Warming, euxinia and sea level rise during the Paleocene–Eocene Thermal Maximum on the Gulf Coastal Plain: implications for ocean oxygenation and nutrient cycling

The Paleocene–Eocene Thermal Maximum(PETM, ?56 Ma) was a ?200 kyr episode of globalwarming, associated with massive injections of 13C-depletedcarbon into the ocean–atmosphere system. Although climatechange during the PETM is relatively well constrained,effects on marine oxygen concentrations and nutrientcycling remain largely unclear. We identify the PETM in asediment core from the US margin of the Gulf of Mexico.Biomarker-based paleotemperature proxies (methylationof branched tetraether–cyclization of branched tetraether(MBT–CBT) and TEX86) indicate that continental air andsea surface temperatures warmed from 27–29 to ?35 ?C,although variations in the relative abundances of terrestrialand marine biomarkers may have influenced these estimates.Vegetation changes, as recorded from pollen assemblages,support this warming.The PETM is bracketed by two unconformities. It overliesPaleocene silt- and mudstones and is rich in angular(thus in situ produced; autochthonous) glauconite grains,which indicate sedimentary condensation. A drop in the relativeabundance of terrestrial organic matter and changesin the dinoflagellate cyst assemblages suggest that risingsea level shifted the deposition of terrigenous material landward.This is consistent with previous findings of eustatic sealevel rise during the PETM. Regionally, the attribution of theglauconite-rich unit to the PETM implicates the dating of aprimate fossil, argued to represent the oldest North Americanspecimen on record.The biomarker isorenieratene within the PETM indicatesthat euxinic photic zone conditions developed, likely seasonally,along the Gulf Coastal Plain. A global data compilationindicates that O2 concentrations dropped in allocean basins in response to warming, hydrological change,and carbon cycle feedbacks. This culminated in (seasonal)anoxia along many continental margins, analogous to moderntrends. Seafloor deoxygenation and widespread (seasonal)anoxia likely caused phosphorus regeneration fromsuboxic and anoxic sediments.We argue that this fueled shelfeutrophication, as widely recorded from microfossil studies,increasing organic carbon burial along many continentalPublished by Copernicus Publications on behalf of the European Geosciences Union.Warming, euxinia and sea level rise during the PETMmargins as a negative feedback to carbon input and globalwarming. If properly quantified with future work, the PETMoffers the opportunity to assess the biogeochemical effects ofenhanced phosphorus regeneration, as well as the timescaleson which this feedback operates in view of modern and futureocean deoxygenation

Expedition 361 summary

International Ocean Discovery Program Expedition 361 drilled six sites on the southeast African margin (southwest Indian Ocean) and in the Indian-Atlantic Ocean gateway, from 30 January to 31 March 2016. In total, 5175 m of core was recovered, with an average recovery of 102%, during 29.7 days of on-site operations. The sites, situated in the Mozambique Channel at locations directly influenced by discharge from the Zambezi and Limpopo River catchments, the Natal Valley, the Agulhas Plateau, and Cape Basin, were targeted to reconstruct the history of the greater Agulhas Current system over the past ~5 My. The Agulhas Current is the strongest western boundary current in the Southern Hemisphere, transporting some 70 Sv of warm, saline surface water from the tropical Indian Ocean along the East African margin to the tip of Africa. Exchanges of heat and moisture with the atmosphere influence southern African climates, including individual weather systems such as extratropical cyclone formation in the region and rainfall patterns. Recent ocean model and paleoceanographic data further point at a potential role of the Agulhas Current in controlling the strength and mode of the Atlantic Meridional Overturning Circulation (AMOC) during the Late Pleistocene. Spillage of saline Agulhas water into the South Atlantic stimulates buoyancy anomalies that may influence basin-wide AMOC, with implications for convective activity in the North Atlantic and global climate change. The main objectives of the expedition were to establish the role of the Agulhas Current in climatic changes during the Pliocene–Pleistocene, specifically to document the dynamics of the Indian-Atlantic Ocean gateway circulation during this time, to examine the connection of the Agulhas leakage and AMOC, and to address the influence of the Agulhas Current on African terrestrial climates and coincidences with human evolution. Additionally, the expedition set out to fulfill the needs of Ancillary Project Letter number 845, consisting of high-resolution interstitial water sampling to help constrain the temperature and salinity profiles of the ocean during the Last Glacial Maximum. The expedition made major strides toward fulfilling each of these objectives. The recovered sequences allowed generation of complete spliced stratigraphic sections that range from 0 to between ~0.13 and 7 Ma. This sediment will provide decadal- to millennial-scale climatic records that will allow answering the paleoceanographic and paleoclimatic questions set out in the drilling proposal

Legacy ExtraGalactic UV Survey with The Hubble Space Telescope: Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 628

We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes $\sim -2$ and a truncation of a few times 105 ${M}_{\odot }$. After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find mass-independent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (≤104 ${M}_{\odot }$) clusters, suggesting that a mass-dependent component is necessary to fully describe the YSC disruption process in NGC 628