Showing papers by "Ellen Thomas published in 1998"

Biogeography of the Late Paleocene Benthic Foraminiferal Extinction

Abstract: During the Late Paleocene Thermal Maximum (LPTM) be nthic fbraminif'era at rniddle bathl'al and greater depths suffered extinct ion of 30-507c of species dul ing a lew thousand ycars. Extinct ion was less sevcrc at neri t ic to upper bathyal depths, where temporary changc-s in launal composit ion prevai led. Preextinct ion dcep-sea taunas were cosmopoli tan and diverse. and contained heavi ly calcif ied species. Imrnediate postextinct ion faunas were more variable geographical ly, exhibited low dil 'ersity. and were donrinated by thin-walled calcareous or agslut inated taxa, possibl l , because CaCO, dissolut ion increased global ly l iom nerit ic to abyssal dcpths just bcfbre the extinct ion. Thcse assernbla-ges were dontinatcd either by long-lived taxa sLrch as Nuttttllide.r truerrtpt ' ior by bul irninid taxa. the latter accompanicd by a-uglut inants in somc areas. Faunas donrinated by N. tmentpri rvere contnton in the Sor.rth Atlantic and at lower bathl'al through upper abyssal depth in the lndian Ocean. and might incl icate ol igotrophic condit ions as well as incrcased corrr)si \L-ness. Bul iminid-dominated launas might indicate high rates of deposit ion of organic matter or lor. l-oxygen condit ions. Such l lunas werc common globl l ly along continental rnargins. and locallv co-occun'ed u'ith sedimcntologic or planktonic taunal indicators of high procluct ivi tr . In the bathyal central Pacif ic. however. bul iminid-dominated faunas co-occun'ed with planktonic faunas suggestins ol i-sotl 'ophi ' . and thev could ref lect low-oxygen condit iorrs lesult in-u from sluggish ocean circulat ion. oxidation of cl issociated methanc hydrates. or r larming ol ' bathl 'al i rbyssal waters caused by a chan-ge in deep-sea circr.r lat ion. Alternatively, they could indicate that thc t iact ion ol 'organic matter rcaching the seafl(x)r increased as a rcsult of decreased occanic oxygenf,t ion. 214 Biogeography of the Late Paleocene Benthic Foraminiferal Extinction

Climate change and the rise and fall of sea level over the millennium

Abstract: Average rates of relative sea level rise (RSLR) along the coast of the eastern United States were 1–2 mm/yr over the last 2,000 years. Higher rates have occurred in recent centuries, and their onset seems to have preceded the period of modern global warming. A modest rate increase started in the 17th century, well before the modern global warming of this century, but the highest rates have occurred during the last 200 years, with a major acceleration around 1800 A.D. No significant acceleration is apparently associated with the rapidly rising temperatures of the last 100 years. How does one establish possible relationships between rates of sea level rise and climate fluctuations? Tide-gauge records are too short and noisy to derive a quantitative, empirical relationship between relative sea level rise rates and climate change [Douglas, 1992], and predictions of future rates of sea level rise are largely based on theory. The recent geological record can provide empirical insights, which can be applied toward the assessment of current rates and those predicted for the next century.