Late Miocene through early Pleistocene nutrient utilization and export production in the Antarctic Zone of the Southern Ocean

Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling

“…This indicates that the EF sat well to the north of its present position, and the two sites were overlain by the nitrate-rich cold tongue, which is consistent with foraminifera data reconstructions (Steph et al, 2009). The intensification of the EEP upwelling is probably linked to the shoaling of the thermocline, the development of a strong zonal and meridional SST gradient in tropical/subtropical regions, which may have enhanced atmospheric circulation and divergent upwelling along the Equator, and brought the nutrient-rich polar water masses escaping the poorly used nutrient pool of the Southern Ocean and North Pacific within reach of the upwelling circulation (Billups et al, 2013;Etourneau et al, 2010;März et al, 2013).…”

“…The influence of preformed changes is not apparent on glacial-interglacial scales Robinson et al, 2009), or on longer timescales (Billups et al, 2013;Etourneau et al, 2009;Giuliani et al, 2011). Low isotopic values have been recently documented in the Southern Ocean at ∼ 1.9 Myr (Billups et al, 2013), during the export production maximum event, and may have had an influence on the EEP records. However, the coeval changes in δ 15 N, SST and paleoproductivity data at this time suggest rather a close connection between nutrient cycling, export production and oceanic conditions, thus not supporting the preformed signature as a strong influential factor on our δ 15 N records.…”

“…On the other hand, the reduced nutrient leakage from polar regions, the main providers of new nutrient in the EEP, may be related to the observed coeval increase in export production and nutrient utilization in the Southern Ocean (Billups et al, 2013;Giuliani et al, 2011;Hillenbrand and Cortese, 2006). Increasing Fe availability in the Southern Ocean (Martinez-Garcia et al, 2011) may also have sustained high productivity in this region and therefore may have played a role in controlling nutrient consumption in polar areas.…”

“…The δ 15 N of subsurface nitrate in the EEP can reflect the isotopic signature of preformed nitrate coming from the Antarctic and North Pacific waters that supplies most of the new nitrate delivered to the EEP through the EUC waters (Rodgers et al, 2003;Rafter et al, 2012). The influence of preformed changes is not apparent on glacial-interglacial scales Robinson et al, 2009), or on longer timescales (Billups et al, 2013;Etourneau et al, 2009;Giuliani et al, 2011). Low isotopic values have been recently documented in the Southern Ocean at ∼ 1.9 Myr (Billups et al, 2013), during the export production maximum event, and may have had an influence on the EEP records.…”

“…In turn, the progressive depletion of the marine phosphorus pool due to changes on continental weathering could have significantly contributed to lower net production, by altering the N : P ratio and thus participated in the primary productivity decline. Moreover, the export productivity decline might be closely tied to a reduction of silicic acid supply into the EEP, likely diminishing along with the concomitant increase in biological production in the polar oceans (Billups et al, 2013;Giuliani et al, 2011;Hillenbrand and Cortese, 2006) and, in addition to the previous nutrient cited, may have accelerated the biological production collapse. However, such information with respect to the other nutrients is still missing and remains speculative, while further investigations are absolutely needed.…”