Benthic foraminifera

Today’s group of living benthic foraminifera, consists of thousands of taxa, and their distribution is determined by several environmental parameters. Benthic Foraminifera live on (epifaunal)- or within the sediment (infaunal) of the sea floor, and their abundance through time has made them very useful in paleoclimatic research (Sejrup et al., 2004).

The importance of different parameters which determine the distribution of benthic foraminifera has been debated. Depth and the hydrography of different water masses were thought to be the main controlling factors (Mackensen et al., 1985), but in Arctic regions it appears food availability and competition are the controlling factors (Wollenburg and Mackensen, 1998).

Benthic foraminiferal assemblages can be used to indicate parameters such as water depth, water temperature, proximity to glaciers and deep water circulation (Sejrup et al., 2004). Benthic

foraminifera are also indicators of productivity in areas where productivity is high, such as zones of upwelling (Schnitker, 1994).

A short description of the dominating benthic species (>2 % of the identified total) and their

ecological preferences will now follow. A complete list of all benthic foraminiferal species identified within the core, as well as their distribution within the core can be found in Appendix A.

Oridorsalis umbonatus (Reuss, 1851)

Oridorsalis umbonatus is a typical North Atlantic- (Bergsten, 1994) and Arctic deep-water species (Schröder et al., 1990). It is an epifaunal detrivore, that prefers salinities between 34.8 – 35‰, and is associated with deep waters down to ~ 3800 m (Murray, 1991). Schröder et al. (1990) describes O.

umbonatus as a good deep water indicator.

Mackensen et al. (1985) described O. umbonatus as a species that prefers a relatively high oxygen content in the sediment, and that can tolerate relatively low food supply. Oridorsalis umbonatus is the most common deep-sea benthic foraminifera in the GIN-Sea and Arctic Ocean today, and several studies have found that O. umbonatus dominated in this area in periods with increased sea-ice cover (e.g. Streeter et al., 1982; Jansen et al., 1983; Mackensen et al., 1985). The species is believed to be more adaptable to reductions in surface productivity (Jansen et al., 1983).

Cassidulina neoteretis (Seidenkrantz, 1995)

Cassidulina neoteretis is a very frequent benthic foraminiferal species on the continental shelf and slopes of the North Atlantic (Mackensen and Hald, 1988). It is an infaunal detrivore, living within sandy or muddy sediments. It prefers marine salinities and cold to temperate waters. It is most commonly found at depths between 1000 – 1500 m (Seidenkrantz, 1995). Under modern conditions, the species is often tied with the Atlantic Intermediate Water in the Nordic Seas, and an indicator of modified Atlantic Water (Jennings and Helgadóttir, 1994; Jennings et al., 2004).

Triloculina trihedra (Loeblich & Tappan, 1953)

Triloculina trihedra is widely distributed in shallow waters with salinities greater than 32‰, and ranges into northern temperate waters (Huddart & Peacock, 1990). It is considered a part of the Arctic cold-water fauna (McCabe et al., 1986; Jones, 2011).

Cassidulina reniforme (Nørvang, 1945)

Cassidulina reniforme is common in Arctic, glaciomarine environments (Elverhøi and Bomstad, 1980;

Hald and Vorren 1987; Hald and Korsun, 1997) where it lives in silty muds at depths greater than 100 m (Mudie et al., 1984). It is an infaunal detrivore, which prefers marine salinities and cold to

temperate waters (Murray, 1991). Hansen and Knudsen (1995) found the species to be associated with muddy, sediment loaded waters in front of calving glaciers. Jennings et al. (2004) found that C.

reniforme and Elphidium excavatum (Terquem, 1875) would dominate the fauna when the area was affected by cooler waters and variable salinity conditions.

Cibicides wuellerstorfi (Schwager, 1866)

Cibicides wuellerstorfi is a common species in the North Atlantic (Osterman et al., 1999). It is an epifaunal passive suspension feeder that is often attached to hard substrates. It prefers marine salinities and lives in many different environments such as lagoons and shelf-, to bathyal environments

(Murray, 1991).

Mackensen et al. (1985) described C. wuellerstorfi as a species that; “prefer a relatively high primary productivity with high food supply, but can tolerate a relatively low oxygen content in the sediment.”

Several studies have found that over time, C. wuellerstorfi dominated in relatively deep areas of the Norwegian-Greenland Sea during ice-free periods with high primary productivity (e.g. Streeter et al., 1982; Jansen et al., 1983; Mackensen et al., 1985).

Stainforthia loeblichi (Feyling-Hanssen, 1954)

Stainforthia loeblichi is a common Arctic benthic foraminiferal species (Cronin, 1999). Stainforthia species are known to be opportunistic, and they take advantage of pulses of high seasonal productivity (Polyak et al., 2002). The presence of S. loeblichi can therefore be an indication of high productivity at the sea surface.

Ioanella tumidula (Brady, 1884)

Ioanella tumidula is a species which is typical for the North Atlantic assemblages (Bergsten, 1994). It occurs in a variety of environments such as fine grained sediments in areas that are seasonally ice free, and in coarser sediments in areas that have permanent ice cover. Several studies (e.g. Green, 1960;

Lagoe, 1979; Mackensen et al., 1985) found that I. tumidula thrives at different depths (~900 to >3000 m) with relation to ice coverage; The more permanent ice cover in the area, the shallower the depth (Wollenburg and Mackenson, 1998).

Astrononion gallowayi (Loeblich & Tappan, 1953)

Astrononion gallowayi is an epifaunal/infaunal detrivore, which prefers low temperatures and relatively high marine salinities (Murray, 1991). It is associated with shallow waters with increased current activities and coarse sediments (e.g. shallow, river-distal areas) (Polyak et al., 2002).

Astrononion gallowayi found alongside Cibicides lobatulus (Walker & Jacob, 1798), is usually an indication of high energy environments (Polyak et al., 2002; Jennings et al., 2004).

Epistominella arctica (Green, 1959)

Epistominella arctica is a very small epifaunal/semi-infaunal detrivore living in muddy sediments. It prefers marine salinities and temperate to cold temperatures (Murray, 1991). It is a well-known species in the deep central Arctic Ocean (Lagoe, 1977), and occurs mostly at depths between ~1500 to 2000 m (Green, 1960). Epistominella arctica is considered an opportunistic species, which reproduce in large numbers during local blooms of phytoplankton. It can also be an indicator of increased productivity and higher food availability (Wollenburg and Kuhnt, 2000).

Figure 5: CTD data collected over HH13-089GC core locations in June 2013. PW = Polar Water, AIW = Atlantic Intermediate Water and GSDW = Greenland Sea Deep Water