Oak leaves as biosensors of late neogene and early pleistocene paleoatmospheric CO2 concentrations

Stomatal density and stomatal index as indicators of paleoatmospheric CO2 concentration

“…Petit et al, 1999) of the same species. This approach has been successful in the Holocene with Salix herbacea (Beerling and Chaloner, 1993a;Rundgren and Beerling, 1999) and Betula pubescens and B. pendula (Wagner et al, 1999), and in the Miocene with Quercus petraea and Betula subpubescens (van der Burgh et al, 1993;Ku Èrschner, 1996;Ku Èrschner et al, 1996). While this approach produces the most accurate CO 2 reconstructions, it is limited by its requirement to compare identical species (or highly similar species within a genus; Wagner et al, 1999).…”

“…Estimates of CO 2 for the Miocene (ªvº) calculated from a herbaria-based training set. Data from van der Burgh et al (1993) andKu Èrschner et al (1996).…”

“…1); brief but large CO 2 excursions discernable with the various proxy methods are probably too temporally constrained to in¯uence Berner's model . In cases where experimental and subfossil responses are used to generate a standard curve upon which CO 2 concentrations are directly calculated from fossil responses, ice core data Wagner et al, 1999;Rundgren and Beerling, 1999) or the presence of temperature excursions (van der Burgh et al, 1993;Ku Èrschner, 1996;Ku Èrschner et al, 1996) are used to corroborate the stomatal-based estimates.…”

“…Concerns have been raised regarding this method's reliability (Ko Èrner, 1988;Poole et al, 1996), and it is the purpose of this paper to address these concerns via an extensive analysis of the literature. Analysis includes stomatal responses from fossil observations as well as short-term (experimental, natural CO 2 springs, altitudinal transects, and herbaria) observations, as responses from the latter category are often used to generate standard curves for estimating CO 2 from fossil observations (van der Burgh et al, 1993;Ku Èrschner, 1996;Ku Èrschner et al, 1996;Rundgren and Beerling, 1999;Wagner et al, 1999). Speci®cally, the utility of stomatal indices will be examined, an approach not analyzed in previous reviews Chaloner, 1992, 1994;Woodward and Kelly, 1995).…”

Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf

“…; Kürschner et al 1996). Other studies have conversely suggested that concentrations were lower and closer to that during the Last Glacial Maximum ( More speculative theories include Southern Ocean circulation changes such as increases in eddies and jets within the main current of the ACC (Thompson 2008) and the southward migration of the Antarctic Polar Frontal Zone (APFZ) (Whitehead and McMinn 2002).…”