Ocean Circulation Research Articles

A Non-Uniform Grid Graph Convolutional Network for Sea Surface Temperature Prediction

Sea surface temperature (SST) is an important factor in the marine environment and has significant impacts on climate, ecology, and maritime activities. Most existing SST prediction methods consider the ocean as a uniform field and use a uniform grid to predict SST. However, the marine environment is a complex system, and factors such as solar radiation, differences in land and sea thermal properties, and ocean circulation lead to uneven spatial distributions of SSTs. We propose a non-uniform grid construction method based on an SST spatial gradient to encode SST data, as well as a Non-uniform Grid Graph Convolutional Network (NGGCN) model. The NGGCN consists of two spatiotemporal modules, each of which extracts spatial features from the GCN module, captures temporal correlations through the GRU module, and performs feature restoration and output results through the fully connected module. We selected data from the Yellow Sea and Bohai Sea to validate the effectiveness of the NGGCN in predicting SST at different time scales and prediction steps. The results indicate that our model shows a significant improvement in prediction performance compared to other models.

Examining fishing activities based on in-situ tracking and oceanographic characteristics in Aru Sea and surroundings

Fisheries activites and oceanographic conditions have a strong relationship. Understanding the complex interplay between fisheries and oceanographic conditions is essential for effective fisheries management. The aim of this research is to analyze the in-situ fishing activities with oceanographic conditions in the Fisheries Management Area (FMA) or WPP-NRI 718 located in the Aru Sea and its surroundings. The main data source is from open global data ship tracking and oceanographic conditions from satellite data. In general, fishing is conducted around the waters of Aru Island. The fishing grounds are strongly influenced by a combination of environmental factors, including sea surface temperatures, chlorophyll-a (Chlor-a) concentrations, sea surface height, and current velocities. A decrease in fishing patterns around Aru Island waters occurs in the eastern season, where fishing tends to occur in the western region (near Timor-Leste). Based on the oceanographic conditions, fishing tends to occur in regions with warmer conditions ranging from 27 to 29 °C, moderate Chlor-a (1.02–3.01 mg/m3), a relatively high surface height (0.17–0.32 m), and slow surface currents.

Interacting internal waves explain global patterns of interior ocean mixing

Across the stable density stratification of the abyssal ocean, deep dense water is slowly propelled upward by sustained, though irregular, turbulent mixing. The resulting mean upwelling determines large-scale oceanic circulation properties like heat and carbon transport. In the ocean interior, this turbulent mixing is caused mainly by breaking internal waves: generated predominantly by winds and tides, these waves interact nonlinearly, transferring energy downscale, and finally become unstable, break and mix the water column. This paradigm, long parameterized heuristically, still lacks full theoretical explanation. Here, we close this gap using wave-wave interaction theory with input from both localized and global observations. We find near-ubiquitous agreement between first-principle predictions and observed mixing patterns in the global ocean interior. Our findings lay the foundations for a wave-driven mixing parameterization for ocean general circulation models that is entirely physics-based, which is key to reliably represent future climate states that could differ substantially from today’s.

Upwelling current and its relationship to the enrichment of organic matter in the Lower Silurian Longmaxi Formation, northern Chongqing–western Hubei area, southern China

Upwelling currents play a crucial role in the enrichment of organic matter, yet the mechanisms driving this process remain incompletely understood due to methodological and data resolution limitations. In this paper, we employ a combination of biostratigraphic classification, qualitative methods, and quantitative methods to systematically analyze the sedimentological and geochemical characteristics of the Lower Silurian Longmaxi Formation in the northern Chongqing–western Hubei area, southern China. The relationship between the upwelling currents and organic matter enrichment in the shale of the Longmaxi Formation is investigated. Results indicate that the upwelling currents in the study area were primarily influenced by the foreland flexure process. From the Rhuddanian (flexure–sedimentation stage) to the Aeronian (flexure–migration stage), the more intense tectonic activity led to gradual opening of the barrier between the South Qinling Ocean and the Yangtze Platform, resulting in an increase in the influx of the oceanic current. The upwelling currents significantly contributed to the organic matter production, albeit without substantially affecting the preservation conditions. Throughout the succession of the Longmaxi Formation, the organic matter content decreased gradually from the passive continental margin to the foreland flexural stagnant basin, which was mainly due to deterioration of the preservation conditions as a result of sea level fall and increased terrigenous input. Despite the increase in the upwelling currents, they did not decisively control the organic matter enrichment. Spatially, during the Rhuddanian to Aeronian period, the organic matter content decreased similarly from the passive continental margin to the foreland flexural stagnant basin, influenced by reduced organic matter production caused by weakening of the upwelling currents and the worsening preservation conditions caused by sea-level fall. The terrigenous input had a relatively minor impact. The results of this study provide new insights into the role of upwelling currents in the organic matter enrichment within the Longmaxi Formation, overcoming previous methodological and resolution barriers.

Study of Chlorophyl-A Variability in Bone Bay Waters During High Wave Events

Research has been carried out on the distribution of chlorophyll-a in the waters of Bone Bay during high wave events based on the parameters of sea surface temperature, wind speed and ocean currents. The aim of this research is to analyze parameters related to high waves which influence chlorophyll-a concentrations in the waters of Bone Bay. Chlorophyll-a patterns in Bone Bay waters were studied based on Aqua MODIS satellite data for chlorophyll-a data and ECMWF for wind speed, sea surface temperature and ocean current data. The average value was determined using Aqua MODIS and ECMWF satellite data for 10 years from 2011 to 2020. These parameters were analyzed to determine the correlation with chlorophyll-a. The calculation results show that sea surface temperature and wind speed decreased after high waves, while ocean currents and chlorophyll-a increased after high waves in Bone Bay waters. The correlation between chlorophyll-a and wind speed is 0.15, with sea surface temperature -0.44, and with ocean currents -0.26. Spatially, high concentrations of chlorophyll-a are found in the coastal waters of the South Sulawesi region with chlorophyll-a concentrations reaching 0.4-5 mg/m3. Temporally, high chlorophyll-a concentrations occur after high wave events with an average chlorophyll-a concentration of 0.32 mg/m3.

Variability of biophysical parameters during La Niña condition in the Eastern Region of the Indian Ocean

The La Niña event not only affected global ocean dynamics but also marine productivity. Due to its importance to the life of organisms and ecosystems, the biophysical aspects should be analyzed. One of the important regions in the eastern region of the Indian Ocean is located in the upwelling system and central marine biodiversity. The study aims to investigate several parameters, including SSTs, dissolved oxygen levels, nitrate distribution, and Chlor-a concentration, which are combined with ocean currents. These parameters are then analyzed in the period 2020 to 2022, which is La Niña condition. Based on the results, significant changes occur in SST during the first transitional season of 2022, where the increase reaches 1–4 °C. There was an increase in La Niña during this period. For marine productivity parameters, the recorded DO is in the range of 197 to 218 mmol/m3, nitrate with a value range of 0 to 0,02 mmol/m3, nanoplankton with a value range of 0 to 0.03 mg/m3, and Chlor-a with a value range of 0 to 4 mg/m3. We also found that changes in ENSO events affect the productivity of the Eastern Region of the Indian Ocean, especially in the Chlor-a parameter, where the occurrence of La Niña extreme is the most important parameter.

Episodic intensification of marine phosphorus burial over the last 80 million years

Marine phosphatization events cause episodic carbonate fluorapatite (CFA) precipitation on seamounts, and are commonly linked to growth hiatuses in ferromanganese (Fe-Mn) crusts. However, the complete record of these events and their paleoenvironmental significance remains poorly understood, in large part due to poor age constraints. Here, we apply U-Pb dating to CFA in Fe-Mn crusts from Western Pacific seamounts. These data exhibit good alignment with Sr isotope ages, revealing six potential phosphatization events. This established CFA chronology tightens the timespan of phosphatization events and refines the age framework of Fe-Mn crusts. We subsequently utilize a multiproxy approach to demonstrate that the phosphatization events occurred coeval with the expansion of oceanic oxygen minimum zones. The Western Pacific Fe-Mn crusts thus document major perturbations in global oceanic phosphorus cycling, which appear to have been driven by climate-induced increases in primary productivity linked to changes in global ocean circulation.

Conceptual Models for Exploring Sea-Surface Temperature Variability Vis-à Long-Range Weather Forecasting

This paper analyzes the ability of three conceptual stochastic models (one-box, two-box, and diffusion models) to reproduce essential features of sea surface temperature variability on intra-annual time scales. The variability of sea surface temperature, which is particularly influenced by feedback mechanisms in ocean surface–atmosphere coupling processes, is characterized by power spectral density, commonly used to analyze the response of dynamical systems to random forcing. The models are aimed at studying local effects of ocean–atmosphere interactions. Comparing observed and theoretical power spectra shows that in dynamically inactive ocean regions (e.g., north-eastern part of the Pacific Ocean), sea surface temperature variability can be described by linear stochastic models such as one-box and two-box models. In regions of the world ocean (e.g., north-western Pacific Ocean, subtropics of the North Atlantic, the Southern Ocean), in which the observed sea surface temperature spectra on the intra-annual time scales do not obey the ν−2 law (where ν is a regular frequency), the formation mechanisms of sea surface anomalies are mainly determined by ocean circulation rather than by local ocean–atmosphere interactions. The diffusion model can be used for simulating sea surface temperature anomalies in such areas of the global ocean. The models examined are not able to reproduce the variability of sea surface temperature over the entire frequency range for two primary reasons; first, because the object of study, the ocean surface mixed layer, changes during the year, and second, due to the difference in the physics of processes involved at different time scales.

From Bottom‐Water Production to Warm Water Intrusions—The Cenozoic History of Bottom‐Current Evolution Offshore the Denman‐Shackleton Region, East Antarctica

AbstractThe deep glacial trough and hinterland of the Denman Glacier (East Antarctica) makes the area around the Shackleton ice shelf sensitive to ice loss due to warmer deep water intruding onto the continental shelf in the near future. In addition, the configuration of the ocean currents offshore is an important factor in priming the local and regional vulnerability to warm water intrusions. Here, we use reflection seismic data sets from the Bruce Rise offshore the Denman‐Shackleton region to investigate the Cenozoic history of the ocean bottom current configurations offshore and their influence on the Cenozoic sedimentation patterns of the Denman‐Shackleton region. On the Bruce Rise, sediment drift building, and erosional features indicate three distinct ocean current configurations, (a) the production of dense shelf waters in times of a smaller East Antarctic Ice Sheet (EAIS), (b) periods dominated by a strong Antarctic Slope Current (ASC) and (c) periods with a weak ASC. During the early establishment of the EAIS, the Denman‐Shackleton area contributed to the production of Antarctic Bottom Water, a process which stabilizes the regional ice sheet. With a growing icesheet, the ASC strengthened representing an effective barrier between the continental shelf and the warmer water masses of the deeper ocean during most of the times of an extended EAIS. The transition in the paleoceanographic setting from a strong, erosive ASC, toward a weak ASC increases the vulnerability of the Denman‐Shackleton continental shelf to deep water intrusions as we are observing today.

Resilience Improvement of Microgrid Cluster Systems Based on Two-Stage Robust Optimization

For microgrids in deep and remote sea areas, ocean currents are widely used as an emerging power generation resource. Implementing ES systems is crucial for smooth power output and grid stability. The stability of power output from sea current energy generation faces challenges due to speed fluctuations. Enhancing resilience requires addressing transmission line failures caused by extreme seabed conditions, and ensuring operational security. An ES configuration method considering line faults based on two-stage robust optimization is presented in this paper. First, in order to simultaneously consider planning and operation, a defender–attacker–defender (DAD) model was established. Additionally, the capacity, rated power, and charging/discharging power of ES during operation were jointly optimized through the column-and-constraint generation (C&CG) algorithm. In addition, the rationality and effectiveness of the proposed method were demonstrated through experiments on modified IEEE six-bus and fifty-seven-bus systems. The results show that a distributed ES configuration increased system resilience by 54.60% and reduced abandoned power rate by 57.06% compared with the situation without ES configuration.

Upwelling-driven high organic production in the late Ediacaran

The Ediacaran ocean (635-541 million years ago) is typically viewed as a stagnant, redox-stratified ocean with low phosphorus availability. However, this contradicts the high total organic carbon (up to 15 wt%) recorded in the upper Ediacaran Doushantuo Formation in South China. Here, we present a quantitative reconstruction of primary productivity and sediment total organic carbon using basin-scale simulations based on various redox-nutrient scenarios. Our results indicate that oceanic upwelling was the primary driver of enhanced primary productivity, with estimates over 2.5 times the modern ocean’s average, providing quantitative evidence for oceanic circulation in the Ediacaran Nanhua Basin. Our results also indicate the development of spatially linked but opposing redox trends, i.e., a ‘redox anticouple’, whereby the expansion of the oxic surface layer occurred concurrently with intensification of deep-water anoxia due to enhanced PP in surface and its consumption of oxidants in underlying waters. This model may explain the conflicting redox records across the Nanhua Basin. Our findings explain the unusually high rates of organic matter production and preservation in the low-pO2 Ediacaran ocean and provide a mechanism for its progressive oxygenation.

Nutrient Shift in the Yucatan Basin during the late Early Miocene: Evidence from calcareous nannofossils and stable isotopes at ODP Leg 165 Site 998 Hole A

Paleoceanographic reconstructions in the Caribbean Sea during past climate transitions, namely the Late Oligocene to Early Miocene (up to the Miocene Climatic Optimum and Monterey Excursion) are crucial to understanding the effects of the Eastern Pacific interchange with the Atlantic Ocean. Studies of the planktonic domain in the Yucatan Basin during the Early Miocene are limited, with most Caribbean research focused on reconstructing the series of events that precede the final closure of the Isthmus of Panama in the Early Pliocene. Furthermore, paleoceanography of the Yucatan Basin is largely unrefined during this time, even though it is an important transition for ocean gateways, and development of Atlantic deepwater and Atlantic Meridional Overturning Current (AMOC), driving global ocean circulation. Here we conduct a relative percent abundance analysis of calcareous nannofossils and stable isotopes from bulk sediment of drill cores spanning the Upper Oligocene to Lower Miocene in the central Yucatan Basin, collected by the Ocean Drilling Program Leg 165 at Site 998 Hole A. Nannofossil assemblage data record a shift from a eutrophic to oligotrophic system ∼19.2–17.65 Ma. Eutrophic taxa (Reticulofenestra spp. and Cyclicargolithus floridanus) decline at ∼20.23 Ma, while oligotrophic taxa (discoasters and sphenoliths) increase as stable carbon isotope values decline. The palaeoecological turnover coincides with a possible restriction in the Central American Seaway (CAS) ∼20.7–21 Ma. Population dynamics of the Hole 998 A nannofossil assemblage track with global declines in C. floridanus relative abundance between ∼20.2 to ∼20.5 Ma, followed by a subsequent decrease in Reticulofenestra spp. These data suggest water mass stratification in the Yucatan Basin during the Early Miocene ∼19.2–17.65 Ma, likely due to restriction of the CAS.

A climatological overview of surface currents in the Arabian Gulf with special reference to the Exclusive Economic Zone of Qatar

AbstractThis study derives the climatology of surface currents in the Arabian Gulf using the current velocities obtained from the Copernicus Marine Service (CMEMS) for the period 1993–2019. It reveals distinct temporal and spatial variability in the surface current speeds induced by the variability in surface winds, bathymetry and the changes in the lateral gradients in density. The mean speed of the Iranian Coastal Current (ICC) during summer reaches up to 0.33 m·s−1 along the coast of Iran, while the mean speed of Arabian Coastal Current (ACC) reaches up to 0.26 m·s−1 along the coast of Saudi Arabia. We found the occurrence of 2 major and 1 minor cyclonic eddies in the annual, seasonal and monthly climatology, while these eddies are more prevalent during summer. The major cyclonic eddy in the central Gulf develops in May and persists till November with varying patterns, and decays in December. The climatological mean current speeds are higher during summer compared to winter, due to the seasonal changes in thickness of the surface layer by the stratification/destratification processes. The highest mean current speeds along the coast of Qatar are found in June and the lowest in winter months. The highest annual, monthly and seasonal mean current speeds are observed along the north and northeast coast of Qatar, while the lowest are observed along the west coast and southeast coast of Qatar. Interannual variability in surface current speeds is evident, with notable links with the El Niño–Southern Oscillations (ENSO) and Indian Ocean Dipole (IOD). The annual mean current speeds show positive trends, of the order of 0.06–0.14 cm·s−1·year−1 in the offshore regions and 0.05–0.24 cm·s−1·year−1 in the nearshore regions, wherein the highest positive trend is observed off Ras Laffan and the lowest off Dukhan.

Energy Conversion by Helical Hydrokinetic Turbine in A Pipe

Hydrokinetic turbines are mechanisms designed for the purpose of utilizing the kinetic energy present in the movement of water bodies like rivers, tidal currents, or ocean currents, and transforming it into electrical power. These turbines function based on a principle akin to that of wind turbines; however, they are positioned underwater to harness the energy of the water flow. This study focuses on the fundamentals of hydrokinetic turbines and presents existing research. Additionally, simulations have been conducted to observe how the hydrokinetic turbine responds hydrodynamically inside a pipe. A three-bladed vertical-axis helical hydrokinetic turbine was installed within a circular conduit and subjected to analysis under varying flow conditions. The k-ω SST turbulence model was employed in the analyses. The results indicated that increasing the turbine's angular velocity initially raises the torque and the power coefficient until a peak is reached, after which the power coefficient decreases. The highest power coefficient was observed at a flow velocity of 2 m/s. Additionally, consistent with previous studies, the hydrokinetic turbine within the pipe surpassed the Betz limit.

Order of magnitude increase in power from flow-induced vibrations

Natural hydro environments such as rivers and ocean currents provide abundant and essentially free sources of kinetic energy. Although significant research has been devoted to harnessing this power through traditional turbine systems, there are also studies on the novel use of flow-induced vibration of a bluff body. The large oscillations of an elliptical cylinder resulting from the newly-discovered hyper branch have raised interesting questions about its potential as a source of effective renewable energy. This study investigates the power extraction characteristics of the hyper branch over a range of flow velocities. A factor-of-ten increase in the maximum time-mean power coefficient relative to an established flow-induced vibration system — the vortex induced vibration for aquatic clean energy converter is demonstrated. This suggests the possibility of a new and effective strategy to utilise flow-induced vibrations for energy generation and could help drive the commercial implementation and uptake of oscillating energy converters.

Numerical experiments investigating the influence of drag on trajectory patterns of floating macroalgae

Abstract Ocean currents are a crucial means of dispersing natural and human-made materials on the ocean surface. Macroalgae are among the most conspicuous natural dispersers, often called the ‘tumbleweeds of the ocean.’ Despite numerous studies on the subject, the relative influence of wind and surface currents on the trajectory of macroalgal dispersal remains uncertain. Previous studies have focused on kelp rafts of varying sizes, making it challenging to determine the impact of wind versus currents. These studies have also disregarded the macroalgae’s drag characteristics and surface area, which have been shown to impact the trajectory and accumulation of floating flotsam. This numerical study aims to shed light on the relative influence of wind and currents and the role of drag in determining the course and accumulation of macroalgae. By comparing simulations of virtual kelp ‘particles’ that incorporate drag and those without, this study focused on solitary kelp plants and considered the impact of morphological characteristics, flow-field combinations, and the presence of Stokes drift. Our results show that virtual kelp particles generally followed ocean currents, but the inclusion of drag caused deviations from purely Lagrangian particles’ trajectories and sheds light on the complex interplay of factors affecting macroalgal dispersal in the ocean.

A functional-group-based perspective on the response of marine phytoplankton to mesoscale eddies

This study analyzed the response of marine phytoplankton to environmental changes induced by mesoscale warm eddies through the lens of functional groups, highlighting the complex interactions within the ecosystem. It was found that warm eddies significantly affected phytoplankton distribution, with cell abundance in the center being only 75.60 cells/L, compared to 1095.00 cells/L in the periphery. Vertical transport within warm eddies altered light conditions, affecting photophilic diatoms more, while increased temperatures favored the growth of warm-water dinoflagellates. This study also emphasized that ocean currents were significant factors, showing correlations with various functional groups and playing a key role in material transport and phytoplankton distribution. Additionally, the distinct responses of different functional groups to temperature and salinity underscored their unique adaptations to environmental changes. In periods without warm eddies, phytoplankton primarily congregated in shallower water layers.

Mapping Ocean Gateways from 3D Seismic Data Using Color Processing and Analogues from Seismic Data

Mapping sedimentary features to delineate ancient ocean gateways from 3D seismic data has long been a challenge due to their limited vertical resolution. We present the technique of color processing of seismic data which improves the vertical resolution to very few seismic samples corresponding to 5–10 m. The result is a representation of the seismic impedance contrast correlation in Red-Green-Blue (RGB) colors, which creates images similar to satellite images that assist the geological interpretation because the RGB colors can be associated with mud-rich and sand-rich sediments. Using this approach, we have extracted six different sedimentary bedforms from different bottom flow settings and correlated these with the bedform-velocity matrix by Stow et al. (2009). Then we studied bedform assemblies in their regional context for the area covered by the 3D seismic data set. We conclude with comparing a modern and an ancient analogue – both from 3D seismic data – and infer paleo flow direction and velocity using oceanographic measurements available for the modern analogue. The method provides insights into ocean bottom currents and their impact on the formation of contourite depositional systems in modern and ancient ocean gateways which contribute to the reconstruction of the paleoclimate as an input to present day climate change models.

Evaporite sequences as archives for Mg isotope compositions of seawater - Evidence from a Tethys marginal shelf basin in the Anisian

Evaporites have recently been suggested as a potential archive for recording the Mg isotope compositions (δ26Mg) of coeval seawater. However, episodic dolomitization during the deposition of massive evaporites could cause considerable Mg removal and isotopic fractionation. To constrain the hydrological changes and influence of dolomitization on ambient brine δ26Mg, we present petrographic and mineralogical features, as well as Mg-C-O-Sr isotope data extracted from carbonate phases of a middle Triassic (ca. 247 Myr) marine anhydrite-dolostone sequence from a drill core in eastern China. The drilled lithologies are characterized by massive dolostone layers in the lower part, followed by an upward decline in dolomite contents accompanied by a rise in anhydrite. Multiple lines of evidence consistently point to a syn-depositional origin for the dolostones in a marginal basin of the Tethys Ocean and a lack of diagenetic alteration since deposition. We reconstructed the dynamic changes of δ26Mg values of basin waters based on Mg isotope compositions in dolomite leachates. According to our findings, the δ26Mg values of the basin waters were remarkably high (about 0.38 ± 0.05‰) at the onset of evaporation, indicating a significant Mg sink of the massive dolomitization. The δ26Mg of brine in the basin then changed towards the value of coeval seawater (about −0.32 ± 0.05‰) starting with the deposition of evaporites. Concurrently, 87Sr/86Sr ratios of dolomites shift from radiogenic values towards contemporaneous seawater composition. Our results demonstrate that the evaporite basin was not strictly restricted, and water exchange with the open ocean never ceased. Modeling calculation reveals that, even when the seawater exchange rate is far below the average ocean circulation, δ26Mg of brine in the basin will reach the value of open ocean within 1 Myr, completely removing the influence of early dolomitization. We suggested that massive marine evaporite sequences have the potential to record the long-term evolution of seawater Mg isotopes.

High-resolution UK’37 sea surface temperature reconstruction in the southwestern Atlantic Ocean during the Holocene

Modern sea surface temperatures (SST) were assessed using the alkenone calibration index (UK′37; SST-UK′37) values from twenty-one core-top sediment samples collected along the Southwestern Atlantic Ocean and validated by comparison with satellite-derived SSTs. The SST-UK′37 values revealed an annual signal between 28 and 30°S and a winter signal (83% of the region samples) between 30 and 34° S, with deviations falling within the UK′37 calibration error range. The paleotemperature (SST-UK′37) reconstruction through the Holocene was performed using two high-resolution marine sediment cores from 33 to 34°S latitude band. Millennial-scale variations dominate most of the SST-UK′37 results with changes up to ∼6 °C. Considering the modern ocean circulation dynamics, the SST-UK’37 in our records likely stems from the combined influence of the Subtropical Shelf Front (STSF) position and the interaction between the warm, salty, and nutrient-poor Subtropical Shelf Water (STSW) and the cold, fresh, and nutrient-rich Subantarctic Shelf Water (SASW). Our SST-UK’37 results also suggest that the northernmost position limit of the STSF reached around 33°S during the mid-to-late Holocene, while after ∼5500 cal yr BP the Plata Plume Water became the dominant influence on the regional SST-UK’37 signal. Spectral analyses revealed statistically significant oscillations of ∼8600 and ∼ 2250 years in record MDBT 557, and ∼ 5300 and ∼ 2600 years in record MDBT 561 which suggests the influence of Southern Westerly Winds (SWW) on the SST-UK’37, and therefore, on the STSF dynamic through the Holocene.