological, physical, and chemical processes which interact to determine the composition of snow and firn at Summit. Evolving understanding of this system will allow improved reconstruction of the composition of the atmosphere over Greenland in the past from the detailed Summit ice‐core records. This paper provides an overview of air‐snow exchange investigations at Summit, including their development through the course of the drilling programs (1989–1993), significant findings related to both air‐snow exchange issues and the present state of the Arctic free troposphere, as well as the major outstanding questions which are being addressed in ongoing experiments at Summit.
Aspects of climate variability in the North Atlantic sector: Discussion and relation to the Greenland Ice Sheet Project 2 high‐resolution isotopic signal
Authors: Barlow L. K. , Rogers J. C. , Serreze M. C. , Barry R. G.
Published: February 2004

This paper reviews aspects of climate variability in the North Atlantic sector that may influence the seasonal to decadal scale isotopic signal in the Greenland Ice Sheet Project 2 (GISP2) ice core. Interpretation of the isotopic signal and its spatial applicability at the seasonal level requires investigation into synoptic scale climatology. We discuss possible climatic influences of (1) likely source regions of precipitation reaching the GISP2 site, (2) the characteristics of cyclone activity over the North Atlantic sector, and (3) changes in major atmospheric features such as the mean sea level Icelandic Low and Azores High pressure systems, the North Atlantic Oscillation, and the Baffin trough. Next, we evaluate correlations between the GISP2 deuterium isotopic signal and coastal temperatures with atmospheric pressure patterns, thereby deriving climatic interpretations of the high‐resolution isotopic record. The GISP2 site is influenced by both the Icelandic Low to the southeast and Davis Strait/Baffin Bay storms to the southwest and west. The North Atlantic Oscillation influences the GISP2 isotopic signal through the seesaw in winter temperatures between west Greenland and northern Europe. Agreement in excursion directions of GISP2 isotopes and east Greenland and Iceland temperature records is associated with different positions of the Baffin trough in winter and also with anomalous 500‐mbar net geostrophic flow. Linkages between isotopic excursion direction and atmospheric variability need to be explored further by comparison with additional seasonal data sets from other Greenland ice cores.
Reducing the effects of fouling on chlorophyll estimates derived from long‐term deployments of optical instruments
Authors: Davis R. F. , Moore C. C. , Zaneveld J. R. V. , Napp J. M.
Published: February 2004

Two methods to alleviate the problem of fouling of moored flow tube optical instruments are presented. A chemical method diffuses a concentrated solution of bromine into the flow tube between sampling periods, creating a toxic environment for microorganisms. An optical method removes a baseline value from the red peak of chlorophyll a. Three spectral absorption meters equipped with the chemical system were deployed in the southeastern Bering Sea from March to September 1993. For a 40‐m instrument the system prevented biofouling for the entire deployment, while an 11‐m instrument was free of contamination for approximately 3.5 months. Reasonable estimates of in situ chlorophyll a were obtained from all three instruments by the subtraction of the baseline.
Volume and freshwater transport of the Labrador Current in Flemish Pass
Authors: Petrie Brian , Buckley Joseph
Published: February 2004

A current meter array of 3 months duration from the Newfoundland shelf edge to the 400‐m isobath gives a mean southward transport of the Labrador Current of 3.7 Sv with a freshwater component of 0.1 Sv. Over a 2‐month period, the volume and the freshwater flow increased by 3 and 0.09 Sv, respectively. Mean currents exceeded the variable components by a factor of 3. This estimate of the total transport of the Labrador Current is low because the flow extends eastward of the array beyond the 400‐m isobath to at least 1000 m. The total volume transport of the Labrador Current through Flemish Pass is estimated roughly to range between 6.3 and 9.8 Sv if archived current meter data are incorporated with the observations from this array. The mean freshwater transport is estimated to be 0.13 ± 0.03 Sv.
Wind‐forced modeling studies of currents, meanders, and eddies in the California Current system
Authors: Batteen Mary L.
Published: February 2004

This process‐oriented study of the California Current system (CCS) uses a high‐resolution, multilevel, primitive equation ocean model on a β plane to isolate the response of that eastern boundary oceanic regime to temporal and spatially varying wind forcing. To study the generation, evolution, and maintenance of many of the observed features such as currents, meanders, and eddies in the CCS, the model is forced from rest with seasonal climatological winds. In response to the prevailing wind direction, surface equatorward currents develop, along with upwelling of cooler water along the coast and a poleward undercurrent. Baroclinic/barotropic instabilities in the equatorward surface current and poleward undercurrent result in the generation of meanders near the coast. As the meanders intensify, cold upwelling filaments develop along the coast and subsequently extend farther offshore. In time, the meanders form both cyclonic and anticyclonic eddies, which subsequently propagate farther offshore. Longer simulation times (∼3–4 years), in which a quasi‐equilibrium state for the CCS is reached, show a seasonal cycle in response to the wind forcing for the coastal currents, upwelling, and filaments. The meanders and eddies, however, can be quasi‐permanent as well as seasonal features. The quasi‐permanent features play a significant role in modifying coastal currents, upwelling, and filaments, which leads to large temporal and spatial variability in the CCS. In a sensitivity study, the results from several numerical experiments are used to examine the dependence of the generation of the currents, meanders, and eddies on the type of Coriolis parameterization, wind forcing, and coastline geometry. Both the meridional variability of ƒ(β plane) and the alongshore component of the wind stress are shown to be key ingredients for generating realistic vertical and horizontal structures for the cores of the surface equatorward and the subsurface poleward currents. With such structures the currents are baroclinically and barotropically unstable, resulting in the generation of meanders, filaments, and eddies. Irregularities in the coastline geometry are shown to be important for “anchoring” upwelling and filaments as well as for enhancing the growth of meanders and eddies. Cyclonic eddies tend to form in the vicinity of capes, while anticyclonic eddies tend to form in the coastal indentations between capes. The region off Cape Blanco is identified as the location where the coastal, equatorward flow off Oregon leaves the coast to develop a meandering jet off California. The results from these experiments support the hypothesis that wind forcing and coastline irregularities on a beta plane are important mechanisms for the generation of many of the observed features of the CCS.
Determination of the depth dependent scattering coefficient in sea ice
Authors: Haines E. M. , Buckley R. G. , Trodahl H. J.
Published: February 2004

Measurements of the spatial spreading of light in typical first‐year sea ice in McMurdo Sound, Antarctica, have been characterized in terms of depth dependent scattering using Monte Carlo simulations. The results are shown to place constraints on models of the optical transmission of sea ice and on the relationship of the optical scattering parameters to the physical structure of the ice. Comparisons for different sites and seasons within a given year and between years are presented. The backscattering spatial profiles are shown to fix the scattering parameters of the strongly scattering top layer and the horizontal component of the anisotropic scattering parameter in the bulk layer. The transmission spatial profiles determine the anisotropy of the bulk layer and the absorption by algae near the base of the ice. It is demonstrated that the top layer is very sensitive to warming of the ice and that the scattering properties of this layer largely determine the albedo of sea ice while the transmission is affected by the nature of the top layer, the scattering in the bulk layer, and the absorption in the algal layer. A quantitative relationship between the scattering length and the air volume fraction is demonstrated.
Near‐inertial internal wave interactions with mesoscale fronts: Observations and models
Authors: Lee Craig M. , Eriksen Charles C.
Published: February 2004

Moored observations of near‐inertial currents and buoyancy fluctuations from the Frontal Air Sea Interaction Experiment (FASINEX) may be understood as nearinertial internal waves reflecting off sheared background currents. The FASINEX moored array measured upper ocean currents, temperature, and conductivity between January and June 1986 in a region of the Sargasso Sea heavily populated by strong upper ocean fronts. The background jets associated with these features have typical cross‐front scales of 20km, maximum currents of 0.5 m s−1, and relative vorticities of ±0.3ƒ. In the vicinity of fronts, observed near‐inertial currents have short horizontal scales, show no clear horizontal phase structure, and trace out elongated current ellipses with elevated across‐front over along‐front variance. During these periods, inertial band‐pass buoyancy fluctuations often correlate with major‐axis currents. WKB ray‐tracing models of propagating, monochromatic plane waves exhibit horizontal phase propagation and correlations between minor‐axis currents and buoyancy and thus cannot explain these results. Models of near‐inertial internal waves reflected or trapped by a barotropic frontal jet produce mode‐like structures with short horizontal scales, little horizontal phase propagation, and anisotropic current ellipses aligned primarily cross front. Model buoyancy may correlate with one or both current ellipse components, depending on the incidence angle of the wave and the degree to which it reflects. Completely reflected waves with horizontal scales similar to those of the front and near‐normal incidence angle produce current ellipses and correlation patterns consistent with the observations.
A new nested boundary condition for a primitive equation ocean model
Authors: Perkins A. L. , Smedstad L. F. , Blake D. W. , Heburn G. W. , Wallcraft A. J.
Published: February 2004

Nested boundary techniques are developed based on the results of Perkins [1993] and Blake [1991]. We focus on the numerical and physical consistency needs across the nested boundary. These techniques replace the transition zone used by other researchers with a numerically and a physically based correction step. We demonstrate our method using a nested, reduced gravity version of the Naval Research Laboratory (NRL) primitive equation ocean model and a two‐layer hydrodynamic finite‐depth version of the same model. Numerical experiments are performed using integrations of both an idealized double gyre and a realistic Greenland Iceland Norwegian (GIN) Sea configuration. To illustrate the need for improved boundary treatment, we present a numerical study of boundary errors. The study illustrates the fragile nature of nested boundary conditions. With even small errors, a dramatic impact is observed on the formation (or lack thereof) of the Atlantic‐Norwegian Current, which is responsible for transporting North Atlantic water to the Arctic Ocean, in the GIN Sea configuration.
Subtidal velocity correlation scales on the northern California shelf
Authors: Dever E. P.
Published: February 2004

Along‐ and cross‐shelf correlation scales of subtidal cross‐shelf (u) and along‐shelf (v) velocities are estimated using moored records from several field programs over the northern California shelf. Over record lengths of 4–6 months, along‐shelf correlation scales of v are greater than maximum mooring separations (60 km). In the cross‐shelf direction, v is generally correlated between the 60 and 130 m isobaths (10–15 km separation). Along‐shelf correlation scales of u are much smaller than those of v and are often not resolved by minimum mooring separations. Time series between November 1988 and May 1989 do resolve along‐shelf correlation scales of near‐surface u and indicate that they are 15–20 km. During this time the along‐shelf correlation scale of near‐surface u shows variability on a monthly scale. It is generally long (30 km or more) when correlation of u with wind stress is high and short (15 km or less) when correlation with wind stress is low. On at least one occasion, short along‐shelf correlation scales coincide with the intrusion of an offshore mesoscale feature onto the shelf. Cross‐shelf correlation scales of u are resolved for typical mooring separations. In general, u is correlated between the 90 and 130 m isobaths (7–13 km separation) and between the 60 and 90 m isobaths (∼5 km).
An optimal interpolation scheme for the assimilation of spectral wave data
Authors: Hasselmann S. , Lionello P. , Hasselmann K.
Published: February 2004

An optimal interpolation scheme for assimilating two‐dimensional wave spectra is presented which is based on a decomposition of the spectrum into principal wave systems. Each wave system is represented by three characteristic parameters: significant wave height, mean propagation direction, and mean frequency. The spectrum is thereby reduced to a manageable number of parameters. From the correction of the wind‐sea system a correction of the local wind is derived. A 2‐month test of the system using wave spectra retrieved from ERS 1 synthetic aperture radar wave mode data in the Atlantic yielded consistent corrections of winds and waves. However, the corrected wind data alone, although valuable in identifying wind errors in critical high wind speed regions, are too sparsely distributed in space and time to be used in isolation and need to be combined with other data in an atmospheric data assimilation scheme. This emphasizes the need for the development of combined wind and wave data assimilation schemes for the optimal use of satellite wind and wave data.
Parameter estimation solving a weak constraint variational formulation for an Ekman model
Authors: Eknes Mette , Evensen Geir
Published: February 2004

A weak constraint variational formulation is used for inverse calculations and parameter estimation in a one‐dimensional Ekman model. When parameters in the model are allowed to contain errors, the inverse problem becomes nonlinear even if the model itself is linear. It is shown that a convergent iteration can be defined for the nonlinear system of Euler‐Lagrange equations and that improved estimates of the poorly known parameters can be calculated by solving the inverse problem for each of the linear iterates using the representer method. The formulation of the variational problem and the solution methods are illustrated using a simple example. The use of a simple dynamical model makes it possible to give an instructive presentation of the representer method. The method is finally used in an example using real current meter data. It is shown that the weak constraint formulation results in smooth solutions in good agreement with the data all through the water column and that it is superior to the traditional strong constraint inverse estimate.
Increased coastal upwelling in the California Current System
Authors: Schwing Franklin B. , Mendelssohn Roy
Published: February 2004

State‐space statistical models are applied to long environmental time series of monthly northward wind stress, sea surface temperature (SST), salinity (SSS), and sea level (SL) from the west coast of North America. The models use a combination of Kalman filtering and maximum likelihood methods, which estimate a nonlinear trend, a nonstationary and nondeterministic seasonal signal, and an autoregressive term, and effectively separate the seasonal signals from the long‐term trends. The seasonal series are examined for behavior consistent with increasing coastal upwelling during the spring‐summer upwelling “season,” presumably in response to a pattern of long‐term global warming. Over a region of the California Current System (CCS) where coastal upwelling is a dominant process (32–40°N), wind stress, SST, SSS, and SL all show strong evidence of a systematic intensification of upwelling during April–July. Model trend series suggest a linear tendency for increasing equatorward stress (in agreement with the seasonal tendency), but warmer SST (opposite the seasonal and the expectation of greater upwelling). The linear tendencies of the SST and stress trends are generally an order of magnitude greater than the seasonal tendencies. Thus the long‐term trend in SST masks the cooling effect of increased seasonal upwelling, and the trend in equatorward stress suggests an artificially large seasonal increase in the observed spring and summer stress. A key to identifying these patterns has been the ability to separate the long‐term nonlinear trend, using the state‐space models, which mask the signal of increased upwelling in the observations.
Motional induction in North Atlantic circulation models
Authors: Flosadóttir Á. H. , Larsen J. C. , Smith J. T.
Published: February 2004

Motionally induced voltage differences provide one of the few observation methods sensitive to fluctuations of large‐scale ocean transports. However, uncertainties of interpretation have impeded widespread oceanographic use of voltages measured on open‐ocean cables. To resolve these uncertainties, we have developed a numerical simulation of the flow‐induced voltages in general circulation models. The model includes the effects of flow meandering, the spatial and temporal variations of seawater temperature and salinity, three‐dimensional Earth models with realistic sediment conductances, and the full physics applicable to the large‐scale, long‐period circulation when self‐induction may be neglected. For the oceanographic input, we used the World Ocean Circulation Experiment Community Modeling Effort's model, which simulates the wind‐driven and thermohaline circulation in the North Atlantic using mean monthly winds and realistic topography with resolution permitting mesoscale eddies. The results are in good agreement with the experimental cable calibration results from the Straits of Florida and with the Mid‐Ocean Dynamics Experiment. We find less influence of large‐scale electric current loops on the seafloor horizontal electric field than has previously been feared, our results supporting a local relationship of the seafloor electric field and ocean transport and the interpretation of seafloor horizontal electric field measurements in terms of local transport over much of the North Atlantic basin.