Marine Geology carbonate-rich, pinkish-white layers, with variable characteristic contents of quartz-feldspar,

detrital carbonate grains, foraminifers, and Fe-Mn particles. The content of sand-sized material (enriched in units C, F, H, J, L, and parts of M) and the pink-white layers were considered to be the key sedimentary characteristic used for correlation of these lithostratigraphic units (Fig.

10.6.12; Stein et al. 2010a).

Fig. 10.6.12: Main lithologies (brown to dark brown and beige silty clays) of sediment cores recovered during Expedition ARK-XXIII/3 (Jokat 2009) across the central Mendeleev Ridge (for core location on

transect see Fig. 10.6.11). Occurrence of brown intervals, pink layers and sandy intervals (light blue) are highlighted. Furthermore, standard lithological units A to M of Clark et al. (1980) and proposed

chronology (Marine Isotope Stages MIS) are shown. Fig. from Stein et al. (2010a).

10.6 Main lithologies and lithostratigraphy of PS87 sediment cores

In addition, the dark brown horizons (cf., Jakobsson et al. 2000; Polyak et al. 2004) are key elements for a lithostratigraphic framework and related tentative age model developed by Stein et al. (2010a, 2010b) for the sediment cores recovered on the transect across the Mendeleev Ridge. Based on this approach, Marine Isotope Stage (MIS) 16 to MIS 1 are represented in these sediments (Fig. 10.6.12; for more details and background see Stein et al. 2010).

Fig. 10.6.13: Main lithologies (mainly brown to dark brown, beige and gray to dark gray silty clays with some more sandy intervals) of sediment cores recovered during Expedition XIX/1 in 1995 (Rachor 1997) across the southern Lomonosov Ridge (for core location on transect see Fig. 10.6.11). Intervals

with brown, beige and dark gray sediment colours, intervals with lamination and different degrees of bioturbation as well as proposed chronology (Marine Isotope Stages MIS) are indicated. Figure from

Stein et al. (1997, supplemented).

For sediment cores recovered in 1995 from the Siberian side of the Lomonosov Ridge (for core locations see Fig. 10.6.11), Stein et al. (1997) established a first lithostratigraphic framework based on a detailed visual core description (and supported by physical property data; Niessen

10. Marine Geology et al., 1997), and proposed an age model representing MIS 6 to 1 (Fig. 10.6.13). This tentative age model has later been further supported by a few AMS ¹⁴C datings, magnetic stratigraphy, correlation with other dated sediment cores, etc. (see Stein 2008 details and references). The stratigraphic framework shown in Fig. 10.6.13 is still valid.

Work at sea

During the Polarstern Expedition PS87 (ARK-XXVIII/4), 43 long sediment cores were taken on Lomonosov Ridge (Figs. 10.1.2 and 10.1.3; Table 10.1.2). Already onboard Polarstern, a larger number of the sediment cores have already been studied onboard Polarstern, as outlined in more detail in the previous Chapters 10.2 – 10.5 and 10.7 – 10.9. In the following subchapters, main lithologies of the recovered sediments from selected areas are described, and a lithostratigraphic concept and preliminary age model as well as some preliminary interpretations are presented.

Fig. 10.6.14: Part of Fig. 10.6.11 showing main surface water circulation systems (i.e., Transpolar Drift and Beaufort Gyre), and main minerals indicative for specific circum-Arctic Ocean source regions of terrigenous sediments (for details see complete Fig. 10.6.11), overlain by a semi-transparent map with

locations of PS87 sediment cores in white and yellow numbers (cf., Fig. 10.1.2)

Preliminary results

Lithostratigraphy and preliminary age model of Cores PS87/023-1 and PS87/030-1

Cores PS87/023-1 and PS87/030-1 recovered on the „Greenland/Canadian side“ of Lomonosov Ridge and thus influenced predominantly by the Beaufort Gyre System (Fig. 10.6.14), are mainly composed of brown to dark brown and beige silty clay, with a couple of intercalated more sandy intervals (Figs. 10.6.15 and 10.6.16). The more sandy intervals generally correlate with increased wet bulk density values. A few horizons with pink/pale layers and/or lenses occur in Core PS87/023-1 at 92-93, 177-179, and 260-270 cm and in Core PS87/030-1 at 87-92, 123-125, 171, and 216-218 cm. These horizons are characterized by detrital carbonate as determined in smear slides (Figs. 10.6.15 and 10.6.16; cf. Chapter 10.6.1), indicative for detrital sediment supply from the Canadian Arctic via the Beaufort Gyre System (Clark et al.

1980; Stein et al. 2010a, 2010b and references therein).

10.6 Main lithologies and lithostratigraphy of PS87 sediment cores

Fig. 10.6.15. Linescan image (with Mn/Al record in yellow) and summary of visual core description, indicating main lithologies (brown to dark brown silty clay horizons; B1-B27; sandy intervals; pink

horizons and lenses = pink arrows) of sediment core PS87/023-1 (see Fig. 10.6.14 for location).

Pink asteriks indicate detrital carbonate peaks in smear slides (cf. Fig. 10.6.1). Occurrence of sandy intervals are highlighted as light blue bars. Furthermore, standard lithological units L, J, H, F and C of Clark et al. (1980). In addition, the sand content and the occurrence of planktic foraminifers (red circles) and calcareous benthic foraminifers (blue circles) (adapted from Fig. 10.8.1), the wet bulk density and magnetic susceptibility (cf., Chapter 10.3 for MSCL background), and the preliminary XRF

scanning record of Mn/Al (cf., Chapter 10.4 for XRF scanning background). Proposed MIS 5a based on benthic foraminifer data (see Chapter 10.8). Proposed MIS 5 to MIS 19 based on lithostratigraphy,

MSCL data and Mn/Al record (cf., Stein et al. 2010a, 2010b; Alexanderson et al. 2013).

10. Marine Geology

Fig. 10.6.16: Linescan image (with Mn/Al record in yellow) and summary of visual core description, indicating main lithologies (brown to dark brown silty clay horizons, B1-B27; sandy intervals; pink horizons and lenses = pink arrows) of sediment core PS87/030-1 KAL (see Fig. 10.6.14 for location).

Pink asteriks indicate detrital carbonate peaks in smear slides (cf. Fig. 10.6.2). In addition, the sand content and the occurrence of planktic foraminifers (red circles) and calcareous benthic foraminifers

(blue circles) (adapted from Fig. 10.8.2), the wet bulk density and magnetic susceptibility (cf., Chapter 10.3 for MSCL background), and the preliminary XRF scanning record of Mn/Al (cf., Chapter

10.4 for XRF scanning background) are shown. Orange bar indicates yellow (10YR7/6) clay layer characterized by a prominent WBD minimum („peach layer“?). Proposed MIS 5a based on benthic foraminifer data (see Chapter 10.8). Proposed MIS 5 to MIS 19 based on lithostratigraphy, MSCL data

and Mn/Al record (cf., Stein et al. 2010a, 2010b; Alexanderson et al. 2013).

10.6 Main lithologies and lithostratigraphy of PS87 sediment cores

In order to get a first stratigraphic framework we tried to correlate cores PS87/023-1 and PS87/030-1 more influenced by the Beaufort Gyre System and detrital sediment input from the Canada (cf., Fig. 10.6.14), with the 2008 cores recovered along the transect across Mendeleev Ridge (Fig. 10.6.12). Especially for Core PS87/023-1, the brown layers and the occurrence of sandy intervals (lithological units L, J, H, F and C according to Clark et al. 1980) and pink, detrital-carbonate-rich layers seems to be very similar to those features identified in the cores from Mendeleev Ridge (Stein et al. 2010a, 2010b). In general, the dark brown layers B1 to B27 are characterized by minima in wet bulk density and maxima in Mn content (Fig. 10.6.15).

The more coarse-grained lithological units L, J, H, F and C are interpreted as glacial intervals (i.e., probably MIS 6, 8, 10, 12, and 16) characterized by extended North American/Canadian ice sheets and increased input of ice-rafted debris (IRD) into the Arctic Ocean. The intervals composed of prominent (bundles of) dark brown and Mn-rich layers, on the other hand, probably represent more the interglacial intervals (cf., Jakobsson et al. 2000; Polyak et al. 2004; Stein et al. 2010a; Löwenmark et al. 2012, 2014; Alexanderson et al. 2013). The dark brown, Mn-rich intervals are more distinct at Core PS87/023-1 than at Core PS87/030-1, and 27 intervals (B1 to B27) were identified at the former, probably representing MIS 1 to MIS 19 (Fig. 10.6.15), i.e., the last about 800 ka. This tentative lithostratigraphic framework and age model has been transferred to Core PS87/030-1, probably representing the same time span of MIS 1 to MIS 19 (Fig. 10.6.16). In both cores, MIS5a was determined by the occurrence of specific benthic foraminifers, i.e., O. tener, B. arctica and/or B. aculeata (see Chapter 10.8 for details).

Lithostratigraphy and preliminary age model of sediment cores from the Siberian side of the Lomonosov Ridge

Based on the main lithologies, the new PS87 cores from the Siberian side of Lomonosov Ridge more influenced by the Transpolar Drift System (Fig. 10.6.14), can be correlated very well with the sediment cores recovered from this area in 1995 (Fig. 10.6.17; Stein et al. 1997).

Main characteristics in grain size, structure and sediment colour were identified and allowed to tranfer the age model of the 1995 cores to those recovered during Expedition PS87. Based on these data, a preliminary age model has been established, i.e., the sediment cores shown in Fig. 10.6.17 probably represent MIS 6 to MIS 1. The sediments of MIS 6 consists of very dark gray (sandy) silty clay, separated by more coarse-grained, partly laminated sediments (correlating with Termination II; TII) from the overlaying MIS 5 sediments. The latter are characterized by dominantly dark brown and beige silty clay. The warm interstadials MIS5e, 5c and 5e are represented by prominent dark brown intervals. The sediments of MIS 4 consist of mainly beige silty clay and more coarse-grained sandy intervals. In the upper MIS 4, a distinct gray clayey horizon occurs in most of the cores (Fig. 10.6.17). The upper part of the sediment sequences representing MIS 3 to 1, are composed of dark brown, brown and beige silty clay.

The correlation based on main lithologies and the obtained age model (cf., Stein et al. 1997) are supported by wet bulk density (WBD) and magnetic susceptibility (MS) records (cf., Niessen et al. 1997). Especially MIS 6 and TII, MIS5b/5c as well as MIS 4 display prominent WBD and MS signatures recorded in most of the studied cores from this area, that can be used for regional core correlation and age classification very well (Figs. 10.6.18 and 10.6.23). The dark gray sediments of MIS 6 (characterized by high content of terrigenous organic carbon; Stein et al., 2001) and the coarser-grained sediments of TII are characterized by very high WBD values with a prominent MS minimum just at the base of TII. MIS 4 shows very distinct maxima in WBD and MS values that correlate with the prominent coarse-grained layers (Fig. 10.6.18).

Increased input of coarse-grained (IRD) sediments are related to extended continental ice sheets in western as well as eastern Eurasia (e.g., Arkhipov et al. 1986; Velitchko et al.1997;

Müller 1999; Stein et al. 2001; Niessen et al. 2013).

10. Marine Geology

Fig. 10.6.17: Linescan image and summary of visual core description, indicating main lithologies (brown to dark brown, beige and gray silty clay horizons; sandy intervals) of sediment cores PS87/070,

/079, /086, /093, and /094 recovered on the „Siberian side“ of Lomonosov Ridge (influenced predominantly by the Transpolar Drift System) and correlation with the lithologies of the 1995 cores (see Fig. 10.6.13 for details). Gray arrow marks prominent gray interval (upper MIS 4/boundary to MIS

3). Proposed preliminary chronology (Marine Isotope Stages - MIS - in blue numbers; 5a, 5c, 5d in white numbers) are shown (according to Stein et al. 1997).

10.6 Main lithologies and lithostratigraphy of PS87 sediment cores

Fig. 10.6.18: Correlation of Core PS87/086-3 and Core PS2757-8, using lithology and MSCL (wet bulk density and magnetic susceptibility) data; MSCL data of Core PS2757-8 from Niessen et al.

(1997). Proposed preliminary chronology (Marine Isotope Stages - MIS - in blue numbers) are shown (according to Stein et al. 1997; cf., Fig. 10.6.17)

Main lithologies of Core PS87/040 (central Lomonosov Ridge) and environmental significance

The sedimentary section of Core PS87/040 recovered in a prominant Intra-Basin on Lomonosov Ridge, can be divided into four lithological units (Fig. 10.6.19). Unit I (12.5 - 31 cm; 0-12.5 cm is lost) is composed of very dark grayish brown (10YR 3/2), dark brown (10YR 3/3) and brown (10YR 4/3) silty clay with strong bioturbation in the upper part. Unit II (31 – 216 cm) mainly contains grayish brown (2.5Y 5/2), light olive brown (2.5Y 5/4), yellowish brown (2.5Y 5/6) and olive gray (5Y 4/2) silty clays and sandy silty clays. Rhythmic alternations of silty clay and sandy silty clay with fining-upwards features and the occurrence of more sandy layers/laminae are characteristic for this Unit II. Unit III (216 – 251 cm) is composed of grayish brown (2.5Y 5/2) to olive gray (5Y 5/2) bioturbated (sandy) silty clay, intercalated by a very dark grayish brown (10YR 3/2) sandy silty clay at 242-246 cm. The bottom interval, Unit IV (251 – 260 cm) is a dark grayish brown (2.5Y 4/2) (silty) sand with fining-upwards structures.

10. Marine Geology