ALBERT

Description: The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of approximately 2000 x 10(9) metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowered deep-sea pH, thereby triggering a rapid (〈10,000-year) shoaling of the calcite compensation depth (CCD), followed by gradual recovery. Here we present geochemical data from five new South Atlantic deep-sea sections that constrain the timing and extent of massive sea-floor carbonate dissolution coincident with the PETM. The sections, from between 2.7 and 4.8 kilometers water depth, are marked by a prominent clay layer, the character of which indicates that the CCD shoaled rapidly (〈10,000 years) by more than 2 kilometers and recovered gradually (〉100,000 years). These findings indicate that a large mass of carbon (〉〉2000 x 10(9) metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zachos, James C -- Rohl, Ursula -- Schellenberg, Stephen A -- Sluijs, Appy -- Hodell, David A -- Kelly, Daniel C -- Thomas, Ellen -- Nicolo, Micah -- Raffi, Isabella -- Lourens, Lucas J -- McCarren, Heather -- Kroon, Dick -- New York, N.Y. -- Science. 2005 Jun 10;308(5728):1611-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth Sciences Department, Earth and Marine Sciences Building, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. jzachos@emerald.uscs.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15947184" target="_blank"〉PubMed〈/a〉

Description: The state of Atlantic Meridional Overturning Circulation (AMOC) is influenced by both the strength and the location of the Mediterranean Outflow (MOW) plume in the Gulf of Cadiz (Gulf of Cadiz). To evaluate the influence of MOW on AMOC over deglaciations, precise and accurate salinity and temperature reconstructions are needed. For this purpose, we measured Mg/Ca and clumped isotopes of several benthic foraminiferal species at IODP Site U1390 in the Gulf of Cadiz. The clumped isotope results of Cibicidoides pachyderma , Uvigerina mediterranea and Pyrgo spp. are consistent between species and record no significant difference in Glacial to Holocene DWT. Over the deglaciation, the Mg/Ca-based temperatures derived from U. mediterranea indicate three periods of MOW absence at site U1390. Mg/Ca-based temperatures of Hoeglundina elegans and C. pachyderma are on average 6 °C too cold when compared to the present core-top temperature, which we explain by a carbonate ion effect on these epibenthic species related to the high alkalinity of the MOW. Combining DWT estimates with the benthic oxygen isotope data and considering different relationships between seawater oxygen isotopes and salinity, we infer a salinity decrease of MOW by 3 to 8 units over the deglaciation, and 4 units during S1, accounting for the global δ 18 O depletion due to the decrease in ice volume. Our findings confirm that the Mediterranean Sea accumulates excess salt during a glacial low stand, and suggest that this salt surged into the Atlantic over the deglaciation, presumably during HS1.

Description: Colour and diffuse reflectance records can be used to develop astronomically tuned age models for long sediment cores. Here, we present high-resolution (1 mm) colour records from a sediment core from the western Gulf of Cadiz of SW Spain (D13892), spanning the last deglaciation, in parallel with stable isotope ({delta}18O) and sea surface temperature (SST) proxy data. The age model is based on {delta}18O stratigraphy complemented by five atomic mass spectroscopy (AMS) radiocarbon datings. We find good comparison between the colour record of D13892 and the GISP2 oxygen isotope series (R2 = 0.81), which strongly suggests that the sediment colour reflects the state of the climate. As sediment colour variability has previously been found to be diagnostic of changes in mineralogical/chemical composition, we relate the causes of the colour variability in D13892 to changes in the local particle flux, and support these observations with data from core-logging X-ray fluorescence (XRF) analyses. The colour and XRF logger records for D13892 suggest that the last glaciation and Younger Dryas were characterized by an enhanced supply of terrigenous detritus into the western Gulf of Cadiz. Cyclicities with wavelengths of 607 and 1375 years are recognized in the colour records for the Holocene. This cyclicity also relates to variability in detrital supply, with an important eolian component implied by enrichment in hematite during cycle maxima.

Description: The Milankovitch theory of climate change is widely accepted, but the registration of the climate changes in the stratigraphic record and their use in building high-resolution astronomically tuned timescales has been disputed due to the complex and fragmentary nature of the stratigraphic record. However, results of time series analysis and consistency with independent magnetobiostratigraphic and/or radio-isotopic age models show that Milankovitch cycles are recorded not only in deep marine and lacustrine successions, but also in ice cores and speleothems, and in eolian and fluvial successions. Integrated stratigraphic studies further provide evidence for continuous sedimentation at Milankovitch time scales (10 4 years up to 10 6 years). This combined approach also shows that strict application of statistical confidence limits in spectral analysis to verify astronomical forcing in climate proxy records is not fully justified and may lead to false negatives. This is in contrast to recent claims that failure to apply strict statistical standards can lead to false positives in the search for periodic signals. Finally, and contrary to the argument that changes in insolation are too small to effect significant climate change, seasonal insolation variations resulting from orbital extremes can be significant (20% and more) and, as shown by climate modelling, generate large climate changes that can be expected to leave a marked imprint in the stratigraphic record. The tuning of long and continuous cyclic successions now underlies the standard geological time scale for much of the Cenozoic and also for extended intervals of the Mesozoic. Such successions have to be taken into account to fully comprehend the (cyclic) nature of the stratigraphic record.

Description: 〈p〉Astronomical calculations reveal the Solar System’s dynamical evolution, including its chaoticity, and represent the backbone of cyclostratigraphy and astrochronology. An absolute, fully calibrated astronomical time scale has hitherto been hampered beyond ~50 million years before the present (Ma) because orbital calculations disagree before that age. Here, we present geologic data and a new astronomical solution (ZB18a) showing exceptional agreement from ~58 to 53 Ma. We provide a new absolute astrochronology up to 58 Ma and a new Paleocene–Eocene boundary age (56.01 ± 0.05 Ma). We show that the Paleocene–Eocene Thermal Maximum (PETM) onset occurred near a 405-thousand-year (kyr) eccentricity maximum, suggesting an orbital trigger. We also provide an independent PETM duration (170 ± 30 kyr) from onset to recovery inflection. Our astronomical solution requires a chaotic resonance transition at ~50 Ma in the Solar System’s fundamental frequencies.〈/p〉

Description: Conditions of low oxygen, as well as strong fluctuations in dissolved oxygen concentrations, can substantially affect marine benthic communities. An early assessment of the status of a community after such an event is of fundamental ecological importance and may help to inform management measures. This paper investigates the response of a foraminiferal assemblage, and its relationship with sediment bio-geochemistry, micro-organisms and other fauna, following experimentally induced hypoxia on an intertidal flat in the Scheldt Estuary, The Netherlands. Sediment hypoxia was induced during one experiment in winter and a second in late spring. The foraminiferal assemblages in the upper 0–1 cm of sediment were sampled at two and five months post-hypoxia. Changes in foraminiferal abundance and biovolume were compared to responses of microphytobenthos, bacteria, meiofauna and macrofauna, which have been reported in separate papers. The foraminiferal assemblage comprised three species, Haynesina germanica , Ammonia beccarii and Elphidium excavatum. Their species-specific abundance and estimated biovolume varied with timing of disturbance (winter vs. spring hypoxia) and the duration of recovery (2 vs. 5 months). Although all foraminiferal species were expected to benefit from recolonization of macrofauna, H. germanica was negatively correlated to the abundance of macrofaunal bioturbators during recovery. The abundance of A. beccarii was positively correlated with microalgal biomass. These findings revealed species-specific responses by foraminifera after hypoxia and the concomitant recovery of other biota, further demonstrating the usefulness of foraminifera as ecological indicators.

Description: Series of transient greenhouse warming intervals in the early Eocene provide an opportunity to study the response of rock weathering and erosion to changes in temperature and precipitation. During greenhouse warming, chemical weathering is thought to increase the uptake of carbon from the atmosphere, while physical weathering and erosion control sediment supply. A large ancient greenhouse warming event is the Paleocene-Eocene Thermal Maximum at 56 Ma. In many coastal sites, an increase in the abundance of kaolinite clay during the Paleocene-Eocene Thermal Maximum is interpreted as the result of reworking from terrestrial strata due to enhanced runoff caused by increased seasonal precipitation and storminess during a time of decreased vegetation cover. In the continental interior of North America, Paleocene-Eocene Thermal Maximum paleosols show more intense pedogenesis and drying, which are indicated by deeply weathered and strongly oxidized soil profiles. The weathering and oxidation could be related to temperature and precipitation changes, but also to increased time available for weathering and increased soil permeability in coarser sediment. Here, we provide evidence for enhanced climate seasonality, increased erosion of proximal laterites and intrabasinal floodplain soils, and a potential slight increase in chemical weathering during the smaller early Eocene hyperthermals (Eocene Thermal Maximum 2, including H1 and H2) postdating the Paleocene-Eocene Thermal Maximum, for which no previous clay mineral data were available. Hyperthermal soil formation at the site of floodplain deposition causes a similar, insignificant clay mineralogical change as occurred during the background climates of the early Eocene by showing small increases in smectite and decreases in illite-smectite and illite. Remarkably, the detrital sediments during the hyperthermals show a similar pedogenic-like increase of smectite and decreases of mixed-layer illite-smectite and illite, while the kaolinite and chlorite proportions remained low and unchanged. Since sedimentation rates and provenance were similar during the events, enhanced smectite neoformation during soil formation in more proximal settings, and associated reworking, is the likely process causing this clay mineralogical change. The hundreds to thousands of year time scales at which individual paleosols were formed were probably too short for significant alteration of the rocks by in situ chemical weathering despite changing climates during the two post–Paleocene-Eocene Thermal Maximum greenhouse warming episodes. The relatively small signal, however, raises the question of whether increased chemical weathering can indeed be a strong negative feedback mechanism to enhanced greenhouse gas warming over the time scales at which these processes act.