Meltwater Intrusions Reveal Mechanisms for Rapid Submarine Melt at a Tidewater Glacier

Submarine melting has been implicated as a driver of glacier retreat and sea level rise, but to date melting has been difficult to observe and quantify. As a result, melt rates have been estimated from parameterizations that are largely unconstrained by observations, particularly at the near-vertical termini of tidewater glaciers. With standard coefficients, these melt parameterizations predict that ambient melting (the melt away from subglacial discharge outlets) is negligible compared to discharge-driven melting for typical tidewater glaciers. Here, we present new data from LeConte Glacier, Alaska, that challenges this paradigm. Using autonomous kayaks, we observe ambient meltwater intrusions that are ubiquitous within 400 m of the terminus, and we provide the first characterization of their properties, structure, and distribution. Our results suggest that ambient melt rates are substantially higher (×100) than standard theory predicts and that ambient melting is a significant part of the total submarine melt flux. We explore modifications to the prevalent melt parameterization to provide a path forward for improved modeling of ocean-glacier interactions.This work was funded by NSF OPP Grants 1503910, 1504191, 1504288, and 1504521 and National Geographic Grant CP4-171R-17. Additionally, this research was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under award #NA18NWS4620043B. These observations would not be possible without the skilled engineering team who developed the autonomous kayaks—including Jasmine Nahorniak, June Marion, Nick McComb, Anthony Grana, and Corwin Perren—and also the Captain and crew of the M/V Amber Anne. We thank Donald Slater and an anonymous reviewer for valuable feedback that improved this manuscript. Data availability: All of the oceanographic data collected by ship and kayak have been archived with the National Centers for Environmental Information (Accession 0189574, https://accession.nodc.noaa.gov/ 0189574). The glacier data have been archived at the Arctic Data Center (https://doi.org/10.18739/A22G44).Ye

Carrier transfer between confined and localized states in type II InAs/GaAsSb quantum wells

The work has been supported from iCspec project, which received funding from the European Commission’s Horizon 2020 Research and Innovation Programme under grant agreement No. 636930, and also by the National Science Centre of Poland within Grant No. 2014/15/B/ST7/04663.Temperature-resolved photoluminescence studies were performed on tensely-strained AlSb/InAs/GaAsSb W-shaped type II quantum wells. They revealed two emission bands: one at lower energy of localized origin resulting from carrier trapping states at interfaces and dominates at low-temperature; and one corresponding to the fundamental optical transition in the type II quantum well. With the temperature increase to 170—200 K the low-energy emission is quenched and the high-energy band dominates and its intensity increases, indicating carrier transfer processes between the respective states at elevated temperatures. In addition, the integrated photoluminescence intensity was measured as a function of excitation power. At high excitation regime the emission intensity of the low-energy emission band saturated, indicating low density of states, thus confirming its localized nature. The depth of the localization potential at the InAs/GaAsSb interface was determined to be 13—15 meV.Publisher PDFPeer reviewe

Vector Meson Photoproduction from the BFKL Equation II: Phenomenology

Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation which we use to compare to data collected at the HERA collider.Comment: 39 pages, 29 figure

Influence of fissuring and karstification of the carbonate aquifer unsaturated zone on its vulnerability to contamination (Cracow Upper Jurassic Region, Poland)

The carbonate fissure–karstic aquifer of Upper Jurassic age is the main aquifer in the Cracow Upper Jurassic Region (CUJR). The aquifer is recharged directly or indirectly by Quaternary or Quaternary–Cretaceous overburden of varying permeability, which predominates diffused recharge. Concentrated recharge occurs locally and has a diverse nature. Field studies carried out in 20 quarries show moderate permeability of the unsaturated zone of carbonate massif. Karst funnels are filled with rubble and clay material and dominate filled fissures with an opening b < 10 mm. The average surface fissure porosity of massive with chalky limestones and bedded limestones reach 0.12 and 0.45 %, respectively, while fissure permeability coefficient is, respectively, k S 6.60 × 10−5 and 1.27 × 10−3 m/s. The average karstification in quarries was determined as n k = 2.5 %. Tracer studies, carried out in an unconfined carbonate Zakrzówek horst in Cracow (Kraków), document vertical migration of infiltrating water through the systems with different hydraulic resistance, with a flow rate from 8.1 × 10−6 to 4.9 × 10−5 m/s and the lateral migration velocity between communicated caves from 6.94 × 10−6 to 1.06 × 10−4 m/s. The significant presence of poorly permeable overburden and moderate fissuring and karstification of rock in the unsaturated zone of CUJR are reflected in the assessment of the Upper Jurassic aquifer vulnerability to contamination, performed by a modified DRASTIC method. In the area of unconfined karst, occupying 55 % of the area, vulnerability to contamination is high, while as much as 45 % of the area is characterized by medium and low vulnerability

Testing the dynamics of high energy scattering using vector meson production

I review work on diffractive vector meson production in photon-proton collisions at high energy and large momentum transfer, accompanied by proton dissociation and a large rapidity gap. This process provides a test of the high energy scattering dynamics, but is also sensitive to the details of the treatment of the vector meson vertex. The emphasis is on the description of the process by a solution of the non-forward BFKL equation, i.e. the equation describing the evolution of scattering amplitudes in the high-energy limit of QCD. The formation of the vector meson and the non-perturbative modeling needed is also briefly discussed.Comment: 17 pages, 8 figures. Brief review to appear in Mod. Phys. Lett.

Double diffractive meson production and the BFKL Pomeron at e+e−e^+e^- colliders

In this Letter we study the double diffractive vector meson production in $e^+e^-$ collisions assuming the dominance of the BFKL pomeron exchange. We consider the non-forward solution of the BFKL equation at high energy and large momentum transfer and estimate the total cross section for the process $e^+e^- \to e^+e^- V_1 V_2$ with antitagged $e^+$ and $e^-$, where $V_1$ and $V_2$ can be any two vector mesons ($V_i = \rho, \omega, \phi, J/\Psi, \Upsilon$). The event rates for the future linear colliders are given.Comment: 8 pages, 1 figure, Version to be published in Physical Review

Rapid submarine melting driven by subglacial discharge, LeConte Glacier, Alaska

We show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers.We show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers. This buoyant discharge draws in warm seawater, entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice. To capture the effects of subglacial discharge on submarine melting, we conducted 4 days of hydrographic transects during late summer 2012 at LeConte Glacier, Alaska. A major rainstorm allowed us to document the influence of large changes in subglacial discharge. We found strong submarine melt fluxes that increased from 9.1 ± 1.0 to 16.8 ± 1.3 m d1 (ice face equivalent frontal ablation) as a result of the rainstorm. With projected continued global warming and increased glacial runoff, our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems. These effects must be considered when modeling glacier response to future warming and increased runoff.This work was funded by a grant from the Gordon and Betty Moore Foundation grant GBMF2627 to M.T. and M.F. Additional support for J.M.A. was provided by NSF grant ANT0944193. The manuscript was greatly improved by comments from two anonymous re- viewers. We thank Captain Scott Hursey for vessel support and safely navi- gating us through icebergs. J. Elliot provided the orthorectified World View image in Figure 1c.Ye

Sediment redistribution beneath the terminus of an advancing glacier, Taku Glacier (T’aakú Kwáan Sít’i), Alaska.

The recently-advancing Taku Glacier is excavating subglacial sediments at high rates over multidecadal timescales. However, sediment redistribution over shorter timescales remains unquantified. We use a variety of methods to study subglacial and proglacial sediment redistribution on decadal, seasonal, and daily timescales to gain insight into sub- and proglacial landscape formation. Both excavation and deposition were observed from 2003 to 2015 (2.8 ± 0.9ma−1 to +2.9 ± 0.9ma−1). The observed patterns imply that a subglacial conduit has occupied the same site over the past decade. Outwash fans on the subaerial end moraine experience fluvial sediment reworking almost year-round, with net sediment gain in winter and net sediment loss in summer, and an overall mass gain between 2005 and 2015.We estimate that tens of meters of sediment still underlie the glacier terminus, sediments which can be remobilized during future activity. However, imminent retreat from the proglacial moraine will limit its sediment supply, leaving the moraine vulnerable to erosion by bordering rivers. Retreat into an over-deepened basin will leave the glacier vulnerable to increased frontal ablation and accelerating retreat.Ye