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Data collected by two buoy arrays that operated during the ice seasons of 2014/2015 and 2016/2017 were used to characterize annual cycles of ice motion and deformation in the western Arctic Ocean. An anomalously strong and weak Beaufort Gyre in 2014/2015 and 2016/2017 induced generally anticyclonic and cyclonic sea ice drift during 2014/2015 and 2016/2017, respectively. Cyclonic ice motion resulted in higher contributions of ice divergence to total ice deformation in 2016/2017 than in 2014/2015. In 2014, the autumn ice concentration and multiyear ice coverage were higher than in 2016; consequently, the response of ice motion to wind forcing was weak, and less ice deformation was observed in autumn 2014. During the autumn--winter transition, the ice--wind speed ratio, ice deformation rate and its spatial and temporal scaling exponents, and localization of ice deformation decreased markedly in both 2014/2015 and 2016/2017 as a result of freeze--up and consolidation of ice floes. Such dynamic behavior was maintained through to spring with the further thickening of ice cover. Ice deformation increased due to weakened ice strength as summer approached. The amplitude of the annual cycle of ice deformation rate in the western Arctic Ocean in 2014/2015 and especially in 2016/2017 was larger than that observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) program in 1997/1998. We attribute this phenomenon to ice loss during the recent summers, especially of thick multiyear ice. [ABSTRACT FROM AUTHOR]

High temporal resolution in situ measurements of pancake ice drift are presented, from a pair of buoys deployed on floes in the Antarctic marginal ice zone during the winter sea ice expansion, over 9 days in which the region was impacted by four polar cyclones. Concomitant measurements of wave‐in‐ice activity from the buoys are used to infer that the ice remained unconsolidated, and pancake ice conditions were maintained over at least the first 7 days. Analysis of the data shows (i) the fastest reported ice drift speeds in the Southern Ocean; (ii) high correlation of drift velocities with the surface wind velocities, indicating absence of internal ice stresses >100 km from the ice edge where remotely sensed ice concentration is 100%; and (iii) presence of a strong inertial signature with a 13 hr period. A Lagrangian free drift model is developed, including a term for geostrophic currents that reproduce the 13 hr period signature in the ice motion. The calibrated model provides accurate predictions of the ice drift for up to 2 days, and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions. Plain Language Summary: During the Antarctic winter, small pancake ice floes, which form rapidly in wavy conditions, dominate new ice growth and create a dynamic environment. However, there are only a handful of local observations of pancake ice drift, particularly during the intense polar cyclones that frequently reshape the ice cover. More observations are needed to generate better understanding and modeling of pancake ice response to winds, waves, and currents. We describe a set of pancake ice drift and wave‐in‐ice measurements over 9 days in which four polar cyclones affected the region, from buoys deployed on pancake floes 100 km from the ice edge. We also develop an ice drift model.The data show how the cyclones affect ice drift and contain the fastest reported ice speed in the Southern Ocean (0.75 m s−1). The instantaneous drift speed closely correlates with the wind speed, and the ice also displays a 13 hr period rotational motion that we reproduce in the model with forcing from ocean currents. We show that pancake ice is in free drift, despite sea ice covering the entire ocean surface in the measurement region and that the model predicts drift accurately over 2 days with calibration of only two parameters. Key Points: Ice speed (0.75 m s−1) measured during intense polar cyclones is the fastest recorded in the Southern OceanMean ice drift follows the wind, but with a strong inertial component, period ≈13 hrPancake ice drift agrees with the free drift approximation (no internal ice stresses), even though remotely sensed concentration is 100% [ABSTRACT FROM AUTHOR]

Abstract: The seasonal evolution of sea ice mass balance between the Central Arctic and Fram Strait, as well as the underlying driving forces, remain largely unknown because of a lack of observations. In this study, two and three buoys were deployed in the Central Arctic during the summers of 2010 and 2012, respectively. It was established that basal ice growth commenced between mid‐October and early December. Annual basal ice growth, ranging from 0.21 to 1.14 m, was determined mainly by initial ice thickness, air temperature, and oceanic heat flux during winter. An analytic thermodynamic model indicated that climate warming reduces the winter growth rate of thin ice more than for thick ice because of the weak thermal inertia of the former. Oceanic heat flux during the freezing season was 2–4 W m−2, which accounted for 18–31% of the basal ice energy balance. We identified two mechanisms that modified the oceanic heat flux, i.e., solar energy absorbed by the upper ocean during summer, and interaction with warm waters south of Fram Strait; the latter resulted in basal ice melt, even in winter. In summer 2010, ice loss in the Central Arctic was considerable, which led to increased oceanic heat flux into winter and delayed ice growth. The Transpolar Drift Stream was relatively weak in summer 2013. This reduced sea ice advection out of the Arctic Ocean, and it restrained ice melt because of the cool atmospheric conditions, weakened albedo feedback, and relatively small oceanic heat flux in the north. [ABSTRACT FROM AUTHOR]

Bone marrow osteogenesis in senile osteoporotic bone is impaired and, as such, may have significant implications on the successful outcome of fracture repair. Here we utilize a well-established murine model of senile osteoporosis, the P6 strain of senescence-accelerated mice (SAMP6), to investigate fracture healing in aged osteoporotic bone. A femoral osteotomy was created in SAMP6 and in non-osteoporotic age-matched control R1 senescence-resistant mice (SAMR1). The course of fracture healing was evaluated over a period of 42 days using quantitative µCT and histological analysis. The differentiation capabilities of bone mesenchymal progenitor cells derived from SAMP6 and SAMR1 mice was examined, and their osteogenic potential determined. Although preliminary in vitro analysis confirmed that bone marrow-derived stem cells (BMSC) isolated from SAMP6 mice had a reduced osteogenic capacity, no significant deficit in fracture repair as determined by quantitative µCT could be detected. This was supported by histology assessment, where complete bridging of the fracture gap was evident by day 28 and was fully healed day 42 in both SAMP6 and SAMR1 mice. Further in vitro studies revealed that periosteal-derived progenitor cells (PDPC) isolated from SAMP6 mice had an osteogenic potential comparable to that observed in SAMR1 mice. In conclusion, fracture healing in SAMP6 mice is not detrimentally affected by impairment of BMSC osteogenesis, suggesting that bone marrow-mediated repair processes are dispensable for normal bone healing in this senile osteoporotic fracture model. Furthermore, the influence of PDPC in the repair process may partly explain the absence of any detectable deficits in fracture repair in SAMP6 mice. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:798-804, 2010 [ABSTRACT FROM AUTHOR]