Fig. 16

The 45° longitudinal section of contoured normalized frequencies of G. menardii from Hole 925B through time as illustrated in Fig. 15a but in paleoceanographic context. Contours (method: min, max, count; min = 0.5, max = 10, interval = 1) indicate relative frequencies from 0 to 10 (contour intervals of 1). The base contour (0.5) corresponds approximately to the density iso-surface shown in Fig. 15a. Because of the diagonal orientation of the longitudinal section the axes of spiral height and axial length collapse to one axis with values ranging from 0 to the square root of 2. Red triangles on right side denote positions of the investigated samples at Hole 925B. Pale violet horizontal lines indicate G. menardii-barren intervals (0.51, 0.61, 1.12, 1.47, 1.8, 2.057, 2.154, 2.24, 2.266, and 2.91 Ma. The three G. menardii-barren intervals at 0.61, 2.24 and 2.91 Ma are according to Chaisson and Pearson (1997). At 2.91 Ma G. menardii was absent but G. miocenica and G. exilis were present (Chaisson and Pearson 1997). Colored rectangles on the right side of the diagram indicate important stratigraphic intervals discussed in the text for the G. menardii-limbata-multicamerata succession at Hole 925B. Of these, the lower orange rectangle (2.59–2.88 Ma) represents the interval when G. multicamerata and G. limbata disappeared at this hole. The orange rectangle higher up (2.3–1.95 Ma) indicates absence of large G. menardii at Hole 925B. The blue rectangle (2.58–1.7 Ma) indicates absence of large G. menardii at Site 502. First large G. menardii entered Site 925B at 1.95 Ma, while at Site 502 first large G. menardii entered the sedimentary column at 1.7 Ma, i.e. about 0.25 Myrs later. The colored rectangles on the left side of the diagram indicate paleoclimatic changes, such as the intensification of Late Miocene Antarctic Glaciation (LMAG in dark violet, between 6.3 and 5.9 Ma according to Chaisson and Ravelo 1997), and transition phases from stable warm conditions to intense Northern Hemisphere Glaciation (NHG) (after Chapman 2000). Black horizontal arrows labeled from 1 to 8 in parentheses indicate selected foraminiferal first appearance datum (FAD) and last appearance datum (LAD) events in relation to the history of the NHG: Events 1–6 are from Chapman (2000), event 7 is from Sexton and Norris (2008), and event 8 is from Chaisson (2003). Event 1 = FAD G. menardii (2.13 Ma); event 2 = LAD G. exilis (2.28 Ma); event 3 = LAD G. miocenica (2.34 Ma); event 4 = LAD G. limbata (2.93); event 5 = disappearance Pulleniatina (3.65 Ma); event 6 = re-appearance Pulleniatina (2.3 Ma); event 7 = G. truncatulinoides immigration pulse (MIS 100, 2.54 Ma); and event 8 (gray vertical stripe) = interval when finely perforated menardiforms tended to populate a deeper (cooler) water column (3.01–2.33 Ma). The darkened gray stripe between 6.34 and 5.1 Ma and labeled from 9 to 13 (labels in parentheses) demarcates the study interval of Pfuhl and Shackleton (2004) at Site 925, when G. limbata and G. multicamerata diverged for the first time (phase 1): 9 Top of study interval (5.1 Ma); 10 end of cooling (5.49 Ma); 11 replacement of dominance of G. limbata by dominance of G. multicamerata (5.75 Ma); 12 weakening of mixed layer, onset of cooling (5.82 Ma); and 13 base of study interval of Pfuhl and Shackleton (2004) (6.34 Ma). Green arrows on the right side indicate phases I (7.96–5.78 Ma) and II (4.14–2.88 Ma) of G. limbata development at Hole 925B (see text)