Search

Core samples recovered from the Transkei Basin (Hole U1581B), offshore South Africa, during IODP Expedition 392 include an expansive record of organic-rich sediments from the Campanian to Paleocene (~74-63 Ma). Investigation of the biomarker composition of this sequence revealed significant amounts of polycyclic aromatic hydrocarbons (PAH) reflecting terrestrial sources of organic matter (OM) coupled with evidence for wildfires. Perylene, derived from diagenetic alteration of terrestrial OM, is the dominant PAH in the Campanian sediments. Other prominent PAH components are tetrahydrochysenes and tetrahydropicenes, which are formed by early-stage diagenetic aromatization, with or without loss of the functionalized A-ring, of triterpenoid lipids. The co-occurrence of their precursor alkenes and ketones afforded further evidence for inputs of angiosperm-derived terrigenous OM, whereas the absence of diterpenoids suggests minimal contributions of terrestrial OM from gymnosperms. The dominance of OM originating from angiosperms throughout this interval suggests that these plants were well-established as the principal vegetation in southern Africa following their expansion during the Late Cretaceous. The presence of coronene in the sedimentary succession indicates that the sources of terrestrial OM also include pyrogenic material because this compound is formed during intense combustion and therefore serves as a sedimentary marker for wildfires. Coronene occurs as a minor PAH component in Campanian samples, but it is a prominent PAH component of the Paleocene samples. It is dominant in the basal Paleocene sample consistent with inputs from global wildfires at the K/Pg boundary, confirming their prevalence at high southern latitudes, whereas the lower proportion of perylene in this interval may reflect a diminished supply of unburnt lignin precursors. Coronene remains a substantive component in later Paleocene samples suggesting the protracted occurrence of wildfires. In a

Campanian to Paleocene organic-rich sediments (~74-60 Ma) recovered from the Transkei Basin (Hole U1581B), offshore South Africa, during IODP Expedition 392 contain suites of C37-C40 alkenones derived from haptophyte algae that extend the temporal continuity of their occurrences and expand their paleogeographic range to high southern latitudes (~58°S) during this time interval. Alkenone profiles are broadly similar throughout the stratigraphic section with the similarity between Maastrichtian and Danian samples indicating a conformity in biosynthetic pathways across the K/Pg boundary. Thus, the source haptophytes for alkenones survived and subsequently recovered after the extinction event, consistent with temporal trends for assemblages of calcareous nannoplankton from the southern hemisphere. The lineages of specific alkenones record evolutionary developments in their biosynthetic pathways. The occurrence of a methyl C39:2 alkenone in the Paleocene and both methyl and ethyl C38 and C39 alkenones in the Campanian extends the range of occurrence of alkenone with carbonyl groups at multiple positions, and the required duality in their biosynthetic pathways. The dominance of the C40 alkadien-3-one in several samples contrasts with its scarcity in Neogene marine sediments and presence among extant haptophytes. C40 alkenones are prevalent constituents of coastal and lacustrine species in phylogenic Group II, notably Isochrysis, but have only once been reported in marine species from phylogenic Group III. The sporadic prominence of C40 alkenones prior to the early Eocene seems to reflect a broader suite of active biosynthetic pathways than those expressed by extant marine haptophytes. Thus, Cretaceous through Paleocene marine sediments may reflect alkenone contributions from both Isochrysidaceae (Group II) and Noelaerhabdaceae (Group III) following their divergence in the Early Cretaceous. The accompanying C40:3 alkenone contrasts with the absence of other alkatrienones p

The Cretaceous opening of the Equatorial Atlantic gateway (EAG) is considered a driver of major changes in global oceanography, carbon cycling, and climate. However, the early stages of EAG opening are poorly understood. We present seawater Nd-isotope, bulk geochemical, and micropaleontological data from two South Atlantic drill cores that constrain the onset of shallow (<500 m) and intermediate (<~1000 m) water mass exchange across the EAG to 113 Ma and 107 Ma, respectively. Deep water mass exchange (>2000 m) was enabled by at least ca. 100 Ma, as much as 10 m.y. earlier than previously estimated. In response to EAG opening, deep-water ventilation in the South Atlantic, North Atlantic, and Tethys basins intensified, thereby triggering basin-scale reductions in organic carbon burial. We propose that the consequent drop in carbon sequestration in concert with increased atmospheric CO2 fluxes from subduction zones acted as major amplifiers of global warming that culminated in peak greenhouse conditions during the mid-Cretaceous.

The Paleocene-Eocene Thermal Maximum (PETM) was an abrupt and extreme warming event associated with rapid input of light carbon into the ocean-atmosphere system. The carbon cycle perturbations during the PETM caused significant changes to marine plankton, including extinction of some benthic foraminifers and the appearance of malformed calcareous nannoplankton, possibly related to ocean acidification during the event. The PETM is now considered a potential analog for the effects of anthropogenic climate change due to its rapid onset; thus, study of PETM records offers an opportunity to better understand the potential effects of rapid climate change on marine phytoplankton communities. Here we present calcareous nannofossil assemblage data across a newly recovered PETM section from International Ocean Discovery Program (IODP) Site U1580, drilled on the central Agulhas Plateau during IODP Expedition 392 in early 2022. Present water depth at this site is 2560 m and it sits at 40° 47.15’S, although the site has moved progressively northward since the Agulhas Plateau formed in the mid-Cretaceous, when the site was located about 20° further south. The PETM interval was identified during the expedition by a change in sediment color, increase in magnetic susceptibility, and calcareous nannofossil assemblages. Low-resolution bulk 13C measurements conducted following the expedition confirm a negative isotope excursion and decrease in calcium carbonate content across the interval. The shipboard age model based on nannofossil and planktonic foraminifer biostratigraphy, together with magnetostratigraphy, suggests relatively high sedimentation rates (~2.5 cm/kyr). Nannofossil assemblages are quite well preserved, with PETM-specific taxa present including Rhomboaster calcitrapa, Rhomboaster cuspis, Rhomboaster bramlettei, Discoaster araneus, and Discoaster acutus. Initial qualitative analyses indicate Zygrhablithus bijugatus is particularly abundant within the PETM interval, wher

The Arctic is warming two times faster than the global mean, and a phenomenon known as the ‘Atlantification of the Arctic’ via the Fram Strait is having growing influences on both biological and physical processes in the region. Changes to community composition and function are already underway and these environmental changes will continue to rapidly alter Arctic ecosystems. Greater understanding of how this impacting local marine biodiversity is crucial for formulating accurate predictions of future Arctic marine ecosystems and management decisions. Gelatinous zooplankton (GZP) is a highly diverse group of taxa, including cnidarians, ctenophores and tunicates. Very little is currently known about GZP ecology, particularly in the Arctic Ocean, and even less about how they are being impacted by climate-related changes. Not only are they often actively left out of zooplankton surveys, but GZP are notoriously difficult to catch in good condition because their fragile bodies are easily destroyed by traditional sampling methods. These challenges contribute to GZP taxa regularly being underestimated in biodiversity, distribution and abundance, which has led to a lack of reliable and comprehensive baseline data available, especially in the Arctic. The aim of this study is to apply non-invasive environmental DNA (eDNA) metabarcoding methods to investigate GZP biodiversity and distribution across the Fram Strait. COI mitochondrial and 18s rRNA amplicons from water and sediment samples will be sequenced with Next Generation Sequencing (NGS) and validated with depth-stratified net-catch data. Net-caught specimens will be barcoded where possible, to complement existing reference databases. Oceanographic data will then be incorporated in order to form a holistic baseline dataset of GZP biodiversity across the region. Such data would be a valuable contribution to future research into the deviations in Arctic GZP biodiversity, community composition and distribution over time, as a

Gelatinous zooplankton (GZP) comprising ctenophores, cnidarians and tunicates, gained more interest in recent years. During favorable conditions GZP is known to rapidly increase in biomass and several dominant species are able to exploit the zooplankton standing stock. It is assumed that GZP will increase in biomass with the ongoing warming and Atlantification of the Arctic Ocean. Hence, it is crucial to gain insights into the role of gelatinous zooplankton in the current and future Arctic marine food web . This study targets both the benthic and pelagic components of the Arctic marine food web . First, we aim to determine the role of so-called “jellyfalls”, or jelly carcasses on the seafloor, as a food source for the benthic community. To do so, we investigate the stomach content of benthic scavenging amphipods in Kongsfjorden sampled during Polar night with DNA metabarcoding. By doing so,. Second, we look at the role of jellyfish as predators in the pelagic system. We focus on a widely distributed boreal-Arctic hydrozoan species, Aglantha digitale, which is also assumed to be a climate-change winner in an “Atlantified” Arctic. Its feeding ecology is scarcely studied, in particular in the Arctic region? This jellyfish is believed to feed on a wide range of zooplankton including copepods. Due to its high abundances in the Arctic regions, both in summer and in winter, it is crucial to investigate spatio-temporal patterns in its diet. Hence, we use DNA metabarcoding of Aglantha’s stomach content to reveal its prey composition in different seasons and regions in order to better predict its future role in an ice-free and Atlantified Arctic.

International Ocean Discovery Program (IODP) Expedition 392 cored three sites on the Agulhas Plateau and one site in the Transkei Basin to address questions regarding the origin and timing of emplacement of Agulhas Plateau, as well as examine Southern Ocean climate history and opening of oceanic gateways from the Cretaceous through the Paleogene. Age models for the sites rely primarily on calcareous nannofossils and magnetostratigraphy, with dinoflagellates providing key events for some intervals, and additional contributions from planktonic foraminifers and diatoms. Site U1579, located in a basin on southern the central Agulhas Plateau, records a nearly continuous section dated to the Santonian to earliest Miocene. Dinoflagellates provide age control for the zeolitic sandstone and siltstone with glauconite at the base of the cored section. Above this, nannofossils are common to abundant and moderately preserved in upper Santonian to Maastrichtian calcareous chalks and the assemblages show Southern Ocean affinities. Paleogene nannofossils are abundant and moderately to well preserved. Sedimentation rates were lowest in the Eocene, which includes either condensed intervals or hiatuses. Nannofossils are well preserved in the Oligocene and assemblages consist of primarily mid-latitude species with occasional incursions of cold-water taxa. Site U1580 is also located on the southern Agulhas Plateau adjacent to a basement high. This site records several unconformities, and the lowermost part of the cored interval is interspersed with basalt layers interpreted as sills. The oldest sediment is likely uppermost Cenomanian in age. Overlying the shallowest basalt is Coniacian–Santonian silt- and sandstone with varying proportions of zeolites, glauconite, and carbonate. Sedimentation rates were very high (~10 cm/ky) during this time. Much of the early Campanian and mid-Maastrichtian is missing at this site. Paleocene nannofossils are moderately well preserved and suggest a cont

A series of organic-rich sedimentary sequences that span the Paleocene through the Campanian was recovered from the Transkei Basin during IODP Expedition 392. Preliminary analyses of their organic geochemistry reveals suites of biomarkers that reflect diverse contributions of organic matter from both marine and terrestrial sources. The characteristics of the organic matter (OM) for a range of samples have been determined by shipboard and shore-based analyses that include evaluation of OM type and maturity by Rock-Eval pyrolysis, isotopic compositions of OM and the distributions of biomarkers including GDGTs. Samples from both the Paleocene and Campanian contain series of C37 to C40 diunsaturated alkenones, including the earliest record of C38 alkadien-2-ones and C39 alkadien-3-ones [1]. A sequence of Campanian samples also reveal an abundance of C28 sterenes and steryl ethers potentially indicative of upwelling conditions [2]. Polyaromatic hydrocarbons, including coronene, are present throughout the sequence likely reflecting inputs of OM associated with paleofires [3]. Variations in the abundance of organosulfur compounds [4,5] may afford evidence for temporal changes in redox conditions within the Transkei Basin during the Campanian. These initial results provide evidence that biomarker profiling will facilitate determination of the sources of OM throughout Late Cretaceous and Paleocene and the paleoenvironmental conditions of its deposition. [1] Brassell, 2014; [2] Brassell, 2009; [3] Finkelstein et al., 2005; [4] Valisolalao et al., 1984; [5] Brassell et al., 1986

A series of organic-rich sedimentary sequences that span the Paleocene through the Campanian was recovered from the Transkei Basin during IODP Expedition 392. Preliminary analyses of their organic geochemistry reveals suites of biomarkers that reflect diverse contributions of organic matter from both marine and terrestrial sources. The characteristics of the organic matter (OM) for a range of samples have been determined by shipboard and shore-based analyses that include evaluation of OM type and maturity by Rock-Eval pyrolysis, isotopic compositions of OM, and the distributions of aliphatic and aromatic biomarkers. Samples from both the Paleocene and Campanian contain series of C37 to C40 diunsaturated alkenones, including the earliest record of C38 alkadien-2-ones and C39 alkadien-3-ones [1]. Samples from a section of the Campanian (~72.5 Ma) reveal an abundance of C28 steradienes and steryl ethers potentially indicative of upwelling conditions [2]. Polyaromatic hydrocarbons within the sequence include compounds that reflect inputs of OM derived from angiosperms and paleofires [3,4]. Dominant hopanoids in the samples include -homohopane, hop-17(21)-ene, and 29-norhop-17(21)-ene, accompanied by fernenes [5], a C35 hopanoid thiophene [6] and also dammarenes [7] in Paleocene samples. These initial results provide evidence that biomarker profiling will facilitate determination of the sources of OM from the Late Cretaceous to the Paleocene in the Transkei Basin and paleoenvironmental conditions of deposition.

Rapid warming in the Arctic is drastically impacting marine ecosystems, affecting pelagic communities and food web structure. Themisto amphipods are dominant in the Arctic zooplankton community and represent a key link between secondary producers and higher trophic levels. In the Arctic seas, two coexisting species are found in high biomass: Themisto libellula, considered a true Arctic species and Themisto abyssorum, a sub-Arctic, boreal species. Many aspects of the ecology and genetic structure of these two species are not well studied, despite their importance in the food web. First, we tested both species for levels of genetic diversity and then assessed their diet spectrum with molecular methods, with a regional focus on the Greenland shelf, Fram Strait and Svalbard. Spatial genetic structure was evaluated using the mitochondrial cytochrome c oxidase subunit 1 gene (COI). Our results revealed strikingly different levels of genetic diversity: low levels in T. libellula contrasted with higher diversity in T. abyssorum. No spatial genetic structure was found, and both species exhibited high levels of connectivity and evidence of historic demographic expansion. The observed low genetic diversity, in combination with cold adaptations, could cause T. libellula to be more susceptible to the warming Arctic. In contrast, high diversity likely increases adaptive potential in T. abyssorum. In order to comprehensively characterize the prey spectrum of both Themisto species, we also applied DNA metabarcoding, also using COI, on gut contents. Both species showed a regional variation in prey spectrum. T. abyssorum’s diet showed a clear dominance of reads identified as chaetognath species, whereas T. libellula had a broader prey spectrum, including ice-associated taxa such as polar cod. Calanoid copepods did not appear as important as prey as assumed from previous (morphological) studies. Several previously overlooked jellyfish taxa were found in the stomachs of both species. T

The Southern Ocean, in particular the southwest Atlantic sector, is experiencing rapid environmental changes. A long-term trend of density changes of key pelagic species has been noted over the last decades: Antarctic krill populations are declining whilst salps are on the rise and shifting their distribution poleward. A similar poleward expansion is anticipated for a third key player, the hyperiid amphipod crustacean Themisto gaudichaudii, leading to an increasing overlap of the distributions of these three species. Due to major knowledge gaps in the ecology, and genetic connectivity of T. gaudichaudii, the likelihood of this shift and its consequences for the pelagic food web structure remain largely unexplored. In this context, Themisto’s genetic and trophic connectivity as well as thermal response were investigated with state-of-the-art molecular methods. Phylogeographic analyses showed genetic homogeneity between localities in the Southern Ocean and Atlantic waters combined with high degree of phenotypic plasticity enabling different lineages to thrive in regions further south. Diet analyses using DNA metabarcoding were applied to characterize regional variation in diet. These analyses showed a diet predominantly composed of krill, in particular in the Antarctic Peninsula region, showing that Themisto’s poleward range expansion can further impact the already declining krill stocks. It also unexpectedly revealed ctenophores to be an important prey, despite their reputation as “trophic dead-end”. Transcriptome analyses were used to study the thermal response of Themisto individuals from different geographic populations that were experimentally exposed to heat and cold treatments. The analysis of differentially expressed genes showed that genetic lineages differ in thermal tolerances. It also revealed a wide range of molecular mechanisms in Themisto amphipods to cope with thermal stress. These findings contribute to better predict the impact of climate-driven rang