Curtis C. Ebbesmeyer

Determination of vorticity, divergence, and deformation rates from analysis of drogue observations

Abstract If several drogues (i.e. four or more) are followed simultaneously not only the mean flow, dispersion, and eddy diffusivities but also the field of mean vorticity, and deformation rates can be determined as functions of time. Confidence levels of the latter quantities can also be calculated. These new procedures use a matrix approach to linear regression.

The Local Dynamics of Eddies in the Western North Atlantic

The local dynamics of oceanic mesoscale eddies is a subject of enormous scope and detail. The scope of this paper, on the other hand, is restricted to a particular experiment, the POLYMODE Local Dynamics Experiment (LDE). The LDE is unique among mesoscale experiments to date in its high sampling density and variety of measurements, and thus is well suited to considerations of eddy dynamics in one locale. This uniqueness is, of course, one of degree not kind. Other mesoscale mapping experiments are POLYGON (USSR), MODE, Tourbillon (France), and the USSR component of POLYMODE. We, the authors, are the experimentalists and analysts of the LDE.

Systematic errors in expendable bathythermograph (XBT) profiles

Abstract Intercomparison of 306 casts in the tropical Pacific of Sippican T-4 (∼450-m depth) and 139 casts in the Sargasso Sea of Sippican T-7 (∼750 m depth) expendable bathythermographs (XBTs) and calibrated Neil Brown conductivity-temperature-depth (CTD) profiles has been performed to detect errors in XBT temperature and depth. Also included are results from previous XBT-CTD intercomparisons. Systematic temperature errors were determined in depth ranges where the vertical temperature gradient was small and the contribution from depth errors would be small. In all cases the XBT temperatures were systematically higher than CTD temperatures. Isotherm depths from XBTs were systematically less than CTD depth below an intermediate depth. The depth error dependence is a characteristic of the instrument, and for the T-7 XBT it is repeatable in at least two regions of differing thermal structure. The standard deviation of the depth error is approximately 10 m for both T-4 and T-7 instruments. The accuracy of XBT data can be significantly improved by periodic XBT-CTD intercomparison. An algorithm is given to correct the T-7 XBT systematic depth error.

Imminent climate and circulation shift in northeast Pacific Ocean could have major impact on marine resources

A climate shift is imminent in the northeast Pacific Ocean, research suggests, and may have a major impact on marine resources, particularly Pacific salmon. Scientists anticipate that the shift, driven by large-scale changes in the Earths atmospheric wave pattern, will become evident in the next few years. The most recent shift, characterized by a switch from cold and wet conditions to warm and dry conditions in the Pacific northwest of the United States, occurred in 1977 [e.g., Trenberth and Hurell, 1994]. The expected climate shift is suggested by studies of oscillations in ocean surface water drift and in treering records. Drift trajectories, derived from a new measure of decadal variability, showed well-defined oscillations in the 20th century, but researchers were concerned that this decadal nature might not be as evident over a considerably longer time. Thus because of the possible rarity of the 30-year interval since the last climate shift, treering width data was scrutinized for the western juniper for the period from 1500 to 1900 A.D.

Detection, Structure, and Origin of Extreme Anomalies in a Western Atlantic Oceanographic Section

Abstract Ten anomalous water parcels were detected in the water column of a western Atlantic oceanographic section (0–5550 m; 70°W; 23–33°N). The parcels had extreme properties lying either two standard deviations from historical mean values, or estimated origins lying 2000 km from the oceanographic section. Detection, structure, and origin of the parcels were determined from analyses on isobaric and isopycnal surfaces using eight kinds of measurements temperature, salinity, oxygen, light scattering, silicate, phosphate, nitrate, and tritium. The parcels originated from seven of the major water masses comprising the North Atlantic Ocean. As observed along the oceanographic section the parcels had the following average (range) characteristics vertical pressure extent = 650 db (100–150 db); horizontal extent = 130 km (30–260 km); and distance to origin = 2300 km (400–5200 km). A population density equaling approximately one parcel per 100 km was obtained as the number of parcels (10) divided by the length o...

Shoe spill in the North Pacific

Approximately 80,000 Nike brand shoes were lost overboard on May 27, 1990, in the north Pacific Ocean (˜48°N; 161°W; Figure 2). Six months to a year later, thousands of shoes washed ashore in North America from southern Oregon to the Queen Charlotte Islands. Figure 1 shows six shoes found on the beach. We have gathered beachcomber reports and compared the inferred shoe drift with an oceanographic hindcast model and historical drift bottle returns. This spill-of- opportunity provided a calibration point for the model; computer runs for 1946–1991 suggested that drift of floatable material across the northeast Pacific Ocean for May 1990–January 1991 was farther south than the mean of the forty-five simulations.

Structure and Origin of 18°C Water Observed during the POLYMODE Local Dynamics Experiment

Abstract Two distinct types of 18°C water (Subtropical Mode Water) were observed during the POLYMODE Local Dynamics Experiment (LDE; May–July 1978; 31.0°N, 69.5°W). These were revealed on isopyncals by salinity histograms which were bimodal. Salinity was highly correlated with oxygen, vortex stretching, and 17.5°–18.5°C thickness. The correlations are positive between salinity and both oxygen and thickness and negative between salinity and vortex stretching. The origins of the two water types are deduced using a variety of measurements in the Sargasso Sea including apparent oxygen utilization, vortex stretching and salinity. It is found that the modes were formed approximately 16 months prior to the LDE during the severe winter of 1976/77. Sharp horizontal salinity gradients between the two LDE water types are comparable to those observed more than a year earlier, and the spatial scale (∼100 km) of the regions of saline mode water is smaller in the LDE than immediately after the 1976/77 winter (∼200 km). ...

Pacific toy spill fuels ocean current pathways research

While a container vessel was crossing the North Pacific Ocean along the great circle route from Hong Kong to Tacoma, Wash., severe storm conditions were encountered near the International Date Line on January 10,1992. At44.7°N, 178.1°E, twelve 12.2-m containers were washed overboard, one of which held about 29,000 plastic bathtub toy animals (Figure 1). Some of the steel cargo containers may have been torn open by the vessels stays as they fell overboard or may have been ruptured by collisions with other containers. Ten months after the spill, plastic toys began showing up on beaches near Sitka, Alaska. According to computer simulations the toys drifted toward the southeast Alaska coast, past both the site where about 61,000 Nike shoes spilled from a boat in 1990 and Ocean Weather Station Papa, where many drift bottles have been released.

The Structure, Dynamics, and Origin of a Small-Scale Lens of Water in the Western North Atlantic Thermocline

Abstract A small-scale, isolated, anticyclonically rotating lens of water was observed in the western North Atlantic thermocline during the POLYMODE Local Dynamics Experiment. Using a combination of SOFAR float, hydrographic, nutrient, and moored current and temperature data, we deduce that the lens was about 20 km across with a thickness not greater than 300 m, centered on 750 m; that its shape was not dissimilar to that of a vertical-radial Gaussian eddy; and that at its center, the lens had strong anomalies of salinity, dissolved oxygen, nitrate, and vortex stretching. The water mass properties within the eddy are not inconsistent with an origin for the feature near 15°N, 54°W, several thousand kilometers from where it was observed in the western North Atlantic, although an unambiguous origin cannot be discerned from the data. If such features are not uncommon, they may be an important mechanism for large-scale mixing of water properties in the ocean.

Determination of Lagrangian Deformations from Analysis of Current Followers

Abstract Methods are presented to determine Lagrangian deformations and turbulence statistics from current followers (drogues, neutrally buoyant floats, etc.). Such determinations allow general advection-diffusion equations such as in Okubo (1966) to be directly evaluated. Methods are also presented to transform these deformations into oceanic velocity gradients.