Southern ocean contributions to glacial‐interglacial changes of atmospheric pCO₂: An assessment of carbon isotope records in diatoms

Abstract

Abstract. Eleven new Antarctic records of diatom-bound •j13Corg show significantly lighter values during the Last Glacial

Diatom δ13C, δ15N, and C/N since the Last Glacial Maximum in the Southern Ocean: Potential impact of Species Composition

“…8% has been previously observed, with, just as seen here, more negative values occurring in the Atlantic Sector [Rau et al, 1982[Rau et al, , 1989[Rau et al, , 1997Freeman and Hayes, 1992;Goericke and Fry, 1994]. Other published records of diatom-bound d 13 C also show offsets between the various Southern Ocean sectors [Rosenthal et al, 2000;.…”

“…Can the observed LGM extrema in diatom d 13 C and d 15 N be the result of changes in the species composition of the sediments analyzed? This is a possibility which was not reported in any previous studies, none of which made direct, quantitative comparisons between species abundances and isotopic values [Rosenthal et al, 2000;.…”

“…[18] Of the three cores presented here, only the Scotia Sea core shows peak values in diatom d 13 C during the Holocene and distinctly minimum values at the LGM, as has been seen in several other cores from the Southern Ocean, including ODP Site 1094 which spans seven glacial-interglacial transitions [Shemesh et al, 1993Singer and Shemesh, 1995;Rosenthal et al, 2000;Crosta et al, 2005;Schneider-Mor et al, 2005]. The most striking feature of the d 13 C, d 15 N, and C/N records, when taken together, is that the d 15 N and C/N records are both roughly coincident between Indian sector, Pacific sector, and Scotia Sea sites while d 13 C can differ between two sites by as much as 8% (Figure 3).…”

“…The LGM maximum in d 15 N has been ascribed to nitrate concentrations being drawn down to relatively low levels, because of biological utilization, and, likewise, the minimum in d 13 C has been related to the balance between CO 2 uptake and availability [François et al, 1992[François et al, , 1997Singer and Shemesh, 1995;De La Rocha et al, 1998;Rosenthal et al, 2000;Shemesh et al, 2002;Robinson et al, 2004Robinson et al, , 2005Crosta et al, 2005;Schneider-Mor et al, 2005]. Given the importance of understanding what is going on with the biological pump in the glacial Southern Ocean, and that nutrient utilization proxies based on diatom opal are the most direct way of assessing this, it is worth considering if there is an ecological component to the signal.…”

“…[28] Despite grave differences in cleaning and analytical methods employed in obtaining d 13 C and d 15 N from fossil diatoms in various studies [e.g., Crosta et al, , 2005Robinson et al, 2004Robinson et al, , 2005, most studies of diatom-bound organic matter in Southern Ocean sediments (from south of the present-day Antarctic Polar Front) report an increase in d 13 C [Shemesh et al, 1993De La Rocha et al, 1998;Rosenthal et al, 2000;Crosta et al, 2005;Schneider-Mor et al, 2005;Singer and Shemesh, 1995] and a decrease in d 15 N [François et al, 1992[François et al, , 1997Shemesh et al, 2002;Crosta et al, 2005;Robinson et al, 2005;Schneider-Mor et al, 2005] between LGM and the Holocene. The situation here is more complex.…”