Sea turtles are large migratory animal stay in the water most of their life time. In the east coast of Taiwan, there is a strong northward Kuroshio current. It is hypothesis that ocean current might play an important role to the migration tracks of sea turtles in the region. To test the hypothesis, two turtle tracks based on Argos records were analyzed. The first turtle moved from Lanyu in the NE direction to Ishigaki Island. The second one moved southward from Dong-Auo, along the east coast of Taiwan, to the southern tip of Taiwan, and then detoured westward across the Taiwan Strait, swum southward along coastal China to Leizhou Peninsula finally. In this study, we analyze data of EASNFS model, drifter tracks, weather buoy records and MODIS sea surface temperature, to explore the relationship between the ocean currents and the migration tracks of sea turtles. The Lanyu turtle seems follow very well with Kuroshio current in the early stage of its migration. The migration matches well with many Argos drifter tracks, and Lagragian drifter of EASNFS model. The probability of this turtle arriving Ishigaki Island is 26% if without other help. There is a turning point, as indicated by the comparison of model and real track. The Lanyu turtle swam hard to correct the migration route in order to reach the final destination. The Dong-Auo turtle track is analyzed together with data of winds, waves and drifters. This turtle migrated southward along the east coast of Taiwan seemly agree with the northeast monsoon wind driven coastal current. The migration route turned west at the southern tip of Taiwan. The turn matches well with the currents indicate by Argos drifters, as well as EASNFS modeling. In additional to the guidance of currents, this migration route also followed the sea surface temperature of 21¢J. In conclusion, this study suggests that turtles migration, in additional to the efforts of swimming and temperature guidance, will take advantage of prevailing currents to reach their final destinations.

Ocean circulation in Greenland's large glacial fjords is one mechanism that controls the rate of submarine melting at the termini of Greenland's outlet glaciers. Here we use hourly position data from GPS units deployed on ten large (>100 meter), deep-keeled icebergs in Sermilik Fjord, SE Greenland. We observe and quantify the motions of these icebergs moving through the mélange, fjord, and shelf regimes. In the mélange, icebergs move outward with glacier flow until pushed loose by large calving events. In the fjord, high frequency, low amplitude tidally-driven motions are superimposed on dominant 1-5 day events with net velocities exceeding 0.1 m/s. We interpret these events as two-layer, intermediary circulation driven by winds along the shelf, where icebergs travel southward in the East Greenland Coastal Current. These results showcase the potential of this novel instrumentation to link iceberg motion with circulation in any large glacial fjord.

Entrainment velocity, salt flux and the turbulent diffusivity of salt are estimated in the outflow of a small, radially spreading buoyant outflow, just outside of the Teign Estuary mouth, as a means to compare mixing dynamics between very small and larger-scale estuarine and river plumes, and build on a scant knowledge base regarding the former. The analysis was made using a control volume approach, based on the conservation of momentum, volume and salt, from a Lagrangian perspective. Drifting buoys were used to accomplish this. The analysis was based on that employed by McCabe et al. (2008), with some modifications to fit a small-scale outflow, namely: repeat deployments, shorter drifter tracks, and deployment-specific criteria used for choosing the plume base, a step in the analysis used to calculate vertical entrainment, flux and diffusivity. In addition, temperature was used as a proxy for salinity, and this is evaluated in the results. Overall results were compared to a similar study, which was conducted in the Columbia River plume, a system much larger in scale to the Teign. Drifter experiments were conducted on multiple days, under different conditions (i.e. wind, tides, river flow), and those results are discussed briefly, but the focus is on one specific day, April 3, 2014, where conditions most closely matched those of the comparison study, and those results are compared between the two systems. Entrainment velocity was measured along the drifter tracks, in the near-field plume, where shear-induced mixing dominates. Drifter track subsections were chosen so as to avoid source or frontal dynamics, the plume base was chosen for individual deployments as the plume dynamics could change relatively quickly, and repeat deployments were conducted as a way to look at near-field plume evolution over the course of the ebb (and with a smaller plume, time allowed for this) . On April 3, the mean value for entrainment velocity for the four deployments chosen in the Teign outflow was 4.3 x 10-4 ms-1. The mean cast value was slightly higher at 7.6 x 10-4 ms-1, as casts values were typically measured at the beginning of the drifter tracks. Entrainment values at the cast sites were calculated in the same way as the track values, taking plume thickness from hydrographic casts, as a means to evaluate accuracy of track values, which are based on a modelled plume thickness. A rough estimate for the mean entrainment velocity for one pair of drifters used in the Columbia River was 9 x 10-4 ms-1, approximately double that of the Teign, but within the same order of magnitude. Salt flux values ranged from 0-5 x 10-2 psu ms-1 and from 0-3 x 10-2 psu ms-1 for the Teign and the Columbia, respectively, and diffusivities ranged from 0.5-5.8 x 10-2 m2s-1 and from 0.2-9.6 x 10-3 m2s-1. With a similar range of entrainment and salt flux values, and almost an order of magnitude difference between diffusivity values, it was determined that weaker density gradients in the Teign are responsible for the latter, and that this increased level of mixing results in a larger horizontal horizontal salinity gradient, which balances out the terms in the entrainment equation that are related solely to the physical size of the system (i.e. plume thickness, velocity and the vertical salinity gradient). This higher level of mixing of a smaller physical entity, supports the view that smaller plumes mix more thoroughly over a shorter timescale, resulting in a larger impact to the local environment into which they flow.

In order to understand water quality in the coastal ocean and its effects on human health, the necessity arises to locate the sources of contaminants and track their transport throughout the ocean. Dynamical systems methods are applied to the study of transport of enterococci as an indicator of microbial concentration in the vicinity of Hobie Beach, an urban, subtropical beach in Miami, FL that is used for recreation and bathing on a daily basis. Previous studies on water quality have shown that Hobie Beach has high microbial levels despite having no known point source. To investigate the cause of these high microbial levels, a combination of measured surface drifter trajectories and numerically simulated flows in the vicinity of Hobie Beach is used. The numerically simulated flows are used to identify Lagrangian Coherent Structures (LCSs), which provide a template for transport in the study area. Surface drifter trajectories are shown to be consistent with the simulated flows and the LCS structure. LCSs are then used to explain the persistent water contamination and unusually high concentrations of microbes in the water off of this beach as compared with its neighboring beaches. From the drifter simulations, as well as field experiments, one can see that passive tracers are trapped in the area along the coastline by LCS. The Lagrangian circulation of Hobie Beach, influenced primarily by tide and land geometry causes a high retention rate of water near the shore, and can be used to explain the elevated levels of enterococci in the water.

Most large reef fish use a migratory reproductive strategy and tend to spawn in aggregations that occur at predictable locations and times. Though numerous hypotheses have been formulated to explain the reasons behind this phenomenon, there remain few data to evaluate the relative merits of various hypotheses. Oceanographic variables and lunar cycles are believed to drive the timing and location of this reproductive strategy. However, the dynamics of the interaction between coastal currents, water temperature, biomass concentrations, spawning site selection and gamete transport are still unclear. This study aimed to examine the influence that currents exert on gametes released at spawning aggregations of Cubera snapper Lutjanus cyanopterus (Cuvier, 1828) at Gladden Spit, Belize. It was hypothesized that surface currents flowed offshore at the time and location of spawning. However, observations from this study, using Lagrangian and Eulerian methods, indicated that eggs most likely travel westerly towards the reef and into the reef channel. The dispersal rate of eggs appeared to be explained by a power relationship, with buoyant fertilized eggs dispersing horizontally such that the area of the spawning cloud increased with time. Egg density within the spawning cloud generally decreased over time as it dispersed with the predominant surface currents. Most importantly low-cost surface drifters area an appropriate, highly replicable way to monitor surface ocean currents at spawning sides in areas where more sophisticated methods are not available. Understanding how abiotic factors influence the occurrence of multispecies spawning aggregations will lead to better conservation and management strategies in the Western Caribbean.

The nearshore current field, defined here as the residual horizontal flow after averaging over the incident wave period, exhibits variability at a range of time and space scales. Some of the variable currents are low frequency gravity wave motions. However, variable, rotational (in the sense of possessing vertical vorticity) flow can also exist as part of the overall nearshore current field. A field and numerical modelling investigation of these variable rotational currents has been carried out. Drifters, which were developed for surfzone use, enabled measurement of the nearshore current structure; the design and testing of these new instruments is described. Two sets of field measurements, using the new drifters and Eulerian instruments were carried out for conditions with swell perpendicular to a plane beach and in strong longshore currents. In the perpendicular swell conditions, an interesting and well-defined feature of the measured trajectories was the development of transient rip currents. Discrete vortices were also observed. In the longshore current case, trajectories with the longshore current displacement removed had complex meandering paths. Lagrangian data were used to make estimates of length scales and dispersion, both of which provide strong evidence that the current field cannot be due to low frequency gravity waves alone. Under the assumption of equipartition of kinetic and potential energy for low frequency gravity waves, Eulerian measurements of velocities and pressure show significant energy due to non-divergent, rotational flow in both the perpendicular swell and longshore current case. A numerical model that can simulate horizontal flow with a directionally spread, random wave field incident on a plane beach was implemented. The model developed transient rip currents that are qualitatively very similar to those seen in the drifter trajectories from the field. The number and intensity of rip currents in the model depended on the beach slope and incident wave spectra. The energy content and cross-shore flux (and hence transport of material) of the rotational current flow component in the simulated flow fields is comparable to that due to low frequency gravity waves. The modelling also provided some evidence that there may be universal characteristics of the rotational currents. The field results and modelling show that variable rotational currents are ubiquitous in the field even when longshore currents and hence shear waves are not present. The term “infragravity turbulence” is suggested to describe the general class of nearshore hydrodynamics not directly associated with shear waves, which is largely disorganised, but contains well defined features such as transient rips currents and large scale horizontal vortices. The results have important implications in the understanding of the transport of material, including sediment, biological material, pollution, and sometimes bathers, in the nearshore zone.

Thesis (MPhil)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In the context of both climate change and peak oil, it is clear that the tourism industry cannot continue with a business-as-usual approach. Unfettered fossil fuel use is no longer an option and novel approaches need to be explored in order to change the configuration of energy systems. Transport is particularly energy intense and consequently, since it involves travel, so is tourism. The Drifters Desert Nature Reserve (DDNR) is probably a net carbon sink. The property is large and has thousands of long lived trees and bushes: but this would be an ‘easy out’ in an industry which is has a reputation for evading tough questions. Are there affordable techniques that can be employed by the Reserve that will reduce its carbon footprint and enable it to move toward being entirely carbon neutral, without relying on sequestration? A willingness to pay (WTP) survey investigating if clients were prepared to pay a voluntary amount towards reducing the emissions of the DDNR, thereby offsetting some of their own emissions, was conducted; 121 questionnaires were completed. The results were extrapolated out to represent the WTP of the 1055 clients that visited the DDNR in the last year. It was found that 73% of all the clients who stay at the DDNR are willing to pay toward helping the DDNR change the way its systems are configured as a means to offset some of their own emissions debt in getting to the reserve. Lodge clients were prepared to pay almost double the amount clients staying at the campsite would consider. In both cases, WTP was around 10% of the value of the accommodation package chosen. The fossil fuel use and consequent carbon dioxide debt of the DDNR was calculated and emissions were found to be in the region of 30 tonnes per annum. As per the case in the greater Namibia, transport is responsible for the bulk of the carbon dioxide output, with energy provision in this off-grid reserve being a close second. Of four potential interventions considered, two were found to be financially viable, regardless of the WTP of clientele. It is speculated that WTP on a small scale is administratively laborious and the potential contribution of a voluntary offsetting payment was perhaps not high to justify the implementation of the scheme. It was however found that reconfiguring the energy systems would definitely be a worthwhile exercise. On corporate level where efficiencies of size amplify gains, Drifters, as a group of 14 lodges and an overland company, may well find that a transparent voluntary emissions reduction (VER) payment, ring-fenced, appropriately used, and properly implemented, is worthwhile. Ethically, however, injecting VER payments into a balance sheet is problematic, especially where the payback period of the technological interventions is short and the benefits derived are long term. / AFRIKAANSE OPSOMMING: Die gebruik van fossielbrandstowwe wat in die huidige tydsgewrig tot die opwekking van oormatige kweekhuisgasse lei is nie langer aanvaarbaar nie en innoverende opsies om die voortgesette generasie van energie te verseker, sal nagestreef moet word. Een van die grootste verbruikers van energie is vervoer, en vervolgens is dit ook die geval dat toerisme, wat swaar op vervoer staatmaak, ‘n groot gebruiker van energie is. Aangesien daar etlike gevestigde bome en bosse op hierdie woestynreservaat is, is die Drifters Desert Nature Reserve (DDNR) moontlik ‘n netto bespaarder van koolstofgasse, maar dit kan nie sondermeer daargelaat word in ‘n bedryf wat bekend is daarvoor dat dit graag die moeilike vrae vermy nie. Daar is dus gevra: is daar bekostigbare tegnieke wat moontlik by die DDBR aangewend kan word om die koolstofvoetafdruk te verminder en dit in staat kan stel om totaal koolstofneutraal te word, sonder om op ingryping staat te maak? Navorsing is gedoen en 121 vraelyste is voltooi om vas te stel of kliente gewillig sou wees om ‘n vrywillige bydrae te maak om die afskeid van koolstof te beheer en daardeur hul eie koolstofvoetafrdruk te verminder, in ‘n sg “gewilligheid om te betaal” oftewel “willingness to pay” (WTP) opname. Die resultate is deurgevoer as verteenwoordigend van die 1 055 kliente wat verlede jaar die oord besoek het. Daar is gevind dat 73% van die kliente wat die oord besoek bereid sou wees om die DDNR geldelik te help om sy stelsels te verander as ‘n teenrekening om hul eie koolstofbesoedeling op pad daarheen te vergoed. Kliente wat die losie gebruik het was bereid om meer te betaal as diegene wat by die kampeerterrein tuisgegaan het. Die hele reservaat se jaarlikse koolstofdioksied debiet is bereken, en die jaarlikse opwekking is op ongeveer 30-tonne vasgestel. Nes in Namibie as geheel is vervoeruitlaatgasse verantwoordelik vir die oorgrote meerderheid opwekking, met die voorsiening van energie by die afgelee oord kort op sy hakke. Van die vier moontlike ingrypings wat oorweeg is, is twee finansieel die moeite werd gevind, ongeag die kliente se gewilligheid om geldelik by te dra. Die bestuur van aanvraag is ook oorweeg, en hoewel dit nie gekwantifiseer is nie, is dit nes die moontlikheid van tegnologiese innovering, duidelik deel van die oplossing, Daar is gevind dat ‘n stelsel van betaling op plaaslike vlak moeilik sou wees om die administreer, en aangesien selfs die gewilliges nie oorgretig is nie, is daar tot die gevolgtrekking gekom dat dit nie die moeite sou loon nie. Ongeag bogenoemde beginsel van toersitebydraes is daar gevind dat dit ongetwyfeld die moeite werd sou wees om die energiestelsels aan te pas. Maar dit sal nie noodwendig op ‘n korporatiewe of ‘n makro-skaal werk nie, veral nie waar grote ‘n rol speel nie. As maatskappygroep mag Drifters vind dat met ‘n deursigtige, vrywillige uitlaatverminderingspaaiement, wat afgebaken, korrek aangewend en effektief bestuur word, die kool die sous werd sou wees.

Velocity measurements from drifter GPS records are assimilated and used in an ensemble-based inversion technique to extract the river bathymetry. The method is tested on a deep meandering reach and a shallow braided reach of the Kootenai River in Idaho, USA. The Regional Ocean Modeling System (ROMS) is used to model numerous statistically varied bathymetries to create an ensemble of hydrodynamic states. These states, the drifter observations, and the uncertainty of each are combined to form a cost function which is minimized to produce an estimated velocity ���eld. State augmentation is then used to relate the velocity ���eld to bathymetry. Our goals are to assess whether ROMS can accurately reproduce the Kootenai River ���ow to an extent that depth inversion is feasible, investigate if drifter paths are sensitive enough to bottom topography to make depth inversion possible, and to establish practical limitations of the present methodology. At both test sites, the depth inversion method produced an estimate of bathymetry that was more accurate and more skillful than the prior estimate. / Graduation date: 2013