Heat, salt, and freshwater budgets for a glacial fjord in Greenland

Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2735-2768, doi:10.1175/JPO-D-15-0134.1.In Greenland’s glacial fjords, heat and freshwater are exchanged between glaciers and the ocean. Submarine melting of glaciers has been implicated as a potential trigger for recent glacier acceleration, and observations of ocean heat transport are increasingly being used to infer the submarine melt rates. The complete heat, salt, and mass budgets that underlie such methods, however, have been largely neglected. Here, a new framework for exploring glacial fjord budgets is developed. Building on estuarine studies of salt budgets, the heat, salt, and mass transports through the fjord are decomposed, and new equations for calculating freshwater fluxes from submarine meltwater and runoff are presented. This method is applied to moored records from Sermilik Fjord, near the terminus of Helheim Glacier, to evaluate the dominant balances in the fjord budgets and to estimate freshwater fluxes. Throughout the year, two different regimes are found. In the nonsummer months, advective transports are balanced by changes in heat/salt storage within their ability to measure; freshwater fluxes cannot be inferred as a residual. In the summer, a mean exchange flow emerges, consisting of inflowing Atlantic water and outflowing glacially modified water. This exchange transports heat toward the glacier and is primarily balanced by changes in storage and latent heat for melting ice. The total freshwater flux increases over the summer, reaching 1200 ± 700 m3 s−1 of runoff and 1500 ± 500 m3 s−1 of submarine meltwater from glaciers and icebergs in August. The methods and results highlight important components of fjord budgets, particularly the storage and barotropic terms, that have been not been appropriately considered in previous estimates of submarine melting.The data collection and analysis was funded by NSF Grants ARC-0909373, OCE-113008, and OCE-1434041

The dynamics of shelf forcing in Greenlandic fjords

Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 2799-2827, doi:10.1175/JPO-D-18-0057.1.The fjords that connect Greenland’s glaciers to the ocean are gateways for importing heat to melt ice and for exporting meltwater into the ocean. The transport of heat and meltwater can be modulated by various drivers of fjord circulation, including freshwater, local winds, and shelf variability. Shelf-forced flows (also known as the intermediary circulation) are the dominant mode of variability in two major fjords of east Greenland, but we lack a dynamical understanding of the fjord’s response to shelf forcing. Building on observations from east Greenland, we use numerical simulations and analytical models to explore the dynamics of shelf-driven flows. For the parameter space of Greenlandic fjords, we find that the fjord’s response is primarily a function of three nondimensional parameters: the fjord width over the deformation radius (W/Rd), the forcing time scale over the fjord adjustment time scale, and the forcing amplitude (shelf pycnocline displacements) over the upper-layer thickness. The shelf-forced flows in both the numerical simulations and the observations can largely be explained by a simple analytical model for Kelvin waves propagating around the fjord. For fjords with W/Rd > 0.5 (most Greenlandic fjords), 3D dynamics are integral to understanding shelf forcing—the fjord dynamics cannot be approximated with 2D models that neglect cross-fjord structure. The volume flux exchanged between the fjord and shelf increases for narrow fjords and peaks around the resonant forcing frequency, dropping off significantly at higher- and lower-frequency forcing.This work was funded by NSF Grant OCE-1536856 and by the NOAA Climate and Global Change Postdoctoral Fellowship

Katabatic wind-driven exchange in fjords

Author Posting. © American Geophysical Union, 2017. 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: Oceans 122 (2017): 8246–8262, doi:10.1002/2017JC013026.The general issue of katabatic wind-driven exchange in fjords is considered using an idealized numerical model, theory, and observations. Two regimes are identified. For fjords narrower than a viscous boundary layer width, the exchange is limited by a balance between wind and friction in lateral boundary layers. For the nonlinear viscous parameterization used here, this boundary layer thickness depends on the properties of the fjord, such as stratification and length, as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant. For wider fjords typical of east Greenland, the balance is primarily between wind, the along-fjord pressure gradient, and acceleration, in general agreement with previous two-layer nonrotating theories. It is expected that O(10%) of the surface layer will be flushed out of the fjord by a single wind event. Application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in Sermilik Fjord, a large glacial fjord in southeast Greenland. The presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness, in which cases the exchange is reduced. It is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east Greenland represent an important mechanism of exchange between the fjord and shelf, with implications for the renewal of warm, salty waters at depth and for the export of glacial freshwater in the upper layer.National Science Foundation Grant Numbers: OCE-1533170, OCE-1434041, PLR-1418256; NOAA Climate and Global Change Postdoctoral Fellowship2018-04-2

Dynamics of Greenland’s glacial fjords

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 June 2016Glacial fjords form conduits between glaciers of the Greenland Ice Sheet and the North Atlantic. They are the gateways for importing oceanic heat to melt ice and for exporting meltwater into the ocean. Submarine melting in fjords has been implicated as a driver of recent glacier acceleration; however, there are no direct measurements of this melting, and little is known about the fjord processes that modulate melt rates. Combining observations, theory, and modeling, this thesis investigates the circulation, heat transport, and meltwater export in glacial fjords. While most recent studies focus on glacial buoyancy forcing, there are other drivers – e.g. tides, local wind, shelf variability – that can be important for fjord circulation. Using moored records from two major Greenlandic fjords, shelf forcing (from shelf density fluctuations) is found to dominate the fjord circulation, driving rapid exchange with the shelf and large heat content variability near the glacier. Contrary to the conventional paradigm, these flows mask any glacier-driven circulation in the non-summer months. During the summer, when shelf forcing is reduced and freshwater forcing peaks, a mean exchange flow transports warm Atlantic-origin water towards the glacier and exports glacial meltwater. Many recent studies have inferred submarine melt rates from oceanic heat transport, but the fjord budgets that underlie this method have been overlooked. Building on estuarine studies of salt fluxes, this thesis presents a new framework for assessing glacial fjord budgets and revised equations for inferring meltwater fluxes. Two different seasonal regimes are found in the heat/salt budgets for Sermilik Fjord, and the results provide the first time-series of submarine meltwater and subglacial discharge fluxes into a glacial fjord. Finally, building on the observations, ROMS numerical simulations and two analytical models are used to investigate the dynamics of shelf-driven flows and their importance relative to local wind forcing across the parameter space of Greenland’s fjords. The fjord response is found to vary primarily with the width relative to the deformation radius and the fjord adjustment timescale relative to the forcing timescale. Understanding these modes of circulation is a step towards accurate modeling of ocean-glacier interactions.Funding for this thesis was provided by the National Science Foundation (OCE-1130008, OCE- 1434041 and OPP-909373), WHOI Coastal Ocean Institute, WHOI Ocean Climate Change Institute, and the Kerr Foundation

Tracking icebergs with time-lapse photography and sparse optical flow, LeConte Bay, Alaska, 2016–2017

We present a workflow to track icebergs in proglacial fjords using oblique time-lapse photos and the Lucas-Kanade optical flow algorithm. We employ the workflow at LeConte Bay, Alaska, where we ran five time-lapse cameras between April 2016 and September 2017, capturing more than 400 000 photos at frame rates of 0.5–4.0 min−1. Hourly to daily average velocity fields in map coordinates illustrate dynamic currents in the bay, with dominant downfjord velocities (exceeding 0.5 m s−1 intermittently) and several eddies. Comparisons with simultaneous Acoustic Doppler Current Profiler (ADCP) measurements yield best agreement for the uppermost ADCP levels (∼ 12 m and above), in line with prevalent small icebergs that trace near-surface currents. Tracking results from multiple cameras compare favorably, although cameras with lower frame rates (0.5 min−1) tend to underestimate high flow speeds. Tests to determine requisite temporal and spatial image resolution confirm the importance of high image frame rates, while spatial resolution is of secondary importance. Application of our procedure to other fjords will be successful if iceberg concentrations are high enough and if the camera frame rates are sufficiently rapid (at least 1 min−1 for conditions similar to LeConte Bay).This work was funded by the U.S. National Science Foundation (OPP-1503910, OPP-1504288, OPP-1504521 and OPP-1504191).Ye

A reconstruction of warm-water inflow to Upernavik Isstrøm since 1925 CE and its relation to glacier retreat

International audienceThe mass loss from the Greenland Ice Sheet has increased over the past 2 decades. Marine-terminating glaciers contribute significantly to this mass loss due to increased melting and ice discharge. Periods of rapid retreat of these tidewater glaciers have been linked to the concurrent inflow of warm Atlantic-sourced waters. However, little is known about the variability of these Atlantic-derived waters within the fjords, due to a lack of multi-annual in situ measurements. Thus, to better understand the potential role of ocean warming on glacier retreat, reconstructions that characterize the variability of Atlantic water inflow to the fjords are required. Here, we investigate foraminiferal assemblages in a sediment core from Upernavik Fjord, West Greenland, in which the major ice stream Upernavik Isstrøm terminates. We conclude that the foraminiferal assemblage is predominantly controlled by changes in bottom water composition and provide a reconstruction of Atlantic water inflow to Upernavik Fjord, spanning the period 1925–2012. This reconstruction reveals peak Atlantic water influx during the 1930s and again after 2000, a pattern that is comparable to the Atlantic Multidecadal Oscillation (AMO). The comparison of these results to historical observations of front positions of Upernavik Isstrøm reveals that inflow of warm Atlantic-derived waters likely contributed to high retreat rates in the 1930s and after 2000. However, moderate retreat rates of Upernavik Isstrøm also prevailed in the 1960s and 1970s, showing that glacier retreat continued despite a reduced Atlantic water inflow, albeit at a lower rate. Considering the link between bottom water variability and the AMO in Upernavik Fjord, and the fact that a persistent negative phase of the AMO is expected for the next decade, Atlantic water inflow into the fjord may decrease in the coming decade, potentially minimizing or stabilizing the retreat of Upernavik Isstrøm during this time interval.climate chang

Searching for Signatures of Cosmic Superstrings in the CMB

Because cosmic superstrings generically form junctions and gauge theoretic strings typically do not, junctions may provide a signature to distinguish between cosmic superstrings and gauge theoretic cosmic strings. In cosmic microwave background anisotropy maps, cosmic strings lead to distinctive line discontinuities. String junctions lead to junctions in these line discontinuities. In turn, edge detection algorithms such as the Canny algorithm can be used to search for signatures of strings in anisotropy maps. We apply the Canny algorithm to simulated maps which contain the effects of cosmic strings with and without string junctions. The Canny algorithm produces edge maps. To distinguish between edge maps from string simulations with and without junctions, we examine the density distribution of edges and pixels crossed by edges. We find that in string simulations without Gaussian noise (such as produced by the dominant inflationary fluctuations) our analysis of the output data from the Canny algorithm can clearly distinguish between simulations with and without string junctions. In the presence of Gaussian noise at the level expected from the current bounds on the contribution of cosmic strings to the total power spectrum of density fluctuations, the distinction between models with and without junctions is more difficult. However, by carefully analyzing the data the models can still be differentiated.Comment: 15 page

Assessment of protein allergenicity on the basis of immune reactivity: animal models.

Because of the public concern surrounding the issue of the safety of genetically modified organisms, it is critical to have appropriate methodologies to aid investigators in identifying potential hazards associated with consumption of foods produced with these materials. A recent panel of experts convened by the Food and Agriculture Organization and World Health Organization suggested there is scientific evidence that using data from animal studies will contribute important information regarding the allergenicity of foods derived from biotechnology. This view has given further impetus to the development of suitable animal models for allergenicity assessment. This article is a review of what has been achieved and what still has to be accomplished regarding several different animal models. Progress made in the design and evaluation of models in the rat, the mouse, the dog and in swine is reviewed and discussed

Cardiovascular Health and Incident Cardiovascular Disease and Cancer

The American Heart Association's “Simple 7” offers a practical public health conceptualization of cardiovascular health (CVH). CVH predicts incident cardiovascular disease (CVD) in younger populations, but has not been studied in a large, diverse population of aging postmenopausal women. The extent to which CVH predicts cancer in postmenopausal women is unknown