ALBERT

Description: The complex interplay between extraterrestrial events and earth-bound processes that triggered one of the greatest biological crises of the Phanerozoic requires a high resolution timescale. Detailed magnetic susceptibility measurements at the Contessa Highway and Bottaccione sections (Italy) span the Cretaceous-Paleogene boundary and reveal clear orbital signatures in the sedimentary record. Identification of precession and 405 kyr eccentricity cycles allows an estimate of 324+/-40 kyr for the duration of the Maastrichtian part of Chron C29r. We present in the same high resolution time frame sites in Spain and the North and South Atlantic and bio-horizons, biotic changes, stable isotopic excursions and the decrease in Osmium isotopes recorded in these sections. The onset of 187 Os/ 188 Os decrease coincides with the d13 C negative excursion K-PgE1, thus suggesting a first pulse in Deccan volcanism at 66.64 Ma. The K-PgE3 d13 C negative excursion is possibly the expression of a second pulse at 66.26 Ma. Late Maastrichtian d13 C negative excursions are of low intensity and span durations of one to two eccentricity cycles, whereas early Danian excursions are brief (about 30 kyr) and acute. In Biotic response to late Maastrichtian perturbations occurred with a delay of ca. 200 kyr after the beginning of K-PgE1 shortly before K-PgE3. The biotic perturbation could be thus either a delayed response to K-PgE1, or a direct response to K-PgE3, and possibly, a threshold response to the stepwise buildup of CO2 atmospheric injections. No delay is evident in response to early Danian hyperthermal events. These differences suggest that short-lived, volcanically-derived environmental perturbations were buffered within the stable late Maastrichtian oceanic realm whereas they were amplified by the more sensitive and highly disturbed early Danian oceanic ecosystem.

Description: Abundance and size changes in the calcareous nannofossil Schizosphaerella are investigated throughout the upper Sinemurian to lowermost Toarcian of the Sancerre-Couy core (Paris Basin). Measurements from 116 samples are compared to 487 and 411 measurements of CaCO3 content and total organic carbon (TOC) content, respectively. Our results confirm that Schizosphaerella was better adapted to proximal areas than coccoliths as expressed by the stepwise rise in abundance of Schizosphaerella, followed later on by the rise in abundance of coccoliths during the major transgression of the Sinemurian. The new results show that changes in the size of Schizosphaerella were mostly a response to Early Jurassic temperature variations (coldhouse-greenhouse changes). Large average sizes of Schizosphaerella correspond mostly to proximal, cool environmental conditions of the late Sinemurian. Medium average sizes correspond to more distal conditions and cool surface waters whereas small average sizes are associated with warm episodes. These results suggest that the size response of Schizosphaerella to the early Toarcian Oceanic Anoxic Event and to preceding environmental perturbations of the Early Jurassic was probably not a physiological response to lower calcification but rather represent changes in abundances of different ecophenotypes or (sub-) species related to climate change. The contribution of Schizosphaerella carbonate (CaCO3schizo) to the total carbonate (bulk CaCO3) in the Paris Basin was minor (〈6 %) and short-term fluctuations of both parameters show no correlation. However, the CaCO3schizo and bulk CaCO3 show similarities in their long-term trends, suggesting a possible relationship between the biotic carbonate production and the export of allochthonous carbonate to the Paris Basin.

Description: The mass loss from the Greenland Ice Sheet has increased over the past two decades. Marine-terminating glaciers contribute significantly to this mass loss due to increased melting and ice discharge. Rapid retreat periods of these tidewater glaciers have been linked to the concurrent inflow of warm, Atlantic derived waters. However, little is known about the 15 variability of Atlantic-derived waters within these fjords, due to a lack of multi-annual, in situ measurements. Thus, to better understand the potential role of ocean warming on glacier retreat, reconstructions that characterize the variability of Atlantic water inflow to these fjords are required. Here, we investigate foraminiferal assemblages in a sediment core from Upernavik Fjord, West Greenland, in which the major ice stream Upernavik Isstrøm terminates. We investigate the environmental characteristics that control species diversity and derive that it is predominantly controlled by changes in bottom water 20 variability. Hence, we provide a reconstruction of Atlantic water inflow to Upernavik Fjord, spanning the period 1925-2012. This reconstruction reveals peak Atlantic water inflow during the 1930s and again after 2000, a pattern that is similar to the Atlantic Multidecadal Oscillation (AMO). We compare these results to historical observations of front positions of Upernavik Isstrøm. This reveals that inflow of warm, Atlantic-derived waters indeed likely contributed to high retreat rates in the 1930s and after 2000. However, moderate retreat rates of Upernavik Isstrøm also prevailed in the 1960s/1970s, showing that retreat 25 continued despite reduced Atlantic water inflow, albeit at a lower rate. Considering the link between bottom water variability and the AMO in Upernavik Fjord and the fact that a persistent negative phase of the AMO is expected for the next decade, Atlantic water inflow into the fjord may decrease in the next ~10 years.

Description: The phytoplankton response (calcareous nannofossils) to the Late Maastrichtian climate evolution is investigated in the South Atlantic DSDP Hole 525A and compared to published geochemical and micropaleontological data. The results point to a succession of dramatic climatic fluctuations. “Cool-water indicators” (Ahmuellerella octoradiata, Kamptnerius magnificus and Nephrolithus frequens) suggest cool surface water conditions prevailed during Chron C30n. At the top of C30n, their sudden drop in abundance, the last occurrence of B. constans and the concomitant increase in the tropical species Micula murus suggest warming and lower surface water productivity. An M. murus acme within Chron C29r reflects maximum warming. During the last 100 kyr of the Maastrichtian, the decrease in M. murus and increase in cool-water indicators reflect rapid cooling with the cool climate persisting over. The calcareous nannoplankton response to climate change correlate with similar findings in the Equatorial Atlantic Hole 1258A and parallels the stable isotope record of planktic and benthic foraminifera of DSDP Hole 525A as well as the decline in 187Os/188Os. Comparison of this marine record and the continental climate record in North America suggests a link between Deccan volcanism and the late Maastrichtian warm event.

Description: Disentangling the external and internal forcing responsible for the variability of the Earth's climate and associated extreme events over the Holocene is crucial for producing reliable scenarios of adaptation to the effects of ongoing climate change. At mid-latitudes, significant relationships between westerly storminess, solar activity and internal atmospheric and oceanic modes of variability have been repeatedly evidenced to exist over millennial and centennial time scales. However, at shorter (decadal) scale, it is still challenging to establish clear control links between the forcing mechanisms and the spatio-temporal variability of past extra-tropical storms. This probably owes to the existence of complex multi-scale relationships and feedback loops, as well as to the difficulty of producing proxy-records of sufficiently high-resolution and wide spatial significance. Here we present a reconstruction of westerly storminess in western Denmark between 4840 and 2300 yrs. cal. B·P. Past-storminess is retrieved from an organic-rich sedimentary succession by combining markers of aeolian sand influx, μ-XRF geochemistry and plant macrofossils. Particular focus is paid to the c. 4840–4350 yrs. cal. B·P. period for which our record is characterized by a pluri-annual resolution. We evidence concurrent pluri-decadal shifts in storminess and humidity regime at our site that we interpret as relocations of the mean westerly storm-track over the North-Atlantic. The signal is dominated by ≈ 90, ≈ 50–80 and ≈ 35-yr periods, evoking possible links with solar activity, the North-Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC) modes of variability, respectively. The ≈ 35-yr periodicity found in our record is especially strong and stationary, suggesting that storminess could have been closely linked with the AMOC over the study period. Our records of storminess indeed show some great similarities with a record of deep overflow of a branch of the AMOC. Opposite to some model outputs, the strength of the AMOC seems to have often co-varied with storminess at pluri-decadal scales over the study period. We also find periods of high storminess activity to be significantly correlated with solar minima and relative pluri-decadal lows in the NAO. We suggest that small lowering in the strength of the NAO in an otherwise positive NAO context may have caused southward relocations of the mean westerly storm-track from subpolar latitudes to northern Europe. This invites to reconsider the importance given to using the NAO as a binary index. Finally, an attempt is made to explore the temporal lead-lag relationships between storminess and different potential forcing agents such as the Total Solar Irradiance, the NAO and the AMOC. Unfortunately, the insufficient chronological precision of the proxy-records available for the TSI, the NAO and the AMOC over the study period prevents us from deriving any robust interpretations regarding potential teleconnections at a decadal-scale between past north-Atlantic westerly storminess activity, solar forcing, the NAO and north-Atlantic surface and deep oceanic circulation.