Workshop on Pliocene Climate

The warm Pliocene epoch (5–3 million years ago) is often cited as a good analog for the near future climate because of its striking resemblance to the predictions of the “Intergovernmental Panel on Climate Change” for the next decades. Indeed, relative to today, during the Pliocene epoch, surface temperatures were 3–4°C warmer, sea level was about 5–40 meters higher, atmospheric CO2 concentrationswere relatively similar or slightly higher (~400 ± 50 ppmv), and ice sheets were restrained to Antarctica. However, since 3.0 Ma ago, the Earth’s climate has undergone a major transition from a warm and relatively stable state towards cold conditions marked by amplified glacial/interglacial cycles and widespread ice sheets in the Northern Hemisphere (NHG), and to a lesser extent over Antarctica. The causes and consequences of this global climate transition—driving warm periods to “icehouse” conditions marked by “Quaternary-style” glacial/interglacial cycles—are still uncertain. Yet, they may include the interaction of several mechanisms tied to oceanic and atmospheric circulations, tectonic-, greenhouse gases-, and biological activity, biogeochemical processes, and changes in Earth’s orbit

Vegetation change across the Drake Passage region linked to late Eocene cooling and glacial disturbance after the Eocene–Oligocene transition

Nick Thompson received funding from the Natural Environment Research Council from a NERC-funded Doctoral Training Partnership ONE Planet (grant no. NE/S007512/1). Funding for this research was also provided by the Spanish Ministry of Science and Innovation (grant nos. CTM2014-60451-C2- 1/2-P and CTM2017-89711-C2-1/2-P) cofunded by the European Union through FEDER funds. Peter K. Bijl received funding from the European Research Council (OceaNice (grant no. 802835)).This work used Deep Sea Drilling Project archived samples provided by the International Ocean Discovery Program (IODP). We thank the staff at the Gulf Coast core repository (GCR) for assistance in ODP Leg 113 core handling and shipping. We thank CNRS for the salary support of MASThe role and climatic impact of the opening of the Drake Passage and how it affected both marine and terrestrial environments across the Eocene-Oligocene transition (EOT ∼34 Ma) period remains poorly understood. Here we present new terrestrial palynomorph data compared with recently compiled lipid biomarker (n-alkane) data from Ocean Drilling Program (ODP) Leg 113, Site 696, drilled on the margin of the South Orkney Microcontinent (SOM) in the Weddell Sea, to investigate changes in terrestrial environments and palaeoclimate across the late Eocene and early Oligocene (∼37.6-32.2 Ma). Early late Eocene floras and sporomorph-based climate estimates reveal Nothofagus-dominated forests growing under wet temperate conditions, with mean annual temperature (MAT) and precipitation (MAP) around 12 C and 1802 mm respectively. A phase of latest Eocene terrestrial cooling at 35.5 Ma reveals a decrease in MAT by around 1.4 C possibly linked to the opening of the Powell Basin. This is followed by an increase in reworked Mesozoic sporomorphs together with sedimentological evidence indicating ice expansion to coastal and shelf areas approximately 34.1 Myr ago. However, major changes to the terrestrial vegetation at Site 696 did not take place until the early Oligocene, where there is a distinct expansion of gymnosperms and cryptogams accompanied by a rapid increase in taxon diversity and a shift in terrestrial biomarkers reflecting a change from temperate forests to cool temperate forests following 33.5 Ma. This surprising expansion of gymnosperms and cryptogams is suggested to be linked to environmental disturbance caused by repeat glacial expansion and retreat, which facilitated the proliferation of conifers and ferns. The timing of glacial onset at Site 696 is linked to the global cooling at the EOT, yet the latest Eocene regional cooling cannot directly be linked to the observed vegetation changes. Therefore, our vegetation record provides further evidence that the opening of the Drake Passage and Antarctic glaciation were not contemporaneous, although stepwise cooling in response to the opening of ocean gateways surrounding the Antarctic continent may have occurred prior to the EOT.NERC-funded NE/S007512/1Natural Environment Research CouncilEuropean CommissionEuropean Research Council 802835Ministerio de Ciencia e Innovación CTM2014-60451-C2- 1/2-P, CTM2017-89711-C2-1/2-PEuropean Regional Development Fun

Pliocene-Pleistocene variability of upwelling activity, productivity and nutrient cycle in the Benguela Upwelling System and the Eastern Equatorial Pacific

The focus of this study is to explore the long term Plio-Pleistocene variability of coastal and open ocean upwelling systems by reconstructing for the last ~3.5 Ma, sea surface temperature (SST), primary productivity and nutrient cycling in the Benguela Upwelling System (BUS) and the Eastern Equatorial Pacific (EEP), two areas particularly sensible and influential to climate change

Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to Late Pliocene/Early Pleistocene climate cooling

The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilisation in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Late Pliocene/Early Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to Late Pliocene/Early Pleistocene cooling

Ocean temperature impact on ice shelf extent in the eastern Antarctic Peninsula

The recent thinning and retreat of Antarctic ice shelves has been attributed to both atmosphere and ocean warming. However, the lack of continuous, multi-year direct observations as well as limitations of climate and ice shelf models prevent a precise assessment on how the ocean forcing affects the fluctuations of a grounded and floating ice cap. Here we show that a +0.3–1.5 °C increase in subsurface ocean temperature (50–400 m) in the northeastern Antarctic Peninsula has driven to major collapse and recession of the regional ice shelf during both the instrumental period and the last 9000 years. Our projections following the representative concentration pathway 8.5 emission scenario from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change reveal a +0.3 °C subsurface ocean temperature warming within the coming decades that will undoubtedly accelerate ice shelf melting, including the southernmost sector of the eastern Antarctic Peninsula.J.E. and C.E. are financially supported by the Spanish Ministerio de Economia y Competitividad (CTM2014–60451-C2–1-P) co-funded by the European Union through FEDER funds. J.-H.K. was supported by the grants funded by the Korea Polar Research Institute (KOPRI, NRF-2015M1A5A1037243 and PE19010). S.S. and J.S.S.D. are supported by the Netherlands Earth System Science Center funded by the Dutch Ministry of Education and Science (OCW). G.S. and D.S. were funded by the EMBRACE project (European Union’s FP7, Grant Number: 282672). We also acknowledge funding from the French ANR CLIMICE, ERC ICEPROXY 203441, ESF PolarClimate, HOLOCLIP 625 and FP7 Past4Future as well as the Netherlands Organisation of Scientific Research (NWO) through a VICI grant to S.S. The HOLOCLIP Project, a joint research project of ESF PolarCLIMATE programme, is funded by national contributions from Italy, France, Germany, Spain, Netherlands, Belgium and the United Kingdom. The research leading to these results has also received support from the European Union’s Seventh Framework programme (FP7/2007–2013) under Grant Agreement No. 243908, “Past4Future, Climate change – Learning from the past climate”

Ocean productivity in the Gulf of Cadiz over the last 50 kyr

Reconstructions of ocean primary productivity (PP) help to explain past and present biogeochemical cycles and climate changes in the oceans. We document PP variations over the last 50 kyr in a currently oligotrophic subtropical region, the Gulf of Cadiz. Data combine refined results from previous investigations on dinocyst assemblages, alkenones, and stable isotopes ( 18O, 13C) in planktonic (Globigerina bulloides) and endobenthic (Uvigerina mediterranea) foraminifera from cores MD04-2805 CQ and MD99-2339, with new isotopic measurements on epibenthic (Cibicides pachyderma–Cibicidoides wuellerstorfi) foraminifera and dinocyst-based estimates of PP using the new n = 1,968 modern database. We constrain PP variations and export production by integrating qualitative information from bio-indicators with dinocyst-based quantitative reconstructions such as PP and seasonal sea-surface temperature and information about remineralization from the benthic 13C (difference between epi- and endo-benthic foraminiferal 13C signatures). This study also includes new information on alkenone-based SST and total organic carbon which provides insights into the relationship between past regional hydrological activity and PP regime change. We show that PP, carbon export, and remineralization were generally high in the NE subtropical Atlantic Ocean during the last glacial period and that the Last Glacial Maximum (LGM) had lower 13C than the Heinrich Stadials with sustained high PP, likely allowing enhanced carbon sequestration. We link these PP periods to the dynamics of upwelling, active almost year-round during stadials, but restricted to spring-summer during interstadials and LGM, like today. During interstadials, nutrient advection through freshwater inputs during autumn–winter needs also to be considered to fully understand PP regimes.info:eu-repo/semantics/publishedVersio

The evolution of the Antarctic Circumpolar Current in the SouthwestPacific sector of the Southern Ocean throughout the Cenozoic era

EGU General Assembly in Viena, Austria, 7–12 April 2019The establishment and evolution of the Antarctic Circumpolar Current (ACC) throughout the Cenozoic remainspoorly known, mainly because of the lack of continuous long-term records at strategic locations. Here we presentnew records from marine sediments collected by the Deep Sea Drilling Project (DSDP) Site 278, located in theSouthwestern Pacific sector of the Southern Ocean (Southern Emerald Basin), spanning from the mid-Oligoceneto the Pleistocene (ie. the∼28-2 Ma). Our site is ideally situated to reconstruct changes in the ACC sincethe mid-Oligocene as it remained along the polar frontal zone as shown by paleolatitude reconstructions andmicrofossil assemblage data. To track its evolution, we combined (i) mean grain size of sortable silt (SS) datawith (ii) primary productivity proxies including biogenic silica (BSi), calcium carbonate (CaCO3) and organicmatter, and (iii) neodymium isotope ratios (εNd) generated from fossil fish teeth and debris. Our results documenta significant increase in SS, enhanced marine productivity and a decrease inεNd values towards present-dayCircumpolar deep waterεNd values, suggesting a progressive strengthening of the proto-ACC flow over the last28 Ma. However, we find that the development of a modern-like, homogenous and deep-reaching current wasfully established solely during the Pliocene-Pleistocene transition, concomitantly with the onset of the NorthernHemisphere glaciation

Absence of a strong, deep-reaching Antarctic Circumpolar Current zonal flow across the Tasmanian gateway during the Oligocene to early Miocene

The vigorous eastward flow of the Antarctic Circumpolar Current (ACC) connects all major ocean basins and plays a prominent role in the transport of heat, carbon and nutrients around the globe. However, the establishment of a deep circumpolar flow, similar to the present-day ACC, remains controversial thereby obscuring our understanding of its climatic impact. Deciphering the chemical composition of Circumpolar Deep Water (CDW) within the ACC can provide critical insights about its development and evolution. Here we present new fossil fish teeth/bone debris neodymium isotope (ε) records from Deep Sea Drilling Project (DSDP) Sites 278 and 274 in the southwest Pacific Ocean, with the aim to trace changes in deep water masses across the Tasmanian Gateway between the early Oligocene and early Miocene (~ 33–22 Ma). Site 274 provides the first Nd isotope record proximal to the Ross Sea during the Oligocene (33.5–23.4 Ma). Its Nd isotope composition shows excursions to very radiogenic values, ε = −3.1 and ε − 3.7, at 33.5 Ma and 23.8 Ma, respectively, in response to major steps in Antarctic ice sheet expansion. A shift to lower, more unradiogenic ε values between 29.7 and 29.1 Ma is linked to an increased influence of proto-CDW upwelling at the site. In contrast, the Nd isotope record from Site 278 in the southern Emerald Basin shows little variability (ε = −6.0 to −6.7) throughout the Oligocene and early Miocene (30.9–21.8 Ma). Comparison with published data north of the ACC path, demonstrates the presence of two deep water masses in the South Pacific prior to the inferred onset of the ACC (33–30 Ma), one occupying depths between ~2500 and 3000 m (ε ~ −3 to −5) and a deep/bottom water mass (> 3000 m) with a more unradiogenic Nd isotope composition (ε ~ −6). Site 278 located close to the proto-polar front (proto-PF) indicates that following the inferred onset of the ACC, deep waters bathing the southern Emerald Basin remained more radiogenic in the Southwest Pacific compared to sites along the proto-PF in the South Atlantic and Indian Ocean (ε ~ −8.1). This indicates a provinciality in Nd isotope compositions of deep waters along the proto-PF across the Tasmanian Gateway. Our data are incompatible with the existence of a modern-like homogenous (lateral and vertical) Nd isotope composition of CDW along the main flow path of the ACC in all oceanic basins in the Oligocene to early Miocene. We attribute distinct Nd isotope compositions of deep waters across the Tasmanian Gateway to reflect a less deep reaching and weaker ACC (proto-ACC) than today. Our findings suggest that the modern strong and deep-reaching ACC flow must have been developed at a later point in the Neogene.Funding to this research is provided by the Alexander S. Onassis Public Benefit Foundation Ph.D. research grant: F ZL 016-1/2015-2016; the Spanish Ministry of Economy, Industry and Competitivity (grants CTM2017-89711-C2-1/2-P), co-funded by the European Union through FEDER funds; and an ECORD Research grant awarded to DE. PKB and FH acknowledge funding through the European Research Council starting grant #802835 OceaNice and NWO polar programme grant ALWPP2016.001. This paper is a contribution to the SCAR PAIS Programme

Antarctic sea ice proxies from marine and ice core archives suitable for reconstructing sea ice over the past 2000 years

Dramatic changes in sea ice have been observed in both poles in recent decades. However, the observational period for sea ice is short, and the climate models tasked with predicting future change in sea ice struggle to capture the current Antarctic trends. Paleoclimate archives, from marine sedimentary records and coastal Antarctic ice cores, provide a means of understanding sea ice variability and its drivers over decadal to centennial timescales. In this study, we collate published records of Antarctic sea ice over the past 2000 years (2 ka). We evaluate the current proxies and explore the potential of combining marine and ice core records to produce multi-archive reconstructions. Despite identifying 92 sea ice reconstructions, the spatial and temporal resolution is only sufficient to reconstruct circum-Antarctic sea ice during the 20th century, not the full 2 ka. Our synthesis reveals a 90 year trend of increasing sea ice in the Ross Sea and declining sea ice in the Bellingshausen, comparable with observed trends since 1979. Reconstructions in the Weddell Sea, the Western Pacific and the Indian Ocean reveal small negative trends in sea ice during the 20th century (1900–1990), in contrast to the observed sea ice expansion in these regions since 1979