ALBERT

Description: Abstract The width of the tropical Hadley circulation (HC) has garnered intense interest in recent decades, owing to the emerging evidence for its expansion in observations and models and to the anticipated impacts on surface climate in its descending branches. To better clarify the causes and impacts of tropical widening, this work generalizes the zonal mean HC to the regional level by defining meridional overturning cells (RC) using the horizontally divergent wind. The edges of the RC are more closely connected to surface hydroclimate than more traditional metrics of regional tropical width (such as the sea level pressure ridge) or even than the zonal mean HC. Simulations reveal a robust weakening of the RC in response to greenhouse gas increases, along with a widening of the RC in some regions. For example, simulated widening of the zonal mean HC in the Southern Hemisphere appears to arise in large part from regional overturning anomalies over the Eastern Pacific, where there is no clear RC. Unforced interannual variability in the position of the zonal mean HC edge is associated with a more general regional widening. These distinct regional signatures suggest that the RCs may be well suited for the attribution of observed circulation trends. The spatial pattern of regional meridional overturning trends in reanalyses corresponds more closely to the pattern associated with unforced interannual variability than to the pattern associated with CO2 forcing, suggesting a large contribution of natural variability to the recent observed tropical widening trends.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Reid, E. C., DeCarlo, T. M., Cohen, A. L., Wong, G. T. F., Lentz, S. J., Safaie, A., Hall, A., & Davis, K. A. Internal waves influence the thermal and nutrient environment on a shallow coral reef. Limnology and Oceanography, 64(5), (2019): 1949-1965, doi:10.1002/lno.11162.

Description: Internal waves can influence water properties in coastal ecosystems through the shoreward transport and mixing of subthermocline water into the nearshore region. In June 2014, a field experiment was conducted at Dongsha Atoll in the northern South China Sea to study the impact of internal waves on a coral reef. Instrumentation included a distributed temperature sensing system, which resolved spatially and temporally continuous temperature measurements over a 4‐km cross‐reef section from the lagoon to 50‐m depth on the fore reef. Our observations show that during summer, internal waves shoaling on the shallow atoll regularly transport cold, nutrient‐rich water shoreward, altering near‐surface water properties on the fore reef. This water is transported shoreward of the reef crest by tides, breaking surface waves and wind‐driven flow, where it significantly alters the water temperature and nutrient concentrations on the reef flat. We find that without internal wave forcing on the fore reef, temperatures on the reef flat could be up to 2.0°C ± 0.2°C warmer. Additionally, we estimate a change in degree heating weeks of 0.7°C‐weeks warmer without internal waves, which significantly increases the probability of a more severe bleaching event occurring at Dongsha Atoll. Furthermore, using nutrient samples collected on the fore reef during the study, we estimated that instantaneous onshore nitrate flux is about four‐fold higher with internal waves than without internal waves. This work highlights the importance of internal waves as a physical mechanism shaping the nearshore environment, and likely supporting resilience of the reef.

Description: We are grateful for the support of the Dongsha Atoll Research Station and the Dongsha Atoll Marine National Park, whose efforts made this research possible. The authors would also like to thank G. Lohmann from Woods Hole Oceanographic Institution and L. Hou, F. Shiah, and K. Lee from Academia Sinica for providing logistical and field support. We thank S. Tyler, and J. Selker from the Center for Transformative Environmental Monitoring Programs, funded by the National Science Foundation (EAR awards 1440596 and 1440506), for timely and effective provision of experimental design support, logistical support, and equipment for the project. We thank R. Branch, University of Washington, and X. Pan, Ocean University of China, for their guidance and SST data that informed this study. Support to G. T. F. Wong is from the Ministry of Science and Technology, Taiwan, grant NSC98‐2611‐M‐001‐004‐MY3 and NSC100‐2611‐M‐001‐001 and from the Academia Sinica through grants titled “Atmospheric Forcing on Ocean Biogeochemistry (AFOBi)” and “Dongsha Ocean Acidification Study (DOcS)”. Support for S. Lentz is from National Science Foundation grant OCE‐1558343. Support for A. Cohen from NSF Grant No. 1220529, by the Academia Sinica (Taiwan) through a thematic project grant to G. Wong and A. Cohen. Support for E. Reid, A. Safaie, and K. A. Davis is from National Science Foundation grant OCE‐1753317, and support to E. Reid from the Environmental Engineering Henry Samueli Endowed Fellowship and the UCI Oceans Graduate Fellowship.

Description: Temperature is highly variable across space and time at multiple scales, shapes landscape pattern, and dictates ecological processes. While our knowledge of ecological phenomena is vast relative to many landscape metrics, thermal patterns which shape landscape mosaics are largely unknown. To address this disconnect, we investigated the thermal landscape by measuring black bulb temperature ( T bb ) at intervals as small as 15 min across 3 yr in a mixed-grass shrub vegetation community. We found that the thermal landscape was highly heterogeneous displaying a prevalence for thermal extremes (i.e., T bb  〉 50°C) and that T bb was driven by the synergism of environmental, terrain, and vegetation factors. Specifically, variation of T bb on the landscape was best predicted by the inclusion of ambient temperature ( T air ), solar radiation ( S rad ), low woody cover, and tall woody cover as variables. Moreover, models of single vegetation parameters (i.e., bare ground, low woody, or tall woody cover) each had greater relative importance than those containing a single terrain variable (i.e., slope or aspect) based on AIC, providing evidence that vegetation is a key driver of T bb on the landscape. Within the thermally heterogeneous landscape, tall woody cover moderated T bb by 10°C more than bare ground, herbaceous, or low woody cover during peak diurnal heating (14:00), and was the only cover type that remained 〈50°C on average. Given that tall woody cover comprises only about 7% of the landscape in our study, these findings have direct conservation implications for species inhabiting shrub communities, specifically that the distribution of tall woody cover is a spatially limited but key predictor of potential thermal refugia on the landscape. Our findings also demonstrate that local interactions between vegetation and temperature can create thermal patterns that shape dynamic landscape mosaics across space and time. Furthermore, we show that structural heterogeneity can maximize thermal complexity across landscapes which can provide greater potential thermal options for organisms. However, our modeled climate projections suggest that far greater thermal extremes will be possible across increasingly larger swaths of the landscape in the future, making assessments and quantifications of thermal landscapes increasingly critical.

Description: The crystallization mechanisms for Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) glass ceramics were studied using thermophysical property characterization techniques. Differential scanning calorimetry (DSC) revealed two separate exothermic events that were ascribed to the initial growth and growth to coherency of a dendritic phase. It was found that the commonly used Johnson-Mehl-Avrami is not a suitable kinetic model for this material. Rather, the Sestak-Berggren (SB) autocatalytic kinetic model was used to analyze the DSC data and the activation energy for initial growth (259 kJ/mol) and coherency (272 kJ/mol) was calculated using isoconversional methods. The calculated parameters for the SB model were used to compare experimental and calculated values for heat flow during the crystallization of LATP and good fits were found for both exothermic events.

Description: Till from moraines at the heads of six major outlet glaciers in the Transantarctic Mountains (TAM) and from till beneath three West Antarctic ice streams have a ubiquitous zircon U-Pb age population spanning the time of the Ross/Pan-African Orogenies (610-475 Ma). Geo- and thermochronology of detrital minerals in these Antarctic glacial tills reveal two different thermal histories for the central and southern TAM. Double-dating of the zircons reveals a geographically widespread (U-Th)/He (ZHe) population of 180-130 Ma in most of the till samples. Sandstone outcrops at Shackleton Glacier, and three Beacon Supergroup sandstone clasts from three moraines, have ZHe ages that fall entirely within this range. The similar population and proximity of many of the till samples to Beacon outcrops lead us to suggest that this extensive ZHe population in the tills is derived from Beacon Supergroup rocks and reflects the thermal response of the Beacon Basin to the breakup of Gondwana. A second population of older (〉200 Ma) ZHe ages in tills at the head of Byrd, Nimrod and Reedy Glaciers. For the tills at the head of the Nimrod and Byrd Glacier, integrating the double-dated zircon results with 40 Ar/ 39 Ar of hornblende, muscovite and biotite, and U-Pb and (U-Th-Sm)/He double-dates on apatite yields a typical pattern of early rapid orogenic cooling (∼4-10˚C/my) 590-475 Ma after the emplacement of the Granite Harbour Intrusives. Low temperature thermochronometers at these sites yield variable but quite old ages (ZHe 480-70 Ma and AHe 200-70 Ma) that require a long history at low temperature. This article is protected by copyright. All rights reserved.