Underwater gliders are autonomous underwater vehicles that profile vertically by changing their buoyancy and use wings to move horizontally. Gliders are useful for sustained observation at relatively ...fine horizontal scales, especially to connect the coastal and open ocean. In this review, research topics are grouped by time and length scales. Large-scale topics addressed include the eastern and western boundary currents and the regional effects of climate variability. The accessibility of horizontal length scales of order 1 km allows investigation of mesoscale and submesoscale features such as fronts and eddies. Because the submesoscales dominate vertical fluxes in the ocean, gliders have found application in studies of biogeochemical processes. At the finest scales, gliders have been used to measure internal waves and turbulent dissipation. The review summarizes gliders' achievements to date and assesses their future in ocean observation.
The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the ...interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago.
Faraday rotation measures (RMs) of extragalactic radio sources provide information on line-of-sight magnetic fields, including contributions from our Galaxy, source environments, and the ...intergalactic medium (IGM). Looking at differences in RMs, ΔRM, between adjacent sources on the sky can help isolate these different components. In this work, we classify adjacent polarized sources in the NRAO VLA Sky Survey (NVSS) as random or physical pairs. We recompute and correct the uncertainties in the NVSS RM catalog, since these were significantly overestimated. Our sample contains 317 physical and 5111 random pairs, all with Galactic latitudes , polarization fractions ≥2%, and angular separations between 1 5 and 20′. We find an rms ΔRM of 14.9 0.4 and 4.6 1.1 rad m−2 for the random and physical pairs, respectively. This means that polarized extragalactic sources that are close on the sky but at different redshifts have larger differences in RM than two components of one source. This difference of ∼10 rad m−2 is significant at 5 and persists in different data subsamples. While there have been other statistical studies of ΔRM between adjacent polarized sources, this is the first unambiguous demonstration that some of this RM difference must be extragalactic, thereby providing a firm upper limit on the RM contribution of the IGM. If the ΔRMs originate local to the sources, then the local magnetic field difference between random sources is a factor of 2 larger than that between components of one source. Alternatively, attributing the difference in ΔRMs to the intervening IGM yields an upper limit on the IGM magnetic field strength of 40 nG.
Large‐scale patterns of positive temperature anomalies persisted throughout the surface waters of the North Pacific Ocean during 2014–2015. In the Southern California Current System, measurements by ...our sustained network of underwater gliders reveal the coastal effects of the recent warming. Regional upper ocean temperature anomalies were greatest since the initiation of the glider network in 2006. Additional observed physical anomalies included a depressed thermocline, high stratification, and freshening; induced biological consequences included changes in the vertical distribution of chlorophyll fluorescence. Contemporaneous surface heat flux and wind strength perturbations suggest that local anomalous atmospheric forcing caused the unusual oceanic conditions.
Key Points
Anomalous surface‐intensified warming in the Southern California Current System during 2014–2015
Depressed thermocline, high stratification, freshening, and deepening of chl a fluorescence maximum
Local anomalous atmospheric forcing caused the unusual oceanic conditions
The 2015–2016 El Niño is by some measures one of the strongest on record, comparable to the 1982–1983 and 1997–1998 events that triggered widespread ecosystem change in the northeast Pacific. Here we ...describe impacts of the 2015–2016 El Niño on the California Current System (CCS) and place them in historical context using a regional ocean model and underwater glider observations. Impacts on the physical state of the CCS are weaker than expected based on tropical sea surface temperature anomalies; temperature and density fields reflect persistence of multiyear anomalies more than El Niño. While we anticipate El Niño‐related impacts on spring/summer 2016 productivity to be similarly weak, their combination with preexisting anomalous conditions likely means continued low phytoplankton biomass. This study highlights the need for regional metrics of El Niño's effects and demonstrates the potential to assess these effects before the upwelling season, when altered ecosystem functioning is most apparent.
Key Points
Impacts of the 2015‐2016 El Nino on the California Current System's physical state are evaluated using model, satellite, and glider data
Local temperature and density anomalies are much weaker than expected based on tropical sea surface temperature anomalies
Relatively weak El Nino imprint occurs on backdrop of large multiyear anomalies that may continue to dominate the biological response
We present deep Very Large Array observations of the polarization of radio sources in the GOODS-N field at 1.4 GHz at resolutions of 1".6 and 10". At 1".6, we find that the peak flux cumulative ...number count distribution is N(>p) ~ 45*(p/30 mu Jy) super(-06) per square degree above a detection threshold of 14.5 mu Jy. This represents a break from the steeper slopes at higher flux densities, resulting in fewer sources predicted for future surveys with the Square Kilometer Array and its precursors. It provides a significant challenge for using background rotation measures (RMs) to study clusters of galaxies or individual galaxies. Most of the polarized sources are well above our detection limit, and they are also radio galaxies that are well-resolved even at 10", with redshifts from ~0.2-1.9. We determined a total polarized flux for each source by integrating the 10" polarized intensity maps, as will be done by upcoming surveys such as POSSUM. These total polarized fluxes are a factor of two higher, on average, than the peak polarized flux at 1".6; this would increase the number counts by ~50% at a fixed flux level. The detected sources have RMs with a characteristic rms scatter of ~11 rad m super(-2) around the local Galactic value, after eliminating likely outliers. The median fractional polarization from all total intensity sources does not continue the trend of increasing at lower flux densities, as seen for stronger sources. The changes in the polarization characteristics seen at these low fluxes likely represent the increasing dominance of star-forming galaxies.
The analysis revisits the calculation of the empirical orthogonal functions (EOFs) and principal components (PCs) of sea surface temperature (SST) in the North Pacific from 1950 to 2021. The first ...EOF and PC of SST has proven to be such a useful metric of variability in the North Pacific that it is called the Pacific Decadal Oscillation (PDO). We find that the period of persistent marine heatwaves beginning in 2014 caused a fundamental change to the first EOF and PC of SST (calculated using data from 1950 to 2021) as compared to the established PDO spatial pattern (calculated using data from 1950 to 1993). The second EOF of SST has also changed during this period, both in spatial pattern and in the amount of variance explained. A conclusion is that the PDO and other EOF based metrics may not be as useful in the future as climate continues to change.
Plain Language Summary
The Pacific Decadal Oscillation (PDO) is a widely used measure of the temperature variability in the North Pacific Ocean. The PDO is the result of a well‐known technique called empirical orthogonal function (EOF) analysis that isolates the most energetic modes of variability of the analyzed variable. The first time EOF analysis was applied to oceanographic data was in the 1970's when it was used to identify the most energetic modes of North Pacific sea surface temperature (SST). The first EOF of North Pacific SST has proved so useful as a measure that it received the moniker PDO. Our analysis suggests that a period of persistent marine heatwaves in the North Pacific since 2014 has been so powerful that this first mode of variability of SST has fundamentally changed and the PDO may not be as useful an indicator as it once was.
Key Points
The calculation of empirical orthogonal functions and principal components of North Pacific sea surface temperature is revisited
The period of persistent marine heatwaves since 2014 has caused most energetic modes to change
A conclusion is that indices based on empirical orthogonal function analysis may not be as useful as climate continues to change
Lithium isotopes are increasingly used to trace both present-day and past weathering processes at the surface of the Earth, and could potentially be used to evaluate the average degree of past ...weathering recorded by the upper continental crust (UCC). Yet the previous estimate of average δ7Li of the UCC has a rather large uncertainty, hindering the use of Li isotopes for this purpose. New δ7Li for desert and periglacial loess deposits (windblown dust) from several parts of the world (Europe, Argentina, China and Tajikistan) demonstrate that the former are more homogeneous than the latter, and may therefore serve as excellent proxies of the average composition of large tracts of the UCC. The Li isotopic compositions and concentrations of desert loess samples are controlled by eolian sorting that can be quantified by a binary mixing between a weathered, fine-grained end-member, dominated by phyllosilicates and having low δ7Li, and an unweathered, coarse-grained end-member, that is a mixture of quartz and plagioclase having higher δ7Li. We use correlations between insoluble elements (REE, Nd/Hf and Fe2O3/SiO2), Li concentrations (henceforth referred as Li), and δ7Li to estimate a new, more precise, average Li isotopic composition and concentration for the UCC: Li=30.5±3.6(2σ) ppm, and δLi7=+0.6±0.6(2σ). The δ7Li for desert loess deposits is anti-correlated with the chemical index of alteration (CIA). Using this relationship, along with our average δ7Li, we infer that (1) the present-day CIA of the average UCC is 61−2+4(2σ), higher than the common reference value of 53, and (2) the average proportion of chemically weathered components is as high as 37−10+17(2σ)% at the surface of the Earth.
•Desert loesses are good proxies to average Li composition of UCC.•δ7Li and Li concentrations are controlled by mineralogical sorting.•New and more precise average δ7Li and Li concentration for the UCC.•Quantification of the degree of weathering experienced by the UCC.
Despite the progress that has been made in understanding radio relics, there are still open questions regarding the underlying particle acceleration mechanisms. In this paper, we present deep 1-4 GHz ...Very Large Array (VLA) observations of CIZA J2242.8+5301 (z = 0.1921), a double radio relic cluster characterized by small projection on the plane of the sky. Our VLA observations reveal, for the first time, the complex morphology of the diffuse sources and the filamentary structure of the northern relic. We discover new, faint, diffuse radio emission extending north of the main northern relic. Our Mach number estimates for the northern and southern relics, based on the radio spectral index map obtained using the VLA observations and existing LOw Frequency ARray (LOFAR) and Giant Metrewave Radio Telescope data, are consistent with previous radio and X-ray studies ( and ). However, color-color diagrams and models suggest a flatter injection spectral index than the one obtained from the spectral index map, indicating that projection effects might be not entirely negligible. The southern relic consists of five "arms." Embedded in it, we find a tailed radio galaxy that seems to be connected to the relic. A spectral index flattening, where the radio tail connects to the relic, is also measured. We propose that the southern relic may trace AGN fossil electrons that are reaccelerated by a shock, with an estimated strength of . High-resolution mapping of other tailed radio galaxies also supports a scenario where AGN fossil electrons are revived by the merger event and could be related to the formation of some diffuse cluster radio emission.
Magnesium isotopic compositions of a profile through saprolites developed on a diabase dike from South Carolina have been measured in order to study the behavior of Mg isotopes during continental ...weathering. As weathering progresses, Mg isotopes are greatly fractionated and are correlated with Mg concentration, clay mineral proportions and density of the saprolites. δ
26Mg values increase from −0.22 in the unweathered diabase to +
0.65 in the most weathered saprolite. These observations are consistent with the release of light Mg to the hydrosphere and formation of isotopically heavy Mg in the weathered products. The loss of Mg during weathering can be modeled by Rayleigh distillation with an apparent fractionation factor between the saprolite and fluid (α) of 1.00005 to 1.0004, i.e., up to 0.4‰ fractionation in the
26Mg/
24Mg ratio between the saprolite and fluid. The large variation in α value reflects a mineralogical control on Mg isotope fractionation during primary dissolution of Mg-rich minerals and formation of secondary minerals during continental weathering. Like Mg isotopes, Li isotopes in the saprolite profile are also greatly fractionated, with δ
7Li values ranging from −6.7 down to −20. The large Li isotope fractionation and variation in Li concentration, as well as irregularities in the δ
7Li profile with depth, however, cannot be explained by Li loss during weathering alone. Instead, Li can be modeled by a two-step process: (1) equilibrium isotope fractionation during continental weathering, which lowered δ
7Li and Li concentrations and produced a Li concentration gradient in the saprolites like that seen in Mg, and (2) subsequent kinetic isotope fractionation produced by diffusion of Li in the saprolites, possibly across a paleo-water table. The results presented here suggest that continental weathering will shift the Mg isotopic composition of the continental crust to values higher than the mantle value, whereas crustal recycling over the history of the Earth will have no discernible effect on the Mg isotopic composition of the mantle.
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