Direct comparison of marine and terrestrial climate variability during marine isotope stages 6 and 5: Results from Santa Barbara Basin ODP Hole 893A

Abstract

[1] Planktonic foraminiferal d 18 O, pollen, and opal records from Santa Barbara Basin are used to evaluate climate changes in the northeast Pacific during marine isotope stages (MIS) 6 and 5. While the oak and foraminifera record the major glacial-interglacial changes, opal is not correlated with these large-scale transitions. Surface water warming in the basin was synchronous with terrestrial warming but earlier than ice sheet melting and increasing Northern Hemisphere insolation at Termination II. During and immediately after deglaciation, our marine proxies indicate the presence of an isothermal upper water column. Later in substage 5E, the water column became thermally stratified, surface productivity increased, and laminated sediments began accumulating. Sediment trap and hydrographic data suggest these changes were due to the onset of a strong seasonal cycle similar to that seen today in the basin. A series of rapid coolings within MIS 5 appears to be synchronous with North Atlantic ice-rafting events and Greenland stadials.

Variability in vertical distributions of planktonic foraminifera in the California Current: Relationships to vertical ocean structure

“…Since there are no clear seasonal signals in test flux, there is little potential for a seasonal bias in δ 18 O values to result from changes in test flux. Furthermore, Friddell et al [2002] found little difference (<0.05 permil) between averaged flux‐weighted δ 18 O values and averaged δ 18 O values for these species in comparing months and years with distinctive patterns of test flux.…”

“…Individuals of G. bulloides collected over the San Pedro Basin in early spring had the compact morphology and lived around 100 m, well beneath the thermocline, whereas samples from upwelling conditions indicate a mixed layer signature [ Sautter and Thunell , 1991a; Spero and Lea , 1996]. Over the SBB, δ 18 O values reflect the species‐specific predicted calcite values for G. bulloides at 20 m, or below that depth, better than those at the surface [ Pak and Kennett , 2002], but do track seasonal and interannual fluctuations of SST [ Thunell et al , 1999; Friddell et al , 2002]. Comparison of δ 18 O values from G. bulloides and N. pachyderma in a deep trap (470 m) with those from a trap at 65 m below the surface indicates that both species acquire a portion of their δ 18 O signature from below 65 m [ Pak and Kennett , 2002].…”

“…The 65 m samples consistently had lighter δ 18 O values than the deeper trap, although the difference was much greater for N. pachyderma [ Pak and Kennett , 2002, Figure 4]. Figure 2 suggests that the greater offset in N. pachyderma results from a greater portion of its population living below 65 m. Although N. pachyderma predominantly has a signature from the thermocline, it can acquire a δ 18 O signature similar to G. bulloides and be indicative of the mixed layer [ Sautter and Thunell , 1991a; Pak and Kennett , 2002; Friddell et al , 2002]. While the flux of N. pachyderma to the San Pedro Basin trap was low when it lived in the mixed layer, this study shows that abundances can be high in the mixed layer.…”

Pollen-based evidence of extreme drought during the last Glacial (32.6–9.0 ka) in coastal southern California

“…During the last interglacial (MIS 5e), pollen deposited in Santa Barbara Basin (SBB) (ODP Hole 893A) from drought-adapted, Mediterranean type vegetation was comparable to, or even more expansive, than present (Heusser, 1995;Friddell, 2002). A short, mid-Wisconsinan pollen record in an organic deposit at Diamond Lake (~30 km east from Lake Elsinore) records expansion of more mesic montane ecosystems to lower elevations during near-peak glacial conditions (Anderson et al, 2002).…”

Vegetation response to southern California drought during the Medieval Climate Anomaly and early Little Ice Age (AD 800–1600)

“…During the last interglacial (MIS 5e), pollen deposited in the Santa Barbara Basin (SBB; ODP Hole 893A) from drought-adapted, Mediterranean type vegetation was comparable to or even more expansive than present (Heusser, 1995;Friddell et al, 2002). Low resolution pollen-based reconstructions (ODP Hole 893B) suggest that drought-adapted vegetation also expanded during the Medieval Climate Anomaly (MCA) and shifted gradually toward more mesic Quercus/Pinus woodlands and forests during the Little Ice Age (LIA) at~AD 1300e1400 (Heusser, unpublished).…”