Latest Eocene–Early Oligocene climate change and Southern Ocean fertility: inferences from sediment accumulation and stable isotope data

Major shifts in calcareous phytoplankton assemblages through the Eocene‐Oligocene transition of Tanzania and their implications for low‐latitude primary production

“…However, the calcareous nannofossil record presented here strongly indicates an increased availability of nutrients in the low-latitude surface ocean, adding to the growing number of studies that document an increase in surface ocean productivity directly coincident with the EOT [Anderson and Delaney, 2005;Diester-Haass et al, 1996;Diester-Haass and Zachos, 2003;Latimer and Filippelli, 2002;Ravizza and Paquay, 2008;Salamy and Zachos, 1999]. This discrepancy between surface ocean productivity records and the extent of organic carbon burial across the EOT needs to be addressed and may indicate a widespread decoupling of productivity and carbon burial due to the increased ventilation of the deep ocean.…”

“…[30] Contrary to previous opinion [Diester-Haass and Zachos, 2003;Salamy and Zachos, 1999;Zachos and Kump, 2005], recent carbon cycle modeling has suggested that organic carbon burial associated with increased productivity across the EOT may have played little or no role in driving either the global positive shift in d 13 C or the rapid deepening of the CCD, which are instead attributed to a reduction in shelf carbonate production and the weathering of exposed and relatively isotopically heavy neritic carbonates [Merico et al, 2008]. However, the calcareous nannofossil record presented here strongly indicates an increased availability of nutrients in the low-latitude surface ocean, adding to the growing number of studies that document an increase in surface ocean productivity directly coincident with the EOT [Anderson and Delaney, 2005;Diester-Haass et al, 1996;Diester-Haass and Zachos, 2003;Latimer and Filippelli, 2002;Ravizza and Paquay, 2008;Salamy and Zachos, 1999].…”

“…The major ocean-wide increase in d 13 C, which appears to lag the shift in d 18 O by $10 ka [Coxall et al, 2005], is compelling evidence for a significant perturbation in the global carbon cycle through the EOT [Merico et al, 2008;Salamy and Zachos, 1999;Zachos and Kump, 2005;Zachos et al, 1996]. This positive shift in d 13 C is indicative of either an increase in the removal rate of light carbon from the ocean-atmosphere system, which has been attributed to the enhanced burial of organic carbon in marine sediments coupled to increased surface water productivity [Diester-Haass and Zachos, 2003;Salamy and Zachos, 1999;Zachos and Kump, 2005] or the input of isotopically heavy carbon via the increased weathering of neritic carbonates during a major sea level fall [Merico et al, 2008]. Both of these hypotheses are associated with a drawdown of atmospheric carbon dioxide that may be the principal positive feedback mechanism that drove the climate system into a strongly glaciated state during the EOGM [Merico et al, 2008;Zachos and Kump, 2005].…”

“…[4] Evidence for significant increases in primary production through the EOT has been documented at a number of deep-sea sites in the Southern Ocean [Anderson and Delaney, 2005;Diester-Haass et al, 1996;Latimer and Filippelli, 2002;Salamy and Zachos, 1999], probably driven by cooling induced increases in surface-ocean divergence and the associated upwelling of nutrient-rich deep waters and/or enhanced fluxes of weathering derived nutrients during rapid sea level fall [Nilsen et al, 2003;Salamy and Zachos, 1999;Zachos and Kump, 2005]. There is however a lack of comparable paleoproductivity records from the low latitudes [but see Diester-Haass and Zachos, 2003;Nilsen et al, 2003;Ravizza and Paquay, 2008] where quantifying changes in primary carbonate and silica fluxes at many deep-sea sites is hampered by the dramatic deepening of the carbonate compensation depth (CCD) and the associated shift from siliceous to calcareous sediments through the EOT [Nilsen et al, 2003].…”

Continental erosion and the Cenozoic rise of marine diatoms

“…Increased opal accumulation rates are also documented across the late Eocene and early Oligocene (22), synchronous with an inflection in the strontium and lithium isotope records and a shift in the mineral composition of clay assemblages in sediments from the Southern Ocean (16,22), all indicative of increased weathering fluxes. Although silica input/output fluxes might be imbalanced on time scales shorter than the residence time of H 4 SiO 4 in the ocean (tens of thousands of years) (23), our analysis of changing silicate weathering fluxes and their effect on diatom diversification encompasses time scales of million years.…”