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Borrelli C.,Rensselaer Polytechnic Institute | Cramer B.S.,Theiss Research | Katz M.E.,Rensselaer Polytechnic Institute
Paleoceanography | Year: 2014

We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ18Obf and δ13Cbf) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning-38.5-Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ18Obf values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene,-1-4-Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (-34-Ma) and the consequent development of a circumpolar proto-ACC. Key Points The opening of Southern Ocean gateways impacted global ocean circulation Late middle Eocene thermal differentiation between SCW and NCW NCW formation in the Labrador Sea starting around 38.5 Ma ©2014. American Geophysical Union. All Rights Reserved.


Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: | Award Amount: 45.90K | Year: 2012

This award supports theoretical research on topics related to gravitational waves. One of these is a study of the properties of extreme mass ratio binary inspirals where a stellar mass black hole orbits a supermassive black hole, emits gravitational waves, and eventually falls in. Such a system could be an important source for the Laser Interferometer Space Antenna (LISA) . Accurate calculation of the orbit of the stellar mass black hole and of the gravitational radiation produced require improved understanding of fundamental issues in Einsteins theory of general relativity such as the self-force on the small black hole due to the gravitational radiation it emits and how that changes the orbit. Another project is to develop a method to extract gravitational waveforms from large scale numerical simulations of (comparable mass) binary black hole systems.

Better understanding of gravitational wave sources and waveforms will maximize the discovery opportunities presented by ground-based gravitational wave detectors now operating and future space-based detectors. Undergraduate and graduate students will participate in this research. The PI plans to continue his program of public outreach and his involvement with nearby minority serving institutions.


de Bakker A.T.M.,University Utrecht | Herbers T.H.C.,Theiss Research | Smit P.B.,Theiss Research | Tissier M.F.S.,Technical University of Delft | Ruessink B.G.,University Utrecht
Journal of Physical Oceanography | Year: 2015

A high-resolution dataset of three irregular wave conditions collected on a gently sloping laboratory beach is analyzed to study nonlinear energy transfers involving infragravity frequencies. This study uses bispectral analysis to identify the dominant, nonlinear interactions and estimate energy transfers to investigate energy flows within the spectra. Energy flows are identified by dividing transfers into four types of triad interactions, with triads including one, two, or three infragravity-frequency components, and triad interactions solely between short-wave frequencies. In the shoaling zone, the energy transfers are generally from the spectral peak to its higher harmonics and to infragravity frequencies. While receiving net energy, infragravity waves participate in interactions that spread energy of the short-wave peaks to adjacent frequencies, thereby creating a broader energy spectrum. In the short-wave surf zone, infragravity-infragravity interactions develop, and close to shore, they dominate the interactions. Nonlinear energy fluxes are compared to gradients in total energy flux and are observed to balance nearly completely. Overall, energy losses at both infragravity and short-wave frequencies can largely be explained by a cascade of nonlinear energy transfers to high frequencies (say, f > 1.5 Hz) where the energy is presumably dissipated. Infragravity-infragravity interactions seem to induce higher harmonics that allow for shape transformation of the infragravity wave to asymmetric. The largest decrease in infragravity wave height occurs close to the shore, where infragravity-infragravity interactions dominate and where the infragravity wave is asymmetric, suggesting wave breaking to be the dominant mechanism of infragravity wave dissipation. © 2015 American Meteorological Society.


Smit P.B.,Technical University of Delft | Smit P.B.,NorthWest Research Associates, Inc. | Janssen T.T.,Theiss Research | Janssen T.T.,NorthWest Research Associates, Inc. | And 2 more authors.
Journal of Physical Oceanography | Year: 2015

Refractive focusing of swell waves can result in fast-scale variations in the wave statistics because of wave interference, which cannot be resolved by stochastic wave models based on the radiative transport equation. Quasi-coherent statistical theory does account for such statistical interferences and the associated wave inhomogeneities, but the theory has thus far been presented in a form that appears incompatible with models based on the radiative transfer equation (RTE). Moreover, the quasi-coherent theory has never been tested against field data, and it is not clear how the coherent information inherent to such models can be used for better understanding coastal wave and circulation dynamics. This study therefore revisits the derivation of quasi-coherent theory to formulate it into a radiative transport equation with a forcing term that accounts for the inhomogeneous part of the wave field. This paper shows how the model can be nested within (or otherwise used in conjunction with) quasi-homogeneous wave models based on the RTE. Through comparison to laboratory data, numerical simulations of a deterministic model, and field observations of waves propagating over a nearshore canyon head, the predictive capability of the model is validated. The authors discuss the interference patterns predicted by the model through evaluation of a complex cross-correlation function and highlight the differences with quasi-homogeneous predictions. These results show that quasi-coherent theory can extend models based on the RTE to resolve coherent interference patterns and standing wave features in coastal areas, which are believed to be important in nearshore circulation and sediment transport. © 2015 American Meteorological Society.


Miller K.G.,Rutgers University | Wright J.D.,Rutgers University | Browning J.V.,Rutgers University | Kulpecz A.,Rutgers University | And 8 more authors.
Geology | Year: 2012

We obtained global sea-level (eustatic) estimates with a peak of ~22 m higher than present for the Pliocene interval 2.7-3.2 Ma from backstripping in Virginia (United States), New Zealand, and Enewetak Atoll (north Pacific Ocean), benthic foraminiferal 18O values, and Mg/Ca- δ18O estimates. Statistical analysis indicates that it is likely (68% confidence interval) that peak sea level was 22 ± 5 m higher than modern, and extremely likely (95%) that it was 22 ± 10 m higher than modern. Benthic foraminiferal δ18O values appear to require that the peak was <20-21 m. Our estimates imply loss of the equivalent of the Greenland and West Antarctic ice sheets, and some volume loss from the East Antarctic Ice Sheet, and address the longstanding controversy concerning the Pliocene stability of the East Antarctic Ice Sheet. © 2012 Geological Society of America.

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