Acid treatment biasing to C/N, δ13C and δ15N of organic matter: A Molecular insight

(DIPPI-C) - Development of Isotopic Proxies for Palaeoenvironmental Interpretation: a Carbon PerspectiveIt is known that acid treatment methods employed to remove inorganic carbon (IC) from sample material prior to analysis for C/N, δ13C and δ15N cause non-linear, unpredictable biasing to the organic matter (OM) fraction. Consequently, measured C/N, δ13C and δ15N have an uncertainty much greater than instrument precision: uncertainties for C/N are reported in the range of 1 – 100, for δ13C in the range of 0.2 – 6.8 ‰ and for δ15N in the range of 0.2 – 1.5 ‰, in both modern and palaeo environmental materials. Brodie et al (2011) extended this investigation to a down-core lake sedimentary archive (Lake Tianyang, South China) and noted the potential for uncertainties to preclude “common” interpretations of the data (e.g., C/N values a s a n OM p rovenance tool; δ 13C as a proxy for changes in C3 and C4 vegetation). It is evident that the size of uncertainty between sample horizons varies considerably implying a differential relative reaction to acid treatment down-core (i.e., as the type, relative amount and physical state of organic and inorganic components change). We are now investigating this biasing at the molecular level by employing 13C-NMR and GCIRMS techniques on a suite of modern and palaeo environmental materials and on a lake sedimentary archive. This will provide an important insight into the effect of acid treatment on organic compounds (i.e. removal from the sample, breakdown of compounds and partial removal) and associated isotopic fractionation. From an improved understanding of the type of compounds most susceptible to alteration/removal during the acid treatment processes it will be possible to consider refinements to the acid pre-treatment process and provide information on the relative down-core changes in those compounds susceptible to change (which we may be able to glean environmental information from).postprintThe 1st DIPPI-C Workshop, Durham, UK., 8-10 May 2012. In Abstract Bok of the 1st DIPPI-C Workshop, 2012, p. 1

Acid treatment biasing to C/N, ð13C and ð15N of organic matter: a molecular insight

Session: Modern Insights into the Paleo-carbon Cycle: d13C and a Biomarker Perspective III Posters: abstract B21E-0301Section: BiogeosciencesIt is known that acid treatment methods employed to remove inorganic carbon (IC) from sample material prior to analysis for C/N, δ13C and δ15N cause non-linear, unpredictable biasing to the organic matter (OM) fraction [1, 2, 3]. Consequently, measured C/N, δ13C and δ15N have an uncertainty much greater than instrument precision with biases for C/N reported in the range of 1 - 100, for δ13C in the range of 0.2 - 6.8 ‰ and for δ15N in the range of 0.2 - 1.5 ‰ [1, 2, 3], in both modern and palaeo environmental materials. Brodie et al [3] extended this investigation to a down-core lake sedimentary archive (Lake Tianyang, South China) and noted the potential for this biasing to preclude “common” interpretations of the data (e.g., C/N values as an OM prov...link_to_OA_fulltex

Late glacial initiation of Holocene eastern Mediterranean sapropel formation

Recurrent deposition of organic-rich sediment layers (sapropels) in the eastern Mediterranean Sea is caused by complex interactions between climatic and biogeochemical processes. Disentangling these influences is therefore important for Mediterranean palaeo-studies in particular, and for understanding ocean feedback processes in general. Crucially, sapropels are diagnostic of anoxic deep-water phases, which have been attributed to deep-water stagnation, enhanced biological production or both. Here we use an ocean-biogeochemical model to test the effects of commonly proposed climatic and biogeochemical causes for sapropel S1. Our results indicate that deep-water anoxia requires a long prelude of deep-water stagnation, with no particularly strong eutrophication. The model-derived time frame agrees with foraminiferal δ13C records that imply cessation of deep-water renewal from at least Heinrich event 1 to the early Holocene. The simulated low particulate organic carbon burial flux agrees with pre-sapropel reconstructions. Our results offer a mechanistic explanation of glacial–interglacial influence on sapropel formation

Holocene Climatic Optimum centennial-scale paleoceanography in the NE Aegean (Mediterranean sea)

Combined micropaleontological and geochemical analyses of the high-sedimentation gravity core M-4G provided new centennial-scale paleoceanographic data for sapropel S1 deposition in the NE Aegean Sea during the Holocene Climatic Optimum. Sapropel layer S1a (10.2–8.0 ka) was deposited in dysoxic to oxic bottom waters characterized by a high abundance of benthic foraminiferal species tolerating surface sediment and/or pore water oxygen depletion (e.g., Chilostomella mediterranensis, Globobulimina affinis), and the presence of Uvigerina mediterranea, which thrives in oxic mesotrophic-eutrophic environments. Preservation of organic matter (OM) is inferred based on high organic carbon as well as loliolide and isololiolide contents, while the biomarker record and the abundances of eutrophic planktonic foraminifera document enhanced productivity. High inputs of terrigenous OM are attributed to north Aegean borderland riverine inputs. Both alkenone-based sea surface temperatures (SSTs) and δO18G. bulloides records indicate cooling at 8.2 ka (S1a) and ~7.8 ka (S1 interruption). Sapropelic layer S1b (7.7–6.4 ka) is characterized by rather oxic conditions; abundances of foraminiferal species tolerant to oxygen depletion are very low compared with the U. mediterranea rise. Strongly fluctuating SSTs demonstrate repeated cooling and associated dense water formation, with a major event at 7.4 ka followed by cold spells at 7.0, 6.8, and 6.5 ka. The prominent rise of the carbon preference index within the S1b layer indicates the delivery of less degraded terrestrial OM. The increase of algal biomarkers, labile OM-feeding foraminifera and eutrophic planktonic species pinpoints an enhanced in situ marine productivity, promoted by more efficient vertical convection due to repeated cold events. The associated contributions of labile marine OM along with fresher terrestrial OM inputs after ~7.7 ka imply sources alternative/additional to the north Aegean riverine borderland sources for the influx of organic matter in the south Limnos Basin, plausibly related to the inflow of highly productive Marmara/Black Sea waters

Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean sapropel

Organic-rich sedimentary units called sapropels have formed repeatedly in the eastern Mediterranean Sea, in response to variations of solar radiation. Sapropel formation is due to a change either in the flux of organic matter to the sea floor from productivity changes or in preservation by bottom-water oxygen levels. However, the relative importance of surface-ocean productivity versus deep-water preservation for the formation of these organic-rich shale beds is still being debated, and conflicting interpretations are often invoked1, 2, 3, 4, 5, 6, 7. Here we analyse at high resolution the differences in the composition of the most recent sapropel, S1, in a suite of cores covering the entire eastern Mediterranean basin. We demonstrate that during the 4,000 years of sapropel formation, surface-water salinity was reduced and the deep eastern Mediterranean Sea, below 1,800 m depth, was devoid of oxygen. This resulted in the preferential basin-wide preservation of sapropel S1 with different characteristics above and below 1,800 m depth as a result of different redox conditions. We conclude that climate-induced stratification of the ocean may therefore contribute to enhanced preservation of organic matter in sapropels and potentially also in black shales.<br/

Sea-level and deep-sea-temperature variability over the past 5.3 million years

Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ18O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0–1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature

Evidence for warm and humid Mid-Holocene in the Aegean and northern Levantine seas (Greece, NE Mediterranean).

International audienc

Bipolar seesaw control on last interglacial sea level

Our current understanding of ocean–atmosphere–cryosphere interactions at ice-age terminations relies largely on assessments of the most recent (last) glacial–interglacial transition1, 2, 3, Termination I (T-I). But the extent to which T-I is representative of previous terminations remains unclear. Testing the consistency of termination processes requires comparison of time series of critical climate parameters with detailed absolute and relative age control. However, such age control has been lacking for even the penultimate glacial termination (T-II), which culminated in a sea-level highstand during the last interglacial period that was several metres above present4. Here we show that Heinrich Stadial 11 (HS11), a prominent North Atlantic cold episode5, 6, occurred between 135 ± 1 and 130 ± 2 thousand years ago and was linked with rapid sea-level rise during T-II. Our conclusions are based on new and existing6, 7, 8, 9 data for T-II and the last interglacial that we collate onto a single, radiometrically constrained chronology. The HS11 cold episode5, 6 punctuated T-II and coincided directly with a major deglacial meltwater pulse, which predominantly entered the North Atlantic Ocean and accounted for about 70 per cent of the glacial–interglacial sea-level rise8, 9. We conclude that, possibly in response to stronger insolation and CO2 forcing earlier in T-II, the relationship between climate and ice-volume changes differed fundamentally from that of T-I. In T-I, the major sea-level rise clearly post-dates3, 10, 11 Heinrich Stadial 1. We also find that HS11 coincided with sustained Antarctic warming, probably through a bipolar seesaw temperature response12, and propose that this heat gain at high southern latitudes promoted Antarctic ice-sheet melting that fuelled the last interglacial sea-level peak