Foraminiferal Evidence of Younger Dryas Age Cooling on the British Columbia Shelf

Abstract

Cluster analysis of foraminifera from a ~12,000-9000 radiocarbon year old piston core from Goose Island Trough, Queen Charlotte Sound, indicates that a cold interval correlative with the Younger Dryas stadial occurred during a shallow water phase. The reduction in depth was caused by the passage across the area, between 11,500 and 10,000 years BP, of a glacial forebulge associated with the retreat of the Late Wisconsinian ice sheets. Published sedimentological evidence indicate that water depths decreased to ~75-90 m, placing the site above the permanent North Pacific pycnocline (100 m). Low salinity-near glacial conditions, at these depths, between -11,100 and 10,000 years BP were recognized by abundant populations of Cassidulina reniforme and lslandiella helenae. This cold interval has also been recognized in cores from elsewhere in Queen Charlotte Sound. The depressed salinity and temperature may have resulted from a modification of regional weather patterns. Decreased mean continental summer temperatures could have reduced the seasonal influence of the North Pacific High and lengthened that of the Aleutian Low. This would have resulted in a near continuous onshore surface Ekman transport and enhanced coastal runoff, effectively blocking the movement onto the shelf of deep, saline, warm water of the California Undercurrent. The resultant isolated inshore basin comprised of present-day Hecate Strait and Queen Charlotte Sound is tentatively named the "Hecate Sea". By ~10,000 years BP, weather and ocean circulation had returned to near modern patterns as indicated by the disappearance of lslandiella helenae and by the development of an Epistominella vitrea - dominated biofacies.L'analyse des groupements effectuée sur des populations de foraminifères d'une carotte à piston couvrant la période de 12 000 à 9000 ans BP, provenant du Goose Island Trough, dans le bassin de la Reine-Charlotte, démontre l'existence d'un intervalle froid contemporain du Dryas récent. Il coïncide avec une phase à bathymétrie réduite qui résulte du déplacement vers l'est, entre 11 500 et 10 000 ans BP, du bombement isostatique associé à l'Inlandsis de la Cordillière à la suite de son retrait. Des données sédimentologiques publiées montrent que la profondeur a diminué jusqu'à ~75-90 m, amenant le site étudié au-dessus de la pycnocline permanente du Pacifique Nord (100 m). L'existence de conditions hyposalines de type glaciaire, à ces profondeurs, entre 11 100 et 10 000 ans BP ont été reconnues grâce à la présence d'assemblages à Cassidulina reniforme et lslandiella helenae. Cet intervalle froid a également été reconnu ailleurs dans le bassin de la Reine-Charlotte. Les salinités et les températures réduites sont peut-être le résultat d'un changement dans les configurations météorologiques régionales. Des températures estivales plus basses sur le continent auraient réduit l'influence saisonnière de l'anticyclone du Pacifique Nord et rallongé celle de la dépression des Aloutiennes. Ceci aurait engendré un transport d'Ekman de surface quasi perm...

Paleoceanography of the Gulf of Alaska during the past 15,000 years: Results from diatoms, silicoflagellates, and geochemistry

“…Sea ice and sea ice-related diatoms are more common in the YD interval (~30-40% of the diatom assemblages) than they are during the Bø-Al (~20-30%), suggesting cooler, more stratified conditions during the YD, similar to the records in core 85JC and elsewhere in the North Pacific. Cooler conditions off southeast Alaska during the YD are consistent with the results of Hetherington and Reid (2003) in the Queen Charlotte Islands and Mathewes et al (1993) and Patterson et al (1995) off British Columbia to the south.…”

Towards radiocarbon dating of single foraminifera with a gas ion source

“…In the case of carbonate samples, CO 2 formed after decomposition with acid, has to be quantitatively trapped and converted to graphite [1][2][3][4]. Carbonate shells from foraminifera are often analysed for radiocarbon to determine the age of deep-sea sediments [5] or to assess radiocarbon reservoir ages [6][7][8]. However, a single foraminifera test contains typically only a few micrograms of carbon, while most laboratories require more than 100 lg carbon for radiocarbon analysis with an AMS system.…”

Advance of alpine glaciers during final retreat of the Cordilleran ice sheet in the Finlay River area, northern British Columbia, Canada

“…Importantly, nothing is known about the effects of late-glacial climatic oscillations such as the Younger Dryas (12,800-11,500 cal yr BP; Alley, 2000) on remnants of the northern half of the Cordilleran ice sheet. A change in ocean circulation and cooling of climate in the northeast Pacific Ocean coincident with the Younger Dryas have been documented in north-coastal British Columbia and adjacent Alaska (Engstrom et al, 1990;Mathewes, 1993;Mathewes et al, 1993;Patterson et al, 1995;Hansen and Engstrom, 1996;Hendy et al, 2002;Hetherington and Reid, 2003;Lacourse, 2005). Younger Dryas glacier advances have been identified in the central and southern Coast Mountains of British Columbia (Clague, 1985;Friele and Clague, 2002a), the southern Canadian and northern American Rocky Mountains (Reasoner et al, 1994;Osborn and Gerloff, 1997), the northern Cascade Range of Washington (Kovanen and Easterbrook, 2001;Riedel et al, 2003), and possibly southwestern Alaska (Briner et al, 2002).…”