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Ratios of glycerol dialkyl glycerol tetraethers (GDGT), which are membrane lipids of bacteria and archaea, are at the base of several paleoenvironmental proxies. They are frequently applied to soils as well as lake- and marine sediments to generate records of past temperature and soil pH. To derive meaningful environmental information from these reconstructions, high analytical reproducibility is required. Based on submitted results by 39 laboratories from across the world, which employ a diverse range of analytical and quantification methods, we explored the reproducibility of brGDGT-based proxies (MBT′5ME, IR, and #ringstetra) measured on four soil samples and four soil lipid extracts. Correct identification and integration of 5- and 6-methyl brGDGTs is a prerequisite for the robust calculation of proxy values, but this can be challenging as indicated by the large inter-interlaboratory variation. The exclusion of statistical outliers improves the reproducibility, where the remaining uncertainty translates into a temperature offset from median proxy values of 0.3–0.9°C and a pH offset of 0.05–0.3. There is no apparent systematic impact of the extraction method and sample preparation steps on the brGDGT ratios. Although reported GDGT concentrations are generally consistent within laboratories, they vary greatly between laboratories. This large variability in brGDGT quantification may relate to variations in ionization efficiency or specific mass spectrometer settings possibly impacting the response of brGDGTs masses relative to that of the internal standard used. While ratio values of GDGT are generally comparable, quantities can currently not be compared between laboratories.

Human activities have increasingly changed terrestrial particulate organic carbon (POC) export to the coastal ocean since the Industrial Age (19th century). However, the influence of human perturbations on the composition and flux of terrestrial biospheric and petrogenic POC sub-pools remains poorly constrained. Here, we examined 13C and 14C compositions of bulk POC and source-specific biomarkers (fatty acids, FA) from two nearshore sediment cores collected in the Pearl River-derived mudbelt, to determine the impacts of human perturbations of the Pearl River watershed on the burial of terrestrial POC in the coastal ocean over the last century. Our results show that although agricultural practices and deforestation during the 1930s–1950s increased C4 plant coverage in the watershed, the export fluxes of terrestrial biospheric and petrogenic POC remained rather unchanged; however, added perturbations since 1974, including increasing coal consumption, embankment and dam constructions caused massive export of both petrogenic POC and relatively fresh terrestrial biospheric POC from the river delta. Our data reveal that human activities substantially enhance the transfer of petrogenic POC and fresh biospheric POC to the coastal ocean after ca. 1974, with the latter process acting as an important sink for anthropogenic CO2.

There is still a paucity of hydrological data explaining the relationship between (rapid, millennial-scale) climate forcing and Mediterranean rainfall since the Last Glacial. We show that distinct lake-level fluctuations at Lake Trasimeno (Italy) are associated with changing aridity in the central Mediterranean during the last similar to 47 800 years. The lake-level fluctuations are reconstructed based on carbonate mineral content and carbonate mineral species, as well as the stable oxygen and carbon isotope (delta O-18 and delta C-13) geochemistry of endogenic carbonates. Low lake levels are linked to high carbonate, Mg-calcite and aragonite contents, and high delta O-18 and delta C-13 values. Inferred hydrological changes are linked to glacial-interglacial and, tentatively within the limitations of our chronology, to millennial-scale climate variability as well as the intensity of the Atlantic Meridional Overturning Circulation (AMOC). Prior to the Last Glacial Maximum (LGM), during intervals equivalent to Marine Isotope Stage 3 (MIS 3), a stronger AMOC associated with Greenland interstadial periods (Dansgaard/Oeschger (D/O) warm periods) and stronger Asian monsoon probably coincide with increased precipitation in central Italy as inferred from high lake levels at Lake Trasimeno. Periods of weak AMOC intensity such as during Greenland stadials (D/O cold periods), during Heinrich events, and weak Asian monsoons are correlated with lake level lowstands, which imply relatively dry conditions in central Italy. Lake Trasimeno's water level during the LGM and the Lateglacial (MIS 2) is relatively stable, with recorded changes showing distinct similarities to orbital configurations. Although muted, high latitude climate forcing is still evident in the data during peak glacial conditions. The transition from D/O-like hydrological variability at Lake Trasimeno during MIS 3 to orbitally controlled fluctuations during the Lateglacial to Holocene transition coincides with an

Redox gradients in oceanic oxygen minimum zones are hotspots of diverse bacterial populations and metabo-lisms. Here, we test whether bacteriohopanepolyols (BHPs), a suite of membrane-regulating pentacyclic tri-terpenoid lipids, are suitable tracers of major bacterial metabolisms and whether their structural diversity (BHP lipidomics) allows tracing the bacterial ecology across the Black Sea chemocline. We analyzed suspended par-ticulate matter (SPM) sampled along depth-profiles across the redox/chemocline at two sites in the eastern and western gyres and underlying core-top sediments at the western gyre site. Our results show that BHPs abun-dances reflect the stratification of the Black Sea and capture ecological niches across the chemocline, being highest in the lower suboxic zone and in upper to deep sulfidic waters. BHP-inferred bacterial metabolisms in the lower suboxic zone are dominated by anammox and aerobic methane oxidizers (primarily by Type I/gammap-roteobacteria). Bacterial biomass production in the upper to deep sulfidic zone is mirrored by a range of BHPs that are normally associated with aerobic metabolisms, most likely explained by either survival in oxygenated micro-niches or production by anaerobic bacteria (which could possibly include sulfate reducers and nitrite -dependent methane oxidizers). Most surprisingly, this ecological niche harbors seemingly unknown anaerobic bacteria which produce abundant C-2 and C-3 methylated BHPs. Core-top sediments reflect the BHP structural diversity found in SPM, but with notable compositional differences. Most strikingly, the export dynamics seem to result in near-absence of C-2 methylated BHPs in surface sediments. Sedimentary BHP distributions therefore underestimate the importance of C-2 methylated BHPs in the water column, which has implications for the geological record.

In this review we look back on 30+ years of bacteriohopanepolyol (BHP) research within the field of organic geochemistry. BHPs are ubiquitous, intact polar lipids in modern environments. They have been found in lacustrine, marine, riverine and soil and peat environments, and they are noteworthy lipids in biological symbiont studies. BHPs are the precursors of hopanoids, which are the most abundant fossil lipids found in the geological record. BHPs are synthesized by members of various bacterial taxa, and their distributions are often used to help to identify bacterial communities, in studies of both modern and past environments. However, less than 10% of known bacterial species are genetically capable of synthesizing BHPs, and many BHPs are not specific to particular bacterial sources. Nonetheless, a range of BHPs with specific side chain configurations and/ or A-ring modifications have proven very useful for tracing bacterial metabolism and for identifying ecological niches in various environments (e.g., aerobic methanotrophy, possibly nitrite-dependent intra-aerobic methanotrophy, and anaerobic ammonium oxidation) or for tracing environmental processes (e.g., soil inputs into aquatic settings). Moreover, BHPs (with previously unknown terminal groups and side chain configurations) are continuously being discovered, thanks to recent methodological and instrumental advances. These highlight the advent of a new era of BHP lipidomics which awaits full exploitation in organic geochemistry. Here, we provide a summary of the state-of-the-art of BHP knowledge, analytical frontiers, and suggest directions for future research.

In a warming climate, thawing permafrost soils in the circumpolar Arctic region are subject to enhanced microbial turnover as well as mass mobilization and other erosion processes. High-Arctic settings such as Svalbard are exceptionally vulnerable to these effects, but the presence of coal deposits obscures the organic carbon (OC) signature of permafrost OC, particularly its carbon isotope composition, when studying OC turnover and export. Here, we analyze the compound-specific δ13C and Δ14C isotopic composition of alkanoic acids from permafrost soils and river and fjord sediments to assess soil turnover in the catchment of the Bayelva River near Ny-Ålesund and trace transport and re-burial of permafrost OC into the adjacent Kongsfjord. Our data confirm the influence of coal-derived OC on δ13C and Δ14C values of bulk soil and sedimentary OC, while alkanoic acid δ13C and Δ14C values are less affected by coal contributions. Alkanoic acid Δ14C values in the soil profile imply long–term residence in soils prior to deposition in river and fjord sediments, that is, multi-millennial turnover that is significantly slower than reported from other environments. Strongly 14C-depleted vascular plant-derived long-chain alkanoic acids can be found in Bayelva River and Kongsfjord sediments revealing substantial input of deep active layer/permafrost OC, particularly in the Bayelva River and off its river mouth. In the central Kongsfjord, long-chain alkanoic acid Δ14C values are higher either reflecting input from other permafrost areas or physical effects resulting, for example, from deposition in settings with different accumulation rates or from sediment sorting.

Marine oxygen minimum zones play a crucial role in the global oceanic carbon, nitrogen, and sulfur cycles as they harbor microbial communities that are adapted to the water column chemistry and redox zonation, and in turn control the water column chemistry and greenhouse gas release. These micro-organisms have metabolisms that rely on terminal electron acceptors other than O-2 and often benefit from syntrophic relationships (metabolic coupling). Here, we study chemo(auto)trophy along the redoxcline in two stratified fjords on Vancouver Island (Canada) using bacterial bacteriohopanepolyols and archaeal ether lipids. We analyze the distribution of these lipid classes in suspended particulate matter (SPM) to trace ammonia oxidation, anaerobic ammonium oxidation (anammox), sulfate reduction/sulfur oxidation, methanogenesis, and methane oxidation, and investigate ecological niches to evaluate potential links between their respective bacterial and archaeal sources. Our results show an unparalleled BHP and ether lipid structural diversity that allows tracing the major redox-driven metabolic processes at the time of sampling: Both fjords are dominated by archaeal ammonia oxidation and anammox; sulfate-reducing bacteria may be present in Deer Bay, but absent from Effingham Inlet; methanogenic Euryarchaeota and archaeal and bacterial methanotrophs are detectable at low abundance. Correlation analysis reveals distinct biomarker clusters that provide constraints on the biogeochemical niches of some orphan BHP and ether lipids such as in situ-produced adenosyl-BHPs or unsaturated archaeols.

Loess-paleosol sequences (LPSs) are important terrestrial archives of paleoenvironmental and paleoclimatic information. One of the main obstacles for the investigation and interpretation of these archives is the uncertainty of their age-depth relationship. In this study, four different dating techniques were applied to the Late Pleistocene to Holocene LPS Balta Alba Kurgan (Romania) in order to achieve a robust chronology. Luminescence dating includes analysis of different grain-size fractions of both quartz and potassium feldspar and the best results are obtained using fine-grained quartz blue-stimulated and polymineral post-infrared infrared-stimulated luminescence measurements. Radiocarbon (C-14) dating is based on the analysis of bulk organic carbon (OC) and compound-specific radiocarbon analysis (CSRA). Bulk OC and leaf wax-derived n-alkane C-14 ages provide reliable age constraints for the past c. 25-27 kyr. CSRA reveals post-depositional incorporation of roots and microbial OC into the LPS limiting the applicability of C-14 dating in older parts of the sequence. Magnetic stratigraphy data reveal good correlation of magnetic susceptibility and the relative paleointensity of the Earth's magnetic field with one another as well as reference records and regional data. In contrast, the application of paleomagnetic secular variation stratigraphy is limited by a lack of regional reference data. The identification of the Campanian Ignimbrite/Y-5 tephra layer in the outcrop provides an independent time marker against which results from the other dating methods have been tested. The most accurate age constraints from each method are used for two Bayesian age-depth modeling approaches. The systematic comparison of the individual results exemplifies the advantages and disadvantages of the respective methods. Taken as a whole, the two age-depth models agree very well, our study also demonstrates that the multi-method approach can improve the accuracy and precision of datin

Sedimentary high molecular weight (HMW) n-alkyl lipids derived from the waxes of terrestrial plants are common target compounds in biogeochemical and paleoenvironmental research. These plant waxes derive predominantly from the epicuticular cover of vascular plant leaves and their relative and absolute abundances and stable isotopic composition can be used as proxies to decipher, e.g., continental climate and land-ocean carbon transfer processes. In marine sediments, however, compound-specific radiocarbon analysis has revealed that plant waxes are often not syn-depositional, but instead are substantially C-14-depleted ('pre-aged') upon deposition. This C-14-depletion can be caused by various processes that either promote retention of plant waxes during transport from source to sink such as storage in soils or entrainment in deposition-resuspension loops in rivers and on continental shelves or, alternatively, by processes that add HMW n-alkyl lipids from other sources (e.g., petrogenic inputs). Here, we review the intrinsic and extrinsic processes affecting the sedimentary plant wax C-14 composition (ranging from chemical processes to continental-scale environmental conditions), how plant wax C-14 compositions translate into mean ages, and which processes control plant wax mean ages in marine sediments. Finally, we use a compilation of available and new compound-specific plant wax C-14 data to provide a synthesis and evaluate the major controls on plant wax mean ages in marine sediments at the global scale. (C) 2021 Elsevier Ltd. All rights reserved.

Fjords are recognized as hotspots of organic carbon (OC) burial in the coastal ocean. In fjords with glaciated catchments, glacier discharge carries large amounts of suspended matter. This sedimentary load includes OC from bedrock and terrigenous sources (modern vegetation, peat, soil deposits), which is either buried in the fjord or remineralized during export, acting as a potential source of CO2 to the atmosphere. In sub-Antarctic South Georgia, fjord-terminating glaciers have been retreating during the past decades, likely as a response to changing climate conditions. We determine sources of OC in surface sediments of Cumberland Bay, South Georgia, using lipid biomarkers and the bulk C-14 isotopic composition, and quantify OC burial at present and for the time period of documented glacier retreat (between 1958 and 2017). Petrogenic OC is the dominant type of OC in proximity to the present-day calving fronts (60.4 +/- 1.4% to 73.8 +/- 2.6%) and decreases to 14.0 +/- 2.7% outside the fjord, indicating that petrogenic OC is effectively buried in the fjord. Beside of marine OC, terrigenous OC comprises 2.7 +/- 0.5% to 7.9 +/- 5.9% and is mostly derived from modern plants and Holocene peat and soil deposits that are eroded along the flanks of the fjord, rather than released by the retreating fjord glaciers. We estimate that the retreat of tidewater glaciers between 1958 and 2017 led to an increase in petrogenic carbon accumulation of 22% in Cumberland West Bay and 6.5% in Cumberland East Bay, suggesting that successive glacier retreat does not only release petrogenic OC into the fjord, but also increases the capacity of OC burial.

Tropical and subtropical rivers deliver large quantities of terrestrial organic carbon (OCterr) to the ocean, acting as a crucial part of the global carbon cycle, but little is known about the timescale and efficiency of its transport to and in the adjacent coastal sea. Here we examined source-specific biomarker (fatty acids, FAs) contents and isotope compositions in surface sediments in an alongshore transect southwestward from the Pearl River mouth. The C28+30, rather than other long-chain saturated FAs, were found to be the most representative for OCterr, and a plant wax mean age of 3060 +/- 90 yr (resulting from protracted storage) was estimated in the Pearl River watershed from the C-14 age of C28+30 FA in a river mouth sample. A compilation of plant wax mean ages in global (sub)tropical river systems including this study suggests that regional differences in climate and morphology may have a limited impact on plant wax mean ages in (sub)tropical regions. A four-source mixing model based on bulk OC and biomarker isotope compositions demonstrated that surface sediments in the Pearl River-derived mudbelt consist of 0.15-0.36 wt.% marine OC, 0.03-0.13 wt.% riverine primary production-derived OC, 0.18-0.49 wt.% soil OC, and 0.07-0.16 wt.% fossil OC. The mean burial efficiency of fossil and soil OC is similar to 85% and 49%, respectively, indicating the refractory nature of fossil OC but a significant loss of soil OC due to remineralization during transport in the marine environment before final burial. Over longer timescales, the OCterr loss experienced during transport may, thus, to some extent reduces the capacity of terrestrial ecosystems (particularly soils) as CO2 sinks. (C) 2021 Elsevier B.V. All rights reserved.

Bacteriohopanepolyols (BHPs) that are commonly associated with soil and peat environments (soil marker BHPs), were analyzed along redox gradients in marine oxygen deficient zones (ODZs). The latter included suspended particulate organic matter (POM) from two fjords on Vancouver Island (Canada) and the Black Sea, as well as sinking POM collected in sediment trap time-series deployed in the Cariaco Basin. Our results show that the so-called soil marker BHPs occur in all ODZ settings. They have distributions that are best explained by in situ chemotrophic production within the chemocline and in anoxic/ euxinic waters, rather than exclusive supply from soils. In particular, adenosylhopane, adenosylhopanetype 2 and 2Me-adenosylhopane-type 2, appear to be produced within a common biogeochemical niche in the water column, irrespective of setting. On the other hand, 2Me-adenosylhopane, adenosylhopanetype 3 and 2Me-adenosylhopane-type 3 may be supplied partly from the continent, as they are also abundant in surface water suspended POM on Vancouver Island and accumulate almost exclusively in the shallower (upper chemocline) trap in the Cariaco Basin. However, their water column suspended POM distributions and time-series sinking POM fluxes also indicate additional chemotrophic sources that have spatially and temporally diverse origins. Our study suggests that caution is warranted when using soil marker BHPs and their associated soil input proxies in ODZ settings, as the diverse microbial community in these settings produces BHP signatures similar to those found in soils. (C) 2020 Elsevier Ltd. All rights reserved.

In a warming climate, thawing permafrost soils in the circumpolar Arctic region are subject to enhanced microbial turnover as well as mass mobilization and other erosion processes. High-Arctic settings such as Svalbard are exceptionally vulnerable to these effects, but the presence of coal deposits obscures the organic carbon (OC) signature of permafrost OC, particularly its carbon isotope composition, when studying OC turnover and export. Here, we analyze the compound-specific delta C-13 and Delta C-14 isotopic composition of alkanoic acids from permafrost soils and river and fjord sediments to assess soil turnover in the catchment of the Bayelva River near Ny-angstrom lesund and trace transport and re-burial of permafrost OC into the adjacent Kongsfjord. Our data confirm the influence of coal-derived OC on delta C-13 and Delta C-14 values of bulk soil and sedimentary OC, while alkanoic acid delta C-13 and Delta C-14 values are less affected by coal contributions. Alkanoic acid Delta C-14 values in the soil profile imply long-term residence in soils prior to deposition in river and fjord sediments, that is, multi-millennial turnover that is significantly slower than reported from other environments. Strongly C-14-depleted vascular plant-derived long-chain alkanoic acids can be found in Bayelva River and Kongsfjord sediments revealing substantial input of deep active layer/permafrost OC, particularly in the Bayelva River and off its river mouth. In the central Kongsfjord, long-chain alkanoic acid Delta C-14 values are higher either reflecting input from other permafrost areas or physical effects resulting, for example, from deposition in settings with different accumulation rates or from sediment sorting.

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 (similar to 3.5 %) organic carbon content of marine sources, the former being deposited during the global Oceanic Anoxic Event (OAE) la, as well as during repetitive intervals before and after OAE la. 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

Advances in sampling tools, analytical methods, and data handling capabilities have been fundamental to the growth of marine organic biogeochemistry over the past four decades. There has always been a strong feedback between analytical advances and scientific advances. However, whereas advances in analytical technology were often the driving force that made possible progress in elucidating the sources and fate of organic matter in the ocean in the first decades of marine organic biogeochemistry, today process-based scientific questions should drive analytical developments. Several paradigm shifts and challenges for the future are related to the intersection between analytical progress and scientific evolution. Untargeted molecular headhunting for its own sake is now being subsumed into process-driven targeted investigations that ask new questions and thus require new analytical capabilities. However, there are still major gaps in characterizing the chemical composition and biochemical behavior of macromolecules, as well as in generating reference standards for relevant types of organic matter. Field-based measurements are now routinely complemented by controlled laboratory experiments and in situ rate measurements of key biogeochemical processes. And finally, the multidisciplinary investigations that are becoming more common generate large and diverse datasets, requiring innovative computational tools to integrate often disparate data sets, including better global coverage and mapping. Here, we compile examples of developments in analytical methods that have enabled transformative scientific advances since 2004, and we project some challenges and opportunities in the near future. We believe that addressing these challenges and capitalizing on these opportunities will ensure continued progress in understanding the cycling of organic carbon in the ocean.

Phospholipid fatty acids (PLFAs) have been used to trace bacterial life in extremely carbon-poor soils of the hyperarid Atacama Desert. However, the low abundances of bacteria and, thus, PLFAs increases the risk of contamination by exogenous PLFAs. Here, we assess whether field sampling strategies (super-clean, clean, and regular sampling protocols) have an effect on PLFA diversity and abundance in hyperarid Atacama soils or whether laboratory processing or true environmental heterogeneity control PLFA inventories. Our results show no exogenous PLFA contribution during sample processing in the lab and statistical analyses (ANOVA, Kruskal-Wallis) reveal that PLFA abundances do not differ significantly between replicate samples (n = 3) taken with the three different sampling strategies. Rather than sampling strategy, our results show that PLFA abundances in the investigated soil replicates rather reflect true environmental heterogeneity of primarily bacterial biomass (in the absence of indigenous fungi), potentially related to small-scale physicochemical differences.

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. (c) 2020 Elsevier B.V. All rights reserved.

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 multi-million 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 tectonic 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 time scales (>1 Myr). The Early Aptian black shale sequence comprises alternations of shales with high (>5%) and relatively low (~3%) organic carbon content of marine sources, the former being deposited during the global Oceanic Anoxic Event (OAE) 1a, as well as during repetitive events before and after OAE 1a. In all cases, these short-term events 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 propose that fluctuations in weathering-derived nutrient input from the southern African continent, linked to fluctuations in pCO2 and/or orbitally driven humidity/aridity, were the underlyi