Paleoceanography and Paleoclimatology

Journal: Paleoceanography and Paleoclimatology

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American Geophysical Union

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2572-4525
2572-4517

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Publications 1 - 10 of 29

Onset and demise of Cretaceous oceanic anoxic events: The coupling of surface and bottom oceanic processes in two pelagic basins of the western Tethys
Gambacorta, Gabriele; Bersezio, Riccardo; Weissert, Helmut Jürg; et al. (2016)
Paleoceanography and Paleoclimatology
The upper Albian–lower Turonian pelagic successions of the Tethys record processes acting during the onset, core, and recovery from perturbed conditions across oceanic anoxic event (OAE) 1d, OAE 2, and the mid-Cenomanian event I (MCE I) relative to intervening intervals. Five sections from Umbria-Marche and Belluno Basins (Italy) were analyzed at high resolution to assess processes in surface and deep waters. Recurrent facies stacking patterns (SP) and their associations record periods of bottom current activity coupled with surface changes in trophic level. Climate changes appear to have been influential on deep circulation dynamics. Under greenhouse conditions, vigorous bottom currents were arguably induced by warm and dense saline deep waters originated on tropical shelves in the Tethys and/or proto-Atlantic Ocean. Tractive facies postdating intermittent anoxia during OAE 1d and in the interval bracketed by MCE I and OAE 2 are indicative of feeble bottom currents, though capable of disrupting stratification and replenish deep water with oxygen. The major warming at the onset of OAE 2 might have enhanced the formation of warm salty waters, possibly producing local hiatuses at the base of the Bonarelli Level and winnowing at the seafloor. Hiatuses detected at the top of the Bonarelli Level possibly resulted from most effective bottom currents during the early Turonian thermal maximum. Times of minimal sediment displacement correlate with cooler climatic conditions and testify a different mechanism of deep water formation, as further suggested by a color change to reddish lithologies of the post-OAE 1d and post-OAE 2 intervals.
Using the natural spatial pattern of marine productivity in the Subarctic North Pacific to evaluate paleoproductivity proxies
Serno, Sascha; Winckler, Gisela; Anderson, Robert F.; et al. (2014)
Paleoceanography and Paleoclimatology
Sedimentary proxies used to reconstruct marine productivity suffer from variable preservation and are sensitive to factors other than productivity. Therefore, proxy calibration is warranted. Here we map the spatial patterns of two paleoproductivity proxies, biogenic opal and barium fluxes, from a set of core-top sediments recovered in the Subarctic North Pacific. Comparisons of the proxy data with independent estimates of primary and export production, surface water macronutrient concentrations, and biological pCO₂ drawdown indicate that neither proxy shows a significant correlation with primary or export productivity for the entire region. Biogenic opal fluxes, when corrected for preservation using ²³⁰Th-normalized accumulation rates, show a good correlation with primary productivity along the volcanic arcs (τ = 0.71, p = 0.0024) and with export productivity throughout the western Subarctic North Pacific (τ = 0.71, p = 0.0107). Moderate and good correlations of biogenic barium flux with export production (τ = 0.57, p = 0.0022) and with surface water silicate concentrations (τ = 0.70, p = 0.0002) are observed for the central and eastern Subarctic North Pacific. For reasons unknown, however, no correlation is found in the western Subarctic North Pacific between biogenic barium flux and the reference data. Nonetheless, we show that barite saturation, uncertainty in the lithogenic barium corrections, and problems with the reference data sets are not responsible for the lack of a significant correlation between biogenic barium flux and the reference data. Further studies evaluating the factors controlling the variability of the biogenic constituents in the sediments are desirable in this region.
Response of planktic foraminiferal size to late Quaternary climate change
Schmidt, Daniela N.; Renaud, Sabrina; Bollmann, Jörg (2003)
Paleoceanography and Paleoclimatology
Anatomy of Heinrich Layer 1 and its role in the last deglaciation
Hodell, David A.; Nicholl, Joseph A.; Bontognali, Tomaso R.R.; et al. (2017)
Paleoceanography and Paleoclimatology
X-ray fluorescence (XRF) core scanning and X-ray computed tomography data were measured every 1 mm to study the structure of Heinrich Event 1 during the last deglaciation at International Ocean Discovery Program Site U1308. Heinrich Layer 1 comprises two distinct layers of ice-rafted detritus (IRD), which are rich in detrital carbonate (DC) and poor in foraminifera. Each DC layer consists of poorly sorted, coarse-grained clasts of IRD embedded in a dense, fine-grained matrix of glacial rock flour that is partially cemented. The radiocarbon ages of foraminifera at the base of the two layers indicate a difference of 1400 ¹⁴C years, suggesting that they are two distinct events, but the calendar ages depend upon assumptions made for surface reservoir ages. The double peak indicates at least two distinct stages of discharge of the ice streams that drained the Laurentide Ice Sheet through Hudson Strait during HE1 or, alternatively, the discharge of two independent ice streams containing detrital carbonate. Heinrich Event 1.1 was the larger of the two events and began at ~16.2 ka (15.5–17.1 ka) when the polar North Atlantic was already cold and Atlantic Meridional Overturning Circulation (AMOC) weakened. The younger peak (H1.2) at ~15.1 ka (14.3 to 15.9 ka) was a weaker event than H1.1 that was accompanied by minor cooling. Our results support a complex history for Heinrich Stadial 1 (HS1) with reduction in AMOC during the early part (~20–16.2 ka) possibly driven by melting of European ice sheets, whereas the Laurentide Ice Sheet assumed a greater role during the latter half (~16.2–14.7 ka).
Glacial reduction of AMOC strength and long-term transition in weathering inputs into the Southern Ocean since the mid-Miocene: Evidence from radiogenic Nd and Hf isotopes
Dausmann, Veit; Frank, Martin; Gutjahr, Marcus; et al. (2017)
Paleoceanography and Paleoclimatology
Combined seawater radiogenic hafnium (Hf) and neodymium (Nd) isotope compositions were extracted from bulk sediment leachates and foraminifera of Site 1088, Ocean Drilling Program Leg 177, 2082 m water depth on the Agulhas Ridge. The new data provide a continuous reconstruction of long- and short-term changes in ocean circulation and continental weathering inputs since the mid-Miocene. Due to its intermediate water depth, the sediments of this core sensitively recorded changes in admixture of North Atlantic Deep Water to the Antarctic Circumpolar Current as a function of the strength of the Atlantic Meridional Overturning Circulation (AMOC). Nd isotope compositions (εNd) range from −7 to −11 with glacial values generally 1 to 3 units more radiogenic than during the interglacials of the Quaternary. The data reveal episodes of significantly increased AMOC strength during late Miocene and Pliocene warm periods, whereas peak radiogenic εNd values mark a strongly diminished AMOC during the major intensification of Northern Hemisphere Glaciation near 2.8 Ma and in the Pleistocene after 1.5 Ma. In contrast, the Hf isotope compositions (εHf) show an essentially continuous evolution from highly radiogenic values of up to +11 during the Miocene to less radiogenic present-day values (+2 to +4) during the late Quaternary. The data document a long-term transition in dominant weathering inputs, where inputs from South America are replaced by those from Southern Africa. Moreover, radiogenic peaks provide evidence for the supply of radiogenic Hf originating from Patagonian rocks to the Atlantic sector of the Southern Ocean via dust inputs.
Reply to comment by Matthew J. Higginson and Mark A. Altabet on ''Sedimentary phosphorus record from the Oman margin: New evidence of high productivity during glacial periods''
Tamburini, Federica; Bernasconi, Stefano M.; Föllmi, Karl B.; et al. (2004)
Paleoceanography and Paleoclimatology
Productivity Proxies in Surface Sediment of the East Antarctic Margin: A Focus on Excess Ba
Creac'h, Layla; Noble, Taryn L.; Chase, Zanna; et al. (2024)
Paleoceanography and Paleoclimatology
Components such as organic carbon (Corg), carbonate, opal or barite are valuable paleoceanographic proxies, enabling the reconstruction of past changes in carbon cycling under various climate regimes, particularly when 230Th-normalization is used to reconstruct particulate vertical rain rates. However, these components can be affected by poor preservation in the sediment. Barite is generally better preserved compared to other productivity proxies, but its estimates using “excess barium” (xsBa) calculations or Ba/Al ratios may not always be reliable, especially near the continental margin. This study presents a multi-proxy investigation of surface sediments from the East Antarctic margin to assess the robustness of xsBa as a paleo-productivity proxy. 230Th-normalized fluxes of Corg and opal record consistent variations within the sediment, while xsBa appears to be affected by different processes. Results suggest that xsBa may not robustly reflect marine barite in sediment close to the Antarctic Ice Sheet, because (a) the authigenic signal is overprinted by large lithogenic inputs; and (b) other mineral phases (e.g., Fe oxides) may be important Ba carrier phases in the region. 230Th-normalized Ba concentrations in the oxide-free sediment fraction, which was reductively leached to remove Fe-Mn oxides, aligns with the other biogenic fluxes, implying that specific leaching for barite isolation might be required in sediment proximal to the Antarctic Ice Sheet, rather than using the standard “xsBa” calculation or Ba/Al ratios. This study gives new insights into the sedimentary cycle of Ba in East Antarctic sediment and confirms the importance of using multi-proxy records to perform paleo-reconstructions.
Persistent East Equatorial Pacific Carbon Storage at the Middle Pleistocene Transition
Diz, Paula; Cobelo-García, Antonio; Hernández-Almeida, Iván; et al. (2020)
Paleoceanography and Paleoclimatology
New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio‐Pleistocene
Reilly, Brendan T.; Hernández-Almeida, Iván; et al. (2021)
Paleoceanography and Paleoclimatology
International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world. © 2021 American Geophysical Union
Effects of the Pliensbachian–Toarcian Boundary Event on carbonate productivity of a Tethyan platform and slope
Fleischmann, Sarah; Picotti, Vincenzo; Rugenstein, Jeremy Kesner Caves; et al. (2022)
Paleoceanography and Paleoclimatology
We explore the effects of the Pliensbachian–Toarcian Boundary Event (P–ToBE) on tropical carbonate productivity in the interior to margin and slope of the Venetian Platform (Northern Italy). We document the P–ToBE for the first time in the shallow-water platform margin, and we bio- and chemostratigraphically tie it to transgressive/regressive cycles. Following the latest Pliensbachian sea-level drop and emersion, transgressive grainstones at the platform edge record the P–ToBE negative carbon isotope excursion (CIE) of 1–1.5‰, also found in marl/limestone couplets on the slope. Recovery of platform productivity was ephemeral, as the platform drowned right after the peak negative CIE and was covered by deep-sea thin-bedded micritic limestones. The end of the P–ToBE correlates with a regression and renewed recovery of carbonate productivity. The negative CIE of the subsequent Toarcian Oceanic Anoxic Event is recorded in open-sea cherty limestones both at the marginal and interior platform. These limestones document an even wider transgression and the renewed partial drowning of the platform in the Serpentinus Zone. We investigate the causes of the carbon perturbation at the P–ToBE, using a simple carbon cycle model. The duration and magnitude of the CIE suggest a rapid release of methane in driving the CIE, perhaps related to the preceding sea-level drop and associated cryosphere perturbation, or to thermogenic alteration of coals near the Karoo-Ferrar Large Igneous Province (LIP). The extent of the warming and the magnitude of the P–ToBE CIE implies a contribution of volcanogenic carbon dioxide from the Karoo-Ferrar LIP.

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Journal: Paleoceanography and Paleoclimatology

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