Only a single genetic type of the spinose morphospecies, Orbulina universa, Type III, was identified in the North Atlantic. This type showed a pronounced distribution, being almost entirely restricted to the northeast of the region (stations 1-7; Fig. 4.4A, maps). Both SST and salinity are lower here than in the west (fig. 4.1C, 4.1D), however, temperature is likely to be the most important factor in restricting its distribution. Orbulina universa is a ubiquitous species, but is restricted to water temperatures of between 10 °C and 30 °C (Bé & Tolderlund, 1971). In the North Atlantic it occurs only in the transitional waters (~ 10 – 18 °C) of the NA current, at a minimum of 11°C (figs. 4.1B, 4.1C, 4.4A), and is absent from the sub-polar waters of the west (~ 10 °C – 6 °C). In addition, localised distribution in O. universa is strongly correlated to the level of primary productivity in the water column (de Vargas et al., 1999, Darling & Wade, 2008). Type III appears in areas of upwelling and high
chlorophyll concentration, as is found in the most northerly reaches of the North Atlantic. Orbulina universa has not been studied in the North Atlantic previously, however, it has been sampled further south, in the transitional waters off the west coast of France (de Vargas et al., 1999).
4.5.2.2 Globigerina bulloides
Two genotypes of the spinose morphospecies G. bulloides, types IIa and IIb, were identified among the samples collected in the North Atlantic. Both belong to the cool- water type II grouping. The most numerous genotype, Type IIb, was abundant from stations 4 – 14, but absent from the western leg of the transect (stations 15 – 27) (fig. 4.4b). Poor success of PCR amplifications unfortunately meant that only two specimens of G. bulloides Type IIa were amplified, making it difficult to determine its geographical distribution in the region. The two Type IIa samples amplified were found at either end of the transect (east & west) (fig. 4.4B), suggesting a broad distribution across the region. Globigerina bulloides has been extensively sampled in the North Atlantic (Stewart et al., 2001) and though types IIa and IIb co-habit the region, the extent of their distributions is different, reflecting independent ecological adaptations. Both in this study and that of Stewart et al., (2001), G. bulloides Type IIb was found to be restricted to the east of the North Atlantic, the western limit of its distribution terminating between 30° - 35° W. Stewart et al., 2001 recorded high numbers of Type IIa in the northwest of the region, and only small numbers to the east. Sea surface temperature is the primary factor shaping the distributions of these types. Type IIa predominates in the colder subpolar waters (~ 5 – 10 °C) of the East Greenland (EG) Current (figs. 4.1B, 4.1C), whereas Type IIb predominates in the warmer, transitional waters (~ 10 – 18 °C) of the Irminger (IR) Current to the east
(figs. 4.1B, 4.1C) (Stewart et al., 2001). Type IIa tolerates colder conditions than Type IIb, extending further north in the Atlantic (Darling & Wade, 2008; Stewart et
al., 2001), whereas Type IIb has a greater abundance in slightly warmer waters and
extends further south (Stewart, 2000). Darling & Wade (2008) report that Type IIa advances north ahead of Type IIb during the spring plankton blooms of the North Atlantic, and is the only genotype present in the most northerly subpolar latitudes.
Globigerina bulloides is a typical eutrophic morphospecies, occurring primarily in
high-nutrient environments and during phytoplankton blooms (Deuser et al., 1981; Ganssen & Kroon, 2000; Hemleben et al., 1989; Kroon, 1988; Ottens, 1991). It has been shown, through carbon isotope analysis, to reflect the northward migrating spring bloom in the North Atlantic Ocean (Ganssen & Kroon, 2000). With greater sampling of the Type IIa and IIb genetic types in the North Atlantic it may be possible to distinguish different nutrient requirements on an intraspecific level, and thus enhance the utility of G. bulloides as a proxy for paleonutrients and productivity.
4.5.2.3 Turborotalita quinqueloba
Two genetic types of the spinose morphospecies Turborotalita quinqueloba were found in the North Atlantic, types IIa and IIb, both belonging to the cold-water group II genotypes. Neither occurred in very high numbers across the transect (fig. 4C), though it has been noted by Darling et al. (2008) that the small size of this morphospecies can mean that individuals pass through the net or sieve used for sampling, leading to their abundance being underestimated. Stewart et al. (2001), found types IIa and IIb to co-exist in the east of the North Atlantic, but found only Type IIa in the colder waters of the EG Current in the northwest. We find both types
occurring along the whole transect from east to west, in both transitional (~ 10 – 18 °C) and subpolar (5 – 10 °C) waters (figs. 4.4C & 4.1C). Although the western limit of the current transect passes further south than that of Stewart et al. (2001), the Sea surface temperature (SST) at the stations harbouring type IIb (16 & 19; Figs. 4.1A) is actually the same as the EG Current (~ 8 °C; Fig 4.1C). This suggests that low sample numbers were responsible for Type IIb failing to be found in the western part of the Stewart et al. (2001) transect, rather than a superior adaptation of type IIa to cooler temperatures. Additionally, in the Norwegian Sea (65°N) only 2 T. quinqueloba Type IIa samples were identified compared to 14 of Type IIb, and further north only Type IIb was found (Darling et al., 2008). Although sample numbers were low, this points towards an adaptation of Type IIb to colder temperatures than Type IIa, the converse of the findings of Stewart et al. (2001). Clearly further sampling is needed to resolve this matter. It can also be noted that the results of this transect put the range of T. quinqueloba into the edge of the Labrador Sea (west of the region), an area reported to be devoid of this morphospecies by Bé & Tolderlund (1971).
4.5.2.4 Neogloboquadrina incompta
Until recently N. incompta was considered to be the right-coiling variety of N.
pachyderma. However, they have since been re-designated as separate species based
on biogeography, ecology, and degree of genetic distinction (Darling et al., 2000, 2004, 2006, 2008). Only a single genetic type was found in the North Atlantic, Type I. Neogloboquadrina incompta Type I occurs from station 1-19 and is most numerous in the east but is completely absent from the far west (stations 20-27) (fig. 4.4D). Sea surface temperature is most likely determining the distribution of this genetic type.
and transitional waters (Darling et al., 2004, 2006; Stewart et al., 2001), and is found restricted to the warmer (subpolar ~ 5 – 10 °C & transitional ~ 10 – 18 °C) waters of the North Atlantic in this study (figs. 4.1C, 4.4D).
4.5.2.5 Neogloboquadrina pachyderma
Neogloboquadrina pachyderma Type I, conversely, only begins its range at station 22
and extends to station 27 (fig. 4.4E). It appears to be cold-water adapted and has only been found in polar waters to date (Darling et al., 2004, 2007). Here in the North Atlantic, N. pachyderma Type I is most likely being transported down from the polar waters in the north via the East Greenland (EG) Current. Stewart et al. (2001) found no N. pachyderma Type I in the North Atlantic, only N. Incompta (named right- coiling N. pachyderma at the time). The transect extended only from the UK to Greenland, passing through the relatively warm North Atlantic (NA) and Irminger (IR) currents (Fig 4.1B). It did not extend to the southwest, into the colder region (stations 16-27, current transect), where the Labrador (LA) current flows. There is a striking pattern in the geographical distribution of N. incompta and N. pachyderma along the North Atlantic transect. Each morphospecies occupies a geographical range that is completely uninhabited by the other (figs. 4.4D, 4.4E), offering an excellent example of separation due to differing ecological requirements.
4.5.2.6 Globigerinita uvula
The microperforate species Globigerinita uvula was the most abundant morphospecies collected along the North Atlantic transect. All samples belonged to a single genetic type, the same as that identified in the same locality by Stewart et al. (2001) (note: 5 bp different in variable regions). Stewart et al. (2001), however, found only 4
specimens of G. uvula in the North Atlantic, 2 to the east of the region, and 2 in the EG current to the northwest. The distribution of G. uvula specimens found on the current transect appears heavily skewed towards the west of the region (stations 10- 27) (fig. 4.4E), an area not covered by the Stewart et al. (2001) transect. Again, the distribution of this morphospecies is likely to be determined by localised differences in SST. Bé (1977) recorded that G. uvula (G. bradyi) only occurs in subpolar waters, at temperatures of between 5 °C and 10 °C. This finding is supported here where the majority of specimens were found in an area with a SST of 7 °C to 12 °C (figs. 4.1C, 4.4E), consistent with the subpolar province (Bé & Tolderlund, 1971). Some of the samples were found just inside the warmer transitional waters, but only 2 in 87 samples occurred in the transitional waters further to the east (station 5), and are likely to have been transported here passively by the IR current. It is probable that there is an aspect of seasonality in the distribution of planktonic foraminifera, such as G.
uvula, in the North Atlantic Ocean. The transect of Ottens (1992), bisects the current
transct at approximately station 10. In the relatively cool month of April (1988), they recorded low numbers of G. uvula at this locality and in the warmer months of August/September (1986), they recorded none.
4.5.3 Global biogeography of the North Atlantic planktonic foraminiferal