Unit 11-1 (597-0 cm)

Core HH13-011-GC-TUNU was retrieved at 210 m water depth in sub-basin 2 (Fig. 5.4) and is 597 cm long. It is made up by one single unit (Unit 11-1), containing lithofacies M (mud), sM (sandy mud), Si (silt), sSi (sandy silt), and siS (silty sand) along with laminations (l) and a few clasts (c).

6.6.1.1. Lithology and stratigraphy

Like core HH13-010-GC-TUNU, the sediment colors of core HH13-011-GC-TUNU change frequently between gray (5Y 5/1), dark grayish brown (2.5Y 4/2) and olive gray (5Y 5/2) (Fig. 6.16). The gray color dominates the fine sediments from the bottom of the core and up to approximately 150 cm depth. From here and up the fine sediment has dominantly an olive gray color. Thin laminas of dark grayish color containing higher sand fractions are present throughout the core.

Large fluctuations in grain-size are observed throughout the core, accompanied with dark grayish brown color (Fig. 6.16 & 6.17). The grain-size distribution shows average dominant volumes of silt (67%), with clay and sand having 21% and 12%, respectively. The core consists of massive silt (Si) interrupted by thin layers of lamina comprising mud (M), sandy mud (sM), sandy silt (sSi) and silty sand (siS). The largest sand fractions are seen near the bottom of the intervals between 515-503 cm (up to 62% sand), 443-432 cm (72%), 362-348 cm (78%), 289-271 cm (74%) and 114-99 cm (67%). Clasts (c) are identified at 587 cm, 541 cm, 455 cm and 16 cm.

93

Figure 6.16: Lithological log of core HH13-011-GC-TUNU showing color image, Munsell color codes, bioturbation, units, lithofacies codes and structures. The dated interval is indicated by an arrow.

94

Bioturbation occurs in the intervals containing mud or silt, with the most pronounced degree of bioturbation in the intervals between 385-364 cm, 357-289 cm, 99-91 cm and 48-32 cm (Fig. 6.16).

6.6.1.2. Physical properties

The water content shows relatively large fluctuations with a minimum of 10%, a maximum of 37% and a mean value of 24% (Fig. 6.17). However, unlike the previous described sediment cores, the measured water content fluctuates around a relative constant value, increasing slightly with depth. This indicates that the sediments have not gone through normal consolidation and are therefore suggested to have been deposited rapidly. The wet bulk density, p-wave velocity, acoustic impedance and fraction porosity vary only slightly around the mean values in the fine-grained intervals of the core. In the top ~190 cm of the core, however, more frequent layers containing sand fractions up to 10% leads to increased fluctuations in the fine-grained intervals. In the coarser intervals more noticeable changes and large peaks occur due to changes in the P-wave velocity and higher density of the sediments.

The magnetic susceptibility of the core show more frequent fluctuations than in the aforementioned cores (see Fig. 6.5, 6.8 and 6.12), influenced by the grain-size distribution with negative peaks in the coarser intervals. The magnetic susceptibility is high compared to the other sediment cores studied (see Table 6.1) with a minimum of 70 (*10^-8SI(m³/kg)), a maximum of 96 and a mean value of 87.

6.6.1.3. Element geochemistry

Fluctuations in element geochemistry are observed in all of the plotted graphs (Fig. 6.18). The Ca/Fe, Ti/Sum and K/Sum reflect the variations in grain-size and color of the deposits with larger peaks in intervals with higher fractions of dark grayish brown sand. Fe, Ti and K decrease in the coarser intervals. Si shows small peaks in the coarser intervals, whereas Al and Ca appear to be unrelated to the sediments grain-size distribution.

6.6.1.4. Chronology and sedimentation rates

Three samples were collected for radiocarbon dating for this core, located at 593-592 cm, 401-400 cm and 219-218 cm depth. The material sampled at 401-400 cm contained too little carbonates and was therefore not further prepared for radiocarbon dating. Also, the sample at

95

219-218 cm, containing ostracoda and shell fragments was prepared and attempted to be dated but failed due to too little material available.

The sample containing diverse benthic foraminifera at 593-592 cm has been dated to 1130 cal.

yr. BP (Table 6-2). If assuming a linear sedimentation rate from 592-0 cm (in addition to the 10 cm lost during core retrieval), the average sedimentation rate is 533 cm/ka (Table 6-4).

With the bottom of the core (593-592 cm) being dated to be 1130 cal. yr. BP and the estimated average sedimentation rate being 533 cm/ka., the sediments from the bottom and up to ~416 cm have been deposited during the Medieval Warm Period, from ~416 cm to ~43 cm in the Little Ice Age, while the upper ~53 cm are of modern times.

6.6.1.5. Interpretation

Core HH13-011-GC-TUNU is interpreted to comprise sediments representing a glacimarine environment where Waltershausen Gletscher is the dominant sediment source. The mud is interpreted to be essentially deposited by suspension settling from overflows, whereas the sand content is deposited by density-currents related to underflows (Benn & Evans, 2010).

The clasts and some of the laminas are related to IRD. As the content of thin sand layers increases upcore, the upper part of the core represents a period of enhanced glacial activity compared to the underlying sediments (cf. Forwick and Vorren, 2009, Baeten et al., 2010;

Jessen et al., 2010).

96

Figure 6.17: Grain-size distribution, estimated linear sedimentation rate and the measured physical properties of core HH13-011-GC-TUNU. Color image and lithological log are included for reference. Unit is indicated. The depth of the dated intervals is indicated by an arrow, while the largest fluctuations in the measured physical properties are indicated by gray horizontal lines.

97

Figure 6.18: Measured element geochemistry for core HH13-011-GC-TUNU. Color image and lithological core is included for reference. Unit is indicated. The depth of the dated intervals is indicated by an arrow, while the largest fluctuations in the element geochemistry are indicated by gray horizontal lines.

98