ALBERT

Description: The Tibetan Himalaya represents the northernmost continental unit of the Indian plate that collided with Asia in the Cenozoic. Paleomagnetic studies on the Tibetan Himalaya can help constrain the dimension and paleogeography of ‘Greater India', the Indian plate lithosphere that subducted and underthrusted below Asia after initial collision. Here, we present a paleomagnetic investigation of a Jurassic (limestones) and Lower Cretaceous (volcaniclastic sandstones) section of the Tibetan Himalaya. The limestones yielded positive fold test, showing a pre-folding origin of the isolated remanent magnetizations. Detailed paleomagnetic analyses, rock magnetic tests, end-member modeling of acquisition curves of isothermal remanent magnetization, and petrographic investigation reveal that the magnetic carrier of the Jurassic limestones is authigenic magnetite, whereas the dominant magnetic carrier of the Lower Cretaceous volcaniclastic sandstones is detrital magnetite. Our observations lead us to conclude that the Jurassic limestones record a prefolding remagnetization, whereas the Lower Cretaceous volcaniclastic sandstones retain a primary remanence. The volcaniclastic sandstones yield an Early Cretaceous paleolatitude of 55.5°S [52.5°S, 58.6°S] for the Tibetan Himalaya, suggesting it was part of the Indian plate at that time. The size of ‘Greater India' during Jurassic time cannot be estimated from these limestones. Instead, a paleolatitude of the Tibetan Himalaya of 23.8°S [21.8°S, 26.1°S] during the remagnetization process is suggested. It is likely that the remagnetization, caused by the oxidation of early diagenetic pyrite to magnetite, was induced during 103-83 Ma or 77-67 Ma. The inferred paleolatitudes at these two time intervals imply very different tectonic consequences for the Tibetan Himalaya. This article is protected by copyright. All rights reserved.

Description: In this paper, the field experiments on ground surface spectral broadband solar radiation (SR) and corresponding albedo were introduced at three man-made sites at Gobi, desert and bare loess zones during three different intensive observational periods (IOP) from 2010 to 2013 in Gansu Province, respectively. The continuous and high temporal resolution records of ground surface solar radiation are presented, including global (GR), ultraviolet (UV), visible (VIS), and near-infrared radiation (NIR). The corresponding albedos are analyzed over three typical non-vegetated underlying surfaces in arid and semi-arid and semi-humid regions of northwestern China. The preliminary investigations were carried out. The results show: the variation trends of UV, VIS and NIR are coincident with the GR, and the irradiances are gradually decreasing throughout the IOP at each site; the energy ratios of VIS/GR are all approximately 40.2%, and the ratios of NIR/GR are all approximately 54.4% at the Gobi, desert and bare loess zones; the averaged albedos of the soil for VIS are 0.231, 0.211 and 0.142, for the NIR are 0.266, 0.252 and 0.255 over the Gobi, desert and bare loess land surfaces, respectively. The energy ratios of VIS/GR and NIR/GR are not 50% as prescribed for all of the soil color classes in most of land surface models (LSMs). The observational soil albedo values for NIR are not twice to that of the VIS as predicted in some LSMs for the underlying surface at the three sites. GR albedo is determined by the energy ratios of SR/GR and SR albedos.

Description: An analysis of the recently reconstructed gridded May-September total precipitation in the Indian monsoon region for the past half millennium discloses significant variations at multidecadal timescales. Meanwhile, paleo-climate modeling outputs from NCAR CCSM4 show similar multidecadal variations in the monsoon precipitation. One of those variations at the frequency of 40–50 years per cycle is examined in this study. Major results show that this variation is a product of the processes in that the meridional gradient of the atmospheric enthalpy is strengthened by radiation loss in the high-latitude and polar region. Driven by this gradient and associated baroclinicity in the atmosphere, more heat/energy is generated in the tropical and subtropical (monsoon) region and transported poleward. This transport relaxes the meridional enthalpy gradient and, subsequently, the need for heat production in the monsoon region. The multidecadal timescale of these processes results from atmospheric circulation-radiation interactions and the inefficiency in generation of kinetic energy from the potential energy in the atmosphere to drive the eddies that transport heat poleward. This inefficiency creates a time delay between the meridional gradient of the enthalpy and the poleward transport. The monsoon precipitation variation lags that in the meridional gradient of enthalpy but leads that of the poleward heat transport. This phase relationship, and underlining chasing process by the transport of heat to the need for it driven by the meridional enthalpy gradient, sustains this multidecadal variation. This mechanism suggests that atmospheric circulation processes can contribute to multidecadal timescale variations. Interactions of these processes with other forcing, such as SST or solar irradiance anomalies, can result in resonant or suppressed variations in the Indian monsoon precipitation.

Description: The impact on the dynamics of the stratosphere of three approaches to geoengineering by Solar Radiation Management is investigated using idealized simulations of a global climate model. The approaches are geoengineering with sulfate aerosols, titania aerosols and reduction in total solar irradiance (representing mirrors placed in space). If it were possible to use stratospheric aerosols to counterbalance the surface warming produced by a quadrupling of atmospheric carbon dioxide concentrations, tropical lower stratospheric radiative heating would drive a thermal-wind response which would intensify the stratospheric polar vortices. In the Northern Hemisphere this intensification results in strong dynamical cooling of the polar stratosphere. Northern Hemisphere stratospheric sudden warming events become rare (1 or 2 in 65 years for sulfate and titania respectively). The intensification of the polar vortices results in a poleward shift of the tropospheric midlatitude jets in winter. The aerosol radiative heating enhances the tropical upwelling in the lower stratosphere, influencing the strength of the Brewer-Dobson Circulation. In contrast, solar dimming does not produce heating of the tropical lower stratosphere so there is little intensification of the polar vortex and no enhanced tropical upwelling. The dynamical response to titania aerosol is qualitatively similar to the response to sulfate.

Description: Sea ice is an active source or a sink for carbon dioxide (CO 2 ), although to what extent is not clear. Here, we analyze CO 2 dynamics within sea ice using a one-dimensional halo-thermodynamic sea ice model including gas physics and carbon biogeochemistry. The ice-ocean fluxes, and vertical transport, of total dissolved inorganic carbon (DIC) and total alkalinity (TA) are represented using fluid transport equations. Carbonate chemistry, the consumption and release of CO 2 by primary production and respiration, the precipitation and dissolution of ikaite (CaCO 3 •6H 2 O) and ice-air CO 2 fluxes, are also included. The model is evaluated using observations from a 6-month field study at Point Barrow, Alaska and an ice-tank experiment. At Barrow, results show that the DIC budget is mainly driven by physical processes, wheras brine-air CO 2 fluxes, ikaite formation, and net primary production, are secondary factors. In terms of ice-atmosphere CO 2 exchanges, sea ice is a net CO 2 source and sink in winter and summer, respectively. The formulation of the ice-atmosphere CO 2 flux impacts the simulated near-surface CO 2 partial pressure ( p CO 2 ), but not the DIC budget. Because the simulated ice-atmosphere CO 2 fluxes are limited by DIC stocks, and therefore 〈 2 mmol m -2 day -1 , we argue that the observed much larger CO 2 fluxes from eddy covariance retrievals cannot be explained by a sea ice direct source and must involve other processes or other sources of CO 2 . Finally, the simulations suggest that near surface TA/DIC ratios of ~2, sometimes used as an indicator of calcification, would rather suggest outgassing. This article is protected by copyright. All rights reserved.

Description: A 15 year time series (1999-2014) from the 0°, 23°W Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) mooring, which includes an 8-month record (10/2008-6/2009) of high-resolution near-surface velocity data, is used to analyze the diurnal variability of sea surface temperature, shear, and stratification in the central equatorial Atlantic. The ocean diurnal cycle exhibits pronounced seasonality that is linked to seasonal variations in the wind field. In boreal summer and fall steady trade winds and clear skies dominate, with limited diurnal variability in sea surface temperature. Diurnal shear layers, with reduced Richardson numbers, are regularly observed descending into the marginally unstable equatorial undercurrent below the mixed layer, conditions favorable for the generation of deep-cycle turbulence. In contrast, in boreal winter and spring winds are lighter and more variable, mixed layers are shallow, and diurnal variability of sea surface temperature is large. During these conditions diurnal shear layers are less prominent, and the stability of the undercurrent increases, suggesting seasonal covariance between diurnal near-surface shear and deep-cycle turbulence. Modulation of the ocean diurnal cycle by tropical instability waves is also identified. This work provides the first observational assessment of the diurnal cycle of near surface shear, stratification, and marginal instability in the equatorial Atlantic, confirming previous modeling results, and offering a complementary perspective on similar work in the equatorial Pacific. This article is protected by copyright. All rights reserved.

Description: For this paper, a coupled physical-biological model was developed in order to study the mechanisms of the winter bloom in the Luzon Strait (referred as LZB). Based on a simulation for January, 2010, the results showed that the model was capable of reproducing the key features of the LZB, such as the location, inverted-V shape, twin-core structure and bloom intensity. The simulation showed that the LZB occurred during the relaxation period of intensified northeasterly winds, when the deepened mixed layer started to shoal. Nutrient diagnostics showed that vertical mixing was responsible for the nutrient supply to the upper ~40 m layer, while subsurface upwelling supplied nutrients to the region below the mixed layer. Hydrodynamic diagnostics showed that the advection of relative vorticity (RV) primarily contributed to the subsurface upwelling. The RV advection was resulted from an offshore jet, which was associated with a northeasterly wind, flowed across the ambient RV field. This article is protected by copyright. All rights reserved.

Description: Accurate estimation of the absorption coefficient ( a g ) for chromophoric dissolved organic matter (CDOM) over ultraviolet (UV) and short visible radiation wavelengths (with λ = 275-450 nm) is crucial to provide a robust assessment of the biogeochemical significance of UV in the global ocean. Using a training data set spanning a variety of water types from the clearest open ocean to dynamic inshore waters, a novel algorithm to accurately resolve CDOM absorption spectra from ocean color is presented. Employing a suite of multivariate statistical approaches (principal component analysis, cluster analysis, and multiple linear regression), this new algorithm was developed with matched field data for CDOM spectra and remote sensing reflectance ( R rs ) at Sea-viewing Wide Field-of-view Sensor (SeaWiFS) bands. Freed from any presupposition about CDOM spectral shape or conventional spectral extrapolations from visible data, our algorithm allows direct retrieval of a fully resolved CDOM absorption spectrum over UV wavelengths from visible R rs , and further enables a global scale view of the dynamics of CDOM over different water types. Accuracy of a g retrieval is good, with a mean absolute percent difference for a g in the UV of ~25%. With fully resolved spectra, maps of calculated CDOM spectral slopes ( S 275-295 , S 350-400 ) and slope ratios ( S R ) are presented with the potential to provide new information about the chemical composition (e.g., molecular weight, aromaticity), sources, transformation, and cycling pathways of CDOM on global as well as regional scales. The new algorithm will contribute to improved accuracy for photochemical and photobiological rate calculations from ocean color. This article is protected by copyright. All rights reserved.