James Girton

Physical Oceanography Lunchtime Seminar, Spring 2016

Wednesday, March 16, 2016

12:30pm Wednesdays, OSB 425 (unless otherwise noted).

Seminar organizer: James Girton, girton (at) uw.edu, 543-8467.

To add your name to the announcement list, please visit https://mailman1.u.washington.edu/mailman/listinfo/phys_ocean_seminars.

Date Speaker Institution Title Abstract

April 4

(Mon 3:30pm)

PO Candidate:

Jorn Callies

MIT Submesoscale turbulence in the upper ocean  

April 11

(Mon 1:30pm in MSB 123)

PO Candidate:

Nick Beaird

WHOI Fingerprints of ocean-glacier interaction in Greenlandic fjords The Greenland Ice Sheet is losing mass at an accelerating rate. Changes in the ice sheet and the ocean are coupled — the ice sheet both responds to ocean forcing and contributes significantly to global sea level rise. The increased freshwater discharge has myriad potential impacts on the ocean including: altered transports of heat and freshwater in subpolar boundary currents; large scale connections from changing stability of boundary and open ocean convection; influences on marine ecosystems via altered stratification and nutrient delivery. Many of these impacts are dependent on the way in which glacial freshwater is mixed into the ocean.

The mixing of glacial freshwater and ocean water occurs in fjords, which form links between the ocean, with its reservoir of heat, and the ice sheet, with its reservoir of freshwater. Observations of glacier-driven water mass transformation can provide an integrated view of ice-ocean interaction and circulation in these fjords, telling us how glacial freshwater is exported to the coastal and open ocean. We use a new technique employing noble gases that allows, for the first time, unambiguous identification and quantification of meltwater spreading in the coastal waters around Greenland. The geochemical tracer studies are extended with ship-based and moored observations to investigate the seasonal cycle of ice-ocean interactions and the impact on the coastal physical and biological environment.

April 11

(Mon 2:30pm)

Ph.D. Defense: Melinda Webster


Pondering about snow on Arctic sea ice  

April 25

(Mon 3:30pm)

PO Candidate:

Sarah Purkey

LDEO A declining ventilation rate of Antarctic Bottom Water within the Ross Gyre The global abyssal ocean has warmed significantly over the past two decades, possibly linked to a decrease in the production rate of Antarctic Bottom Water (AABW), the cold dense water mass formed around Antarctica that feeds most of the global abyssal ocean.  Here I use chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6) and conservative tracers along the repeat S4P sections along 67 S to quantify a decrease in the ventilation rate of Antarctic Bottom Water (AABW) in the Pacific sector of the Southern Ocean.  Regionally generated AABW is a combination of cold dense Shelf Water formed over the continental shelf during sea ice production and warmer Circumpolar Deep Water entrained during flow down and along the continental slope.  An optimum multi-parameter analysis shows no significant change in the relative fraction of these two end members between 1992 and 2011, suggesting their mixing processes have not changed over the past 20 years.  However, the CFC and SF6 concentration histories in the Shelf Waters component within the Ross Gyre was 8 years older in 2011 than in 1992.  The OMP and CFC analyses thus provide strong evidence that the rate of ventilation and circulation within the abyssal Pacific sector of the Southern Ocean have significantly decreased over the 19 years between the two occupations.

May 2

(Mon 3:30pm)

PO Candidate:

Alison Gray

Princeton Observations of the Southern Ocean meridional overturning circulation and its impact on air-sea CO2 flux  
May 10 (Tues 3:00pm) Eleanor Frajka-Williams NOC, Univ. Southampton Wind-driven overturning in the North Atlantic, from RAPID 26N moorings and GRACE satellites  
May 18 Jeffrey Early NorthWest Research Associates The diffusivity of surface drifters from internal waves: observations, modeling, and theory.  
May 25 Gregory C. Johnson

NOAA/PMEL & UW/Oceanography

Improving Estimates of Earth’s Energy Imbalance
June 1 Pierre Dutrieux APL-UW Polar Science Center Ocean-Ice Sheet interactions: the case of the Amundsen Sea, West Antarctica  
June 1 (2pm, MSB 123) Ph.D. Defense: Tyler Hennon UW    
June 2 (3:30pm, OTB 14) ChemO Candidate: Angelicque White OSU    
June 6 (Mon 1:30pm) M.S. Presentation: Jake Steinberg UW The Evolution of a California Undercurrent Submesoscale Eddy (Cuddy) Long-lived subthermocline eddies generated by the California Undercurrent, termed ”Cuddies”, have long been recognized as elements of the California Current System that carry warm, saline, low oxygen Undercurrent waters offshore. Multiple autonomous underwater vehicles (Seagliders) were used to identify and continuously survey a Cuddy offshore of Washington State and Vancouver Island, British Columbia, Canada, for four months during the winter of 2013-2014. Repeat sections across the eddy enabled characterization of its water properties and current structure. The Cuddy surveyed consisted of an isolated mass of high spice/low oxygen water with its core at 200m depth and its radius of maximum velocity at roughly 11km. It had little discernible surface expression, while beneath its core, isopycnal deflection extended to at least 500m depth. Rotating anti-cyclonically, a core region in solid body rotation was observed out to, at most, 1/2 of the radius of maximum velocity where speeds reached over 0.2 m/s. At radii greater than the radius of maximum velocity, a transition region existed where exterior waters were stirred by the Cuddy. In this region layered lateral intrusions were observed, presumed sites for enhanced lateral and vertical mixing. This mixing was subsequently characterized using scalar field variance and variations in spice curvature. At radii greater than twice the radius of maximum velocity, currents returned to background flow values. During its survey the Cuddy traveled northwest in the along-slope direction (between the 1000m and 2000m isobath) over 400km at speeds ranging up to 0.08 m/s. After an initial period of near stationarity, it translated poleward rapidly until reaching a second period of slow movement by which time its rotary strength was markedly weakened. Its Rossby Number, weakened by nearly half while the core scalar field values (spice and oxygen) remain fairly constant. This highlights the difference between the spin down time-scale and lateral diffusion time-scale, and also offers insight into submesoscale horizontal mixing regimes. Due to the large across-shore gradient in water mass properties, the Cuddy anomaly magnitude and shape varied as it moved on and offshore. A second, much larger Cuddy was likely observed further offshore at the very end of the glider missions.
June 6 (Mon 3:30pm, OTB 14) MG&G/APL Candidate: Kerry Key Scripps Marine Elecromagnetic imaging of plate boundary fluids at subduction zones  
June 7 (Tues 3:30pm) Ph.D. Defense: John Guthrie UW Mixing in the central Arctic Ocean: quiet and quieter  

June 29

Ali Mashayek MIT *cancelled*  


Physical Oceanography Lunchtime Seminar, Spring 2013

Tuesday, March 26, 2013

12:30 Wednesdays, OSB 425, unless otherwise noted.

Seminar organizer: James Girton, girton (at) apl.washington.edu, 543-8467.

(The schedule of future seminar organizers can be found here.)

To add your name to the announcement e-mail list, please visit https://mailman1.u.washington.edu/mailman/listinfo/phys_ocean_seminars

Date Speaker Institution Title Abstract
Apr 3

Luc Rainville

APL-UW The Tortoise and the Hare: Observations of Internal Waves and Turbulence from Seagliders      

Apr 10

Eric Steig UW Earth and Space Sciences Antarctic surface melt, sub-ice-shelf-melt and the role of the atmosphere and the ocean. An update from the very latest research.  
Apr 17 Zhongxiang Zhao APL-UW

Internal tides from satellite altimetry

Apr 24 Tom Rossby Univ. Rhode Island OceanScope, a new approach to monitoring the oceans – with examples drawn from the recently reprocessed Nuka Arctica ADCP data.                        This talk will focus on the SCOR/IAPSO working group report ‘OceanScope’, which outlines in some detail a proposed partnership with the global shipping industry, and the opportunities it opens up in terms of observation, innovation, and scalability. The initial phase of OceanScope would focus on the North Atlantic for several reasons including already established activities, the strong call for improved observation, and the willingness of industry to assist in developing this capability. By way of example, we will discuss the recently reprocessed Nuka Arctica ADCP data (between Cape Farewell and Scotland), which reveal the striking constraint imposed by bathymetry on both the mean velocity field and the distribution of eddy kinetic energy. The results point to the some tantalizing possibilities for improved observation of the ocean as a dynamic system.
May 1 Ramsey Harcourt APL-UW Modeling Langmuir Turbulence  
May 8 (10 am) Melinda Webster UW Oceanography Spring snow depth on Arctic sea ice using iceBridge Masters Presentation; Advisor: Ignatius Rigor. Note special time: 10am, OSB 425.
May 8 (12:30 pm) Jennifer MacKinnon Scripps/UCSD Diapycnal mixing in the ocean: processes, patterns, and parameterizations  
May 15 Meghan Cronin  NOAA PMEL  Benthic Storms, Dust Storms, and Monitoring Ocean Storms in the Greater Agulhas System                                    Deep current meter data and output from two high-resolution global ocean circulation models are used to determine the prevalence and location of strong bottom currents in the greater Agulhas Current system. The two models and current meter data are remarkably consistent, showing that benthic storms, with bottom currents greater than 0.2 m s-1, occur throughout the Agulhas retroflection region south of Africa more than 20% of the time. Furthermore, beneath the mean Agulhas Current core and the retroflection front, bottom currents exceed 0.2 m s-1 more than 50% of the time, while away from strong surface currents, bottom currents rarely exceed 0.2 m s-1. The study was motivated by the lead author's efforts to deploy a NOAA surface mooring near the Agulhas Return Current. Implications for sediment transport are also discussed and the results are compared to atmospheric storms. Benthic storms of this strength (0.2 m s-1) are comparable to a 9 m s-1 (Beaufort 5) windstorm, but scaling shows that benthic storms may be less effective at lifting and transporting sediment than dust storms. A manuscript describing this study has been accepted for publication in GRL: Cronin, M. F., T. Tozuka, A. Biastoch, J. V. Durgadoo, L. M. Beal. Prevalence of strong bottom currents in the Greater Agulhas System. Geophys. Res. Let., Accepted, 2013.
May 22 Gary Lagerloef Earth and Space Research Latest Results from the Aquarius Salinity Satellite Mission  
May 29 Stephanie Waterman Univ. New South Wales Eddy-mean flow interactions in an idealised western boundary current jet: New insights from the consideration of eddy shape, orientation and propagation


June 5 Noel Pelland UW Oceanography (More) Dispatches from the Washington Coast: Seaglider Surveys Reveal Seasonal Cycles, Mesoscale Variability, and Links to Biology at Multiple Trophic Levels  
June 12 (10:30 am, APL HCC) Beth Curry UW Oceanography An observational study of Davis Strait transports

Davis Strait is one of two main gateways where freshwater from the Arctic enters the North Atlantic. An observing system began operating in Davis Strait in September 2004 with the goal of providing sustained, long-term quantification of Arctic-subarctic exchange west of Greenland. The system, including moorings, Seaglider surveys and autumn hydrographic sections, was designed to quantify volume, freshwater and heat transports and associated uncertainties. The goal of this analysis is to quantify Davis Strait transport variability and identify atmospheric forcing mechanisms driving the variability to help aid in understanding how exchanges between the Arctic and North Atlantic are being modified due to recent changes observed in the Arctic.

Data from six years (2004-10) of continuous measurements give annual volume,
liquid freshwater and temperature transports through Davis Strait of -1.6 ± 0.5
Sv, -93 ± 6 mSv and 23 ± 2 TW, respectively (negative sign indicates southward
transport). Sea ice export contributes additional 11 mSv of freshwater
transport. The array provides the first year-round measurements in the upper
100m and over the shelves, accounting for 38% (-0.6 Sv) of the net volume and 55%
(-51 mSv) of the net freshwater transports. Davis Strait volume and freshwater
fluxes are the same order of magnitude as those from Fram Strait, the other
Arctic outflow gateway.

Although there are no clear trends in the 2004-10 transports, reanalysis of
Davis Strait mooring data from 1987-90 reveals that less Arctic outflow and more
warm, salty North Atlantic inflow occurred in 2004-10 as compared to the
earlier period. A change in Arctic freshwater storage may have also caused a
freshening event observed between September 2009 to August 2010.

Lagged correlation analysis between Davis Strait transport and regional sea
level pressure (SLP) and winds reveals that atmospheric variability within
Baffin Bay significantly influences circulation and transport through Davis
Strait. A seasonal SLP trough, related to high SLP over the Arctic and low SLP
over the subpolar North Atlantic around Greenland and Iceland, establishes in
Baffin Bay beginning around October and weakens rapidly around March and April.
The SLP trough is an important mechanism driving Davis Strait transport.
Transport both northward and southward through Davis Strait is enhanced when the
SLP trough is present and transport is reduced when SLP variability throughout
Baffin Bay and Davis Strait is weak. Variations in winds and SLP in Baffin Bay
are associated with variations observed in the Arctic and North Atlantic but
they are modified and altered due to the inflows and adjustment caused by the
presence of Greenland.

Ph.D. Defense; Advisor: Craig M. Lee. Note special time and location: APL 6th floor Hardisty Conference Center (Henderson Hall Room 602).

June 13 (Thurs) Caroline Harbitz UW Oceanography Upper ocean temperature and salinity response to global tropical cyclones M.S. Exam; Advisors: Riser and Rhines. 12:30 P.M., 425 Ocean Sciences Building. Note special date.
June 18 (Tues, 123 MSB) Nan-Hsun Chi UW Oceanography Variations of Surface Mixed Layer Heat Budget During MJO Events in Central Indian Ocean M.S. Defense; Advisor: Lien. 12:30 pm, 123 Marine Sciences Building. Note special date and location.
June 21 (Fri) Randy Watts Univ. Rhode Island Divergent Eddy Heat Fluxes in Northern Drake Passage 12:30pm; OSB 425; Note special date.
July 10 Dr. Yusuke Kawaguchi JAMSTEC, Yokosuka, Japan A study of a warm baroclinic eddy in the Canda Basin of the Arctic Ocean: Its generation and estimation of heat impact onto environmental waters 12:30pm; OSB 425; Wednesday (i.e., off-season but regular day, time, and place.)