Stable carbon and oxygen isotope rates of Maastrichtian ODP samples from Shatsky Rise

We present new isotopic and micropaleontological data from a depth transect on Shatsky Rise that record the response of the tropical Pacific to global biotic and oceanographic shifts during the mid-Maastrichtian. Results reveal a coupling between the upper ocean, characterized by a weak thermocline and low to intermediate productivity, and intermediate waters. During the earliest Maastrichtian, oxygen and neodymium isotope data suggest a significant contribution of relatively warm intermediate water from the North Pacific. Isotopic shifts through the early Maastrichtian suggest that this warmer water mass was gradually replaced by cooler waters originating in the Southern Ocean. Although the cooler water mass remained dominant through the remainder of the Maastrichtian, it was displaced intermittently at shallow intermediate depths by North Pacific intermediate water. The globally recognized "mid-Maastrichtian event" ~69 Ma, manifested by the brief appearance of abundant inoceramid bivalves over shallow portions of Shatsky Rise, is characterized by an abrupt increase (~2°-3°C) in sea surface temperatures, a greater flux of organic matter out of the surface ocean, and warmer (~4°C) intermediate waters. Results implicate simultaneous changes in surface waters and the sources/distribution patterns of intermediate water masses as an underlying cause for widespread biotic and oceanographic changes during mid-Maastrichtian time.

(Table 1) Magnetic susceptibility, lithologic composition and stable isotope record for ODP Hole 132-810C

Site 810 was drilled atop Shatsky Rise during Ocean Drilling Program (ODP) Leg 132. The principal objective at Site 810 was to drill interbedded cherts and chalks of Mesozoic age using the diamond coring system (DCS). The objective was not achieved because of difficulties in setting up the reentry cone on the seafloor; however, a shortened section of Cretaceous-Cenozoic nannofossil ooze was recovered with the advanced piston corer (APC). Although the section is interrupted by hiatuses, the upper 50 m carry detailed information relating to biogenic productivity, water chemistry, and eolian input during the Pliocene and Pleistocene. Four holes were drilled at Site 810. Hole 810A consists of a single mud-line core for an ongoing ODP geriatric study. The second hole (Hole 810B) was washed to 60 mbsf (without core recovery) to provide information required for setting the 16-in. casing attached to the reentry cone. Hole 810C penetrated 136.1 mbsf, mostly with the APC, with a total recovery of 143.81 m of nannofossil ooze. A reentry cone was placed over Hole 810D but no casing was successfully suspended in the hole and no sediment was cored. This data report presents the results of shore-based high-resolution analyses of carbonate and oxygen isotopic variations in the upper 50 m of the section at Site 810 and compares these variations with the shipboard determinations of magnetic susceptibility and GRAPE bulk density from the multisensor track.

Stable carbon and oxygen isotope ratios of foraminifera from Cretaceous and Paleocene sediments

Detailed analysis of over 200 samples of uppermost Cretaceous and Paleocene sediments from Atlantic Ocean DSDP Sites 384, 86, 95, 152, 144, 20C, 21, 356, 357, and 329 provides new information on the temperature stratification of Paleocene planktonic foraminifera, the temperature and carbon isotopic changes across the Cretaceous/Tertiary boundary, and the fluctuating temperature and carbon isotopic records through the Paleocene ~64.5-54 m.y.). There was a significant temperature rise across the Cretaceous/Tertiary boundary both at the surface and in deep waters of the Atlantic Ocean. This temperature rise occurred before the basal Tertiary 'Globigerina' eugubina Zone, so that in the oldest Paleocene sample yet analyzed from the deep sea (Site 356) temperatures are already three degrees higher at the bottom and at the surface than in the Cretaceous. The temperature rise across the boundaryis more pronounced on the bottom and in samples from higher latitudes. Accompanying the temperature rise across the boundary there is a significant shift in the carbon isotope profile. In the basal Paleocene the foraminifera of the surface zone demonstrate very negative carbon isotope values (unlike in the Cretaceous of today's ocean), while deeper dwelling species have more positive values which then decrease to the bottom. The unusual carbon isotope gradients persist through the first three million years of the Paleocene until towards the top of planktonic foraminiferal Zone P.1 (G. trinidadensis Zone) the foraminifera record a profile more positive at the surface and decreasing towards the bottom (as in today's ocean). During the Paleocene there are two noteworthy rises in surface water temperature; the first around 62-61 m.y. (G. trinidadensis Zone), and the second near the base of the Globorotalia angulata Zone, 60-59 m.y. At this time surface temperatures at low to mid latitudes reached values near 25°C, while at mid-latitude Site 384 temperature highs near 22°C were registered. At a sample spacing of around one per million years, we have only produced some of the detail of these temperature fluctuations. The later Paleocene is generally cooler and there do not seem to be any large variations either through time or latitude. Middle-latitude sites average temperatures near 15°C at the surface, while high lower latitude site temperatures range near 18°C. The most salient feature of the bottom temperature record (based on multispecific samples) through the Paleocene is its lack of fluctuations. There is an overall temperature range of 5°C at these intermediate depth sites (paleodepth estimates between 1500 and 3000 m). Higher values near 13°C accompany the surface temperature peaks around 62 and 60 m.y., while low values near 8°C occur in Zone P.2 (61-60 m.y.). We detected no change in bottom temperature across the paleocene/Eocene boundary in the few samples studied so far. While there are several fluctuations in the carbon isotope values through the early Paleocene, the general trend is one of increasingly positive values at the surface and at depth. This trend culminates in the late Paleocene (upper Zone P.4, about 56-57 m.y.) with a major excursion in the carbon isotope values. At low latitudes the range between the surface and the deepest planktonic foraminifera is a delta13C of 4 per mil as compared with a range of 2 per mil today. The carbon values drop off slightly, but remain strongly positive through the remainder of the Paleocene at most sites. Accompanying the carbon isotope excursion at Site 384 is a productivity increase and a proposed rise in the CCD.

Susceptibility, d13C and Iron of Site 171-1051

Current models of the global carbon cycle lack natural mechanisms to explain known large, transient shifts in past records of the stable carbon-isotope ratio (delta13C) of carbon reservoirs. The injection into the atmosphere of ~1,200-2,000 gigatons of carbon, as methane from the decomposition of sedimentary methane hydrates, has been proposed to explain a delta13C anomaly associated with high-latitude warming and changes in marine and terrestrial biota near the Palaeocene-Eocene boundary, about 55 million years ago. These events may thus be considered as a natural 'experiment' on the effects of transient greenhouse warming. Here we use physical, chemical and spectral analyses of a sediment core from the western North Atlantic Ocean to show that two-thirds of the carbon-isotope anomaly occurred within no more than a few thousand years, indicating that carbon was catastrophically released into the ocean and atmosphere. Both the delta13C anomaly and biotic changes began between 54.93 and 54.98 million years ago, and are synchronous in oceans and on land. The longevity of the delta13C anomaly suggests that the residence time of carbon in the Palaeocene global carbon cycle was ~120 thousand years, which is similar to the modelled response after a massive input of methane. Our results suggest that large natural perturbations to the global carbon cycle have occurred in the past-probably by abrupt failure of sedimentary carbon reservoirs-at rates that are similar to those induced today by human activity.

Isotope analysis and heat flow measurements of Maria S. Merian cruise MSM21/4 on the western Svalbard margin

Methane hydrate is an ice-like substance that is stable at high-pressure and low temperature in continental margin sediments. Since the discovery of a large number of gas flares at the landward termination of the gas hydrate stability zone off Svalbard, there has been concern that warming bottom waters have started to dissociate large amounts of gas hydrate and that the resulting methane release may possibly accelerate global warming. Here, we can corroborate that hydrates play a role in the observed seepage of gas, but we present evidence that seepage off Svalbard has been ongoing for at least three thousand years and that seasonal fluctuations of 1-2°C in the bottom-water temperature cause periodic gas hydrate formation and dissociation, which focus seepage at the observed sites.

Öate Cretaceous to early Paleogene nutrient and paleoproductivity records of ODP Leg 171 sites

We evaluate phosphorus (P) and biogenic barium (bio-Ba) as nutrient burial and export productivity indicators for the Late Cretaceous and early Paleogene, combining these with calcium carbonate (CaCO3), organic carbon (C), and bulk CaCO3 C isotopes (d13C). Sample ages span 36-71 Ma (~1 sample/0.5 m.y.) for a depth transect of sites in the western North Atlantic (Blake Nose, Ocean Drilling Program Leg 171B, Sites 1052, 1051, and 1050). We use a multitracer approach including redox conditions to investigate export productivity surrounding the global Paleocene d13C maximum (~57 Ma). Reducing conditions render most of the bio-Ba record not useful for export productivity interpretations. P and organic C records indicate that regional nutrient and organic C burial were high at ~61 and ~69 Ma, and low during the Paleocene d13C maximum, a time of proposed global high relative organic C burial. Observed organic C burial changes at Blake Nose cannot explain this C isotope excursion.

Age model and chemistry of sediment core STK7 from Steisslinger See

Stable isotope records for carbon and oxygen in bulk carbonates, carbon in bulk organic matter, and for total and chromium-reducible sulfur in a lacustrine sediment core from Lake Steisslingen (Southwest Germany) show several distinct and abrupt shifts during the last 15,000 years. Variations in the isotopic composition of authigenic carbonates indicate two major phases in the lake history. In the pre-Holocene, the hydrological budget of the lake was apparently stable. Variations of delta18O values of authigenic carbonates were, therefore, dominantly controlled by temperature changes. A decrease in the delta18Ocarb values of about 2 per mil at the Allerød/Younger Dryas transition is interpreted as a drop in mean annual air temperatures of approximately 5°C. An abrupt temperature increase of a similar magnitude is inferred at the Younger Dryas/Preboreal boundary. Throughout most of the Holocene, the isotopic composition of authigenic carbonates was influenced by marked changes in the hydrological budget of the lake. A major positive excursion in the delta13Ccarb and delta18Ocarb values at the beginning of the Atlantic and a smaller one in the Preboreal were related to evaporation effects, which indicate that dry climatic conditions must have prevailed at that time. A simultaneous increase in delta13C values of bulk organic matter at the beginning of the Atlantic suggests a high level of productivity in the lake. As a consequence, aqueous sulfate became limited as indicated by variations in the delta34S values of total and chromium-reducible sedimentary sulfur. Therefore, we conclude that the beginning of the Atlantic was characterized not only by dry but also by warm climatic conditions, which triggered a higher productivity in the lake. In the Subatlantic sediments, large variations in carbon, oxygen, and sulfur isotope ratios were observed as a result of human activities, causing considerable perturbations in the biogeochemical element cycling of Lake Steisslingen. Results obtained by the study of the continuous 15 ka record of Lake Steisslingen document clearly that isotopic proxy data from lacustrine sediments can provide useful information on environmental and climatic changes of local, regional, and in the case of the Younger Dryas event, of even hemispherical significance.

Carbon and oxygen isotope ratios of Selinde River, southeastern Siberian platform

Carbon isotopic data from the Selinde section in the southeastern part of the Siberian platform area are correlated with the reference isotopic profile from the Lower Cambrian stratotype sections of the Lena Aldan region, but also show additional d13C excursions unrecognized there. The chemostratigraphic correlation suggests that the geological and fossil record of the lower Pestrotsvet Formation in the Selinde section has a deeper history than the stratotype region. This conclusion is important for both constraining the age of the earliest Cambrian marine transgression on the Siberian platform and providing a clearer understanding of the pace and order of early Cambrian geochemical and biological events.

Stable carbon isotope ratios and accumulation rates of organic carbon and nutrients of DSDP Hole 79-545 (Appendix A)

Future warming is predicted to shift the Earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming. This study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world ~112 Myr ago. Our study focuses on the Cretaceous Oceanic Anoxic Event (OAE) 1b and explores how the Earth system responded to a moderate ~25,000 yr lasting climate perturbation that is modelled to be less than 1 °C in global average temperature. Using a new chronological model for OAE 1b we present high-resolution elemental and bulk carbon isotope records from DSDP Site 545 from Mazagan Plateau off NW Africa and combine this information with a coupled atmosphere-land-ocean model. The simulations suggest that a perturbation at the onset of OAE 1b caused almost instantaneous warming of the atmosphere on the order of 0.3 °C followed by a longer (~45,000 yr) period of ~0.8 °C cooling. The marine records from DSDP Site 545 support that these moderate swings in global climate had immediate consequences for African continental supply of mineral matter and nutrients (phosphorous), subsequent oxygen availability, and organic carbon burial in the eastern subtropical Atlantic, however, without turning the ocean anoxic. The match between modelling results and stratigraphic isotopic data support previous studies [summarized in Jenkyns 2003, doi:10.1098/rsta.2003.1240] in that methane emission from marine hydrates, albeit moderate in dimension, may have been the trigger for OAE 1b, though we can not finally rule out alternative mechanisms. Following the hydrate mechanism a total of 1.15 * 10**18 g methane carbon (delta13C=-60 ?), equivalent to about 10% to the total modern gas hydrate inventory, generated the delta13Ccarb profile recorded in the section. Modelling suggests a combination of moderate-scale methane pulses supplemented by continuous methane emission at elevated levels over ~25,000 yr. The proposed mechanism, though difficult to finally confirm in the geological past, is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously. This study shows that, once set-off, this mechanism can maintain Earth's climate in a perturbed mode over geological time leading to pronounced changes in regional climate.

The influence of temperature and seawater carbonate saturation state on 13C-18O bond ordering in bivalve mollusks

The shells of marine mollusks are widely used archives of past climate and ocean chemistry. Whilst the measurement of mollusk delta 18O to develop records of past climate change is a commonly used approach, it has proven challenging to develop reliable independent paleothermometers that can be used to deconvolve the contributions of temperature and fluid composition on molluscan oxygen isotope compositions. Here we investigate the temperature dependence of 13C-18O bond abundance, denoted by the measured parameter Delta 47, in shell carbonates of bivalve mollusks and assess its potential to be a useful paleothermometer. We report measurements on cultured specimens spanning a range in water temperatures of 5 to 25 °C, and field collected specimens spanning a range of -1 to 29 °C. In addition we investigate the potential influence of carbonate saturation state on bivalve stable isotope compositions by making measurements on both calcitic and aragonitic specimens that have been cultured in seawater that is either supersaturated or undersaturated with respect to aragonite. We find a robust relationship between Delta 47 and growth temperature. We also find that the slope of a linear regression through all the Delta 47 data for bivalves plotted against seawater temperature is significantly shallower than previously published inorganic and biogenic carbonate calibration studies produced in our laboratory and go on to discuss the possible sources of this difference. We find that changing seawater saturation state does not have significant effect on the Delta 47 of bivalve shell carbonate in two taxa that we examined, and we do not observe significant differences between Delta 47-temperature relationships between calcitic and aragonitic taxa.