LATE QUATERNARY FORAMINIFERAL RECORD OF RAPID ENVIRONMENTAL CHANGE AND BIOTIC RESPONSE ALONG THE NORTHEAST PACIFIC MARGIN

Foraminiferal microfossils are highly sensitive monitors of past environmental change. While their tests provide material for geochemical proxies of environmental parameters, their assemblages are an undervalued resource for both validating the proxies and monitoring the biotic response to climate change. Used in conjunction, benthic and planktonic records provide a powerful tool for understanding the climate system. These aspects have been exploited to reconstruct rapid changes in Northeast Pacific margin coastal marine environments and the biotic response associated with late Quaternary millennial-scale global climate change.

Planktonic and benthic foraminiferal assemblages and isotopic values exhibit major oscillations synchronous with late Quaternary decadal- through millennial-scale global climate cycles. Planktonic foraminifera record rapid switches in sea-surface temperature and hydrography of the California Current. Interstadials exhibit rapid, major warmings (including brief overshoots) and a stratified water column while stadials exhibit coolings and a less stratified water column. Benthic assemblages record major oxygen-minimum zone strength fluctuations related to productivity and ocean ventilation oscillations. These fluctuations were widespread along the margin - weakening, perhaps disappearing during stadials and strengthening during interstadials. Repeated turnovers of entire benthic faunas occurred rapidly without extinction or speciation. Interstadials exhibit consistent faunal successions. Benthic assemblage and carbon isotope oscillations suggest sedimentary methane flux variations while brief benthic and planktonic excursions reflect methane release throughout the water column and possibly into the atmosphere.

The rapid benthic and planktonic assemblage switches, highly tolerant, opportunistic planktonic assemblages, and consistent benthic faunal successions imply extreme sensitivity and adaptation of both ecosystems to the rapid environmental changes that marked the late Quaternary. This suggests that broad segments of the biosphere are well adapted to natural rapid climate change. Late Quaternary millennial-scale climate change may have affected the tempo and mode of speciation and extinction. Specific benthic assemblages and isotopic values may be indicative of high levels of methane in sedimentary microenvironments.