Evolution of deep-sea sediments across the Paleocene-Eocene and Eocene-Oligocene boundaries

Abstract

The composition and distribution of deep-sea sediments is the result of a multitude of climatic, biotic and oceanic conditions relating to biogeochemical cycles and environmental change. Here we utilize the extensive sediment archives of the International Ocean Discovery Program (IODP) and its predecessors to construct maps of deep-sea sediment type across two critical but contrasting boundaries in the Paleogene, one characterised by an interval of extreme warmth (Paleocene/Eocene) and the other by global cooling (Eocene/Oligocene). Ocean 2 sediment distribution shows significant divergence both between the latest Paleocene and Paleocene Eocene Thermal Maximum (PETM), across the Eocene-Oligocene Transition (EOT), and in comparison to modern sediment distributions. Carbonate sedimentation in the latest Paleocene extends to high southern latitudes. Disappearance of carbonate sediments at the PETM is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon-cycle perturbation. Biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early Paleogene ocean. In the Southern Ocean, we attribute the low in biosiliceous burial, to the warm deep water temperatures which would have impacted biogenic silica preservation. In the late Eocene, our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial Pacific. Enhanced biosiliceous deposits in the late Eocene equatorial Pacific and Southern Ocean are due to increased productivity and the spin-up of the oceans. Our compilation documents the enhanced global carbonate sedimentation in the early Oligocene, confirming that the drop in the carbonate compensation depth was global.

Temperature Gradients Across the Pacific Ocean During the Middle Miocene

“…Shoaling of the EEP thermocline and expansion of the cold tongue have been linked to cooling and the expansion of subpolar oceans on more recent timescales (Martinez‐Garcia et al., 2010), though processes that influence the range and intensity of the cold tongue are not well understood. Whilst a cold tongue comparable to the modern may not have developed until the late Miocene or younger (Liu et al., 2019; Steph et al., 2010), there is widespread evidence that upwelling in the EEP initiated in the mid Eocene (Lyle et al., 2002; Moore et al., 2004; Wade et al., 2020; Zhang et al., 2017), thus, the EEP would have developed a proto‐cold tongue, due to advection of cold, deep water.…”

North Atlantic marine biogenic silica accumulation through the early to middle Paleogene: implications for ocean circulation and silicate weathering feedback

“…to middle Paleogene at Blake Nose bio SiO 2 production, export, and preservation in marine sediments are influenced globally by dissolved silicon supply to the oceans derived from terrestrial weathering, which is closely linked to climate via a negative feedback (e.g., Walker et al, 1981), and by ocean circulation patterns and upwelling, which supply the bulk of macronutrients to surface waters (Miskell et al, 1985;Handoh et al, 2003). In order to gain insight into the influence that each of these factors has exerted on bio SiO 2 accumulation through the early to middle Paleogene at BN, we compared the bio SiO 2 flux composite record to published composite global benthic foraminiferal δ 18 O and δ 13 C records, pCO 2 proxy estimates, proxy records of continental weathering ( 87 Sr/ 86 Sr, 187 Os/ 188 Os and δ 7 Li), and modeled silicate weathering flux (SWF) (Figs.…”

“…One fundamental control on marine siliceous plankton production is the amount of dissolved silicon supplied to the oceans from terrestrial silicate weathering, a chemical process that ultimately consumes atmospheric CO 2 and releases silicic acid and alkalinity to the oceans (i.e., when combined with carbonate burial in the oceans; Walker et al, 1981;Fontorbe et al, 2020;Penman et al, 2020). By moderating atmospheric CO 2 , the silicate weathering feedback is postulated to operate as a thermostat, maintaining the Earth's surface within a habitable range of temperatures since early in geological history (Kasting, 2019).…”

Bentho‐Pelagic Decoupling: The Marine Biological Carbon Pump During Eocene Hyperthermals

“…These hyperthermal events are linked to massive emission of isotopically depleted carbon compounds into the ocean‐atmosphere system (e.g., Vervoort et al., 2019; Westerhold et al., 2020) and were characterized by globally elevated temperatures, low equator‐to‐pole sea surface temperature gradients, reduced Ekman‐induced upwelling, with less vigorous deep ocean ventilation further limiting upwelling (Schneider et al., 2013; Thomas et al., 2000; Winguth et al., 2012; Zachos et al., 2008). It is less certain whether baseline Eocene conditions outside the hyperthermal events were characterized by vigorous upwelling (e.g., Huber, 2002) or not (e.g., Wade et al., 2020).…”