ALBERT

Description: Physical properties (water content, bulk density, magnetic susceptibility, natural remanent magnetization, nature of magnetization, and composition of ferromagnetic fraction), chemical, and (optionally) mineral composition of bottom sediments from the north-west Sea of Japan have been studied. Their stratigraphic subdivision based on composition of diatoms has been carried out. Obtained data have allowed to find out some aspects of influence of paleogeographic conditions and diagenetic processes on change of physical properties of the sediments, as well as on their composition in Holocene and Late Pleistocene.

Description: The long-chain diol index (LDI) is a new organic sea surface temperature (SST) proxy based on the distribution of long-chain diols. It has been applied in several environments but not yet in subpolar regions. Here, we tested the LDI on surface sediments and a sediment core from the Sea of Okhotsk, which is the southernmost seasonal sea ice covered region in the Northern Hemisphere, and compared it with other organic temperature proxies, i.e. Uk'37 and TEXL86. In the surface sediments, the LDI is correlated with autumn sea surface temperature, similar to the Uk'37 but different from the TEXL86 that correlates best with summer sea subsurface temperature. Remarkably, the obtained local LDI calibration was significantly different from the global core-top calibration. We used the local LDI calibration to reconstruct past SST changes in the central Sea of Okhotsk. The LDI-SST record shows low glacial (Marine Isotope Stage, MIS 2, 4, 6) and high interglacial (MIS 1 and MIS 5) temperatures and follows the same pattern as the Uk'37-SST and a previously published TEXL86 temperature record. Similar to the modern situation, the reconstructed temperatures during the interglacials likely reflect different seasons, i.e. summer for the TEXL86 and autumn for Uk'37 and LDI. During glacials, the reconstructed temperatures of all three proxies are similar to each other, likely reflecting summer temperatures as this was the only season free of sea ice. Our results suggest that the LDI is a suitable proxy to reconstruct subpolar sea water temperatures.

Description: Sediment core LV53-27 (41° 54′ N, 132° 33′ E) was retrieved in the northwestern Sea of Japan (Pervenets Seamount) at 1698 m depth during a joint Russian-Chinese expedition LV53 on RV “Akademik M.A. Lavrentyev” in 2010-11-10T23:39:00. The 757-cm long core was characterized by clay/silty clay sediments with alternating dark and light layers. in order to investigate millenial-scale climate changes with ultra-high resolution digital image of this sediment core was processed. Sediment core LV53-27 recovered about 120 kyr according to age model (Gorbarenko et al., submitted to Global and Planetary Changes). Age model was based on correlation of magnetic susceptibility, chlorin content and lightness records with similar records of well-dated sediment core MD01-2407. The magnetic susceptibility (MS) of the sediments was measured in cube samples throughout the core at 2-cm intervals using an AGICO Kappabridge MFK1-FA. These measurements were performed at the Laboratory of Cenozoic Geology and Paleomagnetism of the North-East Interdisciplinary Scientific Research Institute in Magadan, Russia. Data presented as natural logarithm of units SI (International System of Units) Chlorin content was measured with pretreatment procedures and analytical reagents, as proposed by Harris et al. (1996), using a Shimadzu UV-1650PC spectrophotometer at 1 cm resolution. Color lightness (CL) of the sediments was measured using the original photocolorimeter based on a Canon 50D digital camera. One-meter core sections with 14 cm diameter were split into two halves, while performing surface smoothing. Two flash units with soft boxes were used for creating an even and diffused illumination of the sediment surface. Camera shooting was performed with the following settings: ISO 100, 1/100'' exposure, and 8.0 focal ratio. Every image covered approximately 40 cm of the core section with approximately 11 pixels per 1 mm stratigraphic resolution. The X-rite Color Checker was used for calibrating the white balance of each image. Digital images were processed with the RTImageProc software for calculating the CL data from black (0) to white (255) with 1-pixel resolution and averaged with 1 mm step. Need to note that the width of the analyzed window of each image (80 mm) in the studied core allow to significantly reduce the possible effect of the sediment bioturbation by organisms several millimeters in diameter.

Description: Reconstruction of regional climate and the Okhotsk Sea (OS) environment for the Last Glacial Maximum (LGM), deglaciation and Holocene were performed on the basis of high-resolution records of ice rafted debris (IRD), CaCO3, opal, total organic carbon (TOC), biogenic Ba (Ba_bio) and redox sensitive element (Mn, Mo) content, and diatom and pollen results of four cores that form a north-southern transect. Age models of the studied cores were earlier established by AMS 14C data, oxygen - isotope chronostratigraphy and tephrochronology. According to received results, since 25 ka the regional climate and OS environmental conditions have changed synchronously with LGM condition, cold Heinrich event 1, Bølling -Allerød (BA) warming, Younger Dryas (YD) cooling and Pre-Boreal (PB) warming recorded in the Greenland ice core, North Atlantic sediment, and China cave stalagmites. Calculation of IRD MAR in sediment of north-south transect cores indicate an increase of sea ice formation several times in the glacial OS as compared to the Late Holocene. Accompanying ice formation, increased brine rejection and the larger potential density of surface water at the north shelf due to a drop of glacial East Asia summer monsoon precipitation and Amur River run off, led to strong enhancement of the role of the OS in glacial North Pacific Intermediate Water (NPIW) formation. The remarkable increase in OS productivity during BA and PB warming was probably related with significant reorganisation of the North Pacific deep water ventilation and nutrient input into the NPIW and OS Intermediate Water (OSIW). Seven Holocene OS millennial cold events based on the elevated values of the detrended IRD stack record over the IRD broad trend in the sediments of the studied cores have occurred synchronously with cold events recorded in the North Atlantic, Greenland ice cores and China cave stalagmites after 9 ka. Diatom production in the OS were mostly controlled by sea ice cover changes and surface water stratification induced by sea-ice melting; therefore significant opal accumulation in sediments of this basin begin from 4-6 ka ago simultaneously with a remarkable decrease of sea ice cover.

Description: Composition and distribution of benthic foraminifers together with isotopic data on Upper Pleistocene and Holocene sediments from the southern Bering Sea demonstrate variations in bottom water properties during the last 54 ka. Their abundance increased to some extent during a short periods corresponding to warm Dansgaard-Oeshger interstadials 14, 12, 8, and 2 of marine isotopic stages (MIS) 3 and 2. The first and second deglaciation phases separated by the Younger Dryas cooling episode are marked by significant abundance peaks of benthic foraminifers (an order magnitude higher than in the glacial period), although their share in community of benthic and planktonic foraminifers taken together decreases. Species typical of stable high-productivity areas gain a dominant position. A significant proportion of agglutinated species in Holocene sediments is indicative of Ca ions deficiency that accelerated dissolution of carbonate tests up to their disappearance approximately 2.5-3 ka ago.