The Geoscience of Climate and Energy 7. The Oceanic Climate Capacitor

In this study, 14C age dating of biogenic carbonates in high-deposition-rate marine sediment cores from the Pacific Ocean is used to establish the relative phasing of low and high latitude ocean warming at the beginning of the last glacial termination. The results indicate the Southern Ocean began to warm as much as 1000 years before deglacial warming began in the western tropical Pacific Warm Pool region. Importantly, it appears that much of the deep Pacific warming occurred between 19 and 14 ky BP, prior to the major deglaciation of the northern hemisphere ice sheets. These results further indicate that d18O stratigraphies from deep sea carbonates are not synchronous throughout the oceans over a glacial/interglacial termination and. therefore, d18O stratigraphies are not precise enough to establish temporal phase relationships. SOMMAIRE Dans la présente étude, on a utilisé la datation par 14C de carbonates biogéniques, sur des carottes de sédiments marins de milieux à forts taux de sédimentation du Pacifique, dans le but de quantifier la progression relative du réchauffement à basse et à haute latitude, à partir de la fin de la dernière glaciation. Les résultats indiquent que le sud de l’océan a commencé à se réchauffer jusqu’à 1 000 ans avant que le réchauffement de déglaciation ne débute dans la portion ouest tropicale du Bassin d’eau chaude du Pacifique. On notera qu’il semble qu’une grande portion du réchauffement des couches profondes du Pacifique se soit produite entre 19 ka et 14 ka avant le présent, soit avant le gros de la déglaciation des calottes glaciaires. Les résultats montrent aussi que les stratigraphies établies par δ18O sur les carbonates des fonds marins ne sont pas synchrones au travers des fonds marins durant la période glaciaire terminale et inter-glaciaire, ce qui indique que les stratigraphies établies par δ18O ne sont pas assez précises pour permettre d’établir des relations de phases temporelles

A re-evaluation of the age and nature of Cenozoic erratics from McMurdo Sound, Antarctica

Late Eocene and Miocene marine erratics recovered from Minna Bluff and Mt. Discovery in Southern Victoria Land, Antarctica range from micritic cemented, variably sorted sandstones and conglomerates to impure micritic limestones. Lithologically, the erratics are similar to strata of the same age recovered from the MSSTS 1 hole in McMurdo Sound and indicate one or more periods of glacial erosion of marine strata in the Ross Sea during the last 15 m.y.No embarg

The atmospheric bridge communicated the δ13C decline during the last deglaciation to the global upper ocean

During the early part of the last glacial termination (17.2-15 ka) and coincident with a ∼ 35 ppm rise in atmospheric CO2, a sharp 0.3‰-0.4‰ decline in atmospheric δ13CO2 occurred, potentially constraining the key processes that account for the early deglacial CO2 rise. A comparable δ13C decline has also been documented in numerous marine proxy records from surface and thermocline-dwelling planktic foraminifera. The δ13C decline recorded in planktic foraminifera has previously been attributed to the release of respired carbon from the deep ocean that was subsequently transported within the upper ocean to sites where the signal was recorded (and then ultimately transferred to the atmosphere). Benthic δ13C records from the global upper ocean, including a new record presented here from the tropical Pacific, also document this distinct early deglacial δ13C decline. Here we present modeling evidence to show that rather than respired carbon from the deep ocean propagating directly to the upper ocean prior to reaching the atmosphere, the carbon would have first upwelled to the surface in the Southern Ocean where it would have entered the atmosphere. In this way the transmission of isotopically light carbon to the global upper ocean was analogous to the ongoing ocean invasion of fossil fuel CO2. The model results suggest that thermocline waters throughout the ocean and 500-2000m water depths were affected by this atmospheric bridge during the early deglaciation

CO2 Release from Pockmarks on the Chatham Rise‐Bounty Trough at the Glacial Termination

Seafloor pockmarks of varying size occur over an area of 50,000 km2 on the Chatham Rise, Canterbury Shelf and Inner Bounty Trough, New Zealand. The pockmarks are concentrated above the flat‐subducted Hikurangi Plateau. Echosounder data identifies recurrent episodes of pockmark formation at ~100,000yr frequency coinciding with Pleistocene glacial terminations. Here we show that there are structural conduits beneath the larger pockmarks through which fluids flowed upward toward the seafloor. Large negative Δ14C excursions are documented in marine sediments deposited next to these subseafloor conduits and pockmarks at the last glacial termination. Modern pore waters contain no methane and there is no negative δ13C excursion at the glacial termination that would be indicative of methane or mantle‐derived carbon at the time the Δ14C excursion and pockmarks were produced. An ocean general circulation model equipped with isotope tracers is unable to simulate these large Δ14C excursions on the Chatham Rise by transport of hydrothermal carbon released from the East Pacific Rise as previous studies suggested. Here we attribute the Δ14C anomalies and pockmarks to release of 14C‐dead CO2 and carbon‐rich fluids from subsurface reservoirs, the most likely being dissociated Mesozoic carbonates that subducted beneath the Rise during the Late Cretaceous. Because of the large number of pockmarks and duration of the Δ14C anomaly, the pockmarks may collectively represent an important source of 14C‐dead carbon to the ocean during glacial terminations

Sea surface temperature changes in the southern California borderlands during the last glacial-interglacial cycle

A variety of evidence suggests that average sea surface temperatures (SSTs) during the last glacial maximum in the California Borderlands region were significantly colder than during the Holocene. Planktonic foraminiferal δ18O evidence and average SST estimates derived by the modern analog technique indicate that temperatures were 6°-10°C cooler during the last glacial relative to the present. The glacial plankton assemblage is dominated by the planktonic foraminifer Neogloboquadrina pachyderma (sinistral coiling) and the coccolith Coccolithus pelagicus, both of which are currently restricted to subpolar regions of the North Pacific. The glacial-interglacial average SST change determined in this study is considerably larger than the 2°C change estimated by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981]. We propose that a strengthened California Current flow was associated with the advance of subpolar surface waters into the Borderlands region during the last glacial

Modelling and experimental study on β-phase depletion behaviour of HVOF sprayed free-standing CoNiCrA1Y coatings during oxidation

This paper investigates the β-phase depletion behaviour during oxidation of free-standing CoNiCrA1Y (Co-31.7%Ni-20.8%Cr-8.1%A1-0.5%Y, all in wt%) bond coats prepared by high velocity oxy-fuel (HVOF) thermal spraying. The microstructure of the coatings was characterised using scanning electron microscopy with energy dispersive X-ray (EDX) analysis and electron backscatter diffraction (EBSD). It comprises a two phase structure of fcc γ-Ni and bcc β-NiA1, with grain sizes varying largely from 0.5 to 2 μm for both phases. Isothermal oxidation tests of the free-standing coatings were carried out at 1100 °C for times up to 250 h. The β phase depletion behaviour at the surface was measured and was also simulated using Thermo-Calc and DICTRA software. An A1 flux function derived from an oxide growth model was employed as the boundary condition in the diffusion model. The diffusion calculations were performed using the TTNi7 thermodynamic database together with the MOB2 mobility database. Reasonable agreement was achieved between the measured and the predicted element concentration and phase fraction profiles after various time periods. Grain boundary diffusion is likely to be important to element diffusion in this HVOF sprayed CoNiCrA1Y coating due to the sub-micron grains

Indo-Pacific Warm Pool convection and ENSO since 1867 derived from Cambodian pine tree cellulose oxygen isotopes

The Indo-Pacific Warm Pool (IPWP) is a major source of heat and moisture to the atmosphere and thus strongly influences the global climate. In this study, we investigate how moisture fluxes from the IPWP influence the stable isotope signature of precipitation over Southeast Asia by analyzing the oxygen isotopic composition (δ^18O) of tree cellulose from southern Cambodia. The cellulose δ^18O record, spanning AD 1867-2006, documents a regular seasonal cycle with an average amplitude of ~4‰ that is primarily controlled by seasonal differences in the isotopic composition of precipitation. Using the outputs from an isotope-enabled atmospheric model, we illustrate how the δ^18O of precipitation at our site is predominantly controlled by the amount of rainout that occurs over the moisture source region, the IPWP. This is verified by strong correlations of our cellulose δ^18O record with instrumental measurements of precipitation and outgoing longwave radiation over the IPWP, suggesting that the cellulose δ^18O could be used to reconstruct the convection intensity over the IPWP. Spectral analysis of the cellulose δ^18O reveals significant peaks at 2-7 years corresponding to ENSO frequencies. The variability of the cellulose δ^18O record on the ENSO band exhibits characteristics that match existing coral δ^18O records from the tropical Pacific, with reduced amplitude of variability in the 1920s through the 1960s, a period of weak ENSO activity

Bulk organic geochemistry of sediments from Puyehue Lake and its watershed (Chile, 40°S) : implications for paleoenvironmental reconstructions

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 294 (2010): 56-71, doi:10.1016/j.palaeo.2009.03.012.Since the last deglaciation, the mid-latitudes of the southern Hemisphere have undergone considerable environmental changes. In order to better understand the response of continental ecosystems to paleoclimate changes in southern South America, we investigated the sedimentary record of Puyehue Lake, located in the western piedmont of the Andes in south-central Chile (40°S). We analyzed the elemental (C, N) and stable isotopic (δ13C, δ15N) composition of the sedimentary organic matter preserved in the lake and its watershed to estimate the relative changes in the sources of sedimentary organic carbon through space and time. The geochemical signature of the aquatic and terrestrial end-members was determined on samples of lake particulate organic matter (N/C: 0.130) and Holocene paleosols (N/C: 0.069), respectively. A simple mixing equation based on the N/C ratio of these end-members was then used to estimate the fraction of terrestrial carbon (ƒT) preserved in the lake sediments. Our approach was validated using surface sediment samples, which show a strong relation between ƒT and distance to the main rivers and to the shore. We further applied this equation to an 11.22 m long sediment core to reconstruct paleoenvironmental changes in Puyehue Lake and its watershed during the last 17.9 kyr. Our data provide evidence for a first warming pulse at 17.3 cal kyr BP, which triggered a rapid increase in lake diatom productivity, lagging the start of a similar increase in sea surface temperature (SST) off Chile by 1500 years. This delay is best explained by the presence of a large glacier in the lake watershed, which delayed the response time of the terrestrial proxies and limited the concomitant expansion of the vegetation in the lake watershed (low ƒT). A second warming pulse at 12.8 cal kyr BP is inferred from an increase in lake productivity and a major expansion of the vegetation in the lake watershed, demonstrating that the Puyehue glacier had considerably retreated from the watershed. This second warming pulse is synchronous with a 2°C increase in SST off the coast of Chile, and its timing corresponds to the beginning of the Younger Dryas Chronozone. These results contribute to the mounting evidence that the climate in the mid-latitudes of the southern Hemisphere was warming during the Younger Dryas Chronozone, in agreement with the bipolar see-saw hypothesis.This research was partly supported by the Belgian OSTC project EV/12/10B "A continuous Holocene record of ENSO variability in southern Chile". S.B. is supported by a BAEF fellowship (Belgian American Educational Foundation), and by an EU Marie Curie Outgoing Fellowship under the FP6 programme