Holocene Sediment Dynamics Research Articles

Deglacial and Holocene sediment dynamics and provenances off Lancaster Sound: Implications for paleoenvironmental conditions in northern Baffin Bay

Since the last deglaciation, Baffin Bay between Greenland and Canada developed from an isolated marginal sea to a major Arctic-Atlantic throughflow closely linked to the North Atlantic circulation. While the initial steps of gateway openings through Lancaster Sound and Nares Strait to northern Baffin Bay are reasonably well documented, far less is known about related regional deglacial-to-Holocene changes in sediment sources and depositional processes due to a lack of continuous and well-dated paleoenvironmental records from northern Baffin Bay. Sedimentological, mineralogical, and radiogenic isotope data of the well-dated sediment core GeoB22336-4 from the mouth of Lancaster Sound provide new insights on the impacts of ice-sheet retreat and opening of the gateways to the Arctic Ocean on the depositional setting. Basal subglacial till deposits point to a grounded ice stream at the mouth of Lancaster Sound before ∼14.5 ka BP. Subsequent glaciomarine sedimentation is characterized by the input of ice-rafted detritus (IRD), bioturbation traces, and foraminifera shells. Decreasing sediment supply and input of IRD through time reflects a period of ice-sheet recession to predominantly land-terminating positions during the Early Holocene. Changes in radiogenic isotope signatures reveal the openings of Lancaster Sound between ∼10.4 and 9.9 ka BP and of Nares Strait between 8.5 and 8.2 ka BP, in alignment with earlier studies. The rapid mid-Holocene (up to ∼5.8 ka BP) deposition of fine-grained sediments is most likely caused by enhanced sea ice-rafted sediment input released under a strong West Greenland Current influence. Finally, a slight increase in IRD input during the last ∼2 ka BP is linked to the neoglacial re-advance of regional glaciers.

Lateglacial and Holocene sedimentary dynamics in northwestern Baffin Bay as recorded in sediment cores from Cape Norton Shaw Inlet (Nunavut, Canada)

The physical, sedimentological, mineralogical and elemental geochemical properties of sediment cores AMD1803‐02BC and 01PC from the Cape Norton Shaw Inlet were investigated to reconstruct glacial sediment discharges from southeastern Manson Icefield and document the impact of ice–ocean interactions on the sediment dynamics and opening of the North Water Polynya (NOW) in northwestern Baffin Bay since the last deglaciation. Laminated glaciomarine sediments rich in quartz and feldspar are observed prior to 11 cal. ka BP and were probably deposited by hyperpycnal currents triggered by the local retreat of the southern margin of the Innuitian Ice. Detrital proxies suggest that Early Holocene sediment dynamics were mainly influenced by sea ice and iceberg rafting and meltwater discharges related to the deglaciation of eastern Smith (~11 to 10.65 cal. ka BP) and Jones (~10.7 cal. ka BP) sounds. This also provides an upper limit to the timing of formation of the NOW. The high detrital carbonate contents during 8.8 to 6.6 cal. ka BP confirm that enhanced carbonate‐rich sediment export from Nares Strait to northern Baffin Bay occurred during and after the deglaciation of Kennedy Channel (8.8 to 8.2 cal. ka BP). Canadian Shield sediment inputs have dominated since 6.6 cal. ka BP, indicating that sedimentation is mainly influenced by Cape Norton Shaw glacier discharges. The lower level of sedimentation recorded in core 01PC during the Middle to Late Holocene suggests an accelerated landward retreat of the Cape Norton Shaw glaciers in response to warmer marine conditions. During the Neoglacial period, higher sedimentation rates and detrital proxies in the cores suggest increased glacial erosional processes, probably associated with the long‐term declines in boreal summer insolation and glacier growth. Finally, mineralogical and grain‐size data in core 02BC support the idea that increased Arctic atmospheric temperatures have had an important influence on the glacial dynamics during the industrial period.

A new model evaluating Holocene sediment dynamics: Insights from a mixed carbonate–siliciclastic lagoon (Bora Bora, Society Islands, French Polynesia, South Pacific)

Mixed carbonate–siliciclastic lagoons of barrier reefs provide great potential as sedimentary archives focusing on paleoenvironmental and paleoclimatic changes as well as on event deposition. Sediment sources include lagoonal carbonate production, the marginal reef and the volcanic hinterland. Mixed carbonate–siliciclastic continent-attached coastal lagoons have been intensively studied, however, their isolated oceanic counterparts have been widely disregarded. Here, we present a new model of Holocene sediment dynamics in the barrier–reef lagoon of Bora Bora based on sedimentological, paleontological, geochronological and geochemical data. The lagoonal succession started with a Pleistocene soil representing the Lowstand Systems Tract. As the rising Holocene sea inundated the carbonate platform, peat accumulated locally ~10,650–9400yearsBP. Mixed carbonate–siliciclastic sedimentation started ca. 8700–5500yearsBP and represents the Transgressive Systems Tract. During that time, sediments were characterized by relatively coarse grain size and contained high amounts of terrestrial material from the volcanic hinterland as well as carbonate sediments mainly produced within the lagoon. Siliciclastic content decreases throughout the Holocene. After the rising sea had reached its modern level, sand aprons formed between reef crest and lagoon creating transport pathways for reef-derived material leading to carbonate-dominated sedimentation ca. 6000–3000years BP during the Highstand Systems Tract. However, mainly fine material was transported and accumulated in the lagoon while coarser grains were retained on the prograding sand apron. From ca. 4500–500yearsBP, significant variations in grain-size, total organic carbon as indicator for primary productivity, Ca and Cl element intensities as qualitative indicators for carbonate availability and lagoonal salinity are seen. Such patterns could indicate event (re-)deposition and correlate with contemporaneous event deposits found in the lagoon of nearby Tahaa, which are supposed to be induced by elevated cyclone activity. Correspondingly, enhanced erosion and run-off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall. Increased amounts of coarse-grained sediment from marginal reef areas would be transported into the lagoon. However, Ti/Ca and Fe/Ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid-Holocene. Also, benthic foraminiferal faunas do not validate reef-to-lagoon transport of sediment. Alternatively, the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher-than-present sea level, which are supposed for the mid-late Holocene in the south Pacific. Sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity. We propose the shift towards coarser-grained sedimentation patterns during the mid-late Holocene to reflect sediment-load shedding of sand aprons due to oversteepening of slopes at sand apron/lagoon edges during times of stronger trades and higher-than-present sea level of the Highstand Systems Tract, which led to redeposition of sediment even within the lagoon center. Modern conditions including a sea-level fall to modern level were reached ca. 1000yearsBP, and lagoonal infill has been determined to a large part by fine-grained carbonate-dominated sediments produced within the lagoon and derived from the marignal reef. Infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons. Contrary to the commonly supposed assumption that coarse-grained sediment layers within fine-grained lagoonal successions represent overwash events induced by storms or periods of higher storm activity, we postulate a new model of long-term lagoonal sediment dynamics including sea level, climatic change and geomorphological variation of the barrier reef lagoon.

Human impact on Holocene sediment dynamics in the Eastern Mediterranean – the example of the Roman harbour of Ephesus

AbstractDuring the past millennia, many erosion and accumulation processes have been modified by anthropogenic impact. This holds especially true for the environs of ancient settlements and their harbours along the Mediterranean coasts. Our multi‐proxy investigations in the Roman harbour and the harbour canal of Ephesus (western Turkey) reveals that humans have significantly triggered soil erosion during the last three millennia. Since the eighth century bc, and especially since the Hellenistic period, a high sedimentation rate indicates fast alluviation and delta progradation of the Küçük Menderes. Deforestation, agriculture (especially ploughing) and grazing (especially goats) were the main reasons for erosion of the river catchment area. One consequence was significant siltation of the Hellenistic/Roman harbour basin. This sediment trap archives the human impact, which was strongly enhanced from Hellenistic/Roman to Byzantine times (second/first centuries bc to the sixth/seventh centuries ad), evidenced by high sedimentation rates, raised values of heavy metal contaminations [lead (Pb), copper (Cu)], the occurrence of fruit tree pollen and of intestinal parasites. From the middle to the end of the first millennium ad, the influence of Ephesus declined, which resulted in a decrease of human impact. Studies of several ancient settlements around the Mediterranean Sea tell a comparable story. They also confirm that during their most flourishing periods the human impact totally overprinted the climatic one. To detect the latter, geo‐bio‐archives of relatively pristine areas have to be investigated in detail. Copyright © 2016 John Wiley & Sons, Ltd.

Holocene sediment dynamics in the environs of the fortification enclosure of Corneşti-Iarcuri in the Romanian Banat

The presented study combines data from geomorphological, geochemical, sedimentological, chronometric, and archaeological records providing first insights into the Holocene landscape development in the environs of the Late Bronze Age fortification enclosure Corneşti-Iarcuri. This large-scale archaeological site is located in a loess-covered, undulating landscape at the eastern edge of the Great Hungarian Plain, in western Romania. Sediment archives from geomorphologically different locations, closely related to the Copper Age to Late Bronze Age settlements, are presented. Mainly stable geomorphic conditions throughout the Holocene occurred on the high plains of the Vinga Plain as indicated by chemical alteration of the loss deposits and soil formation processes exceeding 2 m. In contrast, two cores from an alluvial fan of a minor drainage system in direct vicinity of the archaeological site document varying morphodynamics throughout the Holocene. Phases of geomorphic activity and stability are indicated by the formation of fan deposits and paleosols developed in these sediments. 14C dates from charcoal extracted from the fan sediments show maximum deposition ages between c. 4400 cal. BP and c. 2900 cal. BP. Thus, the formation of the charcoal coincides with the Copper Age to Late Bronze Age development of the settlement sites. Daub pieces, incorporated into these reworked soil sediments, provide evidence for human activities in the catchment. This, in turn, may indicate that the erosion processes that led to the fan formation are linked to those activities. However, reworking and redeposition of the charcoal and daub bearing sediments due to retrogressive erosion during the last millennia cannot be excluded.

Holocene Sediment Dynamics in the Vicinity of a Roman battlefield near Osnabrück (NW-Germany)

The interpretation of the Holocene sediment dynamics at Mount Kalkriese in the Wiehengebirge mountains (northwestern Germany) shows that the onset and the extent of human land use corresponds well with most colluvial archives in Central European loess regions: The onset of soil erosion in the Wiehengebirge mountains started during the Early Neolithic period. For the Bronze Age, erosion and colluviation are documented as well. A considerable increase of soil erosion with correlated reworking of colluvial sediments was found since Roman times, indicated by the burial of Germanic artifacts of Roman Age at the toe-slopes. Unfortunately, no absolute ages exist for the post roman period. However, in analogy to other sites it can be assumed that highest erosion rates occurred during the Middle Ages. This study also shows typical problems when using the soilscape model for calculating the sediment budget: since truncated soil profifi les are used to model eroded volumes, only minimum soil erosion is mapped. This can lead to a considerable discrepancy between eroded and accumulated volumes. Therefore, we have to assume that soil erosion at the plateau and in upslope areas at Mount Kalkriese was much higher than predicted by the soilscape model. In addition, extensive anthropogenic accumulation soils (Plaggen soils) were deposited in the downslope areas, thereby increasing the discrepancy between erosion and accumulation volumes. The combination of mapping erosion and accumulation with augerings and trenches, calculation of the mass balance by GIS, relative and absolute dating and geophysical evidence provides a powerful tool in landscape interpretation. Due to the small number of numerical ages, the landscape model at Mount Kalkriese has to be considered preliminary.

Anthropogenic and climatic impact on Holocene sediment dynamics in SE Spain: A review

The climatic and anthropogenic control on Holocene sediment dynamics was not well constrained for the Western Mediterranean basin. The paucity of high resolution palaeoenvironmental records long hampered a detailed understanding of the human impact on erosion rates. This paper analyses Holocene sediment dynamics in the context of regional climatic conditions, land cover and human occupation based on an extended compilation of recently published high-resolution paleoenvironmental proxy data from both terrestrial and marine environments. The palaeoenvironmental reconstruction identified four main aridification episodes (A) at 5600–4700 (A4), 4100–3400 (A3), 2800–2500 (A2), and 1900–1300/1200 (A1) cal. BP. Most of the severe aridification phases were climatically induced, not human-driven and well correlated with a large dataset of paleoenvironmental records from the Western Mediterranean Basin and North Atlantic Ocean. The phases of enhanced aridity are generally associated with enhanced sediment dynamics, independent of the intensity and type of human occupation. In contrast, wet climatic conditions are found to be associated with both high and low sediment dynamics dependent on the human impact on the environment. The mid-late Phoenician, Phoenician II/Republican Rome civilizations and the Christian Reconquest are all associated with high human impact on the environment, and high erosion rates are reported for the Vera basin and NE Spain despite the improved hydrological conditions. Human occupation is not necessarily associated with geomorphic instability, as shown by the Post Argaric, Omeya and Nazarene periods that are characterized by low erosion rates and geomorphic stability.

The Temporal and Spatial Quantification of Holocene Sediment Dynamics in a meso-scale catchment in northern Bavaria / Germany

The Temporal and Spatial Quantification of Holocene Sediment Dynamics in a meso-scale catchment in northern Bavaria / Germany

The temporal and spatial quantification of Holocene sediment dynamics in a meso-scale catchment in northern Bavaria, Germany

The Aufsess River catchment (97 km2) in northern Bavaria, Germany, is studied to establish a Holocene sediment budget and to investigate the sediment dynamics since the early times of farming in the third millennium BCE. The temporal characterization of the sediment dynamics is based on an intensive dating program with 73 OSL and 14 14C ages. To estimate soil erosion and deposition, colluvial and alluvial archives are investigated in the field by piling and trenching, supported by laboratory analyses. The sediment budget shows that 58% of these sediments are stored as colluvium in on- and foot-slope positions, 9% are stored as alluvium in the floodplains and 33% are exported from the Aufsess River catchment. Colluviation starts in the end-Neolithic ( c. 3100 BCE), while first indicators of soil erosion-derived alluviation is recorded c. 2–3 ka later. The pattern of sedimentation rates also displays differences between the colluvial and alluvial system, with a distinct increase in the Middle Ages ( c. 1000 CE) for the alluvial system, while the colluvial system records low sedimentation rates for this period. A contrast is also observed since Modern times ( c. 1500 CE), with increasing sedimentation rates for the colluvial system, whereas the alluvial system records decreasing rates. The different behavior of the colluvial and alluvial systems clearly shows the non-linear behavior of the catchment’s fluvial system. The results further suggest that human impact is most probably the dominant factor influencing the sediment dynamics of the catchment since the introduction of farming.

Changing hillslope and fluvial Holocene sediment dynamics in a Belgian loess catchment

AbstractFloodplain deposition is an essential part of the Holocene sediment dynamics of many catchments and a thorough dating control of these floodplain deposits is therefore essential to understand the driving forces of these sediment dynamics. In this paper we date floodplain and colluvial deposition in the Belgian Dijle catchment using accelerator mass spectrometric radiocarbon and optical stimulated luminescence dating. Relative mass accumulation curves for the Holocene were constructed for three colluvial sites and 12 alluvial sites. A database was constructed of all available radiocarbon ages of the catchment and this database was analysed using relative sediment mass accumulation rates and cumulative probability functions of ages and site‐specific sedimentation curves. Cumulative probability functions of ages were split into different depositional environments representing stable phases and phases of accelerated clastic deposition. The results indicate that there is an important variation between the different dated sites. After an initial stable early and middle Holocene phase with mainly peat growth in the floodplains, clastic sedimentation rates increased from 4000 BC on. This first phase was more pronounced and started somewhat earlier for colluvial deposits then for alluvial deposits. The main part of the Holocene deposits, both in colluvial and alluvial valleys, was deposited during the last 1 ka. The sedimentation pattern of the individual dated sites and the catchment‐wide pattern indicate that land use changes are responsible for the main variations in the Holocene sediment dynamics of this catchment, while the field data do not provide indications for a climatological influence on the sediment dynamics. Copyright © 2011 John Wiley & Sons, Ltd.

Holocene sediment dynamics in an upland temperate lake catchment: climatic and land-use impacts in the English Lake District

Accelerated erosion and transport of fine sediment from upland temperate catchments can reflect increased erosivity and/or erodibility, due in turn to climatic and/or human forcing. Identification of sediment fluxes and sources over Holocene timescales can both enable understanding of the relative impacts of these forcings and provide perspective on recent sediment fluxes. Here we present a ~ 5500 yr record of sediment fluxes and sources from Lake Bassenthwaite in the English Lake District, utilizing magnetic measurements and fuzzy clustering, coupled with independent pollen and archaeological records, to identify the timing and impact of catchment disturbance. This record shows that recent sediment flux increases (ie, within the last 150 years) are unprecedented in scale throughout the mid—late Holocene and appear to be in response to specific human changes occurring within the catchment. Earlier episodes of human activity, from the mid Holocene onwards, show no link with increased lake sediment fluxes, indicating either limited catchment impact and/or `buffering' through within-catchment sediment storage. Increasingly intensive land use and reduction of sediment storage through revetment construction on a key inflow, Newlands Beck, have resulted in 3 × increases in lake sediment flux. These data may be significant for other upland temperate areas, as increasing land-use pressures and reduced sediment storage capacity may not only increase contemporary sediment flux, but increase sensitivity to predicted increases in rainfall and storminess as a result of global climate change.

Acoustic facies on the inner Kara Sea Shelf: Implications for Late Weichselian to Holocene sediment dynamics

We studied the impact of the last glacial (late Weichselian) sea level cycle on sediment architecture in the inner Kara Sea using high-resolution acoustic sub-bottom profiling. The acoustic lines were ground-truthed with dated sediment cores. Furthermore we refined the location of the eastern LGM ice margin, by new sub bottom profiles. New model results of post-Last Glacial Maximum (LGM) isostatic rebound for this area allow a well-constrained interpretation of acoustic units in terms of sequence stratigraphy. The lowstand (or regressive) system tract sediments are absent but are represented by an unconformity atop of Pleistocene sediments on the shelf and by a major incised dendritic paleo-river network. The subsequent transgressive and highstand system tracts are best preserved in the incised channels and the recent estuaries while only minor sediment accumulation on the adjacent shelf areas is documented. The Kara Sea can be subdivided into three areas: estuaries (A), the shelf (B) and (C) deeper lying areas that accumulated a total of 114 × 10 10 t of Holocene sediments.

Integration of shelf evolution and river basin models to simulate Holocene sediment dynamics of the Humber Estuary during periods of sea-level change and variations in catchment sediment supply

Three modelling elements and sedimentary evidence provide an understanding of sediment characteristics, river basin processes, tidal regimes and sea-level changes to explain sediment supply to the Humber Estuary through the Holocene (the last 10 000 years). An upscaled cellular catchment model simulates water and sediment fluxes from river basins, illustrating significant variations in response to climate change, especially precipitation and vegetation changes, principally deforestation. Much of the sediment mobilised remains in stores within the catchment and only a small fraction reaches the Humber tidal system. An empirical model helps to explain sediment erosion, transport and deposition from the offshore and coastal zones through the Holocene and sea-level rise caused the transgression of the continental shelf of the North Sea. Comparison with the sediment fill of the lowlands around of the Humber estuary, that represent the extent of the estuary during the Holocene, demonstrates that most of the fill (∼95–98%) was derived from non-fluvial sources. A shelf evolution model, with reconstructions of sea level, palaeogeography and palaeobathymetry for 1000 year time steps through the Holocene predicts significant changes in tidal regimes, first over wide areas of the coast as the transgression of the continental shelf progresses. The most significant changes occur with the inner reaches of the palaeo-estuaries, especially those of the Humber and the Fenland. Throughout the mid-Holocene they are characterised by significantly lower tidal ranges (MWHST ∼2.5 m less than present) and low tidal currents. The simulated patterns of tidal currents concur with the transport of fine grain sediment from the coastal zone into the estuaries. The major tidal range changes revise estimates of late Holocene and ongoing relative sea and land level changes.

Holocene Sediment Dynamics on a Cool-Water Carbonate Shelf: Otway, Southeastern Australia

The Otway Shelf is covered by cool ocean waters and veneered by bryozoan-dominated carbonate sediments. Radiocarbon dating and stratigraphy of shelf vibracores and slope gravity cores document late Pleistocene/Holocene deposition. Shelf sediments of the late Pleistocene highstand (60-26 ky) are rare, either never having been deposited or having been removed during the following sea-level fall (26-17 ky). During the subsequent lowstand the shelf was exposed, facies shifted basinward, and beach/dune complexes were constructed near the shelf edge. The deep shelf was characterized by nondeposition and hardground formation, and the shelf margin became locally erosional. Upper-slope bryozoan/sponge assemblages continued to grow actively, and lower-slope foraminifera and nannofossil ooze was increasingly enriched in hemipelagic terrigenous mud swept off the wide shelf. Coarse shelf debris and lowstand dune sands were erosively reworked and transported onto the upper slope and redistributed to deep-slope aprons during early transgression (17-10 ky). This event locally terminated shelf-edge bryozoan and sponge growth. Continued erosive shoreface retreat formed a bored and cemented ravinement surface, mantled by bivalves and lithoclasts, across the open shelf. Base-level rise reduced the amount of terrigenous material reaching the continental slope. Slower transgressive flooding from 10 to 6.5 ky allowed infilling of shallow embayments on the shelf, and outer-shelf sediment accumulation began by 7 ky. Sea level stabilized near its present level by 6.5 ky and the area is now partitioned into three zones by an energetic wave and swell regimen: (1) inboard, protected embayments and/or beach/dune complexes with high sediment accumulation rates (about 100 cm/ky), (2) an open shelf where, although sediment production is active, accumulation is patchy (3-5 cm/ky) to nonexistent within the zone of wave abrasion, and minimal (about 23 cm/ky) between maximum abrasion depth and swell wave base, and (3) a deep shelf edge and upper slope where sediment is accumulating at rates of 2-50 cm/ky. Interpreted deep-water (> 100 m) bryozoan/sponge mounds are growing at rates of 105 cm/ky. Accumulation decreases progressively down slope with deep-slope, pelagic carbonate sedimentation at rates of 5 cm/ky. The late Quaternary shelf record resembles that of flat-topped, warm-water platforms with Holocene sediment overlying Pleistocene/Tertiary limestone, but for different reasons. Much of this high-energy shelf is still within lag depth, more than 10 ky after flooding. The steady-state deep-water, shelf-margin bryozoan factory has been largely unaffected by 50-100 m eustatic changes in sea level, and has contributed to slow but continuous platform progradation. The slow growth potential, uniform profile of sediment production and distribution, and inability of constituent organisms to construct rigid frameworks favor maintenance of a shallow ramp profile and makes the cool-water carbonate system an excellent modern analog for interpretation of many ancient ramp successions.

Sedimentology and geochemistry of surface sediments, outer continental shelf, southern Bering Sea

Present-day sediment dynamics, combined with lowerings of sea level during the Pleistocene, have created a mixture of sediments on the outer continental shelf of the southern Bering Sea that was derived from the Alaskan Mainland, the Aleutian Islands, and the Pribilof ridge. Concentrations of finer-grained, higher-organic sediments in the region of the St. George basin have further modified regional distribution patterns of sediment composition. Q-mode factor analysis of 58 variables related to sediment size and composition — including content of major, minor, and trace elements, heavy and light minerals, and clay minerals — reveals three dominant associations of sediment: 1. (1) The most significant contribution, forming a coarse-grained sediment scattered over most of the shelf consists of felsic sediment derived from the generally quartz-rich rocks of the Alaskan mainland. This sediment contains relatively high concentrations of Si, Ba, Rb, quartz, garnet, epidote, metamorphic rock fragments, potassium feldspar, and illite. 2. (2) The next most important group, superimposed on the felsic group consists of andesitic sediment derived from the Aleutian Islands. This more mafic sediment contains relatively high concentrations of Na, Ca, Ti, Sr, V, Mn, Cu, Fe, Al, Co, Zn, Y, Yb, Ga, volcanic rock fragments, glass, clinopyroxene, smectite, and vermiculite. 3. (3) A local group of basaltic sediment, derived from rocks of the Pribilof Islands, is a subgroup of the Aleutian andesite group. Accumulation of fine-grained sediment in St. George basin has created a sediment group containing relatively high concentrations of C, S, U, Li, B, Zr, Ga, Hg, silt, and clay. Sediment of the Aleutian andesite group exhibits a strong gradient, or “plume”, with concentrations decreasing away from Unimak Pass and toward St. George basin. The absence of present-day currents sufficient to move even clay-size material as well as the presence of Bering submarine canyon between the Aleutian Islands and the outer continental shelf and slope, indicates that Holocene sediment dynamics cannot be used to explain the observed distribution of surface sediment derived from the Aleutian Islands. We suggest that this pattern is relict and resulted from sediment dynamics during lower sea levels of the Pleistocene.