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Papers by Evgenia Dorokhova

Oceanology, Sep 1, 2019

In AMK-4474 marine sediment core, recovered from the northern part of the eastern (left) levee of... more In AMK-4474 marine sediment core, recovered from the northern part of the eastern (left) levee of the Northwest Atlantic Mid-Ocean Channel, two stratigraphic units were identified. The lower unit is represented by the Late Quaternary fine-grained sediments of the upper turbidite sequences. The presence of a 17-24 µm mode in grain-size distributions within the thin silt interlayers in the lower unit may reflect a sorting process of sedimentary material by the spillover of turbidity currents which is similar to the contour currents activity. This allows applying an indicator of the contour current speed-sortable silt (SS) content-to estimate the intensity of the spill-over current. The upper unit, formed during the last 26 ka, is represented by pelagic sediments. The presence of the fine-grained interlayer in the upper unit of AMK-4474 core is apparently due to a decrease in IRD supply to the study area.

Oceanology, Feb 1, 2022

Abstract During the 56th cruise of the P/V Akademik Ioffe (August 2020) in the Baltic Sea, hypoxi... more Abstract During the 56th cruise of the P/V Akademik Ioffe (August 2020) in the Baltic Sea, hypoxia was registered at a water depth of 80 m, hydrogen sulfide in the East Gotland Basin was detectable at 90 m above bottom, which is 25 m higher than in August 2019. In area of the “benthic desert” local habitats of species of bivalve mollusc Astarte borealis were found. Based on hydrophysical sounding data, a regional scheme of bottom currents induced by Major Baltic inflow events has been developed. High-resolution sub-bottom profiling and side-scan sonar in the East Gotland Basin allowed defining the thickness of marine sediments more precisely and revealing their asymmetry, as well as developing a digital terrain model. A detailed picture of the mosaic distribution of acoustic anomalies associated with the seeps of hydrocarbon gases to the bottom surface was obtained. New areas of distribution of iceberg plough marks, including buried ones, have been revealed. A previously unknown contourite drift was found in the northeastern part of the Slupsk Furrow.

Marine Geology, 2014

Abstract The easternmost Gulf of Finland is the recipient of the Neva River, the largest river dr... more Abstract The easternmost Gulf of Finland is the recipient of the Neva River, the largest river draining to the Baltic Sea. The depositional history and endozoobenthic activity in the area have not been studied before based long sediment cores, although such studies are desirable to provide a paleoenvironmental context for the recent environmental changes and the ecosystem projections for the future Baltic Sea. Two replicate long sediment cores from the easternmost Gulf of Finland record brackish-water mud accumulation beginning at 5900 ± 60 calendar years before present (cal. BP). The brackish-water muds are characterized by thin beds with erosional bases, fining-upward grain sizes and increasing-upward organic contents. A storm-induced flow origin is inferred for the thin mud beds, contrasting with previous interpretations that these muds accumulate by quiescent suspension settling. The bed primary microstructures are overprinted by biodeformation and burrow mottling by incipient small Planolites and Arenicolites / Polykladichnus ichnofossils of the continental Skolithos Ichnofacies, left behind by endobenthic oligochaetes and chironomid larvae. The depositional succession is cut by a strong erosional hyperpycnal flow event at 3320 ± 40 cal. BP, caused by the birth of the Neva River, which is now documented offshore for the first time. Mineral magnetic properties show pseudosingle-domain magnetite as the main magnetic mineral present. Increased magnetic grain sizes and reduced LOI values indicate a strong lithic influx immediately after the Neva River birth. The dominance of riverborne material in the accumulating sediments ever since highlights the strong influence of reworking in the shallow sea area. Increased diameters and the deeper penetration of biogenic sedimentary structures demonstrate improved seafloor oxygenation after the river birth. During the Medieval Warm Period (ca. 1000–700 cal. BP) and the last century, increased sedimentary lithic contents and magnetic grain sizes indicate an elevated riverine influx due to increased precipitation, and/or the increased reworking of sediments by storms. The results provide a paleoenvironmental context for the study area, and deepen the understanding of storm-induced sediment dispersal and the formation of sedimentary fabric in shallow, wave-dominated sea areas.

Deep Sea Research Part I: Oceanographic Research Papers, 2021

2012 IEEE/OES Baltic International Symposium (BALTIC), 2012

On the base of the data of seasonal surveys (May 2003-November 2011) carried out during complex e... more On the base of the data of seasonal surveys (May 2003-November 2011) carried out during complex ecological monitoring of offshore oilfield Kravtsovskoye (D6), the data from automatic hydro-meteorological station MiniKrams-4 (January 2004-December 2011) seated on the offshore ice-resistant fixed platform Lukoil-Kaliningradmorneft and the data measured in Baltiysk sity, Svetlogorsk sity, P-1, the seasonal and interannual variability of follow parameters on the east of Gdansk Basin were investigated: water salinity S and temperature Tw, air temperature Ta, dew-point temperature Td, atmospheric pressure on sea level P0 and wind speed W. It was shown that seasonal trend of Tw, Ta, Td and W is characterized by annual harmonic, in seasonal trend of S half year harmonic becomes pronounced, and for P0 half year harmonic becomes prevalent. Interannual variability of hydro-meteo elements of the region has cyclical character. Quasi two years, 3- and 5-years periodicities were marked off, and it is proposed of 7-8-, 10-12-, 19-, 22-24-years and century cycles.

Lithology and Mineral Resources, 2017

⎯Facts confirming the hypothesis of contourite sediment infill of the Equatorial Mid-Ocean Canyon... more ⎯Facts confirming the hypothesis of contourite sediment infill of the Equatorial Mid-Ocean Canyon (EMOC) are presented. We examined two cores recovered in Cruises 37 and 43 of the R/V Akademik Ioffe (2012, 2013). The cores recovered upper Quaternary miopelagic clays on the EMOC floor (AI-3149) and the adjacent abyssal plain (AI-2620). The study of these cores unraveled significant differences in their composition. In contrast to the lithologically homogeneous Core AI-2620, Core AI-3149 includes interlayers enriched in the biogenic CaCO 3 , terrigenous silt, and authigenic ferromanganese micronodules. These peculiarities are attributed to activity of the Antarctic Bottom Water (AABW) contour currents along the EMOC.

Lithology and Mineral Resources, 2018

This brief communication describes the first finding of glauconite sand alternating with calcareo... more This brief communication describes the first finding of glauconite sand alternating with calcareous foraminiferal-coccolithic ooze on the Piedra Buena contourite terrace of the Patagonian continental slope at a depth of 2327 m. It is suggested that the fine-sand glauconite grains were supplied from the shelf during glaciations, rewashed and sorted by alongslope (contour) currents of the Circumpolar Antarctic waters with the formation of sandy glauconite contourites.

Lithology and Mineral Resources, 2019

The submarine Shirshov Ridge is an independent system of terrigenous sedimentation, which is geom... more The submarine Shirshov Ridge is an independent system of terrigenous sedimentation, which is geomorphologically isolated from bottom terrigenous influx into the deep-water basin of the Bering Sea. Using the ridge as example, we studied background hemipelagic sedimentation of the finely dispersed terrigenous suspended matter from water column and deposition of the coarser grained ice-rafted material in the western part of the deep-water basin. Both the grain-size and mineral composition of postglacial sediments of the Shirshov Ridge were studied in cores SO201-2-85KL and SO201-2-77KL taken in local basins in the central and southern parts of the ridge, respectively. Statistic processing of uninterrupted grain-size distributions (GD) of terrigenous component of the postglacial sediments by end-member (EM) modeling revealed that the grain-size composition of sediments from two cores is determined by the mixing of three EMs. EM-1 and EM-2 reflect the hemipelagic sedimentation with and without bottom currents, respectively, while EM-3 with mode at fine-grained sand characterizes GD of the ice-rafted material. Reconstructed mechanisms of terrigenous influx on the Shirshov Ridge involve advection of the suspended matter with surface and intermediate water masses and ice-rafting. The relative role of both mechanisms of terrigenous sedimentation is evaluated. The conditions of the varying bottom current velocities are taken into account for intervals of Last Glacial Maximum, early deglaciation, Heinrich event 1, Bølling-Allerød, Younger Dryas, and Early Holocene. It is established that the grain-size composition of terrigenous component is controlled by climatic variations, sea ice coverage, drift pathways, conditions of fast sea ice melting, and mobility of bottom waters. High concentrations of drifting ice or permanent sea ice cover likely existed above the southern part of the ridge during the second half of the Heinrich 1 event. The low mobility of bottom waters facilitated only the subice hemipelagic sedimentation of fine fractions from the background reserve of suspended matter. A sharp reduction of ice-rafted flux was reconstructed for the Bølling-Allerød warming interval. Bottom currents affected sedimentation in the central part of the ridge during the entire deglaciation (in addition to the second half of the Heinrich 1 event), and in the southern part during the Bølling-Allerød, Younger Dryas, and Early Holocene.

Oceanology, 2017

Planktonic foraminiferal and ice-rafted debris count data, as well as the mean size of mineral pa... more Planktonic foraminiferal and ice-rafted debris count data, as well as the mean size of mineral particles of the 10-63 μm fraction (sortable silt,) were used as a proxy for surface and near-bottom paleocurrent intensity variations. The data obtained support our hypothesis about turbiditic origin of the lower (80-370 cm) section of the studied AMK-4515 core. Stratigraphic subdivision of the upper section (0-80 cm) makes it possible to allocate two marine isotope stages (MIS) covering the last 27 ka. The main intervals of the North Atlantic Polar Front (PF) migrations were recorded: south of the modern PF position during early MIS 2 (24-27 ka) with PF presence in the study area during MIS 2 (20-24 ka); south of the study area during the last glacial maximum (18-20 ka). Influence of the near-bottom currents within the investigated interval led to beginning of the channel-related drift formation on the northern slope of the southern channel of the Charlie-Gibbs Fracture Zone. There is a weak relationship between intensity of near-bottom contour currents and long-term climatic cyclicity. However, intervals corresponding to Heinrich events coincide with decrease in bottom currents activity.

Oceanology, 2015

The mean size of mineral particles of the 10-63 µm fraction (the so called "sortable silt" mean s... more The mean size of mineral particles of the 10-63 µm fraction (the so called "sortable silt" mean size ()) was used as proxy for the variations in paleocurrent intensity. The modes of grain size distribution were also examined. Sediments with bimodal grain size distribution (the second mode varies from 10 to 28 µm) cor relate with the increased mean size of sortable silt (up to 18-23 µm) at the Hatton and Snorry Drifts. These parameters indicate an increase in bottom current intensity during MIS 1, 3, and 5e. There is no correlation between grain size distribution and climatic cyclicity of variations in contour current intensity at the Gloria Drift. The similarity between AMK 4493 sediments and IRD containing hemiturbidites of the Labrador Sea render doubtful the contourite nature of the Gloria Drift.

Russian Journal of Earth Sciences, 2019

The sediment drift north of the Kane Gap has been investigated by means of the seismoacoustic pro... more The sediment drift north of the Kane Gap has been investigated by means of the seismoacoustic profiling. The surface area of the drift is about 500 km 2 and maximal thickness is 70 m. The contourite drift was formed under the control of the Antarctic Bottom Water (AABW) flow in the Kane Gap. It is suggested naming this contourite fan as the "Kane Drift". Variations in the activity of the AABW current were registered in the sediment core ANS-33056, retrieved near the summit of the drift. For this purpose, the mean size of sortable silt (, mineral fraction 10-63 m) was used. It was shown that during the Mid-Pleistocene to Holocene, the speed of the AABW flow north of the Kane Gap was not strictly determined by the alternation of the climatic cycles. A strong relationship between the AABW flow and the short-time climatic fluctuations was found only during the marine isotope stages (MIS) 4 and 5: intensification of the near-bottom current coincides with the cold intervals. Moreover, during the Terminations II and I (MIS 2/1 and MIS 6/5, respectively), the intensity of the current also increased. Maximal near-bottom current activity was registered at the end of the MIS 2.

EGU General Assembly Conference Abstracts, Apr 1, 2016