The dataset contains reconstructed daily streamflow records for 816 snowmelt-dominated catchments worldwide covering the period 1950-2023. Streamflow series were reconstructed using an observation-prioritized, performance-based weighted ensemble framework that integrates deep learning models and differentiable hybrid hydrological models. The reconstruction framework was developed to generate continuous daily streamflow records in catchments affected by incomplete observations and varying data availability. The dataset is distributed as a pickle file ( ensemble_1950_2023_obs_prioritized.pickle ). The file contains a dictionary in which each key corresponds to a unique basin identifier (e.g., GRDC_1 ), and each value is a pandas DataFrame containing daily streamflow records for that basin. The obs column contains the original observed streamflow records where available. The ensemble column provides continuous daily streamflow estimates for the entire study period, including both observed and missing intervals. The file gauge_information.csv contains geographic information and reconstruction statistics for the 816 snowmelt-dominated catchments included in the reconstructed streamflow dataset. The file includes the following variables: gauge_id : Unique identifier of the gauging station obtained from the Global Runoff Data Centre (GRDC). lat : Latitude of the gauging station (decimal degrees). long : Longitude of the gauging station (decimal degrees). reconstruction_rate : Percentage of reconstructed daily streamflow values relative to the total length of the streamflow record. This variable quantifies the proportion of missing observations that were filled using the ensemble reconstruction framework. Higher values indicate a greater degree of reconstruction, whereas a value of 0% indicates a fully observed streamflow record.
The dataset comprises a comprehensive 15-year spatiotemporal record of the unvegetated Sulengguole River, integrating high-resolution satellite imagery, field surveys, and derived morphodynamic metrics to document a complete post-avulsion cascade. High-resolution optical imagery and in-situ photographs visually capture the multi-stage morphological evolution, detailing the 2019 annexational flow capture, subsequent rapid channel widening, and the critical emergence of alternate bars. These visual observations are directly substantiated by extensive quantitative spatial analyses, which track the downstream kinematic propagation of both the channel-widening waves and the critical half-width-to-depth ratio ( β ) instability fronts. Ultimately, this combination of planform imagery and extracted geometric data explicitly links the macroscopic avulsion-driven reorganization to the extreme, width-dependent acceleration of local meander migration.
This repository contains: "predicted_nitrate_concentrations_global.txt" - global dataset with ensemble averaged long-term mean ntirate concentration (mean_nit, mg/l), their standard deviation (sd_nit, mg/l), coefficient of variation (cv_nit, %), median (p50_nit, mg/l), 10th (p10_nit, mg/l) and 90th (p90_nit, mg/l) percentile of predicted nitrate concentrations across 1000 models in 2895895 global river segments (MERIT Hydro COMID used as identifiers) along with their landuse, aridity class, income class, rural-urban class and stream order "global_river_nitrate_model_v1.0.0.zip" - code used to generate global river nitrate dataset Global River Nitrate Model V1.0.0 A global scale approach for estimating long term mean nitrate concentrations across the global river network using land use, climate, soil and other catchment attributes Overview Nitrate continues to be a persistent global problem, causing eutrophication, endangering aquatic life and human health, and driving higher drinking water treatment costs. Human nitrogen input is considered as the main driver of high nitrate concentrations. Catchment factors including climate, soil and aquifer properties are known to moderate the effect of human nitrogen input; yet there is a lack of global framework explaining these interactions. While rivers in North America and Europe are relatively well monitored, rivers in other continents have huge gaps in their monitoring network. This work aims to 1) generate a global map of river nitrate concentrations and 2) show ariditiy as an important control over river nitrate concentrations along with nitrogen input. For this purpose, an ensemble of 1000 machine learning (boosted regression tree) models was trained on data from 7213 sites (Global River Quality Archive, GRQA) representing 6601 river segments to predict nitrate concentration across the global river network (Multi-Error-Removed Improved Terrain Hydrography, MERIT-Hydro). The predicted nitrate concentrations were used to additionally assess the global area and population exposed to high nitrate concentrations. Repository Structure - `data/` - Input datasets - `raw/` - Unprocessed input data (from original databases or repositories) - `processed/` - Processed data created by scripts for model training and prediction - `models` - Models are saved here - `results` - Predicted river nitrate concentrations - `scripts` - Scripts that clean raw data, trains model on it and predict nitrate concentrations - `01_nitrate_data_cleaning` - cleans raw data and calculate mean river nitrate concentrations in GRQA sites - `02_identify_river_segments_with_data` - identifies the river segments on which the GRQA sites are located - `03_train_BRT_model` - trains 1000 machine learning models to predict mean nitrate concentrations - `04_predict_global_nitrate` - predicts nitrate concentration in 2895896 segments in the global river network Requirements The scripts run in R (version 4.3.2) and requires the following packages: - readr (2.1.5) - dplyr (1.1.4) - lubridate (1.9.4) - sf (1.0.16) - parallel (4.3.2) - caret (6.0.94) - xgboost (1.7.7.1) - hydroGOF (0.6.0) Data Nitrate concentration data: Global River Quality Archive (GRQA) (1) Global river network: Multi-Error-Removed Improved Terrain Hydrography (MERIT Hydro) (2) Catchment characteristics: - Terra and Aqua combined Moderate Resolution Imaging Spectroradiometer (MODIS) Land Cover Type MODIS Land Cover Type Product (MCD12Q1, version 6.1) (3) - Climatologies at High Resolution for the Earth's Land Surface Areas (CHELSA version 2.1) (4) - Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) (5) - SoilGrids version 2.0 (6) - Global Geo-processed Data of Aquifer Properties by 0.5° Grid, Country and Water Basins (7) Notes The data for training the models are provided in the file "BRT_train_data_7213_catchments.txt" in the folder "data/processed". The "BRT_input_global_subset.txt" file in the same folder contains catchment characteristics for 5000 river segments as an example dataset to demonstrate prediction of river nitrate concentration in these segments. Citation 1. H. Virro, G. Amatulli, A. Kmoch, L. Shen, E. Uuemaa, GRQA: global river water quality archive. Earth System Science Data Discussions 2021, 1-30 (2021) 2. D. Yamazaki et al., MERIT Hydro: A high‐resolution global hydrography map based on latest topography dataset. Water Resources Research 55, 5053-5073 (2019) 3. M. Friedl, D. Sulla-Menashe, MODIS/Terra+ Aqua land cover type yearly L3 Global 0.05 Deg CMG V061, MCD12C1. 061, NASA EOSDIS Land Processes Distributed Active Archive Center (DAAC), (2022) 4. D. N. Karger et al., Climatologies at high resolution for the earth's land surface areas. Scientific data 4, 1-20 (2017) 5. J. J. Danielson, D. B. Gesch, Global multi-resolution terrain elevation data 2010 (GMTED2010), US Geological Survey, (2011) 6. L. Poggio et al., SoilGrids 2.0: producing soil information for the globe with quantified spatial uncertainty. Soil 7, 217-240 (2021) 7. H. Niazi et al., Global Geo-processed Data of Aquifer Properties by 0.5 Grid, Country and Water Basins, MultiSector Dynamics-Living, Intuitive, Value-adding, Environment, (2024)
40 RGB PNG frames of ERA5 vertically integrated water-vapour transport (IVT) magnitude over the North Pacific, 6-hourly from 2 to 11 February 2017, derived from the public ARCO-ERA5 archive (IVT = sqrt(u^2 + v^2)). Each frame renders an atmospheric river as a bright filament on a dark background and is named NPacific_IVT_0000.png ... NPacific_IVT_0039.png. This is the Earth-observation dataset for the Galaxy Training Network tutorial 'Object tracking using CellProfiler' (https://gxy.io/GTN:T00516), used to demonstrate that a CellProfiler nucleus-tracking pipeline can be reused to detect and track atmospheric rivers. Preprocessing notebooks, full Galaxy run provenance, and the software archive: https://github.com/annefou/fiesta-galaxy-cellprofiler-eo (DOI 10.5281/zenodo.20811614). Part of the OSCARS-FIESTA project.
This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45210**6 t/a) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10210**6 t/a, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4210**6 t/a) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6210**6 t/a is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.
The patterns of spatial variation of diatom assemblages from surface sediments in Lake Lama were quantified using a combined approach of ordination and geostatistics. The aims were (i) to estimate the amount of variation between diatom assemblages within the lake, (ii) to model the spatial variability of the diatom assemblages and their diversity, and (iii) to map the diatom distributions in the lake. A correspondence analysis (CA) separated the diatom assemblages into a planktonic and a periphytic group. Rheophilic taxa were found within the periphytic group. Variogram analysis showed that only the sample scores of the first CA axis and the Shannon diversity index were spatially structured. The range of spatial correlation was estimated to be 55 km for both variables. The diversity and, to a lesser extent, the sample scores had considerable small-scale variability of about 20 and 3%, respectively. Estimates of the first component of the CA and the Shannon index were derived using block-kriging. The maps of the estimates provided a basis for partitioning Lake Lama according to the spatial structures into an eastern and a western basin, a north–south connection between the basins, and a north–south directed tip at the far eastern end. It was shown that variation in diatom assemblages is mainly spatially structured at the catchment scale and that there is a considerable amount of variation at smaller scales. According to the modeled spatial distribution, the assemblages are most likely affected by the lake size, morphology, and the water and nutrient input introduced by rivers. This has to be taken into account when paleolimnological interpretations are drawn from records of complex lake systems like Lake Lama.
Stein, Ruediger · Dittmers, Klaus Hauke · Fahl, Kirsten · et al.
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In this paper, we summarize data on terrigenous sediment supply in the Kara Sea and its accumulation and spatial and temporal variability during Holocene times. Sedimentological, organic-geochemical, and micropaleontological proxies determined in surface sediments allow to characterize the modern (riverine) terrigenous sediment input. AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 cal kyr BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge. Based on sediment thickness charts, echograph profiles and sediment core data, we estimate an average Holocene (0–11 cal kyr BP) annual accumulation of 194,106 t/yr of total sediment for the whole Kara Sea. Based on late Holocene (modern) sediment accumulation in the estuaries, probably 12,106 t/yr of riverine suspended matter (i.e. about 30% of the input) may escape the marginal filter on a geological time scale and is transported onto the open Kara Sea shelf. The high-resolution magnetic susceptibility record of a Yenisei core suggests a short-term variability in Siberian climate and river discharge on a frequency of 300–700 yr. This variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the High Northern Latitudes over the last decades, such as the NAO/AO pattern. A major decrease in MS values starting near 2.5 cal kyr BP, being more pronounced during the last about 2 cal kyr BP, correlates with a cooling trend over Greenland as indicated in the GISP-2 Ice Core, extended sea-ice cover in the North Atlantic, and advances of glaciers in western Norway. Our still preliminary interpretation of the MS variability has to be proven by further MS records from additional cores as well as other high-resolution multi-proxy Arctic climate records.
During spring, ammonium oxidation and nitrite oxidation rates were measured in the NW basin of the Mediterranean Sea, from mesotrophic sites (Ligurian Sea and Gulf of Lions) to oligotrophic sites (Balearic Islands). Nitrification rates (average values for 37 measurements) ranged from 72 to 144 nmol of N oxidised/l/d, except in the Rhône River plume area where the rates increased to 264-504 nmol/l/d because of the riverine inputs of nitrogen. Maximal rates were located around the peak of nitrite within the nitracline at about 40 to 60 m and just above the phosphacline. At 1 station, relatively high values of nitrification (50 to 130 nmol/l/d) were also measured deep in the water column (240 m). Day-to-day variations were measured demonstrating the response within a few hours to hydrological stress (wind-induced mixing of the water column) and showing the role of hydrological characteristics on the distribution of nitrification rates. Because of the homogenous temperature (13°C) in the Mediterranean Sea, the spatial (geographical and vertical) fluctuations of nitrifying rates were linked to the presence of substrate due to mineralisation processes and/or Rhône River inputs. We estimate the contribution of nitrate produced by nitrification to the N demand of phytoplankton to range from 16% at mesotrophic to 61% at oligotrophic stations.
DNA reference database for the fishes of the Yangtze River Basin with a particular focus on 12S and COI sequences. These sequences were compiled from four sources: 1) BOLD, 2) MIDORI2, 3) MitoFish, 4) NCBI nucleotide database (nuccore) and supplemented by local DNA sequence samples for rare taxa. See README for descriptions of each file.
Are, Felix · Grigoriev, Mikhail N · Hubberten, Hans-Wolfgang · et al.
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Field investigations of the Laptev Sea shoreface morphology were carried out (1) off erosional shores composed of unconsolidated sediments, (2) off the modern delta shores of the Lena River, and (3) off rocky shores.It was found that profiles off erosional shores had a concave shape. This shape is not well described by commonly applied power functions, a feature, which is in disagreement with the generally accepted concept of the equilibrium shape of shoreface profiles. The position of the lower shoreface boundary is determined by the elevation of the coastal lowland inundated during the last transgression (at -5 to -10 m) and may easily be recognized by a sharp, an order of magnitude decrease in the mean inclination of the sea floor. The mean shoreface inclination depends on sediment grain-size and ranges from 0.0022 to 0.033. The concave shape of the shoreface did not change substantially during the last 20-30 years, which indicates that shoreline retreat did not slow down and hence suggests continued intensive coastal erosion in the 21st century.The underwater part of the Lena River delta extends up to 35 km offshore. Its upper part is formed by a shallow and up to 18-km wide bench, which reaches depths of 2-3 m along the outer edge. The evolution of the delta was irregular. Whereas some parts of the delta are advancing rapidly (58 m/year), other parts are eroding. Comparison of measured profiles with older bathymetric data gave an opportunity to evaluate the changes of the underwater delta over past decades. Bathymetric surveys of the seabed around the delta can thus contribute towards a quantification of the sediment budget of the river-sea system.In addition, some sections of the Laptev Sea coast are composed of bedrock that has a comparatively low resistance to wave erosion. These sections may supply a considerable amount of sediment, especially if the cliffs are high. This source must therefore also be taken into account when assessing the contribution of shore erosion to the Laptev Sea sediment budget.
Raw data and R code used to produce the publication "Physical Disturbance Outlasts Chemical Disturbance in Two Amazonian Rivers Affected by Artisanal Gold Mining" by Alex Pelletier, Francisco Villamarin, and Tim Jardine.
Gallego-Torres, David · Martinez-Ruiz, Francisca C · Paytan, Adina · et al.
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A multiproxy geochemical study of nine sapropel layers from ODP Hole 964A, ODP Leg 160 in the eastern Mediterranean spanning the Pliocene-Holocene time interval provides new insights into the evolution of sapropel deposition. Paleoenvironmental proxies were used for reconstruction of productivity (Ba derived from marine barite), oxygen conditions (trace metal ratios) and sedimentary regime (clay minerals, detrital elements). These proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval. Ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition, although preservation also played an important role. Furthermore, major differences exist in depositional conditions, including both oxygenation and productivity since the Pliocene. Productivity fluctuated substantially and was higher during the Pliocene and Pleistocene than during the Holocene; at the same time decreasing oxygen availability parallels the enhanced productivity. Dysoxic to anoxic conditions appear to coincide with marine productivity maxima, thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation. This correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability.
A gridded time-series dataset reconstructing population distribution across the Yellow River Basin, China, from 1000 to 2000 AD, with a temporal resolution of one century and a spatial resolution of 10 km.
Schmiedl, Gerhard · Mackensen, Andreas · Müller, Peter J
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Sixty surface sediment samples from the eastern South Atlantic Ocean including the Walvis Ridge, the Angola and Cape basins, and the Southwest African continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences.Live (stained with Rose Bengal) and dead faunas were counted separately and then each grouped by Q-mode principal component analysis into seven principal faunal end-members. Then, multiple regression technique was used to correlate Recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages: (1) seasonality of food supply and organic carbon flux rates, together with oxygen content in the pore and bottom waters; (2) lateral advection of deep-water masses; (3) bottom water carbonate corrosiveness; and (4) energetic state at the benthic boundary layer and grain size composition of the substrate.Food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the Recent benthic foraminifera. At the continental margin, in the zone of coastal upwelling and its mixing area, benthic foraminiferal assemblages are dominated by stenobathic high-productivity faunas, characterized by elevated standing stocks, low diversities and a large number of endobenthic living species. At the continental shelf and upper continental slope the live assemblages are characterized by Rectuvigerina cylindrica, Uvigerina peregrina s.1., Uvigerina auberiana and Rhizammina spp. while the dead assemblages are characterized by Cassidulina laevigata, Bolivina dilatata, Bulimina costata and B. mexicana. At the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the Cunene river mouth, where the live assemblage is dominated by Uvigerina peregrina s.1., the corresponding dead assemblage by Melonis barleeanum and M. zaandamae. In the adjacent areas of the lower continental slope the biocoenosis is characterized by Reophax bilocularis, and Epistominella exigua which becomes dominant in the corresponding dead assemblage.At the Walvis Ridge and in the abyssal Angola and Cape basins, where organic matter fluxes are low and highly seasonal, benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration. The top and flanks of the Walvis Ridge are inhabited by the Rhizammina, Psammosphaera and R. bilocularis live assemblages, the corresponding dead assemblages are dominated by G. subglobosa on the ridge top and E. exigua on the flanks. Within the highly diverse E. exigua dead assemblage several associated epibenthic species coincide with the core of NADW between about 1600 and 3700 m water depth. These species include Osangularia culter, Cibicidoides kullenbergi, Melonis pompilioides, Bolivinita pseudothalmanni and Bulimina alazanensis. The assemblages of the abyssal Cape and Angola basins are characterized by Nuttallides umbonifer and a high proportion of agglutinated species. These species are adapted to very low organic matter fluxes and a carbonate corrosive environment.
This repository contains a reproducible EPA SWMM model package developed to evaluate low-impact development / sustainable urban drainage system (LID/SUDS) scenarios for pluvial flood mitigation in a school area of Durán, Ecuador. The package includes Python scripts for generating Chicago design hyetographs at 5-minute temporal resolution, station rainfall data, generated storm hyetographs, EPA SWMM input models, archived outputs from 60 SWMM simulations, R scripts for extracting and analysing SWMM report files, final tables and figures, and files required to restore the reproducible R environment. The design storm set combines three return periods, 5, 10, and 20 years, with five storm durations, 30, 60, 120, 180, and 240 minutes, producing 15 synthetic rainfall events. These storms were applied to four SWMM scenarios: a baseline model and three LID/SUDS scenarios. The archived SWMM simulations include input, report, output, and log files for each scenario-storm combination. The main R analysis script extracts hydrological and hydraulic indicators from SWMM report files, checks continuity errors, calculates percentage reductions relative to the baseline scenario, ranks LID/SUDS alternatives using multicriteria indicators, estimates uncertainty using bootstrap resampling, and evaluates exploratory robustness across design storms. This dataset is intended to support reproducibility, transparency, and independent verification of the modelling workflow used in the associated study on urban pluvial flood mitigation using LID/SUDS alternatives in data-limited educational infrastructure.
Planktic foraminifers Neogloboquadrina pachyderma (sin.) from 87 eastern and central Arctic Ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition. Additional results from 52 stations were taken from the literature.The lateral distribution of delta18O (18O/16O) values in the Arctic Ocean reveals a pattern of roughly parallel, W-E stretching zones in the Eurasian Basin, each ~0.5 per mil wide on the delta18O scale. The low horizontal and vertical temperature variability in the Arctic halocline waters (0-100 m) suggests only little influence of temperature on the oxygen isotope distribution of N. pachyderma (sin.). The zone of maximum delta18O values of up to 3.8 per mil is situated in the southern Nansen Basin and relates to the tongue of saline (> 33%.) Atlantic waters entering the Arctic Ocean through the Fram Strait. delta18O values decrease both to the Barents Shelf and to the North Pole, in accordance with the decreasing salinities of the halocline waters. In the Nansen Basin, a strong N-S delta18O gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources, i.e. salinity reduction from sea ice meltwater in the south and from light isotope waters (meteoric precipitation and river-runoff) in the northern part of the basin. North of the Gakkel Ridge, delta18O and salinity gradients are in good accordance and suggest less influence of sea ice melting processes.The delta13C (13C/12C) values of N. pachyderma (sin.) from Arctic Ocean surface sediment samples are generally high (0.75-0.95 per mil). Lower values in the southern Eurasian Basin appear to be related to the intrusion of Atlantic waters. The high delta13C values are evidence for well ventilated surface waters. Because the perennial Arctic sea ice cover largely prevents atmosphere-ocean gas exchange, ventilation on the seasonally open shelves must be of major importance. Lack of delta13C gradients along the main routes of the ice drift from the Siberian shelves to the Fram Strait suggests that primary production (i.e. CO2 consumption) does probably not change the CO2 budget of the Arctic Ocean significantly.
Palynological investigation of the marine core, GeoB1008-3, from near the mouth of the Congo river (6°35.6'S/10°19.1'E), provides information about the changes in vegetation and climate in West Equatorial Africa during the last 190 ka. The pollen diagram is divided into zones 1–6 which are considered to correspond in time with the marine isotope stages 1–6. Oscillations in temperature and moisture are indicated during the cold stage 6. During stage 5, two cooler periods (5d and 5b) can be shown with an expansion of Podocarpus forests to lower elevations on the expense of lowland rain forest. Extended mangrove swamps existed along the coast in times of high sea level (stages 5 and 1).
Sayles, Frederick L · Martin, William R · Deuser, Werner G
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Over the past decade an increasing body of evidence has accumulated indicating that much, perhaps most, of the deep sea floor is an environment of substantial temporal variability (Smith and Baldwin, 1984 doi:10.1038/307624a0; Smith, 1987; Deuser and Ross, 1980 doi:10.1038/283364a0; Thiel et al., 1988). This variability is driven largely by seasonal changes of processes occurring in the surface waters (Smith, 1987; Deuser and Ross, 1980; Billett et al., 1983 doi:10.1038/302520a0). The coupling of the deep sea floor environment to the surface waters is the result of rapid vertical transport of particulate matter through the water column (Honjo, 1982 doi:10.1126/science.218.4575.883; Deuser et al., 1986 doi:10.1016/0198-0149(86)90120-2; Lampitt, 1985 doi:10.1016/0198-0149(85)90034-2), affording only limited time for degradation before arrival at the sea floor. Studies in the Pacific Ocean have indicated that temporal variations in particulate organic carbon fluxes to the sea floor are accompanied by temporal variability in sediment oxygen demand by as much as a factor of four (Smith and Baldwin, 1984; Smith, 1987). We report here time-series studies of oxygen fluxes into the sediments of the oligotrophic Atlantic near Bermuda which contrast sharply with these previous reports. At the Bermuda site, despite large seasonal variations in particulate organic carbon fluxes, in situ measured sediment oxygen consumption does not vary significantly. These results imply that large areas of the sea floor may be characterized by seasonally invariant sediment oxygen demand.
The areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes, whereas wind transport is much more important than river transport. Pollen distribution patterns of Pinus, Artemisia, Chenopodiaceae-Amaranthaceae, and Asteraceae Tubuliflorae trace atmospheric transport by the northeast trades. Pollen transport by the African Easterly Jet is reflected in the pollen distribution patterns of Chenopodiaceae-Amaranthaceae, Asteraceae Tubuliflorae, and Mitracarpus. Grass pollen distribution registers the latitudinal extension of Sahel, savannas and dry open forests. Marine pollen distribution patterns of Combretaceae-Melastomataceae, Alchornea, and Elaeis reflect the extension of wooded grasslands and transitional forests. Pollen from the Guinean-Congolian/Zambezian forest and from the Sudanian/Guinean vegetation zones mark the northernmost extension of the tropical rain forest. Rhizophora pollen in marine sediments traces the distribution of mangrove swamps. Only near the continent, pollen of Rhizophora, Mitracarpus, Chenopodiaceae-Amaranthaceae, and pollen from the Sudanian and Guinean vegetation zones are transported by the Upwelling Under Current and the Equatorial Under Current, where those currents act as bottom currents. The distribution of pollen in marine sediments, reflecting the position of major climatic zones (desert, dry tropics, humid tropics), can be used in tracing climatic changes in the past.
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