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  1. Warming in the North Atlantic Ocean has been heterogeneous in recent decades, with locations along the eastern United States seaboard (northwestern Atlantic) seeing some of the largest and fastest warming in the last 100 years. In order to provide a longer temporal context for these changes, we are in the process of developing several master shell growth chronologies and associated geochemical records from theMid-Atlantic coast using the shells of the long-lived marine bivalve Arctica islandica. Based on the shell collection locations (shelf regions offOcean City, Maryland in ~ 61 m water depth and Long Island, New York in ~47 m water depth) and shell geochemistry measurements, we will be able to better ascertain hydrographic spatial and temporal variability of subtropical Atlantic water moving northward through time. These findings will be integrated with similar sclerochronology datasets previously published from the Gulf of Maine region and several others from theMid-Atlantic region that are currently being constructed. Collectively, this network of sclerochronology records will allow us to better characterize changes in the northwestern Atlantic and provide hydrographic insights beyond the relatively short instrumental record and evaluate potential dynamical forcings through time.
    Free, publicly-accessible full text available April 1, 2023
  2. Abstract

    Classical turning surfaces of Kohn–Sham potentials separate classically allowed regions (CARs) from classically forbidden regions (CFRs). They are useful for understanding many chemical properties of molecules but need not exist in solids, where the density never decays to zero. At equilibrium geometries, we find that CFRs are absent in perfect metals, rare in covalent semiconductors at equilibrium, but common in ionic and molecular crystals. In all materials, CFRs appear or grow as the internuclear distances are uniformly expanded. They can also appear at a monovacancy in a metal. Calculations with several approximate density functionals and codes confirm these behaviors. A classical picture of conduction suggests that CARs should be connected in metals, and disconnected in wide-gap insulators, and is confirmed in the limits of extreme compression and expansion. Surprisingly, many semiconductors have no CFR at equilibrium, a key finding for density functional construction. Nonetheless, a strong correlation with insulating behavior can still be inferred. Moreover, equilibrium bond lengths for all cases can be estimated from the bond type and the sum of the classical turning radii of the free atoms or ions.

  3. Free, publicly-accessible full text available July 1, 2023
  4. Abstract. Basic statistical metrics such as autocorrelations and across-region lagcorrelations of sea ice variations provide benchmarks for the assessments offorecast skill achieved by other methods such as more sophisticatedstatistical formulations, numerical models, and heuristic approaches. In thisstudy we use observational data to evaluate the contribution of the trend tothe skill of persistence-based statistical forecasts of monthly and seasonalice extent on the pan-Arctic and regional scales. We focus on the BeaufortSea for which the Barnett Severity Index provides a metric of historicalvariations in ice conditions over the summer shipping season. The varianceabout the trend line differs little among various methods of detrending(piecewise linear, quadratic, cubic, exponential). Application of thepiecewise linear trend calculation indicates an acceleration of the winterand summer trends during the 1990s. Persistence-based statistical forecastsof the Barnett Severity Index as well as September pan-Arctic ice extent showsignificant statistical skill out to several seasons when the data includethe trend. However, this apparent skill largely vanishes when the data aredetrended. In only a few regions does September ice extent correlatesignificantly with antecedent ice anomalies in the same region more than 2months earlier. The springtime “predictability barrier” in regionalforecasts based on persistence of ice extent anomalies is not reduced by theinclusion of severalmore »decades of pre-satellite data. No region showssignificant correlation with the detrended September pan-Arctic ice extent atlead times greater than a month or two; the concurrent correlations arestrongest with the East Siberian Sea. The Beaufort Sea's ice extent as farback as July explains about 20 % of the variance of the Barnett SeverityIndex, which is primarily a September metric. The Chukchi Sea is the onlyother region showing a significant association with the Barnett SeverityIndex, although only at a lead time of a month or two.« less
  5. Abstract

    The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sediment dynamics can control tidewater terminus position on an open shelf under temperate conditions delaying climate-driven retreat.

  6. Retention of students in Science, Technology, Engineering, and Mathematics (STEM) disciplines is a significant concern in higher education. Identity has been identified as an important correlate of academic success that may be important in a robust model of STEM retention. The engineering identity of “early career” university engineering students and its relation to GPA, self-efficacy, and a sense of belonging was examined. Self-efficacy and belonging were demonstrated to be domain dependent. A sense of belonging was much more strongly related to identity than either GPA or self-efficacy. A strong sense of belonging, specifically in the domain of the department of their major, was critical to a strong engineering identity.