Comparison of stable isotope records across the Eastern Equatorial Pacific, from the Biogenic Bloom to Present-day

• Main Authors: Reghellin, Daniele, Coxall, Helen, Backman, Jan, Dickens, Gerald
• Format: Report
• Language: English
• Published: Stockholms universitet, Institutionen för geologiska vetenskaper
• Subjects: Geology; Geologi; Pacific; Planktonic foraminifera
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-168155

The oceanographic evolution of the eastern equatorial Pacific Ocean (EEP) since the late Neogene is still under debate. One school of thought proposes weaker than modern equatorial upwelling and sustained warm sea surface temperatures (SSTs) during the late Miocene to early Pliocene, while another suggests stronger than modern upwelling and cool SSTs over this period. These opposing theories appear to be proxy dependent and new perspectives are needed. Bulk carbonate stable isotopes signals have shown potential to carry information on EEP mixed layer water properties including temperature but the relative contribution of different biogenic carbonate components, and thus the origin of these signals, remains uncertain. Here we measured δ13C and δ18O of bulk carbonate, and several finer fractions that concentrate coccoliths, from ODP Site 851 sediments over the last 7 Ma. These data are compared to a series of new and published planktic and benthic foraminifera and foraminifera fragment δ13C and δ18O records to help disentangle coccolith ecological and ocean signals, and refine the use of bulk carbonate d13C and d18O as palaeoceanographic proxies. Our results imply that, once coccolith vital effects are accounted for, bulk δ13C and δ18O records mixed layer signals shallower than the depth of the planktonic foraminifera Globigerinoides sacculifer. Higher bulk carbonate δ13C, δ18O, sedimentation rate and opal content, combined with lower CaCO3 and >63 µm content during the late Miocene and until 4.6 Ma imply enhanced upwelling and cool SSTs along the EEP at this time, supporting the biogenic bloom hypothesis.