Über die Anwendung von Satellitengradiometrie und terrestrischer Gravimetrie zur Identifikation regionaler Stressanomalien im nordchilenischen Subduktionssystem

The effect of the lithospheric density distribution on physical coupling of the subduction system in the area of the Central Andes (18°–35°S) has been investigated. Amongst the composition of the subducting oceanic plate and properties of the subduction interface itself, there has also been evidence that increased coupling of the system may be linked to excess masses above the descending plate. High plate coupling is associated with an increased risk for megathrust earthquakes which occur at respective locations when the accumulated stresses are released and dispersed as seismic energy. Methodological considerations, forward–modelling as well as GPE- and stress calculations – that base on the utilisation and interpretation of the gravity field and its gradient tensor – have been applied in order to examine and analyse the density- and stress distribution in the target area. Particular attention has also been paid to the evaluation of gravity data from the GOCE satellite mission, which, for the first time, provides near–globally measured full–tensor gradiometric data. Methodological analysis concerning the resolving capacity of gravity and gradiometry reveal that measured gravity gradients of the GOCE mission are just sensitive enough to receive information at the order of the expected coastal batholiths' gravity anomaly in North Chile. Those are believed to significantly affect coupling of the subduction system through their relative excess mass. Synthetic 3D density forward modelling of a standard subduction setting has been applied to further test the analysis. It confirms that density contrasts beyond resolvability for gravity data at the orbit height (~250 km) are just resolved in the gradient tensor and its invariants though. The spatial resolution of most recent potential field models that represent measurements from satellite missions is not better than spherical–harmonic degree and order (d/o) 300 (~67 km half–wavelength). This is still not sufficient for very detailed lithospheric or even crustal studies. It is mainly attributed to the signal–to–noise ratio conditions and to overlapping signals in the measurement systems at large distance to the source–masses. However, satellite-based data are virtually globally available and they are acquired and processed in homogeneous manner. They may therefore be consistently handled, analysed and interpreted. Terrestrial data, on the other hand, are strongly heterogeneously distributed, sometimes inadequately processed and meta-data is often not available. Their advantage is a good spatial resolution because of the short distance to the source–masses which allows the distinction of signals. When satellite–derived data are co–located with ground–based data, the respective advantages of both sets—homogeneous coverage and processing of satellite data and high resolution of terrestrial data—may be jointly utilized in one combined potential field model. Here, the combined regional gravity field model IMOSAGA01C has been employed which incorporates terrestrial gravity data of the Central Andes from more than 20 years and satellite–based data from the GOCO03S gravity field model. It has been used on a 6x6–minute (~11 km) grid at 8 km altitude to optimize a pre–existing 3D–density model of North Chile between 18–31.5°S and 66–73°W. By applying geometry adjustments and density inversion, the standard deviation of the residual anomaly could be reduced by 62.3% to 6.3X10e-5 m/s² for the model area. When also parts of the model area are considered that are not covered by terrestrial gravity data, this correspond to an overall error decrease by 68.7%. The adjusted geometry and density information of the density model served as an input to the computation of static stress anomalies on top of the subducting Nazca Plate. The interface–normal rotated component of the lithostatically–induced stress anomaly exhibits a clear segmentation of the forearc. It is characterized by a sequence of positive stress anomalies of up to 80 MPa along the coastal Jurassic batholith belt. It correlates well with the major seismicity of the active margin in North Chile and is attributed to mass excess in the continental crust and lithosphere above the subduction interface. A joint analysis with coupling coefficients from GPS–modelling revealed that positive stress anomalies in the order of 0–100 MPa act as an approximate threshold for the minimum plate coupling (in per cent) within the scope of the seismogenic zone between 18.75°S and 21.75°S. Thus, there must exist patches along the margin where the plate coupling is generally higher than in areas with less relative load (except co-seismic state). Furthermore, a systematic analysis in the area of the April 2014 megathrust earthquake offshore Pisagua/Iquique revealed that coupling and stress anomalies in the area of the fracture plane form virtual loops in their common parameter–space. This could be understood as a strong indicator for the validity of the stress–induced coupling hypothesis. In the future, this finding could help to better understand the seismo–periodic state of a subduction system. This work comes to the conclusion that potential field data from the GOCE mission, despite its high sensitivity, must be understood to reside at the very edge of an appropriate resolution for detailed lithospheric studies. The IMOSAGA01C combined gravity field model however, which collocates the satellite– and surface–based gravity data, clearly outperforms the existing combined models in this regard. Hereby the quality of density models can be improved, which in turn leads to better constrained derivatives such as dynamic models or stress anomalies. From the latter it could finally be concluded that the hypothesis for the North Chile case is acceptable, that relative mass excess above the subducting Nazca Plate co–generates asperities with increased potential for megathrust earthquakes.Mit der vorliegenden Arbeit wurde der Einfluss der Dichteverteilung kontinentaler Lithosphäre auf die physikalische Kopplung des Subduktionssystems im Bereich der Zentralanden (18°–35°S) untersucht. Neben der Beschaffenheit der subduzierenden ozeanischen Platte und den Eigenschaften der Grenzfläche der Subduktion selbst, gibt es Hinweise darauf, dass ein relativer Massenüberschuss oberhalb der abtauchenden Platte in Zusammenhang mit erhöhter Kopplung des Systems steht. Gleichzeitig erhöht sich die Gefahr durch Starkbeben, die an entsprechenden Lokationen auftreten, wenn die aufgebauten Spannungen an den Blockaden gelöst werden und in Form seismischer Energie freigesetzt werden. Methodische Überlegungen, Forwärtsmodellierungen, sowie GPE- und Stressberechnungen, die auf der Interpretation des Schwerefeldes und seines Gradiententensors beruhen, wurden angewendet, um die Dichte- und Stressverteilung im Untersuchungsgebiet näher zu bestimmen und zu analysieren. Ein besonderes Augenmerk lag auch auf der Evaluierung der Schweredaten der Satellitenmission GOCE, welche erstmals gemessene gradiometrische Daten des gesamten Schwere–Tensors nahezu global zur Verfügung stellte. Methodische Analysen zum Auflösungsvermögen der Schwere– und Gradiometrie–Daten ergaben, dass die gemessenen Gradienten der GOCE Mission hinreichend sensitiv sind, um Informationen in der Größenordnung der erwarteten Schwereanomalie der Küstenbatholithe in Nordchile zu registrieren. Es wird angenommen, dass diese durch ihren Massenüberschuss die Kopplung des Subduktionssystems signifikant beeinflussen. Die synthetische 3D-Dichtemodellierung eines standardisierten Subduktions-Settings wurde verwendet, um diese Überlegung zu überprüfen. Sie bestätigt das Ergebnis, dass Dichtekontraste, die sich für Schweredaten in Orbithöhe (~250 km) jenseits der Auflösbarkeit befinden, durch den Schweregradienten-Tensor und seine Invarianten hingegen gerade noch aufgelöst werden können. Die räumliche Auflösung aktueller Potenzialfeld–Modelle, welche Messungen von Satellitenmissionen wiedergeben, ist nicht besser als Grad/Ordnung 300 (~67 km Halbwellenlänge). Das ist für sehr detaillierte Studien der Lithosphäre oder Kruste noch unzureichend. Ursachen hierfür sind in erster Linie die Kondition des Signal–Rausch–Verhältnisses und sich überlagernde Signale im Messsystem bei großer Distanz zu den verursachenden Massen. Dafür sind Satelliten–basierte Daten quasi–global verfügbar und homogen aufgenommen. Sie können konsistent prozessiert, analysiert und interpretiert werden. Terrestrische Daten hingegen sind zumeist extrem heterogen verteilt, sehr unterschiedlich prozessiert und Metadaten stehen oft nicht zur Verfügung. Der Vorteil bei ihrer Verwendung liegt darin, dass sie aufgrund des geringen Abstandes zu den Quellen ein hohes räumliches Auflösungsvermögen haben und eine entsprechend klare Signaltrennung möglich ist. Die jeweiligen Vorteile beider Datenarten — homogene Aufnahme, Abdeckung und Prozessierung der Satellitendaten sowie hohe Auflösung der terrestrischen Daten — können in einer kombinerten Bearbeitung vereinigt werden, wenn beide Datensätze über Kollokation zusammengeführt werden. In der vorliegenden Arbeit wurde das kombinerte regionale Schwerefeldmodell IMOSAGA01C verwendet, welches terretrische Schweredaten aus mehr als 20 Jahren Bodenmessungen in den Zentralanden, sowie Satelliten-basierte Daten aus dem GOCO03S Schwerefeldmodell zusammenführt. Hier wurde ein 6x6–Minuten (~11 km) Grid in 8 km Höhe verwendet, um ein vorhandenes 3D Dichtemodell von Nordchile im Bereich 18–31.5°S und 66–73°W zu optimieren. Durch Anpassungen der Modellgeometrie und durch Dichte–Inversion konnte die Standardabweichung der Residualanomalie im Bereich der Modellierung um 62,3% auf 6.3x10e-5 m/s² gesenkt werden. Unter zusätzlicher Berücksichtigung der Modellgebiete, die nicht mit terrestrischen Schweremessungen abgedeckt sind, entspricht dies einer Verbesserung um 68,7%. Die angepassten Geometrie– und Dichteinformationen des Dichtemodells dienten als Eingangsgrößen zur Berechnung statischer Stressanomalien auf der subduzierten Nazca–Platte. Die normal zur Subduktion rotierte Komponente der lithostatisch induzierten Stressanomalie weist eine deutliche Segmentierung des Forearcs auf. Diese zeichnet sich durch ein Band mit positiven Stressanomalien von bis zu 80 MPa im Bereich der Jurassischen Küstenbatholithe aus. Es korreliert mit der vorherrschenden Seismizität des aktiven Kontinentalrandes in Nordchile und ist auf Massenüberschüsse innerhalb der kontinentalen Kruste und Lithosphäre oberhalb der Subduktions-Grenzfläche zurückzuführen. Im Gebiet der seismogenen Zone zwischen 18.75°S und 21.75°S zeigte eine gemeinsame Analyse mit Kopplungs-Koeffizienten aus GPS–Modellen, dass positive Stressanomalien im Bereich 0–100 MPa jeweils als näherungsweise Schwellenwerte für die minimale Kopplung (in Prozent) eingesetzt werden können. Demnach muss es Regionen geben, in denen die Kopplung der Platten, bis auf den co-seismischen Zustand, ständig höher ist als in Regionen mit geringerer relativer Auflast. Darüber hinaus zeigte eine systematische Analyse im Bereich des Starkbebens von Pisagua/Iquique vom April 2014, dass Plattenkopplung und Stressanomalien innerhalb ihres gemeinsamen Parameterraumes für den Bereich der Bruchfläche über virtuelle Schleifen verknüpft sind. Dies kann als Kennzeichen für die Gültigkeit der These zur Stress–induzierten Kopplung gewertet werden. Diese Erkenntnis könnte zukünftig dabei helfen, den seismozyklischen Zustand eines Subduktionssystems besser zu verstehen. Die vorliegende Arbeit kommt zu dem Schluss, dass sich die Potenzialfeld–Daten der GOCE Mission trotz der hohen Sensitivität im Grenzbereich der notwendigen Auflösung für detaillierte Lithosphärenstudien liegen. Das kombinierte Schwerefeldmodell IMOSAGA01C hingegen, welches die Satelliten– und Boden–gestützten Schweredaten zusammenführt, übertrifft existierende kombinierte Modelle in dieser Hinsicht deutlich. Hierdurch lässt sich die Qualität der Dichtemodelle erhöhen, was zu einer besser validierten Zusatzinterpretation führt, wie zum Beispiel dynamische Modelle oder Stressanomalien zeigen. Aus letzteren konnte abgeleitet werden, dass die Hypothese, derzufolge relative Massenüberschüsse oberhalb der subduzierenden Nazca–Platte Asperities mit erhöhtem Gefährdungspotenzial für Starkbeben mitverursachen, für das Untersuchungsgebiet in Nordchile gültig ist

Global sea-level budget and ocean-mass budget, with a focus on advanced data products and uncertainty characterisation

Studies of the global sea-level budget (SLB) and the global ocean-mass budget (OMB) are essential to assess the reliability of our knowledge of sea-level change and its contributors. Here we present datasets for times series of the SLB and OMB elements developed in the framework of ESA's Climate Change Initiative. We use these datasets to assess the SLB and the OMB simultaneously, utilising a consistent framework of uncertainty characterisation. The time series, given at monthly sampling and available at https://doi.org/10.5285/17c2ce31784048de93996275ee976fff (Horwath et al., 2021), include global mean sea-level (GMSL) anomalies from satellite altimetry, the global mean steric component from Argo drifter data with incorporation of sea surface temperature data, the ocean-mass component from Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry, the contribution from global glacier mass changes assessed by a global glacier model, the contribution from Greenland Ice Sheet and Antarctic Ice Sheet mass changes assessed by satellite radar altimetry and by GRACE, and the contribution from land water storage anomalies assessed by the global hydrological model WaterGAP (Water Global Assessment and Prognosis). Over the period January 1993–December 2016 (P1, covered by the satellite altimetry records), the mean rate (linear trend) of GMSL is 3.05 ± 0.24 mm yr−1. The steric component is 1.15 ± 0.12 mm yr−1 (38 % of the GMSL trend), and the mass component is 1.75 ± 0.12 mm yr−1 (57 %). The mass component includes 0.64  ± 0.03 mm yr−1 (21 % of the GMSL trend) from glaciers outside Greenland and Antarctica, 0.60 ± 0.04 mm yr−1 (20 %) from Greenland, 0.19 ± 0.04 mm yr−1 (6 %) from Antarctica, and 0.32 ± 0.10 mm yr−1 (10 %) from changes of land water storage. In the period January 2003–August 2016 (P2, covered by GRACE and the Argo drifter system), GMSL rise is higher than in P1 at 3.64 ± 0.26 mm yr−1. This is due to an increase of the mass contributions, now about 2.40 ± 0.13 mm yr−1 (66 % of the GMSL trend), with the largest increase contributed from Greenland, while the steric contribution remained similar at 1.19 ± 0.17 mm yr−1 (now 33 %). The SLB of linear trends is closed for P1 and P2; that is, the GMSL trend agrees with the sum of the steric and mass components within their combined uncertainties. The OMB, which can be evaluated only for P2, shows that our preferred GRACE-based estimate of the ocean-mass trend agrees with the sum of mass contributions within 1.5 times or 0.8 times the combined 1σ uncertainties, depending on the way of assessing the mass contributions. Combined uncertainties (1σ) of the elements involved in the budgets are between 0.29 and 0.42 mm yr−1, on the order of 10 % of GMSL rise. Interannual variations that overlie the long-term trends are coherently represented by the elements of the SLB and the OMB. Even at the level of monthly anomalies the budgets are closed within uncertainties, while also indicating possible origins of remaining misclosures

Global sea-level budget and ocean-mass budget, with a focus on advanced data products and uncertainty characterisation

Studies of the global sea-level budget (SLB) and the global ocean-mass budget (OMB) are essential to assess the reliability of our knowledge of sea-level change and its contributors. Here we present datasets for times series of the SLB and OMB elements developed in the framework of ESA's Climate Change Initiative. We use these datasets to assess the SLB and the OMB simultaneously, utilising a consistent framework of uncertainty characterisation. The time series, given at monthly sampling and available at https://doi.org/10.5285/17c2ce31784048de93996275ee976fff (Horwath et al., 2021), include global mean sea-level (GMSL) anomalies from satellite altimetry, the global mean steric component from Argo drifter data with incorporation of sea surface temperature data, the ocean-mass component from Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry, the contribution from global glacier mass changes assessed by a global glacier model, the contribution from Greenland Ice Sheet and Antarctic Ice Sheet mass changes assessed by satellite radar altimetry and by GRACE, and the contribution from land water storage anomalies assessed by the global hydrological model WaterGAP (Water Global Assessment and Prognosis). Over the period January 1993–December 2016 (P1, covered by the satellite altimetry records), the mean rate (linear trend) of GMSL is 3.05 ± 0.24 mm yr−1. The steric component is 1.15 ± 0.12 mm yr−1 (38 % of the GMSL trend), and the mass component is 1.75 ± 0.12 mm yr−1 (57 %). The mass component includes 0.64  ± 0.03 mm yr−1 (21 % of the GMSL trend) from glaciers outside Greenland and Antarctica, 0.60 ± 0.04 mm yr−1 (20 %) from Greenland, 0.19 ± 0.04 mm yr−1 (6 %) from Antarctica, and 0.32 ± 0.10 mm yr−1 (10 %) from changes of land water storage. In the period January 2003–August 2016 (P2, covered by GRACE and the Argo drifter system), GMSL rise is higher than in P1 at 3.64 ± 0.26 mm yr−1. This is due to an increase of the mass contributions, now about 2.40 ± 0.13 mm yr−1 (66 % of the GMSL trend), with the largest increase contributed from Greenland, while the steric contribution remained similar at 1.19 ± 0.17 mm yr−1 (now 33 %). The SLB of linear trends is closed for P1 and P2; that is, the GMSL trend agrees with the sum of the steric and mass components within their combined uncertainties. The OMB, which can be evaluated only for P2, shows that our preferred GRACE-based estimate of the ocean-mass trend agrees with the sum of mass contributions within 1.5 times or 0.8 times the combined 1σ uncertainties, depending on the way of assessing the mass contributions. Combined uncertainties (1σ) of the elements involved in the budgets are between 0.29 and 0.42 mm yr−1, on the order of 10 % of GMSL rise. Interannual variations that overlie the long-term trends are coherently represented by the elements of the SLB and the OMB. Even at the level of monthly anomalies the budgets are closed within uncertainties, while also indicating possible origins of remaining misclosures

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

The seismically active Andean and Central American margins: Can satellite gravity map lithospheric structures?

The spatial resolution and quality of geopotential models (EGM2008, EIGEN-5C, ITG-GRACE03s, and GOCO-01s) have been assessed as applied to lithospheric structure of the Andean and Central American subduction zones. For the validation, we compared the geopotential models with existing terrestrial gravity data and density models as constrained by seismic and geological data. The quality and resolution of the downward continued geopotential models in the Andes and Central America decrease with increasing topography and depend on the availability of terrestrial gravity data. High resolution of downward continued gravity data has been obtained over the Southern Andes where elevations are lower than 3000 m and sufficient terrestrial gravity data are available. The resolution decreases with an increase in elevation over the north Chilean Andes and Central America. The low resolution in Central America is mainly attributed to limited surface gravity data coverage of the region. To determine the minimum spatial dimension of a causative body that could be resolved using gravity gradient data, a synthetic gravity gradient response of a spherical anomalous mass has been computed at GOCE orbit height (254.9 km). It is shown that the minimum diameter of such a structure with density contrast of 240 kg m−3 should be at least ∼45 km to generate signal detectable at orbit height. The batholithic structure in Northern Chile, which is assumed to be associated with plate coupling and asperity generation, is about 60–120 km wide and could be traceable in GOCE data. Short wavelength anomalous structures are more pronounced in the components of the gravity gradient tensor and invariants than in the gravity field. As the ultimate objective of this study is to understand the state of stress along plate interface, the geometry of the density model, as constrained by combined gravity models and seismic data, has been used to develop dynamic model of the Andean margin. The results show that the stress regime in the fore-arc (high and low) tends to follow the trend of the earthquake distributions.Special Priority Program 1257 ‘Mass Transport and Mass Distribution in the Earth System’UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela Centroamericana de Geologí

Global sea-level budget and ocean-mass budget, with a focus on advanced data products and uncertainty characterisation

Studies of the global sea-level budget (SLB) and the global ocean-mass budget (OMB) are essential to assess the reliability of our knowledge of sea-level change and its contributors. Here we present datasets for times series of the SLB and OMB elements developed in the framework of ESA's Climate Change Initiative. We use these datasets to assess the SLB and the OMB simultaneously, utilising a consistent framework of uncertainty characterisation. The time series, given at monthly sampling and available at https://doi.org/10.5285/17c2ce31784048de93996275ee976fff (Horwath et al., 2021), include global mean sea-level (GMSL) anomalies from satellite altimetry, the global mean steric component from Argo drifter data with incorporation of sea surface temperature data, the ocean-mass component from Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry, the contribution from global glacier mass changes assessed by a global glacier model, the contribution from Greenland Ice Sheet and Antarctic Ice Sheet mass changes assessed by satellite radar altimetry and by GRACE, and the contribution from land water storage anomalies assessed by the global hydrological model WaterGAP (Water Global Assessment and Prognosis). Over the period January 1993–December 2016 (P1, covered by the satellite altimetry records), the mean rate (linear trend) of GMSL is 3.05 ± 0.24 mm yr−1. The steric component is 1.15 ± 0.12 mm yr−1 (38 % of the GMSL trend), and the mass component is 1.75 ± 0.12 mm yr−1 (57 %). The mass component includes 0.64  ± 0.03 mm yr−1 (21 % of the GMSL trend) from glaciers outside Greenland and Antarctica, 0.60 ± 0.04 mm yr−1 (20 %) from Greenland, 0.19 ± 0.04 mm yr−1 (6 %) from Antarctica, and 0.32 ± 0.10 mm yr−1 (10 %) from changes of land water storage. In the period January 2003–August 2016 (P2, covered by GRACE and the Argo drifter system), GMSL rise is higher than in P1 at 3.64 ± 0.26 mm yr−1. This is due to an increase of the mass contributions, now about 2.40 ± 0.13 mm yr−1 (66 % of the GMSL trend), with the largest increase contributed from Greenland, while the steric contribution remained similar at 1.19 ± 0.17 mm yr−1 (now 33 %). The SLB of linear trends is closed for P1 and P2; that is, the GMSL trend agrees with the sum of the steric and mass components within their combined uncertainties. The OMB, which can be evaluated only for P2, shows that our preferred GRACE-based estimate of the ocean-mass trend agrees with the sum of mass contributions within 1.5 times or 0.8 times the combined 1σ uncertainties, depending on the way of assessing the mass contributions. Combined uncertainties (1σ) of the elements involved in the budgets are between 0.29 and 0.42 mm yr−1, on the order of 10 % of GMSL rise. Interannual variations that overlie the long-term trends are coherently represented by the elements of the SLB and the OMB. Even at the level of monthly anomalies the budgets are closed within uncertainties, while also indicating possible origins of remaining misclosures

Organic and inorganic mercurials have distinct effects on cellular thiols, metal homeostasis, and Fe-binding proteins in Escherichia coli

The protean chemical properties of the toxic metal mercury (Hg) have made it attractive in diverse applications since antiquity. However, growing public concern has led to an international agreement to decrease its impact on health and the environment. During a recent proteomics study of acute Hg exposure in E. coli, we also examined the effects of inorganic and organic Hg compounds on thiol- and metal- homeostases. On brief exposure, lower concentrations of divalent inorganic mercury Hg(II) blocked bulk cellular thiols and protein-associated thiols more completely than higher concentrations of monovalent organomercurials, phenylmercuric acetate (PMA) and merthiolate (MT). Cells bound Hg(II) and PMA in excess of their available thiol ligands; X-ray absorption spectroscopy indicated nitrogens as likely additional ligands. The mercurials released protein bound iron (Fe) more effectively than common organic oxidants and all disturbed the Na(+)/K(+) electrolyte balance, but none provoked efflux of six essential transition metals including Fe. PMA and MT made stable cysteine monothiol adducts in many Fe-binding proteins, but stable Hg(II) adducts were only seen in CysXxx(n)Cys peptides. We conclude that on acute exposure: (a) the distinct effects of mercurials on thiol- and Fe-homeostases reflected their different uptake and valences; (b) their similar effects on essential metal- and electrolyte-homeostases reflected the energy-dependence of these processes; and (c) peptide phenylmercury-adducts were more stable or detectable in mass spectrometry than Hg(II)-adducts. These first in vivo observations in a well-defined model organism reveal differences upon acute exposure to inorganic and organic mercurials that may underlie their distinct toxicology