Description: Highlights • New Early Cretaceous South Atlantic TEX86 samples and climate modelling. • Systematic differences in Cretaceous isoGDGT abundances. • Regional similarities to modern Mediterranean and Red Sea sediments. Regional TEX86-temperature calibration enables model-data congruence for OAE 1a. Abstract The Cretaceous Period (145-66 Ma) provides an opportunity to obtain insights into the adaptation of the climate system to increased atmospheric greenhouse gas concentrations. The organic paleothermometer TEX86 is one of the few proxies available for reconstructing quantitative estimates of upper ocean temperatures of this time period. Here we show that the sedimentary TEX86 signal in the Early Cretaceous North and South Atlantic shows systematic differences to other Cretaceous samples. In particular, the relative increase in the fractional abundances of the crenarchaeol isomer compared to crenarchaeol exhibits similarities with surface sediments from the modern Mediterranean and Red Sea. Dedicated climate model simulations suggest that the formation of warm and saline deep waters in the restricted North and South Atlantic may have influenced TEX86 export dynamics leading to a warm bias in reconstructed upper ocean temperatures. Applying a regional calibration from the modern Mediterranean and Red Sea to corresponding TEX86 data significantly improves the model-data fit for the Aptian Oceanic Anoxic Event 1a and the overall comparison with other temperature proxies for the Early Cretaceous. Our results demonstrate the need to consider regional and temporal changes of the TEX86-temperature relation for the reconstruction of deep-time ocean temperatures.

Description: Extensive black shale deposits formed in the Early Cretaceous South Atlantic, supporting the notion that this emerging ocean basin was a globally important site of organic carbon burial. The magnitude of organic carbon burial in marine basins is known to be controlled by various tectonic, oceanographic, hydrological, and climatic processes acting on different temporal and spatial scales, the nature and relative importance of which are poorly understood for the young South Atlantic. Here we present new bulk and molecular geochemical data from an Aptian–Albian sediment record recovered from the deep Cape Basin at Deep Sea Drilling Project (DSDP) Site 361, which we combine with general circulation model results to identify driving mechanisms of organic carbon burial. A multimillion-year decrease (i.e., Early Aptian–Albian) in organic carbon burial, reflected in a lithological succession of black shale, gray shale, and red beds, was caused by increasing bottom water oxygenation due to abating hydrographic restriction via South Atlantic–Southern Ocean gateways. These results emphasize basin evolution and ocean gateway development as a decisive primary control on enhanced organic carbon preservation in the Cape Basin at geological timescales (〉 1 Myr). The Early Aptian black shale sequence comprises alternations of shales with high (〉 6 %) and relatively low (∼ 3.5 %) organic carbon content of marine sources, the former being deposited during the global Oceanic Anoxic Event (OAE) 1a, as well as during repetitive intervals before and after OAE 1a. In all cases, these short-term intervals of enhanced organic carbon burial coincided with strong influxes of sediments derived from the proximal African continent, indicating closely coupled climate–land–ocean interactions. Supported by our model results, we show that fluctuations in weathering-derived nutrient input from the southern African continent, linked to changes in orbitally driven humidity and aridity, were the underlying drivers of repetitive episodes of enhanced organic carbon burial in the deep Cape Basin. These results suggest that deep marine environments of emerging ocean basins responded sensitively and directly to short-term fluctuations in riverine nutrient fluxes. We explain this relationship using the lack of wide and mature continental shelf seas that could have acted as a barrier or filter for nutrient transfer from the continent into the deep ocean.

Description: Understanding the preservation and deposition history of organic molecules is crucial for the understanding of paleoenvironmental information contained in their abundance ratios such as Uk'37 and TEX86 used as proxies for sea surface temperature (SST). Based on their relatively high refractivity, alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) can survive postdepositional processes like lateral transport, potentially causing inferred SSTs to be misleading. Likewise, selective preservation of alkenones and GDGTs may cause biases of the SST proxies themselves and can lead to decoupling of both proxy records. Here we report compound-specific radiocarbon data of marine biomarkers including alkenones, GDGTs, and low molecular weight (LMW) n-fatty acids from Black Sea sediments deposited under different redox regimes to evaluate the potentially differential preservation of both biomarker classes and its effect on the SST indices Uk'37 and TEX86 . The decadal D14C values of alkenones, GDGTs, and LMW n-fatty acids indicate similar preservation under oxic, suboxic, and anoxic redox regimes and no contribution of pre-aged compounds, e.g., by lateral supply. Moreover, similar 14C concentrations of crenarchaeol, alkenones, and LMW n-fatty acids imply that the thaumarchaeotal GDGTs preserved in these sediments are produced in the euphotic zone rather than in subsurface/thermocline waters. However, we observe biomarker-based SSTs that strongly deviate (deltaSST up to 8.4 °C) from in situ measured mean annual SSTs in the Black Sea. This is not due to redox-dependent differential biomarker preservation as implied by their D14C values and spatial SST pattern. Since contributions from different sources can largely be excluded, the deviation of the Uk'37 and TEX86 proxy-derived SSTs from in situ SSTs requires further study of phylogenetic and other yet unknown environmental controls on alkenone and GDGT lipid distributions in the Black Sea.

Description: The dataset contains compound-specific δ13C and Δ14C isotopic composition of alkanoic acids from permafrost soils and river and fjord sediments the Bayelva catchment and Kongsfjord. These were analyzed in order to determine permafrost OC turnover timescales in the Bayelva catchment, assess export mechanisms along the flow path, and characterize the spatial dispersal and reburial of permafrost OC in Kongsfjord sediments. The sampling strategy was designed to obtain an export transect sample set covering the permafrost soil-river-ocean system. Samples were taken during several land- and ship-based campaigns. In 2007, soil samples from the Bayelva River catchment were collected from the thawed active layer in the northern foreland of the East Brøgger glacier. Leirhaugen (LH) is adjacent to the main stem of the Bayelva River (Boike et al., 2008) and permafrost ground temperatures have been monitored at this site since 1998 (Boike et al., 2018; Roth and Boike, 2001). Additional soil profiles in the catchment were sampled from Kolhaugen (KH), Upper Drainage Area (UDA), and Lower Drainage Area (LDA) as described by Rethemeyer et al. (2010). A sample of coal was also obtained from the catchment. Sediment samples from the Bayelva River (BY-R), its river mouth (WP280), and the central Kongsfjord (Station T) were obtained in 2008 using a shovel (BY-R), push cores operated by divers (WP280) or a hand-operated HAPS corer (Station T). All sediment samples were sliced into 0-1 or 0-2cm segments.

Description: Adenosyl-BHP abundances in Vancouver Island and Black Sea total suspended particulate matter and Cariaco sinking particulate organic matter samples were analyzed to study in situ production in oxygen minimum zones. Water column suspended particulate matter samples were obtained using McLane WTS-LV (standard configuration) in situ filtration systems from Vancouver Island fjords aboard R/V Barnes in 2007 and the Black Sea aboard R/V Knorr (cruise 172/8) in 2003. Sinking particulate organic matter was sampled in sediment traps as part of the CARIACO Ocean Time-Series Program in Cariaco Basin. Adenosyl-BHPs were analyzed in trap A (275 m water depth) and trap B (455 m water depth) for 14-day opening intervals from November 1999 through April 2000 and July 2002 through October 2002.

Description: Bulk sediment samples of core WP280 were dried and homogenized. Samples were measured using a HPGe planar gamma detector in air-tight containers after the radioactive equilibrium between 226Ra (used as supported 210Pb proxy) and its daughter products had been reached. The efficiency calibration was performed by a direct transfer using reference materials with mineral matrix (IAEA-385 Irish Sea sediment and CANMET DL-1a Uranium-Thorium Ore with an addition of 137Cs certified solution) measured in comparable geometries. Downcore activities of 210Pbxs data were determined for the age model of core WP280. 137Cs activity depth profiles were used for validating the age model.

Description: Chloropigments and their derivative pheopigments preserved in sediments can directly be linked to photosynthesis. Their carbon and nitrogen stable isotopic compositions have been shown to be a good recorder of recent and past surface ocean environmental conditions tracing the carbon and nitrogen sources and dominant assimilation processes of the phytoplanktonic community. In this study we report results from combined compound-specific radiocarbon and stable carbon and nitrogen isotope analysis to examine the time-scales of synthesis and fate of chlorophyll-a and its degradation products pheophytin-a, pyropheophytin-a, and 132,173-cyclopheophorbide-a-enol until burial in Black Sea core-top sediments. The pigments are mainly of marine phytoplanktonic origin as implied by their stable isotopic compositions. Pigment ?15N values indicate nitrate as the major uptake substrate but 15N-depletion towards the open marine setting indicates either contribution from N2-fixation or direct uptake of ammonium from deeper waters. Radiocarbon concentrations translate into minimum and maximum pigment ages of approximately 40 to 1200 years. This implies that protective mechanisms against decomposition such as association with minerals, storage in deltaic anoxic environments, or eutrophication-induced hypoxia and light limitation are much more efficient than previously thought. Moreover, seasonal variations of nutrient source, growth period, and habitat and their associated isotopic variability are likely at least as strong as long-term trends. Combined triple isotope analysis of sedimentary chlorophyll and its primary derivatives is a powerful tool to delineate biogeochemical and diagenetic processes in the surface water and sediments, and to assess their precise time-scales.