Tefta-

With the exception of Thecidellina congregata which belong to the order Thecideida, the species Macandrevia sp., M. cranium, Magellania joubini, Terebratalia transversa and Terebratulina septentrionalis belong to the order Terebratulida.

The partition coefficient values of the investigated shallow water (<500 m) shells are summarized in Appendix 4-4. They were calculated using Palmer (1985) and Haley et al. (2005) equations assuming 10.46 mmol/L Ca for all water masses (Haley et al., 2005).

The log KD values of the shallow water (<500 m) Terebratulida are depleted relative to those of their deep water (>500 m) counterparts (Table 4-4). However, they exhibit the same incorporation pattern but with slight depletions in the HREEs (Fig. 4-6A). This in turn, confirms the previous suggestion that the ionic radii control the REE incorporation into the calcitic lattice of the articulated brachiopod shells, while the HREEs are impacted by the gradual increase in the amount of their free ions with depth (Zaky et al., 2016).

151 Table 4-4. The partion coefficients of REE in the calcite lattice of Terebratulida, and Rhynchonellida orders, and the different shell structure of M. cranium, T. transversa, T. septentrionalis and T. congregata species.

Note: ^a: from Zaky et al., 2016

152 Fig. 4-6. Distribution diagram of the ionic radii of the REEs Vs. the calculated log KD values for the shells of 1) Terebratulida from shallow (<500 m) and deep (>500 m) settings, and Rhynchonellida orders, 2) Terebratulida order from shallow setting (<500 m) and T. congregata species, 3) M. cranium species from shallow (<500 m) and deep (>500 m) settings, and 4) T. septentrionalis and T. transversa species.

4.6.1.1. Thecidellina congregata

The shell structure of Thecideidines is significantly different from that of other articulated brachiopods in the virtual suppression of the secondary layer (cf. Williams, 1966). Consequently, their shells are made almost exclusively of a granular laminae or blocky rhombohedra primary layer, which can be more than 100 µm thick in mature valves

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(Cusack and Williams, 2003). On the other hand, sporadic traces of secondary fibrous can be traced only on cardinalia and valve floors (Williams, 1973).

The predominant primary layer shell structure of the T. congregata is reflected in the different trace element and REE contents, and the REESN pattern of the Philippine Sea specimens relative to those from the other localities. Although, they display noticeably gradual HREE enrichments similar to those of their ambient Tropical Surface Water (L:H=

0.19, L:M= 0.35 and M:H= 0.55; Table 4-3), their Pr, Nd, Sm and Eu present downward excursions (Fig. 4-5). Quantifying the magnitudes of those excursions by correlating the normalized values of these elements to that of the La show that, the Pr excursion (PrSN/LaSN= 0.57) is relatively similar to that of the Ce(CeSN/LaSN= 0.54), while those of the Nd (NdSN/LaSN= 0.31), Sm (SmSN/LaSN= 0.33) and Eu(EuSN/LaSN= 0.39) are more pronounced. In addition, they display significantly different partition coefficient values (Table 4-4) and pattern (Fig. 4-6B) from their counterparts of the shallow water (<500 m) habitat, which secrete secondary layer (i.e. Terebratulida).

4.6.1.2. Macandrevia cranium

Shallow water specimens of M. cranium from the Denmark Strait, and Norwegian and Irminger seas are depleted in LREE, MREE, HREE and ∑REE contents in comparison to their deep water counterparts (>500m) from the Denmark Strait, and Irminger and Iceland basins (Tables 4-2, 4-5; Zaky et al., 2016). M. cranium shells exhibit consistently negative Ce anomalies, however, values of the shallow water specimens in the Denmark Strait (0.44), and the Norwegian (0.52) and the Irminger seas (0.55) are slightly higher than

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those from deeper waters (Ce/Ce*= 0.31, 0.42 and 0.17, in the Denmark Strait, and the Irminger and the Iceland basins; Zaky et al., 2016; Tables 4-2, 4-5).

Table 4-5. The mean REE concentrations (in ppm), and L:H, L:M, M:H and Ce/Ce* values in the primary and secondary layers of deep-water Macandrevia cranium shells, and their locations and water depths.

Note: (N) number of samples.

LREEs= Sum of La:Nd concentrations.

MREEs= Sum of Sm:Dy concentrations.

HREEs= Sum of Ho:Lu concentrations.

L:H = Sum of (LREEs)SN / 3/5 Sum of (HREEs)SN. L:M = Sum of (LREEs)SN / 3/5 Sum of (MREEs)SN. M:H = Sum of (MREEs)SN / Sum of (HREEs)SN.

1: from Zaky et al. (2015).

2: from Zaky et al. (2016).

All segments display relatively similar REESN patterns of HREE enrichment but with lower magnitude for the shallower (L:H= 0.60, 056 and 0.65) to the deeper samples (L:H= 0.54, 0.51 and 0.44, respectively; Tables 4-2, 4-5; Zaky et al., 2016). The magnitudes of the MREESN enrichments relative to the LREESN also vary, but insignificantly between the shallow (L:M= 0.57, 054 and 0.57) and the deep-water shells (L:M= 0.51, 0.50 and 0.52, respectively; Tables 4-2, 4-5; Zaky et al., 2016).

The variations in the HREESN relative to the MREESN, on the other hand, define relatively different patterns that vary by locality. Shallow water specimens of the Irminger Sea yielded the highest M:H value of 1.12 documenting depletion in HREEs (Fig. 4-7;

Table 4-2). Those from the Norwegian Sea, shallow and deep Denmark Strait yielded lower M:H ratios of 1.04, 1.04 and 1.06 presenting less HREE depletion, while those of the deep Irminger Basin yielded M:H ratio closer to the unity (1.01) displaying a flat pattern after the MREEs (Fig. 4-7; Tables 4-2, 4-5). On the opposite, those of the Iceland Basin present

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an invariant trend of slight HREESN enrichments (M:H= 0.83; Fig. 4-7; Table 4-5). The partition coefficient values of the shallow-water (<500 m) locations are slightly depleted relative to those of the deeper (>500 m) locations (Table 4- 4), but their patterns are similar (Fig. 4-6C).

Figure 4-7. Average REESN patterns of the Macandrevia cranium shells of the shallow (<500 m; this study) and the deep settings (>500 m; Zaky et al., 2016).

The intraspecific variations in REE contents and Ce anomalies of M. cranium in general, and the HREE enrichments on REESN pattern of those from the Iceland Basin in particular, suggest that REE uptake by members of this species may be influenced to some degree by external environmental factor(s).

4.6.1.3. Terebratulina septentrionalis and Terebratalia transversa

The LREE, MREE, HREE and ∑REE concentrations in the specimens from Bonne Bay and Bay of Fundy are similar (Table 4-2). Their REESN patterns (Fig. 4-3) are also similar; they display flat trends with L:H ratios close to unity (0.88 and 0.90; Table 4-2).

Their L:M (0.77 and 0.80), M:H (1.14 and 1.12) and Ce/Ce* (0.41 and 0.42) values are conspicuously close as well (Table 4-2).

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Such resemblance in the REE compositions and REESN patterns of the brachiopods from the two localities does not represent a species dependence but similarity in the environmental conditions. The shells of the two localities arefom bay habitat, and from comparable depths (30 and 10-15 m), salinity (31.1 and 32.2) and temperatures (5.6 and 6.2° C; Table 4-1). In addition, T. septentrionalis shells from Friday Harbor with similar environmental settings (depth= 75 m, salinity= 30.5 and temperature= 8° C; Table 4-1), display a similar REESN pattern (Fig. 4-5), LREE, MREE, HREE and ∑REE compositions, and L:H, L:M, M:H and Ce/Ce* ratios (Table 4-2).

The insignificant variations between the partition coefficient values (Table 4- 4) and patterns of the T. septentrionalis and T. septentrionalis (Fig. 4-6D) confirm that the environmental conditions are the main controller on their REE incorporation not their species.