Abstract. Coherent variation in CaCO3 burial is a feature ofthe Cenozoic eastern equatorial Pacific. Nevertheless, there has been along-standing ambiguity in whether changes in CaCO3 dissolution or changesin equatorial primary production might cause the variability. Sinceproductivity and dissolution leave distinctive regional signals, a regionalsynthesis of data using updated age models and high-resolution stratigraphiccorrelation is an important constraint to distinguish between dissolutionand production as factors that cause low CaCO3. Furthermore, the newchronostratigraphy is an important foundation for future paleoceanographicstudies. The ability to distinguish between primary production anddissolution is also important to establish a regional carbonate compensationdepth (CCD). We report late Miocene to Holocene time series of XRF-derived (X-rayfluorescence) bulk sediment composition and mass accumulation rates (MARs) from easternequatorial Pacific Integrated Ocean Drilling Program (IODP) sites U1335,U1337, and U1338 and Ocean Drilling Program (ODP) site 849, and we also report bulk-density-derived CaCO3 MARs at ODP sites 848, 850, and 851. We usephysical properties, XRF bulk chemical scans, and images along withavailable chronostratigraphy to intercorrelate records in depth space. Wethen apply a new equatorial Pacific age model to create correlated agerecords for the last 8 Myr with resolutions of 1–2 kyr. Large magnitudechanges in CaCO3 and bio-SiO2 (biogenic opal) MARs occurred withinthat time period but clay deposition has remained relatively constant,indicating that changes in Fe deposition from dust is only a secondaryfeedback to equatorial productivity. Because clay deposition is relativelyconstant, ratios of CaCO3 % or biogenic SiO2 % to clayemulate changes in biogenic MAR. We define five major Pliocene–Pleistocene low CaCO3 % (PPLC) intervalssince 5.3 Ma. Two were caused primarily by high bio-SiO2 burial thatdiluted CaCO3 (PPLC-2, 1685–2135 ka, and PPLC-5, 4465–4737 ka),while three were caused by enhanced dissolution of CaCO3 (PPLC-1, 51–402 ka, PPLC-3, 2248–2684 ka, and PPLC-4, 2915–4093 ka). Regional patterns ofCaCO3 % minima can distinguish between low CaCO3 caused by highdiatom bio-SiO2 dilution versus lows caused by high CaCO3dissolution. CaCO3 dissolution can be confirmed through scanning XRFmeasurements of Ba. High diatom production causes lowest CaCO3 %within the equatorial high productivity zone, while higher dissolutioncauses lowest CaCO3 percent at higher latitudes where CaCO3 production islower. The two diatom production intervals, PPLC-2 and PPLC-5, havedifferent geographic footprints from each other because of regional changesin eastern Pacific nutrient storage after the closure of the Central American Seaway.Because of the regional variability in carbonate production andsedimentation, the carbonate compensation depth (CCD) approach is onlyuseful to examine large changes in CaCO3 dissolution.
The reliability of paleoproductivity proxies must be determined before assessing the role of the oceanic carbon (C) cycle in affecting past climate changes. We compare paleoproductivity records of newly generated micropaleontological data (benthic foraminiferal accumulation rates, BFAR) to those of existing geochemical data (reactive phosphorus [reactive P] mass accumulation rates [MAR] and biological barium [bio‐Ba] MAR) for the same Paleogene‐aged sediments. Sediments are from the Atlantic (Maud Rise, Ocean Drilling Program Sites 689/690) and the Indian (Kerguelen plateau, Ocean Drilling Program Site 738) sectors of the Southern Ocean. Reactive P MAR, but not bio‐Ba MAR, correlates to varying degree with BFAR for all three sites investigated. Export productivity, delivery of organic C to the seafloor, and organic C burial calculated here using bio‐Ba MAR, BFAR, and reactive P MAR, respectively, for these sites during the Early Paleogene span 2 orders of magnitude (~0.01 to 1 g C·cm−2·kyr−1). Differences in magnitude of reconstructed organic C fluxes are expected because different proxies record different aspects of the biological pump, and these aspects did not behave proportionally similar for all periods. Proxies studied here indicate that transfer efficiency, the fraction of exported organic matter from 100 m that reaches the deep ocean, was low for the Early Paleogene Southern Ocean, similar to today. Despite this, absolute organic carbon burial was similar or higher than today because export productivity was similar or higher. Elevated temperatures may have increased both biological production and respiration in the Early Paleogene Southern Ocean.
more » « less- NSF-PAR ID:
- 10462817
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 34
- Issue:
- 1
- ISSN:
- 2572-4517
- Page Range / eLocation ID:
- p. 79-97
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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