Sea-level Oscillations Research Articles

Meteotsunami (“Marrobbio”) of 25–26 June 2014 on the Southwestern Coast of Sicily, Italy

A major tsunami-like event, locally known as ‘marrobbio’, impacted the southwestern coast of Sicily on 25–26 June 2014. The event was part of a chain of hazardous episodes in the Mediterranean and Black seas during the last week of June 2014 resulting from an anomalous atmospheric system (“tumultuous atmosphere”) propagating eastward over the region. The synoptic patterns and vertical structure of the atmosphere over Sicily at the time of the event indicate that atmospheric wave ducting was responsible for the generation of tsunamigenic air pressure disturbances that produced especially high sea level responses (“meteotsunamis”) at certain sites along the Sicilian coast. The strongest sea level oscillations were observed at Mazara del Vallo, where a 1-m meteotsunami bore, propagating upstream in the Mazaro River, was generated. The combined effects of external resonance (Proudman resonance on the western Sicilian shelf) and internal resonant conditions (bathymetric and topographic characteristics of specific sites) were found to be the key factors that caused the meteotsunami (marrobbio phenomenon) on the coast of Sicily and the meteobore at Mazara del Vallo.

Sedimentary noise and sea levels linked to land\u2013ocean water exchange and obliquity forcing

In ancient hothouses lacking ice sheets, the origins of large, million-year (myr)-scale sea-level oscillations remain a mystery, challenging current models of sea-level change. To address this mystery, we develop a sedimentary noise model for sea-level changes that simultaneously estimates geologic time and sea level from astronomically forced marginal marine stratigraphy. The noise model involves two complementary approaches: dynamic noise after orbital tuning (DYNOT) and lag-1 autocorrelation coefficient (ρ1). Noise modeling of Lower Triassic marine slope stratigraphy in South China reveal evidence for global sea-level variations in the Early Triassic hothouse that are anti-phased with continental water storage variations in the Germanic Basin. This supports the hypothesis that long-period (1-2 myr) astronomically forced water mass exchange between land and ocean reservoirs is a missing link for reconciling geological records and models for sea-level change during non-glacial periods.

Sedimentary, Geochemical and Micropaleontological Responses to Sea Level Variations in the Vitoria Estuary, Espírito Santo

AbstractMarine insertion indicators in the Vitoria estuary (ES) revealed relative variations in sea level during the Holocene in three sediment cores. Sedimentological, geochemical (C/N ratio), and paleontological (shells and palynomorphs) analysis and14C dating associated five sedimentary facies to different estuarine deposits. A C/N ratio <10 at the core base indicated organic matter of marine origin. Moving up the cores to 110–150 cm, an abrupt increase in C/N to 26–63 in every core suggests the sudden entry of higher plants into the estuary, potentially the moment sea level retreated. High continental (10,743 palynomorphs/g) and low marine palynomorph concentrations (323 palynomorphs/g) suggest a primarily continental source even during transgression and at high sea level. Around 8973 cal BP, an open bay already existed in the region of Vitoria. Sea level potentially exceeded the current level around 7110 cal BP. The transgressive maximum was at 5567 cal BP. Marine insertion indicators, such as marine shells, low C/N ratios and foraminiferal linings, did not always respond directly to sea level oscillations. These discrepancies probably result from lateral variations in sedimentary deposits from transport patterns and from variations in organic matter and palynomorph preservation due to differences in river and obstacle proximity.

Interannual Variation of Surface Circulation in the Japan/East Sea due to External Forcings and Intrinsic Variability

The interannual variation of surface ocean currents can be as large as seasonal variation in the Japan/East Sea (JES). To identify the major factors that cause such interannual variability of surface ocean circulation in the JES, surface circulation was simulated from 1998 to 2009 using a three-dimensional model. Contributions of atmospheric forcing (ATM), open boundary data (OBC), and intrinsic variability (ITV) of the surface flow in the JES on the interannual variability of surface ocean circulation were separately examined using numerical simulations. Variability in surface circulation was quantified in terms of variance in sea surface height, 100-m depth water temperature, and surface currents. ITV was found to be the dominant factor that induced interannual variabilities of surface circulation, the main path of the East Korea Warm Current (EKWC), and surface kinetic energy on a time scale of 2–4 years. OBC and ATM were secondary factors contributing to the interannual variation of surface circulation. Interannual variation of ATM changed the separation latitude of EKWC and increased the variability of surface circulation in the Ulleung Basin. Interannual variation of OBC enhanced low-frequency changes in surface circulation and eddies in the Yamato Basin. It also modulated basin-wide uniform oscillations of sea level. This study suggests that precise estimation of initial conditions using data assimilation is essential for long-term prediction of surface circulation in the JES.

Episodic reef growth in the granitic Seychelles during the Last Interglacial: Implications for polar ice sheet dynamics

We present a detailed taxonomic and lithologic analysis of fossil reefs in the Granitic Seychelles to improve constraints on global mean sea level behavior during the last interglacial sea-level highstand, ~129,000–116,000 years ago. In particular, we have assessed the coralgal reef outcrops for any sedimentalogic evidence of sub-orbital sea level oscillations that may have occurred during this warm, interglacial period. At the outcrop scale, we observe at least three distinct episodes of reef growth punctuated by two discontinuities that typically manifest as coral rubble layers or extensive lateral encrustations of the hydrozoan coral Millepora exaesa. Hiatuses in reef growth at other sites around the world have been interpreted as relative sea level falls and/or environmental disturbances. We have tested the hypothesis that these discontinuities, that we refer to as disturbance horizons, are related to ephemeral drops in sea level that have been inferred at last interglacial reef sites from other sites around the globe. At two sites, there is sedimentological evidence in the form of extensive dissolution and freshwater cements associated with the disturbance horizons that would require subaerial exposure followed by marine inundation. At the remaining sites, evidence is consistent with, but not necessarily indicative of, an ephemeral drop in sea level. To establish if these disturbance horizons are coeval between the outcrops and if they are local or global features, requires high-precision dating of the disturbance horizons along with a critical analysis of sedimentary and chronological evidence from other sites around the globe. If the disturbance horizons observed in the Seychelles represent transient sea-level falls or still stands during the last interglacial, this would imply a dynamic behavior of the polar ice sheets during this past warm period.

No evidence from the eastern Mediterranean for a MIS 5e double peak sea-level highstand

AbstractTo understand past and future sea-level variability, it is important to know if during an interglacial the eustatic sea level is constant or oscillates by several meters around an average value. Several field sites within and outside the tropics have been interpreted to suggest such oscillations during Marine Oxygen Isotope Stage (MIS) 5e (129–116 ka). Here, we present our analysis of one such non-tropical site, Hergla, where a facies succession indicates two foreshore deposits above each other, previously interpreted as MIS 5e sea-level highstand amplified by a second rise. Our study, based on field, microfacies, and optical age Bayesian statistics shows a sea-level rise forming the upper foreshore strata that coincided with the global sea-level rise of the MIS 5a interstadial. The site does therefore not provide evidence for the MIS 5e double peak. We conclude from our analysis that the facies-based proxy is insensitive to small-scale sea-level oscillation. Likewise, uncertainties associated with age estimates are too large to robustly infer a short-term sea-level change.

New evidence for “far-field” Holocene sea level oscillations and links to global climate records

Rising sea level in the coming century is of significant concern, yet predicting relative sea level change in response to eustatic sea level variability is complex. Potential analogues are provided by the recent geological past but, until recently, many sea level reconstructions have been limited to millennial scale interpretations due to age uncertainties and paucity in proxy derived records. Here we present a sea level history for the tectonically stable “far-field” Great Barrier Reef, Australia, derived from 94 high precision uranium–thorium dates of sub-fossil coral microatolls. Our results provide evidence for at least two periods of relative sea level instability during the Holocene. These sea level oscillations are broadly synchronous with Indo-Pacific negative sea surface temperature anomalies, rapid global cooling events and glacial advances. We propose that the pace and magnitude of these oscillations are suggestive of eustatic/thermosteric processes operating in conjunction with regional climatic controls.

Reconstructing the sedimentary evolution of the Miocene Aksu Basin based on fan delta development (eastern Mediterranean-Turkey)

The Aksu Basin in southern Turkey is dominantly represented by an alluvial fan and five fan deltas (FDs) developed along the tectonically controlled margins of the basin during the Miocene. Four alternating compressional and tensional tectonic phases have influenced the basin since its formation. Strong tectonic movements caused high sedimentation rates and progradation of large debris-flow and mass-flow dominated FDs. Here we describe two FDs (the Karadağ and Kargı FDs) in detail. The Karadağ FD began to develop under the control of a compressional regime and continued the evolution under a tensional regime. The same tensional regime caused the separation of the Karadağ FD from its source and the deposition of the Kargı FD into the newly formed accommodation area. The alternating tectonic regimes and sea-level oscillations in the Aksu Basin gave rise to the development of coral colonies on the shallow delta fronts, forming patch reefs despite the large amounts of conglomerates supplied by fan deltaic processes.

Geohistorical evolution and the new geological map of the city of Vitoria, ES, Brazil

The economic growth over the last century, driven by port activities, promoted an artificial territorial expansion since urban growth was limited by the weak development of the coastal plains and the predominance of crystalline hills in Vitoria, Espírito Santo, Brazil. This paper summarizes the geo-historical evolution of Vitoria, the main transformations of the urban area and their relationship with the current landscape while introducing a new geological map of the city produced from the identification and delineation of technogenic deposits. Bibliographical, cartographic and field surveys were done using the Geographic Information System integrated with Remote Sensing products and techniques to produce the maps. The results show that, currently, Vitória has 10 km2 of technogenic deposits, corresponding to about 12% of its geological coverage while 61% of the shoreline perimeter is artificialized. Urban roads, recreational areas, and residential neighborhoods were settled over landfills, 52% of which covered either water depths or mangrove forest. It is concluded that the topography was the greatest obstacle to the occupation and development of Vitoria earlier. Almost the whole perimeter of Vitoria Island and mainland have been altered by landfill. However, these “new” spaces remained as the limiting factor to any re-adaptation attempt of the coastal ecosystems, especially mangroves, in a future scenario of sea-level oscillations.

Paleoenvironmental analysis and paleobiogeography of the Langhian-Serravallian succession in Wadi Trakee, westcentral Sinai (Egypt): An implication for Mediterranean and Paratethys faunal exchange

This paper aims to determine the probable paleoenvironments (ecozones) of Miocene sediments at Wadi Trakee, westcentral Sinai, Egypt. To achieve this work, both benthonic and planktonic foraminiferal assemblages were identified. Six paleoecologic zones (ecozones) are distinguished from Wadi Trakee Miocene succession in west-central Sinai; open marine environments were predominated during the deposition of these sediments; occasionally lagoonal. Great oscillation in sea level represented by lagoons and open marine conditions were prevailed in the earliest Langhian that came after the latest Burdigalian sea regression this was followed by great sea transgression phase and open marine environments during the latest Langhian. Serravallian Sea came after sea regression and a short hiatus preserved at the end of Langhian and ended by lagoons environments in the latest Serravallian. Seventy-one species of the identified benthic foraminifera indicate the Langhian, whereas forty-eight species recorded from the Serravallian. Due to the great similarity between the identified fauna with the previously recorded from the Paratethys countries, it can be suggested that high rate of faunal exchanges occurred and sea connections between the Mediterranean and Paratethys were occurred during these ages. Two unconformity surfaces are detected, the first lies within the Langhian while the second lies at the end of the Serravallian. Thirty-two planktonic foraminiferal species are also recorded from the Langhian – Serravallian succession that helped us to subdivide the studied succession into two planktonic zones; these zones correlated with the international schemes for biozones in the subtropical areas and the Mediterranean regions.

Paleoenvironmental evolution based on benthic foraminifera biofacies of the Paraíba do Sul Deltaic Complex, eastern Brazil

The paleoecology and distribution of benthic foraminiferal assemblages were analyzed in the core 2-MU-1-RJ well, drilled in the Paraíba do Sul Deltaic Complex, Rio de Janeiro (Brazil). An abundant assemblage was found in the upper portion of the well core, inferred to be pleistocenic deposits. The coastal dynamic was recognized from five biofacies based on clusters, the Planktonic/Benthic (P/B) ratios and indicator species distribution in the core. Several biofacies were identified along the core depending on the species dominance. From the bottom to the top of the core, the biofacies succession represents the environmental changes in the coastal area associated to sea-level oscillations. The biofacies ABP dominated by Ammonia parkinsoniana and Bolivina spp. and Pararotalia cananeiaensis represents an inner shelf environment; biofacies QP dominated by shelf miliolids species; biofacies PGH, dominated by P. cananeiaensis, Gavelinopsis praegeri, and Hanzawaia nitidula, represents the estuary complex with middle or outer shelf influence; biofacies QL represents hypersaline waters dominated by lagoonal miliolids; and biofacies HP characterized by Haynesina germanica and P. cananeiaensis is associated with paralic environments. Marine ingressions are recorded and those biofacies show the pleistocenic coastal hydrodinamic in the deltaic complex. The foraminiferal biofacies contribute with detailed information to sedimentary facies previously characterized in the study area by the reconstruction of paleoenvironment succession.

The effects of Quaternary sea-level fluctuations on the evolutionary history of an endemic ground lizard (Tropidurus hygomi)

The Quaternary period is marked by many extensive glaciations and sea level oscillations, mainly during the Pleistocene. Sea level oscillations possibly shaped landscapes in coastal regions, which may have played an important role in the diversification of organisms that live in these areas. In this study, we investigated the population history of the lizard Tropidurus hygomi, which is endemic to a narrow region of the northeastern coast of Brazil, inhabiting areas of white sandy coastal dunes in the Restinga formation. We specifically asked: how did sea level changes in the Quaternary shape population structure and historical demography of T. hygomi? We collected 72 tissue samples throughout the distribution of the species and obtained sequences from the mitochondrial gene cytochrome b. Different tests for population structure identified five distinct mitochondrial DNA clusters (mtDNA clusters) in T. hygomi. Divergence time estimate showed that splits among these mtDNA clusters took place in the Pleistocene, and exhibited temporal agreement with marine transgressive events during these periods. As T. hygomi is a threatened species and our data suggest the presence of five mtDNA clusters, further conservation actions for this species should consider these independent mtDNA clusters in order to preserve the evolutionary history and the diversity within the species.

Relative sea-level variability during the late Middle Pleistocene: New evidence from eastern England

Unravelling patterns of relative sea-level change during previous interglacials enhances our understanding of ice sheet response to changing climate. Temperate-latitude estuarine environments have the potential to preserve continuous records of relative sea level from previous interglacial (warm) periods. This is important because, currently, we typically only have snapshots of sea-level highstands from low-latitude corals and raised palaeoshoreline indicators while the (continuous) deep-sea oxygen isotope record only provides indirect evidence of sea-level changes. Here, we focus on the Nar Valley in eastern England, in which is preserved evidence of a late middle-Pleistocene marine transgression more than 20 vertical metres in extent. By applying a model of coastal succession and sea-level tendencies, as used in Holocene sea-level studies, we assess the mode (abrupt versus gradual) of sea-level change recorded by the interglacial Nar Valley sequences. Compiled palaeo-stratigraphic evidence comprising foraminifera, pollen and amino acid racemization dating, suggests that the mode of sea-level change in the Nar Valley interglacial sequence was gradual, with potentially two phases of regional transgression and relative sea-level rise occurring at two separate times. The first phase occurred during the latter part of marine Oxygen Isotope Stage (MIS) 11 from ∼8 to 18 m OD; and, the second phase potentially occurred during early MIS 9 from ∼-3 to 3 m OD (with long-term tectonic uplift included in these estimates). We cannot conclusively preclude an alternative MIS 11 age for these lower sediments. The lack of indicators for rapid sea-level oscillations in the Nar Valley adds weight to an argument for steady melt of the ice sheets during both MIS 11 and 9.

Spatial and temporal variability of sea level rise hot spots over the eastern United States

AbstractRegional sea level rise (SLR) acceleration during the past few decades north of Cape Hatteras has commonly been attributed to weakening Atlantic Meridional Overturning Circulation, although this causal link remains debated. In contrast to this pattern, we demonstrate that SLR decelerated north of Cape Hatteras and accelerated south of the Cape to >20 mm/yr, > 3 times the global mean values from 2011 to 2015. Tide gauge records reveal comparable short‐lived, rapid SLR accelerations (hot spots) that have occurred repeatedly over ~1500 km stretches of the coastline during the past 95 years, with variable latitudinal position. Our analysis indicates that the cumulative (time‐integrated) effects of the North Atlantic Oscillation determine the latitudinal position of these SLR hot spots, while a cumulative El Niño index is associated with their timing. The superposition of these two ocean‐atmospheric processes accounts for 87% of the variance in the spatiotemporal pattern of intradecadal sea level oscillations.

Tsunami taxonomy and detection from recent Mediterranean tide gauge data

Sea level records, collected in digital form with high sampling rate by recently upgraded tide gauges located along the Mediterranean coasts, are subjected to a posteriori investigation to examine and characterize occurrence of sea level oscillations in the tsunami period range, induced by both underwater or coastal earthquakes and by meteorological events. After performing a rigorous quality control procedure on the raw sea level time series, a wavelet based analysis is applied to 2 h high-pass filtered data to identify oscillations generated by earthquakes, and a few events are modeled aiming to verify travel time and expected spectral shape. Seismic tsunami oscillations that are not reported in published catalogues are identified in the sea level records of the period 2010–2014 just after three different earthquake events. A method is proposed to detect occurrence of tsunami-like oscillations of meteorological origin from the available tidal records based on the distribution of the detided level process over spectral bandwidth parameter and mean period. The developed methodology is also the first presented which allows to distinguish sea wave induced harbor seiches from fluctuations of meteorological origin associated with passage of atmospheric disturbances (meteotsunamis) in sea level time series. The results of the analyses show that, during the considered period, in the Mediterranean Sea tsunamis of seismic origin are rare and weak; meteotsunamis on the contrary are relatively frequent and in critical areas may reach intensities exceeding astronomical tide. The availability of the recently acquired high frequency records and the presented approach allow to extend the list of recorded tsunami events of both seismic and meteorological origin. The identified event sets may be used for improved hazard analyses and risk assessments along the Mediterranean coasts.

Quaternary marine ingressions as indicated by hydrogeochemical evidence in the semi-confined aquifer of the littoral of the Río de la Plata, Argentina

AbstractThe Quaternary is characterized by the occurrence of significant climate oscillations that led to noticeable sea-level changes. On the basis of hydrochemical indicators, the origin of the water salinity in the semi-confined aquifer in the region of the middle Río de la Plata estuary, Argentina is determined. Exploration wells were drilled and sediments were sampled for mineralogical analysis alongside water samples collected to determine major and minor ions and environmental isotopes in the aquifer. The Plio-Pleistocene fluvial sands in which the aquifer occurs are mainly composed of grains of quartz, feldspar, and mafic minerals. The water chemistry shows Na-Cl facies with a marked increase in salinity towards the Río de la Plata. The δ 18O vs. δ 2H, Br− vs. Cl−, and δ 18O vs. Cl− ratios clearly trend towards seawater. Minor ions, such as Si, Sr, Li, Se, Br, and Rb, were the result of the prolonged interaction between the water that occurs in the aquifer and the mineral components of its matrix. The hydrogeochemical data show the marine origin of the saline water and that the hydrogeological evolution of the area during the Quaternary is as a result of sea-level oscillations.

A unique fossil record from neptunian sills: the world’s most extreme example of stratigraphic condensation (Jurassic, western Sicily)

AbstractNeptunian sills at Rocca Busambra, a fragment of the Trapanese/Saccense Domain in western Sicily, host the most abundant ammonite and gastropod fauna which has ever been recorded from the Jurassic of the western Tethys. The fauna is dominated by parautochthonous organisms which were swept into the sills by gentle transport. Ammonites are characterized by perfect preservation and small size, a feature which is due to the predominance of microconchs but also of stunting. The most complete sill is 0.7 m thick and could be separated into 17 levels which range in age from the early Toarcian into the late Kimmeridgian, thus representing the most extreme case of palaeontologically and depositionally documented stratigraphic condensation in Earth history. The unique feature of the Rocca Busambra sills is due to the interaction of three processes: extreme stratigraphic condensation on the sea floor, weak tectonic fracturing of the host rock and repeated reopening on top of already existing sills. Contrasting percentages of gastropods in individual levels reflect sea-level oscillations which correspond to long known low- and highstands during the Jurassic of the western Tethys. Comparisons with other ammonite-bearing sill faunas reveal several similarities, but represent only short-timed phases of tectonic pulses and deposition.

The Pliocene marine megafauna extinction and its impact on functional diversity.

The end of the Pliocene marked the beginning of a period of great climatic variability and sea-level oscillations. Here, based on a new analysis of the fossil record, we identify a previously unrecognized extinction event among marine megafauna (mammals, seabirds, turtles and sharks) during this time, with extinction rates three times higher than in the rest of the Cenozoic, and with 36% of Pliocene genera failing to survive into the Pleistocene. To gauge the potential consequences of this event for ecosystem functioning, we evaluate its impacts on functional diversity, focusing on the 86% of the megafauna genera that are associated with coastal habitats. Seven (14%) coastal functional entities (unique trait combinations) disappeared, along with 17% of functional richness (volume of the functional space). The origination of new genera during the Pleistocene created new functional entities and contributed to a functional shift of 21%, but minimally compensated for the functional space lost. Reconstructions show that from the late Pliocene onwards, the global area of the neritic zone significantly diminished and exhibited amplified fluctuations. We hypothesize that the abrupt loss of productive coastal habitats, potentially acting alongside oceanographic alterations, was a key extinction driver. The importance of area loss is supported by model analyses showing that animals with high energy requirements (homeotherms) were more susceptible to extinction. The extinction event we uncover here demonstrates that marine megafauna were more vulnerable to global environmental changes in the recent geological past than previously thought.

Meteotsunamis Occurring Along the Southwest Coast of South America During an Intense Storm

In this paper, we report meteotsunamis occurring along the Chilean and Peruvian coasts. These atmospherically induced tsunami-like oscillations were instrumentally recorded during an intense storm that affected central Chile on August 8th, 2015. The storm was characterized by strong winds, a locally unprecedented atmospheric low pressure and intense sea-level oscillations which caused six casualties and severe damage to infrastructure along ~500 km of coastline. The meteotsunamis are analyzed on both regional and local scales. On the regional scale, the temporal behavior and spatial behavior were discussed from the analysis of various tide gauges covering roughly 3000 km of the southwest coast of South America, between Callao, in central Peru, and Lebu, in southern Chile. Surprisingly, the phenomenon was recorded in the majority of the tide gauges in this vast region. On the area constrained by the storm region, a more detailed analysis is performed. We confirm the atmospheric origin of these intense sea-level oscillations by further analyzing meteorological records of air pressure and wind. An attempt to explain local (shelf and harbor) resonant mechanisms is achieved by means of wavelet analysis, while Greenspan and Proudman resonance mechanisms are superficially analyzed. Our results indicate that large meteotsunamis can occur along the west coast of South America and, when combined with other meteooceanographic conditions, may cause damage levels comparable to those resulting from Mw >8 earthquake generated tsunamis.

A model for the decrease in amplitude of carbon isotope excursions across the Phanerozoic

The geological cycling of carbon ties together the ocean-atmosphere carbon pool, Earth9s biosphere, and Earth9s sedimentary reservoirs. Perturbations to this coupled system are recorded in the carbon-isotopic (δ13C) composition of marine carbonates. Large amplitude δ13C excursions are typically treated as individual events and interpreted accordingly. However, a recent compilation of Phanerozoic carbon isotopic data reveals that δ13C excursions are a ubiquitous feature of the geologic record, and thus should be considered in concert. Analysis indicates that Phanerozoic carbon isotope excursions, as a whole, have characteristic durations of 0.5 to 10 M.yr. and exhibit declining amplitude over time. These commonalities suggest a shared underlying control. Here we demonstrate that sinusoidal modulation of the sensitivity of organic carbon and phosphate burial in a simple numerical model of the geologic carbon cycle results in large, asymmetric δ13C oscillations that exhibit their largest amplitudes in the 0.5 to 10 M.yr. period range. As anoxia is known to strongly modulate the C:P burial ratio of organic matter in sediments, we propose that sea-level oscillations were the primary source of sinusoidal modulation for the geologic carbon cycle, and that their degree of influence on the carbon cycle was determined by the state of oxygenation of bottom waters overlying the continental shelves. When oxygen minimum zones (OMZs) were large, shallow, and prone to expansion, sea-level changes would have had the capacity to drive large changes in the areal extent of OMZs in contact with the sea-floor, resulting in strong leverage on the burial sensitivity of organic carbon and phosphate, and thus on δ13C. Progressive oxygenation of the oceans, which was facilitated by biological innovations, resulted in a decline in the amplitude of δ13C excursions over the Phanerozoic, and the biogeochemical stabilization of the Earth System.