Interior Basin Research Articles

GHOSTly flute music: drumlins, moats and the bed of Thwaites Glacier

AbstractGlacier-bed characteristics that are poorly known and modeled are important in projected sea-level rise from ice-sheet changes under strong warming, especially in the Thwaites Glacier drainage of West Antarctica. Ocean warming may induce ice-shelf thinning or loss, or thinning of ice in estuarine zones, reducing backstress on grounded ice. Models indicate that, in response, more-nearly-plastic beds favor faster ice loss by causing larger flow acceleration, but more-nearly-viscous beds favor localized near-coastal thinning that could speed grounding-zone retreat into interior basins where marine-ice-sheet instability or cliff instability could develop and cause very rapid ice loss. Interpretation of available data indicates that the bed is spatially mosaicked, with both viscous and plastic regions. Flow against bedrock topography removes plastic lubricating tills, exposing bedrock that is eroded on up-glacier sides of obstacles to form moats with exposed bedrock tails extending downglacier adjacent to lee-side soft-till bedforms. Flow against topography also generates high-ice-pressure zones that prevent inflow of lubricating water over distances that scale with the obstacle size. Extending existing observations to sufficiently large regions, and developing models assimilating such data at the appropriate scale, present large, important research challenges that must be met to reliably project future forced sea-level rise.

Synoptic 129I and CFC–SF6 Transit Time Distribution (TTD) Sections Across the Central Arctic Ocean From the 2015 GEOTRACES Cruises

AbstractMeasurements of the tracers, 129I, CFC‐11, and SF6 on water samples collected in the Arctic Ocean in 2015 have been used to calculate mean ages, Γ and mixing, Δ parameters using transit time distributions (TTDs) to constrain water circulation and mixing time scales. Values of Γ and Δ determined separately using the two tracer pairs, SF6‐CFC‐11, and 129I‐CFC‐11 are in good agreement for gas solubilities estimated for saturation levels of 0.90, but agreement decreases for other gas saturation levels. Both Γ and Δ increase rapidly with increasing depth below the base of the intermediate water layer (ca. 1,000 m), but maintaining a value of Δ/Γ ≅ 1 supporting the use of this proportionality in applications of TTDs to deep ocean transport of substances such as anthropogenic carbon. Isolines of Γ = 20 years deepening to depths below 1,000 m over the flank of the Mendeleyev Ridge near the North Pole outline the bathymetrically steered, return flow of recently ventilated Atlantic Water toward Fram Strait. Basin interior waters are significantly older with the Γ = 25 years mean age isoline shallowing upward to depths above 500 m in the Makarov, Canada, and Eurasian Basins. Values of Δ remain relatively constant in the 6–10 years range in upper intermediate water across all three basins indicating that flow is principally advective and that the mixing specified by Δ likely occurs upstream of the central basins in regions proximal to the outflow from the Santa Anna Trough.

Studying the tidal-induced water circulation pattern within EL-Burullus fishing harbor, Egypt, using CMS-PTM numerical modeling

Protection from waves and providing an appropriate calmness ratio are vital requirements in the designing phase of a harbor. Another crucial issue is guaranteeing sufficient water circulation as a key indicator for water quality and avoiding the associated environmental problems of poor water quality conditions. In a coastal harbor, the interior basin's water quality largely depends on the harbor's natural/self-ability to flush out different existing pollutants. El-Burullus fishing harbors is one of the Egyptian coastal fishing harbors that suffer from environmental issues such as accumulated pollutants, particularly in stagnant areas, and deterioration of water quality within the harbor's basin. Investigating water quality status within the coastal harbors necessitates knowledge about the mechanism of water circulation patterns within the harbor. The most common indicator for the water renewal and circulation pattern evaluation is the flushing time. Therefore, a coupled coastal hydrodynamic modeling system and particle tracking model (CMS-PTM) are utilized to investigate the tidal-induced circulation pattern within the El-Burullus fishing harbor, considering two tide scenarios (best and worst). Three locations (where most operational fishing facilities exist) were selected as point sources (instantaneous mass) for particle release. The results highlight the role of tidal actions on the water circulation within El-Burullus harbor and how the residence time varies based on the source release location.

Applying the NWS’s Distributed Hydrologic Model to Short-Range Forecasting of Quickflow in the Mahantango Creek Watershed

Abstract Accurate and reliable forecasts of quickflow, including interflow and overland flow, are essential for predicting rainfall–runoff events that can wash off recently applied agricultural nutrients. In this study, we examined whether a gridded version of the Sacramento Soil Moisture Accounting model with Heat Transfer (SAC-HT) could simulate and forecast quickflow in two agricultural watersheds in east-central Pennsylvania. Specifically, we used the Hydrology Laboratory–Research Distributed Hydrologic Model (HL-RDHM) software, which incorporates SAC-HT, to conduct a 15-yr (2003–17) simulation of quickflow in the 420-km2 Mahantango Creek watershed and in WE-38, a 7.3-km2 headwater interior basin. We directly calibrated HL-RDHM using hydrologic observations at the Mahantango Creek outlet, while all grid cells within Mahantango Creek, including WE-38, were calibrated indirectly using scalar multipliers derived from the basin outlet calibration. Using the calibrated model, we then assessed the quality of short-range (24–72 h) deterministic forecasts of daily quickflow in both watersheds over a 2-yr period (July 2017–October 2019). At the basin outlet, HL-RDHM quickflow simulations showed low biases (PBIAS = 10.5%) and strong agreement (KGE″ = 0.81) with observations. At the headwater scale, HL-RDHM overestimated quickflow (PBIAS = 69.0%) to a greater degree, but quickflow simulations remained satisfactory (KGE″ = 0.65). When applied to quickflow forecasting, HL-RDHM produced skillful forecasts (>90% of Peirce and Gerrity skill scores above 0.5) at all lead times and significantly outperformed persistence forecasts, although skill gains in Mahantango Creek were slightly lower. Accordingly, short-range quickflow forecasts by HL-RDHM show promise for informing operational decision-making in agriculture. Significance Statement Daily runoff forecasts can alert farmers to rainfall–runoff events that have the potential to wash off recently applied fertilizers and manures. To gauge whether daily runoff forecasts are accurate and reliable, we used runoff monitoring data from a large agricultural watershed and one of its headwater tributaries to evaluate the quality of short-term runoff forecasts (1–3 days ahead) that were generated by a National Weather Service watershed model. Results showed that the accuracy and reliability of daily runoff forecasts generally improved in both watersheds as lead times increased from 1 to 3 days. Study findings highlight the potential for National Weather Service models to provide useful short-term runoff forecasts that can inform operational decision-making in agriculture.

The Changing Behavior of the West Greenland Current System in a Very High‐Resolution Model

AbstractAnalyzing a high‐resolution (1/60°) numerical model over 2008–2018, the inter‐annual variability of the West Greenland Coastal Current (WGCC) on the shelf and West Greenland Current (WGC) at the shelf break is presented. Both currents flow from Cape Farewell and extend to Davis Strait, with their speeds and transports corresponding well with observations. The trend over the study period of the WGCC and WGC strength near southwest Greenland are opposite, with the former declining while the latter strengthened, both by a speed change above 0.1 m/s. Both currents are predominantly buoyancy forced, but wind forcing becomes more dominant approaching Davis Strait. The main exchanges from the two currents with the interior of the Labrador Sea occur between Cape Desolation and Fylla Bank. The net volume, freshwater, heat transport decreases between these two sections are 1.4 Sv, 13 mSv, 36.7 TW, respectively. The freshwater transport of the WGC itself does not drop in between these sections, receiving freshwater from the WGCC to compensate for the losses to the basin interior. Thus, we see significant freshwater (83.1 mSv) and heat transports (70.7 TW) of the WGC remaining at Fylla Bank that reach the northern basin instead of being fluxed into the interior of the Labrador Sea. This suggests that the exchange between the boundary current system and the interior is more limited than previously thought, and most of the Greenland and Arctic melt reaches the northern Labrador Sea. Our results highlight the importance of resolving the WGCC and shelf processes.

Hydrochemical characteristics and paleoclimate changes recorded from Sugan Lake on the northern boundary of Tibetan Plateau since mid-Holocene

The Qaidam Basin, located in the northern Tibetan Plateau, is one of the three largest interior basins in China. It is surrounded by Kunlun, Altun and Qilian mountains with arid climate, sparsely vegetated landscape and a fragile ecological environment. Investigations on Holocene climate variations in this northern part of the Tibetan Plateau are essential for a better understanding of regional climate dynamics. A mid-Holocene sediment record from Sugan Lake in the Qaidam Basin was investigated using the grain size, mineral, total organic matter content (TOC), C:N ratio (C/N) and element analyses. A depth-age model since ∼ 7750 cal a BP had been made based on 8 AMS 14C data after taking out 2200 years carbon reservoir effect. SO42--type water and sparse terrestrial vegetation with considerable evaporation caused by high temperature during the Holocene Megathermal Maximum were recorded from ca. 7750 to 5800 cal a BP. From 5800 cal a BP, hydrochemical characteristics shifted dramatically to the Cl-type, while aeolian activities intensified concurrently. A higher lake level with low evaporation/precipitation ratio as the result of cool and wet conditions were inferred between 5800 and 3580 cal a BP when the EASM weakened and westerly jet intensified. Colder and drier conditions were recorded probably due to the strengthening of the mid-latitude westerly circulation after 3580 cal a BP. However, the EASM probably prevailed shortly at 3580 ∼ 3000 cal a BP and 1800 ∼ 810 cal a BP, respectively. Cold/dry, cold/wet and cold/dry Little Ice Age fluctuation climate conditions and aeolian activities with risen lake level and diluted water were inferred from 580 to 280 cal a BP.

Sedimentation on structurally complex slopes: Neogene to recent deep‐water sedimentation patterns across the central Hikurangi subduction margin, New Zealand

AbstractDeep‐water sedimentation on active margins often entails complex sediment transport pathways through slope accommodation. Sedimentation in such settings is commonly differentiated into ‘fill and spill’ vs. ‘tortuous corridor’ models. To investigate the utility of these models in convergent settings 15,344 km2 of 3D seismic data is used to investigate sedimentation and erosion patterns across the Hikurangi subduction margin. A series of thrust‐bound trench‐slope basins, each tens of kilometres long by kilometres wide, have been diachronously forming, filling and deforming through the Neogene until today. Five primary input points delivered sediment to the basins along the studied part of the margin. Channels display both axial and transverse orientations, the run‐out lengths of which vary temporally. At various times, relatively coarse‐grained sediment was trapped in the interior basins, occasionally then to be cannibalised during landsliding or erosion of growing structures. At other times, coarse‐grained sediment was bypassed to distal basins or the trench. Multiple sediment input points and occasionally tortuous sediment dispersal corridors result in the evolution of convoluted depositional systems, often with similar styles of sedimentation occurring contemporaneously in proximal and distal basins, contrary to simple models of basin fill. A hierarchy of controls on sediment distribution can be distinguished. At the highest level, sediment distribution is controlled by external factors, for example, glacio‐eustacy and tectonics. At basin scale, the interaction of sedimentary systems with local relief (e.g. evolving seafloor structures and landslides) dictates the location and style of deposition. At the lowest level, autocyclic factors (e.g. flow response to earlier deposits) influence the spatiotemporal variation in erosion and sedimentation. The complex interplay of these factors dictates whether basins were filling, spilling or some combination at any point in time, whilst basins that were filled and spilled may subsequently resume filling due to changes in the bounding conditions. Hence simple use of ‘fill and spill’ or ‘tortuous corridor’ models to tectonically active margins is not advised. Furthermore, as sedimentation may influence structure growth, constraining the controls on sediment distribution may improve understanding of the broader evolution of convergent margins and their resource distribution.

The Levantine Intermediate Water in the western Mediterranean and its interactions with the Algerian Gyres: insights from 60 years of observation

Abstract. The presence of two large-scale cyclonic gyres in the Algerian Basin influences the general and eddy circulation, but their effects on water mass transfer remain poorly characterized. Our study has confirmed the presence of these gyres using the first direct current measurements of the whole water column collected during the SOMBA-GE2014 cruise, specifically designed to investigate these gyres. Using cruise sections and a climatology from 60 years of in situ measurements, we have also shown the effect of these gyres on the distribution at intermediate depth of Levantine Intermediate Water (LIW) with warmer (∼ 0.15 ∘C) and saltier (∼ 0.02) characteristics in the Algerian Basin than in the Provençal Basin. The Algerian Gyres, combined with the effect of anticyclonic Algerian Eddies, also impact horizontal density gradients with sinking of the isopycnals at the gyres' centers. Temporal cross-correlation of LIW potential temperature referenced to a signal observed southwest of Sardinia reveals a timescale of transit of 4 months to get to the center of the Algerian Basin. The LIW potential temperature and salinity trends, on average in the basin interior, are estimated to be +0.0022 ± 0.0002 ∘Cyr-1 and +0.0022 ± 0.0001 yr−1, respectively, over the 1968–2017 period and accelerating to +0.048 ± 0.003 ∘Cyr-1 and +0.0076 ± 0.0009 yr−1 over the 2013–2017 period.

Accumulation of organic-rich sediments associated with Aptian–Albian oceanic anoxic events in central-eastern Mexico

Oceanographic and climate conditions during the early Aptian OAE 1a and the late Aptian–early Albian OAE 1b are reported from an organic-rich succession deposited in the central portion of the Mexican Interior Basin, based on the analysis and integration of geochemical data (δ13Ccarb, total organic and inorganic carbon contents, Rock-Eval parameters and major and trace elements concentrations). The carbon isotope record of the studied section displays trends that correlate with segments C2 to C13. The OAE 1a interval is clearly isotopically defined (segments C3–C6) and includes sediments moderately enriched in organic matter. Although the OAE 1b sub-events are not expressed in the isotope record, the Jacob, Kilian and Paquier events may correspond to distinctive organic-rich levels occurring through C10–C12 segments. Evidence indicates that sediments enriched in organic matter through the section were accumulated under oxygen-depleted and high nutrient conditions. Anoxic-eutrophic conditions induced by a high input of continental-derived nutrients (including biolimiting Fe and P) associated to intense chemical weathering under warm and humid conditions took place during the deposition of the Selli and Paquier levels. Enhanced P recycling and regional upwelling reinforced eutrophic conditions during OAE 1a.

Eggshells assemblages and stable isotope composition in the Upper Cretaceous (Campanian) El Gallo Formation of Baja California, Mexico: Paleoenvironmental inferences

Fossil eggshells were recovered from the El Gallo Formation, Baja California, northwest Mexico, is one of the few North American Campanian continental outcrops outside the Western Interior Basin. Based on microstructure, the eggshells are referred to ornithopod (ootaxon Spheroolithus), theropods (ootaxa Prismatoolithus, two Tubercuoolithidae eggshells, Continuoolithus, Tristraguloolithus, Disperituberoolithus, Pseudogeckoolithus, Laevisoolithidae? eggshells and Enantiornithine indet.), and one crocodylomorph (cf. Neokrokolithes). While some of these ootaxa were associated with the modest, but diverse osteological record preserved there; others reveal the presence of small theropods, including as the first evidence of enantiornithine birds in the formation. Because the stable isotopic compositions of the eggshells differ from those of pedogenic carbonate nodules, we infer minimal diagenetic influence. We thus propose that the C3 plants had δ13C compositions between −27‰ and −29‰ and that warm evaporative conditions led to enriched δ18O in ingested water compared to meteoric water at least during the short period of dinosaur eggshell formation.

Rapidly Increasing Artificial Iodine Highlights Pathways of Iceland-Scotland Overflow Water and Labrador Sea Water

Iceland-Scotland Overflow Water (ISOW) and Labrador Seawater (LSW) are major water masses of the lower Atlantic Meridional Overturning Circulation (AMOC). Therefore, the investigation of their transport pathways is important to understand the structure of the AMOC and how climate properties are exported from the North Atlantic to lower latitudes. There is growing evidence from Lagrangian model simulations and observations that ISOW and LSW detach from boundary currents and spread off-boundary, into the basin interior in the Atlantic Ocean. Nuclear fuel reprocessing facilities of Sellafield and La Hague have been releasing artificial iodine (129I) into the northeastern Atlantic since the 1960ies. As a result, 129I is supplied from north of the Greenland-Scotland passages into the subpolar region labelling waters of the southward flowing lower AMOC. To explore the potential of 129I as tracer of boundary and interior ISOW and LSW transport pathways, we analyzed the tracer concentrations in seawater collected during four oceanographic cruises in the subpolar and subtropical North Atlantic regions between 2017 and 2019. The new tracer observations showed that deep tracer maxima highlighted the spreading of ISOW along the flanks of Reykjanes Ridge, across fracture zones and into the eastern subpolar North Atlantic supporting recent Lagrangian studies. Further, we found that 129I is intruding the Atlantic Ocean at unprecedented rate and labelling much larger extensions and water masses than in the recent past. This has enabled the use of 129I for other purposes aside from tracing ISOW. For example, increasing tracer levels allowed us to differentiate between newly formed 129I-rich LSW and older vintages poorer in 129I content. Further, 129I concentration maxima at intermediate depths could be used to track the spreading of LSW beyond the subpolar region and far into subtropical seas near Bermuda. Considering that 129I releases from Sellafield and La Hague have increased or levelled off during the last decades, it is very likely that the tracer invasion will continue providing new tracing opportunities for 129I in the near future.

Water Mass Transports and Pathways in the North Brazil‐Equatorial Undercurrent Retroflection

AbstractThe equatorial retroflection of the North Brazil Current (NBC) into the Equatorial Undercurrent (EUC) and its posterior tropical recirculation is a major regulator for the returning limb of the Atlantic Meridional Overturning Circulation. Indeed, most surface and thermocline NBC waters retroflect at the equator all the way into the central and eastern Atlantic Ocean, before they recirculate back through the tropics to the western boundary. Here, we use cruise data in the western equatorial Atlantic during April 2010 and reanalysis time series for the equatorial and tropical waters in both hemispheres in order to explore the recirculation pathways and transport variability. During the 1998–2016 period, the annual‐mean EUC transports 15.1 ± 1.3 Sv at 32°W, with 2.8 ± 0.4 Sv from the North Atlantic and 11.4 ± 1.3 Sv from the South Atlantic. At 32°W most of the total EUC transport comes from the western boundary retroflection south of 3°N (7.2 ± 0.9 Sv), a substantial fraction retroflects north of 3°N (5.6 ± 0.4 Sv), and the remaining flow (2.3 Sv) joins through the interior basin. The South Atlantic subtropical waters feed the EUC at all thermocline depths while the North Atlantic and South Atlantic tropical waters do so at the surface and upper‐thermocline levels. The EUC transport at 32°W has a pronounced seasonality, with spring and fall maxima and a range of 8.8 Sv. The 18 yr of reanalysis data shows a weak yet significant correlation with an Atlantic Niño index, and also suggests an enhanced contribution from the South Atlantic tropical waters during 2008–2016 as compared with 1997–2007.

Using detrital zircon and rutile to constrain sedimentary provenance of Early Paleozoic fluvial systems of the Araripe Basin, Western Gondwana

The Early Paleozoic of the NE Brazilian sedimentary basins are key to understanding the primeval depositional environments and paleogeography of Western Gondwana after its final assembly. In this context, determining the sedimentary provenance of the Early Paleozoic Cariri Formation (basal unit of the Araripe Basin) may improve paleogeographic reconstructions and stratigraphic correlations. Despite the Araripe Basin being one of the best-studied interior basins of northeastern Brazil, the Cariri Formation lacks detailed geochronological and sedimentary provenance analyses, which hamper precise definitions of its depositional age, sedimentary source areas and paleogeography. Considering this scenario, we performed a combined multiproxy approach, including sedimentologic and stratigraphic analysis, detrital zircon U–Pb dating and provenance studies based on trace elements in detrital rutile. The maximum depositional age for the Cariri Formation suggests that its sedimentation started after the Late Cambrian. Detrital zircon ages and detrital rutile provenance indicate that the primary source areas for the Cariri Formation fluvial system were the orogenic terranes related to the Brasiliano Orogeny, located at the SE of the Borborema Province (e.g., Sergipano Belt), with secondary, but also important, the contribution of Cambrian sources. Records of this event are also found in northern Africa, where units related to the Neoproterozoic East African-Antarctic and Pan African orogens provided sediments for basin-scale fluvial systems.

Rare clutch of Cretaceous turtle eggs preserved in the Kaiparowits Formation of southern Utah

Although turtles are common Mesozoic fossils, their eggs and nests are rare. Here, we describe an in-situ clutch of turtle eggs from the Campanian (Upper Cretaceous) Kaiparowits Formation of southern Utah. The clutch is preserved in a green mudstone associated with aquatic terrestrial gastropods. Eggshell is broadly distributed across an area of 3.75 m2 with three nearly complete, spherical eggs ∼2.9 cm in diameter, and another three partial eggs identified. The aragonitic eggshell is 0.7–1.2 mm thick and consists of closely packed, slightly domed shell units with a height to width ratio of 3.7:1 and nodular ornamentation 53–71 μm in diameter. Eggshell orientation (concave up/concave down) of 54:46 is consistent with in-situ preservation. An eggshell porosity of 42.5 mm correlates to a humid nesting environment. Extrapolating from egg size, the producing adult carapace length is estimated at 24.45 cm with an average clutch size of 9.91 eggs. The unique attributes of the eggshell warrant naming of a new oospecies, Testudoolithus tuberi. This fossil occurrence is another example of exceptional preservation in the Western Interior Basin associated with the Campanian “taphozone.”

Radial Anisotropy and Sediment Thickness of West and Central Antarctica Estimated From Rayleigh and Love Wave Velocities

AbstractMany recent Antarctic seismic structure studies use Rayleigh wave data and thus determine only the SV structure. Love waves provide greater resolution for shallow structure, and coupled with Rayleigh waves, can constrain radial anisotropy by comparing vertically (VSV) and horizontally (VSH) polarized shear velocities. In this study, we jointly analyze Rayleigh and Love wave phase and group velocities from ambient noise to develop a new radially anisotropic velocity model for West and Central Antarctica with an improved shallow crustal resolution using all broadband data collected in Antarctica over the past 20 years. Group and phase velocity maps for Rayleigh and Love waves are estimated and inverted for shear wave velocity structure using a Monte Carlo method. We determine a new sediment distribution map that reveals a thick sedimentary basin (∼4 km) beneath the Southeastern Ross Embayment. Sediment thicknesses at interior basins such as the Polar Subglacial Basin and Bentley Subglacial Trench are modest (<1.5 km), suggesting that these basins are sediment‐starved. The shallow crust as well as the mid‐to‐lower crust in several places shows strong positive anisotropy (VSH > VSV), likely due to lattice preferred orientation of mica‐bearing rocks. However, large regions of the mid‐to‐lower crust show negative anisotropy, likely due to lattice preferred orientation of plagioclase. The uppermost mantle is characterized by strong positive radial anisotropy (4%–8%) in West Antarctica, with the largest anisotropy beneath the Transantarctic and Whitmore Mountains, likely resulting from horizontal olivine preferred orientation due to tectonic activity.

Coherent Lagrangian Pathways Near an East Alboran Front

AbstractIn the eastern Alboran Sea, frontogenesis (FG) is a dominant process for fronts extending from the Spanish coast toward the basin interior, promoting large vertical displacements that connect the surface mixed layer with the oceanic interior. Using a realistic, high‐resolution model simulation for this region, we conduct the offline advection of virtual water parcels released near the surface during a 2‐day episode of intense FG. Three‐dimensional trajectories exhibit high variability depending on the release location, and some large, rapid vertical displacements are induced by different coherent submesoscale flow patterns and by interactions among them: Ageostrophic secondary circulation associated with strain‐ and mixing‐induced FG and internal waves generated by currents over topography. These deep displacements mostly are irreversible, at least on a short time scale, because of the rapidly changing flow patterns. Significant diapycnal mixing and density changes occur along trajectories as they pass through the surface and bottom boundary layers. While we expect these processes to be typical for this region, the computational expense of such a Lagrangian analysis and the complexity of its outcome present a considerable challenge for more comprehensive assessments.

Sequence stratigraphic interpretation in marginal marine settings by the approach of parasequence-thickness-to-sandstone-fraction ratio: Case studies of the Gallup and Ferron outcrops in the Western Interior Basin, U.S.A.

ABSTRACTThe parasequence-thickness-to-sandstone-fraction ratio (TSF) is a simple but potentially powerful tool to identify stratal stacking patterns and associated systems tracts in siliciclastic paralic sequences. Parasequence thickness (T) reflects accommodation, and the sandstone fraction (SF) may serve as a proxy for the rate of sediment supply. Although previous research shows the effectiveness of applying TSF techniques to sequence stratigraphic analyses in siliciclastic depositional environments, constraints and analytical procedures of the technique are still not clearly illustrated. The paleogeography and sequence stratigraphy of the Cretaceous Gallup system and Ferron Notom deltaic complex in the Western Interior Basin have been extensively studied, providing an opportunity to explore the applicability and detailed workflow of the TSF method. TSF analyses are conducted first on two representative measured sections from the Gallup and the Ferron outcrops, respectively. The TSF analyses of the two one-dimensional (1D) sections are capable of identifying transgressive–regressive (T-R) cycles of the two deltas. However, the 1D sections can reflect the accommodation and sediment supply change only at single locations, which limits their usefulness in identification of stratigraphically consecutive parasequences and composite bounding surfaces. The utility of TSF analyses on cross sections is then tested on a depositional-dip transect of the Gallup delta, as well as dip-oblique and strike-oblique cross sections of the Ferron Notom delta. Parameters of T and SF are acquired from measured sections as well as interpolated virtual sections. For both the Gallup system and the Ferron Notom deltaic complex, the cross-sectional TSF analyses are more effective in recognizing systems tracts and associated bounding surfaces than the TSF analyses in 1D sections. Because dip-oriented cross sections usually encompass both proximal and distal parts of parasequences, and preserve stratigraphically continuous successions, they can provide more complete information for TSF interpretations than strike-oriented cross sections. Above all, TSF analysis via both measured and virtual sections along a depositional-dip profile is inclined to result in sequence stratigraphic categories that best match those based on the full set of geological observations.TSF analyses can also be used to identify general direction of shoreline trajectories in both the Gallup and Ferron Notom deltas. Parameterization of T, SF, and maximum progradation distance for both the Gallup and Ferron Notom parasequences are used to indicate shelf gradients throughout their deposition. The prominent differences of the shelf gradients between different deltaic parasequences indicate differences in allogenic and autogenic controls on the development of T-R sequences in these two deltas.

Surface Pathways Connecting the South and North Atlantic Oceans

AbstractThe North Brazil Current (NBC) is considered a bottleneck in the South Atlantic, responsible for carrying upper‐ocean waters into the North Atlantic. This work explores the surface pathways connecting the NBC and 26°N in the North Atlantic. To identify said pathways, we use observational trajectories from surface drifters in conjunction with transition path theory applied on a Markov chain. The pathways are computed as ensembles of paths transitioning directly between the NBC and 26°N. Our results suggest that there are two dominant surface pathways: The first is the traditional pathway through the Caribbean Sea and Gulf of Mexico, carrying waters to the Florida Current, while the second is a direct route east of the Caribbean supplying waters to the Antilles Current and basin interior. The latter is composed of multiple pathways that are collectively more probable than the traditional pathway.

Sedimentology and geomorphology of Lake Yamma Yamma - A long-lived structurally controlled playa lake of the Lake Eyre Basin, Australia

ABSTRACT Intraplate tectonism and continental climate change have important roles in the evolution of the arid Lake Eyre Basin, one of the world’s largest interior basins, and a place with economic, environmental, and cultural significance for many Australians. Just off one of the main rivers of the Basin, Cooper Creek, Lake Yamma Yamma – a 20 km by 40 km ephemeral feature – traps sediment ~750 km upstream and ~90 m higher than the ultimate base level of the Basin – Kati Thanda-Lake Eyre. This paper is the first to report on the sedimentology and geomorphic evolution of this modern ephemeral playa lake. Field-based sedimentology, laboratory-based grain size analysis, satellite image interpretation, inundation frequency maps, hydrological data, and digital elevation data, were used to interpret sedimentary processes and the evolution of the lake. Results suggest Lake Yamma Yamma is a long-lived feature. Evolution is primarily structurally controlled, with the main lake delta migrating north-west over time. Quaternary fluvial, lacustrine and aeolian deposition is likely controlled by intraplate tectonism, and palaeo-shorelines may be remnant features of a prior climate regime. Age dating of this sedimentary archive could provide important information on the history, palaeoclimate, and evolution of the Lake Eyre Basin, and the Australian continent.

Tracking Irminger Rings’ properties using a sub-mesoscale ocean model

A 1/60° numerical simulation is carried out within the Labrador Sea to investigate eddies produced along the western coast of Greenland. These eddies, known as Irminger Rings, carry relatively buoyant water from the West Greenland Current system into the interior Labrador Sea. These eddies can survive for up to 2 years; we detect and track 232 eddies produced within our 14 year simulation to investigate how they evolve during their lifetime. Irminger Rings start with a significant layer of freshwater (median 4.4 m) that quickly erodes during the convective winter. The freshwater layer, as opposed to the warm Irminger Water layer, constitutes the majority of the stratification within each eddy. Eddies generally travel southwestwards after formation, and eddies whose trajectory is close to the continental slope tend to have a reduced lifespan and quicker speed than those which drift into the interior deep basin. We find that eddies which spawn further north are more likely to end up influenced by the boundary currents, while those which form to the south are more likely to live longer and enter the deep interior basin. While the formation rate of eddies is generally uniform across our 2005–2018 simulation, Irminger Rings are far more likely to decay during the convective wintertime.We find that most eddies quickly decay within a few months, although some survive long enough to endure two convective winters. All Irminger Rings increase the local stratification in the Labrador Sea, limiting convection. However, the eddies which endure some part of two winters experience a significant buoyancy loss over a long time span such that they may produce Labrador Sea Water within their core during their second winter. This constitutes a small but non-negligible volume of Labrador Sea Water (0.02 to 0.09 Sv) and updates our understanding of Irminger Ring’s role on stratifying the Labrador Sea.Plain language summary:The Labrador Sea, between Canada and Greenland, experiences deep convection, a process where the surface water cools and becomes denser than the water at depth. This forces the surface water to sink and mix with the water below, homogenizing the water column and producing deepwater, an important component in the distribution of heat between the equatorial and polar regions. Deep convection is also important in ventilating the deep ocean with oxygen and carbon dioxide, sequestering these gasses for thousands of years. Deepwater is strongly influenced by the local weather as well as the current systems which surround the Labrador Sea. Oceanic eddies are produced from these current systems and bring their water mass properties into the region where deepwater is formed. These eddies are relatively buoyant, hindering deepwater formation, but also survive up to 2 years before decaying. We use a high-resolution ocean simulation to resolve these eddies so we can further understand how they evolve after being formed. Our simulation suggests that these eddies decay faster during winter, although eddies which survived to experience two winters often experienced deep convection and the production of Labrador Sea Water. This paints the picture that these eddies not only significantly reduce deepwater formation, but can also act as local sources of deepwater formation.