Coarse fraction components of Lomonosov Ridge sediment cores

Seung-il Nam KOPRI

Objectives

In the Arctic Ocean, variations in the sediment composition are generally related to sub/

surface-water productivity, supply of terrigenous ice rafted-debris, and resuspended material transported by icebergs, sea-ice, and currents from the shallow coastal areas (Stein, 2008).

During glacial periods with a relatively lower level stand than the present, perennial sea-ice coverage, discharge of large amounts of sea-icebergs, and extended continental sea-ice sheets, the sediment transported to the deep-sea floor is dominated by non-biogenic material (e.g.

Ruddiman & Mcintyre 1976; Ruddiman 1977; Stein 2008). In contrast, during interglacial periods, reduced ice coverage and/or open-water conditions coupled with a high sea-level stand have contributed not only to the reduced supply of terrigenous sediment from the surrounding lands, but also to an increase in sub/surface-water productivity resulting in enhanced flux-rates of biogenic material to the sea floor sediments (Gard & Backman 1990).

In general, biogenic components in marine sediments in the Arctic Ocean include carbonate, siliceous and organic-walled microfossils (e.g., de Vernal et al. 2013; see Chapter 10.8).

The biogenic carbonate content (e.g. coccoliths, calcareous foraminifers and ostracodes) of marine sediments are generally related to water-mass properties, open water and/or sea-ice coverage and biological productivity (Wollenburg et al. 2004, 2007; Cronin et al. 2013; Polyak et al. 2013). Other factors such as water depth, sedimentation, preservation, and dissolution are also of major importance. Furthermore, it is known that authigenic compositions such as manganese nodules occurred during interglacials, interstadials and terminations in the Arctic marine sediments (Jokat 2009; Maerz et al. 2011). The main goal of this work is to roughly estimate sediment compositions (siliciclastic, biogenic and authigenic in origin) in the sand fraction (>63 µm) from the four sediment cores recovered with the Kastenlot (KAL) from the western and eastern part of Lomonosov Ridge.

Work at sea

In order to estimate the sediment components within the sand fractions (>63 µm) onboard Polarstern, about 30 cm³ of sediment were taken from the four Kastenlot cores recovered from the eastern and western profiles of the Lomonosov Ridge (see Chapter 10.1). The samples were wet-sieved with a mesh of 63 µm to separate the sand fraction (>63 µm) from the silt and clay fractions. The sand fraction was dried at 60°C, and then sand fractions were roughly estimated using a binocular microscope. The amounts of each component was simply expressed in the five criteria of 0 to 5 (0, barren; 1 very rare; 2, rare; 3, common; 4, abundant;

5, dominant) because the estimation of the sand fraction was carried out based on five simple criteria (0 to 5). This estimation is generally relevant to a scale ranging from 0 (absent) to 4 (abundant) done also in micropaleontology work (see Chapter 10.8).

Preliminary results

According to the semi-quantitative estimation, the sediment components of sand fraction (>63 µm) can be simply classified into siliciclastic (terrigenous), biogenic and authigenic components in origin. In general, the siliciclastic components are mainly composed of quartz, feldspar, rock fragment, mica, carbonate/dolomite, basalt and heavy minerals. The biogenic components consist mostly of planktic and benthic (calcareous and agglutinated) foraminifers, ostracodes, mollusca and biogenic opal such as radiolarian and sponge spicules (see Chapter 10.8). The authigenic component identified is mainly of micro-manganese nodules, whereas authigenic carbonate is also observed in some intervals of cores PS87/023-1 and PS87/030-1 only with very low amounts (Figs. 10.6.7 and 10.6.8).

10. Marine Geology

Preliminary results from the western profile of the Lomonosov Ridge

The first preliminary results are shown in Figs 10.6.7 and 10.6.8 (data are listed in Tables A5.3.1 and A5.3.2 in the Appendix). In most sediment depths of the two cores PS87/023-1 and PS87/030-1 recovered from the western part of Lomonosov Ridge, the dominant siliciclastic components are quartz and feldspar, while rock fragments, detrital carbonate/ dolomite, basalt, mica and heavy minerals occurred in minor amounts throughout the sediment. In contrast, the biogenic components are mostly dominated by planktic foraminifers with a monospecific species of N. pachyderma sin.. N. pachyderma dex. (subpolar species) together with the other subpolar species like as T. quinqueloba, G. bulloides is also present, but with small amounts.

Although subpolar species of planktic foraminifers occurred with low amounts, the most intervals with dominant amounts of both planktic and benthic foraminifera might be tentatively interpreted as interglacial/interstadial periods (e.g., MIS 11, 9, 7, 5.5 and Holocene).

Fig. 10.6.7: Down-core variations in siliciclastic, biogenic and authigenic sediment components roughly estimated from the coarse sand fraction (>63 µm) of core PS87/023-1KAL recovered from the western part of the Lomonosov Ridge. Note that scales from 0 to 5 indicate relative abundance of each component (0, barren; 1, very rare; 2, rare, 3, common; 4, abundant; 5, dominant). Shadow area indicates intervals with high amounts of siliciclastic sediment components dominated by quartz

and feldspar within the sediment cores, whereas biogenic origin sediments are of barren. Micro-manganese nodules occurred in common abundances throughout the cores. Red stars in carbonate

indicate occurrence of authigenic carbonate in few amounts.

It is supposed that there might have been evidence of relatively reduced sea ice coverage, but it seemed to have been less advection of the North Atlantic Intermediate Water into the coring sites in the western part of Lomonosov Ridge mostly during the interglacial/interstadial periods. Further information on biogenic compositions (calcareous and agglutinated benthic foraminifera, ostracode and sponge spicules, etc.) are shown and explained in Chapter 10.8 in more details. The micro-manganese nodules mostly occurred in brown color layers with high variability of lack to predominance in both cores PS87/023-1 and PS87/030-1. However, the micro-manganese nodules decreased toward the upper part of sediment core with relatively low amounts.

10.6 Main lithologies and lithostratigraphy of PS87 sediment cores

Fig. 10.6.8: Down-core variations in siliciclastic, biogenic and authigenic sediment components roughly estimated from the coarse sand fraction (>63 µm) of core PS87/030-1 recovered from the western part of the Lomonosov Ridge. Notice that scales from 0 to 5 indicate relative abundance of

each component (0, barren; 1, very rare; 2, rare, 3, common; 4, abundant; 5, dominant). Shadow area indicates intervals with high amounts of siliciclastic sediment components dominated by quartz

and feldspar within the sediment cores, whereas biogenic origin sediments are of barren. Micro-manganese nodules occurred in common to abundant amounts throughout the cores. Red stars in

carbonate indicate occurrence of authigenic carbonate in few amounts.

Fig. 10.6.9: Down-core variations in siliciclastic, biogenic and authigenic sediment components roughly estimated from the coarse sand fraction (>63 µm) of core PS87/070-1 recovered from the eastern

part of the Lomonosov Ridge. Notice that scales from 0 to 5 indicate relative abundance of each component (0, barren; 1, very rare; 2, rare, 3, common; 4, abundant; 5, dominant). Note that high amounts of siliciclastic sediment components are dominated by quartz and feldspar throughout the sediment cores, whereas biogenic origin sediments occurred in the uppermost part (0-67 cm in core depth) dominated only by planktic foraminifer N. pachyderma sin.. Micro-Mn nodules (brown-color line)

occurred in common to abundant amounts throughout the cores except for some barren zones. Mn/

Fe ratios (black line) based on Avaatech XRF core scanner data (measured on board Polarstern by M.

Forwick). Background image shown in the Mn nodule record is a linescan photography obtained by the 3-CCD (charge-coupled device) camera installed in XRF core scanner.

10. Marine Geology

Preliminary results from the eastern profile of the Lomonosov Ridge

Except for the agglutinated foraminifers occurring with rare to common amounts throughout sediment cores, it is noticed that there are totally barren of biogenic components below 70 cm in core depth of PS87/070-1 and below 40 cm in core depth of PS87/079-1, respectively (Figs. 10.6.9 and 10.6.10; Tables A5.3.3 and A5.3.4 in the Appendix; see also Chapter 10.8).

Extraordinary predominant terrigenous components in both cores PS87/070-1 and PS87/079-1 are mainly composed of quartz (including feldspar), and mica as well as minor amounts of rock fragments, carbonate, heavy minerals and basalt (Figs. 10.6.9 and 10.6.10). In contrast to the cores from the western profile of the Lomonosov Ridge, biogenic components occurred only in the uppermost part of core depth (>70 cm) of core PS87/070-1. Among them, the planktic foraminifer N. pachyderma sin. is mostly dominant biogenic component and calcareous benthic foraminifers also occurred with minor to common amounts (see Chapter 10. 8). In core PS87/079-1, rare amounts of biogenic components occurred that are mostly dominated by the planktic foraminifer N. pachyderma sin. only in the uppermost part of core depth (>40 cm).

Fig. 10.6.10: Down-core variations in siliciclastic, biogenic and authigenic sediment components roughly estimated from the coarse sand fraction (>63 µm) of core PS87/079-1 recovered from the eastern part of the Lomonosov Ridge. Notice that scales from 0 to 5 indicate relative abundance of each component (0, barren; 1, very rare; 2, rare, 3, common; 4, abundant; 5, dominant). Noticed that

high amounts of siliciclastic sediment components are dominated by quartz and feldspar throughout the sediment cores, whereas biogenic origin sediments occurred in the uppermost 67 cm in minor amounts, still dominated by planktic foraminifer N. pachyderma sin.. Micro-Mn nodules occurred in

common to abundant amounts throughout the cores except for some barren zones.

In both cores PS87/070-1 and PS87/079-1, the micro-Mn nodules show high fluctuations varying from lack to abundant amounts. In core PS87/070-1, the occurrence pattern of micro-Mn nodules observed in the sand fraction seems to be relatively well correlated with micro-Mn/Fe ratio analyzed with Avaatech XRF core scanner onboard Polarstern (Fig. 10.6.9).

10.6 Main lithologies and lithostratigraphy of PS87 sediment cores