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doi:10.2204/iodp.proc.347.102.2015

Biostratigraphy

Table T1 provides the master species list for Expedition 347.

Diatoms

During the OSP, selected core intervals were subsampled via toothpick scrape into individual clean glass beakers. Subsamples were then treated with 1–2 mL of 30% H₂O₂ to remove organic material and allowed to react for several hours. The resulting sediment slurry was pipetted onto clean glass coverslips and allowed to dry on a hot plate. Coverslips were permanently affixed to clean glass slides with Naphrax mountant.

Each slide was viewed under light microscopy at a magnification of 400× or 1000× for ~1 h to qualitatively characterize the diatom assemblage. Diatoms were identified primarily according to Snoeijs et al. (1993–1998), with additional identifications from Witkowski (2000), Cleve-Euler (1951), Fryxell and Hasle (1972, 1980), Hasle (1978a, 1978b), Hasle and Lange (1992), Hustedt (1930), Krammer and Lange-Bertalot (1986, 1988, 1991a, 1991b), Muylaert and Sabbe (1996), Mölder and Tynni (1967, 1968, 1969, 1970, 1971, 1972, 1973), Sabbe and Vyverman (1995), Snoeijs (1992), Tomas (1997), and Tynni (1975, 1976, 1978, 1980). Salinity-based affinities of diatoms follow Snoeijs et al. (1993–1998). Silicoflagellates were identified according to Tomas (1997). Chrysophyte cysts were divided into morphotypes by reference to the structure of the cyst walls.

Foraminifers

Variations in benthic foraminiferal assemblages in the Baltic Sea Basin reflect changes in salinity, temperature, oxygen concentration, and water depth that may be representative of glacial–interglacial climatic events (Knudsen, 1994). The presence/absence data and assemblage composition of benthic foraminifers therefore have the potential to be used as a chronologic constraint (Kristensen et al., 2000). Planktonic foraminifers are not found in the modern Baltic Sea because of its low salinity and shallow water depths and are only rarely found in the Kattegat. There was no evidence of planktonic foraminifers in this expedition’s cores, except as occasional redeposited pre-Quaternary specimens. Identification of benthic foraminifers was based on standard reference literature for the Baltic Sea Basin (e.g., Feyling-Hanssen et al., 1971; Feyling-Hanssen, 1972; Austin, 1991; Seidenkrantz, 1993; Alve and Murray, 1999; Murray and Alve, 2011; Pillet et al., 2013).

Offshore, samples for identification of foraminifers and other microfossils were taken from every core catcher sample in both paleoenvironmental and microbiology holes (sediment volumes were generally ~5–20 cm³, or in some cases as much as 30 cm³). Additional onshore ~20 cm³ samples were taken midway between core catchers to improve the resolution and refine biostratigraphic control, resulting in an overall sample resolution of ~1.5 m.

Sandy intervals that yielded samples barren of microfossils were sampled less frequently. Longer intervals between samples also occurred where core catchers were not available, particularly in microbiology holes.

The raw samples were directly washed over a 63 µm sieve with tap water (where necessary, an ultrasonic cleaner or a soft brush was used to disaggregate sediments while rinsing) and rinsed with deionized water. Care was taken to ensure that the sediment used for washing represented all types of material found in the core catcher. However, when sediment smeared from another interval during the drilling process was clearly visible, this “contaminated” sediment was excluded whenever possible.

While offshore, an initial inspection for foraminifers and other microfossils was performed on the remaining (>63 µm) wet sample before a second inspection was conducted on the dry sediment. During the OSP, the samples were oven dried in filter paper at 40°–50°C and were inspected for foraminifers and other microfossils.

Foraminifers were picked from the >63 µm size fraction and identified to species or genus level. In samples with low numbers of foraminifers or limited sample volume, all foraminifers were picked for identification. In high foraminiferal abundance samples, a minimum of ~50 individuals was picked. Visible signs of test dissolution or broken tests were recorded. Redeposited foraminifers, both pre-Quaternary and occasionally also Eemian, commonly occurred in specific intervals at the more westerly located sites (M0059 and M0060) and were noted and excluded from in situ species assemblage and abundance results. Pre-Quaternary foraminifers were distinguished by their often recrystallized or frosty tests (Rasmussen et al., 2005); in the case of Cretaceous foraminifers and nearly all planktonic foraminifers, these were identifiable as pre-Quaternary species. The presence of redeposited Eemian foraminifers could be determined when the faunal assemblage contained both relatively warm and cold water species (Seidenkrantz, 1993).

Abundance of foraminifers and species/genera diversity was recorded at all sites. At sites with foraminifers of more than one species or genus, a count was made of the number of species/genera present in each sample to generate a foraminiferal “diversity” profile. Samples with greater species or genus diversity were interpreted as indicating more saline or more oxic conditions.

Benthic foraminiferal abundance was defined as follows and shown in plots as a 0–5 value:

• 0 = B (barren; 0 specimens).
• 1 = V (very rare; <5 specimens).
• 2 = R (rare; 5–10 specimens).
• 3 = F (few; 10–100 specimens).
• 4 = C (common; 101–500 specimens).
• 5 = A (abundant; >500 specimens).

Benthic foraminiferal diversity was defined as follows:

• B = barren (0 species).
• L = low (1–3 species).
• M = medium (4–6 species).
• H = high (7–10 species).
• V = very high (>10 species).

This diversity classification applied during the OSP is a more rapid approximation of published statistically based species assemblage technique. Postcruise investigation will likely adopt published quantification methods.

In addition to foraminifers, while offshore, ostracods and bivalves were picked from the >63 µm sediment fraction for identification when present, and their abundance was recorded. Other microfossils such as diatoms, pollen, and organic matter (plant, animal, or charcoal) were recorded when present and identified where possible.

Approximately 490 samples for foraminifers were prepared from core catchers during the offshore phase of Expedition 347. The total number of samples prepared during the offshore and onshore phases of the expedition is reported in each site chapter.

Ostracods

The Baltic Sea is a relatively well studied area in terms of its ostracod fauna. Although there is no established biostratigraphy based on ostracods for the Baltic Sea, numerous publications are available on the ecology of the Baltic Sea species (e.g., Rosenfeld, 1977; Borck and Frenzel, 2006; Frenzel et al., 2005, 2010; Veihberg et al., 2008). Salinity is the main factor determining ostracod distribution in the Baltic Sea (Frenzel et al., 2010), making ostracods very useful for paleosalinity reconstructions. Analysis of population-age structure can be used to evaluate the autochthoneity of the assemblage, which is crucial when studying shallow-water environments (Whatley, 1983).

During the offshore phase, ostracods were picked during examination of core catcher samples (typical sample interval = ~3.3 m) of variable volume ranging from 5 to 30 cm³. Additional onshore ~20 cm³ samples were taken halfway between core catchers to improve the sample resolution. The resultant sample resolution is therefore ~1.5 m. Sandy intervals that yielded samples barren of microfossils were sampled less frequently.

All samples were washed over a 63 µm mesh sieve. Subsequently, the samples were oven dried in paper filters at 40°–50°C. Ostracods were picked from the entire sample residues, identified, and counted. Although ostracod abundance was relatively low (<10 specimens in most samples), preservation was good in most samples. Redeposited valves were recorded in several sandy intervals. The number of juvenile specimens was also recorded.

For preliminary paleosalinity reconstruction, ostracods were divided into the following categories: freshwater, very shallow water oligohaline, and shallow-water brackish-marine species and marine species typical of the North Atlantic shelves. For the onshore data plots, the number of valves per sediment volume was plotted against meters below seafloor as an estimation of abundance. The following abundance categories were distinguished and are shown in tables:

• A = abundant (>50 specimens).
• C = common (20–50 specimens).
• F = few (5–20 specimens).
• R = rare (1–5 specimens).
• B = barren (no specimens found).

Palynology

Palynomorphs

Twenty core catcher samples of 5–10 mL volume were processed for palynological analysis during the preonshore phase. The following approach was adopted:

1. Treatment with 40% HCl (1 day), involving dissolving a tablet containing ~18,500 Lycopodium spores;
2. Decanting (3 times);
3. Treatment with 50% HF (1 day);
4. Decanting (4 times); and
5. Sieving through a 10 µm mesh.

The samples were then mounted on slides in glycerine jelly.

During the OSP, 3–10 mL of sediment was processed per sample (depending on sediment type). The following approach was used for the majority of samples:

1. Treatment with 10% HCl (3–12 h, depending on strength of reaction), involving dissolving two tablets containing ~18,500 Lycopodium spores;
2. Neutralizing with 10% KOH;
3. Centrifuging twice (3000 rpm, 5–10 min) and decanting;
4. Treatment with 40% HF (over 1–2 nights);
5. Neutralizing with 40% KOH;
6. Centrifuging twice (3000 rpm, 5–10 min) and decanting; and
7. Mounting on glycerine jelly and/or pure glycerine.

Terrestrial palynomorphs

Slides were examined for terrestrial palynomorphs under 200×, 400×, and 1000× magnification and partly with use of phase contrast. Pollen grains, plant spores, freshwater algae (particularly Botryococcus and Pediastrum), and fungal spores (morphotypes only) and arthropod remains (particularly chironomid remains) were assessed.

The aim was to count as many as 75–150 pollen grains per sample to ensure statistical relevance to a reasonable degree, even if bisaccate pollen were overrepresented. The pollen guides of Beug (2004) and the Faegri and Iversen (1989) pollen key were used for pollen identification.

Marine palynomorphs

Although the palynological focus was on terrestrial palynomorphs, marine palynomorphs (organic-walled dinoflagellate cysts and foraminiferal test linings) were also analyzed (at approximately half the resolution, or 35–75 counts/sample) compared to the pollen analysis, using the same slides as for pollen analysis to achieve a direct land-sea correlation and to differentiate fully marine, brackish, and lacustrine environments. Dinoflagellate cysts (dinocysts) were generally identified to genus or species level. The dinoflagellate atlas of Marret and Zonneveld (2003) and publications on Baltic Sea dinocysts (e.g., Nehring, 1997) were used for dinoflagellate cyst identification. Foraminiferal test linings were divided in two groups (planispiral and trochospiral), and fragments with several chambers were counted as one third foraminifer. The ratio of dinocysts plus foraminiferal test linings versus nonsaccate pollen grains was used as an estimate for the site-shoreline distance.

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