Southern Hemisphere Humpback Whale Song in Pacific Central America

The humpback whale (Megaptera novaeangliae) is a species of marine mammal famed for its charisma and song. This thesis focuses on the population of whales that feeds in the Pacific waters off the coast of Chile and the Antarctic Peninsula and breeds in the Pacific waters off the coast of Ecuador and Central America, which constitutes a poorly known breeding ground. Studies have previously shown that these whales are capable of cultural transmission, which is to pass on song elements over space and time, allowing scientists to track them around the world. Cultural transmission implies acoustic contact and can assist in establishing migratory routes and population overlaps. This thesis has 3 distinct studies which have been segregated by chapters. The first and last chapters of this thesis serve as an introduction and conclusion respectively. In chapter 2, I describe the average breeding song of 2016 of Costa Rica using data collected with autonomous hydrophone recorders. I found 14 phrases grouped into 4 themes. This song changed over the season and varied between individuals, consistent with other studies. In chapter 3, I describe the pace of song change between the period of 2007-2017 using data collected in Panama and Costa Rica. The pace of change increased over this period, suggesting that this population is not acoustically isolated. In chapter 4, we examine the effects of engine noise of acoustic behavior. We find that whales are significantly more quiet in the presence of engine noise. In countries where ecotourism is present, like Costa Rica, the education of boat drivers and fishing industry is imperative to the preservation of this species. Countries fortunate enough to have these creatures call their waters home have an obligation to protect them against anthropogenic threats through education and the implementation of eco-friendly policy

The development of nonlinear surface and internal wave groups

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1982The development of nonlinear surface and internal wave groups is investigated. Surface wave evolution was observed in an unusually long wave channel as a function of steepness and group length. Dissipation and frequency downshifting were important characteristics of the long-time evolution. The amplitude and phase modulations were obtained using the Hilbert transform and specified as an initial condition to the cubic nonlinear Schrodinger equation, which was solved numerically. This equation is known to govern the slowly varying complex modulation envelope of gravity waves on deep water. When dissipation was included, the model compared quite well with the observations. Phase modulation was used to interpret the long-time behavior, using the phase evolution of exact asymptotic solutions as a guide. The wave groups exhibited a long-time coherence but not the recurrence predicted by the inviscid theory. An oceanic field study of the generation of groups of large amplitude internal waves by stratified tidal flow over a submarine ridge indicates that the large amplitude and asymmetry of the topography are critical in determining the type of flow response. The calculated Froude numbers response length scale and duration differ markedly between the two phases of the tide due to the asymmetry.Research assistantship provided by the Office of Naval Research contract no. N00014-80-C-027

cDrake CPIES Data Report November 2007 to December 2011

The goal of cDrake is to quantify the transport and understand the dynamic balances of the Antarctic Circumpolar Current (ACC) in Drake Passage. For this purpose, a transport line spanning all of Drake Passage and a local dynamics array of CPIES were deployed for a period of four years. A CPIES comprises an inverted echo sounder equipped with a bottom pressure gauge and a current meter tethered 50 m above the bottom. In addition to the CPIESs, three current meter moorings were deployed along the continental margins for the initial two years of the field program. Subsequently, a current meter comparison mooring was deployed in a region of strong bottom currents for a period of one year. Conductivity-temperature-depth and lowered acoustic Doppler current profiler measurements were taken at each CPIES site. Shipboard acoustic Doppler current profiler measured the velocity structure along the cruise track. In this report, the CPIES data collected during the field experiment are presented. The collection, processing and calibration of the CPIES are described

Mean jets, mesoscale variability and eddy momentum fluxes in the surface layer of the Antarctic Circumpolar Current in Drake Passage

High-resolution Acoustic Doppler Current Profiler (ADCP) observations of surface-layer velocities in Drake Passage, comprising 128 sections over a period of 5 years, are used to study the surface-layer circulation of the Antarctic Circumpolar Current (ACC). These observations resolve details of the mean flow including the topographic control of the mean Subantarctic Front (SAF) and the multiple filaments of the Polar Front (PF) and Southern ACC Front (SACCF) that converge into single mean jets as the ACC flows through Drake Passage. Subsurface definitions of the SAF and PF applied to expendable bathythermograph temperatures generally coincide with mean jets, while the SACCF is better defined in velocity than temperature. The mean transport in the top 250-m-deep surface layer, estimated from the cross-track transport along three repeat tracks, is 27.8 ± 1 Sv.Eddy momentum fluxes were estimated by ensemble averaging Reynolds stresses relative to gridded Eulerian mean currents. Eddy kinetic energy (EKE) is surface intensified in the mixed layer because of inertial currents and decreases poleward in Drake Passage, ranging from ∼800 cm2 s−2 to ∼200 cm2 s−2. ADCP EKE estimates are everywhere significantly higher than altimetric EKE estimates, although the pattern of poleward decrease is the same. Horizontal-wavenumber spectra of velocity fluctuations peak at wavelengths in the 250–330 km range and are significantly anisotropic. Along-passage fluctuations dominate at wavelengths less than 250 km; cross-passage fluctuations dominate at wavelengths greater than 250 km. Mesoscale eddies dominate the variance in northern Drake Passage. Inertial variability is constant with latitude and together with baroclinic tides accounts for some but not all of the discrepancy between the ADCP surface-layer EKE and altimetry-inferred EKE

Can Drake Passage Observations Match Ekman's Classic Theory?

Ekman's theory of the wind-driven ocean surface boundary layer assumes a constant eddy viscosity and predicts that the current rotates with depth at the same rate as it decays in amplitude. Despite its wide acceptance, Ekman current spirals are difficult to observe. This is primarily because the spirals are small signals that are easily masked by ocean variability and cannot readily be separated from the geostrophic component. This study presents a method for estimating ageostrophic currents from shipboard acoustic Doppler current profiler data in Drake Passage and finds that observations are consistent with Ekman's theory. By taking into account the sampling distributions of wind stress and ageostrophic velocity, the authors find eddy viscosity values in the range of 0.08–0.12 m2 s−1 that reconcile observations with the classic theory in Drake Passage. The eddy viscosity value that most frequently reconciles observations with the classic theory is 0.094 m2 s−1, corresponding to an Ekman depth scale of 39 m

The role of air-sea fluxes in Subantarctic Mode Water formation

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C03040, doi:10.1029/2011JC007798.Two hydrographic surveys and a one-dimensional mixed layer model are used to assess the role of air-sea fluxes in forming deep Subantarctic Mode Water (SAMW) mixed layers in the southeast Pacific Ocean. Forty-two SAMW mixed layers deeper than 400 m were observed north of the Subantarctic Front during the 2005 winter cruise, with the deepest mixed layers reaching 550 m. The densest, coldest, and freshest mixed layers were found in the cruise's eastern sections near 77°W. The deep SAMW mixed layers were observed concurrently with surface ocean heat loss of approximately −200 W m−2. The heat, momentum, and precipitation flux fields of five flux products are used to force a one-dimensional KPP mixed layer model initialized with profiles from the 2006 summer cruise. The simulated winter mixed layers generated by all of the forcing products resemble Argo observations of SAMW; this agreement also validates the flux products. Mixing driven by buoyancy loss and wind forcing is strong enough to deepen the SAMW layers. Wind-driven mixing is central to SAMW formation, as model runs forced with buoyancy forcing alone produce shallow mixed layers. Air-sea fluxes indirectly influence winter SAMW properties by controlling how deeply the profiles mix. The stratification and heat content of the initial profiles determine the properties of the SAMW and the likelihood of deep mixing. Summer profiles from just upstream of Drake Passage have less heat stored between 100 and 600 m than upstream profiles, and so, with sufficiently strong winter forcing, form a cold, dense variety of SAMW.NSF Ocean Sciences grant OCE-0327544 supported LDT, TKC, and JH and funded the two research cruises. BMS’s contribution to this work was undertaken as part of the Australian Climate Change Science Program, funded jointly by the Department of Climate Change and Energy Efficiency and CSIRO. The QuikSCAT wind mapping method [Kelly et al., 1999], used to create the Kelly flux product, was sponsored by NASA’s Ocean Vector Winds Science. NCEP Reanalysis data were provided by the NOAA/OAR/ESRL PSD. WHOI’s OAFlux project is funded by the NOAA Climate Observations and Monitoring (COM) program.2012-09-2

Subantarctic mode water in the southeast Pacific : effect of exchange across the Subantarctic Front

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 2052–2066, doi:10.1002/jgrc.20144.This study considered cross-frontal exchange as a possible mechanism for the observed along-front freshening and cooling between the 27.0 and 27.3 kg m − 3 isopycnals north of the Subantarctic Front (SAF) in the southeast Pacific Ocean. This isopycnal range, which includes the densest Subantarctic Mode Water (SAMW) formed in this region, is mostly below the mixed layer, and so experiences little direct air-sea forcing. Data from two cruises in the southeast Pacific were examined for evidence of cross-frontal exchange; numerous eddies and intrusions containing Polar Frontal Zone (PFZ) water were observed north of the SAF, as well as a fresh surface layer during the summer cruise that was likely due to Ekman transport. These features penetrated north of the SAF, even though the potential vorticity structure of the SAF should have acted as a barrier to exchange. An optimum multiparameter (OMP) analysis incorporating a range of observed properties was used to estimate the cumulative cross-frontal exchange. The OMP analysis revealed an along-front increase in PFZ water fractional content in the region north of the SAF between the 27.1 and 27.3 kg m − 3 isopycnals; the increase was approximately 0.13 for every 15° of longitude. Between the 27.0 and 27.1 kg m − 3 isopycnals, the increase was approximately 0.15 for every 15° of longitude. A simple bulk calculation revealed that this magnitude of cross-frontal exchange could have caused the downstream evolution of SAMW temperature and salinity properties observed by Argo profiling floats.NSF Ocean Sciences grant OCE-0327544 supported L.D.T., T.K.C., and J.H. and funded the two research cruises; NSF Ocean Sciences grant OCE-0850869 funded part of the analysis. BMS’s contribution to this work was undertaken as part of the Australian Climate Change Science Program, funded jointly by the Department of Climate Change and CSIRO.2013-10-2