Paleo‐sea surface temperature calculations in the equatorial east Atlantic from Mg/Ca ratios in planktic foraminifera: A comparison to sea surface temperature estimates from U₃₇^K′, oxygen isotopes, and foraminiferal transfer function

Abstract

Abstract. We present two -270 kyr paleo-sea surface temperature (SST) records from the Equatorial Divergence and the South Equatorial Current derived from Mg/Ca ratios in the planktic foraminifer Globigerinoides sacculifer. The present study suggests that the magnesium signature of G. sacculifer provides a seasonal SST estimate from the upper -50 m of the water column generated during upwelling in austral low-latitude fall/winter. Common to both down-core records is a glacial-interglacial amplitude of-3ø-3.5øC for the last climatic changes and lower Holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5.5 and glacial stage 6 temperatures, respectively. The comparison to published SST estimates from alkenones, oxygen isotopes, and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods.

Alkenone Paleotemperature Determinations

“…The alkenone results (Herbert et al, 2010;Ikehara et al, 1997;Pelejero and Calvo, 2003) contrast with the CLIMAP reconstruction for isotope stage 5e, which showed no systematic departures in SST from modern day values. The alkenone estimates of a warm oxygen isotope stage 5e are consistent, however, with the warm temperatures inferred from Mg/Ca in planktonic foraminifer (Lea et al, 2000;Nuernberg et al, 2000). One should note, however, that the magnitude of the oxygen isotope stage 5e anomaly declines if it is referenced to the Holocene insolation maximum at 9 ka because many alkenone records show 1-2 C warming in the early Holocene compared with the modern day.…”

Planktonic foraminiferal Mg/Ca as a proxy for past oceanic temperatures: a methodological overview and data compilation for the Last Glacial Maximum

“…Results from G. sacculifer indicate that the LH-LGM SST difference was about 2 1C in the Caribbean Sea and in the eastern equatorial Atlantic Ocean (Hastings et al, 1998;Nu¨rnberg et al, 2000) and nearly 3 1C for the Cariaco basin based on G. ruber (w) . G. ruber (w) results from the eastern tropical Atlantic also show a LH-LGM difference of 2 1C (Elderfield and Ganssen, 2000; this manuscript) but the amplitude is larger (4 1C) further north in the eastern tropical Atlantic (this manuscript).…”

“…Barker and Elderfield, 2002;(3) Barker (this manuscript); (4) Cacho et al (in prep. ); (5) Elderfield and Ganssen, 2000;(6) Hastings et al, 1998;(7) Kiefer et al,in press;(8) Koutavas et al, 2002;(9) Lea et al, 2000;(10) Lea et al, 2003;(11) Mashiotta et al, 1999;(12) Nu¨rnberg et al, 2000;(13) Pahnke et al, 2003;(14) Palmer and Pearson, 2003;(15) Rosenthal et al, 2003;(16) Skinner (unpublished data); (17) Stott et al, 2002;(18) Visser et al, 2003. region (Pelejero et al, 1999;Kienast et al, 2001). In the eastern tropical Pacific just north of the equator, Lea et al (2000) estimated a LH-LGM temperature change of $2.8 1C based on four Mg/Ca records from G. ruber (w).…”

Pliocene Changes in Tropical East Pacific Upper Ocean Stratification: Response to Tropical Gateways?

“…Applying the species-specific temperature equation of Nürnberg et al (2000) for G. sacculifer results in ~1°C warmer mixed-layer temperatures (on average ~24.8°C) than using the multispecies equation of Anand et al (2003). This corresponds to modern temperatures at ~30-to 35-m water depth.…”