| 1. |
- Edgar, Kirsty M., et al.
(författare)
-
New composite bio- and isotope stratigraphies spanning the Middle Eocene Climatic Optimum at tropical ODP Site 865 in the Pacific Ocean
- 2020
-
Ingår i: Journal of Micropalaeontology. - : Copernicus GmbH. - 0262-821X .- 2041-4978. ; 39:2, s. 117-138
-
Tidskriftsartikel (refereegranskat)abstract
- The Middle Eocene Climatic Optimum (MECO) at ca. 40 Ma is one of the largest of the transient Eocene global warming events. However, it is relatively poorly known from tropical settings since few sites span the entirety of the MECO event and/or host calcareous microfossils, which are the dominant proxy carrier for palaeoceanographic reconstructions. Ocean Drilling Program (ODP) Pacific Ocean Site 865 in the low-latitude North Pacific (Allison Guyot) has the potential to provide a useful tropical MECO reference, but detailed stratigraphic and chronological constraints needed to evaluate its completeness were previously lacking. We have addressed this deficit by generating new high-resolution biostratigraphic, stable isotope, and X-ray fluorescence (XRF) records spanning the MECO interval ( similar to 38.0-43.0 Ma) in two holes drilled at Site 865. XRF-derived strontium / calcium (Sr/Ca) and barium / strontium (Ba/Sr) ratios and Fe count records allow correlation between holes and reveal pronounced rhythmicity, enabling us to develop the first composite section for Holes 865B and 865C and a preliminary cyclostratigraphy for the MECO. Using this new framework, the sedimentary record is interpreted to be continuous across the event, as identified by a pronounced transient benthic foraminiferal delta O-18 shift of similar to 0.8 parts per thousand. Calcareous microfossil biostratigraphic events from widely used zonation schemes are recognized, with generally good agreement between the two holes, highlighting the robustness of the new composite section and allowing us to identify planktic foraminiferal Zones E10-E15 and calcareous nannofossil Zones NP15-18. However, discrepancies in the relative position and ordering of several primary and secondary bioevents with respect to published schemes are noted. Specifically, the stratigraphic highest occurrences of planktic foraminifera, Acarinina bullbrooki, Guembelitrioides nuttalli, and Morozovella aragonensis, and calcareous nannofossils, Chiasmolithus solitus and Sphenolithus furcatolithoides, and the lowest occurrence of Reticulofenestra reticulata all appear higher in the section than would be predicted relative to other bioevents. We also note conspicuous reworking of older microfossils (from planktic foraminiferal Zones E5-E9 and E13) into younger sediments (planktic foraminiferal Zones E14-15) within our study interval consistent with reworking above the MECO interval. Regardless of reworking, the high-quality XRF records enable decimetre-scale correlation between holes and highlight the potential of Site 865 for constraining tropical environmental and biotic changes, not just across the MECO but also throughout the Palaeocene and early-to-middle Eocene interval.
|
|
| 2. |
- Pagani, Mark, et al.
(författare)
-
The Role of Carbon Dioxide During the Onset of Antarctic Glaciation
- 2011
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 334:6060, s. 1261-1264
-
Tidskriftsartikel (refereegranskat)abstract
- Earth's modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation similar to 33.7 million years ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth's climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO(2)) during major climatic change. Previously published records of alkenone-based CO(2) from high-and low-latitude ocean localities suggested that CO(2) increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO(2) levels, biasing long-term trends. Our results show that CO(2) declined before and during Antarctic glaciation and support a substantial CO(2) decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO(2) thresholds.
|
|
| 3. |
- Pälike, Heiko, et al.
(författare)
-
A Cenozoic record of the equatorial Pacific carbonate compensation depth
- 2012
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 488:7413, s. 609-614
-
Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.
|
|
| 4. |
- Witkowski, Jakub, et al.
(författare)
-
Early Paleogene biosiliceous sedimentation in the Atlantic Ocean : Testing the inorganic origin hypothesis for Paleocene and Eocene chert and porcellanite
- 2020
-
Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 556
-
Tidskriftsartikel (refereegranskat)abstract
- The widespread occurrence of lower Eocene chert and porcellanite has been viewed as a major paleoceanographic issue since the advent of ocean drilling, and both biotic and abiotic forcings have been proposed to explain it. We present a reconstruction of indurated siliceous sediment (ISS) and preserved biosiliceous sediment (PBS) occurrences in the Atlantic Ocean through the Paleocene and Eocene (~66 through 34 Ma). ISS and PBS distributions reveal dissimilar temporal trends, with the peak of ISS occurrences coinciding with the Early Eocene Climatic Optimum, in line with previous studies. PBS occurrences show a generally increasing trend culminating between 44 and 43 Ma. The common co-occurrence of ISS and PBS, and their coherent geographic distribution lends strong support to the biogenic origin of the precursor to the widespread Paleogene ISS, and argues against an inorganic mode of early Cenozoic chert and porcellanite precipitation. Weight per cent biogenic opal records and trends in linear sedimentation rates indicate two plausible modes of silicification: 1) silicification due to prolonged exposure of biogenic opal-rich sediments to corrosive bottom waters; and 2) silicification due to elevated pressures and temperatures caused by rapid burial of biogenic opal-rich deposits. The confinement of ISS and PBS to proximal sites along continental margins points to the reliance of siliceous sedimentation through the Paleocene and Eocene on terrestrial supply of dissolved silicon. Consistent with this, quantitative siliceous microfossil assemblage records from the Blake Nose in the NW Atlantic indicate that the nutrient-rich marginal rather than oligotrophic pelagic settings hosted the majority of siliceous plankton production through the early Paleogene. The inorganic SiO2 precipitation model is unlikely to have been the dominant mechanism responsible for ubiquitous occurrences of early Paleogene ISS. We favor the biogenic ISS precursor scenario and reconcile it with the low-productivity early Cenozoic oceans by showing that large volumes of biogenic silica were supplied to the western North Atlantic Ocean from the North American margin through the Paleocene and Eocene. Dissolution of this surplus silica was facilitated by an early southwestward flow of young, SiO2-depleted waters from the North Atlantic. All these factors contributed to ISS and PBS focusing in the western North Atlantic through the early Paleogene.
|
|
| 5. |
- Brylka, Karolina, et al.
(författare)
-
Biogenic silica accumulation and diatom assemblage variations through the Eocene-Oligocene Transition : A Southern Indian Ocean versus South Atlantic perspective
- 2024
-
Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 636
-
Tidskriftsartikel (refereegranskat)abstract
- It is widely interpreted that there is a significant link between climate cooling at the Eocene-Oligocene Transition(EOT; ~34 Ma) and subsequent diatom proliferation in the world’s oceans during the mid to late Cenozoic. Yet,our understanding of biogenic silica flux through the EOT interval is based on limited data from a few sites, andthere are many complications in making a meaningful comparison based on biogenic silica concentration datagenerated using different techniques. Here, we present new biogenic opal flux and diatom assemblage recordsacross EOT from Ocean Drilling Program Site 748 (Southern Kerguelen Plateau, southern Indian Ocean), inaddition to new biogenic opal flux records from the South Atlantic (Deep Sea Drilling Project Site 511, FalklandPlateau and Ocean Drilling Program Site 1090, Agulhas Ridge). Observed opal flux shifts and variability at Site748 are consistent with published data from nearby Site 744; both sites show considerable shifts in biogenic opalaccumulation rates corresponding to shifts in published benthic oxygen isotope records through the EOT. Incontrast, our new opal flux record for Site 511, derived from biogenic opal concentration measurements viaspectrophotometry, differs from the published record derived from insoluble residues, whereas new datagenerated for Site 1090 are generally consistent with previously published flux reconstructions. The SouthAtlantic biogenic opal flux records, however, are dissimilar from one another, and both are dissimilar from theSouthern Indian Ocean records. Also, the taxonomic composition of the diatom assemblages from Sites 511, 748and 1090 display considerable differences, with hemiauloids and rhizosolenids – generally inferred as indicativeof oligotrophic conditions – being the dominant diatoms at the Southern Kerguelen Plateau (Site 748). Publishedrecords show that hemiauloid taxa are absent from the earliest Oligocene interval at Site 1090, which is widelyseen as a record of deposition from nutrient-rich waters sustaining abundant diatom assemblages. These differencesin diatom assemblages testify to regional differences in nutrient concentrations. In particular, the timingof biogenic opal flux pulses between Sites 1090 and 748 imply a shift in the locus of opal deposition to areasfurther south in the Southern Ocean across the EOT, likely related to proto-ACC development and strengtheningof frontal boundaries. Thus, combined geochemical and micropaleontological evidence points to a regionallyvariable rather than a global, unified opal flux response to climate cooling through the Eocene-OligoceneTransition.
|
|
| 6. |
|
|
| 7. |
- Witkowski, Jakub, et al.
(författare)
-
North Atlantic marine biogenic silica accumulation through the early to middle Paleogene : Implications for ocean circulation and silicate weathering feedback
- 2021
-
Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 17:5, s. 1937-1954
-
Tidskriftsartikel (refereegranskat)abstract
- The Paleogene history of biogenic opal accumulation in the North Atlantic provides insight into both the evolution of deepwater circulation in the Atlantic basin and weathering responses to major climate shifts. However, existing records are compromised by low temporal resolution and/or stratigraphic discontinuities. In order to address this problem, we present a multi-site, high-resolution record of biogenic silica (bioSiO2) accumulation from Blake Nose (ODP Leg 171B, western North Atlantic) spanning the early Paleocene to late Eocene time interval (~65-34 Ma). This record represents the longest single-locality history of marine bioSiO2 burial compiled to date and offers a unique perspective into changes in bioSiO2 fluxes through the early to middle Paleogene extreme greenhouse interval and the subsequent period of long-term cooling. Blake Nose bioSiO2 fluxes display prominent fluctuations that we attribute to variations in sub-thermocline nutrient supply via cyclonic eddies associated with the Gulf Stream. Following elevated and pulsed bioSiO2 accumulation through the Paleocene to early Eocene greenhouse interval, a prolonged interval of markedly elevated bioSiO2 flux in the middle Eocene between ~ 46 and 42 Ma is proposed to reflect nutrient enrichment at Blake Nose due to invigorated overturning circulation following an early onset of Northern Component Water export from the Norwegian-Greenland Sea at ~ 49 Ma. Reduced bioSiO2 flux in the North Atlantic, in combination with increased bioSiO2 flux documented in existing records from the equatorial Pacific between ~ 42 and 38 Ma, is interpreted to indicate diminished nutrient supply and reduced biosiliceous productivity at Blake Nose in response to weakening of the overturning circulation. Subsequently, in the late Eocene, a deepwater circulation regime favoring limited bioSiO2 burial in the Atlantic and enhanced bioSiO2 burial in the Pacific was established after ~ 38 Ma, likely in conjunction with reinvigoration of deepwater export from the North Atlantic. We also observe that Blake Nose bioSiO2 fluxes through the middle Eocene cooling interval (~ 48 to 34 Ma) are similar to or higher than background fluxes throughout the late Paleocene-early Eocene interval (~ 65 to 48 Ma) of intense greenhouse warmth. This observation is consistent with a temporally variable rather than constant silicate weathering feedback strength model for the Paleogene, which would instead predict that marine bioSiO2 burial should peak during periods of extreme warming.
|
|
